Jagoutz Oliver, Macdonald Francis A, Royden Leigh
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139;
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 2016 May 3;113(18):4935-40. doi: 10.1073/pnas.1523667113. Epub 2016 Apr 18.
New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90-70 Ma and at ∼50-40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2 Based on these results, we suggest that the low-latitude closure of ocean basins along east-west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean.
新特提斯洋构造演化的新限制表明，在约90 - 70百万年前和约50 - 40百万年前，大量镁铁质和超镁铁质岩石在低纬度地区侵入热带湿润带内的大陆地壳。这些侵入事件在时间上与终止白垩纪热极大期和早始新世气候适宜期的全球气候变冷事件相对应，并且可能是其成因。我们模拟了在100到40百万年前，由于这些仰冲蛇绿岩的化学风化作用导致大气中二氧化碳减少的时间效应，以及新特提斯弧火山作用向大气中添加二氧化碳的时间效应。模拟的净二氧化碳减少速率变化与该时间间隔内海底水温的同期变化非常吻合，表明蛇绿岩侵入可能在全球气候变化中起了主要作用。我们证明，需要仰冲岩石的岩性（镁铁质/超镁铁质）以及高降水率的热带湿润气候才能产生显著的二氧化碳消耗。基于这些结果，我们认为沿东西向板块边界的低纬度洋盆闭合也可能引发了其他长期全球变冷事件，如与伊阿珀托斯洋闭合相关的中奥陶世到晚奥陶世变冷和冰川作用。
