Geochronologic Characteristics of Al-rich Gneisses in Wulashan-Daqingshan Area,Central Inner Mongolia
The Wulashan rock group,a set of Early Precambrian high-grade metamorphic rock series with high metamorphic degree of amphibolite facies-granulite facies,has been determined in the Wulashan-Daqingshan Area of central Inner Mongolia.The metamorphic plutons of quartz diorite gneiss and perilla granitic gneiss,intruded into the biotite garnet plagioclase gneiss of the Wulashan rock group,were studied by chronology to divide the protolith formation age and metamorphic age of aluminum-rich gneiss in the Wulashan-Daqingshan Area.The results show as follows.The weighted average ages of perilla granitic gneiss(TW7)and granodiorite gneiss(D1227)are(2 462±13)Ma and and(2 512±24)Ma,respectively.It could be inferred that,the formation age of the protolith of the aluminum-rich gneiss in Wulashan is earlier than 2.5 Ga,because of the transformation of rock by later tectonic events.Two metamorphic ages of 2.2 Ga and 1.9 Ga,respectively,could be confirmed from the quartz diorite gneiss(TWB6),indicating that the Wulashan-Daqingshan Area has undergone the superposition of early and late Paleoproterozoic tectonic thermal events.Overall it can be concluded that the latest formation age of aluminum-rich gneiss in the Wulashan-Daqingshan area is limited to 2.5 Ga.
early precambrianWulashan rock groupmetamorphismAl-rich gneissesU-Pb isotope dating
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维普
