摘要
在青海都兰北东40km野马滩一带元古宙变质杂岩中,新发现走向近东西的榴辉岩;可分为南北两带,北带宽约5km,南带宽3～5km。北带榴辉岩相矿物组合为石榴石-绿辉石-多硅白云母-金红石,它们的退变质矿物主要为角闪石及少量高钠的斜长石类。而南带峰期变质矿物为石榴石-绿辉石-蓝晶石-金红石-黝帝石(?),退变质矿物中则出现大量高钠质斜长石。两带另一个明显的区别是北带铁铝榴石端元组分含量较南带的略高,而镁铝榴石端元组分含量则略低。采用Krogh(1988)的石榴石-单斜辉石温度计计算得到,在压力为1.5GPa时,北带温度为652～689℃,南带为873～913℃,两带温度相差约200℃。矿物压力计计算得到北带榴辉岩的压力为2.0～2.6GPa,而根据绿辉石-蓝晶石组合估测南带的压力值大于2.0GPa。都兰榴辉岩及其围岩的岩石矿物特征及形成温压与大柴旦及阿尔金且末-带的榴辉岩十分接近,推断它们为同一条早古生代高压变质带,并有可能与北秦岭、桐柏和大别—苏鲁出露的加里东期榴辉岩共同组成一条横贯东西的巨型高压—超高压带,它们代表了中国南北板块早期的界线。
Eclogite was found in the Proterozoic gneiss about 40 km northeast of the Dulan town, Qinghai Province. It occurs as pods in the gneisses of the Proterozoic Shaliuhe Group, forming an EW trending composite belt composed of a northern sub-belt about 10 km wide and a southern one 3-5 km wide. The peak metamorphic minerals in the eclogites of the northern belt are garnet - omphacite - phengite - rutile and retrograded minerals are mainly amphibole and some high-Na feldspar. In the southern belt the peak metamorphic minerals are garnet - omphacite - rutile -kyanite - zoisite (?), and the retrograded minerals are characterized by the appearance of a large amount of feldspar - amphibole - zoisite - quartz. The compositions of garnets are different in the two belts, 38%-54% almandine, 21%-24% grossular and 19%-37% pyrope molecules in the southern belt and 41%-58%,13%-38% and 10%-27%inthe northern belt, respectively. Grt-Omp geothermometer calculation (using the method by Krogh, 1988) yields a temperature range of 652-698℃ at the pressure of 2. 0 GPa for the northern belt eclogite and 873 -913℃ for the southern belt. The peak pressure of 2. 0-2. 6 GPa for the northern belt by using Grt-Ph geobarometer, and >2. 0 GPa for the south belt, by estimation of the mineral assemblage Grt - Omp - Ky without paragonite. The petrological and mineralogical features and p-t conditions of the Dulan eclogite and their country rocks are very similar to those of the Da Qaidam eclogites and the Altun eclogites, suggesting that they together constitute an Early Palaeozoic high pressure metamorphic belt, probably connecting eastward with the Early Palaeozoic eclogites in the northern Qinling, Tongbo, and northern Dabie, forming a huge HP-UHP metamorphic belt extending from west to east across the central continent of China, and may represent an old boundary between the south China plate and the north China plate.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2000年第2期156-168,共13页
Acta Geologica Sinica
基金
国家自然科学基金(编号49732070)
国家重点基础研究发展规划(编号G1998040800)资助项目
关键词
高压变质带
榴辉岩
柴达木盆地北缘
HP metamorphic belt
eclogite
Dulan
north margin of the Qaidam basin
