Mesozoic thermal events and related gold mineralization in the еastern 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 еastern 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 (~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.

蒙古-鄂霍茨克造山带（Mongol–Okhotsk Orogenic Belt）是东亚地区的重要构造单元，其演化过程中的诸多科学问题仍未明确或存在争议。
本研究针对蒙古-鄂霍茨克造山带东部不同地体、地层中的变沉积岩，以及金矿床的赋矿围岩与热液蚀变岩，开展了40Ar/39Ar年代学研究，现将所得研究结果报道如下。
本次获取的全新40Ar/39Ar数据显示，该造山带东部共发育四期热事件，时限分别为172~166 Ma、157~149 Ma、141~135 Ma及133~128 Ma。上述热事件的年龄既与对应地层的地质时代无相关性，也不受地体分布位置的影响；且该造山带东部的所有热事件均未伴随岩浆活动，据此我们认为这些热事件与构造作用直接相关。
其中172~166 Ma的热事件对应西伯利亚克拉通（Siberian Craton）与阿穆尔超级地体（Amurian Superterrane）碰撞所引发的区域变质作用；其余三期较年轻的热事件（157~149 Ma、141~135 Ma及133~128 Ma）则均形成于碰撞后构造环境。
马洛米尔（Malomyr）、阿尔宾（Albyn）、乌格利奇卡坎（Unglichikan）与埃尔加（Elga）金矿床均形成于碰撞后的两期热事件阶段，即141~135 Ma与133~128 Ma。40Ar/39Ar同位素数据表明，西伯利亚克拉通与阿穆尔超级地体碰撞引发的造山事件与金成矿作用之间存在约30 Ma的时间间隔。
本研究结果支持如下学术观点：蒙古-鄂霍茨克造山带及其区内金矿床的形成，与沿东西向区域蒙古-鄂霍茨克断裂-逆冲系统的走滑（或转换位移）作用密切相关，但上述金矿床的形成与花岗岩类岩体并无关联。