TWO PULSES OF MAGMATIC ACTIVITY DURING THE EARLY RIPHEAN KUONAMKA IGNEOUS PROVINCE FORMATION: PALEOMAGNETIC SUBSTANTIATION OF THE HYPOTHESIS

Abstract

By the beginning of the 20th century, at least ten different generations of intrusive mafic bodies 1800–900 Ma were distinguished on the territory of the Anabar massif. The first modern age estimates, however, indicate the formation of the bulk of these bodies in a relatively short period of time ~1480–1500 Ma. Based on geochronological and paleomagnetic data, intrusive bodies with this age were combined into the Kuonamka large igneous province (LIP). However, a complex of paleomagnetic studies indicated the probable existence of at least two pulses of magmatic activity during the formation of this province, differing in age, possibly by ~20 Ma. We performed a paleomagnetic study of subvolcanic bodies of the main composition of Permo-Triassic (dykes) and Mesoproterozoic (sills) age, emerging to the surface in the valley of the middle reaches of the Kotui River. As expected, the studied dikes contain an ancient magnetization, the direction of which is typical for Permo-Triassic magmatic bodies of the region and the Siberian platform as a whole, and the paleomagnetic directions of the sills are close to those previously determined in the age-related subvolcanic bodies of the Kuonamka igneous province (1501±3 Ma) of the Anabar massif. The data obtained allow us to test the previously proposed hypothesis about the existence of two magmatic pulses ~1480 and 1500 Ma ago during the formation of the Kuonamka igneous province. The results of the analysis of already known and new paleomagnetic data obtained by us do not support this hypothesis. A refined paleomagnetic pole was proposed for the Siberian platform ~1500 Ma ago with coordinates 22.6° S, 65.0° E and A95=4.3°.