东亚陆缘带构造扩张的深部热力学机制

近年来,我国地球科学家提出“陆缘构造扩张”观点,较好的解释了亚洲东部大陆边缘于新生代发生扩张离散运动的原因。本文基于“陆缘构造扩张”观点,探讨东亚陆缘带构造扩张的深部热力学机制。东亚陆缘带是具有强烈岩浆活动和构造变形的扩张带,此构造带的主要地球物理特征是频繁的地震活动和明显的地热异常。东亚陆缘扩张带地震层析成像显示,太平洋板块低角度俯冲到欧亚板块之下并平卧于670km相变界面之上。这种图像可能是俯冲后撤导致陆缘扩张的结果。热模拟及地球动力学计算表明:俯冲后撤时间距今约76Ma,海沟带后撤为陆缘壳体的生长留下空间,并形成东亚陆缘壳体增生扩展的前沿带,陆缘扩张量约700km。

THERMODYNAMICS MECHANISM OF THE MARGINAL EXTENSIONAL BELT OF EAST ASIA

The marginal extension is an importa nt viewpoint in earth science.It is s ignificant to explain the appearance of outspreading movemen t in the East Asia continental margin.This viewpoint was put forward by Chinese scientists in past years.Or iginally,It is used to study the disc rete tectonic belt between the South China continent and the South China Sea.The northern margin of the South China S ea lies in the tectonic zone of the East Asia continental margin.Being the b ackground of active continental margin,the northern margin of the South China Sea has an intense tectonic activity.According to the viewpoint of marginal extension,Chinese geoscientis ts have effectively interpreted the tecton ic evolution of the northern margin o f the South China Sea.Furthermore,S cientists develop this viewpoint for suiting t o all the continental margin belts over eastern Asia.This tectonic zone i s an active tectonic zone of global scale.Its main tectonic characteristics are the continental crust disintegration and the massif splitting.The basic tectoni c pattern of this zone has appeared since the Cenozoic.Based on the point of view of marginal extension,this paper di scusses the thermodynamics mechani sm of the marginal extensional belt o f eastern Asia.In this zone,the typic al geophysical features are frequen t earthquakes and widely geothermal anomaly.The seismic tomography of e astern Asia shows that the pacific pl ate has been subducting in a lower angle under the Eurasia plate and lies on th e 670km sub-interface of the phase boundary between the upper and lower mantle.This image may be the consequ ences of roll-back subduction and ma rginal extension.The results of thermal modeling and geodynamic computing d emonstrate that the roll back subduction occurs at about 76Ma.This movement of trench backing would bring interspaces for the growth of marg inal crust.Then,a frontier develop ment zone of the marginal extensional belt of eastern Asia should come into being.The extending distance is about 600km.