The Queen Maud Block, Nunavut: Genesis of a large felsic igneous province in the earliest Paleoproterozoic and implications for Laurentian geotectonic models.

摘要

New geochemical and Sm-Nd and U-Pb isotope data indicate the Queen Maud Block (QMB) is Paleoproterozoic in age and central to understanding assembly of northwestern Laurentia. Data indicate: (1) Felsic and subordinate mafic magmatism at 2.46-2.50 Ga. Ponding of mafic magmas below induced high-temperature partial melting of refractory lower-crust. (2) A 2.48-2.39 Ga sedimentary belt, the Sherman basin, dominated by 2.452.50 Ga detritus. (3) Regional 2.39 Ga granulite-grade metamorphism, with no evidence of tectonomagmatic activity concurrent with orogenesis in the adjacent Taltson-Thelon belt at 1.9-2.0 Ga. I propose the QMB was an incipient continental rift at ∼2.5 Ga. Exhumation of 2.46-2.50 Ga granitoids produced in early stages of rifting provided detritus to a basin that underwent granulite-grade metamorphism at 2.39 Ga. The switch from extension to compression environments could be a result of Slave-Churchill collision at 2.39 Ga or far-field triggers affecting an intracontinental environment within a contiguous Slave-Churchill craton.