城巴断块震旦系陡山沱组地层对比与划分及沉积相研究

研究城巴断块震旦系陡山沱组沉积相及地层对比与划分,旨在为探讨陡山沱组黑色岩系成矿性打下基础。通过野外观测和室内综合研究,结合区域地层对比,明月剖面的第一、二段大致相当于川西观音崖组第一段的滨海相沉积,第三段大致相当于峡东剖面第二段的深水相沉积,第四段的条带状白云岩组合和川西剖面及峡东剖面基本一致。将明月地区陡山沱期的沉积相模式归结为浅海陆棚盆地—水下隆起带—次深海陆棚边缘盆地的模式,为下一步找矿指明了方向。     

The Early–Middle Triassic Supervolcano in the Yangtze Block,South China and associated obstacles to biotic recovery

The end–Permian mass extinction was one of the major global crises spanning the entire Early Triassic or longer. Eruptions of volcanos were one of the factors that delayed the biotic recovery after this event. Supervolcano eruptions can cause catastrophic effects on global environment, climate, and life. Here we investigate the tuff layers from Early–Middle Triassic boundary in the Yangtze Block and identify a supervolcano eruption event. The zircon U–Pb ages of the section–Langdai, section–Daijiagou and section–Longmendong tuff samples are 247.1 ± 1.9 Ma, 247.6 ± 2.0 Ma and 247.7 ± 1.7 Ma, respectively. These ages mark the Olenekian–Anisian boundary. The zircon grains from the tuff layers have negative ε_Hf(t) (−15.3 to −0.8), two–stage Hf model (T_DM2) ages (1.7 to 2.2 Ga) and display high–δ¹⁸O values (mostly > 10‰). Clay minerals and quartz dominate the rock composition. The whole rock compositions show that the tuff layers were derived from magma of intermediate to felsic composition, which formed by the remelting of Paleoproterozoic materials of continental crust. The volcanic eruption site is located in the Jinshajiang–Ailaoshan–Song Ma suture zone in the southwestern margin of the Yangtze Block. A combination of the closure of the Paleo–Tethys Ocean Basin and the collision of the Indochina Block and South China contributed to the eruption, which was a supervolcano eruption under the active continental margin arc settings. We speculate that this supervolcano eruption might have contributed to the delayed biotic recovery after the end–Permian mass extinction.     

Palaeomagnetic,geochronological and geological constraints on the tectonic evolution of the Mejillones Peninsula,northern Chile

Palaeomagnetic and geochronological data from an Early Palaeozoic high grade metamorphic complex (Jorgina Formation) and Jurassic layered basic intrusion (Moreno Complex) are reported from the Mejillones Peninsula of northern Chile (23–23°30'S). ⁴⁰Ar–³⁹Ar dates from the Lower Palaeozoic Jorgina Formation and the Moreno Complex are between 170 and 158 Ma, coincident with a phase of emplacement of the north Chilean coastal batholith. This suggests that intrusion and magnetization of the Moreno Complex and the metamorphism and remagnetization of the Jorgina Formation were related to batholith emplacement. Extracted stable components of magnetization from all units (17 sites) define site-mean directions with a scattered distribution. The scatter in site-mean directions is interpreted as being due to minor, localized, non-uniform, block-fault related (normal or strike-slip, or both) rotation after 158 Ma. The palaeomagnetic and geochronological data indicate that no significant large-scale latitudinal translation of crustal blocks has taken place in this part of northern Chile since the Late Jurassic. In addition, they indicate that the uniform clockwise rotation after the mid-Cretaceous which affected the adjacent Cordillera de la Costa either did not extend into the Mejillones Peninsula or took the form of localized block-fault rotations. The restriction of palaeomagnetically defined styles of rotation to discrete areas within the north Chilean forearc indicates that forearc wide block-fault rotation models are not applicable to the Pacific margin of northern Chile.     

哈萨克斯坦S区块盐构造类型及其成因机制

哈萨克斯坦S区块构造位于滨里海盆地阿斯特拉罕—阿克纠宾斯克隆起带与中央坳陷带的东部,滨里海盆地是一个典型的含盐盆地,盆地内盐岩经历了多期的构造运动,形成了丰富多样的构造类型。盆地中部阿斯特拉罕—阿克纠宾斯克隆起带和南恩巴隆起之间的区域,是一个重要的油气聚集区。以地球物理学、地质地震模型等理论为基础,针对该区盐构造类型及其成因机制进行分析,总结与盐相关的盆地地质特征,对含盐盆地发现油气具有非常重要的意义。