海南石碌地区早三叠世闪长玢岩脉U-Pb年代学及构造意义

石碌铁矿床位于海南岛五指山褶皱带西段.矿区内外发育以闪长玢岩脉为主的中基性脉岩.LA-ICP-MS锆石U-Pb定年厘定闪长玢岩脉年龄为248±1 Ma(MSWD=0.4)，为早三叠世岩浆活动的产物，与同时代的富碱侵入岩体构成“双峰式”侵入岩.闪长玢岩脉为钾玄质系列，低SiO₂(49.18%~55.25%)、高Al₂O₃(14.36%~16.75%)、FeO_t(5.98%~10.07%)和MgO(3.80%~5.43%)，富集LILE和LREE，亏损HFSE.Nb/Ta、Zr/Hf和La/Nb比值分别为15.33~17.80、36.00~45.23和2.59~8.62；Pb同位素组成(206Pb/204Pb)_t=18.087~18.483，(207Pb/204Pb)_t=15.473~15.587，(208Pb/204Pb)_t=38.272~38.817.LREE/HFSE和LILE/HFSE比值及Pb同位素组成显示为富集地幔来源，但混染有少量的地壳物质.HFSE判别图解指示闪长玢岩脉形成于大陆边缘弧伸展背景，与晚二叠世印支板块NE向向华南地块俯冲造成的大陆边缘弧局部伸展有关. 

Early Triassic Diorite-Porphyrite Dikes from the Shilu Area, Hainan Island:Zircon U-Pb Age and Tectonic Implication

The Shilu iron deposit is located in western section of the Wuzhishan Fold Belt, Hainan island.In this region, numerous intermediate-basic dikes dominated by diorite-porphyrite occurred. The dating of zircon from diorite-porphyrite dikes determined by LA-ICP-MS yields age of 248±1 Ma (MSWD=0.4), maybe bimodal intrusion with contemporary alkali-rich granites. Diorite-porphyrite dikes are dominated by shoshonitic rocks, which have SiO₂ varying from 49.18% to 55.25%, Al₂O₃ from 14.36% to 16.75%, FeO_t from 5.98% to 10.07% and MgO ranging from 3.80% to 5.43%. These dikes are enriched in large ion lithophile elements (LILE) and low rare earth elements (LREE) but depleted in high field strength element (HFSE).The Nb/Ta values of diorite-porphyrite vary from 15.33 to 17.80, Zr/Hf and La/Nb from 36.00 to 45.23 and 2.59 to 8.62, respectively.Two samples have (206Pb/204Pb)_t=18.087-18.483, (207Pb/204Pb)_t=15.473-15.589 and (208Pb/204Pb)_t=38.272-38.817, similar to the data of contemporary alkali-rich granites. Geochemical and Pb isotopic compositions indicate that these dikes are possibly derived from enriched mantle and slightly contaminated with crust.Hf/3-Th-Ta and Zr-Zr/Y discriminant diagrams imply these diorite-porphyrite dikes intruded in a local nextensional tectonic setting in continental arc, caused by the Indian plate northeastern subduction to the South China Block.