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Durham E-Theses
Durham E-Theses Shock metamorphism of potassic feldspars Robertson, P. B. How to cite: Robertson, P. B. (1973) Shock metamorphism of potassic feldspars, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/8594/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk SHOCK METAMORPHISM OF POTASSIC FELDSPARS A thesis submitted for the degree of Doctor of Philosophy in the University of Durham P.B. Robertson Graduate Society October, 1973 ABSTRACT Hypervelocity meteorite impact produces transient pressures as high as several megabars and temperatures in excess of 1500°C. Shock metamorphism describes the effects upon the target rocks, effects most distinctive in the range approximately 100-600kb. Shock deformation produced in potassic feldspars at three terrestrial craters and in experimentally shocked K-spar have been examined. Pressures in natural material were estimated from deformation of coexisting quartz and plagioclase, and in experiments pressures were calculated using impedance matching. -
Terrestrial Impact Structures Provide the Only Ground Truth Against Which Computational and Experimental Results Can Be Com Pared
Ann. Rev. Earth Planet. Sci. 1987. 15:245-70 Copyright([;; /987 by Annual Reviews Inc. All rights reserved TERRESTRIAL IMI!ACT STRUCTURES ··- Richard A. F. Grieve Geophysics Division, Geological Survey of Canada, Ottawa, Ontario KIA OY3, Canada INTRODUCTION Impact structures are the dominant landform on planets that have retained portions of their earliest crust. The present surface of the Earth, however, has comparatively few recognized impact structures. This is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere, both of which serve to obscure and remove the impact record. Although not generally viewed as an important terrestrial (as opposed to planetary) geologic process, the role of impact in Earth evolution is now receiving mounting consideration. For example, large-scale impact events may hav~~ been responsible for such phenomena as the formation of the Earth's moon and certain mass extinctions in the biologic record. The importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate. Impact is a highly transient, high-energy event. It is inherently difficult to study through experimentation because of the problem of scale. In addition, sophisticated finite-element code calculations of impact cratering are gen erally limited to relatively early-time phenomena as a result of high com putational costs. Terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared. These structures provide information on aspects of the third dimen sion, the pre- and postimpact distribution of target lithologies, and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave. -
Monoplacophoran Limpet
16 McLean: Monoplacophoran Limpet FIGURES 17-21. Neopilinid radular ribbons, magnifications adjusted to show a similar number of teeth rows. FIGURE 17, Vema (Vema) ewingi. intact ribbon with teeth aligned (LACM 65-11, 6200 m. 110 mi. W of Callao. Pern. R/V ANTON BRUUN, 24 November 1965). FIGURE 18, Vema (Vema) ewingi. another portion of same ribbon with lateral teeth turned to the side. FIGURE 19. Neopilina veleronis. intact ribbon of paratype, teeth not aligned (AHF 603, 2730-2769 m, 30 mi. W of Natividad Island. Baja California, Mexico). FIGURE 20, Vema (Laevipilina) hyalina new species, intact ribbon with teeth aligned, focused on shafts of lateral teeth (LACM 19148). FIGURE 21, Vema (Laevipilina) hyalina, same ribbon, focused on fringe of first marginal teeth. instead of the highly reduced condition in these two species. Al- small-sized species have similar teeth. Radular differences among though the first lateral of N. veleronis is somewhat larger than it the species examined are quantitative rather than qualitative, sup- is in the other two species, that of V. hyalina is still the larger. porting placement of the four species in the same family. A study The fringed first marginal of V. hyalina is much broader than in of the radulae of the other three living species of neopilinids N. veleronis. Only in V. hyalina is the fringed tooth so broad that should reveal further specific differences. it overlaps the opposite member in the central part of the ribbon. The radula of neopilinid monoplacophorans is very similar to The second and third laterals of V. -
Hydrothermal Alteration at the Lonar Lake Impact Structure, India: Implications for Impact Cratering on Mars
Meteoritics & Planetary Science 38, Nr 3, 365–381 (2003) Abstract available online at http://meteoritics.org Hydrothermal alteration at the Lonar Lake impact structure, India: Implications for impact cratering on Mars Justin J. HAGERTY* and Horton E. NEWSOM Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA *Corresponding author. E-mail: [email protected] (Received 12 June 2002; revision accepted 20 February 2003) Abstract–The 50,000 year old, 1.8 km diameter Lonar crater is one of only two known terrestrial craters to be emplaced in basaltic target rock (the 65 million year old Deccan Traps). The composition of the Lonar basalts is similar to martian basaltic meteorites, which establishes Lonar as an excellent analogue for similarly sized craters on the surface of Mars. Samples from cores drilled into the Lonar crater floor show that there are basaltic impact breccias that have been altered by post-impact hydrothermal processes to produce an assemblage of secondary alteration minerals. Microprobe data and X-ray diffraction analyses show that the alteration mineral assemblage consists primarily of saponite, with minor celadonite, and carbonate. Thermodynamic modeling and terrestrial volcanic analogues were used to demonstrate that these clay minerals formed at temperatures between 130°C and 200°C. By comparing the Lonar alteration assemblage with alteration at other terrestrial craters, we conclude that the Lonar crater represents a lower size limit for impact-induced hydrothermal activity. Based on these results, we suggest that similarly sized craters on Mars have the potential to form hydrothermal systems, as long as liquid water was present on or near the martian surface. -
Shell Microstructures in Early Cambrian Molluscs
Shell microstructures in Early Cambrian molluscs ARTEM KOUCHINSKY Kouchinsky, A. 2000. Shell microstructures in Early Cambrian molluscs. - Acta Palaeontologica Polonica 45,2, 119-150. The affinities of a considerable part of the earliest skeletal fossils are problematical, but investigation of their microstructures may be useful for understanding biomineralization mechanisms in early metazoans and helpful for their taxonomy. The skeletons of Early Cambrian mollusc-like organisms increased by marginal secretion of new growth lamel- lae or sclerites, the recognized basal elements of which were fibers of apparently aragon- ite. The juvenile part of some composite shells consisted of needle-like sclerites; the adult part was built of hollow leaf-like sclerites. A layer of mineralized prism-like units (low aragonitic prisms or flattened spherulites) surrounded by an organic matrix possibly existed in most of the shells with continuous walls. The distribution of initial points of the prism-like units on a periostracurn-like sheet and their growth rate were mostly regular. The units may be replicated on the surface of internal molds as shallow concave poly- gons, which may contain a more or less well-expressed tubercle in their center. Tubercles are often not enclosed in concave polygons and may co-occur with other types of tex- tures. Convex polygons seem to have resulted from decalcification of prism-like units. They do not co-occur with tubercles. The latter are interpreted as casts of pore channels in the wall possibly playing a role in biomineralization or pits serving as attachment sites of groups of mantle cells. Casts of fibers and/or lamellar units may overlap a polygonal tex- ture or occur without it. -
Impact Cratering
6 Impact cratering The dominant surface features of the Moon are approximately circular depressions, which may be designated by the general term craters … Solution of the origin of the lunar craters is fundamental to the unravel- ing of the history of the Moon and may shed much light on the history of the terrestrial planets as well. E. M. Shoemaker (1962) Impact craters are the dominant landform on the surface of the Moon, Mercury, and many satellites of the giant planets in the outer Solar System. The southern hemisphere of Mars is heavily affected by impact cratering. From a planetary perspective, the rarity or absence of impact craters on a planet’s surface is the exceptional state, one that needs further explanation, such as on the Earth, Io, or Europa. The process of impact cratering has touched every aspect of planetary evolution, from planetary accretion out of dust or planetesimals, to the course of biological evolution. The importance of impact cratering has been recognized only recently. E. M. Shoemaker (1928–1997), a geologist, was one of the irst to recognize the importance of this process and a major contributor to its elucidation. A few older geologists still resist the notion that important changes in the Earth’s structure and history are the consequences of extraterres- trial impact events. The decades of lunar and planetary exploration since 1970 have, how- ever, brought a new perspective into view, one in which it is clear that high-velocity impacts have, at one time or another, affected nearly every atom that is part of our planetary system. -
Multiple Fluvial Reworking of Impact Ejecta—A Case Study from the Ries Crater, Southern Germany
Multiple fluvial reworking of impact ejecta--A case study from the Ries crater, southern Germany Item Type Article; text Authors Buchner, E.; Schmieder, M. Citation Buchner, E., & Schmieder, M. (2009). Multiple fluvial reworking of impact ejecta—A case study from the Ries crater, southern Germany. Meteoritics & Planetary Science, 44(7), 1051-1060. DOI 10.1111/j.1945-5100.2009.tb00787.x Publisher The Meteoritical Society Journal Meteoritics & Planetary Science Rights Copyright © The Meteoritical Society Download date 06/10/2021 20:56:07 Item License http://rightsstatements.org/vocab/InC/1.0/ Version Final published version Link to Item http://hdl.handle.net/10150/656594 Meteoritics & Planetary Science 44, Nr 7, 1051–1060 (2009) Abstract available online at http://meteoritics.org Multiple fluvial reworking of impact ejecta—A case study from the Ries crater, southern Germany Elmar BUCHNER* and Martin SCHMIEDER Institut für Planetologie, Universität Stuttgart, 70174 Stuttgart, Germany *Corresponding author. E-mail: [email protected] (Received 21 July 2008; revision accepted 12 May 2009) Abstract–Impact ejecta eroded and transported by gravity flows, tsunamis, or glaciers have been reported from a number of impact structures on Earth. Impact ejecta reworked by fluvial processes, however, are sparsely mentioned in the literature. This suggests that shocked mineral grains and impact glasses are unstable when eroded and transported in a fluvial system. As a case study, we here present a report of impact ejecta affected by multiple fluvial reworking including rounded quartz grains with planar deformation features and diaplectic quartz and feldspar glass in pebbles of fluvial sandstones from the “Monheimer Höhensande” ~10 km east of the Ries crater in southern Germany. -
Bulletin of the Geological Society of Denmark
Muscle scars in For cellia (Gastropoda; Pleurotomariacea) from the Carboniferous of England JOHN S. PEEL Peel, J. S.: Muscle scars in Porcellia (Gastropoda; Pleurotomariacea) from the Carboniferous of England. DGF Bull. geol. Soc. Denmark, vol. 35, pp. 53-58, Copenhagen, October, 29th, 1986 Two shell retractor muscles are described on an internal mould of Porcellia woodwardi, a pleurotomaria- cean gastropod from the Carboniferous of England. The scars are located at the junction between the um bilical wall, and the apical surface and the basal surface, respectively. Similar positioning of muscle scars in Bellerophon of the same age reflects morphological convergence of the planispiral, anisostrophic Por cellia with the planispiral, but isostrophic Bellerophon. It is concluded that the shape of muscle scars, in detail, can not contribute to solving the question of the systematic position of Bellerophon. John S. Peel, Grønlands Geologiske Undersøgelse, Øster Voldgade 10. DK-1350 København K, Denmark, January 8th, 1986. The bellerophontiform molluscs are a complex of its single pair of circumbilical muscles and the more than fifty isostrophically coiled genera of single pair of shell-attachment muscles of some uncertain systematic position. While traditionally extant, slit-bearing pleurotomariaceans. Other considered to be gastropods, an extended debate bellerophontiform molluscs have been conside exists in the literature as to whether or not this red to be monoplacophorans after comparison position should be maintained, or if the group between their multiple pairs of muscle scars and should be transferred in part, or as an entity, to the discrete pairs of muscle scars in the living the Monoplacophora. The central theme in this monoplacophoran Neopilina Lemche 1957, or its debate concerns the presence or absence of tor immediate, but ancient relatives Pilina Koken sion. -
Keeping a Lid on It: Muscle Scars and the Mystery of the Mobergellidae
1 Keeping a lid on it: muscle scars and the mystery of the 2 Mobergellidae 3 4 TIMOTHY P. TOPPER1,2* and CHRISTIAN B. SKOVSTED1 5 6 1Department of Palaeobiology, Swedish Museum of Natural History, P.O. Box 50007, 7 SE-104 05, Stockholm, Sweden. 8 2Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham 9 DH1 3LE, UK. 10 11 Mobergellans were one of the first Cambrian skeletal groups to be recognized yet have 12 long remained one of the most problematic in terms of biological function and affinity. 13 Typified by a disc-shaped, phosphatic sclerite the most distinctive character of the 14 group is a prominent set of internal scars, interpreted as representing sites of former 15 muscle attachment. Predominantly based on muscle scar distribution, mobergellans 16 have been compared to brachiopods, bivalves and monoplacophorans, however a 17 recurring theory that the sclerites acted as operculum remains untested. Rather than 18 correlate the number of muscle scars between taxa, here we focus on the percentage of 19 the inner surface shell area that the scars constitute. We investigate two mobergellan 20 species, Mobergella holsti and Discinella micans comparing the Cambrian taxa with the 21 muscle scars of a variety of extant and fossil marine invertebrate taxa to test if the 22 mobergellan muscle attachment area is compatible with an interpretation as operculum. 23 The only skeletal elements in our study with a comparable muscle attachment 24 percentage are gastropod opercula. Complemented with additional morphological 25 information, our analysis supports the theory that mobergellan sclerites acted as an 26 operculum presumably from a tube-living organism. -
The Recognition of Terrestrial Impact Structures
Bulletin of the Czech Geological Survey, Vol. 77, No. 4, 253–263, 2002 © Czech Geological Survey, ISSN 1210-3527 The recognition of terrestrial impact structures ANN M. THERRIAULT – RICHARD A. F. GRIEVE – MARK PILKINGTON Natural Resources Canada, Booth Street, Ottawa, Ontario, KIA 0ES Canada; e-mail: [email protected] Abstract. The Earth is the most endogenically active of the terrestrial planets and, thus, has retained the poorest sample of impacts that have occurred throughout geological time. The current known sample consists of approximately 160 impact structures or crater fields. Approximately 30% of known impact structures are buried and were initially detected as geophysical anomalies and subsequently drilled to provide geologic samples. The recognition of terrestrial impact structures may, or may not, come from the discovery of an anomalous quasi-circular topographic, geologic or geo- physical feature. In the geologically active terrestrial environment, anomalous quasi-circular features, however, do not automatically equate with an impact origin. Specific samples must be acquired and the occurrence of shock metamorphism, or, in the case of small craters, meteoritic fragments, must be demonstrated before an impact origin can be confirmed. Shock metamorphism is defined by a progressive destruction of the original rock and mineral structure with increasing shock pressure. Peak shock pressures and temperatures produced by an impact event may reach several hundreds of gigaPascals and several thousand degrees Kelvin, which are far outside the range of endogenic metamorphism. In addition, the application of shock- wave pressures is both sudden and brief. Shock metamorphic effects result from high strain rates, well above the rates of norma l tectonic processes. -
Appendix a Recovery of Ejecta Material from Confirmed, Probable
Appendix A Recovery of Ejecta Material from Confirmed, Probable, or Possible Distal Ejecta Layers A.1 Introduction In this appendix we discuss the methods that we have used to recover and study ejecta found in various types of sediment and rock. The processes used to recover ejecta material vary with the degree of lithification. We thus discuss sample processing for unconsolidated, semiconsolidated, and consolidated material separately. The type of sediment or rock is also important as, for example, carbonate sediment or rock is processed differently from siliciclastic sediment or rock. The methods used to take and process samples will also vary according to the objectives of the study and the background of the investigator. We summarize below the methods that we have found useful in our studies of distal impact ejecta layers for those who are just beginning such studies. One of the authors (BPG) was trained as a marine geologist and the other (BMS) as a hard rock geologist. Our approaches to processing and studying impact ejecta differ accordingly. The methods used to recover ejecta from unconsolidated sediments have been successfully employed by BPG for more than 40 years. A.2 Taking and Handling Samples A.2.1 Introduction The size, number, and type of samples will depend on the objective of the study and nature of the sediment/rock, but there a few guidelines that should be followed regardless of the objective or rock type. All outcrops, especially those near industrialized areas or transportation routes (e.g., highways, train tracks) need to be cleaned off (i.e., the surface layer removed) prior to sampling. -
Magnetic, Gravity and Seismic Constraints on the Nature of the Wanapitei Lake Impact Crater
Large Meteorite Impacts (2003) 4016.pdf MAGNETIC, GRAVITY AND SEISMIC CONSTRAINTS ON THE NATURE OF THE WANAPITEI LAKE IMPACT CRATER. E. L’Heureux1, H. Ugalde2, B. Milkereit2, N. Eyles3, J. Boyce4 and W. Morris4,1Dept. of Physics, Univ. Toronto, 60 St. George, Toronto, Ontario, Canada, [email protected], 2Dept. of Physics, Univ. Toronto, 60 St. George, Toronto, Ontario, Canada, 3University of Toronto at Scarborough, Toronto, Canada, 4School of Geography and Geology, McMaster Univ., 1280 Main street West, Hamilton, Canada Introduction: The Wanapitei Lake impact crater fects (quartzite fragments and the presence of glass) (46°45’N, 80°45’W) is located in Northern Ontario, that have been found in glacial drift on the southern bounded on its West side by the deformed East rim of shores of the lake [1, 3, 4]. These include boulders of the 1.85 b.y. old Sudbury impact structure. The crater suevite and glassy breccia as well as samples of coesite is believed to be of medium size (with a diameter of [3]. Dressler [2] observed deformation lamellae in a ~7.5 km) and lies entirely within the central, circular few quartz grains at only three locations in the south- portion of the 9 km diameter Wanapitei Lake [1]. Be- western region of the lake. cause the crater lies underwater, there are few con- straints on its actual size: its suggested diameter is based solely on one gravity survey. There are only few samples presenting shock metamorphic features in proximity of the lake, all of which come from glacial drift South of Wanapitei.