DOCSLIB.ORG

Stratigraphy of the Keku "Islets and Neighboring 1 Parts of Kuiu and < Kupreanof Islands Southeastern Alaska

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Stratigraphy of the Keku ; Stratigraphy of the Keku "Islets and Neighboring 1 Parts of Kuiu and < Kupreanof Islands -3 Southeastern Alaska , By L. J. PATRICK MUFFLER ' CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY BULLETIN 1241-C - Geologic map and preliminary stratigraphic * interpretation of a well-exposed sequence ^of sedimentary and volcanic rocks ranging ^ in age from Late Silurian to Tertiary ^UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1967 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Abstract. _________________________________________________________ Cl Introduction._____________________________________________________ 2 Physical setting_______________________________________________ 2 Previous work.._______________________________________________ 4 Purpose of present study...____________________________________ 5 Fieldwork and acknowledgments.________________________________ 5 Silurian System.__________________________________________________ 6 Bay of Pillars Formation____--_______..__.._._____.____.._..___ 6 Kuiu Limestone_.._-____.__...._.___________ _________________ 11 Red arkose___________________________________________________ 12 Volcanic graywacke and argillite.---________.______________.-__--- 13 Silurian or Devonian System___________________.____________________ 14 Volcanic breccia.___---_____________________-___-______-__-_--- 14 Devonian System..________________________________________________ 15 Gambier Bay Formation _______________________________________ 15 Limestone._ __________________________________________________ 18 Carboniferous Systems._______________.______--__-_-_______-------- 19 Crinoidal limestone._______________________ ___________________ 19 Saginaw Bay Formation.____________.___-_._-___-___._---_---_- 20 Permian System.---______________________________________-_---_--- 22 Halleck Formation________________ ___________________________ 22 Cannery Formation.___________________________________________ 23 Pybus Formation..._______--_____- ___________________________ 25 Triassic System.____.______._.._.___.___.__.____._______.---.-.--- 26 Keku Volcanics_ ______________________________________________ 26 Hyd Group____._.._...._.______._._..._...____.._....____.... 28 Burnt Island Conglomerate.________________________________ 29 Cornwallis Limestone___-_-_______-___-__-----____--------- 34 Hamilton Island Limestone.__________-_____--_____--------- 34 Hound Island Volcanics____________________--______----_--- 35 Jurassic and Cretaceous Systems-----.---.-.------------------------ 44 Seymour Canal Formation.____________________________----_---- 44 Cretaceous System.________________________________________________ 44 Lithic sandstone and mudstone--.___-_--_----------------------- 44 Cretaceous (?) System _________________-_____---__------__---------- 45 Hornblendite..-.___-__._._____--_-_--._---___----------------- 45 Granitic rocks.________________________________-______--------- 45 Tertiary System..___________________________-_____-----_---------- 47 Kootznahoo Formation..__________________________---__-------- 47 Altered dellenite flows____--__-____--_-----------_------------ 48 Gabbro and microgabbro___________________-__----------------- 49 Structure.. __________________________________--__----------_------ 50 References._____________________________________-_--__--_--------- 52 in IV CONTENTS ILLUSTRATIONS Page PLATE 1. Geologic map of Keku Islets and neighboring parts of Kuiu and Kupreanof Islands, Alaska.____________ In pocket FIGURE 1. Index map showing location of the Keku Islets area and of other recently studied nearby areas in southeastern Alaska. _____-------------------- ------------_-- C3 2-5. Photographs showing 2. Interbedded calcareous sandstone and argillite in the Bay of Pillars Formation._____________ 7 3. Thin-bedded argillite and limestone in the Bay of Pillars Formation._._______.._...__..._____ 8 4. Anticline in interbedded argillite and thin-bedded very fine grained calcareous lithic sandstone in the Bay of Pillars Formation..______________ 9 5. Anticline in thick-bedded marble in the Gambler Bay Formation ____________________________ 17 6. Geologic map of the area near Little Hamilton Island____ 31 7. Geologic map of the northwest tip of Hamilton Island-... 32 8. Diagram showing stratigraphic relations of Upper Triassic rocks of the Hyd Group and the Keku Volcanics. _____ 33 9-15. Photographs showing features of the Hound Island Volcanics: 9. Basaltic pillow flQW-----------___-_--_----___ 37 10. Basaltic pillow lava._________________________ 38 11. Basaltic isolated-pillow breccia_-_-_-_____-_____ 39 12. Basaltic broken-pillow breccia _________________ 40 13. Basaltic broken-pillow breccia _________________ 41 14. Aquagene tuff matrix of basaltic broken- pillow breccia_--___________________________ 42 15. Contact between pillow breccia and a limestone inclusion __________________________________ 43 TABLES Page TABLE 1. Age assignments of Upper Triassic fossil collections from the Keku Volcanics_.______________________________________ C28 2. Age assignments of Upper Triassic fossil collections from the Hyd Group___---__-__-_---___-_---__________________ 30 3. Estimated percentages of various rock types in the Hound Island Volcanics _______________________________________ 36 CONTRIBUTIONS TO GENERAL GEOLOGY STRATIGRAPHY OF THE KEKU ISLETS AND NEIGHBORING PARTS OF KUIU AND KUPREANOF ISLANDS, SOUTHEASTERN ALASKA By L. J. PATRICK MUFFLER Bocks ranging in age from Late Silurian to Tertiary are well displayed in shoreline exposures at the north end of Keku Strait between Kuiu and Kupreanof Islands. The section, one of the most nearly complete in southeastern Alaska, is at least 15,000 feet thick, and many units are exceedingly fossiliferous. Upper Silurian rocks crop out extensively on Kuiu Island and include two new formations: the Bay of Pillars Formation, composed of calcareous lithic sandstone, argillite, and limestone, and the Kuiu Limestone, composed primarily of massive limestone that contains sporadic conglomerate and thin-bedded limestone. An unnamed unit of unfossiliferous red arkose is inferred to overlie the Kuiu Limestone and to underlie an unnamed unit of volcanic graywacke and argillite of Late Silurian age. Volcanic breccia, either of Silurian or of Devonian age, crops out in one large fault slice. The Gambier Bay Formation, of Middle (?) Devonian age, is composed of greenstone, greenschist, phyllite, and marble. It crops out on Kupreanof Island but not on Kuiu Island or in the Keku Islets. An unnamed brown fetid limestone of Late Devonian age is exposed at two localities in the Keku Islets, where it is stratigraphically overlain by.an un­ named crinoidal limestone of probable Mississippian age. The Saginaw Bay Formation (new), of Mississippian and Pennsylvanian age, crops out on Kuiu Island and in the Keku Islets. The formation is divided into four informal members: a volcanic member, a black chert member, a chert and limestone member, and a silty limestone member. Permian units comprise the Halleck Formation (new), the Cannery Forma­ tion, and the Pybus Formation (previously described as the Pybus Dolomite on Admiralty Island, 25 miles to the north). The Halleck, which consists of siltstone, sandstone, limestone, conglomerate, and basaltic volcanic rock, is of Early Permian age (probably Leonard) and appears to be restricted to Kuiu Island and the Keku Islets. The Halleck is coeval with the Cannery Forma­ tion, a sequence of volcanic graywacke, volcanic argillite, and chert that crops out on Kupreanof Island and on Admiralty Island but is not found in the Keku Islets or on Kuiu Island. Both formations are overlain by the Pybus Forma­ tion, a prominent cliff-forming unit of white limestone, dolomite, and chert. Cl C2 CONTRIBUTIONS TO GENERAL GEOLOGY The Pybus Formation is overlain unconformably by a sequence of felsic and mafic volcanic rocks, herein named the Keku Volcanics. The unit is restricted to Kuiu Island and is of Late Triassic age, probably early and late Karnian. The Upper Triassic Hyd 'Group, previously described as the Hyd Formation on Admiralty Island, is herein elevated from formational rank and divided into four new formations the Burnt Island Conglomerate, the ornwallis Limestone, the Hamilton Island Limestone, and the Hound Island Volcanics. The Burnt Island Conglomerate is recognized only in the Keku Islets and on Kupreanof Island, where it rests unconformably on either the Cannery Formation or the Pybus Formation. Stratigraphically equivalent 'beds on Kuiu Island are in­ cluded in the uppermost part of the Keku Volcanics and in the lowermost part of the Cornwallis Limestone. The Cornwallis 'Limestone is a medium- to thick- bedded brown-weathering medium-gray oolitic limestone that crops out on Kuiu Island. It is coeval with the Hamilton Island Limestone, a very thin bedded dark-gray to black fetid aphanitic limestone exposed in the Keku Islets and on Kupreanof Island. The Hound Island Volcanics consist of 'basaltic pillow breccia and pillow lava, andesitic volcanic breccia, aquagene tuff, and limestone. Breccia, flow, and aquagene-tuff structures are superbly displayed, and the tuffs locally contain fragments of glass that has not yet 'been devitrified. Forty-seven Upper Triassic (Karnian and Norian) fossil collections from the Keku Islets area make the Hyd Group
Load more

Recommended publications
  • Faults and Joints
    133 JOINTS Joints (also termed extensional fractures) are planes of separation on which no or undetectable shear displacement has taken place. The two walls of the resulting tiny opening typically remain in tight (matching) contact. Joints may result from regional tectonics (i.e. the compressive stresses in front of a mountain belt), folding (due to curvature of bedding), faulting, or internal stress release during uplift or cooling. They often form under high fluid pressure (i.e. low effective stress), perpendicular to the smallest principal stress. The aperture of a joint is the space between its two walls measured perpendicularly to the mean plane. Apertures can be open (resulting in permeability enhancement) or occluded by mineral cement (resulting in permeability reduction). A joint with a large aperture (> few mm) is a fissure. The mechanical layer thickness of the deforming rock controls joint growth. If present in sufficient number, open joints may provide adequate porosity and permeability such that an otherwise impermeable rock may become a productive fractured reservoir. In quarrying, the largest block size depends on joint frequency; abundant fractures are desirable for quarrying crushed rock and gravel. Joint sets and systems Joints are ubiquitous features of rock exposures and often form families of straight to curviplanar fractures typically perpendicular to the layer boundaries in sedimentary rocks. A set is a group of joints with similar orientation and morphology. Several sets usually occur at the same place with no apparent interaction, giving exposures a blocky or fragmented appearance. Two or more sets of joints present together in an exposure compose a joint system.
    [Show full text]
  • Download Article (PDF)
    Open Geosci. 2015; 7:53–64 Research Article Open Access László Molnár*, Balázs Vásárhelyi, Tivadar M. Tóth, and Félix Schubert Integrated petrographic – rock mechanic borecore study from the metamorphic basement of the Pannonian Basin, Hungary Abstract: The integrated evaluation of borecores from the 1 Introduction Mezősas-Furta fractured metamorphic hydrocarbon reser- voir suggests significantly distinct microstructural and Brittle fault zones of crystalline rock masses can serve as rock mechanical features within the analysed fault rock migration pathways or also as sealing surfaces for fluid samples. The statistical evaluation of the clast geometries flow in the Earth’s crust, so the understanding of their in- revealed the dominantly cataclastic nature of the sam- ternal structure is crucial for interpreting hydraulic sys- ples. Damage zone of the fault can be characterised by tems. Earlier studies [1, 2] on the architecture of fault an extremely brittle nature and low uniaxial compressive zones defined two main structural elements: first, a weakly strength, coupled with a predominately coarse fault brec- disaggregated, densely fractured “damage zone” and a cia composition. In contrast, the microstructural manner strongly deformed and fragmented “fault core”, where of the increasing deformation coupled with higher uni- the pre-existing rock fabrics were erased by fault devel- axial compressive strength, strain-hardening nature and opment. These elements can be characterised by the for- low brittleness indicate a transitional interval between mation of diverse tectonite types (fault breccias, catacla- the weakly fragmented damage zone and strongly grinded sites, fault gouges), which often also possess quite hetero- fault core. Moreover, these attributes suggest this unit is geneous rheological features.
    [Show full text]
  • Virgin Islands National Park Geologic Resources Inventory Report
    National Park Service U.S. Department of the Interior Natural Resource Program Center Virgin Islands National Park Geologic Resources Inventory Report Natural Resource Report NPS/NRPC/GRD/NRR—2010/226 THIS PAGE: Underwater ecosystems including coral reefs are a primary natural resource at Virgin Islands National Park. National Park Service photograph. ON THE COVER: This view of Trunk Bay shows the steep slopes characteristic of Virgin Islands Na- tional Park. National Park Service photo- graph courtesy Rafe Boulon (Virgin Islands National Park). Virgin Islands National Park Geologic Resources Inventory Report Natural Resource Report NPS/NRPC/GRD/NRR—2010/226 Geologic Resources Division Natural Resource Program Center P.O. Box 25287 Denver, Colorado 80225 July 2010 U.S. Department of the Interior National Park Service Natural Resource Program Center Fort Collins, Colorado The National Park Service, Natural Resource Program Center publishes a range of reports that address natural resource topics of interest and applicability to a broad audience in the National Park Service and others in natural resource management, including scientists, conservation and environmental constituencies, and the public. The Natural Resource Report Series is used to disseminate high-priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain NPS policy considerations or address sensitive issues of management applicability. All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and designed and published in a professional manner. This report received informal peer review by subject-matter experts who were not directly involved in the collection, analysis, or reporting of the data.
    [Show full text]
  • University Ox Nevada Reno Geology, Geotechnical Properties And
    University ox Nevada - Reno Reno Reno, Key; ;v5 57 geology, Geotechnical Properties and Vesicular Rock Classification of 1onsetown Basalts and Latites, Truckee Area, California A thesis submitted in partial fulfillment ox the requirements for the degree of Master of Science in Geological Engineering far L J Joseph G. Franzone May 1980 HftWttiS U M A I 'f fj'h.i s thesis of Joseph 0. Iran zone is approved: University of Revada. Reno May 19B0 ii ACKNOW LEBGEMENT 3 I am indebted to several people for the assistance and encouragement they gave me dui’ing the preparation of this thesis. Professional advisement of the project and critical reviewing of the manuscript were provided by Sr. Robert J. Watters, Dr. Joseph Lints, Jr. and Dr. Y. S. Kim. Dr. Y. S. Kira graciously made the Rock Mechanics Laboratory and testing equipment available. Dr. Robert J. Watters also allowed unlimited freedom to the Geological Engineering Laboratory equipment and also, along with Dr. Joseph Lintz, Jr., provided invaluable guidance throughout the thesis preparation. Appreciation for help in de-bugging the laboratory equipment goes to my colleague, Ken Krank. Finally, and most importantly, I am indebted to my parents who, whenever I needed them, were always present and supportive. ABSTRACT Geology, physical and engineering properties of the rock units of the lousetown Basalts and Latites in the Trucked Area, California were determined by field and laboratory testing and field ODservations. Of the 16 properties that were calculated for massive samples, 8 were shown to be capable of preuicting i^-e compressive strength and 10 were shown to be capable of predicting the Elastic Modulus.
    [Show full text]
  • Metamorphic Fabrics
    11/30/2015 Geol341 J. Toro Topics • Fabrics • Foliation, cleavage, lineation Metamorphic Rocks and – Cleavage and Folds –Geometry Cleavage Development – Strain significance • Origin of Cleavage – Pressure solution – Passive rotation – Recrystallization • Shear zones Many diagrams are from Earth Structure, van der Pluijm and Marshak, 2004 2013 Geothermal Gradient and Metamorphism Naming of Metamorphic Rocks Slatey cleavage Gneiss Segregation of mafic and felsic components Where does it come from? 1 11/30/2015 Looks like bedding, but is it? Metamorphic layering Brooks Range, AK Quartz-mica schist Isoclinal Fold Transposition of Layering Fabric “Arrangement of component features in a rock” van der Pluijm & Marshak •Includes: •Texture •Composition •Microstructure •Preferred Orientation Horizontal fabric => Vertical fabric 2 11/30/2015 Quartz-mica schist Fabric Elements •Bedding (S0) •Compositional layering •Crystallographic orientation •Fold Hinges •Cleavage planes (S1) •Mineral elongation lineation Passchier and Trouw (1996) Metamorphic Fabrics Metamorphic Fabrics • Foliation : Cleavage, Schistosity • Foliation • Lineation: Mineral Lineation, Intersection Lineation – Cleavage – Schistosity • Lineation Random fabric S-tectonite L-tectonite L/S-tectonite Foliation Lineation S-Tectonites L-Tectonites Schists Columbia Pluton, VA Lineated Gneiss USGS photo U. Western Ontario photo 3 11/30/2015 L-S Tectonites 3D Strain - Flinn diagram No strain along 3rd dimension Cigars S =S >S S1/S2 1 2 3 S1>S2=S3 Lineated and foliated gneiss, Himalayas Prolate
    [Show full text]
  • Fabric Foliation
    2/14/15 Fabric • The characteristics of the geometry and spacing of the elements that make up a rock. – Linear – Planar – Random Foliation • Any fabric-forming planar or curvi-planar structure. • May be primary or tectonic • Many rocks have more than one foliation • Approximate as planes and/or surfaces 1 2/14/15 Cleavage • Describes the tendency of a rock to split along foliation planes • Not the same as cleavage of a single crystal/mineral ! Where well-developed, synonym for foliation. Lineation • Linear elements in a rock • One axis >> other two • Penetrative, surface or geometric Image from your friend Wikipedia 2 2/14/15 Keep thinking about strain ellipse • Foliations form perpendicular to shortening (e3 axis is pole to foliation plane) • Lineations – Elongation – mineral stretching = e1 – Shear lineations – oblique to strain ellipse axes, gives asymmetry/rotation 3 2/14/15 Tectonites • Fabrics in deformed metamorphic rocks are referred to as tectonites L-tectonite 4 2/14/15 S-tectonite Gneissic banding • Gneiss – Early layering is folded – Flattened limbs are parallel • Transposed foliation 5 2/14/15 Mylonites • Contain a “mylonitic foliation” formed by crystal plastic deformation in a shear zone (pure or simple) • Transposed layering • Shear zone fault rocks Describing cleavage 6 2/14/15 Metamorphosis of a pelite • Slaty cleavage – Preferential dissolution of some minerals – Perpendicular to shortening • Minerals line up • Becomes more continuous as it 1mm develops Crenulation = 2nd foliation folds first 7 2/14/15 Crenulation Cleavage
    [Show full text]
  • Columnar Joints
    Columnar Joints The formation of regular shapes by natural processes makes some of the world's most intriguing wonders. The presence of long, mostly six-sided columns (called columnar joints) in cooled lavas is one of those wonders. No one who has seen the awesome grooved structure in Devil's Tower in Wyoming or the Devil's Post Pile in California, can forgot this feature. What about a cooling mass of magma could cause such symmetrical columnar joints? A similar phenomenon can be seen when a mud puddle dries. As it loses water, the mud cracks in symmetric shapes, forming mud polygons. This is because the lose of water causes the mud to shrink. That contraction is relieved by breaking as the dry mud becomes brittle. When things contract like this, they naturally seek the most stable position, For mud, that is a system of natural polygons, separated by vertical cracks. Basalt and other lavas behave similarly. As lava cools, it doesn't dry out like mud, but it does shrink. As it becomes cold and brittle, the lava contracts and relieves the stress by cracking. The cracking produces a polygonal pattern that extends through the lava flow. As weathering cuts into lava, the rock breaks along the joints, exposing this geometric regularity. Although many of the polygons are six- sided, four, five, seven or eight sides columns are also relatively common. The degree and perfection to which this is developed depends on the thickness and composition of the lava and how fast it cools. The long sides of the column form parallel to the direction of heat loss as the lava cools.
    [Show full text]
  • Iceland and the People There, in Particular Ditta, Helga and the Landmannalaugar Crew for Looking After Me and Taking Us in During a Storm and Feeding Us Cake
    Open Research Online The Open University’s repository of research publications and other research outputs Cooling Fractures in Lavas: Mechanisms and Environments of Formation Thesis How to cite: Forbes, Anne (2013). Cooling Fractures in Lavas: Mechanisms and Environments of Formation. PhD thesis The Open University. For guidance on citations see FAQs. c 2013 The Author https://creativecommons.org/licenses/by-nc-nd/4.0/ Version: Version of Record Link(s) to article on publisher’s website: http://dx.doi.org/doi:10.21954/ou.ro.0000f113 Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online’s data policy on reuse of materials please consult the policies page. oro.open.ac.uk U N P>€ ST Rl CT&D Cooling fractures in lavas: mechanisms and environments of formation A thesis submitted for the degree of Doctor of Philosophy in the Earth Sciences By Anne Forbes BA, MSci (Cantab) Department of Environment, Earth and Ecosystems, The Open University December 2012 D ate ol- (S'abr^A'Ssvon; 21 [)2(£n\b£f 2d Date oj l\warcte 3l Jutej 2.o# ProQuest Number: 13835945 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a com plete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest ProQuest 13835945 Published by ProQuest LLC(2019).
    [Show full text]
  • Magmatic and Tectonic Continuous Casting in the Circum-Pacific Region Jon E
    Arizona Geological Society Digest 22 2008 Magmatic and tectonic continuous casting in the circum-Pacific region Jon E. Spencer Arizona Geological Survey, 416 W. Congress St., #100, Tucson, Arizona, 85701, USA Yasuhiko Ohara Hydrographic and Oceanographic Department of Japan, Tokyo, 104-0045, Japan, and Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Kanagawa 237-0061, Japan ABSTRACT Continuous casting is an industrial process for producing metal in continuous linear form. Cooling of the cast medium occurs across a slip surface in this process. The same process was active in geologic settings in which lava extrusion was accompanied by formation of striations on the surface of the extrusion. Such grooves resulted from irregularities on colder and harder rock that formed the confining orifice from which the grooved lava was extruded. In a variant of this process, lavas that emerged from beneath deep-sea lava-lake crusts were striated on their upper surfaces as they emerged. In the case of the grooved extrusion at Sacsayhuamán, Perú, lateral displacement of rock overlying a very shallow intrusion may have caused striations to form on the underlying intrusion as it was exhumed. Deep-sea metamorphic core complexes are known primarily by their corrugated upper sur- faces as identified with multibeam sonar. Recovered samples, including from drilling, typically include gabbro and basalt, indicating that magmatism was a major process in construction of the corrugated normal-fault footwall. The 125-km-long Godzilla Mullion in the Parece Vela Basin of the Philippine Sea, which is the largest known metamorphic core complex on Earth, includes a single antiformal groove 60 km long and 5 km wide.
    [Show full text]
  • Kinematic and Tectonic Significance of Microstructures And
    Transactions of the Royal Society of Edinburgh: Earth Sciences, 77, 99-125. 1986 Kinematic and tectonic significance of microstructures and crystallographic fabrics within quartz mylonites from the Assynt and Eriboll regions of the Moine thrust zone, NW Scotland R. D. Law, M. Casey and R. J. Knipe ABSTRACT: Using a combination of optical microscopy and X-ray texture goniometry, an integrated microstructural and crystallographic fabric study has been made of quartz mylonites from thrust sheets located beneath, but immediately adjacent to, the Moine thrust in the Assynt and Eriboll regions of NW Scotland. A correlation is established between shape fabric symmetry and pattern of crystallographic preferred orientation, a particularly clear relationship being observed between shape fabric variation and quartz a-axis fabrics. Coaxial strain paths dominate the internal parts of the thrust sheets and are indicated by quartz c- and a-axis fabrics which are symmetrical with respect to foliation and lineation. Non-coaxial strain paths are indicated within the more intensely deformed quartzites located near the boundaries of the sheets by asymmetrical c- and c-axis fabrics. These kinematic interpretations are supported by microstructural studies. At the Stack of Glencoul in the northern part of the Assynt region, the transition zone between these kinematic (strain path) domains is located at approximately 20 cm beneath the Moine thrust and is marked by a progression from symmetrical cross-girdle c-axis fabrics (30cm beneath the thrust), through asymmetrical cross-girdle c-axis fabrics to asymmetrical single girdle c-axis fabrics (0-5 cm beneath the thrust). Tectonic models (incorporating processes such as extensional flow, gravity spreading and tectonic loading) which may account for the presence of strain path domains within the thrust sheets are considered, and their compatibility with local thrust sheet geometries assessed.
    [Show full text]
  • Mineralogical Evidence for Partial Melting and Melt-Rock Interaction Processes in the Mantle Peridotites of Edessa Ophiolite (North Greece)
    minerals Article Mineralogical Evidence for Partial Melting and Melt-Rock Interaction Processes in the Mantle Peridotites of Edessa Ophiolite (North Greece) Aikaterini Rogkala 1,* , Petros Petrounias 1 , Basilios Tsikouras 2 , Panagiota P. Giannakopoulou 1 and Konstantin Hatzipanagiotou 1 1 Section of Earth Materials, Department of Geology, University of Patras, 265 04 Patras, Greece; [email protected] (P.P.); [email protected] (P.P.G.); [email protected] (K.H.) 2 Physical and Geological Sciences, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, Gadong BE1410, Bandar Seri Begawan, Brunei Darussalam; [email protected] * Correspondence: [email protected]; Tel.: +30-2610996288 Received: 10 December 2018; Accepted: 14 February 2019; Published: 17 February 2019 Abstract: The Edessa ophiolite complex of northern Greece consists of remnants of oceanic lithosphere emplaced during the Upper Jurassic-Lower Cretaceous onto the Palaeozoic-Mesozoic continental margin of Eurasia. This study presents new data on mineral compositions of mantle peridotites from this ophiolite, especially serpentinised harzburgite and minor lherzolite. Lherzolite formed by low to moderate degrees of partial melting and subsequent melt-rock reaction in an oceanic spreading setting. On the other hand, refractory harzburgite formed by high degrees of partial melting in a supra-subduction zone (SSZ) setting. These SSZ mantle peridotites contain Cr-rich spinel residual after partial melting of more fertile (abyssal) lherzolite with Al-rich spinel. Chromite with Cr# > 60 in harzburgite resulted from chemical modification of residual Cr-spinel and, along with the presence of euhedral chromite, is indicative of late melt-peridotite interaction in the mantle wedge. Mineral compositions suggest that the Edessa oceanic mantle evolved from a typical mid-ocean ridge (MOR) oceanic basin to the mantle wedge of a SSZ.
    [Show full text]
  • Columnar Jointing on Mars: Earth Analog Studies M
    43rd Lunar and Planetary Science Conference (2012) 2726.pdf Columnar Jointing on Mars: Earth Analog Studies M. P. Milazzo?, D. K. Weiss, B. Jackson, J. Barnes, ?U.S. Geological Survey, Astrogeology Science Center, 2255 N. Gemini Dr., Flagstaff, AZ, 86001 ([email protected]) Introduction The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) discovered multi-tiered columnar jointing on Mars [1] (Fig. 1). Since the initial discovery image, more columns, some with entablature, have been observed at multiple sites [2] on Mars. Nearly all of these sites oc- cur in the uplifted walls of impact craters in regions with histories of flood volcanism. The local geologic history leads to the suggestion that these are columnar basalts [1]. Extension of the modeling of terrestrial colum- nar lavas by [3] and [4] to the martian columnar joints and entablature discussed in [1] (and seen in observation PSP 006985 2020; Fig. 1) suggests that the lavas cooled, in the presence of water, over a period of approximately 2 to 14 years, depending on the details of joint formation. Figure 1: Columns seen in the wall of the impact crater at the discovery site, in Marte Vallis between Elysium and Role of Water in the Formation of Terres- Amazonis plana. Observation ID: PSP 006985 2020 trial Columnar Lavas [3] and [4] found that in terrestrial columnar lavas a ma- jor factor controlling the width of columns (entablature 40.0 or colonnade) is the cooling rate of the layer of plas- 35.0 tic lava just beneath (for a horizontally-oriented cooling front) the solidified lava.
    [Show full text]