Paper No. 13
Presentation Time: 4:30 PM


BROWN, Michael, Laboratory for Crustal Petrology, Department of Geology, University of Maryland, College Park, MD 20742, CLARK, Chris, Department of Applied Geology, Western Australian School of Mines, Curtin University, GPO Box U1987, Perth, 6845, Australia and KORHONEN, Fawna J., Department of Mines and Petroleum, Geological Survey of Western Australia, Perth, WA, 6004, Australia,

Some Proterozoic orogens record CCW heating and thickening to peak G-UHTM conditions before close-to-isobaric cooling; the tectonics of such orogens, particularly the heating mechanism, are challenging. Here, we propose a model for the late Mesoproterozoic–early Neoproterozoic Eastern Ghats Province (EGP)–Rayner Province (RP) orogen. In the central EGP, in multiple samples Crd predates Crd + Kfs (± Qtz, Bt, Sil, Pl) intergrowths interpreted to represent Osm that reacted with melt around the metamorphic peak. This interpretation indicates a common prograde evolution to T=945–955°C at P=0.78–0.82 GPa (1130–970 Ma) followed by a slight increase in P before development of retrograde mineral assemblages that record slow close-to-isobaric cooling (980–930 Ma) to elevated solidi at T=940–900°C and P=0.85–0.83 GPa. There is no imprint of this event on the Bastar craton. Based on literature data for the RP, reworked Napier basement records CW P–T–t paths that peaked at T=850–900°C and P=~1.0 GPa in the interval 930–890 Ma (Oygardens) and at T=~900°C and P=0.85 GPa in the interval 940–915 Ma (Stillwell Hills). In MacRobertson Land, supracrustal rocks record CCW P–T–t paths that peaked at T=850–900°C at P=~0.60 GPa in the interval 970–910 Ma. Critical features to be explained in any tectonic model are: a cryptic suture and an apparent absence of eclogite; similar isotopic signatures (TNdDM and THf(c)DM) in EGP and RP; continental basement (no evidence of oceanic basement); G-UHTM with CCW P–T–t paths in supracrustal rocks, and CW P–T–t paths in reworked Napier basement; pervasive ductile strain; absence of reworking of the Bastar craton; and, a slow rate of cooling. We propose that subduction of a restricted ocean basin beneath the EGP brought basement of the central sector of East Antarctica (excluding Napier, part of ‘India’ at this time) to the trench where shallow slab break-off led to extension of the overriding lithosphere and formation of a truncated hot collision (Sizova et al., 2013, GR). Continued convergence during amalgamation of Rodinia shortened and thickened the thinned and weakened lithosphere and HHP supracrustal sequence (CCW P–T–t paths, G-UHTM), which over thrust Napier basement (CW P–T–t paths, granulite facies). The low rate of cooling was due to low rates of erosion, which may reflect a hinterland plateau.