Timing of metamorphism in the central S?r Rondane Mountains, eastern Dronning Maud Land, East Antarctica: Constrains from SHRIMP zircon and EPMA monazite dating

摘要

In order to understand the tectonic evolution of the S?r Rondane Mountains, eastern Dronning Maud Land, East Antarctica, sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon dating and electron probe micro analyzer (EPMA) U-Th-Pb monazite dating were carried out on igneous rocks and metamorphic rocks whose P. T conditions have been well-constrained. Metamorphic rocks from northern part of Austkampane area recording a clockwise P. T path yield 600-640. Ma as the timing of peak granulite-facies metamorphism and 550-570. Ma for subsequent retrograde metamorphism. The same age relations were obtained from the metamorphic rocks from Brattnipene and eastern Menipa areas recording an anti-clockwise P. T path. Contemporaneous peak metamorphism with contrasting P. T paths can be explained by thrusting up (obduction) of the unit showing a clockwise P. T path onto the unit showing an anti-clockwise P-T path at ca. 660-640. Ma, which is considered to be the main metamorphic event. Metamorphic rocks from Lunckeryggen, southern Walnumfjella and western Menipa areas that preserve amphibolite-facies peak metamorphic conditions and are unaffected by the retrograde hydration, yield ca. 550. Ma. Ages of 500-550. Ma were also obtained on igneous rocks distributed throughout the whole area. Based on the close age relation between metamorphism of amphibolite-facies rocks and igneous activity, it is likely that metamorphism at ca. 550. Ma was caused by emplacement of voluminous igneous bodies. These precise correlation of metamorphic evolution and age would provide strong constraints on the construction of a tectonic model for Gondwana amalgamation.