Titanium in quartz as a record of ultrahigh-temperature metamorphism: the granulites of Karur, southern India

摘要

The occurrence is reported of spectacular oriented needles of rutile within quartz veins and pods in granulite-facies rocks that have undergone partial melting under ultrahigh-temperature (UHT) conditions in the Karur region in southern India. Laser Raman spectroscopy and electron microprobe analysis confirm that (1) the mineral inclusions within quartz are pure ratiles, and (2) a second category of quartz contains pure hematite inclusions. The rutile never coexists with the hematite inside the same quartz specimens. Fluid inclusions in the quartz are characterized as a CO_2 + H_2O mixture. Application of two geothermometric calibrations utilizing Ti in quartz yields minimum estimates of approx 1190 deg C, suggesting the formation of the rutile-quartz under UHT metamorphic condition. It is proposed that such Ti-rich quartz segregations could be another indicator for extreme crustal metamorphism at very high temperatures.