Constraining The Ages Of Late Devonian Extinction Events In The Central Asian Orogenic Belt (CAOB): U-Pb Geochronology And Igneous Petrology

The Late Devonian was a time of drastic changes in climate and biodiversity. Two of the top six most devastating extinction events occurred during the Late Devonian, although the reasons for these extinction events remains unknown. More than 96% of studies on these Late Devonian extinction intervals have been conducted on continental margins or in epicontinental basins, with 77% on the Euramerican continent alone. There are very few studies of these Late Devonian mass extinction events in a paleogeographically different region: the open ocean island arc systems in the Central Asian Orogenic Belt (CAOB). Sedimentary rocks and lava flows were collected from the Samnuuruul Formation in western Mongolia during fieldwork in 2014 for U- Pb geochronology analyses of zircons. The chemical-abrasion thermal ionization mass spectrometer (CA-TIMS) technique was used to analyze these zircons. Age results for sample SAM 4-8 show a final age of 375.81 +/- 1.20 Ma, and sample MBL 7 show a final age of 376.75+/- 0.90 Ma. These ages indicate that both samples have a Frasnian age. Until now, the only age constraints that existed for these sections were based on limited biostratigraphy; this is the first study to radiometrically date Late Devonian rocks from western Mongolia. This study will further constrain the location of Late Devonian extinction intervals in a section that was once part of the CAOB, therefore opening doors to new research opportunities of these events in a geographically different region than what has been studied before.