U–Pb Dating of Apatite, Titanite and Zircon of the Kingash Mafic–Ultramafic Massif, Kan Terrane, Siberia: from Rodinia Break-up to the Reunion with the Siberian Craton

Abstract

Abstract The initial stage of Rodinia supercontinent break-up occurred at about 750 Ma. It preceded formation of the Irkutsk and Franklin large igneous provinces (LIPs) at 712 ± 2 to 739 ± 8 Ma. These LIPs were emplaced within the formerly connected Laurentian and Siberian cratons. The Kingash massif is located in the Precambrian Kan terrane in direct contact with the Siberian Craton at its southwestern boundary. It has been linked to an important suite of mafic–ultramafic intrusions that border the southern margin of the Siberian craton, and that have been inferred to belong to the Irkutsk LIP. The massif is also significant, because it hosts platinum group element (PGE)–Cu–Ni-rich mineralization and is the only large deposit in the region. However, despite numerous dating attempts, the age of the massif had not been resolved. A significant difficulty is post-magmatic recrystallization at amphibolite facies that affected the rocks of the massif. In this study we used U–Pb dating of zircon, titanite and apatite from rocks of the Kingash massif and cross-cutting granite and monzonite veins. The oldest igneous zircon grain of the Kingash massif analysed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yields an age of c. 750 Ma, taken as a tentative age of magmatism. Dating of multiple grains of metamorphic zircon by chemical abrasion isotope dilution thermal ionization mass spectrometry yielded 564·8 ± 2·2 Ma, which is in agreement with LA-ICP-MS titanite ages of 557 ± 19, 565 ± 35 and 551 ± 17 Ma. Apatite of two different samples showed ages of 496·4 ± 7·9 and 497·0 ± 1·8 Ma (LA-ICP-MS), which are interpreted as the time when the terrane cooled below the closure temperature of apatite. Using our new data we suggest that at the time of the Irkutsk–Franklin LIP event the Kan terrane was a part of Rodinia, then it separated from either Siberia or Laurentia during the break-up of Rodinia and finally collided with Siberia at 560 Ma, the time of regional amphibole-facies metamorphism.