کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4723690 | 1639675 | 2010 | 13 صفحه PDF | دانلود رایگان |
Granitoids of Neoproterozoic age are well exposed in the Precambrian basement rocks of Madagascar, in the vicinity of and within the Neoproterozoic dextral Angavo shear zone (ASZ). Pre-kinematic granitoids, a syn-kinematic granite, and a granitic gneiss have been dated using Laser Ablation Multicollector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS). One pre-kinematic granitoid yields a weighted mean 206Pb/238U igneous zircon crystallization age of 823.6 ± 6 Ma, and a second a 756.6 ± 9 Ma igneous crystallization age and a 563 ± 11 Ma metamorphic age. A syn-kinematic granite gives a weighted mean 206Pb/238U zircon age of 549.8 ± 4 Ma, which points to the time of movement in the ASZ. A granitic gneiss yields a weighted mean 206Pb/238U protolith age of 732 ± 13 Ma and records a 558.8 ± 4 Ma metamorphic age. Accordingly, the ASZ was active and associated with the high-temperature metamorphism of the Angavo-Nondiana belt during the Ediacaran. The late Proterozoic ages of igneous intrusions recorded by the granites show that pre-tectonic granites were sheared in the ASZ, and recorded granulite–amphibolite facies metamorphic events. These U–Pb data suggest a link between the ASZ and the Achankovil shear zone in India, which were adjacent in several proposed Gondwana reconstructions.
Journal: Precambrian Research - Volume 182, Issues 1–2, September 2010, Pages 30–42