安徽省绩溪黑云母二长花岗岩中高铁铁橄榄石大斑晶的研究

高铁铁橄榄石大斑晶产在安徽省绩溪县黑云母二长花岗岩中。岩石呈细粒花岗结构,矿物成分为条纹长石、更长石、石英和黑云母。大斑晶最大粒径可达5cm,其中含有微小的磁铁矿自形晶,呈浸染状或断续脉状。在表生条件下,高铁铁橄榄石局部氧化成褐铁矿。大斑晶的外形、颜色和光泽等酷似黑钨矿。 大斑晶形成于上地幔高温高压条件下,先从花岗岩浆中结晶出铁橄榄石的高压变晶,岩浆沿深断裂向上部运移过程中,随着氧分压的增加而氧化成高铁铁橄榄石。     

江南造山带西南段梵净山地区镁铁质-超镁铁质岩:形成时代、地球化学特征与构造环境

梵净山地区位于江南造山带的西南缘,这里新元古代的镁铁质-超镁铁质岩浆岩广泛发育,岩性包括枕状熔岩、超镁铁质-镁铁质岩床群以及浅成侵入的辉长岩,成分属拉斑玄武岩系列。其中枕状熔岩以富集轻稀土元素和Rb、Ba、Th、U等强不相容元素,亏损高场强元素Nb和Ta,低的εNd(t)值为特征,明显不同于洋脊玄武岩,推测其成因可能与富集型地幔的部分熔融有关,形成于与俯冲有关的弧后小洋盆环境。超镁铁质-镁铁质岩床群主要由辉绿岩和碳酸辉橄岩组成,其中超镁铁质岩床群中出现大量的原生碳酸盐矿物,指示它们形成于拉张(甚至裂谷)的构造环境。辉长岩可能是区内最晚形成的岩浆岩,其SHRIMP锆石U-Pb年龄为821±4Ma。由枕状熔岩经超镁铁质-镁铁质岩床群到辉长岩,高场强元素Nb和Ta的亏损程度减弱、轻稀土元素的富集程度降低、εNd(t)值由负值变为正值,指示随时间的由早到晚,来自亏损地幔的物质不断增加。推测梵净山地区新元古代岩浆作用的顺序大致为:枕状熔岩(～840Ma)→白云母花岗岩(～838Ma)→碳酸超镁铁质岩床群→镁铁质岩床群→辉长岩(～821Ma),构造环境由俯冲-碰撞到拉张-裂谷。     

夏威夷基拉韦厄火山喷发物中液相铬铁矿的成分分析

细小的铬铁矿自形晶遍存于基拉韦厄熔岩之中。在迅速冷凝的熔岩中,铬铁矿通常被包含在镁质橄榄石斑晶之中,或与其连生。此外它们还呈孤立的颗粒存在于玄武质玻璃之中。这些铬铁矿与橄榄石共生,是基拉韦厄拉斑玄武岩浆的最早的结晶相。铬铁矿及与其共生的橄榄石斑晶的成分系用电子探针进行分析。每次喷发中有一个样品系采自正在上升的熔岩湖的表面,其余样品为浮岩。这类含铬铁矿熔岩的Cr_2O_3含量列于表1,基拉韦厄·伊基和马考普伊铬铁矿的平均成分也列于表1,单个颗粒的分析结果绘于图1之中。     

海南岛晚古生代洋岛玄武岩(OIB型)的发现及地球动力学暗示

海南岛西部的军营-邦溪地区产出一套变质的、晚古生代镁铁质-超镁铁质熔岩系列.根据地质学、岩石学、矿物学和地球化学研究,该套岩石可划分为高镁和低镁两个系列,前者以高镁(Mg# =76.9～81.3)为特征,后者以低镁(Mg#=40.7～48.4)、高钛含量(2.34％ ～3.27％)为特征.这套镁铁质-超镁铁质熔岩具有LREE富集[(La/Yb)N =2.40～7.58]和无明显Eu异常的稀土配分模式,以及无Nb亏损、但略具轻微Ta正异常的微量元素原始地幔标准化曲线;87Sr/86Sr (270Ma)和εNd(270Ma)比值的变化范围分别为0.70645 ～0.70956和+4.7～ +6.5,这些地球化学特征与洋岛玄武岩(OIB)极其相似.一些反映源区特征的比值,如Ta/Hf、Th/Nb、Nb/Zr、La/Ta、La/Sm、(La/Nb)PM、(Th/Ta)PM等均指示其地幔柱成因,是石榴子石二辉橄榄岩地幔低程度部分熔融形成的产物.橄榄石斑晶的矿物化学进一步揭示,岩石的高镁性质是由橄榄石堆晶引起的,而橄榄石斑晶低的Fo(68 ～77)值,暗示其原始岩浆为低镁的玄武质岩浆;低镁系列相对于高镁系列明显低的Cr、Ni含量,说明岩浆随后发生了橄榄石和单斜辉石的分离结晶作用.军营-邦溪地区晚古生代OIB型洋岛玄武岩可能代表了东古特提斯洋在海南岛的又一记录,该认识对深入探讨华南古特提斯洋的演化及其在海南岛的响应提供了新的证据.     

安徽省绩溪黑云母二长花岗岩中高铁铁橄榄石大斑晶的研究

高铁铁橄揽石大斑晶产在安徽省绩溪县黑云母二长花岗岩中.岩石呈细粒花岗结 构，矿物成分为条纹长石、更长石、石英和黑云母。大斑晶最大粒径可达5em，其中含有微小的 磁铁矿自形晶，呈浸染状或断续脉状.在表生条件下，高铁铁橄榄石局部氧化成褐铁矿.大斑晶 的外形、颜色和光泽等酷似黑钨矿. 大斑晶形成于上地慢高温高压条件下，先从花岗岩浆中结晶出铁橄榄石的高压变晶，岩浆沿 深断裂向上部运移过程中，随着氧分压的增加而氧化成高铁铁橄榄石.     

什么是科马提岩?

最早的用法科马提岩一名是由Viljoen兄弟(1969)提出的,当时他们宣布在南非巴伯顿山区发现了超镁铁质熔岩,作为以前未知火山岩类型存在的证据,他们描述了野外的观察结果,如冷凝流顶,似枕状构造,鬣刺结构及超镁铁质岩层与伴生的镁铁质熔岩对比时的系统地层情况。     

金川超基性岩体铬尖晶石的自然分类及其成因意义

铬尖晶石是金川超基性岩体最常见的副矿物,含量约为0.5—1％,其产态主要有两种:一种呈细小(粒径0.02—0.1毫升)的自形晶,晶体棱角有熔圆现象,主要嵌布在橄榄石内,次在斜方辉石内,单斜辉石中较少,斜长石中极少;另一种呈相对较粗(粒径0.15—0.8毫米)的自形一半自形晶,分布在橄榄石和辉石等造岩矿物粒间或硫化物中,常被磁铁矿和硫化物交代。据化学分析,这些铬尖晶石均富含钛(TiO_2 0.97—3.68 wt.％),但电子探针面扫描表明,钛在其中呈不均匀分布,并且矿物X射线粉晶图上有钛铁矿的衍射线出现,高倍镜     

阿尔泰山南缘中泥盆统苦橄岩低钙橄榄石的成因探讨

阿尔泰山南缘中泥盆统北塔山组地层发育世界罕见的总厚度达百米的苦橄质熔岩.苦橄岩的斑晶主要为蛇纹石化的自形一半自形橄榄石.对橄榄石斑晶的电子探针分析结果表明,其成分相当均匀,其Fo含量为79.8%～81.8%,并且具有异常低的CaO含量(0～0.06%),明显比典型岛弧苦橄岩中橄榄石的Fo含量和CaO含量要低的多.根据前人对Ca在橄榄石一硅酸盐熔体中的行为实验成果推测,这种橄榄石可能是高硅、低铁、低碱的玄武质岩浆结晶形成的.     

喀喇昆仑岔路口地区麦美奇质岩石的发现及其构造意义:岩石学、矿物学和地球化学证据

岔路口地区超基性熔岩主要由玻基纯橄岩和玻基辉橄岩组成,呈夹层状断续分布于玄武岩、玄武质火山岩及硅质岩中,总体上构成了深海相火山-沉积建造。玻基纯橄岩和玻基辉橄岩中的橄榄石斑晶多呈自形-半自形晶,11件样品25个测点获得的SiO_2含量为38.68%～40.58%,MgO含量主要为44.43%～46.72%,Ni值主要为1 100×10-6～2 381×10-6,计算得出的Fo值为85.60～87.71。在岩石化学成分上,SiO_2含量为38.51%～42.86%,MgO含量为26.81%～31.28%,TFe O含量为12.17%～14.52%,TiO_2含量为1.00%～1.45%,Na_2O+K_2O含量为0.17%～0.67%,在岩石化学分类上属麦美奇岩。因玻基辉橄岩中存在较多辉石斑晶而与传统麦美奇岩存在明显区别,因此暂将研究区超基性熔岩称为"麦美奇质岩石"。选用橄榄石最高Fo值和其寄主岩石TFe O含量估算出上述麦美奇质岩石原生岩浆中的MgO含量≥18.18%,据此限定地幔熔融温度和压力下限分别为1 580℃和3.9 GPa。结合岔路口地区麦美奇质岩石具有洋岛玄武岩微量元素特征以及前人研究成果,认为该区麦美奇质岩石形成于晚二叠世—晚三叠世的伸展环境,其地球动力学背景与地幔柱有关。     

橄榄石的过冷却结晶与微量元素含量

将霞石岩中的橄榄石(MgO=15.4%,FeO=8.5%)在约1个大气压的氮中完全熔融,在20~250℃过冷却条件下在2~10分钟内结晶。结晶的橄榄石的状态,当过冷却20℃时,为以玻璃为中心的包裹体自形晶,100℃左右时为链状细长骸晶,过冷却再加深时则成树枝状晶体。除树枝状晶体外,橄榄石b轴长度随结晶时间而增大,过冷却90℃在10分钟内结晶时长达70~80μm。在2分钟或4分钟内产生的自形晶与骸晶,呈Fo_(83)~Fo_(87)范围内的均质成分。产生均质的橄榄石时,在基质的玻璃上存在达100μm以上明显的浓度梯度。于是在     

Basic lavas of the Archean La Grande Greenstone belt: Products of polybaric fractionation and crustal contamination

Despite the fact that some greenstone belts preserve the record of contemporaneous komatiitic and tholeiitic volcanism, a genetic link between the two is not widely accepted. The significance of a compositional gap seperating these magma types and differences in their respective degree of light rare earth element (LREE) enrichment, cited as evidence against a derivative relationship, are complicated by the possibility of crustal assimilation by magmas of komatiitic affinity. In the Archean La Grande Greenstone belt of northern Quebec a succession of metamorphosed tholeiitic basalts and younger, high-Mg, LREE-enriched andesites are preserved. The tholeiites are differentiated basaltic rocks whose chemical compositions appear to have been controlled by low pressure, gabbroic fractional crystallization and are similar to Type 1 MORB. Parental magmas were probably high-Mg liquids of compositions similar to komatiitic basalts which also occur in the greenstone belt. These high-Mg liquids are believed to be themselves the product of high pressure, OLIV+OPX fractional crystallization of more magnesian primary liquids of komatiitic composition. The higher La/Sm ratios of komatiitic basalts and tholeiites relative to komatiites in this belt, can be explained by small degrees of crustal assimilation. In the central part of the belt, late-stage, mafic igneous rocks have chemical compositions similar to Archean examples of contaminated volcanic rocks (e.g., Kambalda, Australia). These late-stage lavas consist of basalts and andesites with high-Mg, Ni and Cr abundances, LREE-enriched profiles and low Ti abundances. They are believed to be the products of crustal assimilation and crystallization of OPX-PLAG-CPX from high-Mg liquids of komatiitic affinity. The volcanic stratigraphy records the progressive effects of crustal contamination through time. A light sialic crust may have initially acted as a density barrier, preventing the eruption of primary high-Mg liquids and forcing fractionation at depth which produced more buoyant compositions. With subsequent thinning of the crust, the density barrier presumably failed, and primary liquids migrated directly toward the surface. Reaction of these liquids with tonalitic crust produced contaminated differentiates.     

Petrogenesis of ultramafic and mafic rocks of the Thompson Nickel Belt,Manitoba

Abundant sill-like bodies of serpentinized ultramafic rocks, with associated nickel sulfide deposits, are found on the western side of the Thompson Nickel Belt near the Moak Lake-Setting Lake cataclastic fault zone. The ultramafic rocks range in composition from dunite to orthopyroxenite and feature variable alteration. Chemical variation across the bodies is suggestive of in-situ differentiation controlled mainly by olivine and orthopyroxene. Relative abundances of some elements, incompatible for olivine and orthopyroxene, suggest a parental liquid of komatiitic affinity. Ultramafic and mafic rocks are petrogenetically linked. A high degree of partial melting of mantle material and subsequent low-pressure crystal fractionation are responsible for the spectrum of composition from ultramafic to mafic.Publication 19-84, Ottawa-Carleton Centre for Geoscience Studies     

The basalt clan

The major element compositions of the various rocks that belong to the basalt clan are examined, and the basalt clan is defined as consisting of those volcanic rocks that contain between 44.0% and 53.5% silica. After examining both the diverse tectonic environments in which the basaltic rocks are found, and also the various petrographic suites to which they belong, or appear to belong, new chemical criteria were devised to divide them into the following groups: (1) low-potash basalt, (2) high-alumina basalt, (3) continental-flood basalt, (4) komatiitic basalt, (5) sodic basalt, (6) hawaiite, (7) phonolitic basalt, (8) potassic basalt, (9) trachybasalt, (10) leucitite, (11) sodic transitional basalt, and (12) potassic transitional basalt. The lunar mare-basalts are regarded as being transitional in their chemical character between the low-potash, ocean-floor basalts and the komatiitic basalts. While it was relatively easy to discover petrogenetic models that were able to account for the origin and evolution of the common sub-alkalic basalts, and even the sodic basalts, a variety of possible petrogenetic models had to be explored in order to account for the origin and evolution of the different basaltic rocks of the potash- and high-potash series.     

Magnesite abundance as a guide to gold mineralization associated with ultramafic flows, Timmins area

Altered komatiitic flows of the Tisdale Group locally contain secondary calcite, dolomite or magnesite, where alteration intensity and bulk-rock composition are favourable. Talc is present only in the least carbonatized samples and does not coexist with quartz and magnesite. Magnesite is present only in carbonatized ultramafic komatiitic flows (> 20 wt.% MgO) containing at least 18 wt.% loss on ignition (> 14 wt.% CO₂). Magnesite abundance increases with increasing loss on ignition and ) whole-rock ratio. Altered flows having magnesite to dolomite weight precent ratios exceeding 70 occur in proximity to mineable concentrations of gold and define surface-exploration targets 500 m in diameter.The spatial association of gold with the more magnesian ultramafic komatiitic flows arises in part because of the reactive nature of olivine-rich rocks in the presence of CO₂-bearing aqueous hydrothermal fluids, and possibly because the most magnesian ultramafic flows occur in proximity to an eruptive vent area where the likelihood of rock-fluid interaction is greatest because of the local structural regime.Talc-magnesite—quartz assemblages are present in some ultramafic dykes which cut the older Deloro Group volcanic rocks; the apparent absence of gold in these rocks may be attributed to the higher formation temperature of the talc-bearing, relative to the talc-free, magnesite-quartz assemblages.     

Strontium isotope and alkali element abundances in ultramafic rocks

The concentrations of the trace elements Na, K, Rb and Sr and the isotopic composition of Sr have been measured in a suite of ultramafic rocks, including alpine-type intrusions, inclusions in basalts and kimberlite pipes, zones from stratiform sheets, and a mica peridotite. From these data and those available in the literature the following conclusions can be drawn. Alpine-type ultramafic material appears to be residual in nature and can be neither the source material for the derivation of basalts nor the refractory residue of modern basalts. Alpine-type ultramafic intrusions appear to have no relationship with ultramafic zones in stratiform sheets and were probably derived from the upper mantle. A genetic relationship exists between basalts and their ultramafic inclusions, but it is extremely doubtful that this inclusion material could give rise to basalts by partial fusion. There is a possible genetic relationship between basalts and ultramafic inclusions in kimberlite pipes, and this ultramafic material is a potential source for the derivation of basalts. Ultramafic inclusions in basalts are probably not fragments of an alpine-type ultramafic zone in the mantle. An attempt has been made to synthesize the data and interpretations of this study by way of speculations on the role of ultramafic rocks in the differentiation history of the earth.     

Geochemical characteristics of mafic and ultramafic rocks from the Naga Hills Ophiolite,India:Implications for petrogenesis

The Naga Hills Ophiolite(NHO) represents one of the fragments of Tethyan oceanic crust in the Himalayan Orogenic system which is exposed in the Phek and Kiphire districts of Nagaland, India. The NHO is composed of partially serpentinized dunite, peridotite, gabbro, basalt, minor plagiogranite,diorite dyke and marine sediments. The basalts are mainly composed of fine grained plagioclase feldspar, clinopyroxene and orthopyroxene and show quenching and variolitic textures. The gabbros are characterized by medium to coarse grained plagioclase, orthopyroxene and clinopyroxene with ophitic to sub-ophitic textures. The ultramafic cumulates are represented by olivine, Cpx and Opx.Geochemically, the basalts and gabbros are sub-alkaline to alkaline and show tholeiitic features.The basalts are characterized by 44.1-45.6 wt.% of SiO_2 with 28-38 of Mg#, and the gabbros by38.7-43.7 wt.% of SiO_2, and 26-79 of Mg#. The ultramafic rocks are characterized by 37.4-52.2 wt.% of SiO_2, and 80-88 of Mg#. In multi-element diagrams(spidergrams) both basalts and gabbros show fractionated trends with strong negative anomalies of Zr. Nb. Sr and a gentle negative anomaly of P.However, the rare earth element(REE) plots of the basalts and gabbros show two distinct patterns. The first pattern, represented by light REE(LREE) depletion, suggests N-MORB features and can be interpreted as a signature of Paleo-Tethyan oceanic crust. The second pattern, represented by LREE enrichment with negligible negative Eu anomaly, conforms to E-MORB, and may be related to an arc tectonic setting. In V vs. Ti/1000, Cr vs. Y and AFM diagrams, the basalts and gabbros plot within Island Arc Tholeiite(IAT) and MORB fields suggesting both ridge and arc related settings. The ultramafic rocks exhibit two distinct patterns both in spidergrams and in REE plots. In the spidergram, one group displays highly enriched pattern, whereas the other group shows near flat pattern compared to primordial mantle. In the REE plot, one group displays steeper slopes [(La/Yb)N = 4.340-4.341], whereas the other displays moderate to flat slopes [(La/Yb)N = 0.97-1.67] and negative Eu-anomalies. Our study suggests that the ultramafic rocks represent two possible mantle sources(fertile and refractory).     

The petrogenesis of the Lac Guyer komatiites and basalts and the nature of the komatiite-komatiitic basalt compositional gap

A sequence of ultramafic rocks in the Lac Guyer Archean greenstone belt exhibit brecciated flow tops, pillow structures, and spinifex textures testifying to their volcanic origin. Massive, spinifex-textured and differentiated flows in the sequence have the chemical characteristics of peridotitic komatiite, with MgO ranging from 19–25 wt.%. Associated pillowed flows have compositions that straddle the conventional boundary between komatiite and komatiitic basalt with MgO contents ranging from 16 to 19 wt.% MgO and are best termed pyroxenitic komatiites. Unlike other komatiitic occurrences, the peridotitic and pyroxenitic komatiites at Lac Guyer constitute a continuous chemical spectrum with no evidence of population minimum near 18 wt.% MgO. The contrasting behaviour of highly compatible elements, such as Ni and Cr, versus incompatible elements, such as Zr, indicate that this compositional spectrum was produced by a variation in the extent of partial melting (10–40%) of a garnet lherzolite source in the Archean mantle. The pyroxenitic komatiites represent liquids produced during lower (10–20%) degrees of melting during which garnet remained in the mantle residue. However, a change in slope in the distribution of Zr vs. Y between the pyroxenitic and the peridotitic komatiites indicates that garnet was completely consumed at the more extensive degrees of melting which produced the peridotitic komatiites. The Lac Guyer volcanic rocks display a population minimum at 15 wt.% MgO separating komatiitic magmas whose compositions are controlled by partial melting from basalts whose composition is controlled by crystal fractionation. The population minimum near 18 wt.% MgO which is taken as the boundary between komatiite and komatiitic basalt may have a similar origin.     

Mapping bedrock lithologies through in situ regolith using retained element ratios: a case study from the Agnew-Lawlers area,Western Australia

Large, high-quality multi-element geochemical datasets are becoming widely available in the exploration industry, and afford excellent opportunities to investigate geochemical processes. A dataset of over 2500 analyses of unweathered and variably weathered mafic and ultramafic rocks for over 50 elements has been collected by Gold Fields Ltd. in the auriferous Agnew-Lawlers area of the eastern Yilgarn Craton of Western Australia. This dataset is used to investigate changes in element abundances and inter-element ratios through varying degrees and styles of weathering in an area of thick regolith characterised by deep in situ weathering. Systematic interrogation of the data, using lithostratigraphic controls derived from regional mapping and geophysics, reveals that a suite of elements, including Ti, Al, Zr, Th, La, Sc and Nb, and to a lesser extent Cr and Ni, behave as essentially immobile components during saprolite formation. In some cases diagnostic element ratios persist into siliceous duricrust. Ratios of these elements are used as reliable discriminants of bedrock type, and delineate features such as cryptic layering within fractionated sills and subtle geochemical variants in a sequence of tholeiitic and komatiitic basalts. Mapping on the basis of discriminant element ratios greatly extends previous trace-element ratio-based schemes for rock type discrimination. The potential to determine several of these elements with adequate precision and accuracy using portable XRF technology opens a potentially useful technique for rapid geochemical bedrock mapping in residual terrains.     

Interpretation of trace element and isotope features of basalts: relevance of field relations, petrology, major element data, phase equilibria, and magma chamber modeling in basalt petrogenesis

The concentrations and ratios of the major elements determine the physical properties and the phase equilibria behavior of peridotites and basalts in response to the changing energy contents of the systems. The behavior of the trace elements and isotopic features are influenced in their turn by the phase equilibria, by the physical character of the partial melting and partial crystallization processes, and by the way in which a magma interacts with its wall rocks. Concentrating on the trace element and isotope contents of basalts to the exclusion of the field relations, petrology, major element data, and phase equilibria is as improvident as slaughtering the buffalo for the sake of its tongue. The crust is a cool boundary layer and a density filter, which impedes the upward transfer of hot, dense “primary” picritic and komatiitic liquids. Planetary crusts are sites of large-scale contamination and extensive partial crystallization of primitive melts striving to escape to the surface. Escape of truly unmodified primitive melts to the surface is a rare event, requiring the resolution of daunting problems in chemical and mechanical engineering. Primary status for volumetrically abundant basalts such as mid-ocean ridge basalt, ocean island basalt, and continental flood basalts is denied by their low-pressure cotectic character, first remarked upon on petrological grounds in 1928 and on experimental grounds in 1962. These basalt liquids are products of crystal-liquid separation at low pressure. Primary status for these common basalts is further denied by the phase equilibria of such compositions at elevated pressures, when the required residual mantle mineralogy (magnesian olivine and orthopyroxene) is not stable at the liquidus. It is also denied by the picritic or komatiitic nature of partial melts of candidate upper-mantle compositions at high pressures—a conclusion supported by calculation of the melt composition, which would need to be extracted in order to explain the chemical variation between fertile and residual peridotite in natural ultramafic rock suites. The subtleties of magma chamber partial crystallization processes can produce an astounding array of “pseudospidergrams,” a small selection of which have been explored here. Major modification of the trace element geochemistry and trace element ratios, even those of the highly incompatible elements, must always be entertained whenever the evidence suggests the possibility of partial crystallization. At one extreme, periodically recharged, periodically tapped magma chambers might undergo partial crystallization by ∼95% consolidation of a succession of small packets of the magma. Refluxing of the 5% residual melts from such a process into the main body of melt would lead to eventual discrimination between highly incompatible elements in that residual liquid comparable with that otherwise achieved by 0.1 to 0.3% liquid extraction in equilibrium partial melting. Great caution needs to be exercised in attempting the reconstruction of more primitive compositions by addition of troctolite, gabbro, and olivine to apparently primitive lava compositions. Special attention is focussed on the phase equilibria involving olivine, plagioclase (i.e., troctolite), and liquid because a high proportion of erupted basalts carry these two phases as phenocrysts, yet the equilibria are restricted to crustal pressures and are only encountered by wide ranges of basaltic compositions at pressures less than 0.5 GPa. The mere presence of plagioclase phenocrysts may be sufficient to disqualify candidate primitive magmas. Determination of the actual contributions of crustal processes to petrogenesis requires a return to detailed field, experimental, and forensic petrologic studies of individual erupted basalt flows; of a multitude of cumulate gabbros and their contacts; and of upper-mantle outcrops.     

辽河盆地沙三期火山-侵入岩地球化学与岩石成因

辽河盆地沙三期火山-侵入岩为一套偏碱性的双峰式岩系，其基性端元为碱性玄武岩，中偏碱性端元为粗面质熔岩和侵入岩。碱性玄武岩富集高场强元素(如Nb、Th、Zr、Hf、V等)和轻稀土、Sr、Ba等大离子亲石元素，而亏损Rb和K，具有与板内碱性玄武岩和洋岛玄武岩类似的特征。粗面质岩石显示与基性端元相似的地球化学特征，其不相容元素含量总体上高于碱性玄武岩，但具强烈的Sr和Eu亏损。矿物学、岩石学及地球化学证据表明，玄武质岩石是软流圈地幔低程度部分熔融的产物，并经历了橄榄石和辉石的分离结晶作用，其源区可能有金云母和石榴石残留。玄武质岩浆上升到较浅部位后进一步发生橄榄石、辉石、斜长石和磁铁矿等的分离结晶作用而形成粗面质岩浆，地壳物质混染作用不显著。