海南岛五指山地区顺作花岗岩锆石U-Pb年龄、地球化学特征及其地质意义

Zircon U-Pb age, geochemistry and geological significance of Shunzuo granite in Wuzhishan area, Hainan Island

顺作花岗岩位于海南岛五指山地区白垩纪火山岩的东西两侧,LA-ICP-MS锆石U-Pb定年结果为254.4±2.4Ma,形成于晚二叠世。岩石学及地球化学特征显示,其属于亚碱性岩系列,SiO2含量为69.88%~74.51%,平均72.99%,属酸性岩类。具有明显的Ba、Ta-Nb、P、Ti负异常和较明显的Rb、K、Pb、Nd正异常。初始锶比值为0.70947~0.717388,低于大陆岩石平均锶初始比值(0.719),属中等锶花岗岩。εNd(t)为-9.25^-5.14,T2DM值为1444~1777Ma,其可能是板岩、千枚岩、斜长片麻岩、麻粒岩、斜长透辉石岩等岩石或更深部同类岩石受地壳增厚而发生的深熔作用及NW-SE向挤压应力共同作用的产物,为S型花岗岩。侵位方式是同碰撞构造环境下的强力侵位,最可能的是热气球膨胀式的底侵。属于壳源重熔型花岗岩,形成于同碰撞环境。

Shunzuo granite is located in the Wuzhishan area of Hainan Island, on the east and west sides of the Cretaceous volcanic rocks. The LA-ICP-MS zircon U-Pb dating yielded an age of 254.4±2.4 Ma, suggesting Late Permian. Petrology and geochemistry show that it belongs to the sub-alkaline rock series, with SiO2 content 69.88%~74.51%, 72.99% on average, implying an acidic rock.It has obvious negative anomalies of Ba, Ta-Nb, P and Ti and obvious positive anomalies of Rb, K, Pb and Nd. The initial strontium ratio is 0.70947~0.717388, which is lower than the average ratio of strontium to continental rock(0.719), suggesting moderate strontium granite.εNd(t) is-9.25^-5.14, and T2 DMis 1444~1777 Ma. It might have resulted from the action of crust thickening in the deep melts and NW-SE trending extrusion on slate, phyllite, plagiogneiss, granulite, plagioclase diopside and other rocks or deeper similar rocks, being a product of stress synergy. It is S-type granite, and the emplacement is a strong emplacement type in the syn-collision structure environment. It is of the hot air balloon expansive type underplating. It belongs to the shell source remelting granite, which was formed in the syn-collision environment.