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Evidence of the interaction between deep magma and fluid: Ultrabasic rocks of the Uitkomst Complex, South Africaтезисы доклада
- Авторы: Solovova I., Zinovieva N., Yudovskaya M., Andreeva I.
- Сборник: Fluid and melt inclusions. ECROFI 2017 Biennial meeting. 23-29 June 2017, Nancy, France
- Том: 17
- Тезисы
- Год издания: 2017
- Место издания: University de Lorraine Nancy France. Nancy
- Первая страница: 210
- Последняя страница: 210
- Аннотация: The question of the genesis of the parent magmas, their composition and the thermodynamic conditions for the formation of layered ultramafic complexes, is still debatable. We studied the satellite intrusion Uitkomst of the Bushveld Complex where melt inclusions could preserve in olivine cumulates of chemically primitive rocks, such as dunites and harzburgites. Olivine contains 3 types of inclusions. The first type is single primary natural-crystallized melt inclusions (size 30-40 microns). Among daughter phases, olivine and orthopyroxene were analyzed. At heating, a melting of the phases were observed in interval 1030-1430oC. A similar behavior were observed in the silicate part of the coexisting combined inclusions (Sp+silicate). The melt contains 54-56 wt% SiO2. The main difference between the composition of melt from previously published model composition of the parental Bushweld magma is high concentration MgO (16-18%) and an excessively high concentration of alkali (up to 4.5 wt%). Inclusions of the second type often have a typical crystallographic outlines and a size of 5 to 30 microns. The composition of small inclusions corresponds to albite-oligoclase, without signs of crystallization. These inclusions do not undergo any changes at heating (crystal inclusions). The same, but larger inclusions are finely crystallized in various degrees and contain Cpx, Cl-Ap, sphene, perovskite, amphibole, rutile, ilmenite. At heating the melting of phases is accompanied by the appearance of multiple fluid bubbles. The homogenization temperature varies between 1190-1250оС. Melt of such inclusions is characterized by high concentrations of SiO2 - up to 65%, alkali (up to 8.5 wt%), and not less than 1% of H2O. The variations of the paired ratios of the components normalized by Na (Me/Na-Al/Na, mol. ratio) showed that the high-magnesian inclusions form compact fields, while the inclusions of acid melt including albite lie on a single trend. Moreover, their position depends on the degree of crystallization and the size of the inclusions, as well as the homogenization temperature. However, a different picture is observed for the K/N ratio. All inclusions (acid and high-magnesian) form a single trend. The high concentration of Na2O, K2O and H2O in the inclusions suggests addition of a Na-K rich fluid to the melt during or after olivine crystallization on the floor of the magma chamber. This is consistent with the presence in olivine of primary polycrystalline inclusions (type 3) containing water-saturated phases (Ol+Opx+Amph+Flg+pectolite (Ca2NaSi3O8[OH])+Ab and glass and fluid)
- Добавил в систему: Зиновьева Нина Георгиевна