从中亚正ε_(Nd)值花岗岩看超大陆演化和大陆地壳生长的关系

Correlation between Continental Crustal Growth and the Supercontinental Cycle: Evidence from the Granites with Positive εNd in the Central Asian Orogenic Belt

超大陆演化着重研究超大陆的聚合和裂解、离散,大陆地壳生长着重探索大陆地壳的生长和消亡。长期以来,人们都是如此将两者割裂开来研究的。本文从中亚造山带显生宙花岗岩同劳亚大陆的关系出发,进一步探讨超大陆演化、大陆地壳生长和地幔中俯冲板片雪崩事件(slab avalanche events)三者之间的关系,强调在超大陆形成时伴随大陆地壳急剧生长,在超大陆裂解、离散时大陆地壳的生长和消亡大体上保持平衡。无论超大陆演化或是大陆地壳生长都同地幔对流形式的变化有着密切的联系。

Studies of the supercontinental cycle are mainly concentrated on the assembly, breakup and dispersal of supercontinents, and studies of the continental crustal growth largely on the growth and loss (recycling) of the crust. These two problems have long been studied independently from each other. Paleozoic-Mesozoic granites in the Central Asian orogenic belt have commonly positiveεNd values, implying large-scale continental crustal growth in the Phanerozoic. They coincided temporally and spatially with the Phanerozoic Pangea supercontinental cycle, and overlapped in space the P-wave high-V anomalies and calculated positions of subducted slabs for the last 180 Ma. All these suggest that the Phanerozoic Laurasian supercontinental assembly was accompanied by large-scale continental crustal growth in Central Asia. Based on these observations, this paper proposes that there may be close and original correlations among the supercontinental cycle, continental crustal growth and catastrophic slab avalanches in the mantle. In this model we suggest that a rapid continental crustal growth occurred during the supercontinent assembly, whereas during its breakup and dispersal growths of the crust were balanced by losses, resulting in a steady-state system. The supercontinental cycle and the continental crustal growth are both governed by the changing patterns of mantle convection.