Persistence of partial melting in the southern North China Craton: Evidence from Paleoproterozoic migmatites of the Taihua Complex

Abstract

The Taihua Complex is exposed in the southern North China Craton (NCC), it has experienced a long and complicated history of multiple crustal growth, magmatism, metamorphism and deformation during the early Precambrian. Abundant leucosomes are widely distributed within the migmatites of the Taihua Complex, which occurred as irregular lenses, blocks, layers or dikes with several thickness of millimeters to tens of centimeters wide. Meanwhile, former presence of melt and typical microstructures related to partial melting also can be recognized in the thin sections under the microscope, those provide compelling evidences that the Taihua Complex has extensively suffered partial melting, and can be regarded as the best target to decipher multistage anatexis during metamorphism as well as assembly of the whole NCC. However, the timing and nature of the partial melting in the Taihua Complex have not been well studied up to now. In this contribution, we present an integrated in situ zircon U-Pb ages and Hf isotope compositions for the Paleoproterozoic migmatites from the Taihua Complex in the southern NCC. Both the metasedimentary and metamorphized plutonic rocks of the Taihua Complex have extensively suffered partial melting. The ca. 2.50 Ga magmatic zircons or inherited magmatic cores from the migmatites and leucosomes present similar Hf isotope composition to those of the contemporaneous depleted mantle at ca. 2.50 Ga, suggesting that ca. 2.50 Ga is a major period of crustal growth in the southern NCC as well as the whole NCC. The ages of metamorphic zircons obtained from leucosomes, melanosomes and migmatites show a large time interval of 1909–1798 Ma, indicating that the Taihua Complex has experienced a persistence of partial melting event during Late Paleoproterozoic that lasted more than 100 Ma. The crustal anatexis in the southern NCC probably occurred during the post-peak upper amphibolite- to granulite facies stage with melting temperature of at least 652–753 °C. The decompression melting and widespread migmatization of the Taihua Compelx are probably due to extension related to exhumation of the previously thickened crust during Paleoproterozoic collision between the Eastern and Western block, or between the Southern Archean Block and other micro-continents. The main collision-related assembly and crustal thickening events in the southern NCC likely occurred at ca. 1.95 Ga, rather than ca. 1.85 Ga as previously believed.