DOCSLIB.ORG

Buoyancy-Driven, Rapid Exhumation of Ultrahigh-Pressure Metamorphosed Continental Crust

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read 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. Sustained over decouple from the descending but faltering lithospheric plate '20 million years, rapid ('5mmyyear) exhumation of the and move back up the subduction channel. Exhumation is thin-aspect ratio UHP sialic sheet caught between cooler aided in part by (i) progressive shallowing of the ruptured and hanging-wall plate and refrigerating, downgoing lithosphere now buoyant, rebounding continental-crust-capped litho- sphere, and perhaps more importantly, (ii) due to reduction of allows withdrawal of heat along both its upper and lower the shear force acting along its base due to its increasingly surfaces. The intracratonal position of most UHP complexes ductile behavior as the slab gradually warms with depth in the reflects consumption of an intervening ocean basin and deep upper mantle. Because of continued subduction-induced introduction of a sialic promontory into the subduction zone. refrigeration tectonically beneath the rising UHP complex, UHP metamorphic terranes consist chiefly of transformed, and observed extensional faulting against the overlying, cooler yet relatively low-density continental crust compared with hanging-wall plate, relatively thin slices of UHP terranes displaced mantle material—otherwise such complexes could effectively lose heat along both upper and lower surfaces not return to shallow depths. Relatively rare metabasaltic, during ascent; thus, such complexes may nearly retrace the metagabbroic, and metacherty lithologies retain traces of subduction-zone pressure–temperature (P–T) trajectory dur- phases characteristic of UHP conditions because they are ing decompression (11, 12). massive, virtually impervious to fluids, and nearly anhydrous. Proposed relationships are shown diagrammatically in Fig. In contrast, H2O-rich quartzofeldspathic, gneissosey 1, and apply equally well to the exhumation of high-pressure schistose, more permeable metasedimentary and metagra- (HP) and UHP terranes. An upper normal fault and a lower nitic units have backreacted thoroughly, so coesite and other reverse fault bound the thin-aspect-ratio slab. Such shear UHP silicates are exceedingly rare. Because of the initial senses seem required by structural relations, for example, in presence of biogenic carbon, and its especially sluggish trans- the Dora Maira Massif (13–15), and in the Dabie Shan (16). formation rate, UHP paragneisses contain the most abun- Yet another exhumation scenario involves the antithetic fault- dantly preserved crustal diamonds. ing characteristic of some compressional orogens, in which double vergence is produced during end stages of the collision Previous workers (1) have demonstrated that deep subduction and ascent of sialic crust (17). of continental crust is required to explain the generation of Where thin UHP slices are exhumed during continued ultrahigh-pressure (UHP) terranes. An outstanding petrotec- subductionyrefrigeration, the ascending complex will more- or-less follow the prograde metamorphic P–T path in reverse; tonic problem consists of elucidating the manner in which this phenomenon has been documented, for instance, in these complexes have returned to shallow levels while preserv- HPyUHP terranes of the western Alps and the California ing intact relics of the UHP phase assemblages. The ‘‘two-way Coast Ranges (18–20). For thick, more nearly equidimensional street’’ nature of subduction zones was recognized long ago masses (.30 km thick?), the ratio of cooling surface to mass (2–4). Briefly, salients or peninsulas of old continental crust, is low, and central portions are likely to remain sufficiently hot thoroughly embedded in chiefly cold, oceanic-crust-capped during decompression for the complete obliteration of all UHP lithospheric plates, descend rapidly, generating the character- relics, and perhaps even for partial melting to ensue; accord- istic UHP mineralogy (5, 6). The UHP slabs will be subducted ingly, such ascending, hot bodies retain none of the precursor to depths where the buoyancy forces tending to drive them UHP mineral assemblages. back upward are exactly balanced by the dynamic forces tending to subduct them still further. In a contrasting type of Buoyancy Forces continental collision, where the sialic crust is weak and poorly The densities of unaltered oceanic crust ('3.0), continental The publication costs of this article were defrayed in part by page charge crust ('2.7), and mantle materials ('3.2) increase with ele- payment. This article must therefore be hereby marked ‘‘advertisement’’ in vated pressure, reflecting the progressive transformation of accordance with 18 U.S.C. §1734 solely to indicate this fact. © 1997 by The National Academy of Sciences 0027-8424y97y949532-6$2.00y0 Abbreviations: UHP, ultrahigh pressure; HP, high pressure; P–T, PNAS is available online at http:yywww.pnas.org. pressure–temperature. 9532 Downloaded by guest on September 28, 2021 Geology: Ernst et al. Proc. Natl. Acad. Sci. USA 94 (1997) 9533 will tend to sink. Of course, if the conversion of crustal slices to UHP mineral assemblages is incomplete, continental crust should be even more buoyant than indicated in Table 1, whereas the oceanic crust would be less negatively (even positively) buoyant, depending on the extent of transformation to high-density phases. The several forces acting upon a sheet of subducted sialic crust, illustrated schematically in Fig. 1, may be described as follows. (i) Subduction of a low-density sialic slab occurs provided shear forces caused by underflow (Fs) overcome the combined effects of buoyancy (Fb) and frictional resistance along the upper wall of the subduction channel (Fr). In this case, Fs . Fb sinQ1Fr.(ii) Slab rise—not necessarily the complete section of sialic crust—occurs provided buoyancy is positive, and greater than the combined effects of shearing along its base and resistance to movement along its upper surface. For this situation, Fb sinQ.Fs1Fr. Kinematically, the illustrated process is rather similar to the ‘‘slab-extrusion’’ mechanism that Maruyama et al. (23) pro- posed specifically to account for the Dabie Shan UHP rocks of east-central China, as well as tectonic models advanced for the Himalayas and the Alps (24–27). Explicit in our scenario, however, is body–force propulsion of the UHP metamor- phosed sheet of continental crust back up the subduction zone due to its overall buoyancy, in contrast to the mechanism of compressional extrusion (28–31). But are other observed features of HP and UHP complexes explicable as conse- FIG. 1. Schematic diagram portraying the deep burial and thermal quences of our formation and exhumation mechanism? structure of a subducted microcontinent or continental salient (a), then decompression cooling of a rising slice of UHP quart- Easternmost Java Trench: A Modern Collision Zone zofeldspathic rock—not necessarily the complete section of sialic crust—accompanying steady-state subduction (b) [after Ernst and Peacock (12)]. During uplift of a thin UHP terrane (thickness some- A modern geologic analogue of the model shown in Fig. 1 is what exaggerated for clarity), cooling of the upper margin of the sheet represented by the eastern portion of the Indonesian arc takes place where it is juxtaposed against the shallower, lower tem- (32–34). The strongly curved portion of the Australian– perature hanging-wall plate; cooling along the lower margin of the Eurasian collisional suture zone between Timor and Seram is sheet takes place where it is juxtaposed against the lower temperature, illustrated in Fig. 2a) (33, 35, 36), with the geographic distri- subductingyrefrigerating plate. Stages depicted are as follows: (a) bution of uplifted HP blueschists indicated. The driving force prior to exhumation of the UHP complex; and (b) during exhumation for wedge ‘‘extrusion’’
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]
  • 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]
  • Spatio-Temporal Patterns of Pyrenean Exhumation Revealed by Inverse
    https://doi.org/10.1130/G48687.1 Manuscript received 10 April 2020 Revised manuscript received 2 December 2020 Manuscript accepted 16 January 2021 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 22 March 2021 Spatio-temporal patterns of Pyrenean exhumation revealed by inverse thermo-kinematic modeling of a large thermochronologic data set Magdalena Ellis Curry1, Peter van der Beek2, Ritske S. Huismans3, Sebastian G. Wolf3, Charlotte Fillon4 and Josep-Anton Muñoz5 1 Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas 77204, USA 2 Institute for Geosciences, University of Potsdam, 14469 Potsdam, Germany 3 Department of Earth Science, University of Bergen, 5020 Bergen, Norway 4 TOTAL EP, R&D Nexts, 64018 Pau, France 5 Geomodels Research Institute, University of Barcelona, 08007 Barcelona, Spain ABSTRACT data set (n = 264) and incorporate topographic Large thermochronologic data sets enable orogen-scale investigations into spatio-temporal boundary constraints to evaluate controls on patterns of erosion and deformation. We present the results of a thermo-kinematic model- orogen-scale exhumation in the Pyrenees. We ing study that examines large-scale controls on spatio-temporal variations in exhumation aim to explain two key features of the data: (1) as recorded by multiple low-temperature thermochronometers in the Pyrenees mountains an along-strike trend in exhumation, and (2) the (France/Spain). Using 264 compiled cooling ages spanning ∼200 km of the orogen, a recent existence of post-orogenic cooling ages. Our model for its topographic evolution, and the thermo-kinematic modeling code Pecube, we results show that spatio-temporal patterns of evaluated two models for Axial Zone (AZ) exhumation: (1) thrust sheet–controlled (north- exhumation are controlled by structural inheri- south) exhumation, and (2) along-strike (east-west) variable exhumation.
    [Show full text]