地质学

地质学

封面介绍：受早二叠世冈瓦纳冰川作用及冈瓦纳北缘裂解的影响，拉萨地块晚古生代构造演化环境演化及生物演变一直是学术界讨论的热点问题。拉萨地块下二叠统拉嘎组是一套与冈瓦纳地区晚古生代大规模冰川作用有直接联系的沉积地层，具有近岸冰海环境的特点，是对应冈瓦纳大陆北缘晚古生代裂解过程的沉积响应，其中所产早二叠世孢粉化石与早二叠世大规模冰川消退期事件有着密切的联系。该套孢粉组合中除Parasaccites obscurus，P. cf. radiplicatus，Plicatipollenites indicus等冈瓦纳型分子，其余皆为亚安加拉区常见的双囊具肋花粉Striatoabieites，Hamiapollenites和单气囊花粉Cordaitina等分子。初步研究表明，在早二叠世冈瓦纳北缘和亚安加拉区共有某些植物类群的可能性是极大的，甚至拉萨、南羌塘等地块由冈瓦纳北缘向华夏区转换的过程中微植群中发生的混生可能比古动物群响应的更早，至少在早二叠世的冰期末或冰期结束后就已经发生了。封面显示了西藏申扎地区早二叠世地层剖面，近景为拉嘎组冰海杂砾岩，其中产出早二叠世孢子与花粉化石，远景为早二叠世石灰岩。详见张予杰等人文（p2227）。

西藏申扎地区早二叠世冰海相地层中孢粉化石的发现

张予杰，安显银，张以春，等

拉萨地块下二叠统拉嘎组是一套与冈瓦纳地区晚古生代大规模冰川作用有直接联系的沉积地层，作者在西藏申扎地区的拉嘎组中分析出孢粉化石，说明早二叠世蕨类植物孢子和裸子植物花粉的出现与冈瓦纳大陆冰川消退事件有密切联系。该套孢粉组合中蕨类植物孢子含量远低于裸子植物花粉含量，双囊具肋花粉和单囊花粉含量最高，Hamiapollenites与Striatoabieites两属地位尤为突出；组合中蕨类植物孢子含量虽低但分异度较高，单气囊花粉Cordaitina所占比例较大，双囊具肋花粉Hamiapollenites，Striatoabieites，Protohaploxypinus的种数很多，可建立Hamiapollenites-Striatoabieites组合。值得注意的是，除了少数“冈瓦纳型”分子Parasaccites obscurus，P. cf. radiplicatus，Plicatipollenites indicus的存在外，其余含量极高的分子则可与新疆北部早二叠世孢粉组合相对比，说明早二叠世冈瓦纳和亚安加拉共有某些植物类群的可能性是极大的。这类孢粉组合在早二叠世冰海相沉积物中的出现表明，拉萨、南羌塘等地块由冈瓦纳北缘向华夏区转换的过程中，微植群发生的混生可能比古动物群响应的更早，至少在早二叠世的冰期末或冰期结束后就已经发生了。

西藏；申扎；早二叠世；冰海相地层；孢粉化石

来源出版物：科学通报，2015，60（23）： 2227-2235联系邮箱：张予杰，zebiac@163.com

来源出版物：SCIENCE CHINA Earth Sciences，2015，58（8）： 1305-1319联系邮箱：WANG Li-ning； wanglining@petrochina.com.cn

封面介绍：The extreme modern elevation of the Tianshan Mountains reflects the Cenozoic deformation. However，uncertainties remain over timing constraints on its thermal history since the Cenozoic. Modern river sands are ideal samples to explore the thermal history in a large scale by detrital Apatite Fission Track（AFT）study with statistical features. For more details see the research paper by WANG Li-ning et al. on pages 1305-1319.

Chronological constraints on multi-staged rapid cooling of the Tianshan Mountains inferred from apatite fission track analysis of modern river sands

WANG Li-ning； JI Jian-qing； SUN Dong-xia； et al.

The extreme modern elevation of the Tianshan Mountains reflects the Cenozoic deformation. Apatite Fission Track（AFT）chronometry is widely used to study the latest cooling stages caused by tectonic process or by exhumation in the uppermost crust. However，uncertainties remain over timing constraints on thermal history of the Tianshan Mountains since the Cenozoic though a great mount of dating work had been done in this area. To address this issue，modern river sands from the drainage basin on the piedmont of the Tianshan Mountains were sampled to integrate regional information. Single grains were dated with the AFT method，and then different grain-age components were identified to provide thermochronological constraints of their sources. Combined with discussion of previous dataset，our results show the multi-staged rapid cooling cluster at 46-32，25-24，19-13，8-6，and ～3 Ma，respectively. We interpreted these cooling events as a result of interplays between the Cenozoic tectonic uplift of the mountains and regional climate change.

Tianshan Mountains； detrital apatite fission track； cooling stages； exhumation； thermal history