云开地块晚二叠世富Fe-Ti-P超镁铁质岩的年代学、地球化学与岩石成因

为了更好地理解华南板块南缘二叠纪与三叠纪之交复杂的构造格局，通过岩石学、地球化学和年代学的方法，对粤西云开地区新发现的3处晚二叠世超镁铁质侵入岩进行了研究.这些岩石位于云开地块东缘的阳春三甲和地块中部的高州大井、东岸等地，呈小岩株、岩脉产出于云开岩群的片岩、变粒岩中.它们的主要岩性为辉石岩、角闪石岩、角闪岩和斜长角闪岩，锆石SHRIMP和LA-ICP-MS U-Pb定年获得的岩石形成时代为253~259 Ma.超镁铁质侵入岩富（含钛）磁铁矿、榍石和磷灰石，显示出显著富集Fe-Ti-P的地球化学特征，并表现为轻稀土中等富集，微量元素亏损Nb-Ta-Zr-Hf的特征.全岩ε_Nd（t）集中在-3.4~-10.0之间，锆石ε_Hf（t）介于-1.2~-9.5，锆石δ18O集中于7.01‰~9.71‰，表现为富集岩石圈地幔源区特征.研究认为，二叠纪峨眉山地幔柱活动（~259 Ma）的影响范围可能波及到了粤桂交界的云开地区，地幔柱热流导致岩石圈地幔部分熔融形成玄武质岩浆，经不同程度的结晶分异作用，最终形成了云开晚二叠世富Fe-Ti-P超镁铁质岩. 

Geochronology,Geochemistry and Petrogenesis of Late Permian Fe-Ti-P-Rich Ultramafic Rocks in Yunkai Terrane,South China

In order to better understand the complex tectonic framework on the southern margin of South China block (SCB) between Permian and Triassic, the petrology, geochemistry and chronology of three newly discovered Late Permian ultramafic intrusions in the Yunkai area of West Guangdong were studied. These rocks are located at Yangchun Sanjia on the eastern edge of the Yunkai terrane and at Gaozhou Dajing and Dong'an in the middle of the Yunkai terrane. They are intrusive rocks in schist and paragneiss of the Yunkai Group and out putted as laccoliths or dykes which main lithologies are pyroxenite, hornblendite, amphibolite and plagioclase amphibolite. Zircon SHRIMP and LA-ICP-MS U-Pb age of ultramafic rocks are 253-259 Ma. These intrusive rocks are rich in titanomagnetite, titanite and apatite, showing strong enrichment of Fe-Ti-P, and exhibiting moderate enrichment of LREE and depletion in Nb-Ta-Zr-Hf. Ultramafic rocks exhibit relatively low ε_Nd(t)(-3.4 to -10.0) of whole rocks, ε_Hf(t) (-1.2 to -9.5) and δ18O(7.01‰-9.71‰) values of zircon, showing the enriched lithosphere mantle source affinity. In this study, it is suggested that the influence range of Permian Emeishan mantle plume(~259 Ma) may have spread to Yunkai area. Yunkai Late Permian ultramafic intrusions are generated from the partial melting of the lithospheric mantle which resulted from heat flow of mantle plume. Fe-Ti-P-rich minerals were assembled at the late stage of magma crystallization.