Subduction Reversal in a Divergent Double Subduction Zone Drives the Exhumation of Southern Qiangtang Blueschist‐Bearing Mélange, Central Tibet
Wang, G. H.
Bons, P. D.
Zhao, Z. B.
Du, J. X.
Wang, S. L.
Yuan, G. L.
Liang, X.
Zhang, L.
Li, C.
Fang, D. R.
Tang, Y.
Hu, Y. L.
Fu, Y. Z.
DOI: https://doi.org/10.23689/fidgeo-4024
Zhao, Z. B.; 4 Institute of Geology Chinese Academy of Geological Sciences Beijing China
Du, J. X.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Wang, S. L.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Yuan, G. L.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Liang, X.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Zhang, L.; 5 Institute of Energy Sources General Prospecting Institute of China National Administration of Coal Geology Beijing China
Li, C.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Fang, D. R.; 6 Geoscience Documentation Center, China Geological Survey Beijing China
Tang, Y.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Hu, Y. L.; 1 School of Earth Science and Resources China University of Geosciences Beijing China
Fu, Y. Z.; 2 Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation of Ministry of Natural Resources Chengdu University of Technology Chengdu China
Abstract
(Ultra) high‐pressure (HP) rocks can be exhumed rapidly by subduction reversal or divergent plate motion. Recent studies show that subduction reversal can in particular occur in a divergent double subduction zone when the slab pull of one slab exceeds that of the other, shorter one, which then experiences a net upward pull. This recent hypothesis, first proposed for Triassic HP‐rocks exposed in the central Qiangtang mélange belt in central Tibet, can explain the exhumation of (ultra) HP rocks through upward slab movement. However, this model lacks the support of kinematic evidence. In this study, based on the recognition of multiple deformational phases, we analyze the kinematics of the HP‐bearing mélange in central Qiangtang. Based on new 40Ar‐39Ar geochronology data and those collected from the literature, we present a temporal framework for the new observations. We recognize a switch in sense of shear between the prograde (D1) and exhumation (D2‐3) paths. The change of shear sense reflects the reversal from downward to upward movement of the oceanic slab below. Early D2 represents the early exhumation stage that caused retrograde metamorphism from eclogite to blueschist facies. No magmatism occurred during this period. Continued exhumation from blueschist facies to greenschist facies resulted in D2‐D3 structures. Voluminous igneous activity occurred during this stage. We suggest that subduction reversal in a divergent double subduction zone can best explain the kinematic evolution and temporal framework above. This exhumation model may provide a new perspective on the exhumation mechanism for other HP rocks around the world.
Key Points:
Central Qiangtang HP‐bearing mélange formed by short‐lived southward subduction in a divergent double subduction setting. Progressive inversed shearing exhumed HP rocks. Subduction reversal in a divergent double subduction zone can exhume HP rocks through direct slab movement.
Subjects
Tibetan PlateauSouth Qiangtang Terrane
subduction reversal
divergent double subduction zone
exhumation
high‐pressure rocks