Late Mesozoic Granitoid Magmatism in the Evolution of the Eastern Flank of the Mongol-Okhotsk Orogenic Belt (Russia)

Abstract

In this article, for the first time, a comparison is made of magmatic events that occurred in the northern and southern framing of the eastern flank of the Mongol-Okhotsk orogenic belt. It is established that these events occurred simultaneously. The igneous rocks accompanying these events are identical in their material characteristics. And their geochemical characteristics reflect the geodynamic processes that took place in the frame of the Mongolian-Okhotsk orogenic belt at the end of the Mesozoic. Igneous rocks are represented by a wide range of rocks: from plutonic to volcanic. The range of their material composition is also wide. But the main component belongs to granitoids. At the initial stage of the Late Mesozoic geological events, granitoids of the adakitic series (149–138 Ma) were formed. Then formations of the calc-alkaline series (140–122 Ma) begin to form. However, the rocks of both the first and second stages were formed under suprasubduction conditions. The difference in the composition of these formations is established by the values of Sr-Nd isotopes. This reflects their spatial affiliation. In the northern frame, they break through the widely developed Archean and Proterozoic formations, and in the southern frame, only Proterozoic ones.