Structural constraints on the timing of left-lateral shear along the red river shear zone in the ailao shan and diancang shan ranges, Yunnan, SW China

Michael P. Searle, Meng-Wan Yeh, Te Hsien Lin, Sun Lin Chung

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Abstract

The >1000-km-long Oligocene-Miocene left-lateral Red River shear zone (RRSZ) and metamorphic belt and the Pliocene-active right-lateral Red River fault (RRF), stretching from SE Tibet to the South China Sea, has been cited as one of the primary examples of a lithospheric scale strike-slip fault that has resulted in syn-kinematic metamorphism and partial melting and accommodated several hundred to a thousand kilometers of horizontal motion as a result of the indentation of India into Asia. Alternatively we interpret the metamorphic complexes along the RRSZ as exhumed metamorphic core complexes of older rocks, subsequently affected by Oligocene-Early Miocene leftlateral shear and localized partial melting (leucogranite dykes), Miocene low-angle normal faulting along margins (Range Front faults), and Pliocene active dextral strike-slip faulting (RRF). Along the Ailao Shan (ALS) and Diancang Shan (DCS) ranges in Yunnan, SW China, early amphibolite facies metamorphic rocks were intruded by K- feldspar orthogneisses of Triassic age (Indosinian). LA-ICP-MS U-Pb zircon dating reveals a complex history with zircon cores showing evidence of Indosinian (∼239-243 Ma) to Neoproterozoic magmatism. Zircon rims show an Oligocene (∼26 Ma) magmatic or metamorphic overprint. Biotite granodiorites and syenites of mantle origin intruded the gneisses during the Oligocene (∼35 Ma). Later biotite leucogranites intruded the orthogneisses and migmatite host rocks before a significant phase of tight to isoclinal folding. Ductile, left-lateral strike-slip shear fabrics were superimposed on all lithologies at high temperature (∼500-550 °C) for the ALS and lower temperatures (∼250-150 °C) after peak metamorphism and after granite intrusion. A few very small biotite (±Grt ± Tur) leucogranite veins and dykes crosscut the ductile strike-slip shear fabrics at Yuanjiang, in the Ailao Shan. Low-angle normal faulting along the margins of the metamorphic massif accommodated final exhumation of the Red River gneisses. Using published U-Th-Pb and 40Ar/39Ar ages of granites along the shear zone, the age of left-lateral ductile shearing along the RRSZ can be constrained as between the earlier deformed leucogranites (31.9-24.2 Ma) and the later crosscutting dykes (21.7 Ma) with exhumation-related cooling continuing until ∼17 Ma.

Original languageEnglish
Pages (from-to)316-338
Number of pages23
JournalGeosphere
Volume6
Issue number4
DOIs
Publication statusPublished - 2010 Nov 10

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shear zone
Oligocene
river
biotite
leucogranite
faulting
zircon
Miocene
exhumation
partial melting
Pliocene
metamorphism
migmatite
indentation
amphibolite facies
granodiorite
strike-slip fault
metamorphic rock
host rock
folding

ASJC Scopus subject areas

  • Geology
  • Stratigraphy

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Structural constraints on the timing of left-lateral shear along the red river shear zone in the ailao shan and diancang shan ranges, Yunnan, SW China. / Searle, Michael P.; Yeh, Meng-Wan; Lin, Te Hsien; Chung, Sun Lin.

In: Geosphere, Vol. 6, No. 4, 10.11.2010, p. 316-338.

Research output: Contribution to journalArticle

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