苏鲁-大别山超高压变质带迟家店和碧溪岭石榴二辉橄榄岩橄榄石组构

大别山碧溪岭和山东荣成分别发育壳源和幔源的石榴二辉橄榄岩。它们在扬子板块向华北板块的俯冲过程中与俯冲板片一起经历了超高压变质作用。这两种原岩来源不同的石榴橄榄岩中的橄榄石具有相似的结晶学优选方位(LPO):100]轴主板密垂直于面理面,010]轴主极密平行于线理,这种橄榄石结晶学优选方位明显不同于高温地幔橄榄岩包体中的橄榄石组构,也不同于最近在超高压变质地体中发现的水导致的橄榄石组构。我们认为碧溪岭和荣成石榴二辉橄榄岩中的这种橄榄石组构可能是在相对较干的超高压变质条件下形成的。本研究为大陆深俯冲超高压变质石榴橄榄岩橄榄石组构特征提供了第一手资料。

Olivine fabric in garnet lherzolite from Rongcheng and Bixiling of Sulu-Dabieshan Ultrahigh-pressure (UHP) metamorphic belt,Eastern China

Crust-derived and mantle-derived garnet lherzolite occurs at Bixiling of Dabieshan and Rongcheng of Sulu ultrahigh- pressure(UHP)metamorphic terranes respectively.Both types of lherzolite experienced UHP metamorphism due to the subduction of the Yangtze Craton under the Sino-Korean Craton.The olivine from the two kinds of garnet lherzolite have similar Lattice Preferred Orientation(LPO)with strong maxima of100] subnormal to the foliation and strong maxima of010] subparallel to the lineation, which is different from the high-temperature olivine LPO in mantle xenoliths and from the water-induced olivine fabric in UHP metamorphic terranes.We regard that the LPO found in Bixiling and Rongcheng garnet lherzolite was formed during medium- temperature UHP metamorphism in relative dry environment.These data witness the character of olivine from UHP metamorphic garnet peridotite during the continental deep subduction.