摘要
在苏北超高压变质带以南存在一条与之平行的高压变质带。带内由东南向西北可进一步划分出蓝闪石-黑硬绿泥石带,石榴石-绿帘石带和蓝晶石-黄玉带三个变质亚带。从蓝门石-黑硬绿泥石带到蓝晶石-黄玉带变质温压逐渐升高,其峰期地热梯度为15±3℃/km,属于高压变质相系。北侧超高压变质带的典型矿物组合是石榴石+绿辉石+柯石英+金红石,地热梯度为9±2℃/km。高压变质带峰期变质与北侧超高压带峰期变质的地热梯度明显不同,而与超高压变质体的退变质地热梯度相吻合。结合同位素年代学资料,本文指出本区的高压变质作用与北侧的超高压变质作用不是同时发生,而是与超高压变质体的退变质作用同时发生于中生代的印支期。含柯石英榴辉岩的超高压峰期变质早于印支期,并经两次抬升出露于地表。
A high-pressure (HP) metamorphic belt paralleling to the northern Sulu ultrahigh-pressure (UHP) meta-morphic belt occurs in Northern Jiangsu. Three metamorphic zones are distinguished from the southeast to the northwest in the HP metamorphic belt. They are glaucophane-stilpnomelane zone, garnet-epidote zone and kyanite-topaz zone. Metamorphic P-t conditions increase gradually from the south to the north. The geother-mal gradient of the peak metamorphism is 15±3℃/km, belonging to high-pressure facies series. The typical mineral assemblage of the UHP metamorphism in neighboring region to the north is garnet + omphanite + ru-tile + coesite. Its geothermal gradient is ca. 9±2℃/km. The geothermal gradient of the HP metamorphism is significantly higher than that of the UHP metamorphism, but is consistent with that of the retrograde metamorphism of the UHP metamorphic rocks. Considering isotopic age data, this study indicates that the HP metamorphism is not simultaneous with the UHP metamorphism, but is almost contemporary with the retrograde metamorphism of UHP metamorphic massif, which occurred in Indo-Chinese epoch (Mesozoic). The peak metamorphism forming coesite-bearing eclogites should take place before Indosinian. Accordingly, the UHP metamorphic rocks exhumed to the surface from the upper mantle by two stages of the ascending.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2001年第1期82-90,共9页
Acta Geologica Sinica
基金
南京大学"内生金属矿床成矿机制研究国家重点实验室"资助的成果。
关键词
高压变质带
超高压变质作用
地热梯度
榴辉岩
同位素年代学
high pressure metamorphism
ultrahigh pressure metamorphism
geothermal gradient
two-stage uplift
North Jiangsu
