东准噶尔扎河坝蛇绿混杂岩中的石榴角闪岩

继报道了超高压成因的石榴辉石岩和石英菱镁岩之后，作者在扎河坝地区又发现了具有超高压成因特征的石榴角闪岩。扎河坝石榴角闪岩主要组成矿物为角闪石、石榴石、辉石和钠长石，它不但含硬玉、多硅白云母等高压变质矿物，而且还残留着具有超高压成因特征的超硅石榴石和超硅辉石。根据野外产状和矿物组成特征，扎河坝石榴角闪岩可以细分成含硬玉石榴角闪岩和含多硅白云母石榴角闪岩两类，它们的原岩为大洋玄武岩。石榴角闪岩的厘定进一步证实在扎河坝蛇绿混杂岩带内确实存在着超深俯冲后折返的洋壳，同时超深俯冲洋壳的组成也较复杂，包括沉积岩、辉长岩和大洋玄武岩等。石榴角闪岩、石英菱镁岩及石榴辉石岩等超高压变质岩的存在表明扎河坝蛇绿岩带是一条大洋板块的超深俯冲带，它可能通过克拉玛依蛇绿岩带西延出境，形成一条横贯东西准噶尔北缘的超深俯冲带。这条超深俯冲带的发现为研究新疆北部早古生代洋陆转换过程及机制提供了新的视野和思路，对深入探讨准噶尔盆地北缘及阿尔泰南缘早古生代壳幔相互作用及中亚造山带形成的动力学机制具有重要的启示。

Discovery of garnet amphibolite in Zaheba ophiolitic melange, eastern Junggar, NW China

Following the report on garnet pyroxenite and quartz-magnesitite with the ultra-high pressure (UHP) origin in the Zaheba region, the authors further discovered there the garnet amphibolite in the same origin. The garnet amphibolite is mainly composed of amphibole, garnet, pyroxene and albite. It contains not only the high pressure minerals, such as jadeite and phengite, but also the relicts of supersilicic garnet and supersilicic pyroxene with UHP genetic features. Based on the field occurrence and mineral assemblage, the garnet amphibolite can be sub-divided into two groups: the jadeite-bearing and the phengite-bearing, and their primitive rocks are all oceanic basalts. The identification of garnet amphibolite further confirmed that there is an exhumed oceanic crust after ultradeep subduction in the Zaheba ophiolitic mélange, and the composition of the oceanic crust is more complicated, including sedimentary rocks, gabbros and oceanic basalts. The existence of UHP metamorphic rocks, such as garnet amphibolite, quartz-magnesitite and garnet pyroxenite illustrated that the Zaheba ophiolitic belt was an ultradeep subduction zone of the oceanic slab, and it connected with the Keramay ophiolitic belt at its western section, and then extended westwards out of the national boundary, forming an EW stricking ultradeep subduction zone along the northern Junggar margin. The discovery of this ultradeep subduction offers a new idea in the study on the process and mechanism of ocean-continent transition during Early Paleozoic, and also has a significant enlightenment in the investigations of crust-mantle interaction at the northern margin of the Junggar basin and the southern margin of the Altai mountain during Early Paleozoic, and the geodynamic mechanism of the formation of Central Asian orogen.