U Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism

Details U Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism U Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism

Sep 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005e%26psl.237..729z&link_type=abstract

Earth and Planetary Science Letters, Volume 237, Issue 3-4, p. 729-743.

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We studied the Zhimafang ultrahigh-pressure metamorphic (UHP) peridotite from pre-pilot drill hole PP-1 of Chinese Continental Scientific Drilling project in the Sulu UHP terrane, eastern China. The peridotite occurs as lens within quartofeldspathic gneiss, and has an assemblage of Ol + Opx + Cpx + Phl + Ti-clinohumite (Ti-Chu) + Grt (or chromite) ± magnesite (Mgs). Zircons were separated from cores at depths of 152 m (C24, garnet lhezolite), 160 m (C27, strongly retrograded phlogopite-rich peridotite) and 225 m (C50, banded peridotite), and were dated by SHRIMP mass spectrometer. Isometric zircons without inherited cores contain inclusions of olivine (Fo91 92), enstatite (En91 92), Ti-clinohumite, diopside, phlogopite and apatite. The enstatite inclusions have low Al2O3 contents of only 0.04 0.13 wt.%, indicating a UHP metamorphic origin. The weighted mean 206Pb / 238U zircon age for garnet lherzolite (C24) is 221 ± 3 Ma, and a discordia lower intercept age for peridotite (C50) is 220 ± 2 Ma. These ages are within error and represent the time of subduction-zone UHP metamorphism. A younger lower intercept age of 212 ± 3 Ma for a foliated wehrlite (C27) was probably caused by Pb loss during retrograde metamorphism. The source of zirconium may be partially attributed to melt/fluid metasomatism within the mantle wedge. Geochronological and geochemical data confirm that the mantle-derived Zhimafang garnet peridotites (probably the most representative type of Sulu garnet peridotites) were tectonically inserted into a subducting crustal slab and subjected to in situ Triassic subduction-zone UHP metamorphism.

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