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1.
秦岭造山带勉略缝合带超镁铁质岩的地球化学特征 总被引：13，自引：1，他引：13
勉略缝合带中广泛出露的超镁铁质岩构造块体是D～T_2期间勉咯洋盆古洋壳残片的重要标志之一，属贫铝、贫碱的镁质超基性岩类，其原岩类型主要为方辉橄榄岩和纯橄榄岩。稀土特征有两种类型：轻稀土亏损，Eu富集型；以及轻稀土低度富集，Elf弱亏损型。与原始地慢比较，本区超镁铁质岩中Cs、Rb、Th、U、K、Ta、Nb等强不相容元素大多呈富集状态，暗示古地慢经历过一种富集大离子亲石元素的上地幔流体交代作用。 相似文献
2.
Lawrence Grossman R. Ganapathy Robert L. Methot Andrew M. Davis 《Geochimica et cosmochimica acta》1979,43(6):817-829
INAA data for Ca, Sc, Hf, La, Ce, Sm, Eu, Tb, Yb, Lu, Os, Ir, Ru, Na, Cl, Br, Fe, Mn, Cr, Co, Au, As, and Sb are presented for ten amoeboid aggregates from the Allende meteorite. Only one lacks olivine. Seven of the remainder, as a group, have cosmic proportions of refractory lithophile and siderophile elements and appear to have formed when coarse-grained Allende inclusion material underwent partial reaction with a low-temperature nebular gas and mixture with FeO-rich olivine. The other two have highly fractionated abundances of refractory elements relative to one another compared to Cl chondrites, including Group II REE patterns, and probably formed by the mixing of fine-grained Allende inclusion material with FeO-rich olivine. Non-refractory siderophile components are also different in composition in each type of amoeboid olivine aggregate. 相似文献
3.
Undifferentiated meteorites (chondrites) have the same relative abundances of refractory lithophile elements (Ca, Al, Ti, Sc, REE, etc.), despite variable absolute concentrations. The reasonable assumption of chondritic ratios among refractory elements in the bulk Earth is used to constrain the chemical composition of the upper mantle in the following way: Correlations of the compatible refractory elements Ca, Al, Ti, Sc and Yb with MgO are worldwide very similar in suites of spinel-lherzolite xenoliths from basaltic rocks. Such suites represent upper mantle material depleted to differing degrees by extraction of partial melts. From these refractory elements vs. MgO correlations, ratios of pairs of refractory elements were calculated at various MgO contents. Chondritic and ratios were only obtained for MgO contents below 36%. A chrondritic ratio requires an MgO content above 35%. We therefore accept 35.5% as the most reasonable MgO content of undepleted upper mantle. This MgO content is slightly below the spinel-lherzolite with the lowest measured MgO content (36.22%). The corresponding Al2O3 content of 4.75% is higher than in previous estimates of upper mantle composition. The concentrations of other elements were obtained from similar correlations at a MgO content of 35.5%. The resulting present upper mantle composition is enriched in refractory elements by a factor of 1.49 relative to Si and Cl and by a factor of 1.12 for Mg relative to Si and Cl. These enrichments are in the same range as those for the Vigarano type carbonaceous chondrites. The Mg/Mg + Fe ratio of 89 is slightly lower than previous estimates.The ratio in spinel lherzolite suites is, however, uniformly higher worldwide than the chondritic ratio by about 15%. Orogenic peridotites as well as komatiites appear to have similar non-chondritic ratios. It is therefore suggested that this non-chondritic ratio is a characteristic of the upper mantle, possibly since the Archean. A minor fractionation of about 4% of garnet in an early, global melting event (deep magma ocean?) is presented as the most likely cause for the high . In this case the addition of 4% of such a garnet component to the undepleted present upper mantle would be required to obtain the composition of the primordial upper mantle. The of this primordial mantle would be 15% higher than that of the undepleted present upper mantle, resulting in an enrichment of refractory elements of 1.70 ( relative to Cl) for the primordial upper mantle. 相似文献
4.
The uniformity of concentration of lithophile elements in chondrites—with particular reference to Cs
The paper is in two parts. In the first, the dispersion of concentration of the lithophile elements Li, Na, K, Rb, Mg, Ca, Sr, Ba, Al, Sc, Eu, Si, Ti, Zr, Th and U is examined in chondrites. Where twenty or more analyses have been made, relative deviations have been calculated; these range from 5 to 29 per cent. Some of the variation is clearly due to analytical error and it is concluded that the relative deviations of most, perhaps all, lithophile elements is near the lower limit (5 per cent) of the above range. Such small dispersion of concentration for a wide variety of elements, including Li, K and Mg which are sensitive to fractionation, indicates that chondrites have come from a source with an exceptionally uniform composition. It is concluded further that variation of concentration of a lithophile element in the silicate phase, as distinct from the meteorite as a whole, may be even smaller and that the ratio of one lithophile element to the other lithophile elements may turn out to be extremely small indeed. Analytical data of a very high order of excellence (relative deviation of 1–2 per cent) for all elements are evidently required to estimate such small variations precisely.
The second part of the paper is concerned specifically with caesium. This element has been estimated spectrochemically in K—Rb—Cs fractions obtained by ion exchange techniques from six chondrites and seven specimens of basic rock. In the chondrites, the Cs content (ave. 0.12 p.p.m.) and the K/Cs ratio (ave. 7000) remains constant to within the precision of the method of analysis. The magnitude of the average agrees with that (0.09 p.p.m.) of , and but the small variation of the Cs concentration and of the K/Cs ratio contrasts with their observations as they report large variations (× 30 or more). The K/Cs ratio in the seven basic rocks is fairly uniform (in contrast with granites) and similar in general magnitude to that in the chondrites. 相似文献
5.
中祁连西段花岗岩类的地球化学特征及构造意义 总被引：3，自引：1，他引：2
中祁连西段石板墩地区北部及南部发育有辉长岩、闪长岩及花岗岩。北带岩体的LA-ICPMS锆石U-Pb年龄为(469.3±2.8)Ma,(461.2±3.3)Ma和(470.0±2.5)Ma;岩石Si O2质量百分含量为53.2%~66.11%,高Al,Ti,Mg,Fe,Ca,K,Na,A/CNK1.1;富集大离子亲石元素Rb,K和Pb,亏损高场强元素Nb,Ta,Ce,Sr,Hf,Ti;REE总量较高,LREE富集、HREE近平坦型分布,中等的负Eu异常,δEu=0.6;此外,在构造判别图中,样品落于岛弧环境。南带岩体LA-ICP-MS锆石U-Pb年龄为(470.9±2.8)Ma和(472.3±4.2)Ma,岩石Si O2质量百分含量较高(67.13%~70.73%),高Al,Mg,Fe,Ca,富Na贫K,A/CNK1.1;岩石表现为明显的高Sr低Yb,Y的特点,富集大离子亲石元素R,K,Sr等,亏损高场强元素Nb,Ta,P,Ti等;REE总量较低,LREE富集、HREE亏损,轻重稀土分异明显,轻微的负Eu异常至正异常,δEu=0.74~1.18。研究表明,北带岩体为地幔楔部分熔融产生的,形成于岛弧环境;南带岩体为消减的大洋岩石圈板块部分熔融产生的埃达克岩,是北祁连向南俯冲导致的岩浆作用的产物,"中祁连西段"是早古生代时期在"残留的微陆块"基础上形成的一个岛弧增生杂岩地体。 相似文献
6.
The mineral phases including olivine, orthopyroxene, clinopyroxene, troilite, nickel-iron, plagioclase, chromite and the phosphates were separated from several meteorites. These were a hypersthene chondrite (Modoc), a bronzite chondrite (Guareña), an enstatite chondrite (Khairpur), and two eucrites (Haraiya and Moore County); diopside was separated from the Nakhla achondrite. The purified minerals were analyzed for trace and minor elements by spark source mass spectrometry and instrumental neutron activation analysis. On the meteorites examined our results show that Co, Ni, Cu, Ge, As, Ru, Rh, Pd, Sn, Sb, W, Re, Os, Ir, Pt and Au are entirely or almost entirely siderophile; Na, Rb, Sr, Y, Ba and the rare earth elements lithophile; Se chalcophile. The transition elements So, Ti, V, Cr and Mn are lithophile in most stony meteorites, but show chalcophile affinities in the enstatite chondrites (and enstatite achondrites), as do Zn, Zr and Nb. In the ordinary chondrites Ga shows both lithophile and siderophile affinities, but becomes entirely siderophile in the enstatite chondrites. Molybdenum and tellurium show strong siderophile and weaker chalcophile affinity. The lithophile elements are distributed among the minerals according to the crystallochemical factors, the most effective controlling factor being ionic size. 相似文献
7.
The chemical composition of mineral components of the Omolon pallasite was determined by neutron-activation. Six types of
olivines were distinguished. Four types differ in the abundance of Co relative to Ni of CI chondrites. The fifth and sixth
types were distinguished on the basis of REE distribution in them. Both last types are variably enriched in LREE relative
to CI chondrites. In terms of Ca content relative to CI chondrite, these six types are subdivided into two groups: low-calcium
and high-calcium. The difference in Ca contents can be caused by different cooling rate of the precursor of these olivines.
The distribution pattern of siderophile elements in the pallasite metal indicates that a metallic phase experienced chemical
transformations since the time of its formation. The analysis of chemical composition of accessory minerals showed that: (1)
HREE are accumulated in tridymite; (2) troilite and daubreelite were formed under different temperature conditions; (3) magnetite
is the mineral of the outer zone of melting crust. Four fragments with anomalous contents of lithophile elements were found
in the pallasites and studied. The unusual chemical composition of phases and high degree of HREE fractionation in the fragments
suggest their formation at high temperatures at the early stage of the Solar system evolution. It is assumed that the Omolon
pallasite was formed as impact-brecciated mixture of the asteroid core (with composition close to IIIAB group of iron meteorites)
and mantle olivine from incompletely differentiated parent body of chondrite composition. 相似文献
8.
9.
《Geochimica et cosmochimica acta》1999,63(13-14):2105-2122
We present new bulk compositional data for 6 martian meteorites, including highly siderophile elements Ni, Re, Os, Ir and Au. These and literature data are utilized for comparison versus the siderophile systematics of igneous rocks from Earth, the Moon, and the HED asteroid. The siderophile composition of ALH84001 is clearly anomalous. Whether this reflects a more reducing environment on primordial Mars when this ancient rock first crystallized, or secondary alteration, is unclear. QUE94201 shows remarkable similarity with EET79001-B for siderophile as well as lithophile elements; both are extraordinarily depleted in the “noblest” siderophiles (Os and Ir), to roughly 0.00001 × CI chondrites. As in terrestrial igneous rocks, among martian rocks Ni, Os and Ir show strong correlations vs. MgO. In the case of MgO vs. Ni, the martian trend is displaced toward lower Ni by a large factor (5), but the Os and Ir trends are not significantly displaced from their terrestrial counterparts. For Mars, Re shows a rough correlation with MgO, indicating compatible behavior, in contrast to its mildly incompatible behavior on Earth. Among martian MgO-rich rocks, Au shows a weak anticorrelation vs. MgO, resembling the terrestrial distribution except for a displacement toward 2–3 times lower Au. The same elements (Ni, Re, Os, Ir and Au) show similar correlations with Cr substituted for MgO. Data for lunar and HED rocks generally show less clear-cut trends (relatively few MgO-rich samples are available). These trends are exploited to infer the compositions of the primitive Earth, Mars, Moon and HED mantles, by assuming that the trend intercepts the bulk MgO or Cr content of the primitive mantle at the approximate primitive mantle concentration of the siderophile element. Results for Earth show good agreement with earlier estimates. For Mars, the implied primitive mantle composition is remarkably similar to the Earth’s, except for 5 times lower Ni. The best constrained of the extremely siderophile elements, Os and Ir, are present in the martian mantle at 0.005 times CI, in comparison to 0.007 times CI in Earth’s mantle. This similarity constitutes a key constraint on the style of core-mantle differentiation in both Mars and Earth. Successful models should predict similarly high concentrations of noble siderophile elements in both the martian and terrestrial mantles (“high” compared to the lunar and HED mantles, and to models of simple partitioning at typical low-pressure magmatic temperatures), but only predict high Ni for the Earth’s mantle. Models that engender the noble siderophile excess in Earth’s mantle through a uniquely terrestrial process, such as a Moon-forming giant impact, have difficulty explaining the similarity of outcome (except for Ni) on Mars. The high Ni content of the terrestrial mantle is probably an effect traceable to Earth’s size. For the more highly siderophile elements like Os and Ir, the simplest model consistent with available constraints is the veneer hypothesis. Core-mantle differentiation was notably inefficient on the largest terrestrial planets, because during the final ∼ 1% of accretion these bodies acquired sufficient H2O to oxidize most of the later-accreting Fe-metal, thus eliminating the carrier phase for segregation of siderophile elements into the core. 相似文献
10.
盈江县超上地区橄榄辉石岩脉的全岩地球化学特征表明:岩脉具有高Al、低Ti、贫P2O5和低碱的特点,属于低钾拉斑系列。另外具有与橄榄岩平衡的原生岩浆相一致的Mg#值为(70.89~72.18)、略微的Eu正异常(δEu=1.16~1.40),轻稀土元素富集,重稀土元素相对平缓;微量元素蛛网图上岩脉富集大离子亲石元素U、Th、Pb等,强烈亏损高场强元素Nb、Ta、Hf、P、Ti等。通过综合分析,认为岩脉岩浆源区为被俯冲板片流体改造过的亏损地幔,由其形成的母岩浆在演化过程中遭受了不同程度的下地壳物质的同化混染作用和有限的结晶分异作用,并可能经历了辉石的堆晶作用。结合区域资料,认为盈江县超上橄榄辉石岩脉形成于岛弧环境,超上地区可能在侏罗纪时期经历了中特提斯洋的俯冲消减。 相似文献
11.
The composition of the Earth 总被引：317，自引：0，他引：317
Compositional models of the Earth are critically dependent on three main sources of information: the seismic profile of the Earth and its interpretation, comparisons between primitive meteorites and the solar nebula composition, and chemical and petrological models of peridotite-basalt melting relationships. Whereas a family of compositional models for the Earth are permissible based on these methods, the model that is most consistent with the seismological and geodynamic structure of the Earth comprises an upper and lower mantle of similar composition, an Fe---Ni core having between 5% and 15% of a low-atomic-weight element, and a mantle which, when compared to CI carbonaceous chondrites, is depleted in Mg and Si relative to the refractory lithophile elements.The absolute and relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites are compared. The bulk composition of an average CI carbonaceous chondrite is defined from previous compilations and from the refractory element compositions of different groups of chondrites. The absolute uncertainties in their refractory element compositions are evaluated by comparing ratios of these elements. These data are then used to evaluate existing models of the composition of the Silicate Earth.The systematic behavior of major and trace elements during differentiation of the mantle is used to constrain the Silicate Earth composition. Seemingly fertile peridotites have experienced a previous melting event that must be accounted for when developing these models. The approach taken here avoids unnecessary assumptions inherent in several existing models, and results in an internally consistent Silicate Earth composition having chondritic proportions of the refractory lithophile elements at 2.75 times that in CI carbonaceous chondrites. Element ratios in peridotites, komatiites, basalts and various crustal rocks are used to assess the abundances of both non-lithophile and non-refractory elements in the Silicate Earth. These data provide insights into the accretion processes of the Earth, the chemical evolution of the Earth's mantle, the effect of core formation, and indicate negligible exchange between the core and mantle throughout the geologic record (the last 3.5 Ga).The composition of the Earth's core is poorly constrained beyond its major constituents (i.e. an Fe---Ni alloy). Density contrasts between the inner and outer core boundary are used to suggest the presence ( 10 ± 5%) of a light element or a combination of elements (e.g., O, S, Si) in the outer core. The core is the dominant repository of siderophile elements in the Earth. The limits of our understanding of the core's composition (including the light-element component) depend on models of core formation and the class of chondritic meteorites we have chosen when constructing models of the bulk Earth's composition.The Earth has a bulk Fe/Al of 20 ± 2, established by assuming that the Earth's budget of Al is stored entirely within the Silicate Earth and Fe is partitioned between the Silicate Earth ( 14%) and the core ( 86%). Chondritic meteorites display a range of Fe/Al ratios, with many having a value close to 20. A comparison of the bulk composition of the Earth and chondritic meteorites reveals both similarities and differences, with the Earth being more strongly depleted in the more volatile elements. There is no group of meteorites that has a bulk composition matching that of the Earth's. 相似文献
12.
元素之间的相关特征一直是地球化学过程的重要判据。但通常只有少数几个元素的相关特征为人们所采用。本文通过对大庄科花岗杂岩系列研究表明,许多元素相互之间都存在着显著的线性相关特征,它们是协同共变的——协变特征;另一些元素包括成矿元素,挥发份等,不呈协变特征。前者可能反映岩浆的状态、结构等内部特征和岩浆过程;后者反映了岩浆的成矿专属性特征。 相似文献
13.
新疆哈密黄山东铜镍硫化物矿床成岩成矿作用 总被引：7，自引：1，他引：6
黄山东铜镍硫化物矿床赋存于橄榄岩、苏长岩、辉长岩和闪长岩组成的镁铁-超镁铁质杂岩体中,赋矿岩体包含至少4套岩石组合。不同类型岩石微量元素和稀土元素原始地幔标准化配分模式指示,该矿床明显亏损Nb、Ta、Zr、Hf等高场强元素和Cr元素,富集Sr及大离子亲石元素;(La/Yb)N=1.08～2.70,δEu=0.50～2.57;含矿岩石Cu/Pd比值和Ti/Pd比值大于原始地幔值,表明不同类型岩石是高镁玄武质岩浆在深部分异结晶演化的产物。根据橄榄石和全岩化学组成可估算出母岩浆MgO含量约为12%。成矿岩浆深部演化过程中,富硅的地壳混染组分和外来流体的加入可能促成了岩浆中的硫饱和;深部熔离的不混溶硫化物珠滴被上升岩浆携带,富集在橄榄岩和苏长岩的底部。 相似文献
14.
V. A. Glebovitsky L. P. Nikitina A. B. Vrevskii Yu. D. Pushkarev M. S. Babushkina A. G. Goncharov 《Geochemistry International》2009,47(9):857-881
The paper reports data on the chemical composition of mantle peridotite xenoliths from kimberlites and alkaline basalts that
represent the continental lithospheric mantle (CLM) beneath Early Precambrian and Late Proterozoic-Cenozoic structures, respectively.
In order to identify compositional trends during the melting of primitive material and propose the most reliable criteria
for constraining the conditions of this process and its degree, we analyzed literature data on the melting of spinel and garnet
peridotites within broad temperature and pressure ranges. It was determined that the degree of melting (F%) of pristine peridotite
of composition close to that of the primitive mantle (PM) can be deduced from the Mg/Si and Al/Si ratios in the residue; an
equation was proposed for evaluating F from the Mg/Si ratio. The Ca/Al ratio of residues at low (1–1.5 GPa) pressures and
degrees of melting from 2–3 to 20–25% increases several times but decreases with increasing F at pressures higher than 3 GPa.
The Na partition coefficient between melt and residue decreases at increasing pressure and approaches one at a pressure close
to 20 GPa. Residues after low-degree melting are strongly depleted in Ti, Zr, Y, and Nb but are enriched in Cr. The application
of these criteria to the composition of xenoliths brought to the surface from the mantle occurring beneath tectonic structures
of various age led us to conclude that compositional heterogeneities of CLM (particularly the variations in the concentrations
of major and certain siderophile elements) are controlled, first of all, by the melting of the mantle source material. These
processes occurred under various thermodynamic conditions (T, P, and $
f_{O_2 }
$
f_{O_2 }
) and differed in their intensity, and this predetermined the compositional diversity of the residual mantle material (its
concentrations of Mg, Al, Si, Ca, Na, K, Ni, Co, V, and Cr). Our results are principally consistent with the hypothesis of
the global magmatic ocean. It is thought that the early phases of its consolidation were variably controlled by the fractionation
of minerals, for example, majorite. Moreover, heterogeneities in the distribution of siderophile elements could be partly
predetermined by changes in the properties of these elements at ultrahigh temperatures and pressures. The processes of partial
melting were the most intense during the early evolution of the mantle (perhaps, in the Early Precambrian), and hence, the
mantle has different chemical composition beneath Archean cratons and Phanerozoic foldbelts. 相似文献
15.
Geochemical Features, Age, and Tectonic Significance of the Kekekete Mafic-ultramafic Rocks, East Kunlun Orogen, China 总被引：3，自引：0，他引：3
LI Ruibao PEI Xianzhi LI Zuochen SUN Yu FENG Jianyong PEI Lei CHEN Guochao LIU Chengjun CHEN Youxin 《《地质学报》英文版》2013,87(5):1319-1333
The Kekekete mafic-ultramafic rocks are exposed in the Kekesha-Kekekete-Dawate area,which are in the eastern part of the East Kunlun Orogenic Belt.It outcrops as tectonic slices intruding tectonically in the Paleoproterozoic Baishahe Group and the Paleozoic Nachitai Group.The Kekekete mafic and ultramafic rocks is located near the central fault in East Kunlun and lithologically mainly consists of serpentinite,augite peridotite,and gabbro.The LA-ICP-MS zircon U-Pb age of the gabbro is 501±7 Ma,indicating that Kekekete mafic-ultramafic rocks formed in the Middle Cambrian.This rock assemblage is relatively poor in SiO2 and(Na2 O+K2 O) but rich in MgO and SFeO.The chondrite-normalized REE patterns of the gabbro dip slightly to the right;the primitive mantle and MORBnormalized spidergrams of trace elements show enrichment of large-ion lithophile elements(Cs,Rb,Ba,etc.) and no differentiation of high field strength elements.The general dominance of E-MORB features and the geochemical characteristics of OIB suggest that the Kekekete mafic-ultramafic rocks formed in an initial oceanic basin with slightly enriched mantle being featured by varying degrees of mixing of N-MORB depleted mantle and a similar-OIB-type source.From a comprehensive study of the previous data,the author believes that the tectonic history of the East Kunlun region was controlled by a geodynamic system of rifting and extension in the late stages of the Neoproterozoic to early stages of the Early Paleozoic and this formed the paleo-oceanic basin or rift system now represented by the ophiolites along the central fault in East Kunlun,the Kekekete mafic-ultramafic rocks and Delisitan ophiolite. 相似文献
16.
Geochemistry of peridotites and mafic igneous rocks from the Central Dinaric Ophiolite Belt,Yugoslavia 总被引：2，自引：0，他引：2
Bosko Lugović Rainer Altherr Ingrid Raczek Albrecht W. Hofmann Vladimir Majer 《Contributions to Mineralogy and Petrology》1991,106(2):201-216
In the Central Dinaric Ophiolite Belt (CDOB) peridotites and associated metamorphic rocks of various grades tectonically overlie an olistostrome melange of middle to late Jurassic age. Peridotites and underlying slices of mafic granulites (partially transformed to gamet amphibolites) are intruded by doleritic dikes which do not occur in the melange. The melange contains blocks of subgreywackes and cherts as well as those of pillow lavas and massive diabase (spilites). CDOB peridotites are in the spinel peridotite facies, but locally spinel-plagioclase peridotites occur as well. All peridotites have lherzolitic compositions showing several significant element correlations: Al2O3, CaO, TiO2, Na2O and Cu are negatively correlated and Ni is positively correlated with MgO. Recent estimates of primitive mantle compositions lie near the low-MgO end point of each correlation trend. Al/Ti and Ca/Al ratios of CDOB lherzolites are for the most part higher than the range observed in chondrites. However, when a few samples with extreme compositions are excluded, Al/Ti and Ca/Al are positively correlated with MgO, and the samples at the low-MgO end have near-chondritic Ca/Al but slightly higher than chondritic Al/Ti ratios. Chondrite-normalized REE patterns of CDOB lherzolites show extreme depletions in LREE providing strong evidence for the absence of any metasomatic renrichment. The lack of correlation between highly incompatible elements (LREE) and moderately incompatible elements (HREE, Ti, Na, Al, Ca) together with the extremely low La/Sm ratios suggest that fractional or very small increment melt removal played a role in the genesis of these lherzolites. Four out of five lherzolites yield and apparent Sm-Nd isochron age of 136±15 Ma with an Nb of 6.0±1.1 (bulk rocks and clinopyroxene separates). One sample has an exceptionally high Nd of about 23. The mafic igneous rocks scatter around the lower end of the 136 Ma reference isochron allowing, but not proving, a genetic relationship with a mantle having a Nd isotopic composition which is similar to that of CDOB lherzolites. LIL element abundances of spilites and doleritic dike rocks suggest some hydrothermal alteration. In primitive mantle-normalized concentration diagrams none of these mafic igneous rocks shows a significant negative Nb-Ta anomaly. Chondrite-normalized REE patterns of both rock types are essentially flat. Whereas the inferred primary compositions of the spilites compare well with those of E-type MORBs, the doleritic dike rocks show elemental ratios similar to those normally found in back-arc basin tholeiites. 相似文献
17.
牛毛泉基性杂岩体位于准噶尔古板块博格达-哈尔里克晚古生代岛弧东段,赋存磁铁矿。研究表明,该岩体具有明显成层性和韵律构造特征,主要岩石类型有橄榄辉长岩、含橄榄辉长岩、辉长岩和角闪辉长岩。岩石地球化学特征表明,该套岩石属拉斑玄武岩系列,m/f值介于0.65~1.44之间,属铁质基性-超基性岩。岩石稀土元素总量相对较低,稀土元素配分曲线为轻稀土元素略富集的右倾型;岩石富集大离子亲石元素(Rb、Ba、Sr、U),相对亏损高场强元素(Zr、Hf),具有明显的Nb、Ta负异常和弱的Ti正异常。岩石εNd(t)=-3.4~-0.50,εSr(t)=-3.4~8.5,具有向EMⅠ方向演化的趋势,表明岩浆源区可能为受俯冲流体交代改造的富集岩石圈地幔,是新疆北部早二叠世时期后碰撞伸展阶段的产物,由拆沉的富集岩石圈地幔被软流圈加热后发生部分熔融并上侵形成。 相似文献
18.
《International Geology Review》2012,54(5):448-477
Seventeen upper-mantle ultramafic xenoliths from the Lower Quaternary Tal Khodr Imtan cinder cone in southern Syria have revealed a dominant protogranular texture of nine spinel lherzolites, two spinel harzburgites, four spinel dunites, one spinel olivine websterite, and one spinel clinopyroxenite. The lherzolites, harzburgites, and dunites contain Cr-diopside and brown-red picotite, with a basanitic host rock; the websterite and clinopyroxenite contain Ti-Al-augite and Cr-hercynite. A lherzolite to dunite depletion trend is shown in the abundance of intermediate- and lightrare-earth elements (IREE and LREE) and from analytical data of dunitic olivine, with Ca, Al, Fe, Cr, and Si being the most depleted elements. The depletion probably resulted from successive partial melting. The scoriaceous basanite shows enrichments in REE and trace elements from a plume; the basanitic coating (around ultramafic xenoliths) increases in Mg/Mg+Fe+2 and concentrations of Al2O3, TiO2, and Na2O by contamination from peridotitic olivine, and also from eclogite-gabbro and nephelinite near the bottom of the rifted crust. Differences in the REE and trace-element concentrations among the peridotite xenoliths, the basanite host rock, and websterite indicate at least three different depths for their parent sources. The ultramafic inclusions in the basanitic host rock, as well as xenoliths in a carbonatite dike, suggest a deeper source for the carbonatite magma. At least part of the enrichment of the plume probably was accomplished by the subducted Tethys oceanic crust, suboceanic litho-sphere, and eclogite-gabbro. The thick plateau basalt in southern Syria indicates heavy and deep fracturing, and the extrusions of successive magmas from the upper mantle created a stretching and thinning in the continental crust. The proximity of this plateau basalt area to the Dead Sea-Jordan River Valley Rift, together with the source of the ultramafic xenoliths, points to a possible close relationship between the Red Sea Rift and the fracturing (offshoot rifting) in southern Syria. 相似文献
19.
For the first time occurrence of Ti rich Al depleted ultramafic cumulates having komatiitic signature in the northwestern fringe of Chotanagpur Gneissic Complex is presented. These rocks exhibit intrusive relationship with metasedimentary rocks and metaultramafites. Geochemically they are characterized by Mg# 79.1–91.60, high TiO2 (1.29–1.54 wt%), significantly low Al2O3/TiO2 and (Gd/Yb)n >1. Major oxides, trace and REE content suggest low degree of fractional crystallization and lesser degree of partial melting. These Al depleted komatiites are characterized by high concentration of incompatible elements than most suites of Barberton type komatiites. High Ti content suggests less degree of majorite garnet melting, leaving behind garnet in the restite. The rock shows higher Ti/Sc (190),Ti/V (22), Zr/Y (3), Zr/Sc (4), V/Sc (8), Zr/Sm (28) and Zr/Hf (47) ratios than primitive mantle and REE distribution pattern shows gentle slope from LREE to HREE in most samples pointing towards mantle metasomatism and crustal contamination during emplacement. The observed chemical characteristics indicate derivation of komatiite from an enriched mantle source and represent plume activity in an extensional tectonic regime of intracratonic setting. 相似文献
20.
四川稀土矿（氟碳铈矿）稀土总量的测定方法 总被引：1，自引：0，他引：1
氟碳铈矿矿样经高氟酸分解、脱硅后,稀土元素以氢氧化物和草酸盐形成进行沉淀与干扰元素分离,氢氧化物沉淀使稀土与钙、镁分离,草酸盐沉淀,使稀土与铁、铝、锆、钛等元素分离。适应矿石稀土含量１％～７４％的含量测定。该方法用于氟硕铈矿稀土总量的测定,方法简便、快速、准确。 相似文献