RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 2, NO. 3, PAGES 243–267, doi:10.2205/2000ES000043, 2000

Magmatism of Mon and Knipovich ridges, polar Atlantics spreading zones, petrogeochemical study, Mid-Atlantic Ridge

¹GEOKHI RAS, Moscow, Russia
²VNII Oceanology, Sankt-Peterburg, Russia
³Institute of Oceanology RAS, Moscow, Russia
⁴Institute of geology and geochronology RAS, Sankt-Peterburg, Russia

Abstract

[1]  The aim of this project was the petrogeochemical study of igneous rocks in the areas of the Mon and Knipovich ridges, both being the northern extensions of the Mid-Atlantic Ridge (MAR), using the data available for the quenching glass samples raised during Cruises 36 and 38 of the "Academic Mstislav Keldysh" vessel and during Cruise 15 of the "Logachev" vessel. The results of studying the igneous rocks of the Mon and Knipovich ridges at the background of the evolution of the total North Atlantic Province, which had been identified earlier from the tectonic and geophysical data available, showed that the igneous rocks of the Knipovich Ridge can be ranked as shallow tholeiites, the primary melts of which were relatively rich in Na and Si and poor in Fe. This type of magma is characteristic of the colder regions of the oceanic lithosphere. Its occurrence in the Knipovich Ridge and its potential propagation up to the Gakkel Ridge, suggest that the igneous rocks of this region originated under the conditions of passive spreading in contrast to the MAR region in the vicinity of Iceland and the Azor Islands, where the substantial contribution of the hotter material of the rising plume contributed to the formation of the oceanic crust. The North Atlantic Ocean is the youngest province in terms of the ocean-floor opening. In spite of the fact that the geological and geophysical data available rank it as one of the well studied regions of the World Ocean, some basic key items of its origin still remain to be clarified. As far back as 1975 Scatler et al. proved the specifics of this region, manifested in the growth of the gravity field, and also in the relative height of the ocean floor in the region of 33-70^o N, which was associated by him with the rise of the hotter mantle, compared with the common regions of the Mid-Atlantic Ridge. Later, this view was confirmed by the character of magmatism which differed in the depth of the generation and by the melting degree of the resulting primary magma. The uniqueness of the North Atlantic region was also proved by the fact that this region is marked by extensive geochemical anomalies associated with the Azor Islands, Iceland, and Yan-Main. All of these data allow one to treat the northern part of the MAR (north of 33^o N) as one global geotectonic province. The Mon and Knipovich ridges, located north of Iceland, are situated at the northern end of the province discussed. This is the least known region. Therefore, new data need be collected for the ridge areas of 73-77^o N need be obtained for the more complete geologic history of the Arctic Basin. The aim of this study was to carry out the complex comparison of the magmatism of the Mon and Knipovich ridges with the magmatism of the large segments of the MAR northern province, and reconstruct the mechanisms of primary magma formation, as well as the conditions of their fractionation. This paper was based on the results of studying the quenched glasses which reflect the evolution of melt in the course of its formation.

Received 16 November 2000; published 5 January 2001.

Keywords: magmatism, Knipovich ridge, Atlantics spreading zones,.