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Ar/Ar geochronology of ultrahigh‐pressure metamorphism in central China
Author(s) -
Hacker Bradley R.,
Wang Qingchen
Publication year - 1995
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/95tc00932
Subject(s) - geology , metamorphism , metamorphic rock , geochronology , hornblende , geochemistry , phengite , blueschist , metamorphic core complex , metamorphic facies , fibrous joint , biotite , tectonics , petrology , subduction , paleontology , facies , extensional definition , eclogite , medicine , quartz , anatomy , structural basin
The Dabie Shan of China contain the largest areal exposure of ultrahigh‐pressure regional metamorphic rock known on Earth. The thermal history of these unusual rocks is central to understanding the tectonic processes responsible for their creation, preservation, and exhumation. Published ages of ultrahigh‐pressure metamorphism and subsequent cooling range from Archean to Jurassic. By analyzing 21 Dabie hornblende, phengite, and biotite samples by the 40 Ar/ 39 Ar method, we find that (1) cooling from peak metamorphic temperatures to ∼300°C occurred between about 206 and 178 Ma; (2) widespread Cretaceous ages reflect reheating by a postultrahigh‐pressure magmatic/extensional episode; (3) 40 Ar/ 39 Ar and K/Ar ages older than 230 Ma, and perhaps 210 Ma, are geologically meaningless due to the incorporation of excess 40 Ar; and (4) Dabie ultrahigh‐pressure metamorphic rocks are temporally related to blueschist‐facies rocks farther west in the suture zone.