⁴⁰Ar/³⁹Ar Geochronology of the Malyy (Little) Murun Massif, Aldan Shield of the Siberian Craton: A Simple Story for an Intricate Igneous Complex

Abstract

The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton has long been a kind of the geologists’ Siberian Mecca. It attracted thousands of geologists, prospectors and mineral collectors despite of its remote location. It is famous for a dozen of new and rare minerals, including gemstones charoite and dianite (the latter is the market name for strontian potassicrichrerite), as well as for specific alkaline igneous rocks. Despite of this, the age of the Malyy Murun igneous complex and associated metasomatic and hydrothermal mineral associations remained poorly constrained. In this paper, we provide extensive 40Ar/39Ar geochronological data to reveal its age and temporal history. It appeared that being unique in terms of rocks and constituent minerals, the Malyy Murun is one of multiple alkaline massifs and lavas emplaced in Early Cretaceous (~137-128 Ma) within a framework of extensional setting of the Aldan Shield and nearby Transbaikalian region. The extension has occurred 40-60 million years after the supposed closure of the Mongolia-Okhotsk Ocean and peak of orogeny in Early-Middle Jurassic.