Petrological and mineralogical features of volcanic rocks from the central Kuznetsk Basin (southern Siberia)

The Kuznetsk Basin volcanic rocks are close in age (from 252.3 +/- 0.6 to 246.2 +/- 1.4 Ma) to the traps of the West Siberian Plate and Siberian craton, which formed as a result of the Permo-Triassic plume activity. The geologic and petrographic features evidence that the andesitic basalts exposed in the Karakan and Elbak quarries are effusive rocks; most of them are andesitic basalts, and the rest are trachyandesitic basalts. The mineral composition is as follows: olivine Fo(59-66), plagioclase An(47-60), and clinopyroxene En(47-42)Fs(25-12)Wo(42-33); Mg# = 82-63. Using the COMAGMAT 3.5 program, the magma crystallization conditions during the andesitic-basalt formation were determined: 1109-1105 degrees C, buffer QFM-NNO. The studied rocks are enriched in LREE ((La/Yb)(ch) = 4.7-7.5) and are depleted in HREE ((Sm/Yb)(ch) = 2.0-2.8). A specific geochemical feature of the rocks is strong Nb, Ta, Ti, and Eu negative anomalies ((La/Nb)(PM) = 4.5-1.6, (La/Ta)(PM) = 3.2-2.0, Eu/Eu* = 0.7) and a positive U anomaly on their normalized element patterns; epsilon(Nd)(T) varies from +2.3 to +3.1. The HREE depletion of the Kuznetsk Basin volcanic rock points to the presence of garnet in the mantle source during their generation. The low Mg# indicates that the parental melts are not of the primary-mantle genesis but are probably the product of differentiation in deep-seated intermediate magma chambers. (C) 2012, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.