Re–Os isotopes of sulfides in mantle xenoliths from eastern China: Progressive modification of lithospheric mantle

Abstract

In situ Re–Os isotopic data for sulfide grains in mantle-derived peridotite xenoliths from eastern China demonstrate a close temporal linkage between crustal tectonism and fluid-migration events in the subcontinental lithospheric mantle (SCLM). In the Cathaysia block, T RD and T MA ages of sulfides with 187Re/ 188Os < 0.11 cluster in four groups: Paleoproterozoic (∼ 1.8), Mesoproterozoic (∼ 1.3 to 1.5 Ga) and Neoproterozoic (0.9 Ga and 0.6 Ga), corresponding to known major crustal growth events. In the Sino-Korean block, the most robust T RD and T MA ages from sulfides, and some published whole-rock data, indicate that the earliest SCLM formed together with the oldest Archean crust and was modified in Paleoproterozoic time (ca 1.8 Ga), corresponding to the collision between the eastern and western parts of the block. Meso- to Neoproterozoic ages (ca 1.4 Ga, 0.9 Ga, 0.6 Ga) record younger thermal events, the latest of which also is known from zircon ages in lower-crustal xenoliths. The scarcity of Archean sulfide- and whole-rock model ages may reflect widespread Proterozoic modification of the SCLM, but may also be due to preferential sampling of young SCLM by volcanoes situated along zones of asthenospheric upwelling, controlled by a network of major shear zones. Widespread Mesozoic magmatism in the Cathaysia block may be represented by abundant mantle sulfides with mildly superchondritic 187Os/ 188Os and “future” model ages. This would imply that the sublithospheric mantle has developed a superchondritic Re/Os over perhaps the last 1 Ga, requiring its isolation from the convecting asthenosphere. The SCLM beneath eastern China has had a very complex history, and is now a mixture of refractory and fertile mantle domains with different ages, modified during a number of events.