Evolution of the Paleozoic granitoid magmatism in the Kuznetsk Alatau: new geochemical and U–Pb (SHRIMP-II) isotope data

Abstract

A U–Pb isotope analysis has revealed zircons, dated at ~ 510–490 and ~ 430–400 Ma, in granitoid intrusions on the eastern slope of the Kuznetsk Alatau Range (Batenev Ridge). This suggests two stages of the regional granitoid magmatism: Middle–Late Cambrian and Silurian–Early Devonian. The ages of two zircon grains from the rocks of the Tigertysh pluton are ~ 1.9 and ~ 2.6 Ga; they suggest the involvement of fragments of the Paleoproterozoic continental crust in magma generation. The granitoids, independently of their age, are mostly products of rocks of the calc-alkalic (K2O/Na2O ≈ 0.5–1.7) series. In the proportions of alumina, calcium, and alkalies most of them correspond to I-type granites (A/CNK≤1.1) with reduced Fe/(Fe + Mg) values and contents of HFSE, including REE (ΣREE ≈ 100–300 ppm). The trace-element patterns of the rocks point to the possible participation of both IAB and OIB in magma genesis. Presumably, the influence of the within-plate component increased as a result of the superposition of plume on accretion–collisional structures, and their melting might have favored the preservation of geochemical features of subduction magmatism in the granitoids. The isotopic inhomogeneity (εNd(T) = 2.3–4.8, (87Sr/86Sr)T ≈ 0.7036–0.7051) of the granitoid complexes suggests the heterogeneous composition of the material sources, which consisted of the matter of moderately depleted (PREMA) and enriched (EM) lithospheric mantle and crustal substrate, mixed in different proportions. Some products of the regional alkali-basic magmatism are coeval with the Cambrian granitoids of the Kuznetsk Alatau and are similar to them in isotope composition. This magmatism confirms the interaction of plume with the active continental margin at the Caledonian stage of evolution of the Central Asian Fold Belt.

The Overmaraat-Gol Alkaline Pluton in Northern Mongolia: U–Pb Age and Preliminary Implications for Magma Sources and Tectonic Setting

“…Reverse zonation was also reported for zircons in juvite from the Kurgusul pluton in the Kuznetsk Alatau [12]. A close age of ~ 425-435 Ma was inferred for some granitoids in the Kuznetsk Alatau and Sayan areas [46,47]. Similar Paleozoic alkaline-mafic intrusions in the western CAOB emplaced in discrete events at ~ 500, ~ 400, and ~ 300 Ma, which did not overlap with the U-Pb age of this study [6][7][8]12,14,15].…”

“…The behavior of HFSE corresponds to magma evolution in an active continental margin setting. The inheritance of geochemical signatures from earlier subduction magmatism was discussed previously for alkaline rocks, as well as for Early Paleozoic granitic and gabbro-monzonitic rocks intruding the accretionary-collisional complexes of the Cambrian Kuznetsk-Altai island arc in the western CAOB [6,7,46,50]. Likewise, the alkaline intrusions of Northern Mongolia may have formed during migration of a mantle plume in the ocean-to-continent transition zone.…”

Evolution of Syenite Magmas: Insights from the Geology, Geochemistry and O-Nd Isotopic Characteristics of the Ordovician Saibar Intrusion, Altai-Sayan Area, Russia

“…Within the Saibar intrusion, there are no mafic rocks with a SiO2 content of 52 wt.% that preceded or accompanied the formation of syenites. This limits the po of reconstructing the composition of magmas that was parental for the syenitic r the same time, the other syenite-bearing intrusions of the Altai-Sayan fold belt mafic rocks formed synchronously with examined syenites, which indicates the spondence to the composition of parent magmas [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Accordingly, the geolo finity of the Saibar intrusion to other similar intrusions suggests a genetic conne tween its rocks and the mafic magmas, which occurred at levels of the magmati inaccessible to observation.…”

“…This part of the CAOB covers the sizable Altay-Sayan fold belt, where alkaline magmatism produced the syenites typical of Kuznetsk Alatau and southeast of Tuva in the Eastern Sayan Mountains and Sangilen Highland, as well as in the Minusinsk Trough subdividing these territories. Alkaline magmatism proceeded several times throughout the Paleozoic epoch in the Early Paleozoic (510-450 Ma), Devonian (410-390 Ma), and Late Carboniferous and Early Permian (305-280 Ma) [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. [47,48].…”

The Paleozoic-Aged University Foidolite-Gabbro Pluton of the Northeastern Part of the Kuznetsk Alatau Ridge, Siberia: Geochemical Characterization, Geochronology, Petrography and Geophysical Indication of Potential High-Grade Nepheline Ore

“…Consequently, it will be possible to compare the magmatic events that took place at the University pluton with the events of other alkaline-basic intrusions KA, which will help to reveal the conditions of the formation of the University pluton. Accordingly, as a result of the data from isotope-geochronological studies (Sm-Nd, Rb-Sr, U-Pb and Ar-Ar), alkaline intrusions can be divided into three age groups, corresponding to the Cambrian and Early Ordovician (510-480 Ma), Early and Middle Devonian (410-390 Ma) and Late Permian (265 Ma) [8][9][10][11][12]18,21,27,28,[31][32][33]45,46,48,72].…”