Generation of ca. 900–870 Ma bimodal rifting volcanism along the southwestern margin of the Tarim Craton and its implications for the Tarim–North China connection in the early Neoproterozoic

Abstract

Large scale rift related volcanic suites are widely accepted as the evidence of the initial breakup of supercontinents and thus can be used to reconstruct the relative position of the cratons. Numerous early Neoproterozoic volcanic rocks have been identified in the Tiekelik Belt, southwestern part of the Tarim Craton. The Sailajiazitage volcanic rocks in the Tiekelik Belt are composed of a suite of bimodal volcanics and related pyroclastic rocks. The geochemical characteristics resemble those of continental flood basalts (CFBs) formed in the shallower mantle dominated by spinel–lherzolite with EM2 affinities. The rhyolites have been dated at 896±11Ma at the base, 881±14Ma at the middle and 872±8Ma at the top by U–Pb method on zircon. They erupted in an intraplate rift environment and are interpreted to have formed by crustal melting. Hf isotopes of individual dated zircon grains show a wide range of initial εHf values, from strongly negative (down to −28) to highly positive (up to +12.8), indicating a mixture of mantle- and crustal-derived materials. The bimodal volcanic suite is overlain by the Bochatetage Formation sediments, deposited sometime after 797±12Ma. An identical ca. 900–870Ma age for rift-related volcanic rocks indicate Neoproterozoic regional extensional processes in the southern margin of the Tarim–North China, which allow us to speculate on the correlation of the Tarim and North China cratons during the Neoproterozoic. This voluminous bimodal magmatism resembles the rift-related magmatism in the North China, West African, Congo and São Francisco cratons of age ca. 925–870Ma, suggesting that the Tarim Craton was located close to these cratons during early Neoproterozoic, or alternatively, that such early Neoproterozoic rift magmatism was widespread over large parts of Rodinia.