Re-examining the Alpine and Otago schists with titanium in quartz geothermometry

King, Charlotte Louise.

The Alpine and Otago schists of New Zealand fmm a contiguous metamorphic belt comprising rocks ranging texturally from zone IIA to IV, and mineralogically from pumpellyite-actinolite to amphibolite facies. Metamorphism associated with formation of these schist appears to have been episodic, occurring in the Jurassic, Cretaceous and late Cenozoic. The bulk rock composition of the schist protolith is depauperate in aluminium, and therefore the schists do not contain phases required for the application of most geothermobarometers. Quartz, however, is present throughout all metamorphic grades and allows the application of titanium in quartz geothermometry. Samples have been taken from the Lake Hawea and Haast River section and cover all textural and mineralogical zones present in the schists. Polished quartz samples were analysed by LA-ICP-MS for their trace element concentrations. The data obtained reveals a strong correlation between the concentration of titanium in quartz and metamorphic grade, indicating that titanium 'temperatures' are retained through subsequent metamorphic deformation episodes. The results of this study correlate well with independent temperature estimates given by previous gamet-biotite geothermometry, and metamorphic phase relations. This analysis also reveals discrete temperature signatures for each of the deformation phases present in the section. The titanium in quartz results appear to give a more constrained range of possible temperatures, hinting that this method could be more precise than those used previously.

66 leaves, : ill., maps ; 30 cm + 2 sheets (48 x 37 cm. folded to 24 x 19 cm.)

2008King_CL

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