Mesozoic thermal events and related gold mineralization in the eastern Mongol-Okhotsk Orogenic Belt: constraints from regional geology and 40Ar/39Ar dating

The Mongol-Okhotsk Orogenic Belt is a major structural element in East Asia. Several aspects of its evolution remain unknown or controversial. In this study, we report the results obtained using 40Ar/39Ar geochronological studies performed on the metasedimentary rocks from various terranes and formations as well as host rocks and hydrothermally altered rocks of gold deposits in the eastern Mongol-Okhotsk Belt. Our new 40Ar/39Ar data suggest that four thermal events occurred in the eastern Mongol-Okhotsk Belt at 172-166, 157-149, 141-135, and 133-128 Ma. The ages of these events do not correlate with the geological age of the formations and not depend on the location of the terranes. None of these events were accompanied by magmatic activity in the east of the belt. Therefore, we believe that these events are related to tectonic. The 172-166 Ma event corresponds to regional metamorphism associated with the collision of the Siberian Craton and Amurian Superterrane. The remaining three younger events of 157-149, 141-135, and 133-128 Ma occurred in the post-collisional setting. The Malomyr, Albyn, Unglichikan, and Elga gold deposits formed during two thermal stages at 141-135 and 133-128 Ma, after the collision. 40Ar/39Ar isotopic data suggest a gap (similar to 30 Ma) between orogenic events caused by the collision of the Siberian Craton and Amurian Superterrane and gold mineralization. Our data are consistent with the idea that the formation of the Mongol-Okhotsk Orogenic Belt and gold ore deposits in this belt occurred in the relation to strike-slip (or transform displacement) along the regional E-W Mongol-Okhotsk fault/thrust system, but without relation of these deposits to granites. [GRAPHICS] The Mongol-Okhotsk Orogenic Belt is a major structural element in East Asia. Several aspects of its evolution remain unknown or controversial. In this study, we report the results obtained using 40Ar/39Ar geochronological studies performed on the metasedimentary rocks from various terranes and formations as well as host rocks and hydrothermally altered rocks of gold deposits in the eastern Mongol-Okhotsk Belt. Our new 40Ar/39Ar data suggest that four thermal events occurred in the eastern Mongol-Okhotsk Belt at 172-166, 157-149, 141-135, and 133-128 Ma. The ages of these events do not correlate with the geological age of the formations and not depend on the location of the terranes. None of these events were accompanied by magmatic activity in the east of the belt. Therefore, we believe that these events are related to tectonic. The 172-166 Ma event corresponds to regional metamorphism associated with the collision of the Siberian Craton and Amurian Superterrane. The remaining three younger events of 157-149, 141-135, and 133-128 Ma occurred in the post-collisional setting. The Malomyr, Albyn, Unglichikan, and Elga gold deposits formed during two thermal stages at 141-135 and 133-128 Ma, after the collision. 40Ar/39Ar isotopic data suggest a gap (similar to 30 Ma) between orogenic events caused by the collision of the Siberian Craton and Amurian Superterrane and gold mineralization. Our data are consistent with the idea that the formation of the Mongol-Okhotsk Orogenic Belt and gold ore deposits in this belt occurred in the relation to strike-slip (or transform displacement) along the regional E-W Mongol-Okhotsk fault/thrust system, but without relation of these deposits to granites. [GRAPHICS]