南苏鲁造山带毛北超高压变质岩体的成因与成矿作用

Petrogenesis and mineralization of the Maobei complex from the southern Sulu ultrahigh-pressure metamorphic belt,eastern China.

毛北超高压变质岩体位于苏鲁造山带南部,是由石榴石橄榄岩、榴辉岩、硬玉石英岩和石榴石多硅白云母石英片岩组成的层状岩体。富金红石榴辉岩和富钛铁矿榴辉岩在岩体中呈连续的层状产出,总厚度达200m,深度>700m,构成了一个大型的钛矿床。岩石学、地球化学和年代学研究表明,毛北岩体的原岩形成在新元古代Rodinia超大陆裂解过程中,基性岩浆经历了强烈的分异结晶作用,形成了由橄榄辉长岩-辉长岩-闪长岩-花岗岩组成的复杂层状侵入体,并在新元古代的全球冰期与高纬度大气降水发生强烈的水-岩交换作用。在印支期的大陆深俯冲过程中,经历了超高压变质作用,其峰期变质温度>800℃,压力>4.5GPa,富钛磁铁矿辉长岩转变成了富金红石榴辉岩,形成了超高压变质的钛矿床。

The Maobei complex located in the southern Sulu orogenic belt is a layered ultrahigh-pressure metamorphic rock body, which consists of garnet-peridotite, eclogite, jadeite-quartzite and garnet-phengite-quartz schist. The rutile- and ilmenite-rich eclogites occur as a continuous layer from the surface to the depth greater than 700m with a total thickness over 200m, forming a large titanium ore deposit. The investigations of petrology, geochemistry and geochronology show that the protolith of the Maobei complex is a layered intrusion consisting of olivine-gabbro, gabbro, diorite and granite, which was formed by intensive fractionation crystallization of a basaltic magma during the breakup of the Rodinia supercontinent at the Neoproterozoic. In addition, the Maobei complex was extensively interacted with meteoric water during the Neoproterozoic global glaciation. This body has been subjected to the ultrahigh-pressure metamorphism with a peak-metamorphic condition of more than 800 degrees C and 4.5GPa during the deep continental subduction in the Triassic. By this process, the titanomagnetite-rich gabbros were transformed into the rutile-rich eclogites which are the parent rocks of the Maobei rutile deposit.