Identification of UHP and Non-UHP Orthogneisses in the Sulu UHP Terrane, Eastern China: Evidence from SHRIMP U-Pb Dating of Mineral Inclusion-Bearing Zircons
Identification of UHP and Non-UHP Orthogneisses in the Sulu UHP Terrane, Eastern China: Evidence from SHRIMP U-Pb Dating of Mineral Inclusion-Bearing Zircons
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DOI：
10.2747/0020-6814.48.12.1067
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发表时间：
2006-12
影响因子：
2.6
通讯作者：
Fulai Liu;J. Liou;H. Xue
中科院分区：
文献类型：
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作者：
Fulai Liu;J. Liou;H. Xue
环带锆石中的矿物包裹体表明，超高压（UHP）和非UHP正片麻岩都出现在东海钻孔CCSD-PP 1，西南苏禄海。超高压正片麻岩中的锆石继承了岩浆核中含有低磷矿物包裹体，超高压矿物包裹体的狭窄地幔，以及含有低磷矿物或无包裹体的边缘。与此相反，非超高压正片麻岩中的锆石只有岩浆核和变质边，两者都具有低磷矿物包裹体的特征，或没有包裹体。超高压正片麻岩中锆石SHRIMP U-Pb分析确定了3个离散而有意义的年龄组：核部的元古代岩浆原岩年龄>753 Ma，含柯石英地幔的超高压变质事件年龄为227 ± 8 Ma，增生边缘的角闪岩相叠加年龄为213 ± 7 Ma。非超高压正片麻岩中的锆石只记录了两个离散的年龄组，继承岩浆核的元古宙原岩年龄>748 Ma，变质边缘的年龄约为211 ± 6 Ma。在分析不确定性范围内，变质边缘与超高压正片麻岩的晚角闪岩相叠加具有相同的三叠纪年龄。结合前人的研究结果，认为扬子克拉通新元古代表壳原岩经历了晚三叠世（227 ± 8 Ma）俯冲至至少120 km深处，然后迅速折返至中地壳深处，在那里，超高压岩石和少量非超高压新元古代花岗质侵入体经历了211 ± 6 Ma的角闪岩相退变质作用。根据锆石年龄数据和前人获得的变质P-T数据，推测折返速率为6.3- 7.1km/m. y。这种快速折返表明，苏禄超高压变质岩返回地壳深处的一部分，浮动银，可能产生的板断裂。
Mineral inclusions in zoned zircons reveal that both ultrahigh-pressure (UHP) and non-UHP orthogneisses occur in cores from drill hole CCSD-PP1 at Donghai, southwestern Sulu terrane. Zircons from the UHP orthogneiss have inherited magmatic cores containing low-P mineral inclusions, narrow mantles with UHP mineral inclusions, and rims that contain low-P minerals or are inclusion free. In contrast, zircons from non-UHP orthogneiss have only magmatic cores and metamorphic rims, both of which are characterized by low-P mineral inclusions, or are inclusion free. SHRIMP U-Pb analyses of zircons from the UHP orthogneiss identify three discrete and meaningful age groups: Proterozoic magmatic protolith ages >753 Ma in the cores, a UHP metamorphic event at 227 ± 8 Ma in the coesite-bearing mantles, and an amphibolite-facies overprint at 213 ± 7 Ma in the overgrowth rims. Zircons from non-UHP orthogneiss record only two discrete age groups, inherited magmatic cores with Proterozoic protolith ages >748 Ma, and metamorphic rims with an age of about 211 ± 6 Ma. The metamorphic rims have the same Triassic age as the late amphibolite-facies overprint of the UHP orthogneiss within analytical uncertainty. These data, together with previous studies, suggest that Neoproterozoic supracrustal protoliths of the Yangtze craton experienced Late Triassic (227 ± 8 Ma) subduction to depths of at least 120 km, and were then rapidly exhumed to mid-crustal depths where both UHP rocks and a few non-UHP Neoproterozic granitic intrusives were subjected to coeval amphibolite-facies retrograde metamorphism at 211 ± 6 Ma. The exhumation rate deduced from the zircon age data and previously obtained metamorphic P-T data is estimated to be 6.3-7.1 km/m.y. This rapid exhumation suggests that the Sulu UHP metamorphic rocks returned to crustal depths as part of a buoyant sliver, possibly produced by slab breakoff.