Oxide, sulphide and carbonate minerals in a mantle polymict breccia: Metasomatism by proto-kimberlite magmas, and relationship to the kimberlite megacrystic suite - ScienceDirect
Export JavaScript is disabled on your browser. Please enable JavaScript to use all the features on this page., 30 August 2013, Pages 4-18Author links open overlay panelShow moreAbstractPolymict breccias entrained by kimberlites are mantle xenoliths comprising coarse-grained mantle minerals (porphyroclasts) and rock clasts, cemented together by ilmenite, rutile, phlogopite, olivine and minor sulphides. These unusual xenoliths are generally considered to result from ascending primitive/precursor kimberlite magmas that crystallised in the magma conduit at lithospheric mantle depths. To enhance our understanding of these processes, we investigated the oxide, sulphide and carbonate minerals of a new polymict breccia (DU-1) from the Bultfontein Dumps (Kimberley, South Africa).Xenolith DU-1 contains heterogeneous domains of ilmenite-rich breccia surrounded by spinel harzburgite wall rock. The breccia domains also host resorbed Cr-diopside porphyroclasts and occasional Fe–Ni–Co sulphides segregations. Ilmenite occurs as large (up to 5 cm), chemically zoned lenses, associated with minor rutile. The ilmenite has Hf isotope values (initial εHf = 2.1–3.0) in the range of South African Group I kimberlites and associated megacrysts. The ilmenite lenses host primary multiphase carbonate-rich, olivine-dominated, phlogopite-dominated and sulphide mineral inclusions. Carbonate-rich inclusions host abundant magnesite and dolomite, with subordinate kalsilite, phlogopite, alkali-carbonates, phosphates and chlorides.The occurrence of carbonate-rich inclusions suggests entrapment of a Ca–Mg-rich alkali-carbonate melt during ilmenite growth. However, geochemical modelling indicates that this melt was not parental to the ilmenite. Instead, it is suggested that the ilmenite (and other cementing phases) crystalised from ilmenite and the other cementing phases crystallised from a S-bearing Ti–Fe–K-rich ultramafic silicate melt, derived from an ascending proto-kimberlite melt, which was modified subsequently by wall rock assimilation and/or magma mixing, porphyroclast dissolution and crystal fractionation. The alkali-carbonate melt could be the residual liquid after these processes occurred. Alternatively, the ultramafic silicate and alkali-carbonate melts were produced by liquid immiscibility from a silicate-carbonate proto-kimberlite melt. The occurrence of ilmenite inclusions in sulphide segregations, and sulphide inclusions in ilmenite lenses is indicative of late-stage silicate-sulphide liquid immiscibility.The major and trace element concentrations, Hf isotope composition and mineral inclusion content of ilmenite are consistent with a genetic relationship between polymict breccia formation and the kimberlite megacryst suite. We propose that polymict breccias and megacrysts were produced at different depths by common silicate-carbonate magmas during the early stages of kimberlite magmatism.Highlights? Polymict breccias are mantle xenoliths regarded as failed kimberlite intrusions. ? We have investigated a new sample of polymict breccia from the Kimberley district. ? Alkali carbonate melt inclusions occur in metasomatic ilmenite. ? Ilmenite crystallised from an ultramafic silicate melt. ? Polymict breccias and kimberlite megacrysts might derive from similar magmas.KeywordsPolymict brecciaIlmeniteAlkali-carbonateKimberliteMegacryst suiteLithospheric mantleCheck if you have access through your login credentials or your institution.ororRecommended articlesCiting articles (0)Fracture mechanics investigations associated with coring and hydraulic induced...
AbstractResults from research on the simulation of hydraulic fracture models are presented. These models include the characterization of the coupled formation structural and fracturing fluid flow responses. The structural model is represented by layered linear elastic media subjected to in situ stress fields and fluid pressure on the vertical crack surface. The flow model includes the effects of flow rate, pumping pressure, fluid viscosity, fluid compressibility and formation reservoir properties. Predictive results for the estimation of the fracture width and area for selected Devonian shale formation properties and hydraulic fracturing treatment parameters are illustrated. In addition, design considerations related to penetration of cracks across layered media, bottom hole treatment pressure control, in situ stress effects, fluid leak-offs in the formation, and foam fracturing are discussed.Do you want to read the rest of this article?Request full-text
This research doesn't cite any other publications.ArticleJanuary 1976Two and three dimensional simulations of crack tip intensity factors and field stresses associated with hydraulic fracturing operations are presented. Finite element modeling and classical elasticity theory results are compared for structural formulations characterized by internally pressurized cracks with different geometrics. Applications pertaining to fracture configuration definition,... [Show full abstract]ArticleThe paper deals with the determination of basic two- and three-dimensional stress distribution patterns in infinite single- and multi-layered, granular media during hydraulic pressure grouting. A majority of previous publications have tended to concentrate on simplified direct methods in which the vicinity of crack tip is defined with a large number of finite elements. Due to the inherent... [Show full abstract]ArticleJanuary 1976Analytical and experimental simulations of structural responses associated with hydraulic fracturing operations in reservoir rock are presented. The analytical studies include results obtained from 2- and 3-dimensional linear elasticity structural model formations. Stress contours are presented for 2- and 3-dimensional finite-element models represented by an internally pressurized line crack... [Show full abstract]ArticleNovember 1975This report describes analytical and experimental simulations of structural responses associated with hydraulic fracturing operations in rock media. The analytical and experimental investigations describe the stress patterns, fracture initiation thresholds, and fracture inclinations along with the governing influence of mechanical properties, crack geometry and primitive stresses. The studies... [Show full abstract]Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.This publication is from a journal that may support self archiving.The Effect of High Dose Insulin Analog Initiation Therapy on LDL/HDL Subfraction Profile and HDL Associated Enzymes in Type 2 Diabetic Patients - ScienceDirect
Export JavaScript is disabled on your browser. Please enable JavaScript to use all the features on this page., May–June 2013, Page 242Author links open overlay panelShow moreCheck if you have access through your login credentials or your institution.ororRecommended articlesCiting articles (0)