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Природа многообразия вулканитов экваториальной части Срединно-Атлантического хребта

Сколотнев С.Г.

Природа многообразия вулканитов экваториальной части Срединно-Атлантического хребта

Сколотнев Сергей Геннадьевич, кандидат геолого-минералогических наук, старший научный сотрудник Геологического института РАН (Москва)

E-mail: sg_skol@mail.ru

На основании изучения состава, геохимии и изотопии вулканитов из осевой части Срединно-Атлантического хребта в Приэкваториальной Атлантике и анализа характера структурно-пространственных вариаций их различных типов показана природа многообразия состава вулканитов региона. Высказывается мнение о том, что блоки континентальной литосферы появились в результате тектонической эрозии Экваториального сегмента Гондваны, расколовшегося и раскрывшегося позднее соседних областей Атлантики.

Ключевые слова: Срединно-Атлантический хребет, Экваториальная Атлантика, базальты N-, T- и P-MORB типов, вулканиты OIB типа, геохимия, изотопия, вещественная неоднородность верхней мантии, плюмы глубинной мантии, тектоника, магматизм.

Skolotnev S.G. The Nature of the Volcanites Diversity of the Mid-Atlantic Ridge Equatorial Part

Sergey G. Skolotnev, Sc.D. (Geology and Mineralogy), Senior Researcher, RAS Geological Institute (Moscow, Russia)

E-mail: sg_skol@mail.ru

Equatorial part of Mid-Atlantic Ridge is characterized by high diversity of volcaniс rocks that form the 2^nd layer of the oceanic crust, and the reasons for this are so far remain the subject of heated discussions. The variety of volcanic rocks comprise of tholeiitic basalts, both depleted and enriched in varying degrees (N-, T-and P-MORB types), alkaline volcanic rocks of basic and ultrabasic composition (OIB type), basalts with high and low concentration of Na2O. I've researched the composition, geochemistry, and isotopic systematic of volcanic rocks from axial zone of the Mid-Atlantic Ridge in subequatorial Atlantic area. My investigation is based on the original data obtained from the materials processing of my expeditions on the research ships ‘Academician Strakhov’ and ‘Gelendzhik’. I also use data from a large number of scientific sources. Research included the results of measuring of both glasses and basalts themselves, as well as analysis of the spatial regularities of volcanic rocks spreading.

My research showed that the extraordinary diversity of volcanic rocks in this region is due to extreme heterogeneity of the upper mantle. This heterogeneity is connected with two factors. The first one is the uplift of deeper and hotter mantle's microplumes from the bottom of upper mantle initiated by convective flows in the asthenosphere. The second factor is the presence of blocks of the lower continental crust and metasomatized continental lithospheric mantle. Blocks of continental lithosphere have resulted from tectonic erosion of the Equatorial segment of Gondwana that has undergone breakup and opening laterthan nearby Atlantic region.

These inhomogeneities give hylic contribution to the volcanic rocks composition and affect the conditions of their melting. Continental lithosphere blocks are cooled the whole upper-mantle terraine in this area, leading to a thermal minimum. Microplumes warm up surrounding mantle locally, what increases a degree of partial melting of a substratum, and promote melting of xenogenic blocks. The superposition of these phenomena leads to the emergence of three major deep levels of partial substrate melting. They are garnet and spinel levels, and intermediate between ones.

Keywords: Mid-Atlantic Ridge; Equatorial Atlantic; basalts of N-, T-, P-MORB types; volcanic rocks of OIB type; geochemistry; isotopy; chemical heterogeneity of the upper mantle; plumes a deeper mantle, tectonic; magmatism.