大别山南部高压-超高压变质地体的峰期变质条件

长期以来,人们普遍认同南大别高压超高压变质地体是由“冷”、“热”榴辉岩带组成的观点,但关于两者的接触关系一直存在着不同的认识。本次研究重点解剖大别山太湖地区花凉亭水库附近地区,力图通过对各类榴辉岩峰期变质P-T条件的研究,揭示南大别变质地体的地质结构。全区由南向北出露4种岩石:云母片岩、黑云母片麻岩、花岗片麻岩和绿帘黑云斜长片麻岩。榴辉岩多呈大小不等的透镜体、岩块或层状分布于后3类岩石中。根据内洽地质温压计的计算结果,并结合各类榴辉岩的地理位置,可以看出榴辉岩的峰期变质PT条件自朱家冲经水口、大坝至金河桥是渐次增高的,并没有明显的压力差存在,其中水口、大坝附近的榴辉岩相当于高压/超高压过渡环境中形成的榴辉岩。因此,我们认为南大别变质地体是一个连续的整体,“冷”、“热”榴辉岩带并不是以断层形式相接触的;真正的断裂应位于南大别与宿松群之间。

PEAK METAMORPHIC CONDITIONS OF THE HIGH-ULTRAHIGH PRESSURE TERRAIN IN SOUTH DABIE MOUNTAINS

For a long time, many geologists accepted the opinion that the high ultrahigh pressure metamorphic terrain in the south Dabie Mountains was composed of the "cold" and "hot" eclogites; however, some different arguments still exited about the relationship between the both. This study tried to reveal the geological architecture of the high-ultrahigh pressure metamorphic terrain in the area of south Dabie Mountains in the light of peak metamorphic P-T conditions of the eclogites. The studied area was located at the Hualiangting reservoirs, Taihu County, where outcropped four types of rocks from the south to the north: the mica-schists, the biotite gneisses, the granitic gneisses and the epidote-biotite-plagioclase gneisses. The eclogites occurred as lens, blocks and/or layers in the later three types of rocks. According to the computation result of the internally consistent thermometers and barometers, combined with distribution of the eclogites, it was found that the peak metamorphic P-T conditions of the eclogites there increased gradually from Zhujiachong, Shuikou and Daba to Jinheqiao, without pressure gap existing among them,and the eclogites in Shuikou and Daba having undergone metamorphism on the HP/UHP mixed conditions. Hence, it could be concluded that the metamorphic terrain of south Dabie Mountains might be a continuous terrain, and the contact relationship between the "cold" and "hot" eclogites did not appear in a form of fault. In fact, the fault situated between the south Dabie Mountains and the Susong group.