Geology and geochronology of the Paleoproterozoic Hart Dolerite, Western Australia

Abstract

Abstract The Hart Dolerite is the intrusive component of the Hart–Carson Large Igneous Province, which extends over an area of >160,000\u202fkm2 in the Speewah and Kimberley Basins in the western part of the North Australian Craton. In the core of the Speewah Dome, a ca. 500\u202fm thick composite sill of Hart Dolerite intruded metasedimentary rocks of the Speewah Group, which have a maximum depositional age of 1814\u202f±\u202f10\u202fMa. Referred to here as the Speewah sill, it comprises four discrete gabbroic units and two later-stage dyke and sill units of potassic granophyre. The gabbros locally contain sulfide-poor, Stella-type platinum-group element enrichment and vanadiferous titanomagnetite mineralisation. New ID-TIMS U-Pb geochronology of baddeleyite from gabbro units in the Speewah sill yield upper-intercept ages (all 2σ) of 1792.7\u202f±\u202f1.3\u202fMa and 1791.7\u202f±\u202f4.1\u202fMa. These results are complemented by a SHRIMP age of 1792.1\u202f±\u202f5.9\u202fMa (2σ) for baddeleyite in a late-stage pigeonite vein in Hart Dolerite 120\u202fkm south of the Speewah Dome. These new data are consistent with previous regional geochronology of late-stage quartz–feldspar granophyres, and with a model of rapid emplacement of the Hart Dolerite at 1792.6\u202f±\u202f1.2\u202fMa in an intracratonic extensional setting. Globally, the period around ca. 1793\u202fMa includes several large igneous provinces, suggesting that this interval was characterised by high mantle heat flow, continental extension, and voluminous mafic magmatism over large areas.