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Combined geochemistry and geochronology constrains coupled subduction of oceanic and continental crust in the Huwan shear zone, central China

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Published/Copyright: January 10, 2015
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American Mineralogist
From the journal American Mineralogist Volume 100 Issue 1

Abstract

Subduction of rocks into the mantle results in high-pressure metamorphism and the formation of eclogites from basaltic precursor rocks. In general, many kilometers of oceanic lithosphere are ultimately consumed prior to the subsequent continental slab subduction and collision. The exposure of the eclogites derived from oceanic subduction and continental subduction at the surface of Earth today record provide different P-T-t records of the subduction process. The Huwan shear zone in the Hong’an orogenic belt, marking a former ocean-continent transition zone, has been the focus of many studies on subduction-related high-pressure metamorphism. In this study, Lu-Hf garnet, U-Pb zircon, and Ar- Ar mica ages are combined with geochemical data to understand the origin of two coexisting eclogite bodies exposed along the Xuehe River in the Huwan Shear zone. In total, the results indicate that the two eclogites have different protoliths but experienced a similar metamorphic history. This observation requires new tectonic model for the coupled subduction of oceanic and continental crust in subduction zones. Combined geochemistry and zircon U-Pb geochronology suggest distinct oceanic and continental affinities for the eclogite protoliths. The Lu-Hf dates of 261.5 ± 2.4 Ma of the continental-type eclogite and 262.7 ± 1.7 Ma of the oceanic-type eclogite reflect garnet growth and are interpreted to closely approximate the age of eclogite-facies metamorphism. Therefore, both the geochemically oceanic- and continental-type eclogites underwent the same episode of Permian eclogite-facies metamorphism. The Permian Lu-Hf ages of ca. 262 Ma and the obtained Triassic Ar-Ar ages (~240 Ma) of the oceanic-type and continental-type eclogites imply coupled subduction and exhumation of oceanic and continental crustal materials in the Hong’an orogenic belt during the Permian and the Triassic. Though limited, the geochemical and geochronological results of this study, together with the discrepant Carboniferous dates for the nearby eclogites of previous studies, apparently suggest that the Huwan shear zone was not always a single coherent unit but instead comprises different tectonic slices that were metamorphosed at different times before final assembly. Some slices of the oceanic and continental crust underwent two subduction cycles during the Carboniferous and the Permian, whereas some eclogites registered only a single subduction-exhumation loop during the convergence between the South China Block and the North China Block in the Huwan shear zone. The consistent ages of the oceanic- and continental-type eclogites disfavor the traditional mélange model that high-pressure rocks are dismembered fragments that have been assembled and intercalated with rocks devoid of any high-pressure history at shallow crustal levels, forming a tectonic mélange.

Keywords: Lu-Hf; Huwan shear zone; eclogite; geochronology
Received: 2014-3-20
Accepted: 2014-6-23
Published Online: 2015-1-10
Published in Print: 2015-1-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2015-4982
Keywords for this article
Lu-Hf; Huwan shear zone; eclogite; geochronology

Articles in the same Issue

  1. The American Mineralogist at 100 years, and a mineralogy renaissance
  2. At the blurry edge of mineralogy
  3. Mineral evolution and Earth history
  4. Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex
  5. The rapid expansion of environmental mineralogy in unconventional ways: Beyond the accepted definition of a mineral, the latest technology, and using nature as our guide
  6. Microelectronic junctions in arsenian pyrite due to impurity and mixed sulfide heterogeneity
  7. The structure of water-saturated carbonate melts
  8. In-situ measurements of fluorine and chlorine speciation and partitioning between melts and aqueous fluids in the Na2O-Al2O3-SiO2-H2O system
  9. High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultrahigh-pressure chromitites in ophiolites
  10. Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate minerals
  11. Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland)
  12. Tourmaline as a petrogenetic monitor of the origin and evolution of the Berry-Havey pegmatite (Maine, U.S.A.)
  13. Applications of Hirshfeld surfaces to mineralogy: An example of alumohydrocalcite, and the classification of the dundasite group minerals
  14. Optical absorption anisotropy of high-density, wide-gap, high-hardness SiO2 polymorphs seifertite, stishovite, and coesite
  15. The system Na2CO3-FeCO3 at 6 GPa and its relation to the system Na2CO3-FeCO3-MgCO3
  16. Chlorine-hydroxyl diffusion in pargasitic amphibole
  17. The use of cation-cation and anion-anion bonds to augment the bond-valence model
  18. AIM analysis and the form of the bond-valence equation
  19. Atomistic simulation on mixing thermodynamics of calcite-smithsonite solid solutions
  20. Combined geochemistry and geochronology constrains coupled subduction of oceanic and continental crust in the Huwan shear zone, central China
  21. Near-infrared investigation of folding sepiolite
  22. First-principles study of sulfur isotope fractionation in pyrite-type disulfides
  23. Tetrataenite in terrestrial rock
  24. Thermo-compression of pyrope-grossular garnet solid solutions: Non-linear compositional dependence
  25. Phase relationships in the system K2CO3-CaCO3 at 6 GPa and 900–1450 °C
  26. Trace-element partitioning between plagioclase, alkali feldspar, Ti-magnetite, biotite, apatite, and evolved potassic liquids from Campi Flegrei (Southern Italy)
  27. Synthetic and natural ammonium-bearing tourmaline
  28. Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas
  29. Nuragheite, Th(MoO4)2·H2O, The Second Natural Thorium Molybdate And Its Relationships To Ichnusaite And Synthetic Th(MoO4)2†
  30. Structural Effects On Incorporated Water In Carbonated Apatites
  31. New Constraints On Electron-Beam Induced Halogen Migration In Apatite
  32. Origin Of The Lunar Highlands Mg-Suite: An Integrated Petrology, Geochemistry, Chronology, And Remote Sensing Perspective
  33. An In Situ High-Pressure Nmr Study Of Sodium Coordination Environment Compressibility In Albite Glass
  34. Hydrothermal Synthesis And Crystal Structure Of Also4(Oh): A Titanite-Group Member
  35. New Mineral Names
  36. Book Review: Thermal Remote Sensing Of Active Volcanoes: A User’S Manual
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