Journal
GEOLOGICAL MAGAZINE
Volume 157, Issue 9, Pages 1409-1427Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S0016756819001389
Keywords
monazite dating; pseudosection; P-Tconditions; Grenvillian orogeny; Pan-African event
Categories
Funding
- Department of Science and Technology [ESS/16/304/2005]
Ask authors/readers for more resources
This paper presents three different age domains, obtained by electron microprobe monazite dating, for granulitic gneisses collected from the Shillong-Meghalaya Gneissic Complex in Sonapahar, NE India, which contain radioactive materials, e.g. thorium (3.32-7.20 wt %), uranium (0.133-1.172 wt %) and lead (0.101-0.513 wt %). The microprobe analyses of monazite grains in the rock samples show that the monazites have three different ages ranging from Mesoproterozoic to Neoproterozoic. The oldest age (1571 +/- 22 Ma) represents a peak metamorphic event, the youngest dominant age indicates the Pan-African tectonic event (478 +/- 7 Ma) and the intermediate age marks the Grenvillian orogeny (1034 +/- 91 Ma) or may be a mixing artefact; these ages are located at the cores, rims and intermediate parts of the monazite grains, respectively. The equilibrium mineral phases calculated for the granulitic gneisses from Sonapahar lie in aP-Trange from 5.9 kbar/754 degrees C to 8.3 kbar/829 degrees C in the NCKFMASH system. Plotting theP-Tconditions of the granulitic gneisses reveals a clockwiseP-Tpath. Two major metamorphic events are observed in Sonapahar. The M(1)metamorphic stage is represented by peak mineral assemblages of prograde garnet-forming reactions (8.2 kbar/similar to 713 degrees C) during Mesoproterozoic time (1571 +/- 22 Ma). The M(2)metamorphic stage featured decompression (3.9 kbar/similar to 701 degrees C) in which garnet-sillimanite broke down to form cordierite along an isothermal decompression path during the Pan-African tectonic event (478 +/- 7 Ma).
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available