Cambrian High-temperature Reworking of the Rayner-Eastern Ghats Terrane: Constraints from the Northern Prince Charles Mountains Region, East Antarctica

Metapelitic rocks from the northern Prince Charles Mountains-East Amery Ice Shelf region of the Rayner Complex, East Antarctica, record high-temperature reworking during Cambrian times. Calculated metamorphic phase diagrams for rocks with varying chemical compositions and mineral assemblages suggest that peak temperatures were 800-870A degrees C at pressures of 5 center dot 5-6 center dot 5 kbar. However, Cambrian-age high-T reworking is patchy and is recorded only in some locations, with other areas recording pristine early Mesoproterozoic-Neoproterozoic assemblages formed during the c. 1000-900 Ma Rayner Orogeny. The spatial distribution of reworking may indicate that the comparatively anhydrous residual rock compositions inherited from the Rayner Orogeny were relatively inert to reworking during the Cambrian. Domains that record Cambrian reworking conceivably underwent hydrous retrogression at the end of the Rayner Orogeny and were therefore comparatively reactive during reheating in the Cambrian. High-T reworking during the Cambrian has previously been recognized in the Prydz Bay region at the margin of the Rayner Complex, but not in the northern Prince Charles Mountains. The Eastern Ghats Province in India, which was formerly contiguous with the Rayner Complex, preserves a similarly enigmatic record of Cambrian geochronology, suggesting that the Rayner-Eastern Ghats terrane as a whole may have experienced selective reworking during the Cambrian. The geodynamic setting for the formation of this thermal regime is not well understood, but the attainment of high crustal temperatures may have been facilitated by a reduced capacity for thermal buffering, arising from limited partial melting within a previously dehydrated crustal column.