DOCSLIB.ORG

Exhumation Processes: Normal Faulting, Ductile Flow, and Erosion

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exhumation Processes: Normal Faulting, Ductile Flow, and Erosion Penrose Conference Report some role. Penetrative deformational fab­ rics are present in most exhumed moun­ tain belts and provide clear evidence that Exhumation Processes: Normal Faulting, ductile flow is an important process that can either increase or decrease the rate of Ductile Flow, and Erosion exhumation, depending upon whether Conveners: the flow causes thinning or thickening in Mark T. Brandon, Department of Geology and Geophysics, Yale University, P.O. Box the vertical direction. Erosion is also an 208109, NewHaven, CT 06520-8109; [email protected] important exhumational process, as indi­ Uwe Ring, Institut fiir Geowissenschaften, Johannes Gutenberg-Universitiit, Postfach 3980, cated by the large volumes of sediment 55099 Mainz, Germany; [email protected] found adjacent to most contractional orogens. Within this context, we organized a Penrose Conference to examine all pro­ Over the past 25 years, there has One of the most difficult questions to cesses that contribute to exhumation of been a growing appreciation of the role answer in most orogenic belts, especially deep-seated rocks in ancient and modern that tectonic processes play in exhuming the older ones, concerns the relative con­ orogens. We started with three broad metamorphic rocks. This trend began with tributions of these different exhumation objectives: (1) to review and synthesize the discovery of highly attenuated crustal processes. Even so, the tectonics commu­ our knowledge about normal faulting, sections in the Basin and Range province nity has moved toward a casual consensus ductile flow, and erosion as exhumation and the recognition that attenuation was that normal faulting is the primary mech­ processes; (2) to examine the geologic caused by regional-scale horizontal exten­ anism for exhumation of deeply seated evidence needed to quantify the relative sion, as manifested by normal faulting. rocks. The most commonly cited evidence contributions of these different processes, This discovery caused many geoscientists is the presence of "younger-over-older" using information from metamorphic to rethink the role that horizontal exten­ relationships, where large faults, with low petrology, isotopic thermochronology, sion or, as it is more commonly called, to moderate dips, have placed younger structural and kinematic analysis, synoro­ tectonic extension, might play in other rocks on older rocks or lower grade rocks genic stratigraphy, geomorphology, and orogenic settings. Of particular interest is on higher grade rocks and, in the process, paleoelevation analysis; and (3) to exam­ emerging evidence that tectonic extension have cut out significant thicknesses of ine relevant geodynamic models and their might be responsible for exhuming meta­ stratigraphic or metamorphic section. But predictions for conditions that might trig­ morphic rocks within convergent orogens, recent papers have shown that this type of ger gravitational collapse. such as onland thrust belts (e.g., Hima­ evidence, by itself, is not diagnostic. Con­ layas, European Alps, Betic Cordillera of tractional faults can also cut out section if THE CONFERENCE southern Spain, Brooks Range of Alaska) the section was tilted back toward the hin­ Theconference was held October 9-13, and subduction-related convergent mar­ terland prior to faulting. A typical contrac­ 1996, at the Orthodox Academy of Greece, gins (e.g., Franciscan of California, Sanba­ tional fault would climb upward toward located near the town of Chania on the gawa of Japan, Hellenic-Aegean conver­ the foreland but would appear to cut · island of Crete in southern Greece. It gent margin of Greece, Hikurangi downward through the tilted section. included three days of presentations accretionary wedge of northeastern Top-to-the-foreland motion would pro­ and two days of field trips. There were 94 New Zealand). duce the appearance of normal offset participants, 42 from the United States, We use the term "exhumation" to where the fault cut through the tilted 15 from England, 13 from Germany, five refer, in a generic way, to all processes section. An additional problem is that from Australia, four each from Greece and that contribute to the unroofing of deeply the total offset and original dip of most Canada, three from Switzerland, and one seated rocks and their rise to the Earth's crustal-scale normal faults, especially those each from France, Israel, Japan, The surface. There are several exhumation pro­ involving deep crustal rocks, are typically Netherlands, New Zealand, Norway, cesses. Normal faulting and extensional poorly resolved. All of these factors make Poland, South Africa, and Spain. The par­ ductile flow operate within the Earth it difficult to quantify the relative contri­ ticipants included 16 Ph.D. students. The and are a direct manifestation of tectonic bution of normal faulting in exhuming conference had a relatively large number deformation, whereas erosion operates at deeply seated rocks. of women participants, 13 professionals the Earth's surface but can be indirectly Despite the current preference for and 9 students, marking a positive trend influenced by tectonically driven changes exhumation by normal faulting, it is clear in topography. that ductile flow and erosion must play Penrose Conference continued on p. 18 PARTICIPANTS Torgeir B. Andersen Jean Crespi Herman Griitter Karen L. Kleinspehn Alan Roberts Stuart Thomson Vaios Avdis George H. Davis Larry Guenther Maarten Krabbendam David Rowley Robert J. Twiss Hans G. John F. Dewey Bradley Hacker Anthi Liati Leigh Royden 0. Vanderhaeghe Ave Lallemant Bill Dinklage Bernard Hallet Gordon S. Lister Elizabeth Schermer Jaume Verges Dov Avigad David Dinter Andreas Henk Lidia Lonergan Fried M. Schwerdtner Lisa A. Verts Gary Axen Theodor Doutsos Ralf Hetzel Neil Mancktelow Jane Selverstone Simon Wallis Suzanne Baldwin W. Gary Ernst Paul Hoffman Stanislaw Mazur Dianne Seward Nicole Wawrzenitz Samantha Barr Hilmar von Eynatten Daniel K. Holm Peter Molnar Eberhard Seidel Laura E. Webb Manfred Brix James Faulds Niels Hovius Patrick O'Brien Sarah Sherlock John Weber Fraukje Brouwer Paul Fitzgerald Simon Inger John S. Oldow Virginia B. Sisson John Wheeler Doug Burbank Marnie Forster Carl Jacobson John P. Platt Colin Stark Donna L. Whitney B. Clark Burchfiel David Foster Rebecca A. Jamieson Raymond A. Price Bernhard Stockhert Sean D. Willett Erin Campbell Wolfgang Franke Barbara E. John Meinert K. Rahn John Tarney Paul F. Williams Christian Chopin Wolfgang Frisch Christopher Johnson Tim Rawling Micheal P. Terry Brian Windley Peter Copeland Dieter Gebauer Sue Keay Steve Reddy Christian Teyssier Meg Coleman Allen F. Glazner Adiamantis Kilias Stephen J. Reynolds GSA TODAY, May 1997 17 Penrose Conference continuedfrom p. 17 exhumation probably operates at very found in the Alps and the Norwegian slow rates. Other evidence is needed to Caledonides, and now known from in the reduction of the gender gap, at least distinguish between tectonic and ero­ numerous places around the world. UHP in the area of exhumation research. sional exhumation. metamorphic rocks are continental or Presentations were divided into six John Platt followed with a keynote oceanic crustal rocks that were metamor­ half-day sessions. Each session had about presentation on synexhumation defor­ phosed within the coesite-eclogite or dia­ two hours of oral presentations, about mation in mountain belts. He reviewed mond-eclogite fades. P-T-t data for these one hour of poster presentations, and geologic evidence for detecting tectonic rocks demonstrate that both oceanic and about one hour for a panel discussion. exhumation, the main clues being the continental crust can be subducted to This report highlights the oral presenta­ excision of metamorphic gradients, the depths >100 km and then returned to the tions and panel discussions. Those who shape of pressure-temperature-time (P-T-t) surface. are interested in further details will find paths, and the kinematics of ductile shear The keynote presentation by Chris­ a complete listing of the conference pro­ zones and brittle faults. tian Chopin provided a general review of gram, including the titles of all presenta­ Jane Selverstone challenged the use the UHP problem. Simon Wallis described tions, at the following Web site: http:// of P-T-t paths to distinguish exhumational some UHP rocks from China and then love.geology.yale.edu/-brandon/exhume. processes. The shape of a P-T-t path is typi­ explored the role that buoyancy might html. cally difficult to resolve, and the youngest play in returning these rocks to the sur­ part of the path, which is most diagnostic face. Paddy O'Brien discussed attempts FIELD TRIPS of process, is the most difficult to con­ to determine the P-T-t path for HP meta­ The field trips were led by Bernard strain. She emphasized her point by show­ morphic rocks in the Bohemian massif Stockhert (Ruhr-Universitat Bochum, ing two sets of published P-T-t paths, one of Germany. Germany) and Eberhard Seidel (Univer­ set attributed to erosion and the other to Dieter Gebauer reviewed his applica­ sitat zu Koln, Germany), and focused on tectonic exhumation. There was no obvi­ tion of SHRIMP U-Pb dating to determine geologic evidence for Miocene exhuma­ ous difference between the sets. The infer­ ages of igneous and metamorphic growth tion in a convergent-margin setting. ence is that steep decompression curves of zircons from HP and UHP metamorphic The island of Crete is.a forearc high that should not be considered diagnostic of rocks of the Alps. His work indicates an formed above the south-facing Hellenic extensional exhumation. Eocene age for metamorphism which subduction zone. The island has spectacu­ Clark Burchfiel reviewed the develop­ would require exhumation rates of -10 to lar exposures of high-pressure-low-tem­ ment of the South Tibetan detachment 30 mm/yr for some of the Pennine nappe. perature (HP) metamorphic rocks that system, a north-dipping system of faults A major problem, however, is that, as of formed at depths of -35 km and were and ductile shear zones with top-north yet, there is no direct tie between exhumed rapidly, starting in the Miocene.
Load more

Recommended publications
  • Exhumation of a Collisional Orogen: a Perspective from the North American Grenville Province
    Geological Society of America Memoir 197 2004 Exhumation of a collisional orogen: A perspective from the North American Grenville Province Margaret M. Streepey* Department of Geological Sciences, Florida State University, Tallahassee, Florida 32306-4100, USA Carolina Lithgow-Bertelloni Ben A. van der Pluijm Eric J. Essene Department of Geological Science, University of Michigan, Ann Arbor, Michigan 48109-1063, USA Jerry F. Magloughlin Department of Earth Resources, Colorado State University, Fort Collins, Colorado 80523-1482, USA ABSTRACT Combined structural and geochronologic research in the southernmost portion of the contiguous Grenville Province of North America (Ontario and New York State) show protracted periods of extension after the last episode of contraction. The Grenville Province in this area is characterized by synorogenic extension at ca. 1040 Ma, supported by U-Pb data on titanites and 40Ar-39Ar data on hornblendes, followed by regional extension occurring along crustal-scale shear zones between 945 and 780 Ma, as recorded by 40Ar-39Ar analysis of hornblende, biotite, and K-feldspar. By ca. 780 Ma the southern portion of the Grenville Province, from Ontario to the Adiron- dack Highlands, underwent uplift as a uniform block. Tectonic hypotheses have invoked various driving mechanisms to explain the transition from compression to extension; however, such explanations are thus far geodynamically unconstrained. Numerical models indicate that mechanisms such as gravitational collapse and man- tle delamination act over timescales that cannot explain a protracted 300 m.y. exten- sional history that is contemporaneous with ongoing uplift of the Grenville Province. Rather, the presence of a plume upwelling underneath the Laurentian margin, com- bined with changes in regional stress directions, permitted the observed uplift and extension in the Grenville Province during this time.
    [Show full text]
  • Exhumation Processes
    Exhumation processes UWE RING1, MARK T. BRANDON2, SEAN D. WILLETT3 & GORDON S. LISTER4 1Institut fur Geowissenschaften,Johannes Gutenberg-Universitiit,55099 Mainz, Germany 2Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA 3Department of Geosciences, Pennsylvania State University, University Park, PA I 6802, USA Present address: Department of Geological Sciences, University of Washington, Seattle, WA 98125, USA 4Department of Earth Sciences, Monash University, Clayton, Victoria VIC 3168,Australia Abstract: Deep-seated metamorphic rocks are commonly found in the interior of many divergent and convergent orogens. Plate tectonics can account for high-pressure meta­ morphism by subduction and crustal thickening, but the return of these metamorphosed crustal rocks back to the surface is a more complicated problem. In particular, we seek to know how various processes, such as normal faulting, ductile thinning, and erosion, con­ tribute to the exhumation of metamorphic rocks, and what evidence can be used to distin­ guish between these different exhumation processes. In this paper, we provide a selective overview of the issues associated with the exhuma­ tion problem. We start with a discussion of the terms exhumation, denudation and erosion, and follow with a summary of relevant tectonic parameters. Then, we review the charac­ teristics of exhumation in differenttectonic settings. For instance, continental rifts, such as the severely extended Basin-and-Range province, appear to exhume only middle and upper crustal rocks, whereas continental collision zones expose rocks from 125 km and greater. Mantle rocks are locally exhumed in oceanic rifts and transform zones, probably due to the relatively thin crust associated with oceanic lithosphere.
    [Show full text]
  • Late-Stage Tectonic Evolution of the Al-Hajar Mountains
    Geological Magazine Late-stage tectonic evolution of the www.cambridge.org/geo Al-Hajar Mountains, Oman: new constraints from Palaeogene sedimentary units and low-temperature thermochronometry Original Article 1,2 3 4 3 4 5 Cite this article: Corradetti A, Spina V, A Corradetti , V Spina , S Tavani , JC Ringenbach , M Sabbatino , P Razin , Tavani S, Ringenbach JC, Sabbatino M, Razin P, O Laurent6, S Brichau7 and S Mazzoli1 Laurent O, Brichau S, and Mazzoli S (2020) Late-stage tectonic evolution of the Al-Hajar 1 Mountains, Oman: new constraints from School of Science and Technology, Geology Division, University of Camerino. Via Gentile III da Varano, 62032 2 Palaeogene sedimentary units and low- Camerino (MC), Italy; Department of Petroleum Engineering, Texas A&M University at Qatar, Doha, Qatar; temperature thermochronometry. Geological 3Total E&P, CSTJF, Avenue Larribau, 64000 Pau, France; 4DiSTAR, Università di Napoli Federico II, 21 Via vicinale Magazine 157: 1031–1044. https://doi.org/ cupa Cintia, 80126 Napoli, Italy; 5ENSEGID, Institut Polytechnique de Bordeaux, 1 allée Daguin, 33607 Pessac, 10.1017/S0016756819001250 France; 6Total E&P, Paris, France and 7Géosciences Environnement Toulouse (GET), Université de Toulouse, UPS, CNRS, IRD, CNES, 14 avenue E. Belin, 31400, Toulouse, France Received: 8 July 2019 Revised: 5 September 2019 Accepted: 15 September 2019 Abstract First published online: 12 December 2019 Mountain building in the Al-Hajar Mountains (NE Oman) occurred during two major short- – Keywords: ening stages, related to the convergence between Africa Arabia and Eurasia, separated by nearly Oman FTB; Cenozoic deformation; remote 30 Ma of tectonic quiescence. Most of the shortening was accommodated during the Late sensing; thermochronology Cretaceous, when northward subduction of the Neo-Tethys Ocean was followed by the ophio- lites obduction on top of the former Mesozoic margin.
    [Show full text]
  • Kinematic Interpretation of the 3D Shapes of Metamorphic Core Complexes Laetitia Le Pourhiet, Benjamin Huet, Dave May, Loic Labrousse, Laurent Jolivet
    Kinematic interpretation of the 3D shapes of metamorphic core complexes Laetitia Le Pourhiet, Benjamin Huet, Dave May, Loic Labrousse, Laurent Jolivet To cite this version: Laetitia Le Pourhiet, Benjamin Huet, Dave May, Loic Labrousse, Laurent Jolivet. Kinematic inter- pretation of the 3D shapes of metamorphic core complexes. Geochemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2012, 13 (9), pp.1-17. 10.1029/2012GC004271. hal-00730919 HAL Id: hal-00730919 https://hal.archives-ouvertes.fr/hal-00730919 Submitted on 17 Sep 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. 1 1 Kinematic interpretation of the 3D shapes of metamorphic core 2 complexes 3 Submitted to G-cubed 4 Authors: 1,2 5 Laetitia Le Pourhiet 3 6 Benjamin Huet 4 7 Dave A. May 1,2 8 Loic Labrousse 5 9 Laurent Jolivet 10 Affiliations: 11 1 UPMC Univ Paris 06, UMR 7193, ISTEP, F-75005, Paris, France. 12 2 CNRS, UMR 7193, ISTEP, F-75005, Paris, France 13 3 Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14 A- 14 1090 Vienna 15 4 Institute of Geophysics, Department of Earth Sciences, ETH Zurich, Switzerland 16 5 ISTO, Université d’Orléans-CNRS, UMR 6113, F-45071 Orléans, France 17 2 18 19 Abstract 20 Metamorphic Core Complexes form dome shaped structures in which the ductile 21 crust is exhumed beneath a detachment fault.
    [Show full text]
  • Exhumation Processes in Oceanic and Continental Subduction Contexts: a Review
    Exhumation Processes in Oceanic and Continental Subduction Contexts: A Review Stéphane Guillot, Keiko Hattori, Philippe Agard, Stéphane Schwartz and Olivier Vidal Abstract Although the exhumation of high pressure (HP) and ultrahigh pressure (UHP) rocks is an integral process in subduction, it is a transient process, likely taking place during the perturbation in subduction zones. Exhumation of HP to UHP rocks requires the weakening of a subduction channel and the decoupling of the exhumed slice from the rest of the slab. Considering more than 60 occurrences of HP to UHP units of Phanerozic ages, we propose three major types of subduction zones: Accretionary-type subduction zones exhume HP metasedimentary rocks by under- plating. The exhumation is slow and can be long-lasting. The serpentinite-type subduction zones exhume HP to UHP in a 1 to 10 km thick serpentinite subduction channel. The serpentinite matrix originates from both subducted abyssal peridotites and hydated mantle wedge. Exhumation velocity is low to intermediate and the exhumation is driven by the buoyancy and the low-viscosity of the serpentinite. The continental-type subductions exhume UHP rocks of continental origin. The UHP rocks together with garnet-bearing peridotites form units from km-scale unit. The exhumation is fast, short-lived and occurs at the transition from oceanic subduc- tion to continental subduction. It is driven by buoyancy forces and asthenospheric return fl ow. Keywords Oceanic subduction · Continental subduction · Exhumation · HP to UHP rocks · Subduction channel 1 Introduction occurrences of pelitic rocks metamorphosed under eclogite facies conditions suggest that these rocks were subducted to great depths before exhumed (Compagnoni Eclogites, HP-LT metamorphic rocks, have been and Maeffo, 1973; Carswell, 1990).
    [Show full text]
  • Buoyancy-Driven, Rapid Exhumation of Ultrahigh-Pressure Metamorphosed Continental Crust
    Proc. Natl. Acad. Sci. USA Vol. 94, pp. 9532–9537, September 1997 Geology Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust W. G. ERNST*, S. MARUYAMA†, AND S. WALLIS‡ *Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115; †Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152, Japan; and ‡Department of Geology and Mineralogy, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan Contributed by W. G. Ernst, June 24, 1997 ABSTRACT Preservation of ultrahigh-pressure (UHP) coupled to the descending lithosphere, continental indentation minerals formed at depths of 90–125 km require unusual would occur instead (7). conditions. Our subduction model involves underflow of a For the UHP case discussed here involving well-bonded salient (250 6 150 km wide, 90–125 km long) of continental crust plus mantle, entrance of increasing amounts of sialic crust embedded in cold, largely oceanic crust-capped litho- material into the subduction zone enhances the braking effect sphere; loss of leading portions of the high-density oceanic of buoyancy; this in turn results in loss of the high-density lithosphere by slab break-off, as increasing volumes of mi- lithospheric anchor leading the downgoing plate at interme- crocontinental material enter the subduction zone; buoyancy- diate upper mantle depths where the sinking lithosphere is in driven return toward midcrustal levels of a thin (2–15 km extension (8). Slab break-off (9, 10) enhances buoyancy fur- thick), low-density slice; finally, uplift, backfolding, normal ther, and causes the sialic prong—or at least a slice thereof—to faulting, and exposure of the UHP terrane.
    [Show full text]
  • RESEARCH Testing Modes of Exhumation in Collisional Orogens: Synconvergent Channel Flow in the Southeastern Canadian Cordillera
    RESEARCH Testing modes of exhumation in collisional orogens: Synconvergent channel fl ow in the southeastern Canadian Cordillera Félix Gervais* and Richard L. Brown DEPARTMENT OF EARTH SCIENCES, CARLETON UNIVERSITY, 2125 HERZBERG BUILDING, 1125 COLONEL BY DRIVE, OTTAWA, ONTARIO K1S 5B6, CANADA ABSTRACT This study investigates exhumation processes in collisional orogens. A critical test between three modes of exhumation is presented based on a review of quantitative numerical and analogue modeling studies. The test is applied to the large tract of migmatites surrounding the Monashee Complex in the southeastern Canadian Cordillera. It reveals that the extensive and multidisciplinary database of this region is entirely compatible with the synconvergent channel-fl ow mode but not with critical wedge and gravitational collapse modes. We propose that a partially molten channel decoupled from its lid and base and started to fl ow in the middle crust toward the foreland at 100–90 Ma. A steady-state channel-fl ow system was established for the following ~30 m.y., during which rocks at the front of the channel were exhumed to upper-crustal levels as they fl owed above an underthrusting basement ramp. Flow was accommodated by oppositely verging shear zones bounding the channel, by internal ductile deformation, and by shortening in the foreland belt. The locus of fl ow migrated downward to exhume rocks of the Monashee Complex between 60 and 50 Ma by a similar process. The southeastern Canadian Cordillera thus constitutes an excellent natural analogue for the channel-fl ow model. In contrast to the commonly held view of large-magnitude extension and core complex formation, the role of extension was limited to the fi nal ~10–15 km of exhumation after 50 Ma.
    [Show full text]
  • Tracking the Oman Ophiolite to the Surface — New Fission Track and (U
    Tectonophysics 644–645 (2015) 68–80 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Tracking the Oman Ophiolite to the surface — New fission track and (U–Th)/He data from the Aswad and Khor Fakkan Blocks, United Arab Emirates Joachim Jacobs a,b,⁎,RobertJ.Thomasc,1, Anna K. Ksienzyk a,IstvánDunkld a University of Bergen, Department of Earth Science, P.O. Box 7803, N-5020 Bergen, Norway b Norwegian Polar Institute, Fram Centre, N-9296 Tromsø, Norway c British Geological Survey, Nicker Hill, Keyworth, Nottingham NG12 5GG, UK d Geoscience Centre, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany article info abstract Article history: The Oman Ophiolite in the United Arab Emirates (UAE) was formed in a supra-subduction zone environment at Received 30 August 2014 about 95 Ma and was almost immediately obducted onto the eastern margin of Arabia. The timing of obduction is Received in revised form 15 November 2014 well constrained, but the post-obduction tectonic, uplift and exhumation history of the ophiolite and associated Accepted 28 December 2014 rocks are less well understood. We present twenty-one new fission track and (U–Th)/He analyses of apatite and Available online 14 January 2015 zircon from the Hajar Mountains. The data show that the Oman Ophiolite had a complex exhumation history to present exposure levels in the Khor Fakkan and Aswad Blocks, resulting from at least three distinct exhumation Keywords: Oman Ophiolite events: 1) initial ophiolite obduction between ca. 93 and 83 Ma is characterised by tectonic exhumation and rapid Thermochronology cooling, as revealed by zircon (U–Th)/He and apatite fission-track data, but it is not associated with major ero- Exhumation sional exhumation; 2) data from the lower part of the ophiolite and the metamorphic sole document a second Zagros orogeny exhumation event at ca.
    [Show full text]
  • Absolute Ages of Multiple Generations of Brittle Structures by U-Pb Dating of Calcite
    Absolute ages of multiple generations of brittle structures by U-Pb dating of calcite Reuben J. Hansman1, Richard Albert2, Axel Gerdes2, and Uwe Ring1 1Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden 2Department of Geosciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany ABSTRACT al., 2013). Hematite (U-Th)/He dating from fault zones is another tech- Direct dating of brittle structures is challenging, especially abso- nique used to date thermal anomalies generated by fault slip (Ault et al., lute dating of diagenesis followed by a series of superimposed brittle 2015), although the high temperatures needed to reset the hematite He deformation events. We report 22 calcite U-Pb ages from tectonites system during faulting may not commonly occur at shallow crustal depths. and carbonate host rocks that date 3 diagenetic and 6 brittle deforma- U-Pb dating of calcite fibers has only recently been used for dating tion events. Results show that U-Pb dating of calcite fibers from these brittle faulting (Roberts and Walker, 2016; Ring and Gerdes, 2016; Nuriel structures is compatible with overprinting relationships. Ages indicate et al., 2017). This method is suitable for carbonates and other rocks that that diagenesis occurred between 147 ± 6 Ma and 103 ± 34 Ma, and contain calcite veins and fibers and is not fraught with closure temperature was followed by top-to-the-south, layer-parallel shearing due to ophio- issues, but is technically challenging because of low U concentrations lite obduction at 84 ± 5 Ma (2σ errors). Sheared top-to-the-northeast, (<10 ppm). The few applications of U-Pb dating of calcite fibers have layer-parallel veins were dated as 64 ± 4 Ma and are interpreted to only focused on the direct dating of a single deformation phase and not have developed during postobduction exhumation.
    [Show full text]
  • Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones: an Introduction
    Downloaded from http://sp.lyellcollection.org/ by guest on October 5, 2021 Channel flow, ductile extrusion and exhumation in continental collision zones: an introduction L. GODIN 1, D. GRUJIC 2, R. D. LAW 3 & M. P. SEARLE 4 1Department of Geological Sciences & Geological Engineering, Queen's University, Kingston, Ontario, K7L 3N6, Canada (e-mail: [email protected]) 2Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, B3H 4J1, Canada 3Department of Geological Sciences, Virginia Tech., Blacksburg, VA 24061, USA 4Department of Earth Sciences, Oxford University, Oxford, OX1 3PR, UK Abstract: The channel flow model aims to explain features common to metamorphic hinterlands of some collisional orogens, notably along the Himalaya-Tibet system. Channel flow describes a protracted flow of a weak, viscous crustal layer between relatively rigid yet deformable bounding crustal slabs. Once a critical low viscosity is attained (due to partial melting), the weak layer flows laterally due to a horizontal gradient in lithostatic pressure. In the Himalaya-Tibet system, this lithostatic pressure gradient is created by the high crustal thicknesses beneath the Tibetan Plateau and 'normal' crustal thickness in the foreland. Focused denudation can result in exhuma- tion of the channel material within a narrow, nearly symmetric zone. If channel flow is operating at the same time as focused denudation, this can result in extrusion of the mid-crust between an upper normal-sense boundary and a lower thrust-sense boundary. The bounding shear zones of the extruding channel may have opposite shear sense; the sole shear zone is always a thrust, while the roof shear zone may display normal or ttuqast sense, depending on the relative velocity between the upper crust and the underlying extruding material.
    [Show full text]
  • Late-Stage Exhumation of Metamorphic Core Complexes and Landscape Development During Orogenic Collapse of the North American
    LATE-STAGE EXHUMATION OF METAMORPHIC CORE COMPLEXES AND LANDSCAPE DEVELOPMENT DURING OROGENIC COLLAPSE OF THE NORTH AMERICAN CORDILLERA A DISSERTATION SUBMITTED TO THE FACULTY OF GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY ERKAN TORAMAN IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY CHRISTIAN TEYSSIER, DONNA L. WHITNEY, ADVISORS FEBRUARY 2014 © Erkan Toraman, 2014 Acknowledgements First and foremost, I would like to thank my advisors, Christian Teyssier and Donna L. Whitney, for their continuous support throughout the years. Without your guidance, patience, and constant encouragement this work would not be possible. You have provided me freedom to pursue many aspects of this research, even though at times when I wasn’t sure if that particular approach would work. Thank you for long discussions that broadened my understanding of science and academic life in general. I can’t express my gratitude for involving me with many other projects you work on, especially the ones in central Turkey, which allowed me to explore different perspectives on Anatolian tectonics and use new research tools. I hope and look forward to work with you in future projects! Many thanks to members of my written, oral, and final exam committee members Martin O. Saar, Karen Kleinspehn, Joshua Feinberg, and Annia Fayon for taking the time to read my work. I am indebted to Annia Fayon for introducing me to the wonders of fission-track analysis and for long, enlightening discussions on diffusional processes in thermochronology. I thank Martin Saar for his encouragement for modeling of thermochronometric data, even though that work has not made into this thesis but still “in progress”.
    [Show full text]
  • Exhumation Rates from Thermochronometric Data
    Open Access Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Earth Surf. Dynam. Discuss., 1, 207–259, 2013 Earth Surface www.earth-surf-dynam-discuss.net/1/207/2013/Earth Surface doi:10.5194/esurfd-1-207-2013 Dynamics Dynamics ESurfD Discussions © Author(s) 2013. CC Attribution 3.0 License. 1, 207–259, 2013 This discussion paper is/has been under review for the journal Earth Surface Dynamics (ESurfD). Exhumation rates Please refer to the corresponding final paper in ESurf if available. from thermochronometric data A linear inversion method to infer M. Fox et al. exhumation rates in space and time from thermochronometric data Title Page Abstract Introduction M. Fox1, F. Herman1,*, S. D. Willett1, and D. A. May2 Conclusions References 1Institute of Geology, Swiss Federal Institute of Technology, ETH Zürich, Zürich, Switzerland 2Institute of Geophysics, Swiss Federal Institute of Technology, ETH Zürich, Zürich, Tables Figures Switzerland * now at: Institute of Earth Science, University of Lausanne, Switzerland J I Received: 1 June 2013 – Accepted: 27 June 2013 – Published: 19 July 2013 J I Correspondence to: M. Fox ([email protected]) Back Close Published by Copernicus Publications on behalf of the European Geosciences Union. Full Screen / Esc Printer-friendly Version Interactive Discussion 207 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract ESurfD We present a formal inverse procedure to extract exhumation rates from spatially dis- tributed low temperature thermochronometric data. Our method is based on a Gaus- 1, 207–259, 2013 sian linear inversion approach in which we define a linear problem relating exhumation 5 rate to thermochronometric age with rates being parameterized as variable in both Exhumation rates space and time.
    [Show full text]