TRIASSIC GRANITE MAGMATISM IN THE KAZAKHSTAN CONTINENT AND ITS IMPLICATIONS TO THE PANGEA SUPER CONTINENT ASSEMBLY

Pangea- the youngest of the supercontinent cycles of Earth’s evolution existed from ca. 300- 200 Ma, included the amalgamation of the Siberian and Kazakhstan continents in its northern part. Previous studies have reported Triassic age on granitoids in Eastern Kazakhstan, which lies at the margin of the suture zone that hosts several metallogenic belts. So far, no Triassic occurrences were reported from Central region of Kazakhstan. In this study, we report the discovery of Triassic outcrop from a quarry belonging to the Akmola Region, in the village Vishnevka that lies to the south-east of the Capital City of Astana. The field observations shows occurrences of three generations of granite with slight variations in mineralogy and texture. The first generation is coarse grained granite with Qtz+Pl+Bt+Kfs having mean U-Pb zircon mean age of 244.4±1.5 Ma (MSWD=1.5). The second generation is fine grained rich in K-feldspar cuts across the first with mean age 241.5±1.9 Ma (MSWD=2.3). The third generation, biotite rich, have an intrusive contact with the first but is equi-granular with a similar age of second generation i.e., 241.8±1.8 Ma (MSWS=1.8). The study area also have a basaltic dyke intruding to the first generation of granite. The major element chemistry of the granite indicates their per-aluminous nature (A/CNK=1.3- 1.4; A/NK= 1.4-1.7) and the trace-element chemistry shows their origin in a collisional environment. The fluid inclusion studies shows first and second generation granites have H₂O in liquid phases and third generation contains water vapor phase, indicating progressive dehydration of the magma during crystallization. We interpret that the first generation S type granite was reworked by the intruded dyke leading to formation of next two generation of granite. These series of evolutionary events give new insights to the rarely recorded crustal processes happened during the Early Triassic Pangea amalgamation, soon after the formation of the massive Siberian Trap at the Permian-Triassic boundary.