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Ultrahigh‐pressure and Retrograde Metamorphic Ages for Paleozoic Protolith of Paragneiss in the Main Drill Hole of the Chinese Continental Scientific Drilling Project (CCSD‐MH), SW Sulu UHP Terrane
Author(s) -
Fulai LIU,
Zhiqin XU,
Huaimin XUE,
Kaifu ZHOU
Publication year - 2006
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2006.tb00253.x
Subject(s) - protolith , metamorphism , geology , terrane , coesite , zircon , geochemistry , metamorphic rock , craton , paleozoic , eclogite , petrology , subduction , paleontology , tectonics
Laser Raman spectroscopy and cathodoluminescence (CL) images show that most zircon crystals separated from paragneiss in the main drill hole of the Chinese Continental Scientific Drilling Project (CCSD‐MH) at Maobei, southwestern Sulu terrane, contain low‐pressure mineral‐bearing detrital cores, coesite‐bearing mantles and quartz‐bearing or mineral inclusion‐free rims. SHRIMP U‐Pb dating on these zoned zircons yield three discrete and meaningful age groups. The detrital cores yield a large age span from 659 to 313 Ma, indicating the protolith age for the analyzed paragneiss is Paleozoic rather than Proterozoic. The coesite‐bearing mantles yield a weighted mean age of 228 ± 5 Ma for the UHP event. The quartz‐bearing outmost rims yield a weighted mean age of 213 ± 6 Ma for the retrogressive event related to the regional amphibolite facies metamorphism in the Sulu UHP terrane. Combined with previous SHRIMP U‐Pb dating results from orthogneiss in CCSD‐MH, it is suggested that both Neoproterozoic granitic protolith and Paleozoic sedimentary rocks were subducted to mantle depths in the Late Triassic. About 15 million years later, the Sulu UHP metamorphic rocks were exhumed to mid‐crustal levels and overprinted by an amphibolite‐facies retrogressive metamorphism. The exhumation rate deduced from the SHRIMP data and metamorphic P‐T conditions is about 6.7 km/Ma. Such a fast exhumation suggests that the Sulu UHP paragneiss and orthogneiss returned towards the surface as a dominant part of a buoyant sliver, caused as a consequence of slab breakoff.