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141.
BERLY THOMAS J.; HERMANN JORG; ARCULUS RICHARD J.; LAPIERRE HENRIETTE 《Journal of Petrology》2006,47(8):1531-1555
Peridotites associated with pyroxenites (with rare olivine andspinel) are exposed on the islands of San Jorge and Santa Isabelin the Solomon Islands. Orthopyroxenite occurs in large outcrops(100 m2) whereas websterite and clinopyroxenite occur as layersand veins/dykes in peridotites. The bulk compositions of thepyroxenites are characterized by high Mg2+/(Mg2+ + Fe2+) (0·780·91)and low Al2O3 (<2·7 wt %). Low rare earth elementabundances are coupled with large ion lithophile element enrichmentsand positive Sr and Pb anomalies (primitive mantle-normalized)relative to adjacent rare earths. Temperatures of equilibrationfor the pyroxenites are between 950 and 1050°C. These relativelylow temperatures, combined with the occurrence of primary fluidinclusions, suggest that the pyroxenites formed by interactionof peridotite protoliths with an aqueous fluid. Bulk-rock andmineral compositions of the orthopyroxenites are similar tothose of mantle-derived pyroxenites, whereas the websteriteshave closer chemical affinity with crustal arc cumulates. Nevertheless,field relationships plus petrological, textural and geochemicalevidence are consistent with formation of all pyroxenite typesin supra-subduction zone mantle, resulting from metasomatismof peridotite by subducted Pacific Plate-derived fluid. Sucha setting for pyroxenite has not previously been reported indetail. We propose that these processes produce mantle pyroxenitewith compositions similar to crustal pyroxenite. KEY WORDS: mantle metasomatism; pyroxenite; supra-subduction zone 相似文献
142.
A. K. ENGVIK K. MEZGER S. WORTELKAMP R. BAST F. CORFU A. KORNELIUSSEN P. IHLEN B. BINGEN H. AUSTRHEIM 《Journal of Metamorphic Geology》2011,29(4):399-423
Widespread metasomatism affected the 100 km long and 25 km wide Proterozoic Bamble and Modum‐Kongsberg sectors, South Norway, resulting in the chemical and mineralogical transformation of wide segments of continental crust. Scapolitization was associated with veining, and was followed by albitization, transforming metagabbros pervasively over large areas. Fluids played an active role in these reactions, forming H2O‐, CO2‐ and Cl‐bearing phases at the expense of the primary volatile‐free minerals, causing depletion in Fe and infiltration of K, Mg, Na, B and P. The transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages: during an incipient amphibolitization stage, the primary mafic minerals were replaced by anthophyllite or hastingsite, followed by pargasitic and edenitic Ca‐amphibole. Magnetite was dissolved, while rutile formed by the breakdown of ilmenite. Plagioclase was replaced by Cl‐rich scapolite (Me19‐42) reflecting Cl‐saturation, while K‐ and Mg‐saturation produced phlogopite, enstatite, sapphirine and rare corundum. The high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of B and P. The albitites consist dominantly of albite (Ab95‐98) with varying, generally small, amounts of chlorite, calcite, rutile, epidote and pumpellyite. They formed from a H2O–CO2‐fluid rich in Na. The gabbro yields a zircon U–Pb age of 1149 ± 7 Ma and tonalite 1294 ± 38 Ma, whereas rutile from scapolite metagabbro and albitite has U–Pb ages of 1090–1084 Ma, and phlogopite produced during scapolitization Rb–Sr ages of 1070–1040 Ma. Temperature conditions for the scapolitization are inferred to have been 600–700 °C. The reported ages, combined with mineralogical and petrographic observations and inferred P–T conditions, indicate that the metasomatism was a part of the regional Sveconorwegian amphibolite facies metamorphic phase. Initial 87Sr/86Sr of the scapolite ranges from 0.704 to 0.709. The Sr‐signature, the Cl‐ and B‐rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism. 相似文献
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144.
尝试用稀土分布的分形结构因子(FSF)值对我国碱性花岗岩的稀土组成进行了分类。可将我国碱性花岗岩的稀土分布分形结构因子划分为4种类型:(1)弱变异型(0.98-0.95);(2)中变异型(0.95-0.92);(3)强变异型(0.92-0.89);(4)超强变异型(0.89-0.86)。其中前两种类型可很好地对应重稀土富集型和中稀土亏损型花岗岩,而后两种类型可对应轻稀土相对富集型和轻稀土特富型花岗岩。利用FSF值对新疆东准噶尔地区三带富碱花岗岩按稀土组成进行了归类。 相似文献
145.
146.
147.
新疆东准噶尔北部碱性花岗岩的特征、成因及构造意义 总被引:24,自引:2,他引:24
新疆东准噶尔北部的碱性花岗岩呈带状分布于乌伦古断裂及额尔齐斯─玛因鄂博断裂之间地区。碱性花岗岩以出现碱性暗色矿物及铁质黑云母为特征,高硅、高碱、低钙、低镁铁,富含高场强元素,属典型的A型花岗岩,它们产出的特定构造环境,据化学成分的构造环境判别为板内非造山的裂谷环境;成因类型相当于Eby(1992)的A1类A型花岗岩,明显不同于东准噶尔中部及南部碱性花岗岩带产出的造山期后张性构造环境。 相似文献
148.
本文回顾了国内外金伯利岩及其它地幔岩中发现的K、Ba、Ca、REE的Ti-Cr-Fe-Mg氧化物矿物的研究现状,包括沂蒙矿系列、蒙山矿系列及柱红石系列。在此基础上概括性地总结了笔者近一、二年对山东蒙阴金伯利岩中蒙山矿矿物所进行的微区矿物学方向研究取得的最新进展,包括:①揭示了K、Ba、Ca、REE等半径较大的元素在蒙山矿中的不均匀分布特点;②首次在金伯利岩中发现了蒙山矿系列矿物的Ca端元——Ca蒙山矿及K-Ba-Ca三个端元蒙山矿在同一矿物颗粒中的共存现象;③进行了高分辨透射电镜工作,拍摄了晶格条纹象,从而完善了蒙山矿的晶体结构资料;④确定了蒙山矿后期熔融交代形成的多种矿物相。这些研究成果,证实了地幔交代作用的存在和复杂性,应引起矿物岩石学界的充分重视。 相似文献
149.
NEUMANN ELSE-RAGNHILD; GRIFFIN WILLIAM LINDSEY; PEARSON NORMAN J.; O'REILLY SUZANNE YVONNE 《Journal of Petrology》2004,45(12):2573-2612
Laser ablation microprobe data are presented for olivine, orthopyroxeneand clinopyroxene in spinel harzburgite and lherzolite xenolithsfrom La Palma, Hierro, and Lanzarote, and new whole-rock trace-elementdata for xenoliths from Hierro and Lanzarote. The xenolithsshow evidence of strong major, trace element and Sr isotopedepletion (87Sr/86Sr 0·7027 in clinopyroxene in themost refractory harzburgites) overprinted by metasomatism. Thelow Sr isotope ratios are not compatible with the former suggestionof a mantle plume in the area during opening of the AtlanticOcean. Estimates suggest that the composition of the originaloceanic lithospheric mantle beneath the Canary Islands correspondsto the residues after 2530% fractional melting of primordialmantle material; it is thus significantly more refractory thannormal mid-ocean ridge basalt (MORB) mantle. Thetrace element compositions and Sr isotopic ratios of the mineralsleast affected by metasomatization indicate that the upper mantlebeneath the Canary Islands originally formed as highly refractoryoceanic lithosphere during the opening of the Atlantic Oceanin the area. During the Canarian intraplate event the uppermantle was metasomatized; the metasomatic processes includecryptic metasomatism, resetting of the SrNd isotopicratios to values within the range of Canary Islands basalts,formation of minor amounts of phlogopite, and meltwall-rockreactions. The upper mantle beneath Tenerife and La Palma isstrongly metasomatized by carbonatitic or carbonaceous meltshighly enriched in light rare earth elements (REE) relativeto heavy REE, and depleted in ZrHf and Ti relative toREE. In the lithospheric mantle beneath Hierro and Lanzarote,metasomatism has been relatively weak, and appears to be causedby high-Si melts producing concave-upwards trace element patternsin clinopyroxene with weak negative Zr and Ti anomalies. TiAlFe-richharzburgites/lherzolites, dunites, wehrlites and clinopyroxenitesformed from mildly alkaline basaltic melts (similar to thosethat dominate the exposed parts of the islands), and appearto be mainly restricted to magma conduits; the alkali basaltmelts have caused only local metasomatism in the mantle wall-rocksof such conduits. The various metasomatic fluids formed as theresults of immiscible separations, meltwall-rock reactionsand chromatographic fractionation either from a CO2-rich basalticprimary melt, or, alternatively, from a basaltic and a siliceouscarbonatite or carbonaceous silicate melt. KEY WORDS: mantle xenoliths; mantle minerals; trace elements; depletion; carbonatite metasomatism 相似文献
150.
Oxygen Isotopic Characteristics of Granitic Intrusions Related to Haobugao Zn-Pb-Cu-Sn Skarn Deposit, East Inner Mongolia, China 总被引:2,自引:0,他引:2
Jingbin Wang Lijuan Wang Yuwang Wang Tiejun Li Hidehiko Shimazaki 《Resource Geology》2004,54(2):205-208
Abstract. Granitic rocks related to the formation of Haobugao Zn-Pb-Cu-Sn skarn deposit, Inner Mongolia, China, show unusual low whole-rock δ18 O values down to -8.8 % (V-SMOW), whereas separated quartz crystals from those rocks give positive δ18 O values of+4.1 to +9.9 %. Chemical analyses and microscopic observation of those granitic rocks confirm that they suffered hydrothermal alteration. Some skarn specimens and quartz from the Haobugao deposit also show negative δ18 O values. The isotopic evidence indicates that intensive meteoric water circulation occurred at the time of granitic intrusion, and caused the pervasive hydrothermal alteration of granitic rocks and the precipitation of skarn deposit in this area. 相似文献