Перевод названия: Petrochemical features and factors of variation of rock composition in the Sredne-Tatarsky Massif
Тип публикации: статья из журнала
Год издания: 2011
Ключевые слова: фойяиты, foyaites, ijolites, Peritectic crystallization, fractionation, ийолиты, перитектическая кристаллизация, фракционирование
Аннотация: Приведены геологическая характеристика Средне-Татарского массива, особенности химического состава породообразующих минералов фойяитов и ийолитов, занимающих преобладающее распространение в составе интрузии. Представлены результаты петрохимической аттестации главных петрографических разновидностей пород, участвующих в строении массиПоказать полностьюва, их петро- химическая специализация. Рассмотрены ведущие факторы вариации состава пород интрузии. The Sredne-Tatarsky (Zaangarsky) alkaline massif located in the south-western part of the Yenisey Ridge, the formation of which occurred as the result of repeated intrusion of mantel feldspathoid magmas in rifting conditions, is characterized by a variety of rocks composing it and presence of rare-earth ? rare-metal mineralization. Foyaites of the early phase and later ijolites often presented by feldspar variations participate mainly in the structure of the massif. The main rock-forming minerals of foyaites and ijolites are presented by two generations and correspond to their standard composition in whole. Alkaline rocks of the massif have similar isotopic composition of primary relations of Sr and Nd isotopes in foyalites and ijolites, characterizing close relation of foid magma sources. By their chemical composition the rocks of the massif in whole are poor in silicic acid (SiO2 = 46-62%), rich in alumina (Al2O3 = 17-28%) and alkalis (K2O + Na2O = 6-17%) with Na2O prevailing. The petrochemical certification of rocks of the massif allowed defining silicate and carbonate associations based on the calcium, silica, alumina and alkali ratio. The silicate association unites plagioijolites, foyalites, muscovite syenites and their weathering products. The assessment of the petrochemical specialization allows considering them as products of potassium-sodium alkaline series and reveals the presence of various evolution trends of imaging rock points in each massif phase, indicating various mechanisms of crystallization during their development. The observed accumulation of salic components in the residual melt in ijolites and their reduction or permanent composition in foyalites (as in case with Al2O3) testify to the fact that the main factor during ijolite crystallization is fractionating of dark-coloured minerals (pyroxenes), and peritectic feldspar and feldspathoid crystallization is noted in foyalites. The component analysis of petrochemical information in the silicate association showed that the variations of petrochemical rock parameters within the selection are defined by three main components. The first factor allows considering fraction crystallization of femic minerals as the leading process during the formation of ijolites. The second component evidently characterizes the orientation of exogenous processes defined by decomposition of dark-coloured minerals and feldspathoids with muscovite formation. The third component characterized by high positive correlation of the sum of alkalis, potassium and the potassium-to-sodium ratio at the background of stable negative relations with silica probably defines the distribution of feldspars in the rocks under study and reflects their peritectic crystallization. The material heterogeneity of main rocks composing the Sredne-Tatar massif, based on the performed study of their silicate analyses, is preconditioned by evolution of the foidite melt, associated with various magma fractionating and crystallization mechanisms.
Журнал: Вестник Томского государственного университета
Выпуск журнала: № 342
Номера страниц: 214-221
ISSN журнала: 15617793
Место издания: Томск
Издатель: Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования Национальный исследовательский Томский государственный университет