The origins of granulites: a metamorphic perspective

摘要: Although many recent reviews emphasize a uniformity in granulite pressure–temperature (P–T) conditions and paths, granulites reality preserve spectrum of important petrogenetic features which indicate diversity their modes formation. A thorough survey over 90 terranes or occurrences reveals that 50% them record P–T outside the 7.5 ± 1 kbar 800 50 °C average regime preferred by authors. In particular, an increasing number very high temperature (900−1000 °C) are being recognized, both on basis distinctive mineral assemblages geothermobarometry. Petrogenetic grid geothermobarometric approaches to determination interpretation histories evaluated within context reaction textures demonstrate large range is indeed real, near-isothermal decompression (ITD) near-isobaric cooling (IBC) paths important. Amphibolite–granulite transitions promoted passage CO2-rich fluids, as observed southern India Sri Lanka, exceptional not representative fluid-related processes majority terranes. It considered, contrary, fluid-absent typical most at near time recorded thermal maxima.ITD interpreted have formed crust thickened collision, with magmatic additions extra heat source. Erosion alone not, however, considered be dominant post-collisional thinning process. Instead, ITD generated during more rapid (1−2 mm/yr exposure) related tectonic exhumation moderate-rate waning extension. IBC may variety settings. Those show anticlockwise beneath areas voluminous accretion, without additional crustal shallow levels (< 5 kbar) also extension normal thickness crust, but deeper-level requires complex models. Many exhibiting deep underwent (5 mm/yr) extensional subsequent collision. suggested preservation rather than primarily rate timescale hybrid should observed.Most granulites, probably been exposed Earth's surface result episodes produced them, resided middle lower for long periods (100−2000 Ma) following these events. The eventual only occur through incorporation later events unrelated