天山东段“北天山洋”构造涵义及演化模式再认识

准噶尔-吐哈地块与伊犁-中天山地块之间分布着多条时代和类型各不相同的古生代蛇绿混杂岩带,前人一般将这些蛇绿混杂岩统一视为北天山洋盆的纪录,并由此推断该洋盆的时代跨度至少始自寒武纪并一直持续到晚石炭世甚至二叠纪。本文基于近几年在东天山地区地质调查工作的新成果,通过新界定的以康古尔塔格-大草滩蛇绿混杂岩带为代表的北天山洋两侧志留纪—泥盆纪活动大陆边缘物源性质和生物古地理对比,对北天山洋的构造属性和演化过程进行了重新厘定。研究揭示,志留纪—早泥盆世,北天山洋两侧的准噶尔-吐哈地块和伊犁-中天山地块分属于不同的物源体系和生物古地理区系,指示该洋盆具有显著的构造古地理分隔意义。至中泥盆世,北天山洋两侧隶属同一生物大区的珊瑚动物群指示该洋盆已演化至残余洋盆阶段;晚泥盆世晚期—早石炭世,天山地区广泛分布的陆相磨拉石-火山岩建造与下伏岩系之间的区域性角度不整合关系以及南北两侧物源的相互贯通说明东天山段的北天山洋已完全闭合,南北陆块的碰撞缝合应发生在此前的晚泥盆世早期(~370 Ma)。石炭纪—早二叠世,可能受南部南天山洋北向俯冲及板片后撤作用影响,在前期已经碰撞拼合形成的统一准噶尔-吐哈-中天山地块之上,沿康古尔-雅山一带重新裂解出具不成熟洋壳的康古尔弧后有限洋盆。该有限洋盆存续至早二叠世早期(~290 Ma)最终闭合,其与北天山洋盆是两个不同阶段不同性质的洋盆体系。

Fossil biotas from Pakistan with focus on dinosaur distributions and discussion on paleobiogeographic evolution of Indo-Pak Peninsula

Recent geological and paleontological exploration in the Indus basin of Pakistan allowed the discoveries of numerous remains of non-marine reptiles( titanosaurian sauropod,abelisaurian and noasaurian theropod dinosaurs),and marine reptiles( crocodiles),flying reptiles( pterosaurs),marine and non-marine mammals,fishes,invertebrates,and plants,especially Pakistan is relatively rich in footprints / trackways in the Mesozoic.These vertebrates of Indo-Pakistan are very significant for paleobiogeographic study due to the present-day connection of this continent with Asia in Northern Hemisphere,whereas during past( Jurassic and pre-Jurassic) it was connected to the Gondwana. The Mesozoic vertebrates show close affinities with Gondwanan landmasses.The Cenozoic vertebrates show Eurasian affinity and migrated from Indo-Pak subcontinent to Eurasia or vice versa via Paleo Indus River systems along Western Indus Suture,after long journey of about 6 000 km the first collision of Indo-Pak subcontinent with Asia occurred at terminal Cretaceous.