Evolution of Cratonic Lithosphere in Eastern China

中朝克拉通是太古代克拉通中罕见的一个具有耐火地幔根缺失证据的克拉通。 在古生代，含金刚石金伯利岩通过克拉通喷发，携带矿物和捕虏体，表明存在200 km厚的耐火岩石圈，与冷地热平衡。 三叠纪，苏鲁地区的石榴橄榄岩在扬子碰撞和中朝碰撞过程中被抬升。 这些橄榄岩可能表明在这个时候存在的岩石根。 与此相反，新生代裂谷相关的玄武岩携带肥沃的地幔捕虏体，记录高平衡温度和样品深度只有80公里。 这些观测结果被解释为反映了中朝克拉通之下的地幔根在奥陶纪之后的某个时候消失，并被克拉通以外地区典型的更肥沃的橄榄岩所取代。悬而未决的问题包括：1）是否所有的地幔根都被移走了，2）何时被移走的，3）被移走的机制。 我们试图通过对上述三种地幔样品的系统岩石学、地球化学和Re-Os同位素研究来解决这些问题。 对苏鲁橄榄岩中的铬铁矿和玄武岩橄榄岩中的全岩进行Re-Os分析，以确定构造岩片的起源和年龄，以及现今岩石圈（以新生代玄武岩为样品）的形成时间，这些数据将使我们能够估计岩石圈的移动时间，假定它一定发生在现今岩石圈形成之前不久。 据此，我们有可能推断出超声波岩石圈的移动机制。

9903159RudnickThe Sino-Korean craton is a rare example of an Archean craton that showsevidence for loss of its refractory mantle root. In the Paleozoic,diamondiferous kimberlites erupted through the craton carrying minerals andxenoliths indicative of the presence of a 200 km thick refractorylithosphere, equilibrated to a cool geotherm. In the Triassic, refractorygarnet peridotite was uplifted in the Sulu region during the collision ofthe Yangtze and Sino-Korean cratons. These peridotites may indicate thepresence of the cratonic root at this time. In contrast, Cenozoicrift-related basalts carry fertile mantle xenoliths that record highequilibration temperatures and sample to depths of only 80 km. Theseobservations have been interpreted to reflect the loss of the cratonic rootbeneath the Sino-Korean craton, sometime after the Ordovician and it'sreplacement with more fertile peridotite, typical of off-craton regions.Outstanding questions include: 1) whether all of the cratonic mantle wasremoved, 2) when it was removed and 3) the mechanism by which it wasremoved. We seek to address these questions through a systematicpetrographic, geochemical and Re-Os isotopic study of the three types ofmantle samples described above. Re-Os analyses of chromites from the Suluperidotites and whole rocks from the basalt-borne peridotites will be madein order to determine 1) the origin and age of the tectonic slivers and 2)when the present lithosphere (as sampled by the Cenozoic basalts) formed.These dates will allow us to estimate the timing of lithosphere removal,assuming that it must have occurred shortly before the present lithosphereformed. Given this, it may be possible to infer the mechanism of removalof the cratonic lithosphere.