T185 Geological and Geophysical Constraints on Orogenic Architecture as Windows to Tectonic Style Through Time (Posters)

Tuesday, 17 October 2023
8:00 AM - 5:30 PM
Hall B

GEOLOGICAL CONSTRAINTS ON THE CRUSTAL ARCHITECTURE OF THE CENTRAL OROGENIC BELT, NORTH CHINA CRATON, REVEAL NEOARCHEAN ALPINE-STYLE TECTONICS

Paper number: T185-6
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

  • Tim Kusky Presenting Author
    School of Earth Sciences, China University of Geosciences, Wuhan, 430078, China, China, Hubei
  • Tim Kusky Presenting Author
    China University of Geosciences Wuhan, Wuhan
  • Lu Wang
    China University of Geosciences, Wuhan, Wuhan, Hubei Province
  • Wenbin Ning
    China University of Geosciences (Wuhan), Wuhan
  • Bo Huang
    China University of Geosciences (Wuhan), Wuhan
  • Junpeng Wang
    China University of Geosciences, Wuhan, Wuhan, Hubei Province
  • Hao Deng
    China University of Geosciences, Wuhan, Wuhan, Hubei Province
  • Yating Zhong
    China University of Geosciences Wuhan, Wuhan
  • Yaying Peng
    China University of Geosciences Wuhan, Wuhan

Abstract

Styles of tectonics on Earth through time are debated. North China Craton’s 1800 km-long Central Orogenic Belt (COB on figure) records the 2.5 Ga collision of a 2.7-2.5 Ga oceanic arc(s) with a collage of slightly older arcs in an accretionary orogen. The orogen has classical orogenic zones, including a 2.7-2.5 Ga arc(s), fore-arc MORB-boninitic-IAT sequences, far-travelled sub-horizontal sheath-folded nappes, poly-genetic mélanges, and fore-arc basinal assemblages. The belts form a classic medium-low dT/dP high dT/dP paired metamorphic belt. Ophiolitic fragments in the mélange range in size from individual outcrop-sized blocks and elongate several-km-long lenses in a metapelitic and locally serpentinitic or mafic matrix. Rock types include serpentinized harzburgite tectonites, rare lherzolites, pyroxenites, garnet pyroxenites, layered gabbro, massive gabbro, local dike complexes, basalts (locally pillowed), cherts, metalliferous deposits, and metapelites. Some blocks have fore-arc geochemical signatures, others have MORB signatures, locally separable into different mappable mélange belts. These belts were thrust over a 2.58-2.50 Ga passive margin-like sequence formed on the back-side of other recently accreted arcs forming the Eastern Block of the craton, and are associated with a 2.50/2.45 – 2.31 Ga foreland basin sequence. The thrusting is well-documented by a belt of Alpine-style sub-horizontal nappes resting allochthonously over the passive-margin sequence.

The ophiolitic fragments provide constraints on conditions in Archean subduction zones, oceanic lithosphere, and deeper mantle. An N-MORB garnet pyroxenite block in mélange experienced eclogite-facies conditions, yielding a dT/dP of 11℃/ km, one of the coldest recorded Archean geotherms. This is confirmed by an Alpine-type peridotitic block in the mélange independently yielding a dT/dP of 11℃/ km. Perhaps most remarkably, some podiform chromitites in harzburgites have yielded a suite of crustal and mantle inclusions, including TiO2(II) stable above 7.5 GPa (~270 km), and the UHP phase of chromite, chenmingite, stable above 14 GPa (~410). These inclusions are similar to those of Phanerozoic ophiolites, demonstrating the operation of deep crust-mantle recycling through plate tectonic processes for at least the past 2.7 Ga.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-393733

© Copyright 2023 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.