Reconstruction of microcontinents during the assembly of Rodinia: A case study from the Central Tianshan Block

Abstract

There are multiple Precambrian microcontinents within the Central Asian Orogenic Belt (CAOB), and the paleogeographic locations of those in the southwest CAOB (e.g. Central Tianshan Block, Yili Block, Aktau-Mointy terrane, Erementau-Niyaz terrane and Kokchetav terrane) remain controversial. The Central Tianshan Block is one of the representative Precambrian microcontinents in the southwest CAOB. It can be divided into the western Central Tianshan Block and eastern Central Tianshan Block. To investigate their relationships and paleogeographic locations, we collected metasedimentary rocks from the Kekesu Group in western Central Tianshan Block. The results of zircon LA–ICP–MS U-Pb dating, combining with previously obtained magmatic ages, suggest that the Kekesu Group was deposited during the latest Mesoproterozoic to earliest Neoproterozoic (ca. 1010–969 Ma). Detrital zircon populations of Kekesu Group were dominated by 2.0–0.9 Ga grains with an age peak at 1474 Ma. The Archean to end-Paleoproterozoic zircon grains had variable εHf(t) values from +9.7 to −8.7, and most of the Mesoproterozoic zircons had positive εHf(t) values (+13.9 to +2.4). The Kekesu Group in western Central Tianshan Block has similar zircon age populations and εHf(t) values to those in eastern Central Tianshan Block. In combination with magmatism, these data suggest that western and eastern Central Tianshan Block had similar tectonic affinities and locations during the earliest Neoproterozoic. We compiled 4566 concordant detrital zircon U-Pb age data of Mesoproterozoic to early Neoproterozoic strata from microcontinents in the southwest CAOB and potential sources. The zircon age probability density plots, kernel density estimates and multidimensional scaling plot suggest that the Central Tianshan and Yili blocks had similar sources mainly derived from the Musgrave Province in central Australia in the latest Mesoproterozoic to early Neoproterozoic, and were possibly located near Australia during assembly of Rodinia. The sources for the Erementau-Niyaz and Kokchetav terranes were probably mainly within the northern Laurentia in the latest Mesoproterozoic to earliest Neoproterozoic.