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2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 4
Presentation Time: 1:30 PM-5:30 PM

SHRIMP U-PB ZIRCON DATING OF THE ECLOGITE AND ASSOCIATED PERIDOTITE FROM THE SULU TERRANE, CHINA: NEW CONSTRAINTS FOR UHP METAMORPHISM OF MANTLE-DERIVED MAFIC-ULTRAMAFIC BODIES


ZHAO, Ruixuan1, LIOU, Juhn G.1, ZHANG, Ru Y.1, WOODEN, Joseph L.2 and LI, Tianfu3, (1)Department of Geological and Environmental Sciences, Stanford Univ, Stanford, CA 94305, (2)U.S. Geol Survey, 345 Middlefield Road, Menlo Park, CA 94025, (3)Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China, rxzhao@stanford.edu

New SHRIMP zircon ages from eclogites and peridotites from the Sulu UHP terrane, eastern China indicate that they experienced Triassic metamorphism at the same time as surrounding gneiss.

Two eclogite samples (XG-3C & XJ-1E) occur as lenses within a garnet peridotite body from Xugou, southern Sulu. Zircon grains show subrounded shapes, ranging from 50 to 250 µm in diameter. Cathodoluminescence (CL) images reveal that zircons from both samples show homogeneous or patchy patterns, without any zoning. SHRIMP U-Pb analyses of zircon separates fall into one population on a Tera-Wasserburg (TW) diagram. U-Pb data of both samples yield a weighted mean age of 237 ± 8 Ma, interpreted as the time of peak UHP metamorphism.

Three eclogite samples (CJ4A, 4C, 4D) occur as lenses within a garnet lherzolite body from Rongcheng, northern Sulu. Zircon grains are rounded, ranging from 50 to 200µm in diameter. Zircons from two eclogites (CJ4A, 4D) show homogeneous or slightly cloudy CL patterns, which is similar to those from Xugou eclogites. Some zircons from sample CJ4C have dark-luminant U-rich cores and light-luminant U-poor rims, but similar ages are obtained from these two domains. SHRIMP U-Pb analyses of zircon from CJ4A, 4C yield weighted mean ages of 238 ± 3 Ma and 232 ± 7 Ma, which are considered to be the peak metamorphic ages. A much younger age (218 ± 5 Ma) is obtained for zircons from CJ4D, but no petrological evidence for a retrograde event was found for this sample and therefore this age is also considered to reflect eclogite-facies growth. One dunite (MC5A) from a nearby peridotite body in Rongcheng is also studied. Zircons from this dunite also show homogeneous CL patterns. SHRIMP U-Pb zircon analyses of this dunite (MC5A) yield a weighted mean age of 242 ± 8 Ma, which is consistent with those ages from eclogites.

Our ages are consistent with previous reported UHP metamorphic ages from other garnet peridotities, eclogites and country rock gneisses in Sulu, thus confirm that these mantle-derived mafic-ultramafic bodies were emplaced into the subduction slab in the Triassic and experienced the UHP metamorphism together with adjacent supracrustal rocks.

Session No. 127--Booth# 80

Petrology and Volcanology (Posters)
Monday, 17 October 2005: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol. 37, No. 7, p.288
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