29-29 Evolution of Devonian volcanic island arcs in the Central Asian Orogenic Belt: three sites from Mongolia

Session: Undergraduate Research, Part II (Posters)

Poster Booth No.: 80

Presenting Author:

Vanya Dill

Authors:

Dill, Vanya¹, Carmichael, Sarah K.², Königshof, Peter³, Munkhjargal, Ariuka⁴, Gonchigdorj, Sersmaa⁵, Waters, Johnny⁶, Dombrowski, Allison⁷

(1) Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC, USA, (2) Department of Geological and Environmental Sciences, Appalachian State University, Boone, NC, , (3) Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany, (4) Mongolian University of Science and Technology, Mongolia; Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany, (5) Mongolian University of Science and Technology, Mongolia, (6) Appalachian State University, Carrollton, GA, , (7) North Carolina Museum of Natural Sciences, Raleigh, NC, USA; Appalachian State University, USA,

Abstract:

The rocks of southern Mongolia were part of a volcanic island arc system in the Central Asian Orogenic Belt (CAOB) during the Devonian (419-358 Ma). Current tectonic models for these volcanic island arcs are based on fossil/microfossil assemblages and sedimentary facies rather than geochemical data of volcanic rock units. Whole rock geochemistry data of volcanic and volcaniclastic rocks and ash were collected from the Early Devonian Chuluun Formation and Late Devonian to Early Carboniferous Indert Formation in the Shinejinst district in southern Mongolia. This data was compared to equivalent Devonian volcaniclastic rocks of the Samnuuruul Formation in the Baruunhuurai Terrane of western Mongolia and the newly mapped volcanic and shallow marine sequences of the Khavtgai and Borteeg sections in Dundgovi Province in central Mongolia. Mineral identification was performed using powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). Mineralogy and microtextures indicate that these rocks have not undergone significant alteration that would affect whole rock geochemistry results. Th, Sc, and Zr ratios of volcanic and volcaniclastic rocks were measured via fusion mass spectrometry (FUS-MS), instrumental neutron activation analysis (INAA), or fusion inductively coupled plasma (FUS-ICP). Th-Sc-Zr ratios in the older Chuluun Formation at Shinejinst indicate that it was formed in a continental island arc to active continental margin setting.  Whole rock geochemistry of the younger Indert Formation is more indicative of an oceanic island arc setting, which is consistent with the rocks from western Mongolia (although that data is more scattered). The geochemical data suggests a clear trend in the change of tectonic setting between the Chuluun and Indert Formations. These results indicate that not all Devonian volcanic rocks of Mongolia had isolated oceanic island arc origin but rather reflect a more complex and evolving tectonic setting with amalgamating terranes. This is consistent with recent sedimentological and biostratigraphic findings. New data from the Khavtgai and Borteeg sections is being processed and will help further refine the volcanic history and Devonian tectonics of southern and western Mongolia.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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