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作为塔里木大火成岩省形成最晚的火成岩,新疆巴楚瓦吉里塔格霞石岩的岩浆源区性质的确定对于揭示塔里木大火成岩省的深部地质过程具有重要的约束作用。对瓦吉里塔格霞石岩的铂族元素地球化学特征进行了研究,铂族元素(PGE)分析结果显示,原始地幔标准化的PGE呈正斜率型分布,且Pd/Ir值高于原始地幔比值,说明霞石岩的铂族元素发生了分异。霞石岩全岩的PGE与Mg O呈正相关,Pd/Ir、Cu/Pd与Mg O则呈负相关,说明PGE的分异主要受到橄榄石的结晶分异作用控制,也是其Cu/Pd值极高及岩浆S饱和的因素之一,同时Cu/Pd值说明霞石岩岩浆为硫饱和岩浆,但是没有因素导致岩浆S过饱和进而发生硫化物的熔离。与其他大火成岩省岩石相比,瓦吉里塔格霞石岩极度亏损PGE,SCSS(硫承载量)计算结果表明母岩浆在形成之初就发生S过饱和,主要是地幔低程度部分熔融造成的,据此认为地幔源区的部分熔融程度在塔里木大火成岩省Cu-Ni硫化物铂族元素矿床形成过程中起着至关重要的作用。 相似文献
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Alain Demant Patrick Lestrade Ruananza T Lubala Ali B Kampunzu Jacques Durieux 《Bulletin of Volcanology》1994,56(1):47-61
Three major phases are distinguished during the growth of Nyiragongo, an active volcano at the western limit of the Virunga
Range, Zaire. Lavas erupted during phase 1 are strongly undersaturated melilitites characterized by the presence of kalsilite
phenocrysts, perovskite, and the abundance of calcite in the matrix. Such lavas crop out mainly on the inner crater wall and
progressively evolve toward more aphyric melilite nephelinites well represented on the flanks of the volcano. Adventive vents
lying at the base of the cone developed along radial fracture systems and erupted olivine and/or clinopyroxene – rich melilitites
or nephelinites. Stage 2 lavas are melilite-free nephelinites. Clinopyroxene is the main phenocryst and feldspathoids are
abundant in the lavas exposed on the crater wall. These flows result from periodic overflowing of a magma column from an open
crater. Extensive fissure flows which erupted from the base of the cone at the end of this stage are related to widespread
draining out of magma which in turn induces the formation of the summit pit crater. Magmas erupted during stage 3 are relatively
aphyric melilite nephelinites and the main volcanological characteristic is the permanent lava lake observed into the pit
crater until the 1977 eruption. Fluctuations of the level of the lava lake was responsible for the development of the inner
terraces. Periodic overflowing of the lava lake from the central pit formed the nepheline aggregate lava flows. Petrography
and major element geochemistry allow the determination of the principal petrogenetic processes. Melilitites and nephelinites
erupted from the summit crater are lavas derived, via clinopyroxene fractionation, from a more primitive melt. The abundance
of feldspathoids in these lavas is in keeping with nepheline flotation. Aphyric melilite nephelinites covering the flanks
and the extensive fissure flows have a homogeneous chemical composition; rocks from the historical lava lake are slightly
more evolved. All these lavas differentiated in a shallow reservoir. Lavas erupted from the parasitic vents are mainly olivine
and/or clinopyroxene-phyric rocks. Rushayite and picrites from Muja cone are peculiar high-magnesium lavas resulting from
the addition of olivine xenocrysts to melilitic or nephelinitic melts. Fluid and melt inclusions in olivine and clinopyroxene
phenocrysts indicate a crystallization depth of 10–14 km. A model involving two reservoirs located at different depths and
periodically connected is proposed to explain the petrography of the lavas; this hypothesis is in accordance with geophysical
data.
Received: July 8, 1993/Accepted: September 10, 1993 相似文献
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Martínková Marta Pros Zdeněk Klíma Karel Lokajíček Tomáš Kotková Jana 《Studia Geophysica et Geodaetica》2000,44(4):581-589
The elastic properties of granites from Western Bohemia which we measured and published earlier have been supplemented with measurements of olivine nephelinite from the same region and with data on lherzolitic xenolith from the vicinity of elezný Brod. The set of velocities measured under laboratory conditions has been compared with depth profiles suggested for the purpose of locating seismic swarm events which occur in this region. P-wave velocities were measured under pressures of up to 400 MPa. This pressure corresponds to depths of about 15 km for this region. The data were extrapolated for larger depths. Comparing laboratory measurements and seismic profiles, we can conclude that the rocks under study may be constituents of crust structures. 相似文献
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Peralkaline silicate lavas at Oldoinyo Lengai, Tanzania 总被引：1，自引：0，他引：1
A detailed study of Oldoinyo Lengai has led to the recognition of two major cone-building stages. An early, predominantly phonolitic stage, Lengai I, forms the southern cone. The recent nephelinitic Lengai II developed following a major sector collapse event over Lengai I. Petrography of Lengai II lavas show that nephelinite is combeite- and wollastonite-bearing. All Oldoinyo Lengai lavas are peralkaline and highly evolved in terms of low Mg#, Ni and Cr values. Within the unique Lengai II combeite–wollastonite–nephelinite (CWN) peralkalinity increases with time to extreme values (Na + K)/Al = 2.36. Mineralogical expression of peralkalinity is the presence of combeite and Na-rich clinopyroxene. In addition, exceptionally high Fe2O3 (up to 10.28 wt.%) in nepheline is an indicator for alumina deficiency. Combeite also shows high Fe3+. Phonolite and CWN of Lengai I and Lengai II show similarly enriched LILE and LREE values and generally parallel patterns in PM normalized and REE plots. 相似文献
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I.P. Solovova A.V. Girnis L.N. Kogarko N.N. Kononkova F. Stoppa G. Rosatelli 《Lithos》2005,85(1-4):113-128
This paper presents a study of melt and fluid inclusions in minerals of an olivine-leucite phonolitic nephelinite bomb from the Monticchio Lake Formation, Vulture. The rock contains 50 vol.% clinopyroxene, 12% leucite, 10% alkali feldspars, 8% hauyne/sodalite, 7.5% nepheline, 4.5% apatite, 3.2% olivine, 2% opaques, 2.6% plagioclase, and < 1% amphibole. We distinguished three generations of clinopyroxene differing in composition and morphology. All the phenocrysts bear primary and secondary melt and fluid inclusions, which recorded successive stages of melt evolution. The most primitive melts were found in the most magnesian olivine and the earliest clinopyroxene phenocrysts. The melts are near primary mantle liquids and are rich in Ca, Mg and incompatible and volatile elements. Thermometric experiments with the melt inclusions suggested that melt crystallization began at temperatures of about 1200 °C. Because of the partial leakage of all primary fluid inclusions, the pressure of crystallization is constrained only to minimum of 3.5 kbar. Combined silicate–carbonate melt inclusions were found in apatite phenocrysts. They are indicative of carbonate–silicate liquid immiscibility, which occurred during magma evolution. Large hydrous secondary melt inclusions were found in olivine and clinopyroxene. The inclusions in the phenocrysts recorded an open-system magma evolution during its rise towards the surface including crystallization, degassing, oxidation, and liquid immiscibility processes. 相似文献
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稀有气体被广泛用作地球化学示踪剂,本文对塔里木大火成岩省西北缘瓦吉里塔格霞石岩中的橄榄石和辉石单矿物进行了稀有气体同位素测定。结果表明,瓦吉里塔格霞石岩中的橄榄石和辉石单矿物具有较低的~3He/~4He值(分别为2.0~2.4 Ra和0.65~0.85 Ra)和略高于大气值的~(40)Ar/~(36)Ar值(342.3~651.7),反映了由古板块俯冲导致的较低的He、Ar同位素比值特征。研究表明,早中古生代南天山洋向南俯冲到塔里木板块之下,将富U或富~4He以及含有大气组分的流体带入到深部地幔,在塔里木地幔柱的作用下地幔源区发生低程度部分熔融产生霞石岩岩浆。 相似文献
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