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

Zhao 0003512两个重要问题阻碍了对中亚大地构造的理解。 第一个是令人不安的低古纬度的一致模式，来自大量高质量的第三纪岩石古地磁研究，这些研究的地点从中国东部一直延伸到吉尔吉斯斯坦，向西3,000公里。在中国西部和吉尔吉斯斯坦，这些古纬度与欧亚大陆的古地磁参考极之间的差异平均为18 °，这意味着在第三纪相对于西伯利亚的北向位移远大于地质学估计的横跨中间山脉带的缩短。许多亚洲大地构造学的研究者已经认识到这个问题。 解决这个问题的一个重要线索可能在于，第三纪的欧亚参考极都不是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趋同。 这个问题必须得到回答，才有可能评估有多少差异是构造，地磁和岩石磁性。 第二个问题是蒙古-鄂霍次克海封闭的历史。 这片大洋曾经将蒙古-华北复合地块与西伯利亚隔开。 有关这一主题的地质证据被解释在各种各样的方式，导致争议的时间和几何形状的关闭，何时和边缘加积的火山岩发生。

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.