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1.
湖北铜绿山铜铁矿床中煌斑岩的矿物学特征及岩石成因初探 总被引:2,自引:1,他引:1
湖北铜绿山矽卡岩型铜铁矿床处于长江中下游铁铜成矿带西部的鄂东南矿集区。最近我们在该矿区工作中采集到两条侵入于含矿石英二长闪长玢岩中的煌斑岩脉。本文对这些煌斑岩脉进行了详细的镜下岩相学观察,并对其中造岩矿物黑云母、辉石和长石进行了电子探针成分分析。根据这些数据本文论述了煌斑岩的物源、形成环境以及岩浆体系的物理化学条件。研究表明,煌斑岩中云母为富镁黑云母,其形成的岩浆体系处于中低氧逸度(近Ni-Ni O);黑云母与全岩都具有高钛特征,表明煌斑岩的物源深度可能来自较深部地幔(如软流圈)。煌斑岩中辉石为单斜辉石,环带较为发育,有韵律环带和正环带,其韵律环带的形成可能是由于岩浆温压环境存在振荡性变化而形成的。铜绿山矿床中煌斑岩属于云煌岩;其岩浆来源具幔源性,受到地壳的混染作用不强。 相似文献
2.
Gaurav J. Kokandakar Sachin S. Ghodke K. Rathna Laxman B. More B. Nagaraju Munjaji V. Bhosle K. Vijaya Kumar 《Journal of the Geological Society of India》2018,91(2):135-146
Three distinct alkaline magmas, represented by shonkinite, lamprophyre and alkali basalt dykes, characterize a significant magmatic expression of rift-related mantle-derived igneous activity in the Mesoproterozoic Prakasam Alkaline Province, SE India. In the present study we have estimated emplacement velocities (ascent rates) for these three varied alkaline magmas and compared with other silicate magmas to explore composition control on the ascent rates. The alkaline dykes have variable widths and lengths with none of the dykes wider than 1 m. The shonkinites are fine- to medium-grained rocks with clinopyroxene, phologopite, amphibole, K-feldspar perthite and nepheline as essential minerals. They exhibit equigranular hypidiomorphic to foliated textures. Lamprophyres and alkali basalts characteristically show porphyritic textures. Olivine, clinopyroxene, amphibole and biotite are distinct phenocrysts in lamprophyres whereas olivine, clinopyroxene and plagioclase form the phenocrystic mineralogy in the alkali basalts. The calculated densities [2.54–2.71 g/cc for shonkinite; 2.61–2.78 g/cc for lamprophyre; 2.66–2.74 g/cc for alkali basalt] and viscosities [3.11–3.39 Pa s for shonkinite; 3.01–3.28 Pa s for lamprophyre; 2.72–3.09 Pa s for alkali basalt] are utilized to compute velocities (ascent rates) of the three alkaline magmas. Since the lamprophyres and alkali basalts are crystal-laden, we have also calculated effective viscosities to infer crystal control on the velocities. Twenty percent of crystals in the magma increase the viscosity by 2.7 times consequently decrease ascent rate by 2.7 times compared to the crystal-free magmas. The computed ascent rates range from 0.11–2.13 m/sec, 0.23–2.77 m/sec and 1.16–2.89 m/sec for shonkinite, lamprophyre and alkali basalt magmas respectively. Ascent rates increase with the width of the dykes and density difference, and decrease with magma viscosity and proportion of crystals. If a constant width of 1 m is assumed in the magma-filled dyke propagation model, then the sequence of emplacement velocities in the decreasing order is alkaline magmas (4.68–15.31 m/sec) > ultramafic-mafic magmas (3.81–4.30 m/sec) > intermediate-felsic magmas (1.76–2.56 m/sec). We propose that SiO2 content in the terrestrial magmas can be modeled as a semi-quantitative “geospeedometer” of the magma ascent rates. 相似文献
3.
Vapor-Absent Melting of Tonalite at 15-32 kbar 总被引:13,自引:0,他引:13
The behavior of igneous continental crust during subductionis modeled by means of vapor-absent partial melting experimentson a tonalite, containing equal amounts of biotite and hornblende,at pressures of 1532 kbar. The experiments produce leucograniticmelts coexisting with garnet + omphacitic clinopyroxene + K-feldspar+ kyanite + quartz/coesite ± phengite ± zoisite.Experimental constraints and geometrical analysis of phase equilibriashow that the hydrous phases that control dehydration-meltingof tonalites in deep thickened continental crust and in theupper mantle are phengite and zoisite. The negatively slopingamphibole + quartz vapor-absent solidus characteristic of amphibolitesis largely suppressed in tonalites, because amphibole is eliminatedby water-conserving reactions that also consume K-feldspar andkyanite and produce phengite and zoisite. The temperature atwhich melt first appears in the experiments varies from <900°Cat 15 kbar, to 1000°C at 27 kbar, to <925°C at 32kbar. Moderate degrees of partial melting (2030%) yieldresidual assemblages with mantle-like densities but which canstill contain minor amounts of hydrous phases. Partial meltingof tonalitic crust during continental subduction can thus generateincompatible element-rich residues that would be able to remainin the mantle indefinitely, acting as long-term sources of metasomaticfluids. KEY WORDS: mantle; melting; metasomatism; tonalite; UHP metamorphism 相似文献
4.
Fluid-Absent Melting Behavior of an F-Rich Tonalitic Gneiss at Mid-Crustal Pressures: Implications for the Generation of Anorogenic Granites 总被引:12,自引:6,他引:12
Fluid-absent melting experiments on a biotite (20 wt.%) andhornblende (2 wt.%) bearing tonalitic gneiss were conductedat 6 kbar (900975C), 10 kbar (8751075C), and14 kbar (950975C) to study melt productivity from weaklyperaluminous quartzofeldspathic metamorphic rocks. At 6 kbar,biotite dehydrationmelting is completed at 975C viaincongruent melting reactions that produce orthopyroxene, twooxides, and {small tilde}25 wt.% granitic melt. At 6 kbar, hornblendedisappears at 900C, probably in reaction with biotite. At 10kbar, biotite dehydrationmelting produces <10 wt.%melt up to 950C via incongruent melting reactions that produceorthopyroxene, garnet, and granitic melt. Hornblende disappearsin the satne temperature interval either by resorption or byreaction with biotite. Widespread biotite dehydrationmeltingoccurs between 950 and 975C and produces orthopyroxene, twooxides, and {small tilde}20 wt.% fluorine-rich (up to 031wt.%) granitic melt. At 14 kbar only a trace of melt is presentat 950C, and the amounts of hornblende and biotite are virtuallythe same as in the starting material. At 975C, hornblende isgone and {small tilde}10 wt.% granitic melt is produced by meltingof both biotite and hornblende. Our results show that hornblende-bearing assemblages cannotgo through dehydrationmelting on their own (althoughthey can in combination with biotite) if the Ca content in thesource rock is too low to stabilize clinopyroxene. In such rocks,hornblende will either resorb or melt by reaction with biotite.Under fluid-absent conditions, intrusion of hot, mantle-derivedmagmas into the lower crust is necessary to initiate widespreaddehydrationmelting in rocks with compositions similarto those discussed here. We argue that the high thermal stabilityof biotite in our starting material is caused mainly by theincorporation of fluorine. The relatively high F content inbiotite in the starting material (047 wt.%) suggests thatthe rock has experienced dehydroxylation in its past. F enrichmentby a previous fluid-absent partial melting event is excludedbecause of the lack of phases such as orthopyroxene and garnetwhich would have been produced. Our experiments show that thedehydrationmelting of such F-enriched biotite producesF-rich granitic liquids, with compositions within the rangeof A-types granites, and leaves behind a granulitic residuedominated by orthopyroxene, quartz, and plagioclase. This studytherefore supports the notion that A-type granites can be generatedby H2O-undersaturated melting of rocks of tonalitic composition(Creaser et al., 1991), but does not require that these sourcerocks should be residual after a previous melting event. 相似文献
5.
D. J. Smith M. G. Petterson A. D. Saunders I. L. Millar G. R. T. Jenkin T. Toba J. Naden J. M. Cook 《Contributions to Mineralogy and Petrology》2009,158(6):785-801
Savo, Solomon Islands, is a historically active volcano dominated by sodic, alkaline lavas, and pyroclastic rocks with up
to 7.5 wt% Na2O, and high Sr, arc-like trace element chemistry. The suite is dominated by mugearites (plagioclase–clinopyroxene–magnetite ± amphibole ± olivine)
and trachytes (plagioclase–amphibole–magnetite ± biotite). The presence of hydrous minerals (amphibole, biotite) indicates
relatively wet magmas. In such melts, plagioclase is relatively unstable relative to iron oxides and ferromagnesian silicates;
it is the latter minerals (particularly hornblende) that dominate cumulate nodules at Savo and drive the chemical differentiation
of the suite, with a limited role for plagioclase. This is potentially occurring in a crustal “hot zone”, with major chemical
differentiation occurring at depth. Batches of magma ascend periodically, where they are subject to decompression, water saturation
and further cooling, resulting in closed-system crystallisation of plagioclase, and ultimately the production of sodic, crystal
and feldspar-rich, high-Sr rocks. The sodic and hydrous nature of the parental magmas is interpreted to be the result of partial
melting of metasomatised mantle, but radiogenic isotope data (Pb, Sr, Nd) cannot uniquely identify the source of the metasomatic
agent. 相似文献
6.
Dehydration melting of tonalitic compositions (phlogopite or biotite-plagioclase-quartz assemblages) is investigated within
a temperature range of 700–1000°C and pressure range of 2–15 kbar. The solid reaction products in the case of the phlogopite-plagioclase(An45)-quartz starting material are enstatite, clinopyroxene and potassium feldspar, with amphiboles occurring occasionally. At
12 kbar, zoisite is observed below 800°C, and garnet at 900°C. The reaction products of dehydration melting of the biotite
(Ann50)-plagioclase (An45)-quartz assemblage are melt, orthopyroxene, clinopyroxene, amphibole and potassium feldspar. At pressures > 8 kbar and temperatures
below 800°C, epidote is also formed. Almandine-rich garnet appears above 10 kbar at temperatures ≥ 750°C. The composition
of melts is granitic to granodioritic, hence showing the importance of dehydration melting of tonalites for the formation
of granitic melts and granulitic restites at pressure-temperature conditions within the continental crust. The melt compositions
plot close to the cotectic line dividing the liquidus surfaces between quartz and potassium feldspar in the haplogranite system
at 5 kbar and a
H
2O = 1. The composition of the melts changes with the composition of the starting material, temperature and pressure. With increasing
temperature, the melt becomes enriched in Al2O3 and FeO+MgO. Potash in the melt is highest just when biotite disappears. The amount of CaO decreases up to 900°C at 5 kbar
whereas at higher temperatures it increases as amphibole, clinopyroxene and more An-component dissolve in the melt. The Na2O content of the melt increases slightly with increase in temperature. The composition of the melt at temperatures > 900°C
approaches that of the starting assemblage. The melt fraction varies with composition and proportion of hydrous phases in
the starting composition as well as temperature and pressure. With increasing modal biotite from 20 to 30 wt%, the melt proportion
increases from 19.8 to 22.3 vol.% (850°C and 5 kbar). With increasing temperature from 800 to 950°C (at 5 kbar), the increase
in melt fraction is from 11 to 25.8 vol.%. The effect of pressure on the melt fraction is observed to be relatively small
and the melt proportion in the same assemblage decreases at 850°C from 19.8 vol.% at 5 kbar to 15.3 vol.% at 15 kbar. Selected
experiments were reversed at 2 and 5 kbar to demonstrate that near equilibrium compositions were obtained in runs of longer
duration.
Received: 27 December 1995 / Accepted: 7 May 1996 相似文献
7.
Ultramafic cumulates, mainly crustal true wehrlites, were discovered and described in the mantle–crust transition zone (MTZ)
and the extremely lower layered gabbro sequence of the Ras Salatit ophiolite, Central Eastern Desert, Egypt. They form either
boudinaged lensoidal tabular bodies or interdigitated layers often concordant with the planolinear fabrics of the Ras Salatit
ophiolite rocks. The contact between wehrlites and the host MTZ dunite or layered gabbro is razor sharp, lobate and/or sinuous,
without chilled margins or any visible deformations. The Ras Salatit wehrlites are orthopyroxene-free and composed mainly
of olivine and clinopyroxene. They are texturally equilibrated and show a characteristic poikilitic texture. Crystallization
order of the Ras Salatit wehrlites is olivine/spinel followed by clinopyroxene with the absence of plagioclase. Olivine and
clinopyroxene of the Ras Salatit wehrlites are compositionally uniform and conspicuously high in Mg#, mostly around 0.93 and
0.92, respectively. Moreover, the clinopyroxene shows low Ti and Al contents coupled with marked depletion in LILE. The calculated
melt in equilibrium with clinopyroxene from the Ras Salatit wehrlites is largely similar to lavas from the Izu-Bonin forearc.
Given the above characteristics, the Ras Salatit wehrlites were produced by crystal accumulation from a hydrous depleted basaltic/tholeiitic
melt corresponding to temperatures between 1,000 and 1,100°C at the oceanic crustal pressure (~2 kbar). The involved hydrous
tholeiitic melt has been probably formed by fluid-assisted partial melting of a refractory mantle source (similar to the underlying
harzburgites) in a somewhat shallow sub-arc environment. 相似文献
8.
西天山吐拉苏盆地安山岩中发现岩石包体及地质找矿意义 总被引:4,自引:0,他引:4
新疆西天山斑岩型铜矿找矿前景良好,但面临攻坚;吐拉苏盆地是西天山浅成低温热液型金矿集区,晚古生代吐拉苏盆地是北天山洋向南向伊犁板块之下俯冲形成的“西南太平洋型”岛弧环境,在金矿深边部寻找斑岩型铜金矿值得关注。笔者最近在岛弧安山岩中发现硫化物矿化二长斑岩、细晶闪长岩等岩石包体。岩石包体发现于塔乌尔别克金矿区,多呈浑圆体或次棱角状,随机分布于安山岩中,与围岩界线截然,常见安山岩围绕岩石包体形成冷凝边。二长斑岩包体显示似斑状结构,斑晶由斜长石和钾长石组成;细晶闪长岩主要由斜长石和角闪石组成,细晶结构,块状构造;寄主安山岩为斑状结构,斑晶为斜长石和少量角闪石及单斜辉石,基质由短柱状斜长石及少量单斜辉石组成,玻基交织结构。二长斑岩包体、细晶闪长岩包体和寄主安山岩三者具有极为相似的微量元素和稀土元素组成,均富集大离子亲石元素、相对亏损Nb、Ta等高场强元素。这些岩石学和地球化学特点反映岩石包体是岛弧火山喷发过程中从下覆地质体捕掳成因,指示安山岩层之下存在同源斑岩体并可能已发生硫化物矿化。综合考虑吐拉苏盆地铜矿化点、酸性热液蚀变、高硫型和低硫型浅成低温热液金矿的组合关系,认为盆地内发育斑岩-浅成低温热液金铜成矿系统,塔乌尔别克是斑岩型铜金矿找矿重要靶区。 相似文献
9.
Portions of the system MgO-CaO-Na2O-Al2O3-SiO2-H2O have beenstudied in the pressure range 1335 kb at near-liquidustemperatures. The liquidus field of forsterite relative to thatof orthopyroxene is considerably wider under anhydrous thanunder anhydrous conditions and it covers part of the plane ofsilica-saturation in a wide pressure range. Partial meltingof simple garnet lherzolite (= forsterite+orthopyroxene+clinopyroxene+garnet)with water produces quartz-normative liquids at pressures upto at least 25 kb regardless of water content. Hydrous mineralsare not encountered at or near the solidus temperatures exceptin a Na-rich part of the system. Microprobe analysis of therun products in this synthetic system shows that the liquid(glass) in equilibrium with the lherzolite mineral assemblageis silica and alumina-rich at 20 kb under vapor-present conditions.With increasing degree of partial melting, the liquid changesits composition, passing into a vapour-absent regionand becoming less silicic. Fractional crystallization of olivinetholeiitic magma under hydrous conditions also produces silica-richmagmas at high pressures. If the system is open to water, andwater pressure is less than total pressure, the compositionof the liquid varies from quartz-normative to olivine (±nepheline)-normativedepending on water pressure. It is suggested that in the presenceof water, silica-rich magmas such as those of calc-alkalic andesiteor dacite may be formed by direct partial melting of the peridotiticupper mantle at depths down to about 80 km. A large degree ofpartial melting of lherzolite under hydrous conditions wouldproduce SiO2 and MgO-rich magmas. The clinoenstatite rock fromCape Vogel, Papua, may have been formed by such a process. Peridotiteswith low CaAl2SiO5/jadeite ratios in the clinopyroxene couldproduce nepheline-normative magma by small degree of partialmelting and tholeiitic magma by large degree of partial meltingunder hydrous conditions. 相似文献
10.
Gautam Sen Andrew Macfarlane N. Srimal 《Contributions to Mineralogy and Petrology》1996,122(4):415-427
Two types of melt pockets occur in Hawaiian mantle xenoliths: amphibole-bearing (AMP) and spinel-bearing (SMP). AMPs contain
amphibole (kaersutite), olivine (Fo92), clinopyroxene (with 7–11% Al2O3), vesicles and glass. SMPs contain olivine, clinopyroxene, spinel, glass, and vesicles. The glasses in SMPs (SiO2=44–45%, 11–12% alkalis, La=90–110 ppm) and AMPs (SiO2=49–54%, 6–8.5% alkalis, La=8–14 ppm) are distinct in color and composition. Both glasses are generally characterized by LREE-enriched
(chondrite-normalized) patterns. Amphibole and clinopyroxene have gently convex upward-to-moderately LREE-enriched patterns.
Mineral/glass trace element abundance ratio plots show a strong negative Ti anomaly and a gentle negative Zr anomaly for clinopyroxene/glass;
whereas amphibole/glass patterns show a distinctive positive Ti spike. The amphibole/glass trace element ratios are similar
to published megacryst/lava values. An earlier study showed that the Hawaiian spinel lherzolites (lithosphere) have largely
been metasomatized during post-erosional Honolulu magmatic activity. REE abundances of SMP glasses (melts) overlap the REE
abundances calculated for such metasomes. The occurrence of hydrous, alkaline, mafic melt pockets in Hawaiian upper mantle
xenoliths implies that (1) such hydrous liquids are generated in the upper mantle, and (2) water plays a role in magmatic
activity associated with the Hawaiian plume. Although we are uncertain about the source (plume, lithosphere, or asthenosphere)
of this water, we speculate that such melts and other alkalic lavas erupted on Oahu and on the sea-floor over the Hawaiian
arch were generated from a broad „wet“ rim of a radially layered Hawaiian plume, whose hot and „dry“ core supplied the shield-forming
magmas.
Received: 6 February 1995 / Accepted: 28 August 1995 相似文献
11.
James S. Scoates Mauro Lo Cascio Dominique Weis Donald H. Lindsley 《Contributions to Mineralogy and Petrology》2006,151(5):582-599
This experimental study examines the role of clinopyroxene fractionation on major element trends and alkalinity variations in mildly alkalic basalts from the Kerguelen Archipelago, Southeast Indian Ocean. Equilibrium crystallization experiments were carried out on a natural basalt (MgO=5 wt.%, alkalinity index=0.10) over a range of pressures (0–1.43 GPa) and water contents (nominally dry to hydrous, 1.2 wt.% H2O) under relatively oxidizing conditions (Δlog FMQ=+1 to +2) at 0 GPa and relatively reducing conditions (Δlog FMQ=0 to –2) at all higher pressures. The hydrous experiments at 0.93 GPa closely reproduce most of the compositional variations in the 24–25 Ma mildly alkalic lavas from the archipelago, which supports a major role for high-Al clinopyroxene fractionation (5–9 wt.% Al2O3) at pressures corresponding to the base of the Northern Kerguelen Plateau (15–20 km). However, clinopyroxene fractionation at depth fails to produce important changes in the alkalinity of the residual melts. The transition from tholeiitic to mildly alkalic basalts on the Kerguelen Archipelago thus reflects primarily changes in melting conditions (lower extents of partial melting at higher pressures), which is related to crustal and lithospheric thickening as distance from the Southeast Indian Ridge increased over time from 43 to 24 Ma. 相似文献
12.
Miroslav Štemprok David Dolejš Axel Müller Reimar Seltmann 《Contributions to Mineralogy and Petrology》2008,155(1):93-109
We report new occurrences of “two-phase” granitic textures from the Western Krušné hory/Erzgebirge pluton (central Europe)
and use crystal-size distribution data and thermodynamic modeling to interpret their crystallization conditions. The two-phase
texture consists of (1) early phenocrysts of quartz, plagioclase, K-feldspar and biotite, (2) medium-grained matrix of the
same phases and (3) interstitial channels and patches of a late-stage, very fine-grained matrix. The porphyritic two-mica
microgranites, which host two-phase textures, occur as minor intrusions in early low-F biotite granites or as marginal parts
of evolved high-F Li-mica granites. Measurements of the crystal-size distribution of quartz revealed three grain populations:
(1) early phenocrysts (0.5–3.0 mm) showing partial resorption by residual melt, (2) a medium-grained population of the equigranular
rock matrix (0.05–0.50 mm) that experienced minor coarsening by subsolidus annealing and (3) a fine-grained population (<0.03 mm)
in the interstitial channels and patches formed during rapid devolatilization; this quartz group shows no or poor grain coarsening.
All samples exhibit similar fraction of the fine-grained population (44–52%) but proportions of phenocrysts to medium-grained
matrix vary significantly. Thermodynamic modeling of liquidus equilibria and experimental data in the hydrous haplogranite
system require: (1) ascent of a granitic suspension (15–25% phenocrysts) under H2O-undersaturated conditions at 25–45 bar/°C and a cooling rate of 40 J/(g kbar) in order to produce partial resorption of
quartz phenocrysts and continued growth of feldspar phenocrysts, followed by (2) emplacement as discrete intrusions or bodies
along pluton roof accompanied by sudden devolatilization. At the onset of matrix nucleation, disequilibrium undercooling of
70–85°C was inferred from the presence of micrographic intergrowths of quartz and K-feldspar. The two-phase granites in the
Western Krušné hory/Erzgebirge pluton and in the Southeast Asian batholith form compositionally narrow groups with high-silica
and moderate volatile enrichments but they differ in peraluminosity and phosphorus concentrations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
海南岛戈枕金矿带煌斑岩的岩石地球化学研究 总被引:6,自引:3,他引:6
许德如 《大地构造与成矿学》1999,23(4):353-360
对海南岛戈枕金矿带与金矿脉在空间上紧密共生的暗色脉岩的地质特征、矿物学、主要元素、微量元素、同位素地球化学的研究,确定这种脉岩为煌斑岩。岩石类型以钙碱性煌斑岩为主,呈现两种稀土配分模式,即平坦向右倾斜型和星四重效应的W型;Sr、Nd同位素及元素地球化学综合研究表明,本区煌斑岩可划分为两组类型,它们时代相同但地幔源区相异,可能形成于特殊的构造环境。 相似文献
14.
Elaborating on the theme of a previous paper (1965) and in responseto Buddingtons criticism (1966) the present discussionis primarily concerned with the high-grade meta-morphic reactionsand regional-metamorphic zoning in the Adirondacks. The hypersthene isograd, delineated by the first appearanceof orthopyroxene as a product of Pw-T-controlted reactions involvinghornblende and biotite in quartz-buartz-bearing rocks. separatesthe almandite-amphibolite-facies terrane of the lowlands fromthe granulite-facies region of the highlands. In the almandite-amphibolite facies of the lowlands at leastone isograd, the orthoclase-garnet isograd, (Ruddington's lstgarnet isograd), can be recognized which is delineated by thePw-T-controlled appearance of these minerals at the expenseof muscovite and part of the biotite and quartz. The granulite-facies terrane of the highlands is characterizedby the predominance of assemblages of the hornblende-granulitefacies in which orthopyroxene cocxists with hydrous mineralssuch as biotite and hornblende in apparent equilibrium. In theAdlrondacks there is no sizeable, regional development of thepyroxene-granulite facies where hydrous minerals are virtuallyabsent. Within the hornblende-granulite-facies terrane two isogradscan be recognized. The garent-clinopyroxene isograd (Buddington's3rd garnet isograd) delineates the regional development of garnet,clinopyroxene, and quartz by P1-T-controlled reaction betweenorthopyroxene and plagioclase. The isograd defines in the easternAdirondack a region of the hornblende-clinopyroxene-almanditesubfacies of the honblende-granulite facies. In the westernAdirondacks, near the hypersthene isograd, a yet uncharted cordieriteisograd may define the areal extent of the biotite-cordierite-almanditesubfacies of the hornblende-granulite facies. The central portionof the Adirondacks, where cordierite is absent and garnet andclinopyroxene do not coexist except in silica-deficient rocks,is the region of the hornblende-orthopyroxene-plagioclase subfaciesof the hornblende-granulite facies. 相似文献
15.
N.M.S. Rock 《Earth》1977,13(2):123-169
Lamprophyres are porphyritic dyke-rocks, readily recognisable in the field, which seemed to have become enveloped in petrological mystery because of their scattered and often contradictory literature. Important characteristics common to all members of this extremely heterogeneous group are suggested to include their intrusion at a late stage in any igneous event, the presence of essential amphibole or biotite coupled with peculiar chemistry, and their lack of felsic phenocrysts. Panidiomorphic texture is usual, though by no means exclusive to lamprophyres.At least four lamprophyre subgroups may be recognised; these are quite distinct in petrology, chemistry, paragenesis and petrogenesis although individual members of each subgroup are closely similar. Thealkaline lamprophyre subgroup is considered in detail: new definitions ofcamptonite andmonchiquite are proposed which are believed to reconcile majority usage whilst accomodating existing analytical data; the termouachitite is reassessed andfourchite suggested to be superfluous;sannaite, an alkali feldspar-rich alkaline lamprophyre, may be more abundant than its frequency within the literature implies — some “minettes” and “vogesites” are more correctly termed sannaite, particularly those occurring in carbonatite complexes.Camptonites most probably represent alkali basalt magmas which became unusually hydrous through influence of an alkaline pluton, and then evolved at relatively low pressures. Varied evidence is considered to suggest that the nearly isotropic base in monchiquites typically consists of altered glass rather than analcime; where analcime is present it probably formed along with zeolites by secondary processes. “Monchiquitic” is not an appropriate synonym for “analcime-bearing”, as in some literature. Field, chemical and statistical evidence is taken to suggest that many monchiquites are either chilled heteromorphs of camptonites or camptonitic magmas which crystallised under high CO2 activities. Liquid immiscibility seems to be more extensively developed in camptonites and monchiquites than in any other igneous rocks, and is probably governed by their hydrous state.The genetic connotations of lamprophyre names, asserted early in their history but later questioned, are here modified but reaffirmed: broadly minettes and related lamprophyres connote post-orogenic granites or mildly potassic (shoshonitic) alkaline rocks, alkaline lamprophyres connote alkali basalts or sodic alkaline rocks, and alnoites connote carbonatites. 相似文献
16.
Michael J. Dorais Raul Lira Yadong Chen David Tingey 《Contributions to Mineralogy and Petrology》1997,130(1):31-46
The Achala batholith of Argentina contains very unusual layered enclaves containing up to 30% apatite and 50% biotite in
some layers. This modal mineralogy produces bulk-rock compositions that cannot represent liquids, having as little as 29%
SiO2 and up to 8% P2O5. Nor can the enclaves represent metasedimentary xenoliths because: (1) none of the Precambrian wall rocks has these compositions;
(2) none of the metasedimentary xenoliths present within the batholith shows any degree of transition to the mica-apatite-rich
enclaves; (3) the compositions and textures in the enclaves are inconsistent with metasediments; (4) a geochronological study
of zircon from an enclave gives an age of 368 ± 2 Ma, the exact age of zircons in the granitic host rocks. For these reasons,
we conclude that the enclaves are neither xenoliths of Precambrian wall rocks nor restite of a Precambrian source. The identical
age of the enclave and the host granites, coupled with textural, mineralogical, and bulk-rock characteristics of the enclaves,
indicates that the enclaves are magmatic segregations, i.e., cumulates. The F-rich nature of the stubby-shaped apatites and
biotites indicates a high F content of the magma parental to the enclaves. We infer that the viscosity of the melt was lowered
sufficiently to allow cumulates to form in spite of the granitic composition of the melt.
Received: 12 December 1996 / Accepted: 11 August 1997 相似文献
17.
In order to explore possible quantitative relations between crystal field stabilization energy, CFSE, and partitioning behaviour
of the 3d 6-configured Fe2+ ion, a suite of 29 paragenetic rock-forming minerals from 12 high-grade metamorphic rock samples of the Ukrainian shield,
including the parageneses garnet/orthopyroxene/clinopyroxene (2x), orthopyroxene/clinopyroxene, garnet/clinopyroxene, garnet/orthopyroxene/biotite,
garnet/biotite, garnet/cordierite, garnet/cordierite/biotite, garnet/orthopyroxene/clinopyroxene/Ca-amphibole, Ca-amphibole/biotite
(retrograde), was studied by electron microprobe analysis to obtain the respective K
D
Fe2+
(Ph1/Ph2) values and by polarized single crystal electronic absorption spectroscopy to evaluate the respective CFSEFe2+ values. Other than in the case of Cr3+, a clear quantitative relation between K
D
(Ph1/Ph2) and the ΔCFSE(Ph1/Ph2) was only observed when geometrical factors, mainly the volume of crystallographic sites and ionic radii of ions competing
in the partitioning process, are similar in the respective two paragenetic phases to within 15–20%. In such cases, the ΔCFSEFe2+ contribution to K
D
(Ph1/Ph2) amounts to 0.1 to 0.2 log K
D
per 100 cm−1ΔCFSE. The conclusion is that ΔCFSEFe2+ plays only a secondary role after geometrical factors, in the partitioning behaviour of Fe2+. The reason for this is seen in the facts that, compared to the 3d
3-configured Cr3+ ion, CFSE of the 3d 6-configured Fe2+ amounts only to 20–25%, and that the former ion enters only octahedral sites with similar geometrical properties in the paragenetic
mineral phases.
Received: 17 November 1998 / Accepted: 28 June 1999 相似文献
18.
Cliff S. J. Shaw 《Contributions to Mineralogy and Petrology》1999,135(2-3):114-132
A large body of recent work has linked the origin of Si-Al-rich alkaline glass inclusions to metasomatic processes in the
upper mantle. This study examines one possible origin for these glass inclusions, i.e., the dissolution of orthopyroxene in
Si-poor alkaline (basanitic) melt. Equilibrium dissolution experiments between 0.4 and 2 GPa show that secondary glass compositions
are only slightly Si enriched and are alkali poor relative to natural glass inclusions. However, disequilibrium experiments
designed to examine dissolution of orthopyroxene by a basanitic melt under anhydrous, hydrous and CO2-bearing conditions show complex reaction zones consisting of olivine, ± clinopyroxene and Si-rich alkaline glass similar
in composition to that seen in mantle xenoliths. Dissolution rates are rapid and dependent on volatile content. Experiments
using an anhydrous solvent show time dependent dissolution rates that are related to variable diffusion rates caused by the
saturation of clinopyroxene in experiments longer than 10 minutes. The reaction zone glass shows a close compositional correspondence
with natural Si-rich alkaline glass in mantle-derived xenoliths. The most Si-and alkali-rich melts are restricted to pressures
of 1 GPa and below under anhydrous and CO2-bearing conditions. At 2 GPa glass in hydrous experiments is still Si-␣and alkali-rich whereas glass in the anhydrous and
CO2-bearing experiments is only slightly enriched in SiO2 and alkalis compared with the original solvent. In the low pressure region, anhydrous and hydrous solvent melts yield glass
of similar composition whereas the glass from CO2-bearing experiments is less SiO2 rich. The mechanism of dissolution of orthopyroxene is complex involving rapid incongruent breakdown of the orthopyroxene,
combined with olivine saturation in the reaction zone forming up to 60% olivine. Inward diffusion of CaO causes clinopyroxene
saturation and uphill diffusion of Na and K give the glasses their strongly alkaline characteristics. Addition of Na and K
also causes minor SiO2 enrichment of the reaction glass by increasing the phase volume of olivine. Olivine and clinopyroxene are transiently stable
phases within the reaction zone. Clinopyroxene is precipitated from the reaction zone melt near the orthopyroxene crystal
and redissolved in the outer part of the reaction zone. Olivine defines the thickness of the reaction zone and is progressively
dissolved in the solvent as the orthopyroxene continues to dissolve. Although there are compelling reasons for supporting
the hypothesis that Si-rich alkaline melts are produced in the mantle by orthopyroxene – melt reaction in the mantle, there
are several complications particularly regarding quenching in of disequilibrium reaction zone compositions and the mobility
of highly polymerized melts in the upper mantle. It is considered likely that formation of veins and pools of Si-rich alkaline
glass by orthopyroxene – melt reaction is a common process during the ascent of xenoliths. However, reaction in situ within
the mantle will lead to equilibration and therefore secondary melts will be only moderately siliceous and alkali poor.
Received: 24 August 1998 / Accepted: 2 December 1998 相似文献
19.
Z. Johan 《Mineralogy and Petrology》2006,87(1-2):1-30
Summary The study of platinum-group minerals (PGM) concentrates from the Nizhni Tagil placers related to the Soloviev Mountain (Gora
Solovieva) Uralian-Alaskan-type intrusion revealed a predominance of (Pt, Fe) alloys over Ir-, and Os-bearing alloys. (Pt,
Fe) alloys (“isoferroplatinum-type”) are interstitial with respect to chromite and show important variations in their chemical
compositions, which are, however, falling within the experimentally determined stability field of isoferroplatinum. Tetraferroplatinum,
enriched in Cu and Ni and tulameenite represent low-temperature mineral phases replacing (Pt, Fe) alloys. Alloys belonging
to the Os–Ir–Ru ternary system have compositions corresponding to native osmium, iridium and ruthenium, respectively, and
to rutheniridosmine. Osmium exsolutions appear in Ir-, and (Pt, Fe) alloys, and iridium exsolutions in (Pt, Fe) alloys. Laurite
is a high-temperature phase included in native iridium and (Pt, Fe) alloys. Low-temperature PGM association comprises Ir-bearing
sulpharsenides, including a phase (Ir, Os, Fe, Pt, Ru, Ni)3(As, Sb)0.85S, and a palladium antimonide Pd20Sb7. These two phases were previously unknown in nature. Furthermore, native palladium occurs in the studied concentrates. This
low-temperature paragenesis indicates an interaction of Pt-, Os-, Ir- and Ru-bearing alloys with late fluids enriched in volatiles,
As and Sb. The chromite composition is characterized by the predominance of Cr3+ → Fe3+ substitution like in other Uralian-Alaskan-type intrusions; that indicates a fO2 variation during the chromite precipitation.
Monomineralic inclusions of euhedral clinopyroxene and chromite crystals in (Pt, Fe) alloys were observed. Furthermore, (Pt,
Fe) alloys contain polyphase silicate inclusions, which occupy the alloy negative crystals. Two types of silicate inclusions
were recognized: (1) Low-pressure inclusions composed of amphibole, biotite, Jd-poor clinopyroxene, magnetite, apatite and
glass; (2) High-pressure inclusions include: omphacitic clinopyroxene (up to 56 mol.% Jd), tremolite, muscovite, apatite,
titanite and glass. In this case, the clinopyroxene is strongly zoned, revealing a pressure drop from about 25 to 5 kbar.
The chemical composition of glass is corundum-normative and its H2O content varies from about 12 to 15 wt.%. The composition of magmatic melts, from which the silicate inclusions have originated
was estimated using EPMA and image analysis interpreted by stereology. Their compositions are close to those obtained experimentally
by hydrous partial melting of upper mantle rocks. The interpretation of analytical data shows that magmatic melts entrapped
by (Pt, Fe) alloys crystallized from about 1100 to 700 °C. The (Pt, Fe) alloys formed after the crystallization of chromite,
clinopyroxene and albite. Consequently, the precipitation temperature of (Pt, Fe) alloys is estimated at about 900 °C. The
significant pressure drop implies a decrease of volatile concentrations in the magmatic melt and the possible formation of
a fluid phase, which might have generated, the precipitation of chromite and PGM. 相似文献
20.
Summary Garnet occurs as a significant mineral constituent of felsic garnet-biotite granite in the southern edge of the Třebíč pluton.
Two textural groups of garnet were recognized on the basis of their shape and relationship to biotite. Group I garnets are
1.5–2.5 mm, euhedral grains which have no reaction relationship with biotite. They are zoned having high XMn at the rims and are considered as magmatic. Group II garnets form grain aggregates up to 2.5 cm in size, with anhedral shape
of individual grains. The individual garnet II grains are usually rimmed by biotite and have no compositional zoning. The
core of group I garnets and group II garnets contains 67–80 mol% of almandine, 5–19 mol% of pyrope, 7–17 mol% of spessartine
and 2–4 mol% of grossular. Biotite occurs in two generations; both are magnesian siderophyllites with Fe/(Fe + Mg) = 0.50–0.69.
The matrix biotite in granites (biotite I) has high Ti content (0.09–0.31 apfu) and Fe/(Fe + Mg) ratio between 0.50 and 0.59.
Biotite II forms reaction rims around garnet, is poor in Ti (0.00–0.06 apfu) and has a Fe/(Fe + Mg) ratio between 0.61 and
0.69. The textural relationship between biotite and garnet indicates that garnet reacted with granitic melt to form Ti-poor
biotite and a new granitic melt, depleted in Ti and Mg and enriched in Fe and Al. In contrast to the host durbachites (hornblende-biotite
melagranites), which originated by mixing of crustal melts and upper mantle melts, the origin of garnet-bearing granites is
related to partial melting of the aluminium-rich metamorphic series of the Moldanubian Zone. 相似文献