闽西-赣南早-中侏罗世盆地及其火成岩特征

Early-Middle Jurassic basins and features of igneous rocks in the western Fujian - southern Jiangxi region

闽西-赣南地区早、中侏罗世陆相盆地带东起福建永定,经江西寻乌到龙南,断续延伸约250km,宽60～80km。受后期构造破坏和花岗岩浆侵入影响,现呈肢解散碎的残留盆地面貌。盆地边界特征和盆区岩层节理测量统计结果反映该区自晚三叠世以来,先后经历了近S-N向水平挤压(T_3-J_(1E)),S-N向垂向挤压、近E-W向水平伸展(J_(1L)-J_2),SE-NW向挤压(K_1)和近E-W向挤压、S-N向伸展(K_2)等复杂的演化过程。早-中侏罗世强烈的拉张-断陷作用导致盆区大量双峰式火山岩的喷发,其基性端员玄武岩的颗粒锆石U-Pb 年龄值为170±1Ma,酸性端员流纹岩Rb-Sr等时线年龄为179Ma～165±2Ma。 流纹岩具有高的SiO_2、Al_2O_3、K_2O含量,ANKC值>1.1;轻稀土富集、稀土总量高,铕亏损,具明显Eu 负异常;富集Rb、Th,贫化Ba、Ti、P、Nb、Zr等特点,属富钾过铝火山岩类。与之共生的玄武岩则以富硅贫碱为特征,轻稀土轻度富集;铕异常不明显;弱富集Rb、Ba、Th、Ce,贫Nb、Zr、Y,配分样式呈上凸型,属拉斑系列玄武岩类,反映一种后造山的陆内裂谷环境。闽西-赣南地区盆山格局的形成经历过多期地球动力学演化:前中生代近E-W向古亚洲构造城的基底阶段,晚三叠世-早侏罗世早期挤压造山阶段,早侏罗世晚期-中侏罗世裂谷盆地阶段,早白垩世太平洋构造域对本区的置?

The Early-Middle Jurassic basin zone is developed in the Western Fujian-Southern Jiangxi region, South China. This E/W-trending basin zone, extending about 250 km long and about 60 similar to 80 km wide from Yongding County to the east, through Xunwu, to Longnan to the west, had been disrupted into a series of relic basins due to late tectonic-granitic magma event. The measurement and statistics on the joints of rocks in the basins reveal that this basin zone experienced a complex geodynamic evolution: a sub-E-W-direction extension during Early-Middle Jurassic, a SE-NW-direction compression during Early Cretaceous and a sub-E-W-direction compression since Late Cretaceous. Strong rifting and faulted depression in Middle Jurassic caused a large scale of bimodal volcanic eruption, of them, zircon grains of basalt rock yielded a U-Pb age of 170 +/- 1 Ma and rhyolitic rock was dated at 165 +/- 2 Ma to 179 Ma by the Rb-Sr isochron method. Geochemically, rhyolitic rocks are characterized by high contents of SiO2 Al2O3 and K2O, ANKC value >1.1, high SigmaREE and rich in LREEs, depleted in Eu and marked negative Eu anomalies; rich in Rb, Th and poor in Ba, Ti, P, Nb, Zr, belonging to the peraluminous volcanic rocks with high-K content. In contrast with it, basaltic rocks are marked by: rich in Si and poor in K + Na, weakly rich in LREEs, weakly depleted in Eu; weakly rich in Rb, Ba, Th, Cc and poor in Nb, Zr, Y, exhibiting a protruding-type distribution patterns, belonging to the tholeiite series. These features reflect a post-collision intra-continent rift environment. The basin-range framework and geodynamic evolution of the Western Fujian-Southern Jiangxi basin zone passed the following four stages: the pre-Mesozoic paleo-Asian basement with a sub-E-W striking, the Late Triassic-Early Jurassic foreland compression orogenics, the Early Jurassic-Early and Middle Jurassic rift basin, and the Pacific tectonic system since Early Cretaceous. The Pacific tectonic system reworked or replaced strongly the Early-Middle Jurassic basin zone in the studied area.