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

中亚古地磁研究：第三纪低古纬度困境与蒙古-鄂霍茨克洋闭合

• 批准号: 0003512
• 负责人: Xixi Zhao
• 金额: $ 24.53万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-01-01 至 2003-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003512&HistoricalAwards=false
• 关键词: Paleomagnetic; Study; Central; Asia; Tertiary

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.

赵0003512两个重要问题阻碍了对中亚构造的理解。 第一个是令人不安的低古纬度的一致模式，这是对第三纪岩石进行的大量高质量古地磁研究得出的，这些研究的地点从中国东部一直延伸到吉尔吉斯斯坦，以西 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古地磁参考极的预期差异平均为 18o，这意味着第三纪相对于西伯利亚的向北位移远大于对中间山带缩短的地质估计。许多亚洲构造学研究人员已经认识到这个问题。 其解决方案的一个重要线索可能在于以下事实：第三纪的欧亚参考极都不是来自西伯利亚附近任何地方的岩石，这表明它们可能不适合计算与西伯利亚的收敛。 必须先回答这个问题，然后才能评估有多少差异是由构造、地磁和岩石磁性造成的。 第二个问题是蒙古-鄂霍茨克洋闭合的历史。 这片大洋曾经将蒙古-华北复合地块与西伯利亚分开。 关于这一主题的地质证据有多种解释方式，导致了关于闭合时间和几何形状以及地体边缘增生何时何地发生的争议。