Geology topics

R. Y. Zhang

Publications and source records attributed to R. Y. Zhang.

3 recordsLinked to original sources

USGS2010

SHRIMP U-Pb dating of zircon from the Xugou UHP eclogite, Sulu terrane, eastern China

clogites, together with garnet clinopyroxenites, occur as lenses within the Xugou garnet peridotite body in the southern Sulu ultrahigh-pressure (UHP) terrane. Combined cathodoluminescence (CL) imaging and SHRIMP U-Pb dating of zircon from two Xugou mafic eclogites provide added constraints on the timing of UHP metamorphism in this area. Zircons from both samples show subrounded to rounded shapes and patchy CL patterns without inherited igneous cores, indicating that they are metamorphic zircons. SHRIMP U-Pb analyses of these zircons yielded apparent U-Pb ages of 214-280 Ma, with a weighted mean age of 237 ± 8 Ma, which is consistent with previous reported UHP metamorphic ages from eclogite pods and country-rock gneisses. The Xugou mafic lenses may have formed by partial melting of the enclosing peridotites in the mantle before subduction (Zhang et al., 2003); then these eclogites, together with the host peridotites, were tectonically emplaced into the subduction zone and subjected to UHP metamorphism at 237 ± 8 Ma.

International Geology Review↗

USGS2006

Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: A non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane

The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes over an area of about 15 km2. The U-Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ???1730 Ma, and the formation of amphibolite-facies assemblages in both metagabbro and granulite occurred at ???340-460 Ma. Petrologic and geochronological data indicate that these various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies metamorphism at ???1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. ?? Springer-Verlag 2006.

Conference Paper↗

USGS2005

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

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. ?? 2005 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗