Structure, geochronology, and petrogenesis of Permian peraluminous granite dykes in the southern Chinese Altai as indicators of Altai−East Junggar convergence

Abstract

How and at which thermal conditions the convergence between the Chinese Altai and East Junggar operated remain poorly understood. This issue is addressed in the current study by focusing on the timing and petrogenesis of syntectonic granite dykes from the representative areas of Fuyun (convergent front) and Kalasu-Aletai (Chinese Altai interior). It is shown that Fuyun and Kalasu-Aletai dykes are fractionated I- and S-type granites, with zircon and monazite U-Pb ages of 300−291 Ma and 281−265 Ma, respectively. Geochemically, the Fuyun dykes have lower contents of aluminous (ASI: 0.97−1.13) and light rare earth element-enriched features, while the Kalasu-Aletai dykes have ASI = 1.01−2.17 and show overall flat rare earth element patterns with tetrad effects. The Fuyun dykes exhibit less evolved Sr-Nd isotopic characteristics (87Sr/86Srinitial: 0.7039−0.7048, εNd(t): + 5.7 to + 6.1) with respect to those of the Kalasu-Aletai dykes (87Sr/86Srinitial: 0.6978−0.7183, εNd(t): −7.6 to +3.0). The Fuyun and Kalasu-Aletai dykes are geochemically compatible with isotopically less evolved East Junggar arc components and heterogeneous Ordovician wedge sediment of the Chinese Altai, respectively, implying genetic links. We propose that the late Paleozoic Chinese Altai−Junggar convergence created a local perturbation of weak mantle beneath the southern Chinese Altai, causing partial melting of the underthrusting East Junggar and the overriding Altai components successively. The resulting magmas were emplaced along northward propagating syn-tectonic tensional fractures perpendicular to the Chinese Altai−East Junggar deformation front that serves as an excellent indicator of the convergent-shortening process.

Crustal‐Scale Disharmonic Structural Pattern of West Junggar: Unveiling a Permian Indentation of Junggar Block Into Northern Kazakhstan Orocline

“…290-260 Ma age of the D2 shortening is best expressed by the dating of rhyolitic dykes perpendicular to the axial planes of F2 folds in the Sharburti area. It is also compatible with the dating and orientation of granite porphyry and pegmatitic dykes intruding the Chinese Altai (Jiang et al, 2019;Shu et al, 2022). These observations indicate that the early Permian deformation of the Chinese Altai units to the north likely operated in the same coordinates and direction as that D1 in the south.…”

Metamorphic and chronological constraints on the early Paleozoic tectono‐thermal evolution of the Olkhon Terrane, southern Siberia

“…Simplified geological map of the Olkhon Terrane, SE Siberian Craton, showing the extents and distributions of main lithological units (modified after Donskaya et al, 2017). The inset shows the position of the Sayan–Baikal metamorphic belt with respect to the Siberian Craton and the Central Asian Orogenic Belt (modified after Shu et al, 2022). Available U–Pb zircon ages for different rocks in the region are also indicated.…”

Impact of Ancient Tectonics on Intracontinental Deformation Partitioning: Insights From Crustal Structures of the East Junggar‐Altai Area

“…Xu et al, 2022). Additionally, during this period, the lower crust of the Chinese Altai Mountains region is proposed to have undergone partial melting (Jiang et al, 2019;Shu et al, 2022), potentially due to local mantle perturbations Journal of Geophysical Research: Solid Earth 10.1029/2023JB027949 (Shu et al, 2022), further enlarging the rheological contrast. Therefore, during the Late Paleozoic, the crustal rheological contrast leads East Junggar to behave as a rigid indenter that underthrusts beneath the Chinese Altai, resulting in northward progressive detachment folding (Figure 8b).…”