Planetary Materials Science and Astrobiology

Spine Title: Planetary Materials Science and Astrobiology

by

Matthew Richard Mitsuomi Izawa Department of Earth Sciences Graduate program in Planetary Science - Geology Specialization Format: Integrated article

submitted in partial fulfillment of the requirements of the degree of Doctor of Philosophy

School of Graduate and Postdoctoral Studies The University of Western Ontario London, Ontario, Canada

© 2012 Matthew R. M. Izawa

CERTIFICATE OF EXAMINATION

Supervisor Examiners

______Dr. Roberta Flemming Dr. Fred J. Longstaffe

______Supervisor Dr. Kim Tait

______Dr. Neil Banerjee Dr. Robert J. Sica

______Dr. Alan R. Hildebrand

Supervisory Committee ______Dr. Roberta Flemming Dr. Neil Banerjee Dr. Gordon Southam

The thesis by

Matthew Richard Mitsuomi Izawa

entitled: Planetary Materials Science and Astrobiology

is accepted in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Date______Chair of the Thesis Examination Board

ii Abstract Planetary materials contain signatures of diverse processes in their , chemistry, textures and assemblages. The record contained in planetary materials reflects the complex and commonly overprinting relationships between many processes. Discerning what mechanisms have operated to produce the rocks we observe requires first a careful characterization of various properties. These include the chemical and structural makeup of the rocks (that is, the mineralogy and mineral chemistry), the textural relations within and between rocks (petrology) Therefore, the key to how the studies here hold together is also in the methodology and guiding philosophy: understanding what is there (what atoms and how they are arranged, what their interrelationships are) is the first step to unravelling the record of processes stored in planetary materials of all kinds. In this thesis, the tools of mineralogy and geochemistry/cosmochemistry and petrology have been used along with an understanding of the grand-scale astrophysical constraints on planetary formation to interpret diverse planetary materials: terrestrial rocks and . In this thesis, detailed mineralogical and chemical study of various planetary materials have enabled some new constraints to be placed on asteroidal melting and shock metamorphic processes, the nature of habitable environments in post-impact hydrothermal systems, and the preservation mechanisms of microbial ichnofossils in basaltic glass. These studies all concern the emergence and development of terrestrial planets and habitable environments within them, and the preservation of records of biological activity through deep geologic time. This work therefore represents, in a broad sense, an exploration of the astrobiological implications of planetary materials including likely precursors to terrestrial planets (enstatite ); and important possible planetary habitats including post-impact hydrothermal mineral deposits and their associated weathering assemblages; and the fossilization of records of an ecosystem based on the microbial leaching of seafloor basaltic glass.

Keywords: Meteorites, Impact processes, asteroidal melting, enstatite chondrites, primitive achrondrites, Post-impact hydrothermal processes, secondary minerals, basaltic glass, ichnofossils, astrobiology

iii Statement of co-authorship Dr. Flemming and Dr. Banerjee provided funding, access to and training in the operation of laboratory equipment, and guidance on the conduct of the research. The co-authors of the various publications associated with the chapters of this thesis have provided their expertise on particular aspects of the relevant work; and guidance on the proper presentation of the material. The intellectual development of the ideas is mine, with guidance and input from my supervisors and collaborators. Any errors are; however, entirely my responsibility.

iv Dedication I dedicate my PhD. thesis to my parents, Richard Izawa and Mary Ashton. They have provided for me and stood by me through many trials through the years, and I would like them to regard this as their victory as well, in whatever way they wish.

v Acknowledgements It takes a village to raise a child, they say. And in that I am naturally very childish, and that attempting a PhD. requires a certain child-like flavour of madness, I would like to acknowledge the very large village (small city?) that has been required to raise me to this point. The order is alphabetical. I appreciate the academic collaborations, personal and professional guidance, inspiration, and friendship that I have received from so many people through the years leading to this point. I have endeavoured to make this list exhausting, but have almost certainly forgotten some names that should sit here, and for that I am truly regretful. My thanks to: Ricardo Amils, Lauren D. Anderson, Clifford Ashton, Mary Ashton, Mildred Ashton, Simon Auclair, Jean-Nicholas Audinot, Neil R. Banerjee, Tim Barfoot, Ivan R. Barker, Nicola Barry, Melissa Battler, Tyler Beaton, Gray E. Bebout, Alexandra Blinova, Tyler Brent, Nathan J. Bridge, Peter G. Brown, Natasha Bumstead, Glen Caldwell, Anna Chanou, Eleni Chanou, Christopher Charles, Edward A. Cloutis, Charles S. Cockell, Michael A. Craig, Mike Daly, Rebecca Draisey-Collishaw, James J. Dynes, Gregg Erauw, David C. Fernández-Remolar, Cam Fleming, Roberta L. Flemming, Ian S. Foster, Candace Freckleton, Alex Frisa, Karl Frisa, Kristen Frisa, Paul Furgale, Zack Gainsforth, Panayiotis Giannarapis, Ashlee Gradkowski, Paul Graham, David Gregory, Richard A.F. Grieve, Mark A. Grimson, Jerôme Guillot, Monika Haring, Ben C. Harwood, Christopher D. K. Herd, Richard Herd, Callum J. Hetherington, Alan R. Hildebrand, Hans J. Hofmann, Richard A. Holt, Li Huang, Jeff Hutter, Brendt C. Hyde, Jen Midori Izawa, Greg Kenji Izawa, Mike Nobuyuki Izawa, Mitsuomi Izawa, Setsuko Izawa, Dazhi Jiang, Jisuo Jin, Penelope L. King, D. Mike Laliberty, Kim R. Law, Jonathan Lee, Fred Longstaffe, Liane Loiselle, Brian Lunn, Lachlan C. W. MacLean, Neil D. MacRae, Paul Mann, Sergei Matveev, Phil J. A. McCausland, Whitney McCutcheon, Jeninen McCutcheon, Jeff Moraal, Desmond E. Moser, Karlis Muehlenbachs, H. Wayne Nesbitt, Ian Nicklin, Henry Ngo, Gordon R. Osinski, John Parnell, Geoff Pearce, Ronald C. Peterson, Duane Petts, Chris Pinciuc, Howard Plotkin, Louisa J. Preston, Kevin Righter, S. David Rosner, Sam D. J. Russell, Monika Sánchez- Román, Haley M. Sapers, Ryan Sawyer, Cynthia Schulz, John Schutt, Jared N. Shivak, Jeramiah Shuster, Robert J. Sica, Cheyenne S. Sica, Todd Simpson, Gordon Southam, Julien Stodolna, Ed Stokan, Phillip J. Stooke, Jessica Stromberg, Laura Thompson, Kim

vi Tait, Kristy F. Tiampo, Cam Tsujita, Dominic Veillette, Pierre Vernazza, Anthony Walton, Gary Weisz, Martin J. Whitehouse, Luke Wilson, Grant Young Thank you all!

I must single out a few for special recognition. Roberta Flemming took a chance on a rather dubious-looking potential grad student some years ago, and for that I am very thankful. Neil Banerjee has occasionally tested the elastic limits of ‘the rules’ to the benefit of my scientific and personal education. Both my co-supervisors have gone above and beyond for me, have provided opportunities that few graduate students can have experienced, and have been unflinchingly supportive academically and personally. I am very grateful for all their help through this journey. Callum Hetherington has been incredibly generous with hospitality, instrument access, and some of Scotland’s finest export products. Gordon Southam has consistently (and sometimes terrifyingly) challenged me with his insightful questions, which have forced me to examine and re- examine my assumptions; he has also put a permanent stamp on my approach to figure drafting and electron microscopy. Bren∂t Hyde, Dominic Veillette and Ryan Sawyer have all been brave (or crazy) enough to live with me... What were you guys thinking?

Finally, I give my heartfelt thanks and love to Anna Chanou. Σε λατρεϖο αγαπι μου.

I would also like to acknowledge financial and other support from: the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Astrobiology Training program (CATp), Barringer Family Fund for Impact Research, the Mineralogical Association of Canada, IODP (Integrated Ocean Drilling Program) Canada, the Centro de Astrobiología (CAB), Le Centre de Recherche Public - Gabriel Lippmann, the Northern Scientific Training Program, the , the Walker Mineralogical Club, the Lunar and Planetary Institute, the Canadian Space Agency (CSA), the Robert and Ruth Lumsden Graduate Fellowship, Dr. Robert Hodder, the Allan D. Edgar Petrology Award of UWO Earth Sciences, the Western Society of Graduate Students/Graduate Teaching Assistants’ Union, and the UWO Graduate Student Thesis Research Award fund.

vii

Last of all, I offer my deep and abiding thanks to 1,3,7-trimethyl-1H-purine-2,6(3H,7H)- dione, methylcarbinol, and Sus scrofa domesticus. Without them note of this would have been possible.

viii Table of Contents Page Certificate of Examination ii Abstract and Keywords iii Statement of co-authorship iv Dedication v Acknowledgements vi Table of Contents ix List of Figures xiii List of Tables xv

Chapter 1: General Introduction 1 1.1.0 General introduction and overall picture 1 1.1.1 Enstatite chondrites 2 1.1.2 Impact Structures and Hydrothermal Activity 4 1.1.3 Subaqueous Basaltic Glass Bioalteration 4 1.1.4 Chapter 1 References 6 Chapter 2: Micro X-ray diffraction assessment of shock stage in enstatite chondrites 10 2.0.0 Chapter summary and key points 10 2.1.0 Introduction 11 2.2.0 Materials and Methods 16 2.2.1 Micro X-ray Diffraction (μXRD) 17 2.3.0 Results 20 2.3.1 Micro XRD 20 2.3.2 Optical Petrography 26 2.4.0 Discussion 37 2.5.0 Conclusions 40 2.6.0 Chapter 2 References 42 Chapter 3: QUE 94204: A primitive enstatite 45 produced by the partial melting of an E--like protolith

ix 3.0.0 Chapter summary and key points 45 3.1.0 Introduction 46 3.2.0 Materials and methods 47 3.3.0 Results 48 3.3.1 Petrography 48 3.3.1.1 Inclusions in QUE 94204 silicates 49 3.3.2 Mineral chemistry 52 3.3.3 Micro X-ray diffraction (μXRD) 57 3.4.0 Discussion 57 3.4.1 Conditions of partial melting, and 57 the nature of melt extraction and migration 3.4.2 Clues to the nature of the QUE 94204 protolith 58 3.4.3 Shock and thermal metamorphic history 60 3.4.4 On choice of the “primitive enstatite achondrite” 62 nomenclature for QUE 94204 and similar rocks 3.4.4.1 Type 7 chondrite 62 3.4.4.2 Impact melt rock 63 3.4.4.3 Melt rock 64 3.4.4.4 64 3.5.0 Conclusions 65 3.6.0 Chapter 3 References 66 Chapter 4: Weathering of post-impact hydrothermal deposits 69 from the Haughton impact structure: implications for microbial colonization and biosignature preservation 4.0.0 Chapter summary and key points 69 4.1.0 Introduction 70 4.1.1 Haughton Impact Structure: A post-impact 71 hydrothermal system in a Mars analogue environment 4.1.2 Styles of hydrothermal mineralization at Haughton 73 4.2.0 Materials and Methods 74 4.2.1 Powder X-ray diffraction 74

x 4.2.2 Micro X-ray diffraction (μXRD) 75 4.2.3 Inductively Coupled Plasma – 75 Optical Emission Spectroscopy (ICP-OES) 4.2.4 Scanning Electron Microscopy (SEM) 76 4.3.0 Results 76 4.3.1 Mineralogy of the Hydrothermal Deposits at Haughton 76 4.3.1.1 Intra-breccia calcite-marcasite vugs 77 4.3.1.2 Small intra-breccia calcite or quartz vugs 80 4.3.1.3 Intra-breccia gypsum megacryst vugs 81 4.3.1.4 Hydrothermal pipe structures and surface ‘gossans’ 81 4.3.1.5 Banded Fe-oxyhydroxide deposits 82 4.3.1.6 Veining in shattered target rocks, blue mineral coatings 85 4.4.0 Discussion 86 4.4.1 Mineral constraints on physicochemical conditions 89 in the post-impact environment 4.4.2 Mineral constraints on possible geomicrobiology 90 of the Haughton post-impact hydrothermal system 4.4.3 Potential microbial habitats and metabolic strategies: 92 Eras of microbial activity in the post-impact environment 4.4.4 Potential for fossilization, mineralization 94 and long-term preservation 4.4.5 Potential for chemical and isotopic biosignatures 95 4.5.0 Summary and conclusions 96 4.6.0 Chapter 4 References 98 Chapter 5: Preservation of microbial ichnofossils in 102 basaltic glass by titanite mineralization 5.0.0 Chapter summary and key points 102 5.1.0 Introduction 103 5.1.1 Background and geologic setting 103 5.1.2 Characteristics of microbial bioalteration textures 104 in basaltic glass

xi 5.1.3 Summary of evidence for biogenicity 105 5.2.0 Experimental methods 106 5.3.0 Results 108 5.3.1 Abitibi Greenstone Belt (AGB) 108 5.3.2 Ontong Java Plateau (OJP) 111 5.4.0 Discussion and Conclusions 116 5.4.1 Implications of mineral preservation 118 of microbial ichnofossils 5.5.0 Chapter 5 References 120 Chapter 6: Proteins & organic matter in microbial borings 123 in ~120 Ma basaltic glass 6.0.0 Chapter summary and key points 123 6.1.0 Introduction 124 6.2.0 Methods 125 6.3.0 Results and discussion 127 6.4.0 Summary and conclusions 135 6.5.0 Chapter 6 References 136 Chapter 7: Basaltic Glass as a Habitat for Microbial Life: 139 Implications for Astrobiology and Planetary Exploration 7.0.0 Chapter summary and key points 139 7.1.0 Introduction 140 7.2.0 Evidence for endolithic microborings in basaltic glasses 142 7.3.0 Biogenicity of endolithic microborings in basaltic glasses 147 7.3.1 Morphological and textural evidence for biogenicity 148 7.3.2 Element distribution evidence for biogenicity 149 7.3.3 Stable Carbon Isotope Signatures 149 7.3.4 Presence of nucleic acids in modern samples 150 7.4.0 Preservation of Microbial Trace Fossils 151 in Basaltic Glass over Geologic Time 7.5.0 Planetary Environments with the Potential 153 to Host Microbial Alteration Textures in Volcanic Rocks

xii 7.5.1 Mars 153 7.5.1.1 Water and other biologically-important materials 154 are present on Mars 7.5.2 Other solar system locales 156 7.5.2.1 Europa 157 7.5.2.2 Other icy satellites 158 (Ganymede, Callisto, Enceladus, Titan) 7.6.0 Conclusions 160 7.7.0 Chapter 7 References 161 Chapter 8: Overall conclusions, or, 169 “how can everything in this thesis ever fit into a coherent picture”?

Appendix A: Curriculum Vitae 172

List of Figures Figure 2-1 Source-sample-detector geometry of 20 the Bruker D8 Discover microdiffractometer Figure 2-2 GADDS images for 22 A: LAP 02225 (S1) and B: PCA 91020 (S5) Figure 2-3 Representative examples of μXRD GADDS frames 23 and D8 Discover microscope images Figure 2-4 Relationship between petrographic shock stage 24 and FWHMχ of 2-dimensional X-ray diffraction peaks Figure 2-5 MAC 02837 – 16 EL3, S3 27 Figure 2-6 PCA 91020 – 43 EL3 S5 28 Figure 2-7 MAC 02747 – 8 EL4 S4 29 Figure 2-8 TIL 91714 – 3 EL5 S2 30 Figure 2-9 ALHA 81021 – 44 EL6 S2 31 Figure 2-10 EET 87746 – 4 EH3 S3 32 Figure 2-11 MET 00783 – 6 EH4 S4 33

xiii Figure 2-12 EET 96135 – 6 EH5 S3 34 Figure 2-13 LEW 88180 – 9 EH5(6?) S2 35 Figure 2-14 QUE 94204 – 26 primitive enstatite achondrite 36 Figure 2-15 LAP 02225 – 9 EH impact melt S1 37 Figure 3-1 Optical images of the QUE 94204 – 26 thin section 50 Figure 3-2 Details of inclusions in QUE 94204 silicates 52 Figure 3-3 Selected EPMA element maps 54 Figure 4-1 Map of the Haughton impact structure 73 Figure 4-2 Mineralization in the large intra-breccia vug 80 Figure 4-3 Mineralization at the hydrothermal pipe structure 82 near Trinity Lake Figure 4-4 Banded deposits 84 Figure 4-5 Representative SEM-BSE image and EDX chemical maps 85 Figure 4-6 Schematic representation of the biogeochemical evolution 94 of the post-impact hydrothermal environment Figure 5-1 Abitibi Greenstone Belt (AGB) thin section 109 Figure 5-2 Micro XRD study of an AGB glass shard 111 Figure 5-3 Ontong-Java Plateau (OJP) sample thin section 112 Figure 5-4 Examples of bioalteration textures in basaltic glass from 113 in situ oceanic crust Figure 5-5 Six point traverse across an OJP glass grain 115 Figure 5-6 Micro XRD of an OJP glass shard 115 Figure 6-1 Focused Ion Beam (FIB) sample petrographic context 126 Figure 6-2 Electron probe microanalyzer (EPMA) chemical maps 127 Figure 6-3 Nitrogen K-edge STXM-XANES results 129 Figure 6-4 Carbon K-edge STXM-XANES results 130 Figure 6-5 Fe L-edge STXM-XANES results 132 Figure 6-6 Ti and Ca L-edge STXM-XANES results 134 Figure 7-1 Microbial alteration textures from both modern and 143 ancient volcanic rocks Figure 7-2 Conceptual model showing the formation of 145

xiv bioalteration textures in volcanic glass

List of Tables Table 2-1 Petrographic shock effects in E chondrites 14 Table 2-2 Summary of petrographic observations and FWHMχ data 25 Table 3-1 QUE 94204 Modal abundances 51 Table 3-2 EPMA analyses of enstatite in QUE 94204 53 Table 3-3 EPMA analyses of plagioclase in QUE 94204 55 Table 3-4 EPMA analyses of QUE 94204 cristobalite 56 Table 3-5 EPMA analyses of QUE 94204 and daubreelite 56 Table 3-5 EPMA analyses of QUE 94204 57 Table 4-1 XRD and ICP-OES analyses 79 Table 4-2 Haughton post-impact hydrothermal mineral deposit types 88 Table 5-1 Measured positions of titanite reflections 114 detected in OJP glass samples Table 7-1 Illustrative limits of extrmophile life 141

xv 1

1.1.0 General introduction and overall picture

Planetary materials are composed largely of minerals. Other constituents include mineraloids (glasses and other amorphous solids), liquid phases (aqueous solutions, melts, pore fluids, organic compounds and others) and (atmospheres). None of the non- mineral components can be completely understood without consideration of the minerals with which they interact. Therefore, an understanding of planetary processes necessarily requires mineralogical investigation. Geochemistry and cosmochemistry are inextricably linked with mineralogy because minerals, and the aforementioned other constituents of planetary materials, are largely chemical systems. Therefore, an approach to planetary science grounded in mineralogy and chemistry can provide a wealth of insight into the processes and conditions that have shaped the solid material of the solar system. The guiding philosophy outlined above has been used as a grand-scale framework for the varied and diverse studies contained herein. Within this framework, mineral structures, assemblages, and compositions are integrated to elucidate planetary processes and environments. The general question addressed may be framed as follows: How can studies of primitive meteorites, impact crater secondary processes, and the bioalteration of subaqueous basaltic glass inform our understanding of the potential for life in the universe? This single question has been addressed in three distinct but related research streams.

1) What records of metamorphism are contained in the mineralogy and chemistry of primitive meteorites, and what boundary conditions do they provide on terrestrial planet formation and habitable environments? Aspects of this question are addressed by the chapters on the shock and thermal metamorphism of enstatite chondrites. 2

2) What can the mineralogical and geochemical record of post-impact hydrothermal activity, and especially the weathering assemblages of primary hydrothermal mineral deposits, tell us about the habitability of impact craters, one of the most ubiquitous features of planetary surfaces? This is the subject of the chapter on the secondary mineral assemblages of Haughton crater.

3) Terrestrial subaqueous basalts interacting with water in hydrothermal systems provide a microbial habitat that appears to have been widespread for billions of years. What mineral and chemical records of this process are preserved in the geological record, how are such records preserved, and what are the implications for the search for life beyond

Earth? Important facets of these questions are addressed in the chapters on the preservation of microbial trace fossils in basaltic glass and on the astrobiological and planetary exploration implications of the phenomenon of basaltic glass bioalteration.

1.1.1 Enstatite Chondrites

Chondritic meteorites are little-processed relics of the early solar nebula, and as such represent our best available samples of the initial materials from which the planets formed. Enstatite Chondrites (EC) are a subclass of chondrites dominated by nearly pure enstatite along with a highly-reduced assemblage including Si-bearing kamacite, troilite,

Fe-Mg-Mn monosulfides (--alabandite), (CaS),

(Fe,Ni)3P, albitic plagioclase, an SiO2 polymorph, and traces of many other phases (e.g.,

Keil, 1968; Kallemeyn and Wasson, 1986; Keil, 1989; Zhang et al., 1995; Rubin, 1997;

Brearley and Jones, 1998). Significant multi-element isotopic differences (including O, N,

Mo, Ru, Cr, Ti, and Os) exist in all known chondrite classes from terrestrial rocks with the sole exception of the EC, differences in W and Si isotope systematics are explicable 3 by core formation (e.g., Javoy, 1995; Righter et al., 2006; Scott, 2007; Javoy et al., 2010).

It is likely, therefore, that EC are closely analogous to a type of primitive solar system material that contributed substantial amounts of matter to proto-Earth, and probably the other terrestrial planets.

All EC have been affected by shock metamorphism to some extent, and petrographic and geochemical evidence supports a greater role for impact in the metamorphic history of EC than other chondrite types (Rubin and Scott, 1997; Rubin et al., 1997; Lin and Kimura, 1998; Kimura et al., 2005; Rubin, 2009). This may be related to the observation that EC have, for the most part, older cosmic ray exposure ages than other chondrite groups (Scott 2007). In fact, all meteorites are in some sense , because all have been affected (at minimum) by at least one , namely the one which ejected them from their prior to their fall on Earth. Understanding the effects of shock on EC is, therefore, a key component to using these rocks to constrain the early history of planetary accretion.

Most EC have also been affected by varying degrees of thermal metamorphism.

The source of heat for thermal metamorphism on chondrite parent bodies remains a contentious issue. Evidence in the form of extinct short-lived nuclides, notably of 26Al, and the higher abundance of long-lived nuclides (e.g., 235U, 238U, 40K) in the past are consistent with much greater radiogenic heating in the early solar system (McCoy et al.,

1995; Keil et al., 1997; McCoy et al., 1997; Keil and Bischoff, 2008). Evidence for multiple heating events and for spatiotemporal heterogeneity in heating of chondrite parent bodies may be more consistent with heating via collisions, that is, with impact heating (Rubin and Brearley, 1996; Rubin and Scott, 1997; Rubin, 2007, 2009). Other mechanisms that have been proposed include so-called Joule heating by electromagnetic 4 induction by powerful solar magnetic fields during the Suns T-tauri phase (Sonnett et al.,

1970; Herbert, 1989). It is possible, perhaps even likely, that a combination of heat sources was ultimately responsible for the thermal metamorphism of chondritic .

1.1.2 Impact Structures and Hydrothermal Activity.

Impact craters are ubiquitous in the solar system, and are expected to form on any solid planetary surface. Heat produced by impact can initiate hydrothermal activity wherever an impact occurs in a water-bearing solid target (e.g., Abramov and Kring, 2004;

Abramov and Kring, 2005; Osinski, 2005; Osinski et al., 2005). Such hydrothermal systems, and the minerals formed within them, can provide a long-lived source of thermal and chemical energy. Microbial life may colonize impact hydrothermal systems soon after impact; however, the circulation of hydrothermal fluids in post-impact hydrothermal systems is a transient phenomenon over geological timescales. Secondary (weathering) mineral assemblages associated with post-impact hydrothermal deposits, and their implications for microbial life, have been less well-studied than the aforementioned high- temperature phase. Weathering of hydrothermally-precipitated minerals (notably Fe- sulphides) can provide an additional source of energy for microbial life, and this energy source may long outlast the era of active hydrothermal circulation.

1.1.3 Subaqueous Basaltic Glass Bioalteration

Basaltic glasses preserved as pillow rims or within volcaniclastic rocks in modern oceanic crust commonly contain tubular and granular microbial alteration textures produced by etching of glass during microbial colonization (e.g., Furnes et al., 2004;

Benzerara et al., 2007; Staudigel et al., 2008a; Walton, 2008; McLoughlin et al., 2009; 5

Bridge et al., 2010). It is hypothesized that microbes enhance glass dissolution to liberate nutrients, notably transition metals, and gain chemical energy from redox reactions

(Banerjee and Muehlenbachs, 2003; Banerjee et al., 2008; Staudigel et al., 2008a;

Staudigel et al., 2008b). The initially hollow etch structures may be preserved by the precipitation of a variety of infilling mineral phases. Among the most important minerals in the preservation process is titanite (CaTiSiO5). Titanite is stable over a wide range of metamorphic conditions (Spear, 1993), allowing for preservation of endolithic microborings in metamorphosed equivalents of subaqueously-emplaced basaltic glass including ophiolite complexes and Archæan greenstone belts (Banerjee et al., 2007).

Tubular etch structures preserved in the Pilbara Craton (Australia) and Barberton greenstone belt (South Africa) constitute some of the oldest potential trace fossils known

(McLoughlin et al., 2008; Staudigel et al., 2008a).

Given reasonable estimates on the cosmic abundances and cosmochemical behaviour of the elements (as measured spectroscopically and inferred from nucleosynthetic models), and the known melting relations under plausible physicochemical conditions (P, T, fO2, etc.), it is reasonable to expect that roughly basaltic rocks will form on most planetary bodies sufficiently large to undergo large-scale melting and differentiation. Indeed, basalts are common among known samples from differentiated bodies such as Moon, Mars, and differentiated asteroids (e.g., Mittlefehldt et al., 1998; Papike et al., 1998; Shearer et al., 1998). Remote sensing data also indicates that basaltic rocks are widely distributed in the solar system (e.g., Christensen et al., 2000;

Christensen et al., 2001; Hamilton and Christensen, 2005; Sprague et al., 2009). If the interaction of water and basalt (sensu lato) has provided a habitat for life for up to ~3.5

Ga of Earth history, it is possible that it is similarly important for life throughout our solar 6 system and potentially beyond, given that the cosmochemical constraints on the emergence and development of life are likely to be broadly similar for many planetary systems.

1.1.4 Overall summary

Enstatite chondrites, impact hydrothermal deposits, and biologically-affected subaqueous basalts have been investigated using a variety of mineralogical and geochemical techniques in the broad context of planetary material constraints on the emergence and evolution habitable environments. Studies of metamorphism of enstatite chondrites provide insight into the earliest stages of the formation of terrestrial planets.

Weathering of impact-generated hydrothermal deposits may represent a relatively understudied setting for microbial life in impact structures. Microbes can use basaltic glass as a growth substrate, and leave a geological record of this process. Investigation of the mechanisms whereby microbial trace fossils are preserved will facilitate searches for similar life traces in diverse terrestrial and extraterrestrial materials. The unifying concept in the diverse studies contained herein is that mineralogy, allied with geochemistry, provides constraints and boundary conditions on life in the universe.

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9438.

13

Chapter 2: Micro X-ray diffraction assessment of shock stage in enstatite chondrites

Chapter summary and key points

A new method for assessing the shock stage of enstatite chondrites has been developed, using in situ micro X-ray Diffraction (μXRD) to measure the full-width at half-maximum

(FWHMχ) of peak intensity distributed along the direction of the Debye rings, or chi angle (χ), corresponding to individual diffractions in two-dimensional XRD patterns. This

μXRD technique differs from previous XRD shock characterization methods: it does not require single crystals or powders. In situ μXRD has been applied to polished thin sections and whole-rock meteorite samples. Three frequently-observed orthoenstatite diffractions were measured: (020), (610) and (131); these were selected as they did not overlap with diffraction lines from other phases. Enstatite chondrites are commonly fine- grained, stained or darkened by weathering, shock-induced oxidation, and metal/sulfide inclusions; furthermore, most E chondrites have little olivine or plagioclase. These characteristics inhibit transmitted-light petrography, nevertheless, shock stages have been assigned: MAC 02837 (EL3) S3, PCA 91020 (EL3) S5, MAC 02747 (EL4) S4, TIL

91714 (EL5) S2, ALHA 81021 (EL6) S2, EET 87746 (EH3) S3, MET 00783 (EH4) S4,

EET 96135 (EH4-5) S2, LEW 88180 (EH5) S2, QUE 94204 (EH7*) S2, LAP 02225 (EH impact melt) S1; for the six with published shock stages, there is agreement with the published classification. FWHMχ plotted against petrographic shock stage demonstrates positive linear correlation. FWHMχ ranges corresponding to shock stages were assigned as follows: S1 < 0.7º, S2 = 0.7º–1.2º, S3 = 1.2º–2.3º, S4 = 2.3º–3.5º, S5 > 3.5º, S6–not measured (no S6 E-chondrites are known as of this writing). Slabs of Abee (EH impact- melt breccia), and NWA 2212 (EL6) were examined using μXRD alone; FWHMχ values 14 place both in the S2 range, consistent with literature values. Micro-XRD analysis may be applicable to other shocked orthopyroxene-bearing rocks.

*The official classification for QUE 94204 is EH7; however, in a subsequent study (see

Chapter 3), I propose that QUE 94204 is more properly referred to as a ‘primitive enstatite achondrite’ in accord with its detailed petrologic and mineral-chemical characteristics.

2.1.0 Introduction

Meteorites are delivered to Earth following ejection from a parent body during hypervelocity impact events. Many meteorites, especially chondrites, originate in regolith breccias, and therefore have experienced multiple shock events (e.g., Bischoff et al., 1982; Rubin et al., 1983; Scott et al., 1983; Scott et al., 1985; Lusby et al., 1986; Scott et al., 1986; Williams et al., 1986; Scott et al., 1991; Stöffler et al., 1991; Scott et al.,

1992). Understanding of shock metamorphic effects in chondritic meteorites is therefore critical to disentangling the signatures of nebular, parent body, and terrestrial processes.

Enstatite (E) chondrites formed under anhydrous, highly reducing conditions fundamentally different from those experienced by ordinary and carbonaceous chondrites

(e.g., Keil, 1968, 1969, 1989; Brearley and Jones, 1998; Scott, 2007).

Enstatite chondrites are thought to originate from parent objects that formed near the proto-sun (e.g., Keil, 1989; Scott, 2007). Based upon oxygen isotopic and compositional data, E chondrites have been proposed as a major component of the terrestrial planets (Javoy, 1995; Righter et al., 2006; Javoy et al., 2010). Enstatite chondrites are divided into EH (high metallic Fe) and EL (low metallic Fe) subclasses, 15 based on the abundance and Si content of Fe-Ni metal, and the composition of the Fe-Mn-

Mg monosulfide phase(s), with EL chondrites containing ferroan alabandite – (Mn,Fe)S and EH chondrites containing niningerite – (Mg,Fe)S (Kallemeyn and Wasson, 1986;

Zhang et al., 1995). Enstatite chondrites are further classified into petrologic grades ranging from 3 to 6, following the textural alteration scheme originally developed for ordinary chondrites by van Schmus and Wood (1967), with some authors adding a type 7 although researchers have used a 7 designation to account for chondrites that have no relict (Brearley and Jones, 1998). The relationship between petrologic grade and thermal history is less straightforward than in ordinary chondrites: EH and EL chondrites both appear to have formed from similar precursor materials under similar conditions; EL chondrites however have experienced more-prolonged low-temperature metamorphism resulting in textural and mineralogical differences (e.g., Zhang et al., 1995;

Zhang et al., 1996; Schneider et al., 2002; Schneider et al., 2003). Enstatite chondrites have generally experienced more intense thermal and shock metamorphism than most other chondrite groups (Zhang et al., 1996; Rubin and Scott, 1997; Rubin et al., 1997).

The thermal metamorphism of E chondrites may therefore reflect a combination of exogenic (impact) and endogenic (26Al and other radionuclides, gravitational compression) heat sources (Rubin et al., 1997; Rubin, 2009).

The standard approach to assessing the shock history of chondritic meteorites is the identification of textural and mineralogical effects of shock metamorphism using optical petrography. Shock stage assessment in ordinary chondrites was developed by

Stöffler et al. (1991) and is based primarily on features in olivine and plagioclase. This scheme was extended to carbonaceous chondrites by Scott et al. (1992). Assigning shock stages to enstatite chondrites using petrographic techniques is challenging, however, 16 because 1) olivine is not present in E chondrites except in the least thermally equilibrated

(type 3), and the olivine that is present is commonly in the form of very small, partly resorbed crystals; 2) large grains of plagioclase are rare in all but the most equilibrated samples; and 3) silicate darkening due to minute metal/sulfide inclusions and/or shock oxidation reduces the ability to distinguish petrographic shock indicators such as twinning, exsolution, amorphization and planar fractures/planar deformation features; and 4) enstatite in E chondrites is commonly very fine grained, as in radial pyroxene chondrules.

Enstatite chondrites also weather rapidly under terrestrial conditions; therefore silicates are often stained by Fe-oxyhydroxides and/or oxides that further obscure petrographic shock indicators. Despite the aforementioned challenges to optical petrography, Rubin et al. (1997) have developed a system of petrographic shock stage indicators for orthopyroxene in enstatite chondrites. The shock stage classification scheme of Rubin et al. (1997) is summarized in Table 2-1.

Table 2-1: Modal abundances in volume % as determined by point counting (n=1650) Mineral points vol. % enstatite 1154 70 plagioclase 133 8 metal 83 5 troilite 79 5 daubreelite 8 <1 cristobalite 47 3 weathering* 146 9 *Terrestrial weathering products consisting of a mixture of very fine-grained goethite, gypsum and calcite.

The passage of hypervelocity shock waves of increasing shock pressures breaks crystals into progressively smaller and increasingly misoriented mosaic blocks or subdomains, which may eventually lead to the complete destruction of long-range order in the crystal 17 structure, i.e. solid state amorphization/diaplectic glass formation (Hörz and Quaide,

1973). The effects, which lead to the diminution of crystal subdomain sizes, are a complex mixture of cataclastic and intergranular flow phenomena within the crystal structure including fracturing, cleaving, slipping, gliding, twinning and kinking (Hörz and

Quaide, 1973; French, 1998a). These processes collectively lead to the breakdown of the originally homogeneous crystal structure into many smaller misoriented subdomains; this is referred to as mosaic spread or ‘mosaicity’ (also called mosaicism). The effects of shock cause ‘streakiness’ in Debye-Scherrer XRD patterns of materials that were single crystals prior to the shock event (Hörz and Quaide, 1973). Indeed, Hörz and Quaide

(1973) used this technique to demonstrate a correlation between peak pressures in shock experiments and ‘streaking’ of X-ray diffraction spots on film. In the study of Hörz and

Quaide (1973), the diffracted X-ray intensity distribution along the Debye rings was shown to change from small discrete spots in unshocked single crystals to increasingly elongate arcs, and the angular extent of these arcs was used as a quantitative measure of mosaicity as defined above. The present study allows for similar measurements to be made in situ with an efficient two-dimensional detector to replace the conventional

Debye-Scherrer film based technique.

In this study we apply the micro X-ray diffraction (μXRD) technique to compliment petrographic assessments of shock level for eleven enstatite chondrites, all of which are Antarctic finds recovered by the ANtarctic Search for METeorites (ANSMET) program. Antarctic meteorites investigated in this study were as follows: MacAlpine Hills

(MAC) 02837, EL3; Pecora Escarpment (PCA) 91020, EL3; MacAlpine Hills (MAC)

02747, EL4; Thiel Mountains (TIL) 91714, EL5; Allan Hills (ALHA) 81021, EL6;

Elephant Moraine (EET) 87746, EH3; Meteorite Hills (MET) 00783, EH4; Elephant 18

Moraine (EET) 96135, EH5; Lewis Cliff LEW 88180, EH5; Queen Alexandra Range

(QUE) 94204, primitive enstatite achondrite (officially EH7); LaPaz Icefield (LAP)

02225, EH impact melt. The μXRD shock criteria developed from the Antarctic samples were applied to two additional E chondrite samples: Abee (EH4 impact melt breccia) and

Northwest Africa (NWA) 2212 (EL6), using rock slab samples. Five of the Antarctic E chondrites investigated in this study have previously been assigned shock stages by Rubin et al. (1997), although different polished sections were used here. Heterogeneity in the meteorites may play a role in creating some discrepancy between these two studies. It is important to note that many investigators have found that the apparent degree of shock expressed in minerals from impact metamorphosed rocks is commonly highly variable

(French, 1998a, b). Because many enstatite chondrites probably originated in asteroid regolith breccias (e.g., Keil, 1989; McCoy et al., 1995; Schneider et al., 2002), it is likely that they are also subject to heterogeneity in shock metamorphism.

2.2.0 Materials and Methods

Polished thin sections of EH and EL chondrites having a range of textural and thermal metamorphic grades were investigated with a petrographic microscope in transmitted and reflected light. Shock stage assignment was made using the shock features in orthopyroxene as described by Rubin et al. (1997). We also applied the criterion of Stöffler et al. (1991) that shock stage must reflect the highest stage indicated by at least 25% of the grains investigated. All thin section samples are Antarctic finds; in addition, slab samples of the Abee and NWA 2212 meteorites were investigated using

μXRD only. Sample identities, types and thin section numbers are summarized in Table

2-2. 19

2.2.1 Micro X-ray Diffraction (μXRD)

Micro XRD data were collected using the Bruker AXS D8 Discover microdiffractometer at the University of Western Ontario, using Cu Kα radiation (λ =

1.5418 Å) with a 500 μm nominal beam diameter, an XYZ sample stage with microscope for target selection, and a Hi-STAR two-dimensional detector using general area diffraction detector system (GADDS) software to detect the diffracted X-rays. In a two dimensional X-ray diffraction (XRD) pattern, a single crystal produces one or more discrete spots, each of which corresponds to a family of lattice planes defined by a Miller index (hkl) (e.g., Azároff and Buerger 1958). A polycrystalline sample (i.e. powder), having crystallites in all orientations, produces a circular arc of diffracted rays corresponding to the intersection of a cone of diffracted rays with Ewald’s sphere, this is termed a Debye ring (e.g., Azároff and Buerger 1958). Micro XRD GADDS images of in situ materials are thus a hybrid between single crystal and powder patterns, commonly having both ‘spot’ and ‘ring’ patterns or intermediate discontinuous ‘spotty rings’ (He,

2003; Helming et al., 2003; Flemming, 2007). Counting time for μXRD data collections was 45 minutes per GADDS frame, over which time the source and detector remained stationary, in ‘coupled scan’ mode. However, an ‘off-coupled’ geometry was used, with the source at 11° 2θ and the detector (which subtends 35°) centered at 15° 2θ, to avoid diffracted X-rays being cut off by the stage. Because the 500 μm nominal X-ray beam diameter is much larger than typical enstatite grains in the samples, the X-rays will certainly have diffracted from many enstatite crystals to produce each GADDS image.

Therefore, it is not possible to exactly correlate the shock features observed petrographically in a particular grain with a particular μXRD GADDS image, although 20 this might be possible with a smaller beam diameter and/or using oriented grain mounts.

The results presented here therefore represent an average measure of shock-induced mosaicity over many crystals. Eight to eleven spots were analyzed on each section, each containing multiple grains (Table 2-2 and Figures 2-5 to 2-15). Peak full width at half maximum (FWHMχ) was measured along the direction of the Debye rings, or chi angle (χ) for three Miller indices [(020), (610) and (131)] using the Bruker AXS EVA software package; this corresponds to up to 20-30 diffractions for each Miller index per spot (e.g.,

Figure 2-2a). The rationale behind using the peak FWHMχ is that it is an easily reproduced and simple measure of the width of the peaks, which is less susceptible to contamination due to peak overlap as compared to measurements of the full peak width at the base of the peak. Measurement of the FWHMχ of peak intensities integrated along the

Debye rings as a quantitative measure of the mosaicity of the sample is a refinement of previously-described methods for inferring degrees of strain and deformation from μXRD

GADDS images (Flemming, 2007; Flemming et al., 2007; Moser et al., 2008), which measured full width at the base of the peak.

Analysis of the distribution of intensity along the Debye rings (the circular patterns of spots produced by the intersection of the cone of diffracted X-rays produced by the crystal lattice of the specimen as determined by Bragg's law with the detector surface) in the GADDS images enables the measurement of textural and microstructural information, including shock-induced asterism. Diffracted X-ray intensity was integrated as a function of chi angle (χ, the angle subtended by the Debye ring) to produce intensity vs. χ plots. In this study, we use the progressive elongation or ‘streakiness’ of diffracted ray ‘spots’ along the arc of the Debye rings to probe the progressive diminution of crystal subdomain size and increase in mosaic spread, with concomitant destruction of long 21 range structural order accompanying increased shock stage. There was, however, no change in FWHM in the 2θ dimension, within error, indicating that particle (or diffracting subdomain) size remained above ~200 nm, which would mark the onset of peak broadening in 2θ (e.g., Brindley, 1945; Azároff and Buerger, 1958; Cullity, 1978;

Pecharsky and Zavalij, 2005).

To ensure that the diffraction phenomena measured are related to orthopyroxene and not to other phases (especially metal and sulfides, which can be highly deformed by processes other than shock, notably in the process of thin section preparation) the peaks integrated for intensity vs. χ plots were chosen so as to avoid overlap with peaks from other minerals. The (020), (610) and (131) diffractions were selected. Because the vectors normal to the (020), (610) and (131) lattice planes constitute a basis for three-dimensional space, this allows, in principle, for the assessment of the strain in any crystallographic direction. Further details of the μXRD apparatus and technique are described by

Flemming (2007). Figure 2-1 shows a schematic of the Bruker D8 Discover microdiffractometer source-sample-detector geometry, illustrating the ability to collect

μXRD data from any sample that can be mounted on the sample stage without colliding with the beam optics.

22

Figure 2-1: Source-sample-detector geometry of the Bruker D8 Discover microdiffractometer. X-rays are produced in a sealed tube source, typically operating at 40 kV accelerating voltage and 40 mA current. A gobel mirror produces a parallel incident X-ray beam and a pinhole collimator snout reduces the beam to 500 microns. The sample is mounted on a stage with independent X Y and Z drives. Areas are selected for analysis using a vertically-mounted microscope and video camera system with a HeNe targeting laser; the instrument is aligned such that the microscope is in focus when the laser is on the crosshairs and that spot is at the center of diffraction. Diffracted X-rays are collected using a Hi-STAR two-dimensional detector using general area diffraction detector system (GADDS) software. This instrument can collect μXRD data for any material that can be mounted on the sample stage including powders, polished sections, rock slabs, and whole meteorites.

2.3.0 Results

2.3.1 Micro XRD

Examination of in situ μXRD GADDS images showed marked differences between samples of different shock stage; examples from LAP 02225 (S1) and PCA

91020 (S5) are shown in Figure 2-2. To quantify the differences observed in GADDS images for samples of various shock stages, the average full width at half maximum as integrated along χ (FWHMχ), was determined for each of the (020), (610) and (131) 23 diffractions, over all pyroxene grains measured for each sample. These results are summarized in Table 2-2. There is a clear correlation between FWHMχ measured by

μXRD and petrographic shock stage as illustrated by Figure 2-3. There appears to be no systematic difference in peak FWHMχ between the three diffractions investigated. Ranges in peak FWHMχ corresponding to each shock stage have been assigned as follows: S1 <

0.7º, S2 = 0.7º–1.2º, S3 = 1.2º–2.3º, S4 = 2.3º–3.5º, S5 > 3.5º, S6 was not measured, as there were no S6 stage E chondrites available for this study. The bounds of the shock stage FWHMχ ranges given are defined by the lowest FWHMχ value for a given shock stage. Micro XRD also confirmed the major mineral identification made by optical petrography in thin-sectioned samples. Two-dimensional GADDS images for each sample are shown in Figure 2-3.

24

Figure 2-2: GADDS images for A: LAP 02225 (S1) and B: PCA 91020 (S5) showing the range of shock effects. There is a general increase in the ‘streakiness’, that is, the spread of the individual diffractions along the arc of the Debye rings (or chi angle χ) with increasing shock stage, this is quantified by measuring the FWHMχ of the diffractions. The increase in FWHMχ is interpreted as representing increasing mosaicity the sample with increased shock stage. Diffraction spots in the LAP 02225 pattern are clearly delineated and circular, while those in PCA 91020 display extreme mosaicity. The extent of mosaicity of individual diffractions is correlated with streak length along the angle χ (i.e. the angle subtended by the Debye rings), here marked by the arrows; examples for the (610) and (131) diffractions are shown. On the right-hand side are the integrated intensity vs. χ plots, with a schematic representation of FWHMχ measurements. 25

Figure 2-3: Representative examples of μXRD GADDS frames and D8 Discover microscope images for the enstatite chondrites in this study. There is a general increase in the FWHMχ of enstatite diffractions with increasing shock stage. Variations in background intensity in GADDS frames are due mostly to the amount of Fe in the analysis volume (Fe fluoresces under Cu Kα radiation). The area within the white circles denotes the nominal 500 μm footprint of the μXRD beam. The spot numbers in each image identify the analysis location in the respective polished section maps in Figures 2-5 to 2-15. 26

For the two slab samples, NWA 2212 and Abee, in situ μXRD data were collected in the same manner as for thin sections, and the average peak FWHMχ for each of the

(020), (610) and (131) diffractions were measured. The values obtained are as follows, for

(020) (610) (131) NWA 2212: FWHMχ = 0.91(2)º, FWHMχ = 0.91(3)º and FWHMχ = 0.91(3)º;

(020) (610) (131) for Abee: FWHMχ = 1.25(15)º, FWHMχ = 0.96(12)º and FWHMχ = 1.10(15)º; placing both meteorites in the S2 range. Stated FWHMχ errors for the slab samples are

±1σ. The large spread and larger standard deviations in FWHMχ values for Abee may be related to the variation in apparent shock stage documented by Rubin and Scott (1997), and is likely related to melting and the possible presence of relict grains of higher shock stage. Reorientation of the crystal structure due to melt-related flow may be difficult to distinguish from the effects of low-level shock.

Figure 2-4: Histogram displaying the relationship between petrographic shock stage and FWHMχ of 2-dimensional X-ray diffraction peaks as integrated along the chi direction (Debye rings). Data correspond to X-ray diffractions from the (020), (610) and (131) diffractions of orthoenstatite. Blue symbols: (020); Green: (610); Red (131). FWHMχ of diffracted X-ray peaks (as derived from intensity vs. χ plots) are directly correlated with petrographic shock stage. In some cases, the FWHMχ data points are offset horizontally for clarity. Error bars are one standard deviation (1σ). Dashed horizontal lines are the estimated FWHMχ ranges for each shock stage.

27

Table 2-2: Summary of the petrographic observations and μXRD FWHMχ data for the 11 Antarctic E chondrites in this study with additional data from Rubin et al. (1997) as indicated. MAC PCA MAC TIL ALHA Meteorite 02837 91020 02747 91714 81021 Type EL3 EL3 EL4 EL5 EL6 Shock stage, this S3 S5 S4 S2 S2 study Thin Section # (this 16 43 8 3 44 study) Shock stage (Rubin N/A S5 N/A S2 S2 et al., 1997) Thin section # N/A 19 N/A 9 46 (Rubin et al., 1997) #μXRD points 11 10 10 10 9 § Average FWHMχ (020) 2.05(47)º 3.69(35)º 2.99(25)º 0.88(6)º 0.85(3)º

(610) 1.53(14)º 4.09(83)º 3.21(35)º 0.84(4)º 0.87(4)º

(131) 1.75(15)º 4.18(64)º 2.87(43)º 0.83(5)º 0.80(4)º Silicate darkening Mod. High Low High Low Weathering* C Ce B/C C A Inclusions in Mod. Low High High Low enstatite

EET MET EET LEW QUE LAP Meteorite 87746 00783 96135 88180 94204 02225 EH imp. Type EH3 EH4 EH5 EH5 EH7 melt Shock stage, this S3 S4 S3 S2† S2 S1 study Thin Section # (this 4 6 6 9 26 9 study) Shock stage (Rubin S3 N/A N/A S3 S2 N/A et al., 1997) Thin section # 32 N/A N/A 19 10 N/A (Rubin et al., 1997) #μXRD points 10 11 10 8 10 10 § Average FWHMχ (020) 1.36(14)º 2.61(7)º 1.43(22)º 1.07(13)º 1.03(14)º 0.78(4)º

(610) 1.23(12)º 2.60(15)º 1.85(21)º 1.12(7)º 1.13(11)º 0.74(3)º

(131) 1.25(20)º 2.65(36)º 2.16(18)º 1.17(18)º 1.01(7)º 0.73(5)º Silicate darkening Mod. Low High High Low Low Weathering* Ce C B B/Ce A-C A Inclusions in Mod. High Low Low High High enstatite *Weathering grades as listed in MetSoc database. †Probably S3-4 which subsequently annealed (our interpretation). §Uncertainties are ±1σ. Abbreviations for meteorites as follows: MAC = MacAlpine Hills; PCA = Pecora Escarpment; TIL = Thiel Mountains; ALHA = Allan Hills; EET = Elephant Moraine; MET = Meteorite Hills; LEW = Lewis Cliff; QUE = Queen Alexandra Range; LAP = LaPaz Icefield. 28

2.3.2 Optical Petrography

The results of petrographic examination in transmitted and reflected light are summarized in Table 2-2. Shock stages are assigned as follows: MAC 02837 (EL3) – S3,

PCA 91020 (EL3) – S5, MAC 02747 (EL 4) – S4, TIL 91714 (EL5) – S2, ALHA 81021

(EL6) – S2, EET 87746 (EH3) – S3, MET 00783, (EH4) – S4, EET 96135 (EH4-5) – S2,

LEW 88180 (EH5) – S2, QUE 94204 (EH7*) – S2, LAP 02225 (EH impact melt) – S1.

Intra-sample heterogeneity may account for the discrepancy in the case of LEW 88180. In addition to shock stages, features of the meteorites including textures, mineralogy, weathering, silicate darkening, and the presence of minute inclusions in enstatite were noted. Figures 2-5 through 2-15 are transmitted, cross-polarized light maps of the thin sections in this study, and are annotated with the locations of all μXRD analysis. Silicates commonly contain submicron opaque inclusions consisting of metal and sulfides, which form arcuate to linear trails and/or planes that may cross-cut mineral grain boundaries.

Enstatite grains in many of these meteorites also contain abundant transparent inclusions, with morphologies ranging from rounded spheroids a few microns in diameter to elongate needles up to tens of microns in length, which may be melt inclusions or, less likely, voids. The possible melt inclusions or voids are distinct from the metal-sulfide inclusions related to silicate darkening in that they are not opaque, they commonly exhibit elongated habits, and they can have crystallographically-controlled boundaries. Inclusions in enstatite commonly occur along planar and irregular fractures, and may preserve a record of such fractures after thermal annealing. Fe-oxyhydroxides and oxides produced by terrestrial weathering have stained the silicate phases to varying degrees in all of the investigated meteorites.

29

Figure 2-5: MAC 02837 – 16 EL3, S3: Enstatite contains pervasive irregular and planar fractures, displays undulose extinction, and has clinoenstatite lamellae on (100). Plagioclase is rare and very fine grained (~tens of microns), and exhibits irregular fractures and possibly undulose extinction. No olivine was observed in this section. Silicates are extensively stained by terrestrial weathering products and silicate darkening is moderate. Metal and sulfides occur in large (up to mm-scale) masses. Chondrules and fragments are sharply delineated from the matrix; most are radial or porphyritic pyroxene. 30

Figure 2-6: PCA 91020 – 43 EL3 S5: Weathering and staining are extensive. Chondrules and chondrule fragments are sharply delineated, oblate, and possibly weakly aligned or foliated. Radial pyroxene chondrules are most the common type, followed by porphyritic pyroxene. Silicate darkening is pervasive. Metal occurs as irregular masses of up to ~100 μm, sulfides occur as finely disseminated bodies up to a few tens of microns. Veins of highly weathered material extend from the edges of the section inward. The highly weathered material may be a combination of weathered shock veins, weathered melt glass from atmospheric flight, evaporites or reprecipitated leached material. Multiple sets of decorated planar fractures in enstatite were observed. Few possible melt inclusions. No large plagioclase grains were observed. Rare, highly resorbed olivine grains were observed, they are at most a few tens of microns in their longest dimension. Enstatite shows mosaic extinction, clinoenstatite lamellae and polysynthetic twinning, some enstatite grains have an appearance reminiscent of ‘toasted’ quartz in terrestrial impactites (French 1998a). Rare occurrences of small (~tens of microns) purple-blue coloured, isotropic material hosted in enstatite were noted, notably near spot 4; these may be ringwoodite. Micro XRD of spot 4 did not unambiguously detect ringwoodite, likely due to very low concentrations. 31

Figure 2-7: MAC 02747 – 8 EL4 S4: Weathering and silicate darkening are extensive. Chondrules and chondrule fragments have slightly blurred contacts with the matrix. Most chondrules are porphyritic pyroxene, with lesser amounts of radial pyroxene. Metal occurs as irregular blebs up to ~100 μm; sulfides occur as finely disseminated bodies up to a few tens of microns. Possible thin opaque veins, that may be weathered shock veins, weathered melt glass from atmospheric flight, evaporites or reprecipitated leached material. Polysynthetic twins, clinoenstatite lamellae on (100) and weak mosaic extinction are pervasive in enstatite. Enstatite contains extensive planar fractures that are commonly decorated by inclusions, and occur in multiple sets. Olivine is very rare, irregularly fractured and highly resorbed, and displays weak mosaic extinction.

32

Figure 2-8: TIL 91714 – 3 EL5 S2: Weathering and silicate darkening are extensive. Enstatite has irregular fractures and undulose extinction; some rare grains also have planar fractures. This section is likely slightly thicker than a standard thin section, accounting for the apparently high birefringence of some enstatite grains. No olivine or plagioclase grains were observed. Metal and sulfides occur as discrete grains, up to hundreds of microns in size, commonly interstitial to silicates. Chondritic texture is discernable, but the boundaries of chondrules and chondrule fragments are very blurred by recrystallization. Networks of veins of highly weathered material are pervasive, that may be weathered shock veins, weathered melt glass from atmospheric flight, evaporites or reprecipitated leached material. Weathered fusion crust is apparent on one edge of the section. Inclusions in enstatite are abundant.

33

Figure 2-9: ALHA 81021 – 44 EL6 S2: The section consists of enstatite and plagioclase with an interlocking texture and interstitial metal and troilite. Enstatite has weak undulose extinction, and scattered irregular fracturing. Plagioclase is albite twinned and displays weak undulose extinction. Weathering is concentrated within a band 1-3 mm, with small amounts of weathered material extending inward from an edge recognizable as fusion crust. Silicate darkening is very minor. Troilite contains thin exsolved bands of alabandite. Relict chondrules are rare and highly recrystallized with metal and sulfide cores, chondritic texture is barely recognizable. Note a prominent example of a relict chondrule near spots 1 and 2. Enstatite commonly contains some small inclusions.

34

Figure 2-10: EET 87746 – 4 EH3 S3: Chondrules and chondrule fragments are well-delineated from the matrix; porphyritic pyroxene and radial pyroxene are most common chondrule types, some cryptocrystalline pyroxene chondrules as well. Very few chondrules are intact. Some chondrules contain large euhedral enstatite crystals. Enstatite commonly has lamellae of clinoenstatite along (100), displays undulose extinction and irregular fracturing. Plagioclase is rare and fine-grained, possibly displaying undulose extinction. Inclusions are common in enstatite. Metal occurs as large, up to mm-scale grains; sulfides are finely dispersed as small (~ few tens of microns) grains. Sulfides are common along the boundaries of chondrules and chondrule fragments. Fusion crust is recognizable on one edge, and a weathering rind on all others. Light weathering penetrates 1-3 mm inwards from the edges, and occurs along veins within the section. Silicate darkening is moderate.

35

Figure 2-11: MET 00783 – 6 EH4 S4: The section is moderately weathered and stained, silicate darkening is light. Chondrules and chondrule fragments are slightly blurred at their boundaries with the surrounding matrix. Most chondrules are radial pyroxene, with lesser porphyritic pyroxene. Metal and sulfides occur interstitial to silicates in grains of up to a few hundred microns, and as inclusions within chondrules/chondrule fragments. Enstatite has weak mosaic extinction, clinoenstatite lamellae on (100), polysynthetic twinning, irregular and planar fractures, and abundant inclusions. Very rare, tiny (few microns) resorbed olivine crystals were observed in chondrules; olivine displays possible mosaic extinction. Very rare and very small (~few μm) plagioclase grains were observed.

36

Figure 2-12: EET 96135 – 6 EH5 S3: Weathering, staining and silicate darkening are extreme. Chondrules and chondrule fragments are blurred due to recrystallization and often nearly opaque due to metal and sulfide inclusions (silicate darkening). Porphyritic pyroxene chondrules are common (though original chondrule type is difficult to ascertain due to recrystallization) and most chondrules are fragmented. Enstatite has undulose extinction, irregular fractures and some clinoenstatite lamellae on (100). Inclusions in enstatite are rare. Metal occurs as large (up to several millimeters) irregular masses. Sulfides occur as finely disseminated, (~tens of microns) grains, or as larger irregular masses of troilite within metal. Troilite within metal commonly contains thin very thin (~micron) exsolution lamellae, probably of niningerite. Metal commonly has linear, possibly crystallographically-controlled boundaries with euhedral enstatite crystals.

37

Figure 2-13: LEW 88180 – 9 EH5(6?) S2: The section is partially aerodynamically shaped and coated with weathered fusion crust on the shaped face. Silicates are extensively stained by weathering, and silicate darkening is extreme. Chondritic texture is discernable; however, the boundaries between chondrules or chondrule fragments and matrix are blurred by recrystallization. Metal and sulfides are interstitial to silicates. Enstatite has irregular fractures and displays undulose extinction. Plagioclase is rare and has weak undulose extinction. Enstatite commonly contains planar features that have been intruded by metal or sulfide; these may be relict planar fractures and may indicate that LEW 88180 was shocked to ~S4 and had this texture preserved by the intrusions. The classification of LEW 88180 in the Meteoritical Society database is EH6, however, the petrographic features observed in this section are more consistent with a classification of type EH5, in agreement with the findings of Rubin et al. (1997) and Zhang et al. (1995).

38

Figure 2-14: QUE 94204 – 26 primitive enstatite achondrite (Met Soc classification EH7, but see Chapter 3) S2: Extensive weathering and staining. Silicate darkening is very minor. Enstatite occurs in millimeter scale rounded, equant grains, commonly with ~120º triple junction boundaries. Enstatite has undulose extinction and extensive irregular fracturing, and is polysynthetically twinned. Plagioclase has weak undulose extinction and is albite twinned. Plagioclase grains are smaller, (up to several hundred microns), are equant, with have rounded edges and are commonly interstitial to enstatite grains. Metal and sulfides fill the interstices between silicate grains, with textures consistent with a metal-sulfide melt wetting the boundaries between silicates. Troilite is the most common sulfide, and commonly contains thin exsolution lamellae of daubreelite. The meteorite is extensively weathered, with both metal and sulfide are highly weathered and commonly replaced by goethite, the silicates are highly stained along fractures and grain boundaries, and veins of weathered and/or evaporite material are common. No discernable chondritic textures were observed. Melt inclusions and/or voids are very abundant and commonly form long, euhedral needles (~few microns by ~tens of microns) along crystallographic planes. Curvilinear trails of micron-to-submicron scale rounded opaque inclusions, commonly crossing grain boundaries were observed. These inclusion trails are probably metal and/or sulfide melts that intruded into fractures that were later annealed, consistent with at least one episode of shock metamorphism prior to the final thermal metamorphism of QUE 94204.

39

Figure 2-15: LAP 02225 – 9 EH impact melt S1: No chondritic textures observed, instead, LAP 02225 displays a porphyritic texture consisting of elongate laths of enstatite (~tens of microns by ~hundreds of microns), in a groundmass dominated by fine-grained enstatite and plagioclase, with interstitial metal and sulfides including troilite with daubreelite and keilite. Thin perryite exsolution lamellae are common along (111) planes of the metal. Extinction in enstatite and plagioclase is sharp, fracturing is irregular and light. Weathering and staining are moderate to light, silicate darkening is light. Metal and sulfides meet at rounded interfaces that reflect the shape of metal dendrites formed from a single Fe‐Ni‐S liquid. Some large enstatite laths are twinned, and most contain a core with abundant metal/sulfide inclusions. The cores of the enstatite laths may have been riddled with hollow voids which were intruded by metal and sulfides. The shock stage assigned to LAP 02225 in the present study refers to shock metamorphism following crystallization from impact melt.

2.4.0 Discussion

Shock-induced mosaic spread, as inferred from the FWHMχ along the Debye rings of the (020), (131) and (610) diffractions of enstatite, correlates very well with 40

petrographic shock stage (Figure 2-4). There is no systematic variation in FWHMχ between the different Miller indices investigated, within the error of our measurements; this may indicate that the degree of crystal structure misorientation is uniform when averaged over the analysis volume of the μXRD measurements. Petrographic shock stages and μXRD FWHMχ values determined in this study correspond as much as possible to bulk-rock shock effects, insofar as shock veins, melt pockets, faults and other localized excursion regimes have been avoided. Due to the common presence of terrestrial weathering and silicate darkening, the abundance of fine-grained material in many samples, and the heterogeneous nature of chondritic meteorites, it is not possible to be certain that all such materials have been excluded. Careful selection of analysis points using correlated petrographic observation, multiple analyses for each sample and the geometry, whereby each μXRD point generally contains diffractions from multiple crystals, all mitigate the effects of localized excursions.

Silicate darkening due to submicron-scale metal and/or sulfide inclusions is apparent in most of these meteorites (Table 2-1). There is no strong correlation between shock stage and the degree of silicate darkening, in agreement with previous findings

(Stöffler et al., 1991; Rubin et al., 1997). This is not surprising because many effects besides shock, including thermal metamorphism, in situ reduction of FeO in silicates during parent body metamorphism, and terrestrial weathering, can lead to silicate darkening (Stöffler et al., 1991; Rubin et al., 1997). Terrestrial weathering phases including Fe-oxyhydroxides, gypsum, and calcite have been observed petrographically and by μXRD in some samples. The presence of weathering phases does not appear to cause changes the FWHMχ of enstatite diffractions in the same analysis location. 41

Type 5 and 6 E chondrites, and E chondrite melt rocks, are of lower shock stage than types 3 and 4. Many of the higher thermal metamorphic grade E chondrites show evidence of annealing from higher shock stages, such as the preservation of relict exsolution lamellae, fractures, and twin boundaries, injected by metal and/or sulfide; and trains of metal and/or sulfide inclusions along annealed fracture planes. It is possible that the higher petrologic types of E chondrites are the result of intense shock heating rather than metamorphism due to endogenic heating (e.g., Rubin, 2009). Alternatively, evidence for multiple, overlapping episodes of shock metamorphism and thermal annealing could indicate that shock and endogenic thermal metamorphic processes were penecontemporaneous on the parent asteroids of the E chondrites.

Abee is an impact melt breccia, and LAP 02225 is an impact melt rock. The meaning of petrographic shock stage is somewhat ambiguous for melt rocks. The shock stages assigned in the present study pertain to the final state of the samples. In the case of

Abee, this corresponds to an average of primary (relict) and secondary (crystallized from impact melt) crystals. For LAP 02225, no evidence for a population of relict grains has been found; therefore, the shock stage assigned corresponds to shock events that post-date crystallization from an impact melt.

With decreasing grain size, the number of diffracted X-rays detected which correspond to each lattice plane (i.e. Miller index) increases. In the limit of a random distribution of very fine grain sizes, less than ~5 μm, the distribution of intensity along the Debye rings will become uniform (Brindley, 1945; Azároff and Buerger, 1958;

Cullity, 1978; Pecharsky and Zavalij, 2005). Shock metamorphism may produce similar effects in the limit of very small subdomain size and large, randomly-distributed 42 misorientations, the μXRD shock stage assessment technique would not be useful in these circumstances; however, such a situation has not been observed in this study.

High-pressure polymorphs of orthopyroxene including , , and

MgSiO3-perovskite have been reported from highly shocked chondritic meteorites, including , Suizhou and Sixiangkou (all L6); such phases are commonly localized in shock veins (e.g., Putnis and Price, 1979; Sharp et al., 1997; Tomioka and Fujino, 1997;

Zhang et al., 2006). Highly shocked E chondrites might be expected to contain some of the aforementioned phases, however, no high-pressure polymorphs have been definitively observed in the present study either petrographically or by μXRD.

2.5.0 Conclusions

Shock induced crystal structure damage and increased mosaic spread can be readily measured by the FWHMχ of diffracted X-ray peak intensities as a function of chi angle along the Debye rings in μXRD two-dimensional GADDS images. Increased mosaic spread in orthopyroxene, measureable as increased FWHM of the chi angle, correlates very well with increasing petrographic shock stage for the E chondrites in this study. The ranges of FWHMχ values for each of the shock stages are not equal; this is consistent with experimental results indicating that the range of pressures over which S3 and S4 features appear in enstatite is quite large (~10-30 GPa) (Hörz and Quaide, 1973;

Rubin et al., 1997). No significant differences in peak FWHMχ were detected between diffractions of the (020), (610) and (131) planes of enstatite, indicating that shock damage within the orthopyroxenes appears to be distributed isotropically. Shock stages determined by optical petrography in this study are in good agreement with previous work where available (Rubin and Scott, 1997; Rubin et al., 1997). Ranges in peak 43

FWHMχ corresponding to various shock stages have been assigned as follows: S1<0.7º,

S2=0.7º–1.2º, S3=1.2º–2.3º, S4=2.3º–3.5º, S5>3.5º, S6 – not measured. Slabs of the Abee

(EH impact melt breccia), and NWA 2212 (EL6) have average peak FWHMχ values which place them in the S2 range in FWHMχ, consistent with literature shock stage assessments (Rubin and Scott, 1997). The ranges in peak FWHMχ defined for each shock stage are necessarily approximate; it is possible that there are no sharp boundaries in

FWHMχ between the shock stages.

The μXRD shock stage assessment technique presented in this study does not necessarily supplant or replace existing petrographic techniques; rather, it is a valuable adjunct with potential applicability to in situ assessment of unprepared samples (whole meteorites) or intact samples (slices or slabs) and to samples for which optical methods are difficult to apply due to silicate darkening, weathering, small grain sizes, absence of indicator phases such as olivine and plagioclase, and other effects which obscure the petrographic indicators of shock. Micro XRD provides an independent means of assessing shock stage in chondritic meteorites, including both thin sections and intact samples, and provides a means of directly examining the microstructural effects of shock on long-range crystal structure order. It may be possible to differentiate levels of shock more finely using the FWHMχ parameter described in this study than using petrographic evidence, particularly in the S3-S4 range where petrographic shock metamorphic effects in enstatite and other pyroxenes change little with increasing shock pressure (Rubin et al., 1997). In samples containing more than one phase for which a shock stage calibration exists, e.g., ordinary chondrites (plagioclase, olivine, pyroxene) it may be possible to use μXRD to assign mineral-specific shock stage based on the FWHMχ of diffractions from different minerals. 44

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50

Chapter 3: QUE 94204: A primitive enstatite achondrite produced by the partial melting of an E-chondrite-like protolith

Chapter summary and key points

QUE 94204, an enstatite achondrite, is a coarse-grained, highly recrystallized, chondrule- free and unbrecciated rock dominated (~70 vol. %) by anhedral, equigranular crystals of orthoenstatite of nearly end-member composition (Fs0.1-0.4, Wo0.3-0.4) with interstitial plagioclase, kamacite and troilite. Abundant ~120º triple junctions and the close association of metal–sulfide and plagioclase-rich melts indicate that QUE 94204 has undergone limited partial melting with inefficient melt extraction. Mineral chemistry indicates a high degree of thermal metamorphism. Kamacite in QUE 94204 contains between 2.09 to 2.55 wt. % Si, similar to highly metamorphosed EL chondrites.

Plagioclase has between 4.31 and 6.66 wt. % CaO, higher than other E chondrites but closer in composition to plagioclase from metamorphosed EL chondrites. QUE 94204 troilite contains up to 2.55 wt. % Ti, consistent with extensive thermal metamorphism of an E-chondrite-like precursor. Results presented in this study indicate that QUE 94204 is the result of low degree, (~5-20 vol. %, probably towards the lower end of this range) partial melting of an E-chondrite protolith. Textural and chemical evidence suggests that during the metamorphism of QUE 94204, melts formed first at the Fe,Ni-FeS cotectic near ~900 ºC, followed by plagioclase-pyroxene silicate partial melts near ~1100 ºC.

Neither the Fe,Ni-FeS nor the plagioclase-pyroxene melts were efficiently segregated or extracted. QUE 94204 belongs to a grouplet of similar “primitive enstatite achondrites” that are analogous to the acapulcoites-lodranites, but that have resulted from the partial melting of an E-chondrite-like protolith. 51

3.1.0 Introduction

A rare class of meteorites, the acapulcoites and lodranites, represented by ~80 samples, are believed to provide a glimpse into the incomplete melting of chondritic material, providing a window into the early stages of planetary differentiation (e.g.,

Taylor et al., 1993). Ordinary chondrites are by far the most common chondritic material in the world’s meteorite collections, comprising some ~35781 samples at the time of this writing; in contrast 1325 carbonaceous chondrites and 501 enstatite chondrites are currently known (Meteoritical Bulletin Database, accessed July 25th 2011). It therefore stands to reason that samples representative of partial melting of enstatite chondrite precursor lithologies are quite rare. A small number of such meteorites have nevertheless been tentatively identified (e.g., Keil and Biscoff 2008). Enstatite (E) chondrites are important, as they may be linked by their isotopic and bulk siderophile element compositions to the precursors of the terrestrial planets, including Earth (Javoy, 1995,

2010; Righter et al., 2006). In the current study, we present textural, mineralogical and chemical evidence that suggests Antarctic meteorite QUE 94204 is the product of partial melting of an E-chondrite-like material. This is in contrast with previous works, which have identified QUE 94204 as an EH7 chondrite (McBride and Mason, 1996), an EH melt rock (Weisberg et al., 1997; Lin and Kimura, 1998), or an annealed E-chondrite impact melt (Rubin and Scott, 1997; Rubin et al., 1997). It should be noted that of the aforementioned studies, only that of Weisberg et al. (1997) studied QUE 94204 in detail.

Comparison of QUE 94204 with other possible E-chondrite partial melts such as NWA

2526 (Keil and Bischoff, 2008), Itqiy (Patzer et al., 2001), and Yamato 793225 (Lin and

Kimura, 1998) indicates that these meteorites, along with QUE 94204’s paired samples

QUE 97289 and QUE 97348 record partial melting of E-chondrite-like precursor 52 lithologies. QUE 94204 and similar meteorites preserve a record of partial melting on asteroids and provide unique insights into the early stages of planetary differentiation.

3.2.0 Materials and methods

A polished thin section of QUE 94204 (NASA ANSMET section QUE94204-26) was examined microscopically in transmitted and reflected light. Mineral abundances were estimated by point counting. Mineral compositions were determined by Electron

Probe Micro Analysis (EPMA) using a JEOL8900R electron microprobe at the University of Alberta with a 1 μm focused beam, 15 kV accelerating voltage and 30 nA beam current.

Counting times were 20 s on peak and 10 s on background. Separate calibrations for silicate, metal, and sulfide analyses were performed using natural and synthetic mineral standards. A ZAF correction was applied to all EPMA data (Armstrong, 1995).

Micro X-ray Diffraction (μXRD) patterns were collected using a Bruker-AXS D8

Discover diffractometer with Cu Kα radiation (λ = 1.5418 Å) produced by a sealed tube source operating at 40 kV accelerating voltage and 40 mA beam current. Göbel mirror parallel beam optics removed Kβ radiation. A nominal beam diameter of 500 μm was produced using a pinhole collimator snout. In situ data was collected on polished thin section using omega scan mode, where the source (θ1) and detector (θ2) rotated in the same direction through an omega angle of ω, while maintaining constant 2θ (θ1 + θ2 = 2θ); this enabled a larger number of lattice planes to satisfy Bragg’s law while the sample remained stationary. Diffracted X-rays were detected with a two-dimensional general area diffraction detector system (GADDS). The integrated GADDS images were analysed using Bruker-AXS DiffracPlus® Evaluation software (BrukerAXS, 2005), and the 53

International Center for Diffraction Data (ICDD) Powder Diffraction File (PDF-4) database (rev. 2006) for phase identification. Comprehensive descriptions of the μXRD apparatus and techniques used in this study and the application of μXRD to geological samples are presented in Flemming (2007).

3.3.0 Results

3.3.1 Petrography

QUE 94204 is a coarse-grained, unbrecciated, achondritic rock dominated by anhedral, equigranular grains of enstatite that commonly meet at ~120° triple junctions.

Figure 3-1 shows the textural relationships between enstatite, plagioclase, metal and sulfides in QUE 94204. Coarse grained, equigranular, rounded enstatite crystals comprise

~70 vol. % of the section. Figure 3-1, panels A and B show the entire thin section in plane- and crossed-polarized light respectively, and shows the equigranular, highly recrystallized texture of QUE 94204 Figure 3-1, panels C-E, F-H, and I-K are series in crossed-polarized, plane-polarized and reflected light showing textural details, including interstitial plagioclase, metal and troilite (C-E and F-H), corona-like texture of cristobalite between metal and enstatite (I-K), and rounded grains of troilite enclosed in enstatite

(Figure 3-1 E, K). Enstatite crystals are dominantly orthoenstatite, and contain abundant clinoenstatite-bearing lamellae along (100), giving the enstatite grains a striated appearance in crossed-polarized light (Figure 3-1 D, G, J) . Curviplanar trails of troilite or metal inclusions are very common in QUE 94204 enstatite. Irregular fractures, commonly stained by Fe-oxyhydroxide terrestrial weathering products pervade the enstatite crystals.

Plagioclase comprises ~8 vol. % of the section, occurs interstitial to enstatite grains

(Figure 3-1 C,D,F,G), and also contains curviplanar trails of troilite-metal inclusions that 54 occasionally continue between enstatite and plagioclase. The abundance of metal-troilite inclusions in plagioclase is somewhat lower than in enstatite. All plagioclase grains observed exhibit albite twinning and lack compositional zoning as determined optically and confirmed by EPMA. Cristobalite, identified by μXRD, is a minor constituent of

QUE 94204 (~3 vol. % of the section) and is commonly observed between enstatite crystals and metal, in a corona-like texture (Figure 3-1 I, J). Kamacite comprises ~5 vol.

% of the section. Metal and sulfides occur interstitially and as rounded blebs enclosed in silicates. Where sulfides and metal occur in contact, they display immiscible textures.

Troilite is by far the most common sulfide observed, comprising ~5 vol. % of the section.

Daubreélite is rare (<1 vol. %), and is always associated with troilite, commonly as exsolution lamellae (Figure 3-1 H). Metal and sulfides are commonly substantially weathered and replaced, partially or completely, by an assemblage of fine-grained terrestrial alteration minerals comprising goethite, gypsum and calcite. Terrestrial weathering products also form along some grain boundaries (Figure 3-1 E, H, K) but it is not possible to be certain whether these features correspond to pre-terrestrial structures or are entirely the result of remobilized migration of terrestrial weathering products in solution. Terrestrial weathering products comprise ~9 vol. % of the section. Staining of the silicate phases by Fe-oxyhydroxide terrestrial weathering products is also pervasive throughout the section. Modal abundances are summarized in Table 3-1. It should be noted that within the thin section, many phases are heterogeneously distributed, particularly metal (Figure 3-1 A and B). The modal abundances have also been affected strongly by terrestrial weathering which preferentially affects metal and sulfides.

55

Figure 3-1: Optical images of the QUE 94204 – 26 thin section. A) Transmitted, cross polarized light map. B) Transmitted plane polarized light map. Areas in the boxes are enlarged in C-K as denoted; the arrows indicate the up direction in the individual images. The section is dominated by equigranular, rounded, orthoenstatite crystals containing lamellae of clinoenstatite along (100). Orthoenstatite grains commonly meet at ~120° triple junctions, and the interstices are filled with kamacite, sulfides and plagioclase. These textural relationships are highly suggestive of partial melting and extensive thermal metamorphism and equilibration. Terrestrial weathering products have heavily stained the silicates and replaced significant quantities of the metal and sulfides. C-K) Cross polarized (C, F, I), plane polarized (D, G, J) and reflected light (E, H, K) images showing details of the relationships between enstatite, plagioclase, sulfides (dominated by troilite) and kamacite. Plagioclase is albite-twinned and is interstitial to enstatite grains. Kamacite and troilite have been extensively replaced by terrestrial weathering products. 56

Table 3-1: Modal abundances in volume % as determined by point counting (n=1650) Mineral points vol. % enstatite 1154 70 plagioclase 133 8 metal 83 5 troilite 79 5 daubreelite 8 <1 cristobalite 47 3 weathering* 146 9 *Terrestrial weathering products consisting of a mixture of very fine-grained goethite, gypsum and calcite.

3.3.1.1 Inclusions in QUE 94204 silicates

Two major types of inclusions have been observed in QUE 94204 silicates and examples of each appear in Figure 3-2. The first inclusion type consists of curviplanar trails of micron to submicron troilite and/or kamacite inclusions that may continue across enstatite and plagioclase grain boundaries, and do not appear to follow twin or planes (Figure 3-2 A-C). These inclusions are more common in enstatite than plagioclase.

The troilite and/or kamacite inclusions appear to follow annealed fractures that originally cross-cut silicate grain boundaries and may be the result of thermal annealing of shock- injected Fe,Ni-FeS melts (e.g., Rubin 1992). The second type of inclusion (Figure 3-2 D-

F) consists of euhedral, acicular to lath-like transparent inclusions in plagioclase, up to several tens of microns in their longest dimension, with forms that appear to be crystallographically-controlled. Because the exposure of these inclusions on the surface of the section is typically somewhat less than ~1 micron, the identity of the phase(s) comprising these inclusions is difficult to determine by EPMA. They are rich in K, Na, Al, and Si compared to the plagioclase and may contain alkali feldspar.

57

Figure 3-2: Details of inclusions in QUE 94204 silicates, marked by green boxes in Fig. 1G and J. A) The double-headed arrow shows a curviplanar trail of minute troilite and kamacite inclusions that cross-cuts enstatite and plagioclase. B) Interstitial plagioclase crystal with multiple curviplanar trails of troilite and metal inclusions. Area in the box is enlarged in C. D) Area within a plagioclase crystal with abundant needle-like, transparent inclusions with crystallographically-controlled forms; these inclusions are interpreted as areas of melt. E) Enlargement of box in D showing details of melt inclusion morphology. F) Another example of acicular melt inclusions in plagioclase. The two apparent parallel trails of opaque objects, one in-focus and the other out of focus are actually inclusions oriented nearly perpendicular to the plane of the thin section. The orientations of these acicular inclusions do not appear to be related to any existing crystallographic features of the host plagioclase such as cleavage or twin planes.

3.3.2 Mineral chemistry

Enstatite in QUE 94204 is very uniform in composition, and approaches end- member enstatite, with between 0.06 and 0.27 wt. % FeOT (Fs0.1-0.4) and 0.16 to 0.24 wt.

% CaO (Wo0.3-0.4). The composition of enstatite is probably even more Fe-poor than noted, as it is unlikely that the Fe-rich troilite-metal inclusions and Fe-oxyhydroxide-bearing terrestrial weathering products were excluded from all EPMA excitation volumes.

Plagioclase composition ranges from 4.31 to 6.66 wt. % CaO (An20.6-31.6) and from 0.25 to

0.38 wt. % K2O (Or1.4-2.1). Kamacite contains 5.42 to 9.76 wt. % Ni and 2.09 to 2.47 wt.

% Si. Troilite contains between 1.19 and 2.55 wt. % Ti and 0.82 to 0.93 wt. % Cr.

Cristobalite-bearing regions (commonly observed at the interface of enstatite and metal) 58

also contain small amounts of Al2O3, K2O, Na2O and FeO. Chemical compositions of enstatite are summarized in Table 3-2, those of plagioclase and K-rich acicular inclusions hosted in plagioclase, in Table 3-3, and those of cristobalite in Table 3-4, those of troilite and daubreélite in Table 3-5, and those of kamacite in Table 3-6. Chemical element maps showing the distribution of Si, Mg, Al, Ca, S, Na, Fe, and Ni in a representative region of the QUE 94204 section are shown in Figure 3-3.

Table 3-2 Representative EPMA analyses of enstatite in QUE 94204, oxide values in wt. %, En, Fs and Wo in mole %. SiO2 60.27 60.02 59.97 59.49 59.97 59.95 60.08 59.77 59.87 TiO2 b.d. b.d. b.d. b.d. 0.02 b.d. b.d. 0.02 b.d. Al2O3 0.08 0.10 0.12 0.07 0.08 0.08 0.07 0.10 0.09 Cr2O3 0.03 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. FeOT 0.09 0.11 0.12 0.23 0.27 0.22 0.05 0.19 0.06 MnO 0.02 0.02 0.02 0.00 0.02 0.01 b.d. b.d. b.d. MgO 39.35 39.47 39.41 39.72 39.11 39.13 39.19 39.19 39.27 CaO 0.23 0.24 0.24 0.18 0.18 0.24 0.22 0.20 0.21

Na2O 0.03 b.d. 0.02 0.03 0.02 0.02 b.d. 0.02 0.01 K2O 0.01 b.d. b.d. b.d. b.d. b.d. b.d. 0.02 0.01 total 100.12 99.98 99.90 99.73 99.66 99.66 99.62 99.52 99.52

En 97.9 98.3 98.3 99.4 97.8 97.8 97.9 98.1 98.3 Fs 0.1 0.2 0.2 0.3 0.4 0.3 0.1 0.3 0.1 Wo 0.4 0.4 0.4 0.3 0.3 0.4 0.4 0.4 0.4

SiO2 60.01 59.64 59.76 59.69 59.35 59.54 59.80 59.53 59.51 TiO2 0.01 0.01 b.d. b.d. 0.02 0.01 0.02 b.d. b.d. Al2O3 0.06 0.14 0.06 0.08 0.13 0.10 0.06 0.06 0.08 Cr2O3 0.02 b.d. b.d. 0.02 b.d. b.d. b.d. b.d. 0.04 FeOT 0.11 0.09 0.11 0.09 0.15 0.09 0.09 0.14 0.19 MnO 0.03 0.02 0.01 0.02 0.03 0.00 0.02 0.01 0.01 MgO 39.07 39.39 39.23 39.35 39.50 39.40 39.16 39.35 39.26 CaO 0.18 0.21 0.20 0.16 0.21 0.22 0.16 0.19 0.22

Na2O 0.02 0.02 0.02 0.00 0.01 0.01 0.02 0.01 b.d. K2O b.d. b.d. 0.01 b.d. b.d. b.d. b.d. b.d. 0.01 total 99.52 99.51 99.42 99.42 99.41 99.37 99.35 99.32 99.32

En 97.7 98.6 98.3 98.6 99.1 98.8 98.2 98.7 98.6 Fs 0.2 0.1 0.2 0.1 0.2 0.1 0.1 0.2 0.3 Wo 0.3 0.4 0.4 0.3 0.4 0.4 0.3 0.3 0.4 b.d. = below detection (0.01 wt. %). All Fe reported as FeO.

59

Figure 3-3: Selected EPMA element maps for an illustrative region of the QUE 94204 section; also shown in transmitted and reflected light in Figure 3.1 I-K. The scale bar is identical in all images. The very Si-rich material lining the boundary between kamacite (Fe- and Ni-rich) and enstatite (Mg-rich) is cristobalite. Note also the slight Al-enrichment of cristobalite. - and Ni-rich weathering products have intruded within many grain boundaries and fractures. Plagioclase is visible as Al-rich material interstitial to enstatite, or as blebs enclosed within enstatite. Rounded sulfide blebs consisting of troilite and daubreélite occur enclosed within enstatite. 60

Table 3-3: Representative EPMA analyses of plagioclase and of possible melt inclusion in plagioclase, oxide values in wt. %, Ab, An and Or in mole %. plagioclase

SiO2 60.92 60.56 61.10 59.81 62.97 62.11 TiO2 0.01 0.02 0.03 0.01 b.d. b.d. Al2O3 24.09 24.75 23.92 24.30 22.50 23.70 Cr2O3 b.d. 0.03 0.03 0.01 b.d. 0.03 FeOT 0.09 0.09 0.12 0.08 0.15 0.10 MnO b.d. 0.01 0.01 b.d. 0.01 0.01 MgO 0.01 0.03 0.03 0.02 0.03 0.03 CaO 5.80 6.27 5.63 6.65 4.31 5.24

Na2O 8.15 7.72 8.28 7.70 9.06 8.54 K2O 0.33 0.29 0.35 0.30 0.38 0.37 total 99.41 99.79 99.52 98.90 99.43 100.14 Ab 70.7 66.7 71.7 67.3 78.2 73.4 An 27.8 29.9 26.9 32.1 20.6 24.9 Or 1.9 1.7 2.0 1.7 2.1 2.1

SiO2 62.45 60.09 60.10 61.83 59.83 60.36 TiO2 0.01 0.01 0.00 b.d. b.d. 0.03 Al2O3 23.58 24.66 24.45 24.06 24.43 24.86 Cr2O3 0.03 b.d. b.d. 0.01 b.d. b.d. FeOT 0.24 0.06 0.15 0.18 0.19 0.18 MnO 0.01 0.01 0.02 0.01 b.d. 0.02 MgO 0.01 0.02 b.d. 0.02 0.03 0.02 CaO 4.97 6.44 6.58 5.34 6.66 6.52

Na2O 8.74 7.87 7.65 8.43 7.71 7.79 K2O 0.35 0.30 0.30 0.29 0.28 0.25 total 100.41 99.47 99.25 100.18 99.14 100.02

Ab 74.9 68.3 66.6 72.4 67.2 67.3 An 23.5 30.9 31.6 25.4 32.1 31.1 Or 2.0 1.7 1.7 1.6 1.6 1.4 K-rich inclusions

SiO2 76.06 76.97 TiO2 0.04 b.d. Al2O3 12.22 11.98 Cr2O3 b.d. b.d. FeOT 0.15 0.28 MnO b.d. 0.02 MgO 0.01 0.02 CaO b.d. b.d.

Na2O 2.18 2.21 K2O 6.36 6.26 97.01 97.74 b.d. = below detection (0.01 wt. %). All Fe reported as FeO.

61

Table 3-4: Representative EPMA analyses of QUE 94204 cristobalite, oxide values in wt. %. SiO2 96.55 96.47 96.47 96.32 96.27 96.04 95.82 95.77 95.77 95.67 TiO2 b.d. b.d. 0.01 b.d. 0.02 b.d. b.d. b.d. b.d. b.d. Al2O3 1.87 1.96 1.94 1.88 2.02 1.80 1.83 1.87 1.95 1.90 Cr2O3 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.01 b.d. b.d. FeOT 0.15 0.17 0.37 0.69 0.22 0.14 0.17 0.19 0.31 0.15 MnO b.d. b.d. b.d. b.d. 0.01 0.01 0.01 b.d. 0.01 b.d. MgO b.d. b.d. b.d. 0.01 b.d. b.d. b.d. b.d. 0.01 b.d. CaO b.d. 0.01 0.03 0.42 0.01 0.01 b.d. 0.01 0.01 0.01

Na2O 0.13 0.51 0.53 0.55 0.16 0.12 0.53 0.13 0.55 0.58 K2O 0.24 0.27 0.13 0.08 0.23 0.20 0.24 0.24 0.28 0.25 total 98.94 99.39 99.50 99.95 98.93 98.31 98.61 98.22 98.88 98.57 b.d. = below detection (0.01 wt. %). All Fe reported as FeO.

Table 3-5: Representative EPMA analyses of QUE 94204 troilite and daubreelite, values in wt. %. troilite Fe 57.52 59.75 58.42 58.91 58.79 59.17 58.77 58.95 58.97 59.36 Mg 0.01 0.01 0.02 b.d. 0.01 0.01 0.01 0.01 b.d. 0.03 Ca 0.02 b.d. 0.02 0.05 b.d. b.d. 0.00 0.01 b.d. b.d. Ti 2.54 1.19 2.36 1.68 1.92 1.70 1.56 1.80 1.67 1.21 Cr 0.82 0.82 0.71 0.93 0.88 0.72 0.87 0.86 0.84 0.87 Mn 0.03 0.05 0.05 0.08 0.06 0.06 0.06 0.06 0.07 0.01 Co 0.13 0.12 0.02 0.10 0.14 0.15 0.15 0.16 0.11 0.14 Ni 0.03 0.04 0.04 0.04 0.08 0.06 0.05 0.04 0.05 0.08 Cu 0.04 0.09 0.01 0.18 0.01 b.d. 0.14 b.d. 0.09 0.14 Zn b.d. 0.03 0.01 b.d. 0.06 b.d. b.d. 0.03 b.d. b.d. Si 0.04 0.03 0.05 0.03 0.05 0.03 0.04 0.03 0.04 0.02 S* 37.16 36.86 36.61 36.75 36.92 36.42 36.44 36.85 36.93 36.58 total 98.35 99.00 98.30 98.75 98.90 98.32 98.07 98.81 98.77 98.42 daubreelite Fe 16.3 16.51 16.11 16.31 17.67 19.2 16.41 17.57 17.18 15.9 Mg 0.02 0.01 0.01 0.02 0.02 0.01 0.01 0.02 0.03 0.04 Ca 0 0.01 0.03 0.03 0.03 b.d. 0.03 b.d. 0.02 0.11 Ti 0.12 0.17 0.11 0.16 0.29 0.17 0.11 0.12 0.07 0.07 Cr 35.19 35.23 35.21 35.3 33.33 33.97 35.13 34.73 34.74 34.88 Mn 2.44 2.38 2.44 2.54 2.08 1.20 2.42 1.46 1.63 3.15 Co 0.07 0.04 0.03 0.07 0.09 0.05 0.05 0.05 0.07 0.04 Ni 0.05 b.d. 0.01 0.01 0.28 b.d. b.d. 0.02 0.02 b.d. Cu 0.11 0.16 0.15 0.11 0.28 0.28 0.11 0.12 0.06 0.14 Zn 0.01 0.03 0.01 b.d. 0.06 0.11 0.06 0.04 0.05 0.04 Si 0.03 0.02 0.02 0.03 0.05 0.02 b.d. 0.05 0.03 0.02 S* 43.71 43.9 43.6 44.29 43.42 43.03 43.36 43.97 43.91 43.56 total 98.05 98.46 97.73 98.87 97.6 98.04 97.69 98.15 97.81 97.95 b.d. = below detection (0.01 wt. %). *S was measured rather than calculated assuming stoichiometric compositions.

62

Table 3-6: Representative EPMA analyses of QUE 94204 kamacite, values in wt. %. Fe 91.13 89.80 89.22 90.43 90.37 86.67 90.83 89.35 Ni 5.42 6.37 7.88 6.53 6.38 9.76 7.28 7.01 Si 2.09 2.39 2.29 2.32 2.46 2.55 2.15 2.36 Co 0.42 0.44 0.41 0.44 0.40 0.42 0.44 0.44 Cr b.d. b.d. b.d. b.d. 0.01 b.d. b.d. b.d. P 0.01 0.02 0.05 0.05 0.05 0.17 0.05 0.06 total 99.07 99.03 99.85 99.77 99.67 99.57 100.76 99.22

Fe 90.29 89.96 90.79 89.64 90.10 88.72 89.98 90.48 Ni 6.41 6.59 5.90 6.61 6.62 7.91 6.33 5.81 Si 2.20 2.30 2.10 2.47 2.31 2.30 2.40 2.42 Co 0.45 0.44 0.44 0.43 0.44 0.41 0.41 0.42 Cr b.d. b.d. b.d. b.d. 0.01 0.01 b.d. b.d. P 0.05 0.03 0.02 0.08 0.03 0.08 0.05 0.02 total 99.40 99.32 99.24 99.23 99.49 99.42 99.17 99.16 b.d. = below detection (0.01 wt. %).

3.3.3 Micro X-ray diffraction (μXRD)

Interpretation of μXRD results is somewhat complicated by the very strong signal from the large, well-crystallized enstatite grains. Nevertheless, micro XRD confirmed the majority of mineral identifications made using optical petrography and EPMA. Micro

XRD also identified the fine-grained weathering products goethite, gypsum and calcite and confirmed the presence of cristobalite.

3.4.0 Discussion

3.4.1 Conditions of partial melting, and the nature of melt extraction and migration

The presence of troilite and kamacite in close association with plagioclase in the interstices of equigranular enstatite demonstrates that heating on the QUE 94204 parent asteroid produced both cotectic Fe,Ni-FeS melt near 900 ºC (Kullerud, 1963); and plagioclase ± pyroxene ‘basaltic’ partial melts near 1100 ºC (McCoy et al., 1997b;

McCoy et al., 1999). Possible melt inclusions within plagioclase (Figure 3-2 D-F) but not in enstatite supports a paucity of enstatite melting. Moreover, complete melting or the 63

QUE 94204 protolith (by any heat source) should have allowed the rapid segregation of dense metal-sulfide melt unless the cooling rate was very high. The textures of QUE

94204 are inconsistent with rapid cooling.. The slight depletions in kamacite, troilite and plagioclase contents in QUE 94204 compared with other enstatite chondrites suggest that the melt did not migrate efficiently out of the rock. By analogy with observations of acapulcoite-lodranite meteorites, and modeling of melt formation and migration in chondritic precursor lithologies, melt migration is suggested to be highly complex over all spatial scales during the melting of chondritic material (e.g., McCoy et al., 1997b).

Therefore, any estimate of the degree of partial melting experienced by QUE 94204 is subject to considerable uncertainty. Quantitative analysis, phase relations, and observations from acapulcoites and lodranites suggest that plagioclase-pyroxene partial melts first appear near ~5 vol. % partial melting and that melt extraction increases and becomes increasingly efficient between ~5-20 vol. % partial melting (McCoy et al.,

1997b). We suggest that these values roughly bracket the volume of partial melting experienced by QUE 94204, and that the lower end of the range is more likely. In contrast with NWA 2526, plagioclase and abundant troilite were observed in QUE 94204, perhaps indicating that the latter has experienced a lower degree of partial melting or that melt extraction was even less efficient than in NWA 2526. In this case, NWA 2526 may represent an enstatite meteorite analog to the lodranites, while QUE 94204 is more analogous to the transitional acapulcoites (c.f. Patzer et al., 2004).

The coexistence of Fe,Ni-FeS and plagioclase ± pyroxene partial melts indicate that temperatures of at least ~1100 ºC were reached during the thermal event(s) that produced partial melting on the QUE 94204 parent asteroid (McCoy et al., 1999). The lack of large-scale enstatite melting indicates that sustained temperatures did not exceed 64 the solidus of enstatite, 1557 ºC at atmospheric pressure (Bowen and Anderson, 1914;

Boyd et al., 1964).

3.4.2 Clues to the nature of the QUE 94204 protolith

The QUE 94204 protolith was likely highly reduced, and similar to enstatite chondrites. Mineral chemistry provides some clues to the possible nature of the QUE

94204 protolith. Kamacite in QUE 94204 contains between 2.09 to 2.55 wt. % Si. The Si content of kamacite in EH chondrites ranges from ~2 wt. % in EH3s up to ~4 wt. % in

EH6s (e.g., Keil, 1968; Sears et al., 1982; Zhang et al., 1995); that of Itqiy is ~3 wt. %

(Patzer et al., 2001) and that of NWA 2526 is ~5 wt. % (Keil and Bischoff, 2008). In contrast, EL chondrites range from ~1–2 wt. % Si in kamacite (e.g., Keil, 1968; Sears et al., 1982; Zhang et al., 1995), and aubrites range from 0.1 up to 2.5 wt. % (Casanova et al., 1993). Therefore, while the Si content of kamacite in QUE 94204 does not unambiguously establish a kinship with other enstatite meteorites, and could be consistent with little-metamorphosed EH chondrite material, or highly metamorphosed EL chondrite material, we favor the latter interpretation because of the recrystallized texture of QUE

94204. The CaO content of QUE 94204 plagioclase ranges from 4.31 to 6.66 wt. %, higher than is typical for either EL or EH chondrites, however, high anorthite contents of plagioclase are more commonly observed in EL chondrites (Brearley and Jones, 1998).

Troilite in QUE 94204 contains 1.19 to 2.54 wt. % Ti, and has Cr content between 0.71 and 0.93 wt.%. Troilite in EH chondrites contains up to ~0.5 wt. % Ti and 3.7 wt. % Cr; troilite in EL chondrites contains up to ~0.8 wt. % Ti and ~1.5 wt. % Cr (Keil, 1968, 1969;

Zhang et al., 1995). The Ti content of troilite has been shown to increase and the Cr content to decrease, with thermal metamorphism under the highly reducing conditions of 65

E-chondrite metamorphism (Komatsu et al., 2010). The high content of Ti and low content of Cr in QUE 94204 troilite are consistent with extensive thermal metamorphism of E-chondrite material. Daubreélite in QUE 94204 contains between 1.20 and 2.41 wt. %

Mn, slightly above the range of known EH chondrites (0.4-1.1 wt. %) and towards the lower end of the range of known EL chondrites (1.4-4.0 wt. %) (Keil, 1968; Brearley and

Jones, 1998). Daubreélite is also notably low in Zn, ranging from below detection to 0.11 wt. %, consistent with the trend with increasing thermal metamorphism reported by

Chikami et al. (1998). The lack of Zn in both daubreélite and troilite, and the lack of Zn- bearing phases in general (also noted by Weisberg et al., 1997) could be more consistent with an EL than and EH protolith, as EL chondrites are typically depleted in Zn relative to EH (Brearley and Jones, 1998).

The mineral-chemical characteristics of QUE 94204 are perhaps more consistent with an EL-chondrite kinship, but there are many ambiguities involved and this possible linkage must be regarded as extremely tentative. Following Keil and Bischoff (2008) and

Lin and Kimura (1998), we conclude that QUE 94204 belongs to a new grouplet of meteorites also including QUE 97289 and QUE 97348 (which are paired with QUE

94204), NWA 2526, Itqiy, and possibly Yamato 793225 (Lin and Kimura, 1998), and that these represent partial melts of E-chondrite. It is also possible (though highly speculative) that some of these rocks may sample new enstatite meteorite parent asteroids.

3.4.3 Shock and thermal metamorphic history

Shock injection of metal and troilite into fractures, followed by thermal annealing

(possibly beneath a thick, insulting regolith) likely produced the ubiquitous curviplanar trails of troilite-metal blebs in QUE 94204 silicates. Izawa et al. (2009; 2011) showed by 66 micro X-ray diffraction and petrographic analysis that QUE 94204 is mildly shocked (S2) according to the criteria of Rubin et al. (1997). This was inferred from the minor undulose optical extinction of enstatite and plagioclase, the lack of shock-induced raggedness in kamacite and the lack of pervasive planar fracturing in enstatite. Lamellae of clinoenstatite along (100) in orthoenstatite can result from shock deformation (Rubin et al., 1997); however, such lamellar intergrowths of orthorhombic and monoclinic enstatite polymorphs can also result from inversion of protoenstatite (e.g., Smyth 1974; Chen and

Presnall, 1975). Clinoenstatite formation by shock seems more likely than by thermal metamorphism, given the degree of subsolidus annealing indicated by the textures of

QUE 94204; however, the clinoenstatite lamellae in QUE 94204 orthoenstatite are not necessarily diagnostic of shock metamorphism. It is possible that the enstatite was shocked to a higher stage (S3-4) and subsequently annealed, and that the clinoenstatite lamellae are thus a relict shock feature. This interpretation is consistent with the presence of annealed fractures containing micron-scale metal and sulfide inclusions.

Transparent, acicular to lath-like inclusions in QUE 94204 plagioclase grains may be melt inclusions. Melt inclusions are expected in instances of inefficient melt removal.

Melt inclusion morphologies commonly evolve rapidly from irregular and rounded to negative crystal form during annealing at subsolidus temperatures (e.g., Frezzotti, 2001).

The fact that plagioclase contains possible melt inclusions while enstatite does not supports the textural inference that plagioclase underwent melting while enstatite largely did not.

Keilite, (Fe>0.5,Mg<0.5)S, was not observed in QUE 94204 in the present study, or in that of Weisberg et al. (1997). Keil (2007) has shown that keilite is stable only in quickly-cooled impact-melt rocks and impact-melt bearing breccias, according to the 67 phase relations, experimentally determined stability parameters, and required cooling rates as established by Skinner and Luce (1971) for the system MgS-MnS-CaS-FeS.

QUE 94204 may have a relationship with enstatite chondrites analogous to the one inferred between acapulcoites/lodranites and a chondritic precursor (McCoy et al., 1992;

McCoy et al., 1996; McCoy et al., 1997a; McCoy et al., 1997b; Mittlefehldt et al., 1998;

Patzer et al., 2004; Rubin, 2007). Following this analogy, QUE 94204 may be an enstatite meteorite analogous to the transitional acapulcoites (Patzer et al., 2004), which are the product of small volume percentage partial melting that included the formation of cotectic

Fe,Ni-FeS and plagioclase ± pyroxene partial melts, which were not efficiently extracted from their source regions.

3.4.4 On choice of the “primitive enstatite achondrite” nomenclature for QUE 94204 and similar rocks

QUE 94204 has variously been termed an EH7 chondrite, an annealed impact melt rock, and a melt rock. The following section, describes the reasons choosing “primitive enstatite achondrite” instead of one of the aforementioned terms.

3.4.4.1 Type 7 chondrite: There is, as yet, no clear consensus on the precise meaning of the term “type 7 chondrite”. Most definitions are along the following lines (e.g., Brearley and Jones, 1998; Hutchison, 2004): “a highly-recrystallized chondrite which may have experienced incipient partial melting”; with some definitions adding “…but lacking detectable melt”. This is a somewhat confusing definition, and the “type 7” classification has not been universally accepted (Brearley and Jones, 1998). QUE 94204 was initially classified as EH7, but our observations indicate that it contains detectable Fe,Ni-FeS and 68 plagioclase-enstatite melts, so it cannot be a type 7 chondrite with the “no detectable melt” criterion cited above.

3.4.4.2 Impact melt rock: A rock which has been (at least partly) melted by impact. The

International Union of Geological Sciences (IUGS) subcommittee on the nomenclature of metamorphic rocks recommends a further subdivision into clast-rich, clast-poor, and clast-free impact melt rocks (Stöffler and Grieve, 2007). Under this scheme, “impact melt breccia” meteorites like Abee (e.g., Rubin and Scott, 1997) would correspond to clast-rich to clast-poor impact melt rocks, and “impact melts” would correspond to clast-free impact melt rocks. It should be noted that the aforementioned IUGS recommended nomenclature is not without its own attendant controversies (e.g., Osinski et al., 2008). QUE 94204 shows no evidence of brecciation or breccia clasts, therefore, it cannot be an impact melt breccia. If QUE 94204 is a clast-free impact melt rock, then it must have first cooled very rapidly, otherwise, metal-sulfide and silicate melts should have rapidly segregated

(Arculus et al., 1990). Rapid cooling must then have been followed by extensive thermal annealing leading to the observed highly-recrystallized texture, equilibrated mineralogy and mineral chemistry, and evidence for partial (re)melting. This scenario could be correct, however, we are not able to unambiguously determine whether or not it is.

Moreover, in terms of the nomenclature question, we would still be left with a highly recrystallized achondritic rock with a near-chondritic mineralogy. If it is termed a

(annealed) clast-free impact melt rock, this carries genetic connotations which we cannot establish with certainty. For this reason, we have opted for the “primitive achondrite” nomenclature as described in detail below.

69

3.4.4.3 Melt rock: In the sense which Weisberg et al. (1997) used “melt rock”, this term was meant to indicate that QUE 94204 crystallized from a complete melt of its observed composition, and proposed following Olsen et al., (1977) that QUE 94204 crystallized deep within its parent asteroid following congruent melting and that low gravitational acceleration could account for the fact that the dense metal-sulfide melt did not separate from the silicates. In the same abstract, however, Weisberg et al. (1997) also correctly point out that in the case of total impact melting, metal-sulfide melts should segregate efficiently unless the melt is very rapidly cooled. The texture of QUE 94204 is completely inconsistent with rapid cooling. The preservation of abundant metal-troilite inclusions along annealed fractures, and the presence of possible melt inclusions in plagioclase but not in enstatite are consistent with most of the enstatite remaining unmelted, that is, with minor partial melting producing Fe,Ni-FeS and plagioclase- enstatite partial melts, but insufficient melt separation to form a differentiated rock.

3.4.4.4 Primitive achondrite: A primitive achondrite is usually described as “A meteorite that has lost its chondritic texture due to heating and partial melting, but still has a nearly chondritic composition” (e.g., Brearley and Jones, 1998; Hutchison, 2004). We consider

“primitive achondrite” to be the most suitable definition for QUE 94204 based on observable characteristics of the rock, notably the near-chondritic (little differentiated to undifferentiated) composition, achondritic texture, evidence for extensive thermal annealing with minor melt generation but little melt extraction.

Adopting the “primitive achondrite” nomenclature could actually be advantageous when considering the possibility that QUE 94204 and similar meteorites could have formed by impact heating, endogenous heating, or a combination. “Primitive achondrite” 70 need not have a genetic connotation. It denotes a “primitive” character – i.e. chondritic to subchondritic mineralogy and composition, and an achondritic texture. In contrast, calling these rocks “type 7”, given the widely-accepted connection between progressive

(endogenous) thermal metamorphism and increasing petrologic grade from 3-6 (or 7) necessarily has a genetic connotation; likewise, considering these rocks as impactites (and possibly adopting the IUGS recommended nomenclature for impactites (Stöffler and

Grieve, 2007) in some modified form) obviously excludes the possibility that they are not all, in fact, impactites.

3.5.0 Conclusions

QUE 94204 is an enstatite meteorite which is the product of a low degree of partial melting of an E-chondrite-like precursor material. It is impossible to be certain whether any known E-chondrites correspond to the protolith of QUE 94204, however, mineral chemistry suggests a tentative link with the EL chondrites. The co-existence of metal-sulfide and silicate melts, the presence of possible melt inclusions in plagioclase but not enstatite, and the abundance of annealed fractures in silicates all indicate that melting of the QUE 94204 protolith was limited. The term “primitive enstatite achondrite” is proposed here for QUE 94204 and similar rocks because it encapsulates 1) the nearly-chondritic mineralogy and composition, 2) the evidence for partial melting without efficient melt separation, 3) the recrystallized, achondritic texture, 4) mineral and chemical evidence for extensive thermal metamorphism, and 5) lack of a genetic connotation regarding the mechanism(s) of formation, i.e., whether the metamorphism observed is due to heat from endogenic, exogenic or a combination of sources.

71

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Chapter 4: Weathering of post-impact hydrothermal deposits from the Haughton impact structure: implications for microbial colonization and biosignature preservation

Chapter summary and key points

Meteorite impacts are among the very few processes common to all planetary bodies with solid surfaces. Among the effects of impact on water-bearing targets is the formation of post-impact hydrothermal systems and associated mineral deposits. The Haughton impact structure, (Devon Island, Nunavut, Canada, 75.2° N, 89.5° W) hosts a variety of hydrothermal mineral deposits that preserve assemblages of primary hydrothermal minerals, commonly associated with secondary oxidative/hydrous weathering products.

Hydrothermal mineral deposits at Haughton include intra-breccia calcite-marcasite vugs; small intra-breccia calcite or quartz vugs; intra-breccia gypsum megacryst vugs; hydrothermal pipe structures and associated surface ‘gossans’; banded Fe-oxyhydroxide deposits; and calcite and quartz veins and coatings in shattered target rocks. Of particular importance are sulfide-rich deposits and their associated assemblage of weathering products. Hydrothermal mineral assemblages were characterized structurally, texturally and geochemically using X-ray diffraction, micro X-ray diffraction, optical and electron microscopy, and inductively coupled plasma atomic emission spectroscopy. Primary sulfides (marcasite and pyrite) are commonly associated with alteration minerals including jarosite – (K,Na,H3O)Fe3(SO4)2(OH)6, rozenite – FeSO4•4(H2O), copiapite –

(Fe,Mg)Fe4(SO4)6(OH)2•20(H2O), fibroferrite – Fe(SO4)(OH)•5(H2O), melanterite –

FeSO4•7(H2O), szomolnokite – FeSO4•H2O; goethite – α-FeO(OH), lepidocrocite – γ-

FeO(OH) and ferrihydrite – Fe2O3•0.5(H2O). These alteration assemblages are consistent 78 with geochemical conditions that were locally very different from the predominantly circumneutral, carbonate-buffered environment at Haughton.

Mineral assemblages associated with primary hydrothermal activity, and the weathering products of such deposits, provide constraints on possible microbial activity in the post- impact environment. The initial period of active hydrothermal circulation produced primary mineral assemblages including Fe-sulfides and was succeeded by a period dominated by oxidation and low-temperature hydration of primary minerals by surface waters. Active hydrothermal circulation can enable the rapid delivery of nutrients to microbes. Nutrient availability following the cessation of hydrothermal circulation is likely more restricted; therefore the biological importance of chemical energy from hydrothermal mineral deposits increases with time. Weathering of primary hydrothermal deposits, and dissolution and re-precipitation of mobile weathering products also creates many potential habitats for endolithic microbes; and provides a mechanism which may preserve biological materials, potentially over geologic timescales.

4.1.0 Introduction

Meteorite impact craters are possibly the most common geological landforms in the solar system. Hydrothermal systems driven by impact heating are likely to form wherever a hypervelocity impact occurs in a water-bearing solid target (e.g., Abramov and Kring, 2004; Naumov, 2005; Osinski, 2005; Osinski et al., 2005a; Abramov and

Kring, 2007). Post-impact hydrothermal systems represent a source of chemical and thermal energy which may make the impact crater environment among the most important for astrobiology and planetary exploration (e.g., Nisbet and Sleep, 2001; Kring,

2003; Abramov and Kring, 2005; Cockell and Bland, 2005; Cockell, 2006; Versh et al., 79

2006; Hode et al., 2008; Lindgren et al., 2010). Hydrothermal activity in the impact crater environment produces characteristic mineral and chemical signatures in the geological record (e.g., Allen and Keil, 1981; Zurcher and Kring, 2004; Osinski, 2005; Osinski et al.,

2005a). Mineralogy and geochemistry provide records of important boundary conditions for life in the post-impact environment; the understanding of these boundary conditions is highly relevant to astrobiology and planetary exploration (e.g., Cockell, 2006). Potential metabolic strategies and ecological niches may be inferred from examination of hydrothermal mineral assemblages and their weathering products. As a result, post-impact hydrothermal systems will likely be among the most sought-after science targets during future exploration of Mars (Schwenzer and Kring, 2009). An understanding of the mineralogical record of post-impact hydrothermal activity in a terrestrial Mars analogue environment is of value to future planetary exploration.

4.1.1 Haughton Impact Structure: A post-impact hydrothermal system in a Mars analogue environment

The Haughton impact structure is located on Devon Island, Nunavut, Canada

(75.2°N, 89.5°W). A simplified geological map of the Haughton impact structure based on work by Osinski et al. (2005) is presented in Figure 4-1. The target rock sequence consists of nearly flat lying Ordovician carbonate rocks, with some evaporite and sandstone layers, overlying Precambrian basement of the Canadian Shield (Osinski et al.,

2005b). Impacts produce heat both by direct impact heating and by enhanced heat flow from hot rocks excavated from depth in the central uplift (Osinski et al., 2005a; Osinski et al., 2005b). Its relatively simple regional geology makes the Haughton impact structure valuable for the study of all impact processes (e.g., Osinski and Spray, 2005). 80

Furthermore, Haughton is also the only terrestrial impact structure known to be set in a polar desert and has experienced a predominantly cold and relatively dry climate throughout most of its history. For this reason, it is exceptionally well preserved despite its age. The environmental conditions at Haughton are certainly not as extreme as those encountered on Mars at present. However, due to the setting in an environment that is, by terrestrial standards extremely cold, dry, rocky, dusty, and sparsely vegetated, the site presents several properties analogous to those on Mars, either at the present day or sometime in the past (Lee, 1997; Lee and Osinski, 2005). Haughton, therefore, combines an excellent environment for Mars analogue research with the opportunity for valuable research on impact and post-impact processes.

Haughton hosts a well-exposed and well-preserved example of a post-impact hydrothermal system. There has been no tectonic, igneous or other geothermal activity near Haughton since well before the impact event at ~39 Ma (Sherlock et al., 2005); therefore, the heat source for the hydrothermal system must have been impact-generated

(Osinski et al., 2005a). In addition to its scientific value for understanding post-impact environments on Earth, this fossil hydrothermal system is of potential relevance to Mars.

Impact structures in ice-rich areas of the Martian surface, such as the northern plains, could potentially develop post-impact hydrothermal systems (Kring, 2003). Post-impact hydrothermal systems represent a long-lived source of thermal and chemical energy with associated liquid water; furthermore, the impact process creates many potentially habitable microenvironments such as porous impactites which may be colonized by microbial life (e.g., Cockell and Lee, 2002; Cockell et al., 2002; Cockell et al., 2003;

Kring, 2003; Cockell et al., 2005). Large impacts also deeply fracture the crust, and central uplifts may raise deep-seated crustal material by up to several kilometres (Melosh, 81

1989). On Earth, therefore, impacts provide a potential mechanism for interaction between the deep biosphere and the near-surface. If a deep biosphere ever existed (or still exists) on Mars, impact structures are among the most promising areas for detection during near-future missions.

Figure 4-1: Map of the Haughton impact structure, showing the spatial distributions of different hydrothermal mineral deposit types and host rock lithologies; modified from Osinski et al., 2005b. Representative examples of many deposit types were studied in detail herein: A) Large intra-breccia vug dominated by calcite and marcasite, associated with complex hydrous sulfate weathering assemblages. B) Hydrothermal pipe structure and associated gossan deposit near Trinity Lake. C) Banded Fe-oxyhydroxide deposits associated with deeper levels of a hydrothermal pipe structure, exposed by stream erosion. D) Blue encrustations near Perseverance Hill.

4.1.2 Styles of hydrothermal mineralization at Haughton

Osinski et al., (2001; 2005a) described several distinct settings and styles of hydrothermal mineralization at Haughton: 1) vugs and veins hosted in impact melt 82 breccias, with an increase in intensity of alteration towards the base. Vug and vein deposits may be further subdivided into those dominated by calcite and sulfides, calcite alone, quartz, and gypsum megacrysts; 2) hydrothermal pipe structures and mineralization along fault surfaces around the faulted crater rim. The surface exposure of pipe deposits are commonly gossans dominated by secondary and/or remobilized minerals including

Fe-oxyhydroxides and gypsum; 3) intense calcite-and-quartz veining around the heavily faulted and fractured outer margin of the central uplift; and 4) cementation of brecciated lithologies by quartz and/or calcite in the interior of the central uplift.

4.2.0 Materials and Methods

Samples were collected from various hydrothermal mineral assemblages throughout Haughton. Some materials collected, notably secondary minerals from the intra-breccia calcite-marcasite vugs were clearly susceptible to dehydration during transport to the lab, based on observations at the field sites. These samples were carefully sealed in Falcon tubes (Becton, Dickinson and Company, Franklin Lakes, New Jersey,

U.S.A.) for transport and were prepared and analyzed within minutes of removal from the tubes. In addition, many of the samples were extremely porous and friable. Such materials were carefully wrapped in padding materials (paper towels, bubble wrap, polyurethane foam sponge) and placed in hard plastic containers.

4.2.1 Powder X-ray diffraction

Powders were prepared by grinding with an agate mortar and pestle for ~30 minutes. Back-packed mounts were used to reduce the effects of preferred orientation and surface roughness effects. X-ray diffraction data were collected from 2º to 82º 2θ with a 83 step size of 0.02º and scanning speed of 10º/min using the Rigaku Rotaflex diffractometer

(Rigaku, Tokyo, Japan) at the University of Western Ontario (UWO), operating at 45 kV and 160 mA with a Co rotating anode source (Co Kα, λ = 1.7902 Å). Diffractograms were analyzed using the BrukerAXS EVA software package (BrukerAXS, 2005) and the

International Center for Diffraction Data (ICDD) PDF-4 database.

4.2.2 Micro X-ray diffraction (μXRD)

Selected samples were analyzed mineralogically in situ using Micro X-ray

Diffraction (μXRD). Micro XRD data were collected in coupled scan geometry using the

Bruker D8 Discover micro X-ray diffractometer (Bruker AXS, Madison, WI, USA) at the

UWO, operating at 40 kV and 40 mA with a Cu sealed tube source (Cu Kα, λ = 1.5418

Å), equipped with a HI-STAR two-dimensional detector using General Area Diffraction

Detection System (GADDS) software. The 2-dimensional GADDS images were integrated to produce conventional angle versus intensity diffractograms, which were analyzed using the BrukerAXS EVA software package (BrukerAXS, 2005) and the

International Center for Diffraction Data (ICDD) PDF-4 database. More details on µXRD can be found in Flemming (2007), who presents a detailed introduction to μXRD for the geosciences.

4.2.3 Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES)

Powders for ICP-OES were prepared from a selected set of the same samples as used for XRD to enable direct correlation of the chemical and structural data sets. The samples selected are representative of the large intra-breccia calcite-marcasite mineralized vugs and their associated weathering assemblages. Samples aliquots of 0.2 g 84

each were fused at 1000°C with 1.5 g of LiBO2 flux, and then digested in 100 mL of 5%

HNO3. Concentrations of Na, Mg, Al, Si, P, K, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr,

Y, Zr, Nb, Ba, Ce were determined using a Perkin Elmer Optima 7300 DV ICP-OES instrument. Loss on ignition was determined by weight differences pre and post-ignition of the molten bead, and total carbon and sulfur were determined on the same sample split by the LECO method. These analytical techniques have been prepared and developed by

ACME Analytical Laboratories, Vancouver, BC, Canada.

4.2.4 Scanning Electron Microscopy (SEM)

SEM imaging including secondary electron (SE), backscattered electron (BSE) and qualitative chemical analysis using energy-dispersive X-ray spectroscopy (EDX) were carried out using a Hitachi S-4300SE/N Field Emission SEM (FESEM) (Hitachi

High Technologies America, Dallas, TX, USA) at Texas Tech University Imaging Center.

Samples were carbon coated prior to analysis. Operating conditions were 15 kV accelerating voltage with a working distance of ~10-13 mm. Additional FESEM imagery was collected for the banded materials using with the Leo 1540 FIB/SEM CrossBeam field emission SEM at the Nanofabrication laboratory at UWO, equipped with an Oxford

Instruments INCA EDX system allowing for qualitative elemental analysis.

4.3.0 Results

4.3.1 Mineralogy of the Hydrothermal Deposits at Haughton

Field observations, supported by powder XRD and µXRD analysis, ICP-AES chemical analysis and SEM imaging, reveal a diversity of mineral assemblages associated with the hydrothermal mineral deposits of the Haughton impact structure. Hydrothermal 85 mineral occurrences at Haughton include: intra-breccia calcite-marcasite vugs; small intra-breccia calcite or quartz vugs; intra-breccia gypsum megacryst vugs; hydrothermal pipe structures and associated surface ‘gossans’; banded Fe-oxyhydroxide deposits; and calcite and quartz veining and coatings in shattered target rocks. The aforementioned deposit types represent a combination of hydrothermal precipitates with varying degrees of subsequent weathering, remobilization and redeposition. Each deposit type was sampled in as complete a manner as possible, with particular attention to obtaining complete weathering product assemblages as well as primary high-temperature hydrothermal minerals and lower-temperature precipitates. This sampling strategy was designed to ensure that mineralogical boundary conditions for biological activity at all stages of post-impact hydrothermal system evolution could be investigated.

4.3.1.1 Intra-breccia calcite-marcasite vugs: Intra-breccia vugs with calcite and marcasite mineralization occur in the impact melt breccia and are associated with an array of weathering phases (Figure 4-2A). Such vugs and associated vein networks may be several meters in size. One example of such a large vug has been erosionally exposed near the

Haughton River (location A in Figure 4-1), and has been the focus of detailed study here.

The main body of the vug is lined with sulfides, dominantly marcasite with minor pyrite

(cf. Osinski et al., 2001; Osinski et al., 2005a). Layered deposits of calcite with a flowstone or travertine texture, and hydrothermal breccias surround the sulfide mineralization. The terminations of calcite layers are commonly encrusted with sulfides.

Sulfide encrustations appear to begin as scattered euhedral crystals forming marcasite rosettes that eventually merge into continuous layers (Figure 4-2B). Rare occurrences of alternating bands of coarsely crystalline calcite and marcasite ± pyrite are observed. 86

Sulfides in the calcite-marcasite vugs are commonly partially replaced or overgrown by a mixture of secondary phases including hydrous sulfates and Fe-oxyhydroxides. Marcasite and pyrite dominate the primary hydrothermal assemblage. Weathering of primary sulfides has produced a variety of secondary assemblages. Dark brown, goethite-bearing material commonly forms pseudomorphs after primary sulfides. Sulfides and goethite- rich materials are coated with a powdery, fine-grained, rusty-orange to rusty-brown material consisting of a mixture of jarosite – (K,Na,H3O)Fe3(SO4)2(OH)6, rozenite –

FeSO4•4(H2O), fibroferrite – Fe(SO4)(OH)•5(H2O), goethite – α-FeO(OH) and ferrihydrite – Fe2O3•0.5(H2O). The uppermost exposed surfaces of weathering assemblages are commonly composed of low-density, fine-grained ‘fluffy’ or ‘popcorn- textured’ efflorescent growths consisting of fibroferrite, copiapite –

(Fe,Mg)Fe4(SO4)6(OH)2•20(H2O) and gypsum – CaSO4•2H2O (Figure 4-2C). Wet material in direct contact with ice and melt water near the base of the vug contained fine- grained marcasite, pyrite and blue-green transparent crystals of melanterite –

FeSO4•7(H2O) (Figure 4-2D). Melanterite rapidly dehydrates to form a mixture of szomolnokite – FeSO4•H2O with minor rozenite; an assemblage that is observed in close proximity to the melanterite-rich material at the base of the vug.

A discontinuous sublinear feature, several meters in length and up to ~0.5 m wide, consisting of highly friable, very fine-grained, grey to brownish-grey material extends along an apparent structural weakness away from the main vug and into the surrounding impact melt breccia. A small patch of this material is marked by the arrow in Figure 4-2C.

Samples collected from this area include a grey-white material consisting of a mixture of calcite and quartz with minor amounts of montmorillonite. The brownish-grey material also consists of calcite and rozenite, with minor amounts of montmorillonite, marcasite, 87 pyrite, and gypsum. Chemical analysis of representative vug samples are summarized in

Table 4-1.

Table 4-1: Representative XRD and ICP-OES analyses of materials from the large intra-breccia hydrothermal calcite-marcasite vug locality. A B C D E F G Major Cal Mrc Cal, Roz Gp, Jrs Fib Fib, Cop Gp, Cop minerals Minor & Cal, Mrc, Mnt, Py, Jrs, Roz, trace Qtz Py, Cal Qtz, Gth, Roz, Gp Mrc, Gp Frh minerals Frh

SiO2 8.97 1.05 2.47 9.28 5.34 0.29 0.77

TiO2 0.07 <0.01 0.02 0.05 0.04 <0.01 <0.01

Al2O3 1.49 0.11 0.34 1.19 0.78 0.06 0.09

Cr2O3 <0.01 0.01 <0.01 <0.01 <0.01 <0.01 <0.01

Fe2O3 0.51 28.32 13.87 20.12 15.70 31.52 31.68 MnO <0.01 <0.01 0.01 <0.01 <0.01 <0.01 <0.01 MgO 1.28 0.53 0.79 2.31 0.91 0.87 0.40 CaO 47.48 32.43 41.14 21.87 21.26 1.03 3.31

Na2O <0.01 <0.01 <0.01 <0.01 0.03 0.01 <0.01

K2O 0.88 0.07 0.23 0.38 0.37 0.01 0.05

P2O5 0.03 0.02 <0.01 0.02 0.02 <0.01 <0.01 Ba 327 8 10 19 50 <5 <5 Sr 126 147 83 121 680 17 120 Co <20 <20 <20 <20 <20 <20 <20 Ni <20 24.00 <20 <20 <20 <20 <20 Cu 6 <5 <5 <5 <5 <5 <5 Zn 5 5 10 50 14 79 <5 Zr 35 22 16 10 29 <5 <5 Y 3 <3 <3 <3 <3 <3 <3 Sc 1 <1 <1 <1 <1 <1 <1 Nb 6 9 9 6 9 <5 <5 Ce <30 36.00 39.00 <30 <30 <30 <30 LOI 39.15 28.60 32.30 22.40 30.80 66.10 63.70 C 10.75 7.50 8.47 1.54 1.06 0.05 0.05 S 0.14 19.60 11.30 9.07 22.66 15.09 14.43 Sum 99.97 91.19 91.21 77.61 75.40 99.96 100.00 A: Laminated 'flowstone-textured material B: Botryoidal sulfides on carbonate C: Grey-brown fine- grained powder D: Dark orange-brown material E: Yellow-brown powdery material F: ‘Popcorn- textured’ material G: White crusts on ‘popcorn-textured’ material Oxides, C, S, and LOI in wt. %; others in ppm. Gp = gypsum, Cal = calcite, Mrc = marcasite, Qtz = quartz, Py = pyrite, Fib = fibroferrite, Cop = copiapite, Jrs = jarosite, Roz = rozenite, Mnt = montmorillonite, Lpd = lepidocrocite, Gth = goethite, Frh = ferrihydrite.

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Figure 4-2: Mineralization in the large intra-breccia vug (Fig. 1, location A). A) Intra-breccia vug with calcite-marcasite-pyrite mineralization and an array of secondary/weathering phases. Layered travertine and hydrothermal breccias surround the sulfide mineralization. The grey clastic material is a hydrothermal breccia dominated by calcite with minor dolomite and traces of quartz. Dark brown material consists of gypsum, jarosite, with minor calcite, marcasite, quartz and goethite. B) Botryoidal marcasite and pyrite (metallic yellow-green-bronze), with a thin trail of weathering products including brown jarosite and rozenite, and white-yellow fibroferrite with copiapite and gypsum. C) pale yellow-white, ‘fluffy’ or ‘popcorn’ material, consisting of fibroferrite with copiapite, gypsum, and rozenite. The dark grey material at the boundary of hydrothermal breccia and vug mineralization, marked by the arrow in C, is a fine grained, friable mixture of calcite, rozenite, with minor montmorillonite, pyrite, marcasite, and gypsum. D) Sample from the underside of the vug containing translucent green-blue melanterite with rozenite, gypsum, jarosite, szomolnokite, marcasite and pyrite.

4.3.1.2 Small intra-breccia calcite or quartz vugs: Small (up to tens of centimetres) vugs of calcite and/or quartz are commonly encountered in the impact melt breccia. Such small vugs may be concentrated at the tops of melt breccia hills by the preferential erosion of fine-grained impact melt breccia. Quartz in these vugs is commonly milky white and drusy-textured. Some vugs also contain opal-α, identified by µXRD. Calcite is fine- grained, colourless, or pale blue, sometimes with prismatic crystal terminations. Both quartz and calcite may have concentric banded textures. Sulfides and sulfates are rare in the small calcite or quartz vugs. 89

4.3.1.3 Intra-breccia gypsum megacryst vugs: Gypsum megacrysts occur within impact melt breccia, and consist of aggregations of colourless, transparent crystals of gypsum protruding from the impact melt breccia (Osinski et al., 2001; Osinski et al., 2005a). The gypsum megacrysts form clusters of intergrown prismatic, lath-like or platy crystals, with individual crystals up to ~1 metre in their longest dimension. Twinning on a (100) composition plane, and cleavage along (010) planes were commonly observed. Some gypsum megacrysts contain inclusions that include microbial colonies and organic matter

(Cockell et al., 2010); as well as fine-grained detrital material trapped along crystal edges or within cleavage planes. Fluid inclusions are common in the gypsum megacrysts

(Osinski et al., 2005a).

4.3.1.4 Hydrothermal pipe structures and surface ‘gossans’: Pipe-like structures are hosted in highly fractured carbonate rocks of the faulted rim of the Haughton structure

(Osinski et al., 2001; Osinski et al., 2005a). A typical example of a hydrothermal pipe structures is located near Trinity Lake (location B in Figure 4-1). The surface exposure of the pipe structures is commonly highly friable, porous Fe-oxyhydroxide stained materials, that previous workers (e.g., Osinski et al., 2005a) at Haughton have termed ‘gossans’ by analogy with the oxidized, acid-leached zone of massive sulfide ore deposits (e.g., Wolf,

1981). Pipe structures and associated gossan deposits at Haughton are dominated by a variety of dissolution and re-precipitation textures, as shown in Figure 4-3. Gossans contain abundant macroporosity, featuring delicate honeycomb and colonnade textures

(Figure 4-3A). Gossans are dominated by poorly-sorted dolomite, calcite and quartz clasts ranging in size from fine silt to coarse pebbles, cemented by fine grained Fe- 90 oxyhydroxides (ferrihydrite and minor goethite) and gypsum (Figure 4-3B and 4-3C). The surface layers are commonly highly friable and porous, with textures consistent with formation by dissolution and reprecipitation. Thin rinds of goethite, which formerly surrounded carbonate clasts that have subsequently dissolved, are common in the gossans.

Continuous layers of gypsum, up to a few centimetres thick, commonly occur in the near subsurface of the gossan deposits (Figure 4-3C and 4-3D).

Figure 4-3: Mineralization at the hydrothermal pipe structure near Trinity Lake, representative of hydrothermal pipes hosted in the faulted rim of the Haughton impact structure. A) Colonnade structure composed of gypsum, ferrihydrite and traces of goethite. This material is highly porous and friable and could provide sheltered microenvironments. B) Gravel- to pebble-sized blocks of dolomitic country rock cemented by gypsum, ferrihydrite and goethite. C) and D) Continuous white gypsum crusts in the near subsurface (within ~30 cm), beneath which are small open cavities.

4.3.1.5 Banded Fe-oxyhydroxide deposits: A small stream has deeply eroded a hydrothermal pipe structure at one locality in the East of the crater (location C in Figure 91

4-1), exposing a deposit of banded material consisting of alternating dark to pale rust brown, millimetre-to-micrometer scale laminae (Figure 4-4A). Darker layers contain abundant goethite, with ferrihydrite, dolomite, calcite, and traces of quartz (Figure 4-4B and C). Lighter-coloured materials are dominated by dolomite with some calcite, quartz and traces of ferrihydrite and goethite. Goethite and ferrihydrite form thin coatings around dolomite grains. Vugs lined with coarse ~several millimetre long euhedral calcite crystals also occur sparsely at this locality (Figure 4-4D). The banded material contacts sharply and irregularly with brecciated dark grey-brown, organic-bearing dolomitic country rock with pervasive pale white calcite veining (Figure 4-4 B and C; Figure 4-5).

At the microscopic scale, the banded materials consist of clastic dolomite grains surrounded by veins of calcite with quartz (Figure 4-5). It is possible that similar deposits occur at depth at other hydrothermal pipe locations, but no other locations with a similar exposure of the deeper parts of a hydrothermal pipe deposit are known.

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Figure 4-4: Banded deposits consisting of thin laminae of dark brown-black goethite-rich material, ranging in thickness from a few hundred microns to several millimeters, interspersed with lighter- coloured yellow-tan-rust brown bands dominated by dolomite with some calcite and quartz (A-C). Banded materials occur on a substrate of dolomite with calcite and minor quartz. The dolomite is heavily veined with calcite, and the contact of veined dolomitic country rock with the banded material is sharp at both the field scale (B and C, marked by white lines) and SEM scale (Figure 4-5). Sparse vugs lined with coarse calcite crystals also occur at this locality (D).

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Figure 4-5: Representative SEM-BSE image and EDX chemical mapping of the contact between brecciated dolomite with calcite veining and Fe-oxide/oxyhydroxide-rich material. The contact between these materials is very sharp at both the field and microscopic scales, as is particularly well- illustrated by the Fe map. Note the presence of Si associated with the Fe-rich material, possibly indicative of a rapid change in the solubilities of both Si and Fe.

4.3.1.6 Veining in shattered target rocks, blue mineral coatings: Shattered dolomitic country rock commonly hosts pale tan-yellow quartz-rich veins. In many instances, preferential weathering of the carbonate has left the resistant veins as sharp raised-relief 94 on the exposed surfaces of the outcrops. Quartz veining is also very common in large meter-scale brecciated blocks that lie beneath the crater-fill melt rocks.

Numerous samples collected near Perseverance Hill, located in the central uplift

(location D in Figure 4-1), have thin coatings ranging in colour from deep blue through sky blue to white. The blue coatings consist primarily of fibrous layers of microcrystalline quartz with traces of a sodalite-structured mineral, probably lazurite,

(Na,Ca)8(AlSiO4)6(SO4,S,Cl)2. The quartz comprising the majority of the blue coatings is drusy-textured. Similar drusy-textured quartz coatings occur sporadically near the large calcite-marcasite intra-breccia vug, however, the intense blue-coloured material has been observed only at Perseverance Hill.

4.4.0 Discussion

This study presents a detailed mineralogical characterization of the various styles of hydrothermal mineral deposits at Haughton, concentrating on numerous weathering features that have not been studied in detail previously. Weathering assemblages are important from a planetary exploration perspective; as such materials are likely to form an obvious surface expression of hydrothermal systems in the impact crater environment in lieu of active or recent hydrothermal activity. The assemblages of primary and secondary minerals, furthermore, point towards potential metabolic pathways (such as those based upon the oxidation of Fe and S) which might have been exploited by microbes, analogous to microbial communities documented in acid rock drainage environments (e.g., Baker and Bandfield, 2003). Several stages or modes of microbial activity may have been present. First, a high-temperature thermophile or hyperthermophile stage, featuring high-temperature hydrothermal fluids; followed and 95 partly overlapping with a lower temperature, neutral to acidic staged where the oxidation of hydrothermally-precipitated minerals such as marcasite and pyrite became progressively more important as cooling progressed; this stage would then grade into a final ‘holdout’ phase, where endolithic and/or hypolithic communities inhabiting such niches as porous impactites, fluid inclusions, and microhabitats within weathered hydrothermal mineral deposits would be most important. Table 4-2 summarizes the hydrothermal mineral deposit types, their mineral assemblages and parageneses; and their implications for microbial colonization.

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Table 4-2: Summary of Haughton post-impact hydrothermal mineral deposit types, their primary and secondary assemblages and parageneses; and possible implications for microbial life. Deposit type Assemblage Paragenesis Potential implications for microbial life Large calcite- Primary: calcite, Marcasite, pyrite and Hyperthermophile/thermophile marcasite marcasite, minor calcite precipitated near sulfide production possible during vugs pyrite and quartz base of impact melt 'phase of thermal biology'. Secondary*: breccia at high Weathering assemblage suggests a goethite, jarosite, temperatures during role for 'acid rock drainage' fibroferrite, active hydrothermal metabolisms including Fe- copiapite, circulation. Sulfides oxidization, S-oxidization. rozenite, oxidized and hydrated ferrihydrite, during later alteration, szmolnokite, producing varied melanterite, weathering assemblages. montmorillonite, gypsum Small calcite- calcite, quartz, Crystallized within impact Possible colonization during ‘phase quartz vugs rare opal-α melt breccia, widely of thermal biology’, particularly if distributed, may be connected/related to large calcite- smaller versions of marcasite vugs. Later, sheltered calcite-marcasite vugs but environments. lack major sulfides. Gypsum gypsum Precipitated at lower Entrapment of microbial colonies in megacryst temperatures in sheltered within crystal inclusions vugs hydrothermal system and between crystals. hosted in impact melt breccia; later or in lower- temperature zones; possibly stratigraphically higher than large calcite- marcasite vugs. Hydrothermal gypsum, calcite, Areas of focused Colonization during active pipes and dolomite, hydrothermal fluid flow, hydrothermal phase possible. Highly 'gossans' ferrihydrite, concentrated in faulted oxidized, potential role for microbial goethite crater rim. weathering. Porous remobilized materials produce microhabitats. Banded calcite, dolomite, Hydrothermal calcite and Possible biological role in deposits quartz, quartz veins deposited in sedimentation. Sharp redox contrast ferrihydrite, fractures. Banded suggesting niche for Fe-oxidizing goethite materials form thin microbes. laminae rich in Fe- oxyhydroxide phases that cement clastic debris. Veining in Primary (country Pervasive shattering of Increased porosity and fluid flow shattered rock): dolomite, target rocks provided during ‘phase of thermal biology’; target rocks, calcite conduits for hydrothermal chasmoendolithic and other sheltered coatings Secondary: quartz, fluids which precipitated microhabitats later. lazurite (rare quartz-rich veins; such coatings) veins commonly exposed during later weathering. *Details of individual assemblages within the secondary minerals of the calcite-marcasite vugs are given in section 4.3.1.1 and Table 4-1.

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4.4.1 Mineral constraints on physicochemical conditions in the post-impact environment

The textural relationship between calcite and marcasite indicates that marcasite most commonly precipitated after calcite (although rare instances of interlayered calcite- marcasite have been observed). Calcite and marcasite precipitation were likely associated with near-neutral pH, and have been linked to pH increases due to the degassing of CO2

(Osinski et al., 2001). More acidic conditions developed in spatially restricted areas during the subsequent aqueous weathering and oxidation of the hydrothermal marcasite deposits, as evidenced by the presence of low-pH phases including copiapite, jarosite, fibroferrite and rozenite in the weathered zones of the hydrothermal deposits (e.g., Jerz and Rimstidt, 2003). Locally acidic conditions occurred despite the presence of abundant carbonate which might be expected to buffer the system at higher pH. The presence of highly acidic microenvironments in a circumneutral to mildly alkaline carbonate terrain highlights the potential for great variability in local physicochemical conditions that is possible in the post-impact environment. Such variability is an important consideration for microbial colonization. For example, Parnell et al. (2010) observed sulfur isotope fractionation between sulfides and sulfates from Haughton that are indicative of microbially-mediated sulfate reduction.

The presence of gypsum megacryst vugs throughout the melt breccia units indicates that the parts of the hydrothermal system that produced gypsum vugs were more oxidized and near neutral pH. If the gypsum megacryst vugs were connected to parts of the hydrothermal systems that precipitated the calcite-marcasite vugs, some of the gypsum may be the result of the neutralization of H2SO4 by reaction with the carbonates in the impact melt breccia. Most of the gypsum, however, was likely remobilized from the impact melt breccia and target rocks by hydrothermal fluids. Previous work has 98 shown that the gypsum megacrysts likely formed at lower temperatures than the calcite- marcasite vugs (Osinski et al., 2005a), either because they formed somewhat later, or due to heterogeneities in temperature within the hydrothermal system. It is not possible to place temporal constraints on the microbial colonization of gypsum, because it is likely to be a continuous process, as new organisms are probably constantly being entrained, whilst older colonies persist.

Many of the Fe-sulfate dominated weathering deposits also contain gypsum, commonly as thin powdery rinds or flaky to fibrous efflorescences on the outer surfaces of other sulfates, or as encrustations on the surfaces of distal host rock material. The presence of gypsum in such environments is consistent with neutralization over very small spatial scales. Fe3+ may be reprecipitated, perhaps as Fe-oxyhydroxides (e.g., goethite, lepidocrocite, ferrihydrite), which are commonly associated with gypsum in the

‘gossan’ deposits associated with hydrothermal pipes in the faulted rim. The target rocks at Haughton contain bedded gypsum, some of which was incorporated into the impactites

(Osinski and Spray, 2003; Osinski et al., 2005b). Some of the gypsum in gossans therefore has likely been remobilized from pre-existing material by dissolution and reprecipitation, and some has likely formed via more complex pathways involving sulfide precipitation and subsequent oxidation (Parnell et al., 2010).

4.4.2 Mineral constraints on possible geomicrobiology of the Haughton post-impact hydrothermal system

The sulfide weathering at Haughton points to potential metabolic pathways and can be used to illustrate the influence of mineralogy on geomicrobiology. Iron and sulfur oxidation reactions in aqueous solutions are particularly relevant to microbial 99 colonization of the post-impact hydrothermal environment at Haughton. During the

2- 6+ 2- oxidation of FeS2 in the presence of water, S is oxidized to S in the form of SO4 with the simultaneous production of H+ ions are produced via reactions such as (e.g., Madigan and Martinko 2006):

2+ 2- + 2FeS2 + 7O2 + 2H2O → 2Fe + 4SO4 + 4H (4-1)

Chemolithotrophic microorganisms such as bacteria of the genera Acidithiobacillus,

Thiomicrospira, and Sulfolobus can catalyze the sulfide weathering process, gaining energy via the oxidation of reduced sulfur (e.g., Madigan and Martinko, 2006).

Furthermore, some bacteria catalyze the oxidation of sulfides, creating and sustaining very low pH environments: If iron-oxidizing bacteria are present, they will enhance the production of Fe3+ from Fe2+, via the reaction (e.g., Madigan and Martinko, 2006)

2+ + 3+ 4Fe + O2 + 4H → Fe + 2H2O (4-2)

3+ The Fe produced by this process can also oxidize additional FeS2 via reactions such as

(e.g., Madigan and Martinko, 2006)

3+ 2+ 2- + FeS2 + 14Fe + 8H2O → 15Fe + 2SO4 + 16H (4-3)

The oxidation of S2- and/or S0 may provide energy for microbial metabolism. The predominant source of reduced sulfur at Haughton was likely the S2- present in hydrothermally-precipitated sulfide minerals. Native sulfur has not been detected among the hydrothermal and weathering assemblages investigated in the present study. Although chemolithoautotrophic carbon fixation processes are of high interest for extraterrestrial settings, it is likely that phototrophic microorganisms were important (perhaps dominant) contributors to primary productivity in the Haughton post-impact environment.

Heterotrophic microorganisms were also likely abundant, given the availability of organic 100 compounds from organic material derived from the target rocks (e.g., Parnell et al., 2005a;

Parnell et al., 2005b; Eglinton et al., 2006; Parnell et al., 2007), as well as from primary production, both phototrophic and chemolithoautotrophic. In addition to the above- mentioned anaerobic metabolic pathways, processes including anaerobic iron oxidation

(using nitrate as the terminal electron acceptor); sulfur reduction; and iron reduction may be supported by primary hydrothermal mineral assemblages or their weathering products, or by materials (e.g., sulfate) mobilized in the post-impact hydrothermal environment.

Such anaerobic metabolisms may have been locally important in anoxic microenvironments or in the subsurface.

4.4.3 Potential microbial habitats and metabolic strategies: Eras of microbial activity in the post-impact environment.

The hydrothermal mineral deposits at Haughton are consistent with a general progression from high-temperature, neutral to moderately acidic conditions to locally highly acidic conditions with progressive oxidation and hydration of primary sulfide minerals. As the intensity of hydrothermal activity decreased, chemical energy sources would have become increasingly important for any non-phototrophic microbial communities present. Stages of microbial activity may be subdivided as follows: A high- temperature ‘stage of thermal biology’ (c.f. Cockell and Lee, 2002), with active hydrothermal circulation. During this initial stage, heating from the passage of the shockwave, heat in melt rocks lining the crater, and the higher temperature of the rocks comprising the central uplift provided the energy to drive the circulation of fluids. This stage corresponds with the deposition of the flowstone-travertine calcite plus marcasite intra-breccia vugs, hydrothermal pipe deposits, and possibly the deposition of intra- 101 breccia gypsum megacrysts. Microbial life present during the stage of thermal biology would be expected to include thermophilic and hyperthermophilic organisms.

Temperatures of hydrothermal fluids at Haughton in the range of 100-200 °C were estimated by Osinski et al. (2005a) using fluid inclusions. Auclair et al. (2009) estimated vug calcite formation temperatures of >130 ºC using oxygen isotope thermometry.

Microbial metabolisms based upon chemical energy, from processes such as Fe2+ and S2- oxidation (and possibly reduction in anoxic regions), were progressively more important as the heat provided by the impact was exhausted and active hydrothermal fluid circulation ceased. This ‘acid rock drainage stage’ corresponds with the Fe-sulfate and oxyhydroxide secondary stage associated with marcasite, and possibly with the banded materials and gossans associated with hydrothermal pipes.

The final biological stage is characterized by ‘long-term holdouts’ in habitable microenvironments, which may persist long after the cessation of hydrothermal circulation. Examples of such ‘holdout’ environments include fluid inclusions (Edwards et al., 2005), porous impactites, and beneath or within rocks as hypolithic or endolithic communities (e.g., Cockell et al., 2002; Cockell and Osinski, 2007). Hydrothermal mineral deposits important to this phase of biological activity include gypsum megacrysts, gypsum/anhydrite clasts within impact melt breccia, and the gossan deposits associated with hydrothermal pipes. Figure 4-6 presents a schematic representation of the potential succession and diversification of microbial habitats in the post-impact environment.

Microbial communities have been observed in gypsum megacrysts at Haughton (Cockell et al., 2010).

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Figure 4-6: Schematic representation of the biogeochemical evolution of the post-impact hydrothermal environment. Stages of microbial activity may be conceptually subdivided as shown, although it is recognized that the stages are likely members of a continuum.

Physicochemical changes in the post-impact hydrothermal environment, as the initial heat pulse diminishes and hydrothermal mineral deposits weather can provide evolutionary selection pressures leading to diversification in metabolic strategies and habitats. Substantial ranges in pH, temperature, and redox state can occur over very short spatial (and probably temporal) scales, producing a large number of possible ecological niches in a limited area. The impact crater environment enables microbial life to

‘experiment’ with a wide range of physicochemical conditions, and offer possibilities for

‘opportunists’ coming from outside. The impact crater is potentially a biodiversity hotspot with a high likelihood for colonization and diversification.

4.4.4 Potential for fossilization, mineralization and long-term preservation

Gypsum crystals may trap microbes within fluid inclusions or between crystals.

Halophilic microorganisms were reported by Edwards et al. (2005); and cyanobacterial colonies by Parnell et al. (2004), within gypsum crystals from Haughton (Cockell et al., 103

2010). Similar entombment could occur within the gypsum crystals associated with the gossan deposits at hydrothermal pipe localities.

Endolithic habitats within impactites have previously been described in numerous studies (e.g., Cockell and Lee, 2002; Cockell et al., 2002; Kring, 2003). Microbial communities inhabiting such impact-produced endolithic habitats (‘long-term hold-outs’) may be in part descended from both microbial life inhabiting the more transient high- temperature hydrothermal environments following the impact, and from the chemical weathering influenced stage of microbial colonization (Figure 4-6).

The banded materials bear a striking resemblance to microbialites or stromatolites.

Stromatolites and other fossils are common in carbonate sediments. Therefore it is possible that the banded materials are simply the result of infilling or staining of pre- existing structures in the rock; however, no such fossils have been observed from the host dolomitic country rock units anywhere near the locality in question. Cross-cutting and contact relations between the banded materials, calcite veins and the dolomite host rock indicate that the banded materials post-date the impact, and may have formed penecontemporaneously with the calcite veins. The textures of the banded materials are strongly suggestive of formation via a combination of physical and chemical sedimentation, possibly involving biological processes.

4.4.5 Potential for chemical and isotopic biosignatures

The hydrothermal mineral deposits at Haughton have the potential to contain chemical and isotopic signatures indicative of past biological activity. Parnell et al. (2010) have reported isotopic evidence in the form of isotopically-light sulfur from Haughton sulfides, which they interpreted as the result of microbial sulfate reduction by 104 thermophilic microbes. The sulfur isotopic composition of the sulfates present in sulfide weathering assemblages, the gypsum, and other sulfates in intra-breccia vugs and veins could also contain signatures of microbially-mediated sulfur redox reactions. Other chemical biosignatures might include concentrations of biologically important elements such as transition metals, C, N, Na, P, and Cl; and the presence of biogenic organic molecules. Finally, isotopically light carbon in carbonate minerals can be indicative of biological fractionation during microbial metabolic reactions.

4.5.0 Summary and conclusions

The post-impact hydrothermal deposits at Haughton have provided numerous potential habitats, and several possible chemical energy sources. Our results do not demonstrate unambiguous morphological or chemical biosignatures; they do, however, suggest several niches in which biological activity could play a role and in which biota may have gained and held a foothold. The wide distribution of oxidized and reduced sulfur species suggests the possibility of a complex sulfur cycle containing niches that could be occupied by both sulfur-oxidizing and sulfur-reducing microorganisms. Both Fe- oxidizing and Fe-reducing (in anoxic regions) metabolisms could similarly be present. In addition to the aforementioned chemolithotrophic niches, the porous, reworked deposits of gypsum, Fe-oxyhydroxides and hydrous Fe-sulfates provide an abundance of sheltered microenvironments. The present study provides mineral and chemical context for biological activity in the post-impact environment, particularly during the little-studied

(but extensive) time period after the cessation of hydrothermal activity.

It is now widely recognized that impact events can produce transient warm oases that are suitable for microbial colonization (Osinski et al. 2001; Cockell and Lee 2002; 105

Abramov and Kring 2005; Versh et al. 2006). The movement of hydrothermal fluids in the post-impact environment (facilitated by extensive fracturing and faulting) should also lead to conditions conducive to the formation of various hydrothermal mineral deposits.

The spatial distribution of post-impact hydrothermal deposits at Haughton should be broadly analogous to those in similar-sized impact structures in diverse planetary settings, because impact structures are broadly similar despite differences in lithology and other target parameters (e.g., Melosh, 1982; Melosh, 1989; Grieve and Therriault, 2004;

Osinski et al., 2008).

Post-impact hydrothermal environments produce a wide range of physicochemical conditions which may be conducive to colonization by a correspondingly diverse array of microbial life. Impactites and the weathered products of primary hydrothermal minerals also provide environments in which endolithic microorganisms may remain for geologically relevant timescales, and where traces of such microbial life may be preserved or fossilized. The role of impact craters as microbial habitats may have been much more important on ancient Earth, when the impactor flux was higher, particularly during the late heavy bombardment (e.g., Cockell 2006).

The alteration, remobilization and reprecipitation of post-impact hydrothermal minerals at Haughton required the action of transient near surface liquid water and oxidative near-surface conditions. Such conditions are likely to have prevailed over much of Martian history, therefore the Haughton deposits are a useful terrestrial model for post- impact processes on Mars. Martian post-impact hydrothermal mineral deposits and their weathering products, especially Fe-sulfides, sulfates, and oxyhydroxides, may be analogous to those at Haughton. Mars lacks an oxygen-rich atmosphere, but the Martian surface is highly oxidizing due to the presence of peroxides, perchlorates and other 106 oxidants (e.g., Clark et al., 1976; Squyres and Knoll, 2005). The Martian crust contains abundant water which could be mobilized in post-impact hydrothermal systems.

Because impact craters are expected to be a feature of any solid planetary surface, the importance of craters and their associated post-impact hydrothermal systems as biodiversity hotspots and environments of preservation is not limited to Earth. In particular, post-impact hydrothermal systems provide a spatially-restricted near-surface environment with sources of thermal and chemical energy, combined with numerous habitable niches. Mars in particular is very likely to host post-impact hydrothermal deposits (e.g., Abramov and Kring, 2005; Schwenzer and Kring, 2009); and some form of post-impact hydrothermal activity could also occur on icy bodies including Europa and

Titan. The potential for microbial colonization of post-impact hydrothermal systems, and for continued habitation of such environments long after the cessation of hydrothermal activity, demonstrates that impact structures and associated hydrothermal systems are potential planetary biodiversity hotspots with high preservation potential.

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Chapter 5: Preservation of microbial ichnofossils in basaltic glass by titanite mineralization

Chapter summary and key points

Glassy volcanic rocks and their metamorphosed equivalents are a recently-realized setting in the search for traces of early life on Earth; however, numerous studies have demonstrated that the record of microbial colonization of submarine basaltic glass in extends to at least 3.5 Ga. Microbes rapidly colonize the glassy surfaces along fractures and cracks exposed to water, producing characteristic granular and tubular bioalteration textures. We present a mineralogical study of the materials mineralizing bioalteration structures in oceanic crust samples from the Ontong Java Plateau (OJP); and subaqueously emplaced, formerly glassy, basaltic rocks from the Abitibi Greenstone Belt

(AGB). Previously-reported Ca- and Ti-rich material in the OJP tubules was determined to be very fine-grained crystalline titanite (CaTiSiO5) by micro X-ray diffraction (μXRD).

Formerly-glassy pillow lavas and inter-pillow hyaloclastites in AGB samples contain tubular and granular structures which also have been preserved by titanite mineralization, as confirmed by μXRD. Titanite mineralization associated with bioalteration in the OJP samples strongly suggests that mineralization of these trace fossils occurs penecontemporaneously with bioalteration. Early precipitation of titanite within the alteration structures enables their preservation in the geological record, potentially for billions of years in the absence of penetrative deformation. Mineralogical identification of titanite by in situ non-destructive μXRD has provided essential phase information, which is complimentary to other microscopic and microanalytical data.

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5.1.0 Introduction

Many searches for traces of early life on Earth have concentrated on sedimentary rocks and rocks interpreted to represent metamorphosed sediments. Preserved traces of ichnofossils in basaltic glass from in situ oceanic crust (Banerjee and Muehlenbachs,

2003; Benzerara et al., 2007), ophiolite complexes (e.g., Furnes et al., 2005) and Archean greenstone belts (e.g., Furnes et al., 2004; Bridge et al., 2010) have extended the ichnofossil record to igneous rocks. In greenstone belts and ophiolites, traces of microbial alteration of glass are preserved by mineralization of fine-grained titanite, identified by petrographic and chemical methods (Banerjee et al., 2006; McLoughlin et al., 2008;

Staudigel et al., 2008a). Important questions remaining are the timing and conditions of titanite formation, in particular whether titanite formation begins while the host glass is part of in situ oceanic crust or during subsequent metamorphism.

In this study we present a mineralogical characterization of the materials associated with bioalteration structures from in situ oceanic crust from the Ontong Java

Plateau (OJP) and preserved in the Archean (2.7 Ga) Abitibi Greenstone Belt (AGB) using Micro X-ray Diffraction (μXRD). Previous studies have indicated that the tube- filling material in modern basaltic glass bioalteration textures includes a phase enriched in

Ti and Ca (Banerjee and Muehlenbachs, 2003; Walton and Schiffman, 2003). Micro XRD analysis has enabled the identification of titanite (CaTiSiO5) associated with bioalteration textures hosted in OJP basaltic glass and confirmed its presence in AGB samples.

5.1.1 Background and geologic setting

Numerous studies have presented convincing evidence that subaqueous basaltic glasses are colonized by microbes soon after cooling from a molten state is complete; the 115 activity of these microbes leaves behind traces that reveal their former presence: microbial colonization of basaltic glass leads to the alteration and modification of the rocks and produces characteristic granular and tubular textures (e.g., Thorseth et al., 1995;

Torsvik et al., 1998; Furnes et al., 2001; Banerjee and Muehlenbachs, 2003; Furnes et al.,

2004; Banerjee et al., 2006; Staudigel et al., 2008a). Bioalteration textures have been documented in samples from a range of ages and geological settings, including modern oceanic crust, ophiolite complexes throughout the Phanerozoic, and Archean greenstone belts.

5.1.2 Characteristics of microbial bioalteration textures in basaltic glass

The characteristics of tubular and granular bioalteration textures have been thoroughly described elsewhere (e.g., Furnes et al., 2007; McLoughlin et al., 2008;

Staudigel et al., 2008a; and references therein), and are summarized briefly. Granular textures are roughly hemispherical agglomerations of micrometric cavities that radiate from a single point at a crack or surface, reminiscent of microbial growth cultures in agar

(Furnes et al., 2007; Staudigel et al., 2008a). Tubular bioalteration textures extend into unaltered glass, commonly perpendicular to the fracture or surface upon which they originate. Tubules are typically a few micrometers wide and range in length from a few to several hundred μm. A variety of tubule morphologies have been documented, including segmented, bifurcated and spiral or helical forms (Banerjee and Muehlenbachs, 2003;

Staudigel et al., 2006; Furnes et al., 2007; Staudigel et al., 2008a; Walton, 2008;

McLoughlin et al., 2009).

5.1.3 Summary of evidence for biogenicity 116

The evidence supporting a biogenic origin of the microbial alteration textures discussed here has been reviewed in several recent publications; therefore only a short enumeration of the key points is presented here. For complete discussions, see for example Furnes et al. (2007), McLouglin et al. (2008), Staudigel et al. (2008a); and references therein.

The tubular structures possess textural criteria (size, morphology, log-normal size distributions) indicative of a biogenic origin. Biologically important elements such C, N,

P, and S are associated with biologically induced corrosion structures in modern and ancient glasses (Banerjee and Muehlenbachs, 2003; Banerjee et al., 2006; Benzerara et al.,

2007; Banerjee et al., 2010). The disseminated carbonates within the altered glass rims of pillows have characteristically low δ13C values compared to their crystalline interiors.

Staining with DAPI (4,6 diamino-phenyl-indole) dye probes, which bind to nucleic acids and fluorescent oligonucleotide probes (ethidium bromide) that target bacterial and archeal RNA, indicate that biological material is concentrated at the interface between the fresh and altered glass, especially in the walls and tips of tubular structures (Banerjee and

Muehlenbachs, 2003). Bioalteration structures are always rooted on surfaces that are exposed to external water, and have not been reported completely enclosed in glass.

Tubules located on conjugate sides of a crack are not aligned, as would be expected if the tubules formed as a result of dissolution along pre-existing weaknesses in the glass (e.g.,

Banerjee and Muehlenbachs, 2003; Staudigel et al., 2006; Furnes et al., 2007; Staudigel et al., 2008a).

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5.2.0 Experimental methods

Polished thin sections of volcaniclastic tuff from the Ontong-Java Plateau (OJP) and metamorphosed flow-top hyaloclastite from the Abitibi greenstone belt, Quebec

(AGB) were analyzed by micro X-ray diffraction (µXRD). The same polished sections were investigated with a petrographic microscope in transmitted light. As discussed by

Flemming (2007), the µXRD approach is powerful and versatile in the examination of geological materials in situ. The µXRD technique extends X-ray diffraction analysis to spatial resolutions of tens to hundreds of μm, enabling the correlation of crystal structural data with other microscopic and microanalytical data. The ability for rapid, non- destructive and in situ mineral identification makes μXRD the ideal analytical technique for the present study.

Micro XRD data were collected using a Bruker D8 Discover at the University of

Western Ontario, with Cu Kα radiation (λ = 1.5418 Å), 40 kV accelerating voltage and 40 mA beam current and a nominal 50 or 500 μm beam diameter. A two-dimensional

General Area Diffraction Detector System (GADDS) collects the diffracted X-rays. In a two-dimensional X-ray diffraction (XRD) pattern, a single crystal produces one or more discrete spots, each of which corresponds to a set of lattice planes defined by a Miller index (hkl) (He, 2003; Helming et al., 2003; Flemming, 2007). A powder containing crystallites in all orientations produces a circular arc of diffracted rays, corresponding to the intersection of a cone of diffracted rays with the detector; this is termed a Debye ring

(e.g., Azároff and Buerger, 1958). MicroXRD GADDS images generally contain both

‘single crystal’ and ‘powder’ patterns, having ‘spot’ and ‘ring’ patterns, respectively, or intermediate discontinuous ‘spotty rings’ indicating intermediate grain-sizes. The minimum crystallite diameter required to produce diffraction maxima visible above 118 background is ~10 nm; broad, diffuse diffraction patterns correspond to crystallites with average diameter in the range of ~10 to 200 nm; sharp, homogeneous ‘powder rings’ are produced by crystallites ranging from ~200 to ~5 μm in diameter, corresponding to the ideal grain size for powder XRD; crystallites from ~5 to ~50 μm in diameter show inhomogeneities in the Debye rings, creating a discontinuous chain of spots along the

Debye ring; above ~50 μm in diameter, crystals produce progressively fewer large isolated spots, approaching a single-crystal pattern (e.g., Azároff and Buerger, 1958). The aforementioned size ranges naturally grade into each other, and are only semi- quantitative.

Counting times of four hours were required for the OJP sample owing to the small amount of crystalline matter as compared to glass and because of the 50 μm nominal beam diameter used. Fluorescence of Fe caused by Cu Kα radiation also contributed to high levels of the background. Thirty-minute counting times were used for the AGB sample, using a 500 μm nominal beam diameter.

Micro XRD data were processed using the Bruker AXS EVA software package

(BrukerAXS, 2005) and the International Center for Diffraction Data Powder Diffraction

File (ICDD PDF-2004) database. Background corrections for all samples were made using visually-determined Bezier curves in EVA. An alternative approach to minimizing the signatures of glass and Fe-fluorescence subtraction was also developed and tested.

Multiple diffractograms were collected from areas of pristine glass that were free of crystalline matter, using scan parameters identical to those used to analyze bioalteration textures. The diffraction patterns of pristine glass were averaged, and then smoothed using the Savitzky-Golay algorithm in EVA (Savitzky and Golay, 1964; BrukerAXS,

2005). The averaged, smoothed pattern of glass was then subtracted from other measured 119 diffractograms collected from areas that contain crystalline phases in addition to glass.

Results from both procedures were essentially identical; therefore, the less time- consuming Bezier curve method was used throughout this study.

5.3.0 Results

5.3.1 Abitibi Greenstone Belt (AGB)

The AGB sample is a flow-top hyaloclastite from the Hurd property, Blake River

Group of the Abitibi greenstone belt, Quebec. The outcrops at the Hurd property consist of a 62 m-thick volcanic sequence consisting of massive pillowed and brecciated flows and sills of greenschist-facies metabasic rocks (Bridge et al., 2010). Preservation of the original jigsaw breccia textures in the hyaloclastite indicates that deformation has been minimal. The delicate volcaniclastic textures in the flow-top hyaloclastite have been preserved by extensive silicification in a low-temperature hydrothermal environment prior to regional greenschist-facies metamorphism (Bridge et al., 2010). Regional metamorphism, dated to between 2677 Ma and 2643 Ma, has produced a typical greenschist-facies assemblage of chlorite, albite, amphibole, quartz, sulfides, with scattered occurrences of prehnite and pumpellyite (Powell et al., 1995).

The thin section sample of the AGB is shown in Figure 5-1. It represents a classic flow-top breccia at the top of a mafic volcanic unit at the Hurd property. This sample is part of a facies distinguished by amoeboid hyaloclastites. The preservation of irregular, amoeboid forms indicates that the hyaloclastite is autoclastic. The AGB samples preserve rimmed, concentric layers of chlorite pseudomorphically replacing palagonite (a poorly crystalline, fine grained mixture of phyllosilicates and Fe-oxyhydroxides), textually 120 similar to the concentric layers of abiotic palagonite alteration of basaltic glass found in modern, less-strongly altered hyaloclastites.

Figure 5-1: AGB thin section from the flow-top breccias at the Hurd property, Blake River Group, sample RN-7. The section includes: (a) formerly glassy fragment with abiotic palagonitized rims, (b) matrix material of quartz, minor calcite and remnant glass. The areas in boxes around (c) and (d) show the areas which contain biological alteration textures within the formerly glassy fragments which are not preserved as titanite infilled tubules.

The AGB sample contains very well-preserved examples of tubular bioalteration textures completely replaced by titanite (Figure 5-2). The bioalteration textures are defined by titanite deposition along structures with a tubular morphology, within hyaloclastite fragments with a palagonitized rim. The structures are characterized by a central fracture with titanite nucleation on both sides and granular, uneven boundaries.

The preservation of microbial trace fossils by titantite deposition over geological timescales is demonstrated by the AGB sample. Titanite mineralized tubular bioalteration-induced textures from the AGB are mineralogically and morphologically 121 similar to previously reported ichnofossils from other greenstone belts and ophiolite complexes (Furnes et al., 2004; Banerjee et al., 2006; Furnes et al., 2007; Staudigel et al.,

2008a).

Tubular structures due to bioalteration preserved by titanite occur in chlorite- altered glass shards, an example of which is shown in Figure 5-2. Titanite in the AGB tubules is easily identified by optical microscopy, and confirmed by μXRD. The original morphology of the tubules has been well-preserved by deposition of fine-grained titanite.

The groundmass in these samples consists of micrometric quartz grains with minor calcite, chloritized glass shards, and plagioclase. Tubular structures do not occur in the groundmass. Uncommon veins of calcite cross-cut the formerly glassy fragments. The original hyaloclastite textures are preserved in the AGB sample, demonstrating the absence of penetrative deformation, consistent with field observations at this site reported by Bridge et al. (2010).

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Figure 5-2: Micro XRD study of an AGB glass shard. (a) Plane polarized light photomicrograph of the AGB glass shard, nominal 500 µm footprint of the µXRD beam shown in white. (b) Two- dimensional diffraction data (GADDS image) from the AGB sample with continuous Debye rings consistent with polycrystalline matter. (c) Integrated diffraction pattern showing matches to titanite (ICDD card 01-087-0256), quartz (ICDD card 01-078-1254), plagioclase (01-089-1461), and chlorite (00-046-1322).

5.3.2 Ontong Java Plateau (OJP)

The Ontong Java Plateau (OJP) sample was recovered during leg 192 of the

Ocean Drilling Program (ODP) from Hole 1184A located at a water depth of 1661.1 m on the eastern lobe of the OJP (Mahoney et al. 2001). The sample is a volcaniclastic tuff, shown in Figure 5-3, consisting of ash- to lapilli-sized clases and vitric shards, accretionary lapilli, armoured lapille, and crystal fragments (pyroxene and plagioclase) in a matrix of fine-grained vitric and lithic ash, clay and other alteration-induced minerals 123 cemented by smectite, analcime, calcite, rare celadonite and several zeolites (Mahoney et al. 2001). Coarsely crystalline zeolites, including chabazite and phillipsite, occur sparsely as vug fillings, some of which are concentrically zoned. The sample was previously described in detail by Banerjee and Muehlenbachs (Banerjee and Muehlenbachs,

2003)(2003). Large (mm to cm scale) glass shards are amorphous to X-rays and optically isotropic, indicating that they have not recrystallized. Large glass shards are commonly rimmed by concentric layers of palagonite.

Figure 5-3: Ontong-Java Plateau (OJP) sample thin section from Ocean Drilling Program leg 192, sample 1184A 13R3 145 – 148A. The section includes a examples of: (a) lithic clasts dominated by pyroxene and plagioclase, (b) fine grained groundmass of glass and authigenic minerals including, phyllosilicates, Fe-oxyhydroxides and zeolites; (c) coarse grained zeolites-dominated vug fills; and (d) glass shards with a concentric palagonite rims formed by abiotic alteration and dense bioalteration textures extending from the palagonitized rim inward, or nucleating along cracks within the glass grains. The area in the box around (d) is enlarged in Figures 5-4, 5-5 and 5-6.

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Tubular structures attributed to bioalteration extend from the edge of glass shards into pristine glass, ahead of the abiotic glass-dissolution front. Tubular textures are densest near the rims of glass shards and become progressively rarer or absent towards the center of glass shards. Tubules commonly show a general trend in the direction within individual shards that may relate to the behaviour of the microbes responsible

(McLoughlin et al., 2008; Staudigel et al., 2008b) or to mild deformation of the glass shards during shallow burial on the seafloor. Tubules occasionally terminate in highly convoluted clusters or knots. Tubules display some variation in morphology, including segmentation, bifurcation and rare spiral morphologies; Figure 5-4 shows several examples of bioalteration textures.

Figure 5-4: Photomicrographs showing examples of bioalteration textures in basaltic glass from in situ oceanic crust, from the Ontong Java Plateau (OJP). (a) glass shard concentrically rimmed by palagonite (Pal) produced by abiotic glass alteration; (b) Bioalteration along a crack within the glass grain, including examples of granular texture (GT) and a segmented tubule (Seg) (c) Tubules extending away from the edge of the glass shard into fresh glass (d) Examples of a tubule exhibiting spiral form (Sp). Very fine grained authigenic minerals including titanite partially fill many of the bioalteration textures.

125

Titanite has been detected by μXRD and is directly correlated with the surface exposure of the tubular texture in these glass shards, as shown in Figures 5-5 and 5-6. In contrast to the AGB sample, titanite in the OJP sample is too fine grained to be detected by optical microscopy. GADDS images show continuous Debye rings for titanite (Figure

5-5a), confirming that the titanite consists of submicroscopic crystallites (~5 to 15 μm).

Amorphous scatter from glass and fluorescence due to Fe excitation by Cu Kα radiation both contribute to a poor signal-to-noise ratio in the OJP samples, limiting the number of titanite reflections that can be detected; however, four of the strongest reflections were identified as shown in Figures 5-5 and 5-6 and summarized in Table 5-1.

Table 5-1: Measured positions of titanite diffractions detected in OJP glass samples, compared with ICDD card 01-087-0256. Measured (average of all points with Titanite reflections from ICDD card 00-087-0256 titanite, n = 53) d-spacing (Å) 2-theta (Cu Kα) d-spacing 2θ (Cu I/Imax (%) (hkl) (Å) Kα) 4.978 17.817 4.958 17.877 26.4 (-110) 3.234 27.583 3.246 27.453 100.0 (21-1) 3.023 29.548 3.010 29.659 76.3 (-200) 2.641 33.942 2.623 34.159 68.0 (12-2), (031)

The concentration of titanite is highest near the boundaries of glass shards, where tubular structures are most concentrated (Figure 5-5). Zeolites and phyllosilicates also occur near the boundaries of glass shards. No examples of tubular structures or titanite were found in the groundmass or in pyroxene or plagioclase grains. The processes responsible for creating titanite and tubular bioalteration in these samples are confined to basaltic glass. 126

Figure 5-5: Six point traverse across an OJP glass grain containing abundant tubular alteration (white edge and wispy lines) by μXRD (with 50 μm beam diameter). Coloured circles 1-6 in (a) indicate the approximate beam footprint for the corresponding diffraction pattern in (b). XRD patterns, where dotted lines show the positions of titanite reflections from ICDD card 01-087-0256. Other peaks correspond to phyllosilicates (probably nontronite) and zeolites (probably chabazite and phillipsite). Diffraction patterns are vertically offset in height for clarity. As the density and surface exposure of tubes decreases, the titanite signature weakens and disappears. Integration time 4 hours.

Figure 5-6: Micro XRD of an OJP glass shard. (a) Plane polarized light photomicrograph of the OJP glass shard, the nominal footprint of the μXRD beam is shown in white. (b) Plane polarized light photomicrograph from within μXRD area showing detail of partially infilled tubules. (c) 2-D diffraction data (GADDS image) with continuous Debye rings corresponding to fine-grained (less than ~5 μm) titanite and chabazite. (d) Integrated diffraction pattern showing matches to titanite (ICDD card 01-087-0256) and chabazite (ICDD card 00-034-0137).

127

5.4.0 Discussion and Conclusions

The association of titanite with bioalteration textures indicates that titanite nucleation begins soon after tubule formation. Several authors have suggested that microbes dissolve basaltic glass to obtain nutrients such as Fe, Mn, Zn and Co, that may play a role in metabolic redox reactions or as cofactors and coenzymes (Torsvik et al.,

1998; Furnes et al., 2001). Titanium is likely not involved directly in microbial metabolism (Ehrlich, 1997), and is likely passively accumulated during microbially- mediated dissolution of glass and precipitated as titanite (Banerjee and Muehlenbachs,

2003). The nature of Ti in aqueous solution is still a matter of some uncertainty. Ti is generally regarded highly immobile element under most circumstances. However, several studies have shown that Ti is mobilized during the aqueous alteration of basaltic glass, for example, Zhou and Fyfe (1989) observed ‘Ti-rich nodules’ associated with palagonitized rims on basaltic glass; and they concluded that Ti can be locally mobilized during the early stages of basaltic glass alteration. Most experimental and theoretical work has investigated the solubility of Ti-bearing minerals, rather than glasses. Experiments reported by Manning et al. (2008) on the solubility of rutile demonstrated increased concentrations of dissolved Ti in the presence of Na, Al and Si. Experiments by Rapp et al. (2009) showed that presence of Cl- and F- enhanced the solubility of Ti. Ab initio molecular dynamics simulations by van Sijl et al. (2010) demonstrated that halides enhance the solubility of Ti via a shared hydration shell mechanism rather than by the formation of Ti-Cl or Ti-F bonds. The experiments and simulations noted above were carried out at higher temperatures than those plausible for known microbes, however, it is likely that the mechanism(s) of Ti mobility at high temperature also act lower temperatures but at much slower rates. 128

Titanite is more abundant in ancient, more highly metamorphosed samples.

Titanite in ophiolite and greenstone belt ichnofossils may therefore be a combination of titanite formed in in situ oceanic crust and titanite formed in subsequent metamorphism.

This would be consistent with metamorphic ages for titanite in greenstone belt samples obtained using U-Pb geochronology by Banerjee et al. (2007). Early-formed, fine-grained titanite such as we have observed in the OJP samples may provide sites for additional titanite nucleation during subsequent metamorphism leading to the petrographically- observable titanite observed in tubules in ophiolites and greenstone belts. Thus the early formation of very fine-grained titanite provides a plausible mechanism for ichnofossil formation. Precipitation of large crystals within hollow glass structures would obliterate the characteristic tubular and granular morphologies. Therefore, in order to preserve bioalteration textures in basaltic glass, titanite must form as very fine grained, submicrometric crystals in an environment where the nucleation rate is greater than the rate of crystal growth.

In this study we have demonstrated that the previously-reported Ti-bearing phase associated with bioalteration structures in basaltic glass from in situ oceanic crust is titanite. Titanite nucleation begins soon after the formation of the initially hollow structures. The age of formation of the titanite can therefore be regarded as close to that of the microbial alteration structures. The early precipitation of fine-grained titanite enables the preservation of the morphology of bioalteration structures in the rock record.

The formation of titanite is a highly plausible mechanism for the preservation of microbial bioalteration structures in basaltic glasses or their metamorphic equivalents, so long as metamorphic grade remains low. 129

Mineralogy provides important insights into ancient biological systems: minerals may be directly precipitated by biological activity (biomineralization) or precipitated indirectly as a result of biological processes; they act as a mechanism of preservation or fossilization and incorporate chemical and isotopic records of biological activity. In the present study, the formation of fine-grained titanite, possibly as a result of passive Ti accumulation during microbial alteration of glass, enables the preservation of once-hollow bioalteration-induced structures in basaltic glass over geological time.

Micro-XRD is a valuable new tool for the study of mineralogical traces of early life, enabling the structural characterization of minerals without disturbing morphological evidence of their origin. The μXRD studies presented here can also provide context for, and assist in, targeting locations for higher resolution structural-chemical analyses using transmission electron microscopy and synchrotron methods. Micro-XRD provides a spatially resolved probe of crystal structure that may be used to complement chemical microanalytical data.

5.4.1 Implications of mineral preservation of microbial ichnofossils

The presence of a thermophyllic ‘root’ or ‘bottleneck’ in the 16S RNA phylogenetic tree of life has been interpreted by many authors as evidence that high- temperature hydrothermal environments were important to the early development of terrestrial life; and possibly that life on Earth originated in a hydrothermal environment

(Nisbet and Sleep, 2001; Sugden et al., 2003). Understanding the mineral record of microbial activity in subaqueous basaltic rock therefore provides insights into a widespread and ancient microbial ecosystem. 130

Most products of biological activity are too delicate to survive weathering, erosion, and deformation. These are destructive processes that overprint previous evidence over geological time. Thus it has proven to be increasingly difficult to find preserved evidence for life as the age of a rock approaches the age of the oldest rocks on Earth (Schopf, 1992;

Westall and Southam, 2006). Studies of the earliest traces of life are also plagued by problems of fossil preservation and poor or ambiguous evidence for fossil material.

Purported chemical, isotopic and textural biomarkers in Archean metasediments have been questioned (Brasier et al., 2002; Garcia-Ruiz et al., 2003; Westall and Southam,

2006). Mineral biosignatures, including titanite-mineralized tubular and granular textures due to microbial bioalteration, are robust biomarkers that may remain detectable through significant alteration processes and recrystallization. Titanite is stable across a broad range of metamorphic conditions (López Sánchez-Vizcaíno et al., 1997; Troitzsch and

Ellis, 2002), making these titanite-decorated trace fossils a potentially robust biomarker.

Titanite is also directly datable using U-Pb geochronometry under suitable conditions

(Simonetti et al., 2006; Banerjee et al., 2007). The early formation of titanite inferred from its presence in the OJP sample indicates that the age of formation of the titanite is close to that of the microbial bioalteration textures. Thus, titanite growth is a highly plausible mechanism for the preservation of these textures in the geological record. This study highlights the importance of mineralogy in the search for traces of biological activity in the ancient and modern rock records. Finally, we note that many of the conditions required for the formation of the ichnofossils reported on here are also thought to have occurred on ancient Mars. These include basaltic volcanic rocks and substantial liquid water bodies. Future missions to Mars might profitably seek out mineralogical 131 evidence for preserve subaqueous volcanic rocks as a potential host for a similar ichnofossil record (Izawa et al., 2010).

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137

Chapter 6: Proteins & organic matter in microbial borings in ~120 Ma basaltic glass

Chapter summary and key points

Hollow and partly-mineralized tubular structures in seafloor basaltic glass have been interpreted as trace fossils created by microbially-mediated glass dissolution (Banerjee and Muehlenbachs, 2003; Benzerara et al., 2007; McLoughlin et al., 2008). Mineralized structures containing titanite (CaTiSiO5), of similar morphology and spatial distribution observed in ancient, metamorphosed basaltic rocks have been interpreted as ichnofossils, possibly dating to ~3.5 Ga or greater – making them among the most ancient putative microfossils (Furnes et al., 2004; Banerjee et al., 2007; Staudigel et al., 2008a). In this study, we report the direct detection of proteins associated with tubular textures in basaltic glass, using Scanning Transmission X-ray Microscopy (STXM). Protein-bearing organic matter is particularly associated with the interfaces between unaltered basaltic glass and alteration products, consistent with the preservation of cellular remnants derived from microbes that formerly colonized and etched the glass. Tubule-filling materials also include phyllosilicate-rich material dominated by Fe3+ (likely palagonite) and Ti-rich particles with mixed Fe3+ and Fe2+; the surrounding basaltic glass is Fe2+-dominated.

Boundaries between unaltered glass and alteration materials commonly contain a mixture of Fe valence states, providing direct evidence to support previous suggestions (Thorseth et al., 1995; Torsvik et al., 1998) that biological Fe-oxidation plays an important role in microbial dissolution of basaltic glasses. Ti-rich materials within tubular microtextures are potential nucleation sites for the later growth of titanite, pointing to a mechanism for the preservation of these trace fossils through geologic time. Our observations support both the biogenicity of tubular microtextures in basaltic glass and a direct correspondence 138 between bioalteration in modern oceanic crust and ancient mineralized tubules thought to constitute the oldest presently-known microfossils.

6.1.0 Introduction

Basaltic glasses are formed wherever basaltic melts are rapidly cooled, and are a common constituent of the Earth’s seafloor in the form of pillow rims, hyaloclastites, and volcaniclastic debris. Basaltic glasses are likely to be widely distributed in the solar system in space and time, and thus represent an important habitat on early Earth, Mars, and elsewhere (Izawa et al., 2010b). The alteration of basaltic glasses is an important process that influences the cycling of numerous elements between the Earth’s hydrosphere, lithosphere, and biosphere (Staudigel and Hart, 1983; Furnes et al., 2001).

Multiple lines of evidence point to an important role for biology in the alteration of submarine basaltic glass, including isotopically light carbon from carbonates in pillow basalt rims compared to their crystalline cores, microbial staining and sequencing, and in the form of hollow, micron-scale tubular and granular structures associated with surfaces and fractures (Thorseth et al., 1995; Torsvik et al., 1998; Furnes et al., 2001; Banerjee and

Muehlenbachs, 2003; Furnes and Muehlenbachs, 2003; Staudigel et al., 2006;

McLoughlin et al., 2008; Santelli et al., 2008; McLoughlin et al., 2009). Tubular textures in particular display morphologies including spirals, segmentation and branching that are highly suggestive of a biological origin (McLoughlin et al., 2009). It has been hypothesized that microbes enhance the dissolution of basaltic glass in order to obtain energy and nutrients (e.g., Fe, Mn, P) (Thorseth et al., 1995; Furnes et al., 2001; Staudigel et al., 2008b). Observations of seafloor samples, and experimental studies, have demonstrated that the timescales over which tubular structures are formed are likely to be 139 very long, perhaps decades (Staudigel et al., 2008b). Therefore, a “smoking gun” in the form of the observation of a microbe caught in the act of forming a tubule in basaltic glass is extremely unlikely. Direct detection of unambiguously biogenic material associated with tubular structures constitutes the next best (and much more achievable) goal. In the present study, we have directly detected protein-rich organic matter associated with the margins of hollow and partly-mineralized tubular structures in basaltic glass. Proteins are only known to form via biological activity; therefore, their association with the margins of tubular bioalteration structures is among the strongest evidence to date for the origin of the textures through biological processes.

6.2.0 Methods

The sample is a volcaniclastic tuff from the Ontong-Java Plateau recovered by the

Integrated Ocean Drilling Program leg 192. A petrographic thin section was examined in transmitted light to identify a region with abundant tubular textures (Figure 6-1). The section was sputter-cleaned using an Ar+ beam, and a 30 keV Ga+ Focused Ion Beam

(FIB) was used to prepare a thin (~100 nm) foil containing partly-mineralized tubules. X- ray imaging and spectromicroscopy were carried out at the Canadian Light Source using the STXM microscope on the SM beamline (10D-1) (Kaznatcheev et al., 2007).

Absorption edges examined were the C and N K-edges, and the Ti, Fe and Ca L-edges.

On- and off-resonance images were collected of the entire FIB section for each edge, the difference of the optical density (OD, absorbance) images mapped the element distributions (Dynes et al., 2006). Image difference maps were created as follows:

Organic material, difference between 288.2 eV (C 1s π*C=O of protein) and 280 eV (onset of the C K-edge); Ca, difference between 352.6 eV (Ca 2p1/2 Ca 3d resonance) and 350.2 140

+3 eV (dip between 2p3/2 and 2p1/2 resonances); Fe, difference between 710 eV (Fe 2p3/2 resonance) and 700 eV (onset of the Fe L-edge); Ti, difference between 460 eV and 455 eV (onset of the Ti L-edge); N, difference between 401.4 eV (π* resonances) and 395 eV

(onset of the N K-edge). Image stacks were collected on selected areas, and the chemical speciation was mapped by spectral fitting of these stacks with linear combinations of reference spectra using Singular Value Decomposition (SVD) (Koprinarov et al., 2002).

Image and spectral processing was performed with aXis2000 (Hitchcock, 2012).

Figure 6-1: A) Image of the entire Ontong-Java Plateau (OJP) petrographic thin section. The sample contains abundant vitric clasts, along with lithic clasts, cemented by basalt alteration products including phyllosilicates, zeolites, and Fe-oxyhydroxides. B) Example of a little-altered vitric clast containing abundant tubular bioalteration textures. Flattening during compaction of the volcanic pile may be responsible for some of the preferred orientation of bioalteration textures. C) Enlargement near the margin of the clast in B showing tubular textures concentrated near the edge of the clast and projecting into the interior unaltered glass. D) High-magnification image showing the location of the FIB foil, approximately perpendicular the trend of the tubular textures. E) Electron microscope image of the FIB foil after extraction and thinning.

Electron Probe Micro-Analysis (EPMA) was carried out using a Cameca SX-50 instrument (operating conditions 15 kV and 30 nA). Matrix-matched natural and synthetic 141 standards were used for calibration. Representative areas of the OJP thin section were mapped for C, Ti, Fe, Si, Mg, and Ca (Figure 6-2).

Figure 6-2: Electron microprobe backscattered electron image and chemical maps showing the distribution of C, Fe, Ca, Si and Ti in a representative area of the OJP sample. Carbon and Ti are both associated with tubular textures, visible as thin lines in the BSE image trending approximately perpendicular to the shard boundary into unaltered glass. Numbers on the right hand correspond with signal intensity scale (counts).

6.3.0 Results and discussion

Scanning Transmission X-ray Microscopy (STXM) allows chemical analysis with sub-micron spatial resolutions, and is capable of distinguishing the subtle differences in absorption edge energy structures due to differing bonding environments. Previous studies using similar approaches have provided tentative identification of both carbonates and organic carbon associated with tubular textures, but more specific identification of the organic constituents has not been possible (Benzerara et al., 2007).

Spectromicroscopy of ultrathin (electron transparent, ~100 nm) Focused Ion Beam (FIB) 142 sections through basaltic glass containing tubular textures reveals concentrations of protein-bearing organic matter associated tubular textures and commonly concentrated at the margins of such tubules. The total N map of the FIB section is shown in Figure 6-3a.

The N in Areas 1 and 2 were mapped with spectra extracted from unaltered glass and tubule-filling materials (Figure 6-3 b). The N spectrum extracted from the tubule-filling materials was similar to that of albumin (Figure 6-3 b) and other amide and amine compounds, and showed distinct features near 401.4 eV due to π* resonances, while the

N spectrum extracted from the glass had a broad peak about 405.2 eV, attributed to 1s →

σ* transitions (Leinweber et al., 2007). Hence, it is very likely that the tubule-filling materials contain proteins. Carbon is much more abundant within tubule-filling alteration assemblages than in the surrounding basaltic glass (Figure 6-4 a). Comparison of measured and reference spectra showed that concentrations of organics, carbonate, and K were higher in tubule-filling materials (Figure 6-4 b). For the organics, the characteristic peak of C-OH at around 289.5 eV was not apparent, indicating that the tubules did not contain abundant polysaccharides (Figure 6-4 b). Proteins have a characteristic sharp peak at 288.2 eV, and in bacteria this peak is very apparent (Dynes et al., 2009). Lipids contain carboxylic groups, and have a broad characteristic peak from about 287 to 288 eV.

The spectrum extracted from the tubules is compared to the protein and lipid standard spectra at an expanded scale (Figure 6-4 c), and are consistent with the presence of both lipids and proteins. Mapping of smaller regions of interest (Figure 6-4 d-k) shows the heterogeneous distribution of organic matter as well as inorganic carbonate and potassium

(likely associated with phyllosilicates). Taken together, the N and C STXM-XANES spectra provide clear evidence for the presence of proteins and lipids within the partially mineralized tubular textures. Protein- and lipid-bearing organic matter is commonly 143 associated with the margins of tubules, as would be expected if the tubules form via microbial glass dissolution and the proteins and other organic matter represent fossil cellular material (cells and extracellular materials) trapped and preserved by alteration minerals. Previous studies using confocal microscopy and fluorescent staining with

Ethidium Bromide have demonstrated a likely association of nucleic acids with tubule walls; however, some doubts have remained due to the possible roles of non-specific binding and capillary action, and possible contamination. In the present study, proteins associated with tubular textures in basaltic glass have been directly detected by STXM, providing an independent confirmation of previous observations of nucleic acids associated with the margins of tubular bioalteration textures.

Figure 6-3: Nitrogen K-edge results. (a) N image difference map (OD401.4-OD395) of the entire FIB section. The dashed white rectangle (Area 1) and the solid white rectangle (Area 2) show the areas from the FIB section where the metal speciation and organics were studied in detail. The grey scale indicates optical density. (b) N K-edge X-ray absorption spectrum of albumin (protein) compared to spectra derived by threshold masking of the high-intensity pixels from the tubule-filling material and glass from Area 1. Area 1 & 2 component maps. (c, f) tubules, (d, g), glass and color-coded (rescaled) overlays (e, h) of the component maps (tubules = red, glass = blue). The maps were derived by SVD of the image sequences (395-430 eV). 144

Figure 6-4: Carbon K-edge results. (a) Total C image difference map (OD288.2-OD280.0) of the entire FIB section. The dashed white rectangle (Area 1) and the solid white rectangle (Area 2) show the areas from the FIB section where the metal speciation and organics were studied in detail. (b) C K- edge X-ray absorption spectra of albumin (protein), 1-Palmitoyl-2-hydroxy-sn-glycero-3- phosphocholine (lipid), aragonite (CaCO3), K compared to spectra derived by threshold masking of the high-intensity pixels of the tubule-filling material and the glass from Area 1. (c) Expanded scale of an overlay of the spectra from the tubule-filling material and reference compounds, showing the presence of both protein and lipids. Area 1 & 2 component maps (d, f) organic (see methods summary for details), (e, i) K, and (f, j) carbonate and the color-coded (rescaled) overlays of the composite maps (organic=red, K=green and carbonate=blue ). The grey scales of the component maps indicate the equivalent thickness in nanometres.

145

The total Fe map of the FIB section is shown in Figure 6-5 a. Both the tubule- filling materials and the surrounding basaltic glass contained Fe. The oxidation state of the Fe in the tubules and bulk was determined by fitting of the Fe 2p stack with the

FeCl3·6H2O and FeCl2·4H2O reference spectra (Figure 6-5 b). Spectra derived by threshold masking of the high intensity pixels from the component maps (Figure 6-5 b) confirmed that the Fe in the tubules was predominantly Fe3+ (Figure 6-5 c, f), while that in the glass was Fe2+ (Figure 6-5 d, g). The spectra extracted from the interface (50 to 100 nm thick) between the unaltered glass and the tubule-filling materials showed that the oxidation state of the Fe was mixed (Figure 6-5b). Most of the tubule-filling materials are similar to palagonite, a common alteration product of basaltic glass consisting of a mixture of poorly-crystalline mixture of Fe-oxyhydroxides, phyllosilicates, and zeolites

(Stroncik and Schmincke, 2002).

146

Figure 6-5: Iron L-edge results. (a) Fe image difference map (OD710-OD700) of the entire FIB section. The dashed white rectangle (Area1) and the solid white rectangle (Area 2) show the areas from the FIB section where the metal speciation and organics were studied in detail. The grey scale indicates optical density. (b) Fe L-edge X-ray absorption spectra of FeCl3·6H2O and FeCl2·4H2O compared to spectra derived by threshold masking of high-intensity pixels glass and tubule-filling material in Area 1, and from the interface between the tubules and glass for both Area 1 and 2. Area 1 & 2 component maps (c, f) Fe3+, and (d, g ) Fe2+ and (e) color-coded (rescaled) overlays of the composite maps (Fe3+ =red, interface=green and Fe2+=blue. The grey scales of the component maps indicate equivalent thickness in nanometres.

The tubule-filling materials also contain Ti-rich particles (Figure 6-6), occasionally in close contact with protein-rich organic matter (Figure 6-3 a, d, h) . The spectra extracted from the high intensity pixels of the particles in the tubules and of the bulk, by threshold masking, confirmed that the particles were anatase-like (β-TiO2)

(Figure 6-6c, d) (Liu et al., 2010). The presence of Ti-rich materials has important implications for the preservation of bioalteration textures in basaltic glass through geologic time. Titanite-mineralized tubular textures are widely reported for ancient, metamorphosed basaltic glasses, and have been interpreted as trace fossils (Furnes and

Muehlenbachs, 2003; Furnes et al., 2004; Banerjee et al., 2006; Staudigel et al., 2008a). 147

The total Ca map of the FIB section is shown in Figure 6-6 e. Calcium is abundant in the unaltered basaltic glass and very low in the tubule-filling materials; however, it is notable that the Ti-rich particles have a slightly higher Ca concentration than the tubule-filling palagonite. Spectra extracted from the high intensity pixels of the glass and from the material in the tubules, by threshold masking of the component map (Figs. 6.6 g, h), showed that these spectra were similar to each other and that of CaHPO4·2H2O and/or Ca adsorbed to microbial exopolymeric substances (EPS); and are clearly not consistent with crystalline CaCO3 (Figure 6-6). Some carbonate may be associated with the very Ti-rich particles (cf. Figure 6-3 f, j and Figure 6-6 c, d).

148

Figure 6-6: Titanium and calcium L-edge results. (a) Ti image difference map (OD460-OD455) of the entire FIB section. The dashed white rectangle (Area 1) and the solid white rectangle (Area 2) show the areas from the FIB section where the metal speciation and organics were studied in detail., The grey scale indicates optical density. (b) Ti L-edge X-ray absorption spectra of anatase (β -TiO2) compared to the spectra derived by threshold masking of high-intensity pixels of the tubule-filling material and glass from Area 1.. Ti component maps (c) Area 1 and (d) Area 2. The grey scales for the component maps indicate equivalent thickness in nanometres.(e) Ca image difference map (OD352.6-OD350.6) of the entire FIB section. The dashed white rectangle (Area 1) and the solid white rectangle (Area 2) show the areas from the FIB section where the metal speciation and organics were studied in detail. The grey scale indicates optical density. (f) Ca L-edge X-ray absorption spectra of calcite (CaCO3), aragonite (CaCO3), CaHPO4·2H2O and Ca adsorbed on exopolysaccharides (EPS) compared to the spectrum derived by threshold masking of the high-intensity pixels of the tubule- filling material and glass of Area 1. Ca component maps of (g) Area 1 and (h) Area 2. The grey scales of the component maps indicate equivalent thickness in nanometres.

149

The link between tubules in modern seafloor glasses and titanite-mineralized tubules in ophiolites and greenstone belts has been questioned, with some authors interpreting the latter as metamorphic features related to dendritic crystal growth (Lepot et al., 2011). Our hypothesis, favouring the interpretation of titanite-mineralized tubules in ancient metamorphosed basaltic glass as trace fossils, is that metamorphic titanite overgrows a pre-existing titanite or Ti-rich precursor assemblage. Previous studies have shown that Ti-rich materials exist within altered basaltic glass (Zhou and Fyfe, 1989), and titanite has been detected associated with the tubule-rich rims of basaltic glass shards

(including the ones studied here) (Izawa et al., 2010a), but a definitive identification of

Ti-rich material in situ within tubular structures has been lacking. The Ti-particles detected here are anatase-like, however, the co-occurrence of Ti with Ca and minor amounts of Fe could indicate that trace amounts of titanite are also present. In any case, the detection of Ti-rich materials here demonstrates that possible precursor materials for metamorphic titanite overgrowth do exist within partly mineralized tubules on the modern seafloor, demonstrating a direct link between modern tubular bioalteration textures in seafloor glasses and the oldest-known microbial trace fossils.

6.4.0 Summary and conclusions

This study has demonstrated the presence of unambiguously biological materials, namely proteins, within tubular structures in basaltic glass. The presence of proteins as well as lipids and other organic compounds constitutes strong evidence for a biogenic origin of tubular textures in modern seafloor basaltic glass. We have also shown that mixed valence Fe is found in a thin layer between reduced glass and fully oxidized tubule filling materials associated with protein-bearing organic matter, substantiating previous 150 suggestions that biologically-mediated Fe-oxidation plays a role in the formation of tubular textures. Finally, Ti-rich particles were identified within tubule-filling materials, indicating that the precursor materials for later metamorphic titanite growth are present, further supporting previous suggestions that passive accumulation of Ti followed by growth of fine-grained titanium-rich phases and later metamorphic titanite overgrowth provide the mechanism whereby tubular textures are preserved in ancient metabasalts.

This study has therefore strengthened both the case for biogenicity and the link between modern bioerosion on the seafloor and one of the oldest traces of life in the geological record.

6.5.0 Chapter 6 References

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155

Chapter 7: Basaltic Glass as a Habitat for Microbial Life: Implications for

Astrobiology and Planetary Exploration

Chapter summary and key points

Recent studies have demonstrated that terrestrial subaqueous basalts and hyaloclastites are suitable microbial habitats. During subaqueous basaltic volcanism, glass is produced by the quenching of basaltic magma upon contact with water. On Earth, microbes rapidly begin colonizing the glassy surfaces along fractures and cracks that have been exposed to water. Microbial colonization of basaltic glass leads to the alteration and modification of the rocks and produces characteristic granular and/or tubular bioalteration textures.

Infilling of the alteration textures by minerals such as phyllosilicates, zeolites and titanite may enable their preservation through geologic time. Basaltic rocks are a major component of the Martian crust and are widespread on other solar system bodies. A variety of lines of evidence strongly suggests the long-term existence of abundant liquid water on ancient Mars. Recent orbiter, lander and rover missions have found evidence for the presence of transient liquid water on Mars, perhaps persisting to the present day.

Many other solar system bodies, notably Europa, Enceladus, and other icy satellites, may contain (or have once hosted) subaqueous basaltic glasses. The record of terrestrial glass bioalteration has been interpreted to extend as far back as ~3.5 billion-years-ago and is widespread in oceanic crust and its metamorphic equivalents. The terrestrial record of glass bioalteration strongly suggests that glassy or formerly glassy basaltic rocks on extraterrestrial bodies which have interacted with liquid water are potentially high-value targets for astrobiological exploration. 156

7.1.0 Introduction

Basaltic rocks are widespread in the silicate crusts of many rocky solar system bodies. Glasses of basaltic composition may form wherever basaltic melts are quenched, such as during volcanic eruptions or impact events. Microbes play an important role in the weathering of basaltic glasses in the terrestrial environment (e.g., Banerjee et al., 2008;

Furnes et al., 2001; Furnes et al., 2008; Staudigel et al., 2006; Staudigel et al., 2008a;

Staudigel et al., 2008b; Thorseth et al., 1995; Torsvik et al., 1998). The record of microbial activity in basaltic glasses extends throughout the geologic record to perhaps

~3.5 Ga (Banerjee et al., 2006; Banerjee et al., 2008; Banerjee et al., 2007; Bridge et al.,

2010; Furnes et al., 2004; Furnes et al., 2008; Furnes and Muehlenbachs, 2003; Staudigel et al., 2008b). It has been suggested that basaltic glass may act as a growth medium for a variety of microbes, providing a source of energy and nutrients (e.g., Banerjee and

Muehlenbachs, 2003; Staudigel et al., 2006; Staudigel et al., 2008b). Basaltic glass in contact with liquid water therefore constitutes a potentially habitable environment which may have been widespread in the early solar system, and may remain important on icy satellites including Europa and Enceladus, or in Martian impact craters and post-impact hydrothermal systems.

The range of physiochemical conditions under which life is known to exist has recently expanded substantially. Accompanying this has been an increased understanding of the ecology of life in environments difficult for humans to access, and a growing comprehension of possible liquid water environments on ancient Mars, modern subsurface Mars, Europa, Enceladus, Titan and other diverse solar system bodies.

Extremophiles, broadly speaking, are organisms that are able to thrive in environments that are extremely hostile to well-known life forms of the Earth's land surface and oceans. 157

Most extremophiles are microorganisms, mainly prokaryotes, that have made unique adaptations in cell size, morphology, metabolic strategy, motility, and many other aspects, that allow them to flourish (e.g., Konhauser, 2007; Madigan and Marrs, 1997). Table 7-1 shows some current limits for extremophile life under a variety of physiochemical conditions of potential astrobiological relevance. Studies of extremophiles in diverse environments such as seafloor hydrothermal vents, the deep subsurface, hot deserts,

Antarctic dry valleys, and acidic/alkaline/salt lakes have demonstrated that life can thrive under conditions very hostile to most known forms of life (e.g., Rothschild and

Mancinelli, 2001, Zierenberg et al., 2000). Many extremophiles can derive energy and nutrients from a diverse range of chemical sources quite independent of photosynthesis.

The ability of life to thrive under such a broad range of conditions has resulted in an expansion of the ‘habitable zone’.

Table 7-1: Illustrative limits of extrmophile lifea Extreme Descriptive Term Genus/Species Min. Optimum Max. Reference Temperature Methanopyrus Takai, High Hyperthermophile 90°C 106°C 122°C kandleri 2008 D'Amico Psuedomonas spp. Low Psychrophile -20°C 2°C 12°C et al., And Vibrio spp. 2006 pH Schleper Picrophilus 0.07 Low Acidophile -0.06 4 et al., oshimae (60°C)b 1995 Natronobacterium 10 (20% Tindall et High Alkaliphile 8.5 12 gregoryi NaCl)c al., 1984 32% Grant and Salinity Halobacterium Halophile 15% 25% (saturati Larsen (NaCl equiv.) salinarum on) 1989 a- current limit for growth conditions; b- P. Oshimae is also a thermophile, growing optimally at 60°C; c- N. Gregoryi is also a halophile, growing optimally at 20% NaCl.

158

In this paper, we summarize key aspects of the textural, mineralogical, and chemical record of microbial life in subaqueous glassy basaltic rocks on Earth. We then explore the astrobiological implications of such environments as a habitat for life on other bodies in the solar system. We propose that microbial colonization of ancient and modern terrestrial subaqueous basalts provides a valuable analog for a potential habitat on Mars,

Europa, Enceladus and elsewhere. Examples of basaltic glass bioalteration preserved as trace fossils in the terrestrial rock record may serve as useful analogues for similar formations on Mars and beyond.

7.2.0 Evidence for endolithic microborings in basaltic glasses

Textural, mineral and chemical traces of microbial life in terrestrial basaltic glasses that extend back ~3.5 Ga, may constitute a remarkably consistent and widespread biomarker that has been the focus of more than a decade of study and has been described in detail in several recent review articles elsewhere (e.g., Banerjee et al., 2008; Furnes et al., 2008; Staudigel et al., 2006; Staudigel et al. 2008a). In this section we summarize some of the most common features of purported microbial traces in terrestrial subaqueous basaltic glass from modern and ancient environments. Figure 7-1 shows examples of bioalteration textures in basaltic glasses or their metamorphic equivalents from a range of geological settings and degrees of metamorphism.

159

Figure 7-1: Microbial alteration textures from both modern and ancient volcanic rocks. A: photomicrograph showing formerly glassy hyaloclastite fragments with brown palagonitized rims (Abitibi Greenstone belt). B: Photomicrograph of glassy fragment containing tubular, curved and straight structures defined by titanite mineralization (brownish-black mineral), preserving evidence for ancient microbial alteration in the Abitibi Greenstone belt. The area in the white box is enlarged in E. C: Microbial alteration textures from interpillow hyaloclastites from the Euro Basalt of Pilbara Craton (Western Australia). Arrow points to area enlarged in F, modified from Banerjee et al., (2007). D: Modern microbial alteration structures in volcanic rocks from the Ontong Java Plateau have similar sizes, shapes, and morphologies to those found in Archean rocks. E: Close-up of B (white box) showing a detailed view of microbial alteration structures (arrow). F: Detailed view of microbial alteration structures with well developed segmented textures marked by arrow, modified from Banerjee et al., (2007). G: Detailed view of tubular microbial alteration structures from the Ontong Java Plateau, a prominent, partially-mineralized tubule is marked by the arrow.

160

Two distinct types of endolithic microborings in basaltic glass have been described in the literature; termed tubular and granular textures (e.g., Banerjee and

Muehlenbachs, 2003; Furnes et al., 2008; McLoughlin et al., 2008a; Staudigel et al,

2008a; Staudigel et al, 2008b). Tubular textures are typically less common than granular because they are quite distinctive and are commonly most easily recognized, particularly in the metamorphosed equivalents of basaltic glass (e.g., Banerjee et al, 2006; Furnes et al., 2004). Tubular bioalteration textures are typically a few microns in diameter and up to hundreds of microns in length. Tubules are commonly vermicular or ramose, and may possess highly regular spiral morphologies, and/or may be regularly segmented. Tubules may also bifurcate. Because of their preservation potential and relative ease of recognition, much of the discussion to follow will concentrate on tubular bioalteration textures.

Granular textures are roughly hemispherical agglomerations of micron-scale cavities that radiate from a single point at a crack or surface. Granular textures commonly possess a sponge-like texture that closely resembles the growth of microbial cultures in agar (e.g., Banerjee et al., 2008; Banerjee and Muehlenbachs, 2003; Staudigel et al.,

2008b). Figure 7-2 shows a simplified model for tubular and granular texture formation and examples of tubular and granular textures, modified from Staudigel et al., 2006.

In both tubular and granular textures, it is inferred that microbes colonize exterior surfaces or surfaces of cracks and begin to dissolve the rock through changes in pH at their contact area (e.g., Banerjee and Muehlenbachs, 2003; Furnes et al., 2001; Staudigel et al., 2006; Staudigel et al., 2008a; Staudigel et al., 2008b; Thorseth et al., 1995; Torsvik et al., 1998). Microbes may also actively remove nutrients such as Fe, Mn, Co and Zn from the glass (Templeton et al., 2004). Bioalteration textures are initially hollow, but 161 may be filled and preserved by a variety of authigenic mineral phases including phyllosilicates, zeolites, Fe-oxyhydroxides, and titanite (Banerjee and Muehlenbachs,

2003; Benzerara et al., 2007; Staudigel et al., 2006). Early mineralization of bioalteration textures with minerals, such as titanite that are stable over variable temperature and pressure regimes, enables their preservation for geologically protracted periods of time

(e.g., Banerjee et al., 2008; Banerjee et al., 2007; Furnes et al., 2004, Staudigel et al.,

2008a).

Figure 7-2: Conceptual model showing the formation of bioalteration textures in volcanic glass with representative images of each type in samples from the Ontong Java Plateau. Figure is modified from Staudigel et al., 2006. A: Granular alteration textures develop as a result of water flow along fractures in the fresh glass (tan) creating areas for microbial colonization to begin (green). B: Progressive alteration leads to the development of granular clusters of bioalteration. C: Scanning electron micrograph of granular alteration along a fracture in basaltic glass. D: Tubular alteration textures begin on fractures and bore into fresh glass roughly perpendicular to the initial fracture. In both granular (B) and tubular (E) textures, authigenic minerals (red) precipitated in the cavities created by the microorganisms eventually cause the cavities to become sealed, preserving the bioalteration texture as ichnofossils. F: Transmitted, plane-polarized light photomicrograph of tubular bioalteration textures in basaltic glass.

Titanite (CaTiSiO5) is a particularly important mineral responsible for preservation of traces of microbial activity in basaltic glass (e.g., Furnes et al., 2004;

Banerjee et al., 2006; 2007; 2008). Bioalteration textures in Archean greenstone belts are commonly filled with titanite, which is stable over a wide range of metamorphic 162 conditions and can be dated using the U-Pb system (Banerjee et al., 2007; Frost et al.,

2000). Titanite mineralization can enable the preservation of morphological and/or chemical signatures of biological activity, either within the titanite itself or by preserving biologically important elements at grain boundaries (Furnes et al., 2004; Banerjee et al.,

2006; 2007; 2008). The preservation of these putative biomarkers allows us to study ancient microbial life in subaqueous basaltic systems on early Earth. In addition to microtubules mineralized by titanite, titaniferous nodules that may constitute a titanite precursor phase have been documented in association with microbial alteration in Hawaii

Scientific Drilling Project hyaloclastite samples (Walton, 2008; Walton and Schiffman,

2003).

In contrast to the biologically-mediated glass alteration processes resulting in tubular and granular textures, abiotic glass dissolution is largely a diffusive chemical exchange process. During abiotic glass alteration, hydration progresses inward, accompanied by the removal of various fractions of the mobile chemical inventory of the glass and the addition of some seawater components (Staudigel and Hart, 1983; Stroncik and Schminke, 2001; 2002). The result of abiotic glass dissolution is the transformation of pale, transparent glass into yellow or tan palagonite. Palagonite refers to a gel-like or poorly-crystalline assemblage of basaltic glass alteration products, including phyllosilicates, Fe-oxyhydroxides, zeolites and other phases (Peacock 1926; Staudigel and Hart, 1983; Stroncik and Schmincke, 2001; 2002). Tubular and granular bioalteration precede and may be halted by palagonite formation (Walton, 2008; Walton and

Schiffman, 2003). Palagonite formation is also preceded by a phase of glass dissolution with precipitation of smectite clay and Ca-Ti oxides (Walton, 2008; Walton and

Schiffman, 2003). Palagonite commonly forms concentric rims around glass clasts and 163 linings along fractures or other surfaces exposed to water. Palagonitization produces textural, chemical and mineralogical signatures that are fundamentally different than those produced by microbial bioalteration. The presence of palagonite is of potential relevance to the search for traces of microbial glass alteration however, as palagonite is strong evidence for water-basaltic glass interaction.

7.3.0 Biogenicity of endolithic microborings in basaltic glasses

The purpose this chapter is not to establish the biogenicity of endolithic microborings in basaltic glass but instead to communicate the potential for glassy basaltic rocks as a microbial habitat both on Earth and other Solar System bodies to broader planetary science, astrobiology and exploration communities. The biogeochemistry of terrestrial water-basaltic glass interaction may elucidate the possibilities of ancient

Martian life in similar environments, such as on Mars, and may inform our choice of future sample return missions. Multiple, converging lines of evidence for biological alteration of terrestrial glassy basaltic rocks from modern ocean crust, ophiolites, and

Archean greenstone belts has been comprehensively described by a number of recent publications (e.g., Banerjee and Muehlenbachs, 2003; Banerjee et al., 2006; 2007; Furnes et al., 2004; 2007; 2008; Staudigel et al., 2006; 2008, Walton 2008). Establishing biogenecity of endolithic microborings in modern basaltic glasses is much simpler than those of ancient remains. The biogenicity of the modern bioalteration textures in volcanic rocks has been established based on converging lines of evidence. Here we provide a brief summary of the lines of evidence for biogenicity of terrestrial endolithic microborings in basaltic glass but for a more detailed summary the reader is referred to 164 several recent reviews on this topic and references therein (e.g., Furnes et al., 2008;

McLoughlin et al., 2008a; Staudigel et al., 2006; 2008a).

7.3.1 Morphological and textural evidence for biogenicity

The morphology of tubular and granular endolithic microborings in basaltic glass is highly suggestive of a biological origin. Tubular and granular textures are always rooted on surfaces which would have been exposed to circulating fluids, and have not been observed completely enclosed in glass (Banerjee and Muehlenbachs, 2003; Furnes et al., 2001; Staudigel et al., 2008a; Torsvik et al., 1998). Cross-cutting relationships between bioalteration structures and authigenic minerals demonstrate that the formation of the bioalteration textures occurs soon after glass formation, after the rocks have cooled to temperatures capable of supporting life. Both tubular and granular textures are of microbe-like sizes, that is, submicron scale to several microns in diameter. Bioalteration textures are distributed asymmetrically across cracks, which would not be expected if the textures formed as a result of dissolution along pre-existing weaknesses in the glass (e.g.,

Banerjee and Muehlenbachs, 2003; Staudigel et al. 2008a). Endolithic microborings commonly take regular spiral forms and/or display regular segmentation, both of which are difficult to reconcile with abiotic formation mechanisms (e.g., Banerjee and

Muehlenbachs, 2003; Staudigel et al 2008a; 2008b; McLoughlin et al., 2009). Bifurcated tubules have also been observed that may form by cell division (Banerjee and

Muehlenbachs, 2003). Microtubules very rarely intersect one another, consistent with formation by microbially enhanced glass dissolution: microbes do not or cannot tunnel into areas which have been leached of nutrients (Staudigel et al., 2008b). Tubular 165 bioalteration textures may be formed in a manner analogous to the tunneling of fungal hyphae into mineral grains, as discussed by Staudigel et al. (2008a).

7.3.2 Element distribution evidence for biogenicity

X-Ray element mapping (Furnes et al., 2001a, Banerjee and Muehlenbachs, 2003,

Banerjee et al., 2006; 2007; Staudigel et al. 2008a) has shown that endolithic microborings in basaltic glass are commonly enriched in carbon, nitrogen and phosphorous. Carbon enrichment along the margins of the tubules in the samples is not correlated with enrichments of elements such as calcium, iron, or that commonly form carbonates; instead this is interpreted to represent residual organic matter

(Torsvik et al., 1998, Banerjee and Muehlenbachs, 2003). Similar element distributions suggestive of residual organic matter have been observed in basaltic glasses from modern oceanic crust, ophiolites and greenstone belts (e.g., Banerjee et al., 2006; 2007; 2008;

Benzerera et al., 2007; Furnes et al., 2004; McLoughlin et al., 2008a; Staudigel et al.,

2006; Staudigel et al., 2008; Torsvik et al., 1998). The speciation of carbon within tubules from the Ontong-Java Plateau is also consistent with the presence of organic carbon within tubular bioalteration textures (Benzerera et al., 2007). The association of biologically important elements with tubules argues for a biological origin, as the abundances of many of these elements in the host basalts are commonly extremely low.

7.3.3 Stable Carbon Isotope Signatures

13 Negative δ Ccarb isotopic signatures have been documented in glasses from several modern oceanic crust sections, including the Ontong Java Plateau (122 Ma), the

Lau Basin (6-9 Ma), and the Costa Rica Subduction Margin (5.8-6.4 Ma) (Banerjee and 166

Muehlenbachs, 2003; Furnes et al., 2001a; 2001b; Furnes et al., 2007; 2008; Staudigel et al., 2008); and in many examples of obducted oceanic crust from ophiolites including

Troodos (90.3-92.4 Ma), Mirdita (160 Ma), Solund-Stavfjord (443 ± 3 Ma) (Furnes and

Muehlenbachs, 2003; Furnes et al., 2001a; 2001b; Furnes et al., 2007; 2008; Staudigel et al., 2008). Archean remnants of oceanic crust, collectively known as greenstone belts, also preserve similar depleted carbonate isotope signatures. Furnes et al. (2004) demonstrated that pillow rims from the Barberton Greenstone Belt preserved formerly

13 glassy rims with δ Ccarb values as low as -17‰; significantly different from that of mantle CO2, marine carbonate, and pristine pillow cores. Since then other studies have shown that these same isotopic signatures are preserved in pillow basalts and hyaloclastites from other Archean greenstone belts (e.g., Banerjee et al., 2006; 2007;

Furnes et al., 2007; 2008; McLoughlin et al., 2008a).

7.3.4 Presence of nucleic acids in modern samples

Independent evidence for the formation of these textures from microbial processes is the presence of DNA/RNA within the alteration zones. However, genetic material is not stable over geological lengths of time; therefore this material can only be extracted from geologically more recent alteration textures. When DAPI (4, 6 diamino-phenyl- indole) dye is added into the samples it binds to nucleic-acids from bacterial and archeal

RNA in the bioalteration textures, revealing biological materials concentrated at the interface between the fresh glass and altered glass (e.g., Giovannoni et al., 1996; Torsvik et al., 1998; Banerjee and Muehlenbachs, 2003; Walton and Schiffman, 2003; Furnes et al., 2001b). In more modern environments, the results of DNA staining show that these microorganisms were, and still could be actively altering the glass (Banerjee and 167

Muehlenbachs, 2003). Nucleic acids degrade rapidly; therefore studies of ancient rocks cannot make use of fluorescence staining methods. However, some indications of the presence of former nucleic acids may be seen by element distributions and carbon isotopic signatures.

Confirming the biogencity and antiquity of ancient bioalteration textures however, it is much more difficult. McLoughlin et al. (2007) have developed criteria for establishing antiquity and biogenicity of microbial borings in volcanic rocks: 1) representation of a geological setting that demonstrates a syngentic origin for the microborings; 2) the presence of microboring morphologies and distributions that are suggestive of biogenic behaviour and distinct from ambient inclusion trails, and 3) elemental and isotopic evidence suggestive of biological processing. Numerous studies have demonstrated that endolithic microborings in basaltic glasses and their metamorphic equivalents are able to meet the criteria for biogenicity, demonstrating that the record of bioalteration in basaltic glasses on Earth extends over the past ~3.5 billion years (e.g.,

Banerjee et al., 2006; Banerjee et al 2007; Banerjee et al., 2008; Banerjee and

Muehlenbachs, 2003; Furnes et al., 2004; McLoughlin et al., 2007; Staudigel et al., 2006;

Staudigel et al., 2008a; Staudigel et al., 2008b, Walton, 2008)

7.4.0 Preservation of Microbial Trace Fossils in Basaltic Glass over Geologic Time

The effective preservation of microbial fossils is important for understanding the paleo-environments in which they were formed (e.g., Brasier et al., 2002; 2004a; 2004b;

2005; 2006; McLoughlin et al., 2008b; Moorbath, 2005; Schopf, 1993; Schopf et al.,

2002). Several criteria for confirming antiquity and biogenecity of ancient microbial alteration structures have been developed (McLoughlin et al., 2007; Schopf et al., 2004; 168

Buick, 1990). The potential for degradation, recrystallization, loss of structure(s), deformation, disruption, and abiotic creation of morphologically similar structures

(‘pseudofossils’) greatly increases the difficulty in establishing criteria for biogenecity in ancient, progressively altered samples (e.g., McLoughlin et al., 2008b; Brasier et al.,

2002). A potential biomarker must be highly robust to remain detectable despite multiple overprinting processes. Titanite preservation of volcanic microbial bioalteration textures is one such robust biomarker, able to withstand metamorphic overprinting up to lower amphibolite facies in the absence of substantial deformation.

In ophiolites and greenstone belts, bioalteration structures are preserved via infilling by several minerals, including phyllosilicates, zeolites, and titanite. Titanite is able to create a stable micro-environment within less stable basaltic glass and/or glass alteration products, enabling the preservation of morphological and biogeochemical signatures of early life (e.g., Banerjee et al., 2006; 2007; Furnes et al., 2004; Staudigel et al., 2008). Titanite is stable over a broad range of metamorphic conditions (Troitzsch and

Ellis, 2002). Titanite can also be dated via U-Pb geochronology techniques under favorable circumstances (e.g., Banerjee et al., 2007; Frost et. al., 2000; Simonetti et al.,

2006). Direct dating of titanite within tubular bioalteration structures hosted in the

Archean Barberton Greenstone Belt produces ages that overlap with the crystallization age of the host rock, indicating that titanite mineralization occurred penecontemporaneously with basaltic glass emplacement (Banerjee et al., 2007).

Combined with overlapping Ar-Ar metamorphic ages and U-Pb crystallization ages for the host rocks, the titanite age demonstrates the antiquity of the bioalteration (Banerjee et al., 2006). 169

An alternative interpretation of titanite-filled microstructures in metabasalts has been put forth by Lepot et al., (2011), who interpret the microstructures as the result of dendritic crystal growth during metamorphism. Their observations, however, would also be consistent with formation of metamorphic titanite overgrowing a pre-existing biogenic structure. Therefore, a role of dendritic crystal growth in the formation of titanite- mineralized tubules is not necessarily incompatible with the interpretation of the microstructures as ichnofossils.

7.5.0 Planetary Environments with the Potential to Host Microbial Alteration Textures in

Volcanic Rocks

Numerous planetary settings may host basaltic glasses which may have interacted with water, or, in some cases, may still be interacting with water. Basaltic glasses formed by both endogenic (partial melting and volcanism) and exogenic (impact melting) processes may be important substrates for microbial life. This section summarizes several potential basalt-water interaction based habitats distributed throughout the solar system in space and time.

7.5.1 Mars

The Martian crust consists largely of basaltic rocks, based on spectroscopic, in situ analyses by landers and rovers, and the 80 known Martian meteorites. Many spectroscopic studies have suggested the presence of palagonite on Mars (e.g., Allen et al.,

1981; Hamilton et al., 2008; Laan et al., 2009). Chemical and mineralogical data from

Martian meteorites and the Martian surface suggest that the abundance of water, carbon and nutrients; along with appropriate temperatures, and biologically exploitable redox 170 gradients are similar to those that make life possible in Earth’s oceanic crust (e.g., Fisk and Giovannoni, 1999). Many studies suggest that conditions on Mars and Earth were much more similar in terms of temperature, atmospheric chemistry and the presence of liquid water in the distant past (e.g., Baker, 2006; Jolliff et al., 2006). Life emerged rapidly in the conditions present on early Earth, as evidenced by the trace fossil and geochemical record. It is therefore highly plausible that similar processes of emergence, diversification, colonization and preservation may have occurred on Mars.

7.5.1.1 Water and other biologically important materials are present on Mars

A compelling body of evidence from a diverse collection of remote sensing and in situ robotic data sets points to a substantially warmer, wetter and more geologically active environment on early Mars than today (e.g., Wyatt and McSween, 2006). Martian meteorites provide additional clues and suggest a past Martian climate that was more hospitable to life as we understand it (e.g., Leshin and Vichenzi, 2006, Wyatt and

McSween, 2006). The orthopyroxenite meteorite ALHA 84001 also contains mineral and chemical evidence for hydrothermal activity in the Martian crust in the distant past. The crystallization ages of Martian meteorites (other than ALHA 84001) imply that magmatic/volcanic activity persisted on Mars for most of the age of the solar system

(McSween and Treiman, 1998; Nyquist et al., 2001). The young apparent age of many volcanic features on Mars such as Tharsis and Elysium suggests that volcanism may not yet have completely ceased (e.g., Spohn et al., 1998). Geophysical evidence also suggests that some liquid remains in the Martian core (Verhoeven et al., 2005; Yoder et al., 2003).

Localized areas of elevated CH4 in the Martian atmosphere may also result from some ongoing liquid water-rock interaction in the Martian deep subsurface, with CH4 being 171 produced by serpentinization reactions (e.g., Mumma et al. 2009; Oze and Sharma, 2005).

The D/H ratio of the Martian atmosphere was among the first lines of evidence suggesting that Mars has lost significant amounts of water over geologic time. The preferential loss of light hydrogen produced by photo-dissociation of H2O over time leads to elevated D/H ratios (e.g., Donahue 1995).

The presence of water ice in the Martian polar caps has been well documented since the first Mariner flyby missions. More recently, the Phoenix lander has provided strong evidence for the presence of near-surface ground ice, as well as calcite and clay minerals in the Martian northern plains (Smith et al. 2008). This result has long been anticipated on the basis of many remote-sensing data sets including orbital imagery showing landforms analogous to terrestrial periglacial features, gamma-ray spectroscopy from the Mars Global Surveyor (MGS) that revealed large amounts of hydrogen at high latitudes, and ground penetrating radar data from the Mars Reconnaissance Orbiter (MRO) shallow subsurface radar (SHARAD) instrument (e.g., Baker, 2006; Levrard et al., 2004;

Sizemore et al., 2009; Spohn et al., 1998).

Impact-related hydrothermal systems and glassy rocks might also have provided an environment for water-basaltic glass interaction on Mars, and a conduit between the deep subsurface and the crust. Impact heating provides both a means of creating glassy rocks and a long-lived source of heat to drive hydrothermal activity (e.g. Abramov and

Kring, 2007, 2005, 2004; Naumov, 2005; Osinski, 2005; Osinski et al., 2005a). Recent studies of terrestrial impact melt glasses from the Ries crater, Germany, have suggested that bioalteration processes similar to those documented in seafloor basaltic glasses may occur in post-impact hydrothermal systems (Sapers et al., 2009). 172

Bulk compositional data on biologically important elements including C, H, N, O,

P, S, from Martian meteorites, and in situ measurements by rovers and landers show that the elements required for biological processes are present on the surface of Mars

(McSween, 2002). This is logical, as Mars should have received essentially the same chondrite-derived initial budget of these elements as Earth (e.g., Righter et al., 2004;

Scott, 2007). The habitability of the surface of Mars, past or present, has been questioned recently by Knoll and Grotzinger (2006) and Tosca et al. (2008). However, the extraordinary diversity of habitable niches that have been discovered in recent years argues for the possible existence of life forms capable of surviving in the Martian near surface (e.g., Rothschild and Mancinelli 2001).

The detection of CH4 in the Martian atmosphere indicates that a source of CH4 persists to the present day. Serpentinization reactions involving ultramafic minerals such as olivine and pyroxene are known to produce H2 that then reacts with CO2 to form CH4

(e.g., Oze and Sharma, 2005), providing a potential source of carbon and chemical energy.

Serpentinization reactions are exothermic and are known to drive long-lived hydrothermal systems on the modern terrestrial seafloor, such as the Lost City hydrothermal field

(Kelley et al., 2001; 2005). The apparent localization and seasonality of Martian CH4 emissions may point to locales where serpentinization is ongoing; to regions where decomposing clathrates are releasing CH4 that was formerly sequestered in their crystal structure; or the presence of methanogenic life forms in the Martian subsurface (Mumma et al., 2009). Other inorganic synthesis reactions are associated with water-basalt interactions, and may provide an important source of organic chemicals in the Martian subsurface (e.g., Shock et al., 1995; Shock and Schulte, 1998).

173

7.5.2 Other solar system locales

There has been a justifiable emphasis on Mars in the discussion of solar system locales with high potential for hosting past or present life. However, other solar system bodies such as Europa, Enceladus, Titan and others, that show evidence of long-term geological activity and abundant water, warrant some consideration. The potential for detecting life on another body in the solar system must be regarded as even more speculative than on Mars. However, many objects in the solar system could potentially host environments where the interaction of water and subaqueous volcanism create conditions suitable for microbial colonization. Even if subaqueous volcanic activity has long ceased on the icy satellites, an earlier phase of basalt-water interactions may have provided an initial boost to biological activity.

7.5.2.1 Europa

The second Galilean moon of Jupiter, Europa, has a surface composed largely of water ice. This surface is relatively young (as evidenced by the extremely low density of impact craters), implying that geological processes are ongoing. Europa is tidally locked with Jupiter; however, gravitational interactions with the other Galilean moons (Io,

Callisto and Ganymede) cause their orbits to be perturbed from tidal lock. The tidal forces induced by this process impart thermal energy to the interiors of the Galilean moons. This is most spectacularly demonstrated by the volcanism of Io, the innermost Galilean moon.

The surface of Europa is covered by a complex network of extensional fractures and fissures. Galileo magnetometer measurements suggest the presence of an internal liquid water ocean on Europa (Kivelson et al., 2000; Zimmer et al., 2000). Moment of inertia data gathered from numerous spacecraft encounters indicates that the interior of Europa is 174

consistent with a differentiated mixture of ices (primarily H2O) and silicates, possibly with an Fe-FeS core (e.g., Kuskov and Kronrod, 2005; Kivelson et al., 2000; Zimmer et al., 2000).

Europa possesses both a long-lived source of energy (tidal heating) and, potentially abundant liquid water. There is therefore potential for hydrothermal activity in the Europan subsurface. It is not yet clear whether a hydrothermal vent regime exists on

Europa as a mechanism of water-rock interaction, although this has long been speculated

(Davis and McKay, 1996). Exclusive of vent activity, however, low-temperature water- rock interactions could be pervasive at the base of an Europan ocean. Spectroscopic measurements of apparent surface magma on the neighboring moon Io indicate basaltic to komatiitic compositions (McEwen et al., 1998), implying that the silicate component of the Galilean moons is not vastly different from inner solar system silicate bodies. Some material ejected by impacts from Earth and Mars has likely been delivered to Europa during the course of solar system history, so contamination by external sources (i.e., lithopanspermia) is possible, though improbable (e.g., Gladman et al. 1996). It is worth noting, however, that NASA considered contamination of Europa by the Galileo probe, a threat sufficient enough to warrant the deliberate destruction of the Galileo probe by impact with Jupiter at the termination of the probe’s mission (Young, 2000).

7.5.2.2 Other icy satellites (Ganymede, Callisto, Enceladus, Titan)

Europa is perhaps the most compelling case of an icy outer-planet satellite with clear evidence of internal heat and geological activity. However, the Galilean moons

Callisto and Ganymede also show evidence in the form of magnetic fields and surface faulting that may indicate that liquid water exists beneath their icy surfaces. Enceladus 175 also displays evidence of active geological processing, perhaps driven by tidal interactions with Saturn and Titan (and the other large moons). The southern regions of

Enceladus are cut by large fissures or ‘tiger stripes’ from which emerge large plumes

2- composed largely of water vapor (with traces of other species such as CO2, CO, N , and possibly NH3, CH4, propane and acetylene (Hodyss et al., 2008; Waite et al. 2006).

Sodium ions have been reported in Saturn’s E-ring based upon Cassini data and interpreted as originating in an ocean beneath the surface of Enceladus (Postberg et al.,

2009). The presence of sodium implies long-term interaction between the postulated

Enceladus subsurface ocean and a silicate mantle (Postberg et al., 2009). Ground-based telescopic observations have not, however, confirmed the presence of sodium in the

Enceladus vapor plume (Schneider et al., 2009).

Titan is the largest satellite of Saturn, and is the only planetary satellite known to possess a dense atmosphere. Titan’s atmosphere is dominated by N2, with traces of other gasses, notably hydrocarbons (Baines et al., 2005). Photochemical reactions involving methane and nitrogen are thought to produce a haze of more complex organics including tholins (CxHyNz) and higher hydrocarbons that collect on the surface of Titan (Bernard et al., 2006; McCord et al., 2006). The surface of Titan has a low crater density, implying active surface processes (e.g., Lorenz, 1997; Lunine et al., 2008). The Cassini-Huygens mission has revealed features consistent with aeolian, fluvial/lacustrine (based on liquid hydrocarbons) and cryovolcanic processes on Titan (e.g., Coustenis, 2007; Lopes et al.

2007). Geophysical data from Cassini may reveal the presence of an ocean deep beneath

Titan’s surface (Rappaport et al., 2008). It is expected that this ocean consists largely of water with substantial ammonia (Lopes et al. 2007). Thus, Titan may possess important raw materials for biology. If impact, cryovolcanic or tectonic processes deliver any of 176 these organics to the subsurface ocean; or if abiotic synthesis reactions produce endogenic organic chemicals, there may be potential for the emergence of life (e.g., Raulin, 2006;

Raulin et al., 2005).

No mission within the foreseeable future will be able to determine whether basaltic rocks on these icy satellites are microbial habitats. Taking a long view, however, we suggest that the potential for diverse locales where water and basaltic rock interact to form niches for life be born in mind when considering the habitability of a planetary object and the potential for discovery of life beyond Earth.

7.6.0 Conclusions

Exploration missions can be expected to proceed from remote-sensing platforms

(ground and space telescopes, flyby probe missions and orbiters) to in situ robotic missions (landers and rovers) and finally, perhaps, human explorers. Areas with the potential to host signs of past or present life can be identified by spectroscopy and imaging from orbit, these areas can then be targeted by landers, rovers and/or humans.

Fluvial, lacustrine, and periglacial/ground ice-related targets have received much attention as astrobiology targets. We suggest that areas of water-basalt interaction as inferred from geomorphology and spectroscopically determined mineralogy be added to this list.

The presence of preserved traces of life in glass or metal-glassy basaltic rocks from Mars or other solar system bodies is at present highly speculative. Numerous studies of terrestrial basaltic glasses or their metamorphosed equivalents, however, have shown that terrestrial microbial life rapidly colonizes basaltic glass. Further, traces of this microbial life are preserved as ichnofossils in the terrestrial geological record. These life 177 traces persist for long periods and through substantial amounts of metamorphic overprinting in the very active terrestrial lithosphere. Upcoming missions to Mars tasked with the detection of past or present life should consider subaqueously erupted basaltic rocks as potential high-value targets.

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192

Chapter 8: Overall conclusions, or, “how can everything in this thesis ever fit into a coherent picture”?

Planetary materials contain signatures of diverse processes in their mineralogy, chemistry, textures and assemblages. The record contained in planetary materials reflects the complex and commonly overprinting relationships between many processes. These include but are not limited to: Presolar processes including element formation during big bang and stellar nucleosynthesis, the formation and alteration of materials in stellar outflows and in interstellar space; solar nebula processes including strong solar outflows, solar irradiation (formation of some short-lived nuclides, mass-independent isotope fractionation, e.g., by CO self-shielding), and the formation of Ca-Al rich inclusions

(CAI), chondrules, other refractory inclusions, and other chondrite components; Parent asteroid processes including accretion of solar nebula components, endogenic and exogenic (i.e. impact) heating and penecontemporenous thermal metamorphism, aqueous alteration, and shock metamorphism; planetary assemblage processes including differentiation into metallic Fe-Ni core and silicate mantle, possibly with an early

‘magma ocean’ stage, and the accretion and outgassing of volatile species to form atmospheres and hydrospheres, including a possible important role for planetary-scale

‘leaching’; bombardment processes following planetary accretion with shock metamorphism, volatile and organic delivery, and impact modification of the biosphere; post-impact processes including ‘magmatic’ – i.e. impact melt igneous and thermal metamorphic processes and hydrothermal alteration, as well as longer-term modification and weathering of post-impact deposits, notably hydrothermal minerals which are out of equilibrium with ambient conditions; basaltic magmatism due to the partial melting of planetary silicates, a process which should be broadly similar throughout the solar system 193

(and perhaps beyond) because of the cosmochemically-constrained abundances of the elements likely to comprise the vast bulk of planetary silicate mantles (O, Si, Al, Mg, Fe,

Ca, Na, K) and the fact that under most conditions of partial melting of such a bulk composition a plagioclase-pyroxene ‘basaltic’ – sensu lato melt will form. The ubiquity of ‘basaltic’ rocks inferred from cosmochemistry has important implications. Basaltic rocks have been shown by various methods to be a substrate for microbial growth on

Earth. Determining the processes whereby microbial trace fossils are preserved in the rock record is of high importance, as this can allow more confident interpretation of possible ancient records of microbial activity. If, as seems likely, basaltic rocks are ubiquitous, habitable under the right circumstances, and have a high preservation potential, then basaltic rocks are high value targets both for astrobiological exploration on other worlds and as terrestrial analogue materials for astrobiology.

How does it all fit together? Discerning the mechanisms that have operated requires first a careful characterization of various properties. These include the chemical and structural makeup of the rocks (that is, the mineralogy and mineral chemistry), the textural relations within and between rocks. Therefore, the key to how the studies here hold together is also in the methodology and guiding philosophy: understanding the materials present is the first step to unravelling the record of processes stored in planetary materials of all kinds. In this thesis, the tools of mineralogy and geochemistry/cosmochemistry have been used along with an understanding of the grand- scale astrophysical constraints on planetary formation to interpret diverse planetary materials: terrestrial rocks and meteorites. Through careful study of these materials, new constraints have been placed on asteroidal processes, habitable environments in post- impact hydrothermal systems, and the preservation mechanisms of microbial ichnofossils. 194

Appendix A: Curriculum Vitae: Matthew Richard Mitsuomi Izawa

Publications Contributions to Refereed Journals (21, 10 first-authored)

Accepted/In press • D. C. Fernández-Remolar, L. J. Preston, M. Sánchez-Román, M. R. M. Izawa, G. Southam, Neil R. Banerjee, G. R. Osinski, R. L. Flemming, D. Gómez-Ortíz, O. Prieto Ballesteros, N. Rodríguez, A. Hill, R. Amils, C. Romanek. Carbonate precipitation under acidic conditions opens new windows for searching life on Mars, in revision for Earth and Planetary Science Letters, September 2011, accepted July 12th 2012 • M. R. M. Izawa, R. L. Flemming, R. Zhang, J. Jin. Characterization of green clay concretions from the Tonggao Formation, South China: Mineralogy, petrogenesis and paleoenvironmental implications, submitted to Canadian Journal of Earth Sciences, Dec. 4th, 2011, returned in revised form May 7th 2012 • M. M. Battler, G. R. Osinski, D. S. S. Lim, A. F. Davila, F. A. Michel, M. A. Craig, M. R. M. Izawa, L. Leoni, G. F. Slater, A. G. Fairen, and N. R. Banerjee, L. J. Preston. Characterization of the acidic cold seep emplaced jarositic Golden Deposit, NWT, Canada, as an analogue for jarosite deposition on Mars, submitted to Icarus, March 9th 2011, accepted May 8th 2012 • J. P. Parnell, A. Boyce, G. R. Osinski, P. Lee, M. R. M. Izawa, R. L. Flemming, N. R. Banerjee. Evidence for Life in the sulfur isotopic analysis of surface sulfates, and potential application on Mars, submitted to Astrobiology, Oct 21st 2010, rejected, sent to International Journal of Astrobiology Apr 14th 2011, accepted Jan 10th 2012 • P. Vernazza, M. Delbo, P. L. King, M. R. M. Izawa, J. Olofsson, P. Lamy, F. Cipriani, R. P. Binzel, F. Marchis, B. Merín, A. Tamanai, High surface porosity as the origin of emissivity features in asteroid spectra, submitted to Icarus Feb 20th, 2012, accepted April 5th 2012

Published • P. Vernazza, P. Lamy, O. Groussin, T. Hiroi, L. Jorda, P. L. King, M. R. M. Izawa, F. Marchis, M. Birlan, R. Brunetto. Asteroid (21) Lutetia as a remnant of Earth’s precursor planetesimals, Icarus, Volume 216, 650-659, 2011, accepted Sept. 30th 2011 (Icarus Notes) • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, S. Matveev. QUE 94204: A primitive enstatite achondrite produced by the partial melting of an E-chondrite-like protolith, Meteoritics and Planetary Science, Volume 46, Issue 11, 1742-1753, 2011 doi: 10.1111/j.1945-5100.2011.01263.x submitted Dec, 16th 2010, reviews received Feb 5th 2011, accepted Sept 2, 2011 • L. J. Preston, N. R. Banerjee, M. R. M. Izawa. Infrared spectroscopic characterization of organic matter associated with microbial bioalteration textures in basaltic glass, Astrobiology, 11, Number 7, 2011 DOI: 10.1089/ast.2010.0604 submitted Sept 17th 2010, accepted Jan 29th 2011 • M. R. M. Izawa, Neil R. Banerjee, G. R. Osinski, R. L. Flemming, J. Parnell, and C. S. Cockell. Post-impact hydrothermal deposit mineralogy, from the Haughton impact 195

structure, Nunavut, Canada: Secondary mineral assemblages and implications for microbial colonization and biosignature preservation, Astrobiology Volume 11, Number 6, 2011 DOI: 10.1089/ast.2011.0612 submitted Jan 13th 2011, accepted May 30th 2011. • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, P. J. A. McCausland. Micro X-ray diffraction (μXRD) assessment of shock stage in enstatite chondrites. Meteoritics and Planetary Science Volume 46, Issue 5, pages 638–651, May 2011. Submitted April 21st 2010, reviews received Oct. 22nd 2010, returned in revised form Dec, 16th 2010, accepted Jan 27th 2011 • M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, N. J. Bridge. Preservation of microbial ichnofossils in basaltic glass by titanite mineralization, Canadian Mineralogist, Volume 48, pages 923-933. doi: 10.3749/canmin.48.5.000. submitted Dec. 23rd 2009, accepted Sept 2010 • M. R. M. Izawa, H. W. Nesbitt, N. D. MacRae, E. L. Hoffmann. Composition and evolution of the early oceans: Evidence from the meteorite. Earth and Planetary Science Letters, Volume 298, issue 3-4, pages 443-449 submitted Feb. 17th 2010, accepted August 20th 2010, doi: 10.1016/j.epsl.2010.08.026 • N. R. Banerjee, M. R. M. Izawa, H. M. Sapers, M. Whitehouse. Geochemical Biosignatures Preserved in Microbially Altered Basaltic Glass, Surface and Interface Analysis, 43, 452–457 doi: 10.1002/sia.3577. submitted September 30th 2009, accepted April 11th 2010 • M. R. M. Izawa, R. L. Flemming, P. L. King, R. C. Peterson, P. J. A. McCausland. Mineralogical and spectroscopic investigation of the Tagish Lake by X-ray diffraction and infrared reflectance spectroscopy, Meteoritics and Planetary Science, submitted July 2008, accepted Feb 20th 2010. Volume 45, Issue 4, pages 675–698, April 2010. doi: 10.1111/j.1945-5100.2010.01043.x • M. R. M. Izawa, P. L. King, R. L. Flemming, R. C. Peterson, P. J. A. McCausland. Mineralogical and spectroscopic investigation of enstatite chondrites by X-ray diffraction and infrared reflectance spectroscopy, Journal of Geophysical Research – Planets, 115, E07008, doi:10.1029/2009JE003452. submitted June 13th, 2009, accepted March 18th 2010 • M. R. M. Izawa, R. L. Flemming, P. J. A. McCausland, G. Southam, D. E. Moser, I. R. Barker. Multi-technique Investigation Reveals New Mineral, Chemical, and Textural Heterogeneity in the Tagish Lake C2 Chondrite, Planetary and Space Science, submitted Dec. 1st 2009, accepted May 21st 2010. Volume 58, Issue 10, August 2010, Pages 1347-1364. doi:10.1016/j.pss.2010.05.018 • M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, N. J. Bridge, C. Schultz. Basaltic Glass as a Habitat for Microbial Life: Implications for Astrobiology and Planetary Exploration, Planetary and Space Science 58 (4), 583-591 (2010), doi: 10.1016/j.pss.2009.09.014 submitted Feb 28th 2009, accepted 14 September 2009, available online 20 September 2009 • G. R. Osinski, T. Barfoot, N. Ghafoor, M. R. M. Izawa, N. R. Banerjee, P. Jasiobedzki, J. Tripp, R. Richards, T. Haltigin, S. A. Auclair, H. M. Sapers, L. Thomson, R. L. Flemming. Lidar and mSM as scientific tools for planetary exploration. Planetary and Space Science, Volume 58, Issue 4, March 2010, Pages 691-700 submitted Feb 18th 2009, accepted August 14th 2009. 196

• M. R. Carleer, C. D. Boone, K. A. Walker, P. F. Bernath, K. Strong, R. J. Sica, C. E. Randall, H. Vömel, J. Kar, M. Höpfner, M. Milz, T. von Clarmann, R. Kivi, J. Valverde-Canossa, C. E. Sioris, M. R. M. Izawa, E. Dupuy, C. T. McElroy, J. R. Drummond, C. R. Nowlan, J. Zou, F. Nichitiu, S. Lossow, J. Urban, D. Murtagh, and D. G. Dufour. Validation of water vapour profiles from the Atmospheric Chemistry Experiment (ACE) Atmospheric Chemistry and Physics Discussions, 8, 4499-4559, 2008 • R. J. Sica, M. R. M. Izawa, K. A. Walker, C. Boone, S. V. Petelina, P. S. Argall, P. Bernath, G. P. Burns, V. Catoire, R. L. Collins, W. H Daffer, C. De Clerq, Z. Y. Fan, B. J. Firanski, W. J. R. French, P. Gerard, M. Gerding, J. Granville, J. L. Innes, P. Keckhut, T. Kerzenmacher, A. R. Klekociuk, J. C. Lambert, E. J. Llewellyn, G. L. Manney, I. S. McDermid, K. Mizutani, Y. Murayama, C. Piccolo, C. Robert, W. Steinbrecht, K. A. Strawbridge, K. Strong, R. Stübi, B. Thurairajah. Validation of the Atmospheric Chemistry Experiment (ACE) version 2.2 temperature using ground- based and space-borne measurements, Atmospheric Chemistry and Physics, 8, 35-62, 2008. Alternate journal Atmospheric Chemistry and Physics Discussions, 7, 12463– 12539, 2007. • R. C. Rivest, M. R. M. Izawa, S.D. Rosner, T.J. Scholl, G. Wu, and R.A. Holt. Laser spectroscopic measurements of hyperfine structure in Pr II (2002), Canadian Journal of Physics, 80, 557-562. • C. M. Pinciuc, R. C. Rivest, M. R. M. Izawa, R. A. Holt, S. D. Rosner, and T. J. Scholl (2001). Measurement of Radiative Lifetimes in Nd II, Canadian Journal of Physics, 79, 1159-1167.

In Revision (4, 0 first authored) • G. R. Osinski, L. L. Tornabene, N. R. Banerjee, C. S. Cockell; R. L. Flemming, M. R. M. Izawa, J. McCutcheon, J. Parnell, L. J. Preston, A. Pickersgill, A. Pontefract; H. M. Sapers, G. Southam. Impact-generated hydrothermal systems on Earth and Mars, submitted to Icarus, Jan 1 2012 • J. Shuster, M. R. M. Izawa, A. Smith, R. L. Flemming, N. R. Banerjee, G. Southam. The occurrence of argentojarosite in the Iberian Pyrite Belt: the implication of bacteria in its formation, submitted to Economic Geology, June 22nd 2011 • H. M. Sapers, G. R. Osinski, N. R. Banerjee, L. Ferrière, P. H. Lambert, and M. R. M. Izawa. Re-evaluating impactites from the Rochechouart impact structure, France, in revision for Meteoritics and Planetary Science

Submitted (1, 0 first authored) • H. He, M. R. M. Izawa, P. Keech, R. L. Flemming, D. W. Shoesmith, Characterization of the Defect Structure of UO2+x and the Determination of the Phase Transition Boundaries using Rietveld Refinement and Raman Spot Analyses, submitted to Journal of Nuclear Materials, May 8th, 2010 – present status awaiting rework and resubmission led by Dr. H.

Extended Abstracts (23) 197

• M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, L. C. W. MacLean, J. J. Dynes, S. Matveev, G. Southam, Proteins and organic matter preserved in microbial borings in ~120 Ma basaltic glass, Astrobiology Science Conference 2012, Abstract #2223 • G. E. Bebout, K. Lazzeri, L. D. Anderson, M. R. M. Izawa, N. J. Bridge, R. L. Flemming, N. R. Banerjee, Nitrogen Concentrations and Isotopic Compositions of Altered Terrestrial Glassy Basaltic Rocks, and Implications for Astrobiology, Astrobiology Science Conference 2012 Abstract #2221 • M. Sánchez-Román, D. C. Fernandez-Remolar, N. Sanchez-Navas, C. Romanek N. T. Schmid, F. Nieto, M. Oggerin, N. Rodriguez, L. J. Preston, M. R. M. Izawa, G. Southam, N. R. Banerjee, G. R. Osinski, D. Dyar, D. Gomez-Ortiz, O. Prieto- Ballesteros, R. Amils, Carbonate precipitation in acidic environments, a potential biosignature for searching life on Mars Astrobiology Science Conference 2012, Abstract #1072 • D. C. Fernández-Remolar, M. Sánchez-Román, O. Prieto Ballesteros, D. Gómez-Ortíz, M. García-Villadangos, A. Molina, N. Rodríguez, T. Barragán, D. Gleenson, N. R. Banerjee, G. Southam, M. R. M. Izawa, L. Loiselle, P. Schmitt-Kopplin, A. Granda, C. Quesada, R. Amils, Searching for Biosignatures in Deep Regions of the Rio Tinto Aquifer: The Iberian Pyritic Belt Subsurface Life (IPBSL) Project. Astrobiology Science Conference 2012, abstract #3108 • M. R. M. Izawa, D. E. Moser, I. R. Barker, R. L. Flemming, Z. Gainsforth, J. Stodolna, S. Matveev, N. R. Banerjee. Exploring the distribution and nature of shock deformation in an enstatite chondrule at submicron resolution by a combination of CL, electron backscatter diffraction, EDS mapping and EPMA, 43rd Lunar and Planetary Science Conference, 2012, Abstract # 2735 • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee. QUE 94204: A primitive enstatite achondrite produced by partial melting of an E-chondrite-like protolith, 42nd Lunar and Planetary Science Conference, 2011, Abstract # 1275 • P. L. King, M. R. M. Izawa, P. Vernazza, W. A. McCutcheon, J. A. Berger, & T. Dunn. Salt – An essential material to consider when exploring the solar system, 42nd Lunar and Planetary Science Conference, 2011, Abstract # 1985 • P. Vernazza, P. King, M. R. M. Izawa, A. Maturilli, J. Helbert, J. Emery, D. Cruikshank, R. Brunetto, F. Marchis, R. P. Binzel, Opening the Mid-IR Window on Asteroid Physical Properties, 2011, 42nd Lunar and Planetary Science Conference, Abstract # 1344 • J. Parnell, A. J. Boyce, G. R. Osinski, M. R. M. Izawa, & P. Lee, Searching for life in the sulphur isotopic analysis of surface sulphates on Mars, 42nd Lunar and Planetary Science Conference, 2011, Abstract # 1023 • G. E. Bebout, L. D. Anderson, M. R. M. Izawa, N. R. Banerjee, N. J. Bridge, R. L. Flemming, Nitrogen concentrations and isotopic compositions of altered terrestrial glassy basaltic rocks, and implications for astrobiology 42nd Lunar and Planetary Science Conference, 2011, Abstract #2500 • M. M. Battler, G. R. Osinski, D. S. S. Lim, A. F. Davila, F. A. Michel, M. A. Craig, M. R. M. Izawa, L. Leoni, G. F. Slater, A. G. Fairen, and N. R. Banerjee, The cold- seep-emplaced Golden Deposit in the Canadian high arctic as an analogue for jarosite deposition at Meridiani Planum and Mawth Vallis, Mars, 42nd Lunar and Planetary Science Conference, 2011, Abstract # 2759 198

• N. R. Banerjee, J. Lee, M. R. M. Izawa, K. Tiampo, The Tortoise versus the Hare: Computer Simulation of Euendolithic Microbial Alteration Textures. Astrobiology Science Conference, 2010 • L. D. Anderson, M. R. M. Izawa, G. E. Bebout, N. J. Bridge, N. R. Banerjee, Low- temperature hydrothermal alteration fo 2.7 G.a. basaltic andesites and implications for past fluid-rock interactions on Mars. 41st Lunar and Planetary Science Conference, 2010 • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, Shock Stage Assessment and Petrography of 11 Antarctic Enstatite Chondrites. 40th Lunar and Planetary Science Conference, 2009, Abstract # 1322 • M. R. M. Izawa, I. R. Barker, D. E. Moser, R. L. Flemming, P. J. A. McCausland, Colour SEM-Cathodoluminescence Investigation of the Tagish Lake C2 Chondrite. 40th Lunar and Planetary Science Conference, 2009, Abstract # 1757 • N. R. Banerjee, N. J. Bridge, M. R. M. Izawa, L. D. Anderson, G. E. Bebout, R. L. Flemming, Glassy Subaqueous Lavas as a Habitat for Life on Earth, Mars, and Elsewhere? 40th Lunar and Planetary Science Conference, 2009, Abstract # 1331 • N. J. Bridge, M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, The Textural and Mineralogical Record of Microbial Glass Alteration: Implications for Astrobiology. 6th Canadian Space Exploration Workshop, Dec 1-3, 2008 Montréal, QC. • H. M. Sapers, G. R. Osinski, M. R. M. Izawa, S. Auclair, N. R. Banerjee, C. S. Cockell, Impact craters as hydrothermal habitats for life on Early Earth and Mars. 6th Canadian Space Exploration Workshop, Dec 1-3, 2008 Montréal, QC. • G. R. Osinski, T. Barfoot, N. Ghafoor, J. Tripp, R. Richards, P. Jasiobedzki, T. Haltigin, N. R. Banerjee, M. R. M. Izawa, P. Furgale, Lidar and mSM as scientific tools for the geological mapping of planetary surfaces. 6th Canadian Space Exploration Workshop, Dec 1-3, 2008 Montréal, QC. • M. R. M. Izawa, R. L. Flemming, P. L. King, R. C. Peterson, Bulk Mineralogy and Spectral Properites of the C2 Chondrite Tagish Lake: A Correlated X-ray Diffraction (XRD) and Biconical Reflectance Infrared Spectroscopy Study. 39th Lunar and Planetary Science Conference, 2008, abstract #2149 • M. R. M. Izawa, A. J. Wright, P. J. A. McCausland, R. L. Flemming, D. K. Muirhead, J. Parnell, Combined in situ micro X-ray diffraction and Raman study of carbonaceous matter in and terrestrial materials. 39th Lunar and Planetary Science Conference, 2008, abstract #1459 • M. R. M. Izawa, R. L. Flemming, P. J. A. McCausland, Investigation of the Tagish Lake carbonaceous chondrite by X-ray microdiffraction. 38th Lunar and Planetary Science Conference 2007, abstract #1923 • R. L. Flemming, P. J. A. McCausland, M. R. M. Izawa, and N. Jacques. Reconnaissance Micro-XRD studies of meteorites: Rapid, in situ mineral identification and textural information. 38th Lunar and Planetary Science Conference, 2007, abstract # 2363

Non-refereed contributions (36) • G. E. Bebout, K. E. Lazzeri, L. D. Anderson, M. R. M. Izawa, N. J. Bridge, R. L. Flemming, N. R. Banerjee, Nitrogen concentrations and isotopic compositions of altered terrestrial glassy basaltic rocks, and implications for astrobiology, Misasa 199

International Symposium IV: Solar System Exploration and New Geosciences – Perspectives for the Next Decade, Misasa, Japan • M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, C. J. Hetherington, J. C. Shervais, C. Schultz, Fossilization of microbial etchings from the Stonyford volcanic complex: a link between modern seafloor bioalteration and putative ichnofossils in ophiolites and greenstone belts. 2012 GAC-MAC-SEG-SGA meeting, St. John’s. • R. L. Flemming, P. J. A. McCausland, M. R. M. Izawa, M. A. Craig, M. M. M. Haring, D. R. Edey, J. N. Shivak, J. Kanhai, N. R. Banerjee, G. R. Osinski, D. W. Holdsworth, E. A. Cloutis, P. L. King. Astromaterials I: Representative materials from across the Solar System. 2011 Center for Advanced Materials and Biomaterials Research (CAMBR) Distinguished Lecturer and Research Day • R. L. Flemming, P. J. A. McCausland, M. R. M. Izawa, M. A. Craig, D. R. Edey, J. N. Shivak, M. M. M. Haring, J. Hainge, N. R. Banerjee, G. R. Osinski, Department of Earth Sciences, UWO, London, ON, N6A 5B7; E. A. Cloutis 2011 Center for Advanced Materials and Biomaterials Research (CAMBR) Distinguished Lecturer and Research Day • P. J. A. McCausland, R. L. Flemming, M. R. M. Izawa. Shock stage determination from the measurement of olivine and pyroxene crystalline mosaicity by in situ micro- XRD, 2011 Canadian Geophysical Union conference, Banff, Alberta • M. M. Battler, L. Leoni, L. J. Preston, G. R. Osinski, D. S. S. Lim, A. F. Davila, F. A. Michel, M. A. Craig, M. R. M. Izawa, G. F. Slater, A. G. Fairén, N. R. Banerjee. Habitability and organic preservation in cold seep precipitated jarosite on Earth and Mars, Exploring Mars Habitability 13 - 15 June 2011 Lisbon, Portugal • L. J. Preston, M. R. M. Izawa, N. R. Banerjee. Infrared spectroscopic characterization of organic matter associated with microbial bioalteration textures in basaltic glass, Exploring Mars Habitability 13 - 15 June 2011 Lisbon, Portugal • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, Enstatite chondrites and enstatite chondrite melt rocks: A petrographic, mineral and geochemical study, GAC-MAC- SEG-SGA 2011 Joint annual meeting, Ottawa, abstract #667 • P. J. A. McCausland, R. L. Flemming, M. R. M. Izawa, Quantitative shock stage assessment in olivine and pyroxene bearing meteorites via in situ micro-XRD, 2010 American Geophysical Union Fall meeting, San Francisco • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, P. J. A. McCausland, L. J. Preston, D. E. Moser, I. R. Barker, M. A. Craig, E. A. Cloutis, S. Matveev, Multimethod Study of E Chondrite Shock, 73rd Annual Meeting of the Meteoritical Society, June 25-30 2010, New York, abstract #5345 • P. J. A. McCausland, R. L. Flemming, M. R. M. Izawa, Shock Stage Measurement in Ordinary Chondrites and Achondrites by In-Situ Micro XRD, 73rd Annual Meeting of the Meteoritical Society, June 25-30 2010, New York, abstract # 5246 • M. R. M. Izawa, J. Shuster, N. R. Banerjee, R. L. Flemming, G. Southam. Microbes influence the mobilization and re-precipitation of Ag in gossans. 2010 Goldschmidt Conference, Knoxville, Tennessee • M. R. M. Izawa, R. L. Flemming, N. R. Banerjee, A micro X-ray diffraction (μXRD) technique for shock stage assessment in enstatite chondrites, 2009 Planetary Science Research Symposium, Oct 7th 2009, Toronto, ON. 200

• H. M. Sapers, G. R. Osinski, M. R. M. Izawa, N. R. Banerjee, Reclassification of the Rochechouart Impactites, 2009 Planetary Science Research Symposium, Oct 7th 2009, Toronto, ON. • H. M. Sapers, M. R. M Izawa, M. J. Whitehouse, N. R. Banerjee, Geochemical Biosignatures Preserved in Microbially Altered Basaltic Glass, 17th international conference on secondary ion mass spectrometry, Sept 14th-19th 2009, Toronto, ON. • M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, N. S. McIntyre, Investigating mineral and chemical signatures of microbial glass alteration using synchrotron radiation, Canadian Light Source Saskatoon Synchrotron Summer School IV, June 13th – 18th, 2009 • M. R. M. Izawa, R. L. Flemming, P. L. King, R. C. Peterson, P. J. A. McCausland, I. Barker, G. Southam, D. E. Moser, Multi-method investigation of several fragments of the Tagish Lake C2 carbonaceous chondrite, a co-ordinated mineralogical, imaging, chemical and spectroscopic reconnaissance. American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 387 (Invited) • M. R. M. Izawa, P. L. King , R. L. Flemming, R. C. Peterson, P. J. A. McCausland. Mineralogical and spectroscopic investigation of enstatite chondrites by X-ray diffraction and infrared reflectance spectroscopy. American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 1167 • M. R. M. Izawa, H. M. Sapers, G. R. Osinski, N. R. Banerjee, R. L. Flemming, A. C. Singleton, L. Thompson, S. A. Auclair, D. M. Laliberty, H. Q. Ngo, Mineralogy of post-impact hydrothermal deposits at the Haughton impact structure, and implications for microbial colonization, American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 429 • N. J. Bridge, M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, C. Schultz. Preliminary Astrobiological and Planetary Exploration Implications of Microbial Ichnofossils in Terrestrial Basaltic Glasses, American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 1158 • M. Battler, G. R. Osinski, N. R. Banerjee, M. R. M. Izawa. Mineralogical and Geological Characterization of the Lost Hammer Perennial Spring, Axel Heiberg Island, Nunavut. American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 2398 • S. Auclair, G. R. Osinski, N. R. Banerjee, M. R. M. Izawa, L. Huang, A. C. Singleton, L. Thompson. Evaluating the Stable Isotopic Composition of Impact-Induced Hydrothermal Carbonates at the Haughton Impact Structure, Devon Island, Nunavut, Canada. American Geophysical Union 2009 Joint Annual Meeting, Toronto, ON, Abstract # 2565 • M. R. M. Izawa, N. J. Bridge, N. R. Banerjee, R. L. Flemming, W. Mueller, K. Muehlenbachs, T. Chacko, Mineralization of microbial trace fossils in fresh basaltic glass, and their preservation in Archean greenstone belts. American Geophysical Union Fall meeting, Dec 14th-19th, 2008, San Francisco, CA, Abstract #583 Eos Transactions AGU, 89(53), Fall Meeting Supplement, Abstract P583, P51A-1397 • G. R. Osinski, T. Barfoot, N. Ghafoor, P. Jasiobedzki, J. Tripp, R. Richards, T. Haltigin, N. Banerjee, M. R. M. Izawa, S. Auclair, Optimizing lunar surface activities: Lidar and mSM as Scientific Tools?. Joint Annual Meeting of LEAG- ICEUM-SRR, Oct 28-31, 2008, Cape Canaveral, FL, abstract #4061 201

• C. J. Hetherington, M. R. M. Izawa, R. L. Flemming, C. W. Kirby, Structure refinement and spectroscopic analysis of Ba-bearing di-octahedral mica. 2008 Goldschmidt Conference, Vancouver, BC, Canada. • M. R. M. Izawa, N. R. Banerjee, R. L. Flemming, Mineralization of microbial trace fossils in fresh basaltic glass, and their preservation in Archean greenstone belts. Joint annual meeting of GAC-MAC-SEG-SGA 2008, Quebec City, PQ, abstract #583 • M. R. M. Izawa, R. L. Flemming, P. J. A. McCausland, Correlated SEM-EDX and μXRD survey of the Tagish Lake carbonaceous chondrite. Paper presented at the Geological Society of America Northeastern Section - 43rd Annual Meeting (27-29 March 2008), Buffalo NY. • M. R. M. Izawa, R. L. Flemming, P. J. A. McCausland, Investigation of matrix mineralogy in the Tagish Lake and Gao-Guenie B carbonaceous chondrites by micro X-ray diffraction, in Abstracts from the Planetary Science Research Symposium Compiled by P. J.A. McCausland. Journal of the Royal Astronomical Society of Canada, Volume 102 Number 2, p 49, 2008. • M. R. M. Izawa, Investigation of meteorites by X-ray diffraction and diffuse- reflectance infrared spectroscopy, talk presented at the Center for Chemical Physics seminar series, September 28 2007. • M. R. M. Izawa, R. L. Flemming, R. C. Peterson, Mineralogical analysis of the Tagish Lake carbonaceous chondrite by X-ray diffraction and Rietveld refinement, Poster presented at the Kobe School of Planetary Science 2007, abstract # 23. • M. R. M. Izawa, R. J. Sica, P. S. Argall, K.A. Walker, C. D. Boone, P. F. Bernath, Comparison of Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and Purple Crow Lidar (PCL) Temperature Profiles in the Middle Atmosphere, 41st Canadian Meteorological and Oceanographic Society Conference abstract # 2078 (2007) • M. R. M. Izawa, R. J. Sica, P. S. Argall, K. A. Walker, C. D. Boone, P. F. Bernath, Temperature Profiles in the Middle Atmosphere measured by Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and Purple Crow Lidar (PCL). Environmental Research Western Earth Day Colloquium 2007. • R. L. Flemming, M. R. M. Izawa, & C. W. Kirby, Characterization of a multiphases 17 27 in the system MgO-Al2O3-TiO2, by O and Al MAS NMR, Rietveld refinement of X-ray diffraction (XRD) data, and Electron Probe Microanalysis (EPMA). 90th Canadian Chemistry Conference (2007) • M. R. M. Izawa Investigation of the Tagish Lake Carbonaceous Chondrite using X- ray Microdiffraction. Bruker AXS 2006 Excellence in X-ray Diffraction Scholarship competition. 2nd place in the geological sciences category. • M. R. M. Izawa Coincident Temperature Measurements with the Purple Crow LIDAR and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer. 40th Canadian Meteorological and Oceanographic Society conference (2006) • M. R. M. Izawa Measurement of radiative lifetimes and hyperfine structure in singly ionized lanthanides. Canadian Undergraduate Physics Conference (2000).

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Major Awards Canada IODP research grant 2012 – $3000 Cdn

Mineralogical Association of Canada Foundation Scholarship (2011-12) – $5000 Cdn

CREATE Astrobiology fellowship (2010-2012) – $2100 Cdn per travel/research year plus $21000 Cdn support scholarship in last year

CREATE Astrobiology fellowship (2009-10) – $2100 Cdn

Barringer Family Fund for Meteorite Impact Research (2009) – $3000 USD

NSERC PGS-D 3 (2008) – $63000 Cdn over 3 years

Ontario Graduate Scholarship (2008) – $15000 Cdn per year, up to 3 years – Declined, in accordance with OGS regulations, as the winner of an NSERC scholarship cannot also accept OGS funding.

NSERC CGS – M (2007) – $17500 Cdn.

Ontario Graduate Scholarship (2007) – $15000 Cdn. – Declined, in accordance with OGS regulations, as the winner of an NSERC scholarship cannot also accept OGS funding

NSERC USRA (2006) – $4000 Cdn.

Gold Medal – Honours specialization in Planetary Science 2006 (Highest mark in graduating class)

Other Awards UWO Graduate Student Thesis Research Award, 2012 – $1000 Cdn.

CSA travel subsidy for CATp meeting (2011) – $500 Cdn.

Nanobeams School attendance scholarship cycle 6 2010-2012 – 1980 € awarded for 4 sessions (total = 7920 €)

Meteoritical Society travel grant for 2010 Met Soc meeting – $700 US

Northern Scientific Training Program Northern Training Grant (2010) – $2100 Cdn.

CSA travel subsidy for CATp meeting (2010) – $500 Cdn.

Western Society of Graduate Students/Graduate Teaching Assistants’ Union Student Teaching Award (2009) – $500 Cdn.

Northern Scientific Training Program Northern Training Grant (2009) – $2000 Cdn.

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Robert Hodder graduate travel bursary (2009) – $ 500 Cdn.

Mineralogical Association of Canada Travel and Research Bursary (2009) – $900 Cdn.

Partial Scholarship and admittance to International Space University Summer Studies Program – forced to decline, insufficient spaces in program

Robert and Ruth Lumsden Graduate Fellowship (2009) – $1000 Cdn

Lunar and Planetary Institute Career development award (2009) – $750 USD

Allan D. Edgar Petrology Award – Department of Earth Sciences UWO – $1000 Cdn

Peacock Memorial Prize of the Walker Mineralogical Club (2008) – $1500 Cdn (National level competition)

Geological Association of Canada - Jerome H. Remick Poster Award, – $1000 Cdn (Gold) GAC-MAC-SEG-SGA meeting, 2008, Quebec City, QC

University of Western Ontario Faculty of Science Graduate Student Teaching Award 2008

University of Western Ontario Department of Earth Science Outreach Award (2008)

CSA travel subsidy for GAC-MAC 2008 – $250 Cdn.

Northern Scientific Training Program Northern Training Grant (2008) – $1604 Cdn.

Western Graduate Thesis Research Award (2008) – $500

Kobe School of Planetary Science Support Scholarship (2007) – 190000 ¥

Canadian Geophysical Union Travel Bursary (2007) – $150 Cdn.

Mineralogical Association of Canada Travel and Research Bursary (2007) – $800 Cdn.

Robert & Ruth Lumsden award – Dept. of Earth Sciences, University of Western Ontario – Graduate level (2007) - $1000 Cdn.

University of Western Ontario Faculty of Science: Deans honour list 2004-05, 2005-06

Deep River Science Academy – Full scholarship to attend, summer 1995. $2500 Cdn.

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Education Post Secondary • PhD. (Began Sept. 2008) • MSc. (Completed August 2008). Bulk mineralogy and remote sensing properties of the Tagish Lake C2 chondrite, and enstatite chondrites using sample-correlated X-ray diffraction and thermal infrared diffuse (biconical) reflectance. • Bachelor of Science, honours specialization in Planetary Science, University of Western Ontario, awarded 2006.

Short Courses • 2010-ongoing Nanobeams PhD school, Le Centre de Recherche Public - Gabriel Lippmann – theoretical and instrumental training in SIMS, nanoSIMS, TEM, Auger spectroscopy and X-ray photoelectron spectroscopy • 2010 Modular course in Planetary Science, University of Western Ontario • 2009 Canadian Light Source Saskatoon Synchrotron Summer School IV • 2009 GAC-MAC Secondary Ion Mass Spectroscopy short course (Toronto) • 2009 Hydrothermal Ore Deposits, Joint modular course Ottawa University/Laurentian • 2007 Kobe school of Planetary Science, Kobe, Japan • 2007 Workshop on Powder Diffraction and Rietveld Analysis, Université du Québec, Trois-Rivières • 2007 W. S. Fyfe short course in Sustainable Development, University of Western Ontario