Late Paleozoic arc magmatism in the southern Yili Block (NW China): Insights to the geodynamic evolution of the Balkhash – Yili continental margin, Central Asian Orogenic Belt

Abstract

The Yili Block represents the easternmost segment of the Kazakhstan–Yili microcontinent. Late Paleozoic magmatic rocks are extensively exposed in the Yili Block and are essential in understanding the tectonic development of the SW Central Asia Orogenic Belt (CAOB). We conducted field investigations, zircon U–Pb dating, whole-rock geochemical and Sr–Nd isotopic studies on the magmatic rocks from the Wusun Range, southern Yili Block. The Late Paleozoic volcanic and plutonic rocks of the Wusun Range show geochemical features consistent with that of calc-alkaline series, and they have positive εNd(t) values (0.9 to 5.6), Neo- to Mesoproterozoic single-stage Nd model ages (0.80~1.33Ga), and variable initial 87Sr/86Sr ratios (0.7041–0.7059), suggesting that these magmatic rocks are likely derived from partial melting of a moderately depleted mantle wedge with minor involvement of a Precambrian continental crust. These new data, combined with previously published results put constraints on the Late Paleozoic magmatic and geodynamic evolution of the Balkhash–Yili active continental margin. The Late Paleozoic arc magmatism initiated from ~386Ma along the northern Yili Block, and migrated southward to have occurred since ~340Ma along its southern margin. Subsequently, the arc-related magmatism moved back northward and terminated at 310Ma in the south and at ~295Ma in the north. The OIB-like geochemical features of some volcanic rocks indicate incipient marginal rifting occurred along the southern Yili Block during Late Carboniferous. Taking into account the regional structural and tectonic data, the Carboniferous Yili magmatic arc may be laterally correlated with the Balkhash–Yili active margin of the Kazakhstan microcontinent, which was likely resulted from the southward subduction of the Junggar – North Tianshan Ocean.