Passage through India: the Mozambique Ocean suture, high-pressure granulites and the Palghat-Cauvery shear zone system

摘要

The Mozambique Ocean closed as Gondwana formed. Its suture has been identified in Madagascar (Betsimisaraka suture), but its continuation, into India, is controversial. The Palghat-Cauvery shear system appears an ideal candidate as it: (i) lies along strike of the Betsimisaraka suture in Gondwana; (ii) forms a high-pressure granulite be and (iii) separates crustal domains with different geological histories. However, existing age constraints have been used to suggest that the structure is Archaean/Palaeoproterozoic. Here we date metamorphic zircons using secondary ion mass spectrometry (535.0 +/- 4.9 Ma) and monazites using electron probe micro-analysis (537 +/- 9, 532 +/- 8, 525 +/- 10 Ma). No evidence for an earlier metamorphic event was found. The identification of Palghat-Cauvery high-pressure metamorphism as Cambrian, and recognition that it bounds crustal domains of contrasting origin, points to it being the southern continuation of the Betsimisaraka suture and southern margin of Neoproterozoic India.