Paleomagnetism of Neoproterozoic to Lower Paleozoic Rocks on Microcontinents of Central Asia: Implications for the Precambrian Glacial Paradox and Amalgamation of Eurasia

构成欧亚大陆的小大陆是在寒武纪（约5.2亿年前）开始的漫长时期内合并而成的。位于这些微大陆上的岩石含有更古老的（前寒武纪）火成岩和沉积岩，这些岩石至少部分形成于被认为以全球气候极端波动为特征的时期。这些严重的气候变化时期被称为“雪球地球”时期。这些微大陆在并入欧亚大陆之前的位置以及保存在这些微大陆上的冰川事件的确切年龄都鲜为人知。这项工作的重点是获取现在位于蒙古、哈萨克斯坦和吉尔吉斯斯坦的各种微大陆的古地磁和地质年代学数据。本研究收集的数据使研究人员能够更好地确定这些微大陆合并到欧亚大陆之前的位置。这些数据还为研究人员提供了保存在微大陆上的冰川沉积物的重要古纬度和地质年代学约束。由于雪球地球假说假定地球上的冰川作用几乎是全球同步的，这些数据为雪球地球假说提供了一个关键的检验，也为这个古老的冰河时代的其他相互竞争的解释提供了检验。最后，研究数据对乌拉尔-蒙古褶皱带构造演化的一般样式有很强的约束，该褶皱带是由微大陆块体与古海洋闭合碰撞而形成的。该项目由构造学计划和国际科学与工程办公室的俄罗斯和欧亚小组提供支持。

The microcontinents that make up Eurasia were amalgamated over a protracted period beginning in the Cambrian Period (~520 million years ago). The rocks that lie on these microcontinents contain older (Precambrian-age) igneous and sedimentary rocks that formed, at least in part, during a period of time thought to be characterized by extreme swings in global climate. These episodes of severe climate change are dubbed the "Snowball Earth" epochs. Both the location of these microcontinents prior to their incorporation into Eurasia and the exact age of the glacial events preserved on the microcontinents are poorly known. This work focuses on obtaining paleomagnetic and geochronologic data from various microcontinents now located in Mongolia, Khazakhstan and Kyrgystan. The data collected in this study allow the investigators to better constrain the position of these microcontinents prior to their amalgamation into Eurasia. The data also supply researchers with important paleolatitudinal and geochronologic constraints on the glacial sediments preserved on the microcontinents. Since the Snowball Earth hypothesis posits near global synchroneity of glaciation across the planet, these data provide a critical test of the Snowball Earth hypothesis as well as a test of other competing explanations for this ancient ice age. Lastly, the data obtained in the study impose strong constraints on the general style of tectonic evolution for the Ural-Mongol fold belt that developed as a result of collisions between the microcontinental blocks and the closure of an ancient ocean.Support for the project is provide by the Tectonics Program and by the Russia and Eurasia Group of the Office of International Science and Engineering.