Paper No. 6
Presentation Time: 9:30 AM
GEOLOGICAL, AGE, AND GEOCHEMICAL CONSTRAINTS ON THE EVOLUTION OF THE NORTHEASTERN PALEOPROTEROZOIC TRANS-HUDSON OROGEN FROM THE SOUTHERN HALL PENINSULA, BAFFIN ISLAND, CANADA
New mapping in 2012 on the southern Hall Peninsula, Baffin Island was undertaken to elucidate the tectonostratigraphic relationships in a poorly understood area of the northeastern Paleoproterozoic Trans-Hudson Orogen (THO). The focus of this study is the Qaqqanittuaq area (QA), a southeast-trending, doubly plunging synformal structural basin which contains rock units and relationships representative of the eastern Hall Peninsula. Archean biotite tonalite gneiss, and minor monzogranite and syenogranite gneisses are overlain by supracrustal rocks dominated by micaceous psammite with lesser quartzite and pelite. The supracrustal rocks contain primarily Archean detritus but also have a significant Paleoproterozoic component, constraining the maximum age of deposition. This supracrustal package is intruded by a series of mafic and ultramafic intrusions followed by younger cross-cutting monzogranite sills and dykes which record the dominant regional fabric developed during collision-related crustal thickening. The monzogranite dykes yield an age of 1.87 Ga, placing a minimum age constraint on sediment accumulation, mafic intrusion and regional deformation. Biotite – garnet – sillimanite – K-feldspar mineral assemblages from the pelites indicate that the rocks attained upper amphibolite metamorphic conditions. The mafic rocks have strongly negative Nb anomalies, and MORB-normalized Th, Ce, Zr, Ti and Y concentrations typical of within plate environments suggesting that they were derived from partial melting of a subduction-modified mantle. The rarer ultramafic intrusions typically have high Cr and Ni (>2000 ppm) and may be either high degree partial melts or cumulates. Geochemical modification of the mantle involved in partial melting may have occurred during subduction around the margins of the Meta Incognita/Hall Peninsula terrane as the Manikewan Ocean closed during the THO.