塔里木盆地北缘幔源岩石包体特征及岩石圈上地幔流变规律

CHARACTERISTICS OF MANTLE XENOLITHS AND RHEOLOGICAL REGULARITY OF LITHOSPHERIC UPPER MANTLE IN THE NORTHERN MARGIN OF TARIM BASIN

岩石圈上地幔岩石包体保存着上地幔物质组成和岩石学的特征以及岩石圈上地幔构造变形特性、岩石变形机制和流变性质的丰富信息。塔里木盆地西北缘的巴楚地区的幔源包体主要由橄榄岩组成,次为单辉橄榄岩,与中国东部以及西部其他地区发育的尖晶石、石榴石二辉橄榄岩幔源包体有所区别。从莫霍面至岩石圈上地幔下部,随着深度、温度和压力的增高,幔源包体橄榄石中出现直线状位错、位错缠结、网络—曲线状、环状位错—直线状位错、位错缠结、网络—曲线状位错,环状位错的变化规律;其微观变形机制有从碎裂—位错滑移—位错蠕变—扩散蠕变的变化规律;差异应力值有从低—高—低—高的正弦波状变化趋势,在莫霍面附近以及上地幔韧性软层与脆性层附近差异应力值一般较高;应变速率值则是逐渐减慢的总体变化趋势,整体反映出岩石和矿物从脆—韧性的流变性质。

Mantle xenoliths contain a lot of information about the compositions,deformation,deformation mechanisms and rheological property of the lithospheric upper mantle.Compared with the spinel buchnerites and garnet buchnerites widespread in the east and west China,the mantle xenoliths from the northern margin of Tarim basin was mainly composed of peridotites with minor clinopyroxene peridotites.Microfabric study indicated that,as the depth,temperature and confining pressure increased in the lithospheric upper mantle,the dislocation lines in the olivine from the mantle xenoliths varied from straight dislocation to curved dislocation and dislocation loops corresponding to the variations of deformation mechanisms of cataclasis-dislocation slip-dislocation creep-diffusion creep,the strain rates slowed down gradually and the differential stresses went up and down with concentration at the interface of crust and mantle as well as at the strongly deformed shear zones.