Abstract
A new occurrence of Permian volcanic and volcaniclastic rocks in the Mongolian Altai south of the Main Mongolian Lineament was described between soums of Tugrug and Tseel in Gobi-Altai aimag. Studied vitrophyric pyroxene basalt lies in a layer of agglomerate and amygdaloidal lavas, which is a part of NE–SW trending subvertical sequence of varicolored siltstones and volcaniclastic rocks in the Tsengel River valley. This high-Mg basalt is enriched in large ion lithophile elements, Pb and Sr and depleted in Nb and Ta. LA-ICP-MS dating on 44 spots reveals several concordia clusters. The whole rock geochemistry of sample fits volcanic arc characteristic in the geotectonic discrimination diagrams. Dominant zircon data yield Upper Carboniferous and Permian magmatic ages 304.4 ± 2.3 and 288.6 ± 1.9 Ma. Two smaller clusters of Upper Devonian (376 ± 4.7 Ma) to Lower Carboniferous ages (351.9 ± 3.5 Ma) indicate probably contamination of ascending magmatic material. Youngest Triassic age found in three morphologically differing grains reflects probably lead loss. Described high-Mg basalt lava represents sub-aerial volcanism in volcanic arc environment developed over the N dipping subduction zone in the southwestern Mongolia in the time span from Uppermost Carboniferous to Permian during terminal stage of its activity.
Highlights
The presence and character of volcanic rocks can provide number of valuable geological data enabling to decipher environment and processes of evolution of the particular blocks of the Earth's crust
This contribution describes a new occurrence of Permian volcanic rocks south of the Main Mongolian Lineament in the area of the Tsengel River northwest of the Tseel soum (Gobi-Altai aimag) in the Mongolian Altai
SUMMARY AND DISCUSSION The new occurrence of Permian volcanic and volcaniclastic rocks was found in the valley of the Tsengel River inside the area formerly considered to be Lower Paleozoic (Togtokh et al, 1995)
Summary
The presence and character of volcanic rocks can provide number of valuable geological data enabling to decipher environment and processes of evolution of the particular blocks of the Earth's crust This scheme can be applicable for evolution history of the Central Asian Orogenic Belt (CAOB, Mossakovsky et al, 1993), developed between the Siberian. Of CAOB, A-type granitoids and a bimodal alkaline volcanic series developed in the environment analogous to continental rifts during the Permian (Kozlovsky et al, 2015) This contribution describes a new occurrence of Permian volcanic rocks south of the Main Mongolian Lineament in the area of the Tsengel River northwest of the Tseel soum (Gobi-Altai aimag) in the Mongolian Altai. The presented petrological and geochemical data, including radiometric age, complement and specify the lithostratigraphic classification of units in the area which is generally based on the geological map 1: 200,000, sheet L-46-XXIV (Togtokh et al, 1995)
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