Is the Tarim Craton Composed of Multiple Terranes?

Is the Precambrian basement of the Tarim Craton in NW China composed of discrete terranes?

Authors:

Zhang et al

Abstract:

The Precambrian evolution of the Tarim Craton in NE China, in particular during the early Precambrian stage, remains enigmatic. In this contribution, we report field observation, petrology, geochemistry, zircon Lu-Hf isotopes and U-Pb ages of the major rock formations of the Aketage area in the southeastern section of the Tarim Craton. The Milan Group in Aketage is dominantly composed of 2.7-2.5 Ga gneissic amphibolite–TTG complex with minor paragneiss. Both the mafic and silicic rocks exhibit geochemical features consistent with an arc affinity. The arc-signature of the 2.01-2.03 Ga gneissic granites and gabbros which intrude the Archean basement, as well as the major 2.0 Ga metamorphic event revealed by zircon U-Pb dating, suggest an important subduction-collision event possibly related to the assembly of the Paleoproterozoic Columbia supercontinent. The ca.1848-1856 Ma massive potassic granites, 1867 Ma mafic dyke swarm and 1844 Ma massive leucogranite dykes reveal magmatism in a post-collisional extensional setting.

A comprehensive synthesis of the major orogenic events and continental crust growth process from the different Precambrian terranes in Tarim Craton show significant discrepancy in time related to the late Neoarchean crust formation ages and the Paleoproterozoic orogenic events. For example, the major orogenic event took place at ∼1.85 Ga in Quruqtagh-Dunhuang terrane, at ∼1.90 Ga in the southwest Tarim Craton and at ∼2.0 Ga in the Aketage-Qaidam terrane. These different terranes exhibit distinct periods of continental crust growth in the early Precambrian. Continental growth in the Aketage area took place during 2.7 Ga to 4.3 Ga. The 3.6 Ga xenocrystic zircons as well as the peak of 4.2 Ga zircon Hf model ages, indicate the possible existence of Paleoarchean and even Hadean crust in the Aketage area. In the Quruqtagh-Dunhuang terrane, the growth of early Precambrian continental crust took place at 2.6-3.3 Ga with peaks at ca. 2.6-2.7 Ga and 3.0 Ga. The diachronous late Paleoproterozoic orogenic events and the significant difference in continental growth process suggest that the Precambrian basement of the Tarim Craton is composed by independent continental terranes possibly detached from the cores of discrete ancient cratonic nuclei, which were not unified until the early Neoproterozoic during assembly of the Rodinia supercontinent.