ESTABLISHING SPACE-TIME-GEOCHEMICAL RELATIONSHIPS IN THE FERRAR LARGE IGNEOUS PROVINCE, ANTARCTICA

The Jurassic Ferrar Large Igneous Province crops out along the length of the Transantarctic Mountains. The magmatism, associated with the break-up of Gondwana, resulted in extrusive pyroclastics and lava flows and intrusive dikes and sills, all of tholeiitic composition. The best estimate of the age of the Ferrar, based on limited zircon geochronology, is 183.6±1.8 Ma, but extensive Ar⁴⁰/Ar³⁹ dating of feldspars (mainly lavas) indicates a short episode of emplacement of about 1 My. Current zircon geochronologic studies are anticipated to yield an order of magnitude better age resolution. Geochemical analysis of Ferrar rocks (mainly lavas) has led to the recognition of two compositions: the Scarab Peak Chemical Type (SPCT) and the Mt. Fazio Chemical Type (MFCT). The SPCT, with MgO concentrations of ≈2.3%, makes up ~1% of the total volume of the Ferrar rocks; the lavas forming the predominant MFCT have MgO concentrations ranging between 3 and 7.5%. With one exception, all sills have MFCT compositions but include more mafic sills, which have MgO concentrations up to 9%. Analysis of samples from the Skackleton Glacier region suggests the MFCT may be divided into 3 compositional subgroups based on concentrations of MgO. The study reported here on samples from the Queen Alexandra Range, located approximately 100 miles from the Shackleton Glacier, shows compositions which indicate the samples belong to the MFCT, but do not as yet show the subgroups identified in that region. Further analytical work (XRF and ICP-MS) on additional samples from the Queen Alexandra Range is being undertaken. When the results of the high resolution dating are available, it is anticipated that space-time-geochemical relationships will be established for the Ferrar Large Igneous Province.