Abstract
We report the first radiogenic Nd-Sr isotope data in the magmatic rocks island-arc ophiolite assemblage from the middle branch of the East Sayan ophiolite complexes to better constrain geodynamic processes in this segment of the CAOB in southern central Siberia. The magmatic rocks belong to the following geochemical types: (1) Ensimatic island-arc boninites; (2) island-arc assemblage; (3) enriched basalts of mid-ocean ridges; and (4) oceanic island-like basalts. The boninites have a positive value εNd (T), which is generated from a depleted mantle source (N-MORB). The island-arc assemblage has negative or slightly positive εNd (T) and was formed from an enriched mantle source due to the subduction of terrigenous rocks. The source of the terrigenous material was most likely the rocks of the Archean TTG (Trondhjemite Tonalite Granodiorite) complex of the Gargan block. Isotopic ratios for E-MOR and OIB-like basalts are characterized by positive or slightly negative values of εNd (T). The mafic dike, which crosscut ophiolite rocks, corresponds to OIB-like basalts. The values of εNd (T), measured 87Sr/86Sr and I (Sr), in the mafic dike correspond to the EM I mantle source. The E-MOR and OIB-like basalts appear to be formed in late-stage asthenospheric mantle melting via the decompression melting processes. The obtained isotope geochemical data for the E-MOR and OIB-like basalts probably indicate the mixing of island-arc melts with asthenospheric melts. We undertook 40Ar/39Ar dating of the mafic dike, which crosscut the ophiolite unit. The mafic dike has a whole-rock 40Ar/39Ar weighted mean plateau age of 799 ± 11 Ma. The dating constrains the minimum age of the ophiolite and island-arc magmatism in the region.
Highlights
Introduction iationsThe studied area is located in the southeastern region of Eastern Sayan, southernSiberia
This region was tectonically juxtaposed during the Neoproterozoic accretionary orogeny of the Central Asian Orogenic
During the early Paleozoic to late Mesozoic periods, the island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateau, and microcontinents were joined to the Siberian craton [2,7,14,15] (Figure 1)
Summary
The studied area is located in the southeastern region of Eastern Sayan, southern. Siberia (the Buryatia Republic of the Russian Federation). This region was tectonically juxtaposed during the Neoproterozoic accretionary orogeny of the Central Asian Orogenic. The earliest stages in the CAOB formation are related to the development of the Paleo-Asian Ocean [2,3,4,5,8,9,10,11,12,13]. Continental rifting, ocean subduction, and marginal basin formation events began before 1000 Ma and continued until 570 Ma [7]. The southeastern domain of the CAOB includes Archean-Proterozoic terranes—Gargan During the early Paleozoic to late Mesozoic periods, the island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges, oceanic plateau, and microcontinents were joined to the Siberian craton [2,7,14,15] (Figure 1).
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