Abstract
The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton has long been a kind of Siberian Mecca for geologists. It has attracted thousands of geologists, prospectors, and mineral collectors despite its remote location. It is famous for a dozen new and rare minerals, including the gemstones charoite and dianite (the latter is the market name for strontian potassicrichrerite), as well as for a range of uncommon alkaline igneous rocks. Despite this, the age of the Malyy Murun igneous complex and associated metasomatic and hydrothermal mineral associations has remained poorly constrained until now. In this paper, we provide extensive 40Ar/39Ar geochronological data to reveal its age and temporal history. It appears that, although unique in terms of rocks and constituent minerals, the Malyy Murun is just one of multiple alkaline massifs and lavas emplaced in the Early Cretaceous (~137–128 Ma) within a framework of the extensional setting of the Aldan Shield and nearby Transbaikalian region. The extension took place 40–60 million years after the supposed closure of the Mongolia–Okhotsk Ocean and orogenic peak in the Early–Middle Jurassic.
Highlights
The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton (Figure 1), though located in remote Siberia, is familiar to several generations of Russian geologists and to the international community due to a specific assemblage of alkaline igneous rocks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] and mineral deposits for U, Th, Au, Pb, Ti, Sr, and Ba, associated with intrusive and post-intrusive stages of this massif [12,13,14,15,16,17,18,19]
40 Ar/39 Ar dating was performed at the Centre for Geodynamics and Geochronology at the
The age of the Malyy Murun magmatism was considered as the Early Cretaceous based on K-Ar dating of biotite, K-feldspar, and pyroxene separates from feldspar–calcilitic and biotite–pyroxene–K-feldspar syenites of the main intrusive stage [38]
Summary
The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton (Figure 1), though located in remote Siberia, is familiar to several generations of Russian geologists and to the international community due to a specific assemblage of alkaline igneous rocks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] and mineral deposits for U, Th, Au, Pb, Ti, Sr, and Ba, associated with intrusive and post-intrusive stages of this massif [12,13,14,15,16,17,18,19].At last, but not least, the Malyy Murun massif is famous for the only world occurrence of gemstone charoite [20,21,22,23,24].In the 1980s, up to several thousand geologists and miners worked at the Malyy Murun massif during the short Siberian summers in search for various metal and non-metal resources.Today, only limited mining operations are conducted there for the gemstone market (charoite, dianite—the market name for strontian potassicrichrerite [24]), and metallurgy (Ba–Sr benstonite carbonatite [12,13,14]). The Malyy (Little) Murun massif of the Aldan Shield of the Siberian Craton (Figure 1), though located in remote Siberia, is familiar to several generations of Russian geologists and to the international community due to a specific assemblage of alkaline igneous rocks [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] and mineral deposits for U, Th, Au, Pb, Ti, Sr, and Ba, associated with intrusive and post-intrusive stages of this massif [12,13,14,15,16,17,18,19]. But not least, the Malyy Murun massif is famous for the only world occurrence of gemstone charoite [20,21,22,23,24]. In the 1980s, up to several thousand geologists and miners worked at the Malyy Murun massif during the short Siberian summers in search for various metal and non-metal resources. It is worth mentioning that a number of new minerals and mineral varieties have been discovered there (charoite [20,25], tinaksite [26,27], tokkoite [27,28], frankamenite [29,30], strontian potassicrichrerite [31,32], tausonite [33,34], murunskite [35,36], vladykinite [37]), and various exotic rocks such as lamproites, carbonatites, alkaline granites, and various syenitic rocks
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