ISBN:

0026-4598

Keywords:

basalts, Canada, Canadian Shield, cape smith fold belt, Churchill Province, copper ores, fold belts, geochemistry, geophysical methods, geophysical surveys, host rocks, igneous rocks, KOMATIITE, lithostratigraphy, magma contamination, magnetic methods, major elements, mathematical models, metal ores, metals, metamorphic belts, mineral composition, nickel ores, North America, olivinite, Paleoproterozoic, Petrology, platinum group, platinum ores, plutonic rocks, Precambrian, proterozoic, rare earths, sulfides, surveys, Thermal erosion, thermal history, thermomechanical properties, Trace elements, ultramafics, ungava, upper Precambrian, volcanic rocks

Abstract:

Virtually all of the economic Ni-Cu-(platinum group element (PGE)) mineralization in the central part of the Cape Smith Belt of New Quebec is hosted by thick olivine cumulate units in the Katinniq Member of the Raglan Formation at the base of the 1.9 Ga Chukotat Group. These units transgress underlying gabbros and pelitic metasediments, forming 50-200-m deep and 300-1,000-m wide V-shaped embayments and have been interpreted on the basis of surface geology, deep diamond core drilling, and magnetic inversion models to represent the remnants of one or more large, long (at least 20 km, possibly > or =50 km), sinuous, komatiitic basalt lava channels that formed by thermomechanical erosion of their substrates. We have used a mathematical model to test these hypotheses regarding komatiitic lava emplacement and erosion by lava. Our modeling predicts that an initially 10-m thick komatiitic basalt flow should have flowed turbulently near the vent and should have thermomechanically eroded unconsolidated pelitic sediment during emplacement to reach the observed degree of contamination of 10 (super 5) -10 (super 6) m (super 3) /s and eruption volumes of >10 (super 3) -10 (super 4) km (super 3) . Although these flow rates are orders of magnitude larger than those of most modern terrestrial basaltic flows, they are of the same order as those estimated for the largest terrestrial flood basalt flows and with those inferred for some of the largest extraterrestrial flows. Our predicted flow volumes are also of the same order as those of the largest terrestrial flood basalt units, consistent with the great thickness and widespread distribution of the Chukotat Group. Our modeling of thermomechanical erosion of gabbro by komatiitic basalt results in negligible contamination ( Middle REE-Heavy REE > Nb-Ta-Ti represent contamination by underlying Povungnituk semipelites. This result is consistent with present models for the genesis of the Ni-Cu-(PGE) mineralization in the Raglan Formation that involve thermomechanical erosion of unconsolidated, sulfidic semipelitic sediments, and decoupling of the miscible silicate and immiscible sulfide components. Copyright 2011 Springer-Verlag

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2012-035551<br/>Chukotat Group<br/>Katinniq Member<br/>Raglan Formation