Paleomagnetic Study of Central Asia: The Tertiary Low-Paleolatitude Dilemma and Closure of the Mongol-Okhotsk Ocean

两个重要的问题阻碍了对中亚构造的认识。首先是对第三纪岩石进行了大量高质量的古地磁研究，得出了令人不安的低古纬度的一致模式，这些研究地点从中国东部一直延伸到吉尔吉斯斯坦，向西延伸3000公里。在中国西部和吉尔吉斯斯坦，这些古纬度与欧亚大陆古地磁参考极所预测的纬度之差平均为180度，这意味着第三纪相对于西伯利亚的北移要比地质估计的中间山带缩短要大得多。亚洲构造学的许多研究人员已经认识到了这个问题。解决这个问题的一个重要线索可能是，欧亚大陆第三纪的参考极没有一个来自西伯利亚附近的岩石，这表明它们可能不适合计算与西伯利亚的辐合。这个问题必须得到回答，然后才有可能评估有多少差异是构造、地磁和岩石磁造成的。第二个问题是蒙古-鄂霍次克海关闭的历史。这个大洋曾经将蒙古-华北复合块体与西伯利亚分开。关于这一主题的地质证据有各种各样的解释方式，导致了关于关闭的时间和几何形状以及何时以及在何种程度上发生了地体边缘增生的争议。

Zhao0003512Two important problems obstruct understanding of the tectonics of central Asia. The first is the consistent pattern of disturbingly low paleolatitudes derived from a large number of high-quality paleomagnetic studies of Tertiary rocks from sites that reach all the way from eastern China to Kyrgyzstan, 3,000 km to the west. The difference between these paleolatitudes and those expected from paleomagnetic reference poles for Eurasia averages 18o in western China and Kyrgystan, implying northward displacements relative to Siberia in the Tertiary that are much larger than geological estimates of shortening across intervening mountain belts. Many researchers in Asian tectonics have recognized this problem. A significant clue to its solution may lie in the fact that none of the Eurasian reference poles for Tertiary time is from rocks anywhere near Siberia, suggesting that they may not be appropriate for calculating convergence with Siberia. This question must be answered before it will be possible to evaluate how much of the discrepancy is tectonic, geomagnetic, and rock magnetic. The second problem is the history of closure of the Mongol-Okhotsk Ocean. This large ocean used to separate the Mongolia-North China composite block from Siberia. The geologic evidence concerning this subject is interpreted in a wide variety of ways, resulting in controversy over the timing and geometry of closure and when and to which margin accretion of terranes occurred.