Abstract
Despite being the largest accretionary orogen on Earth, the record of crustal growth and reworking of individual microcontinental massifs within the Central Asian Orogenic Belt (CAOB) remain poorly constrained. Here, we focus on zircon records from granitoids in the Erguna Massif to discuss its crustal evolution through time. Proterozoic–Mesozoic granitoids are widespread in the Erguna Massif, and spatiotemporal variations in their zircon εHf(t) values and TDM2(Hf) ages reveal the crustal heterogeneity of the massif. Crustal growth curve demonstrates that the initial crust formed in the Mesoarchean, and shows a step-like pattern with three growth periods: 2.9–2.7, 2.1–1.9, and 1.7–0.5 Ga. This suggests that microcontinental massifs in the eastern CAOB have Precambrian basement, contradicting the hypothesis of significant crustal growth during the Phanerozoic. Phases of growth are constrained by multiple tectonic settings related to supercontinent development. Calculated reworked crustal proportions and the reworking curve indicate four reworking periods at 1.86–1.78 Ga, 860–720 Ma, 500–440 Ma, and 300–120 Ma, which limited the growth rate. These periods of reworking account for the crustal heterogeneity of the Erguna Massif.
Highlights
Because both reworked and juvenile crust could have existed in a given period, we apply the obtained proportions of zircon TDM2 (Hf) ages from granitoids in the Erguna Massif to calculate the distributions of juvenile crust through time
Considering the relationship between zircon U-Pb ages and TDM2 (Hf) ages (Fig. 3), and the variations in εHf(t) values with latitude (Fig. 4), we suggest that reworking was an important factor leading to the heterogeneity of the continental crust, as it was controlled by several regional tectonic processes that occurred on different geological timescales
Plate tectonics is a continuous process on a global scale, it can result in Erguna Massif episodic crustal evolution as recorded in the specific region
Summary
Because both reworked and juvenile crust could have existed in a given period, we apply the obtained proportions of zircon TDM2 (Hf) ages from granitoids in the Erguna Massif to calculate the distributions of juvenile crust through time. TDM2 (Hf) ages from granitoids are often used to represent the formation time of juvenile mafic crust, some younger results might be produced by mixing between melts with more radiogenic Hf and older crustal material, especially the data with εHf(t) values between 0 and depleted mantle values.
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