Water/rock interactions and the origin of H2O in granitic batholiths Thirtieth William Smith lecture

摘要: D\H and 18 O\ 16 O data have now been obtained on a wide variety of granitic batholiths various ages. The primary δD values the biotites hornblendes are remarkably constant at about –50 to –85, identical in regional metamorphic rocks, marine sediments greeenstones, most weathering products temperate climates. Therefore H 2 these igneous rocks is probably not ‘juvenile’, but ultimately derived by dehydration and/or partial melting lower crust or subducated lithosphere. Most δ = + 7.0 +10.0, indicating significant involvement high - metasedimentary altered volcanic process; such an origin required for many other granodiorites tonaloites that 10 +13. Gigantic meteoric-hydrothermal convective circulation systems were established epizonal portions all batholiths, locally producing very low (particularly feldspars) during subsolidus exchange. Some plutons environments also emplaced as low- magmas formed assimilation hydrothermally roofrocks. However, water/rockratios typically enough over areas only evidence meteoric exchange given D/H ratios (δD –180); example, because latitudinal isotopic variations waters, one moves from through Cordilleran western North America increasingly higher proportion haves than –120. lowering commonly correlates