福建漳浦复式岩体同位素地质年代研究

Isotopic Geologic Studies of Zhangpu Complex

漳浦复式岩体位于长乐—南澳断裂带南段,是一个大型的燕山期复式岩体。前人将该复式岩体划分为早侏罗世、晚侏罗世、早白垩世早期、早白垩世晚期、晚白垩世等5期侵入岩。其中,早侏罗世、晚侏罗世、早白垩世早期侵入岩都具有韧性变形、变质的特征,而早白垩世晚期、晚白垩世侵入岩则未发生韧性变形、变质作用。通过对变质侵入岩锆石微区(LA-ICPMS)U-Pb同位素测年研究,结合侵入体之间及其与围岩的接触关系等特征,认为原划为早侏罗世的变质花岗闪长岩(龙海白坑岩体)的时代应为晚侏罗世早期(149.9Ma,LA-ICPMS锆石U-Pb),原定为晚侏罗世古美山序列的变质花岗闪长岩、二长花岗岩、正长花岗岩属晚侏罗世晚期(137～145.4Ma,LA-ICPMS锆石U-Pb),而原划分为早白垩世早期漳浦序列的变质石英闪长岩、花岗闪长岩、二长花岗岩、正长花岗岩应当与以早白垩世漳州序列的相应岩类为同期产物,属早白垩世(106.7Ma,LA-ICPMS锆石U-Pb),是长乐—南澳断裂带受变质变形的产物。

Zhangpu complex is a large Yanshanian periods complex, which located in southern Changle-Nan＇ao fault zone. The previous studies suggested that the complex are composed of early Jurassic, late Jurassic, late Jurassic-early Cretaceous, early Cretaceous and late Cretaceous five periods intrusive rocks. Early Jurassic, late Jurassic, late Jurassic-early Cretaceous intrusive rocks have characteristic of plastic deformation and metamorphic; Eearly Cretaceous and late Cretaceous intrusive rocks, contrariwise, have not characteristic of plastic deformation and metamorphic. By LA-ICPMS U-Pb chronological study of zircons, Considering the geological characteristics of complex, it is believed that the metamorphic granodiorite of Baikeng intrusive, which was divided into early Jurassic periods, is dated at 149.9 Ma using the LA-ICPMS zircon U-Pb method and represents product of the early-late Jurassic magmatism, and the metamorphic Gumeishan sequence belong to the late-late Jurassic periods, which is date at 137-145.4 Ma, and the metamorphic Zhangpu sequence belong to the early Cretaceous periods, which is date at 106.7 Ma. Zhangpu sequence is the product of the early Cretaceous magmatism which forms Zhangzhou sequence, is deformated and metamorphic in the Changle-Nan＇ao fault zone.