Thursday, December 12, 2013

Where was the Tarim Craton in the Columbia Supercontinent?

Geochronology and geochemistry of Early Mesoproterozoic meta-diabase sills from Quruqtagh in the northeastern Tarim Craton: Implications for breakup of the Columbia supercontinent

Authors:


Wu et al

Abstract:

Metadiabase sills are extensively distributed in the Astingbulake region in the central Quruqtagh block of the NE Tarim Craton. Here we report laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U–Pb ages and Hf isotopes, as well as whole rock elemental and Sr-Nd isotopic data for these Mesoproterozoic sills. Zircons from one of the mafic sills yield an emplacement age of 1470 ± 9 Ma (95% confidence, MSWD = 3.2, n = 23) Ma. Despite the greenschist-amphibolite facies metamorphism, most of the immobile elements provide important clues for the petrogenesis and tectonic settings of these rocks. Except for their variable fluid mobile-element contents, all the studied samples show enrichment in incompatible trace elements with no obvious Nb–Ta depletion, similar to the features of continental flood basalts and ocean island basalts (OIB). Combined with their relative higher 87Sr/86Sr (t) ratios (0.70666 to 0.70784), negative ɛNd(t) (-4.30 to -3.96) and ɛHf (t) (-5.49 to -1.13) values, we propose that the protolithic magmas were derived from the high degree partial melting of enriched continental lithospheric mantle within continental rifting settings. The ∼1.5 Ga diabase sills from North Tarim corresponded to the major episode of mafic magmatism during Early Mesoproterozoic time identified from other crustal fragments of Laurentia, Siberia, Greater Congo and South China, and probably belong to one of the three major large igneous provinces associated with the breakup of the Mesoproterozoic Columbia supercontinent. Our data provide important constraints on the configuration of the Tarim Craton within the Columbia supercontinent

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