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1.
大兴安岭中生代火山岩的主要活动时期为晚侏罗世至早白垩世，由碱性系列玄武岩和亚碱性系列玄武岩以及伴生的中酸性火山岩组成。它们与邻区俄罗斯和蒙古同时期火山岩构成面形展布的巨型火山岩带。碱性系列玄武岩高度富集不相容元素，其富集程度类似于板内碱性系列玄武岩，但明显亏损Nb和Ta等高场强元素这一点又类似于活动大陆边缘火山弧或岛弧钙碱性玄武岩。亚碱性系列玄武岩适度富集不相容元素而强烈亏损高场强元素的特征类似于活动大陆边缘火山弧或岛弧火山岩，其中低钾玄武岩类似于拉斑玄武岩。大兴安岭酸性火山岩根据地球化学特征可划分为高Sr流纹岩类和低Sr流纹岩类。前者富集Ti、Ba、Sr、Co和Ni而贫Rb、Zr和Th等强不相容元素，类似于大陆溢流玄武岩省分异作用形成的流纹岩；后者明显富集不相容元素Rb、Zr和Th而亏损Ti、Ba、Sr和Co，它们与碱性系列玄武岩之间形成类似于大陆裂谷环境的双峰式火山岩组合。亚碱性系列玄武岩与高Sr流纹岩的成因关系类似于大陆伸张环境的双峰式火山岩，但前者形成从基性到酸性的连续演化系列，并没有形成Daly成分间断。这表明大兴安岭火山岩在源区及其原始岩浆的性质上明显区别于世界大陆溢流玄武岩省。也就是说，大陆溢流玄武岩省的双峰模式起源于干岩浆体系，这种岩浆分异形成的中性岩浆由于其教度大于玄武岩、挥发分含量低于流纹岩而未能喷出地表。大兴安岭富含水的原始岩浆使分异形成的中性熔岩被挥发分过饱和，导致中性熔岩的爆炸性喷发。 相似文献
2.
白银厂矿田玄武岩主要由玄武岩和碱性玄武岩组成 ,其中玄武岩属于钙碱性系列和拉斑系列 ,碱性玄武岩属于钾质碱性玄武岩系列和钠质碱性玄武岩系列。相对于N -MORB ,本区钙碱性系列和拉斑系列玄武岩明显富集Ba、Rb、Th、U ,而亏损Ti;碱性系列玄武岩高度富集K、Ba、Rb、Th、U ,而Ti、Zr、Ce相对亏损 ,表明该区玄武岩的形成与板块俯冲作用有关。钙碱性玄武岩系列和拉斑玄武岩系列玄武岩具有低的REE含量和亏损的LREE配分型式 ,表明它是由LREE亏损和HREE略有富集的地幔部分熔融形成 ;碱性系列玄武岩的REE含量和 (La/Yb) N 比值高 ,LREE和HREE的分馏程度较高 ,表明其形成于演化的岩浆 ,可能来自于富集LREE的地幔源区或地幔橄榄岩较低程度的熔融。痕量元素地球化学特征表明 ,本区玄武岩应是与板块俯冲作用有关的地幔部分熔融形成 ,成岩环境为火山弧环境 ,是岛弧向成熟岛弧转化过程中的产物。 相似文献
3.
苏海图组火山岩发育自然铜矿化,具有从拉斑玄武岩系列向钙碱性玄武岩系列过渡的特点。依据地球化学特征,表明其TiO2含量较低(1%),玄武岩高的Al2O3含量、低的稀土含量,并且稀土元素曲线具有平缓型到轻稀土低度富集的特点。微量元素原始地幔标准化图解上,它们均富集大离子亲石因素(LILE),亏损高场强元素(HFSE),具有强的Nb和Ta的负异常,Ti的低负异常,以及P和Sm的低正异常。Zr/Nb值和Sm/Nd值接近MORB的范围,Th/Nb值大于0.11,Nb/Zr值小于0.04。以上这些特征均显示出典型岛弧岩浆的特点。所以,苏海图组火山岩为火山弧火山岩,其构造背景为大陆岛弧,源区可能为被流体或沉积物交待改造的亏损地幔。 相似文献
4.
对徐州栏杆地区侵位于元古代地层中的辉绿岩进行了系统的地球化学研究。栏杆地区的辉绿岩属于板内玄武岩系列岩石,地球化学特征上略富集轻稀土元素(LREE),富集大离子亲石元素(LILE),略亏损高场强元素(HFSE),相对富集Cr和Ni;微量元素显示了EM-OIB(富集地幔-洋岛玄武岩)的特征,辉绿岩稀土元素特征显示在岩浆上侵过程中经历了分离结晶作用。结合新元古代全球Rodinia超大陆裂解事件及其岩浆活动与地幔柱的密切关系,认为徐州地区新元古代辉绿岩可能为地幔柱作用在华北陆块边缘的记录。 相似文献
5.
新疆阿舍勒盆地中阿舍勒组火山岩主要为英安质、流纹质火山角砾岩,凝灰岩、沉凝灰岩等火山角砾岩及火山熔岩,顶部为玄武岩及碧玉岩、灰岩。玄武岩亏损Nb,Ta,Ti等高场强元素,富集Ba,Th,U,Sr等大离子亲石元素,具岛弧玄武岩特征;英安岩为钙碱性系列,富集Rb,Ba,Th,U等大离子亲石元素,Nb,P,Ti亏损十分明显,具火山弧英安岩特征。玄武岩和英安岩中分别获得(387±2.8)Ma和(398.1±6.9)Ma的锆石U-Pb年龄。Hf同位素研究表明,玄武岩、英安岩物质主要来自亏损地幔,受部分熔融地壳的混染。地球化学特征显示,早中泥盆世阿舍勒组火山岩形成于俯冲构造环境。 相似文献
6.
岩石化学、微量元素及稀土元素地球化研究表明:歙县蛇绿岩内地幔橄榄岩稀土元素配分为LREE富集型,不同于我国其他造山带地幔橄揽岩。歙县蛇绿岩壳层组合属于钙碱性和拉斑玄武岩间过渡系列,具类似的微量及稀土元素比值和稀土元素配分模型,且大离子亲石元素(LIL)和LREE高度富集。在Zr—Ti—Y和Hf—Ta—Th图解内,蛇绿岩基性熔岩成分点均落入钙碱性玄武岩区。结合岩石及区域地质资料,歙县蛇绿岩应形成于弧后(弧间)盆地环境。 相似文献
7.
在北祁连造山带冷龙岭地区新发现一条蛇绿岩带,该蛇绿岩从下向上由地幔橄榄岩、辉长辉绿岩、玄武岩、硅质岩组成。岩石地球化学特征表明,玄武岩可分类高Ti和低Ti两类,其中高Ti玄武岩具有LREE富集的稀土配分型式,富集K、Rb、Ba、Th、Nb、Ta等不相容元素,呈现隆起型(驼峰式)分布型式,显示了典型的洋岛火山岩地球化学特征,为板内岩浆作用的产物。低Ti玄武岩具有LREE亏损,类似N-MORB的稀土配分模式,同时又具有相对于N-MORB富集的大离子亲石元素,亏损Nb、Ta等高场强元素的岛弧火山岩的地球化学特征,代表了弧后盆地环境岩石组合。蛇绿岩岩石组合和岩石地球化学特征显示该蛇绿岩套形成于弧后盆地环境,是早奥陶世北祁连洋的残留。 相似文献
8.
对博格达—哈尔里克山地区不同地段石炭纪火山岩自然岩石组合、岩石地球化学特征研究,结果表明研究区火山岩组合为玄武岩—玄武安山岩—安山岩—英安岩—流纹岩组合,不同于大陆裂谷环境或伸展环境下的碱性双峰式火山岩构造组合。岩石地球化学特征显示,研究区火山岩大多数为钙碱系列,富Al高Ti,微弱富集大离子亲石元素,亏损高场强元素,表现为火山弧环境。且认为研究区石炭纪火山活动可能与其南侧康古尔洋盆的演化相关。 相似文献
9.
对博格达—哈尔里克山地区不同地段石炭纪火山岩自然岩石组合、岩石地球化学特征研究,结果表明研究区火山岩组合为玄武岩—玄武安山岩—安山岩—英安岩—流纹岩组合,不同于大陆裂谷环境或伸展环境下的碱性双峰式火山岩构造组合。岩石地球化学特征显示,研究区火山岩大多数为钙碱系列,富Al高Ti,微弱富集大离子亲石元素,亏损高场强元素,表现为火山弧环境。且认为研究区石炭纪火山活动可能与其南侧康古尔洋盆的演化相关。 相似文献
10.
为探讨东升庙矿区变质火山岩的地质地球化学特征及其意义,本文对其产出特征、岩石学、岩石化学、地球化学和同位素等方面进行了综合分析研究。结果表明,矿区变质火山岩为一套以玄武岩为主的双峰式火山岩,其原岩为基性的玄武岩和酸性的流纹岩。玄武岩属碱性玄武岩,流纹岩属钙碱性系列,它们具有与火山弧火山岩相似的地球化学特征。基性火山岩的稀土元素分配型式和Nd同位素特征表明其成岩物质来源于（亏损）地幔。构造环境分析表明,矿区变质火山岩的构造环境为大陆边缘火山弧造山带。 相似文献
11.
The abundance of apatite in Phanerozoic mantle may be greatly underestimated. This study shows that apatite has a widespread occurrence in Phanerozoic lithospheric mantle and can be divided into two geochemically distinct types using halogen content, presence or absence of structural CO 2, Sr and trace element (especially U, Th, and light rare earth) ratios and abundances, and association with either metasomatised mantle wall-rock peridotites (Apatite A) or high-pressure magmatic crystallisation products (Apatite B). Apatite A is inferred to result from metasomatism by CO 2- and H 2O-rich fluids derived from a primitive mantle source region, while Apatite B compositions are consistent with crystallisation from magmas within the carbonate–silicate compositional spectrum. The presence of significant apatite in the lithospheric mantle is important not only for the geochemical budget but also for assessing heat production and heat flow in the mantle. The measured U and Th contents of mantle apatite average 60 and 200 ppm, respectively and 0.5% apatite would dominate heat production. Metasomatised mantle may also contain amphibole and mica with K2O and clinopyroxene with detectable U and Th. In lithospheric mantle with a thickness of 70 km, this abundance of apatite would result in mantle heat flow contribution of about 12 mW/m2, a significant proportion of the total “normal” mantle heat flow of about 18 mW/m2. 相似文献
12.
系统地介绍了近二十年来地幔地球化学在全球及区域地幔平均化学组成，地幔的化学不均一性及区域太产分布，地幔交代作用，化学地球动力学，地幔物理化学环境等五个方面的研究现状与进展。 相似文献
13.
Mantle xenoliths and xenocrysts were retrieved from three of the 88–86 Ma Buffalo Hills kimberlites (K6, K11, K14) for a reconnaissance study of the subcontinental lithospheric mantle (SCLM) beneath the Buffalo Head Terrane (Alberta, Canada). The xenoliths include spinel lherzolites, one garnet spinel lherzolite, garnet harzburgites, one sheared garnet lherzolite and pyroxenites. Pyroxenitic and wehrlitic garnet xenocrysts are derived primarily from the shallow mantle and lherzolitic garnet xenocrysts from the deep mantle. Harzburgite with Ca-saturated garnets is concentrated in a layer between 135–165 km depth. Garnet xenocrysts define a model conductive paleogeotherm corresponding to a heat flow of 38–39 mW/m 2. The sheared garnet lherzolite lies on an inflection of this geotherm and may constrain the depth of the lithosphere–asthenosphere boundary (LAB) beneath this region to ca 180 km depth. A loss of >20% partial melt is recorded by spinel lherzolites and up to 60% by the garnet harzburgites, which may be related to lithosphere formation. The mantle was subsequently modified during at least two metasomatic events. An older metasomatic event is evident in incompatible-element enrichments in homogeneous equilibrated garnet and clinopyroxene. Silicate melt metasomatism predominated in the deep lithosphere and led to enrichments in the HFSE with minor enrichments in LREE. Metasomatism by small-volume volatile-rich melts, such as carbonatite, appears to have been more important in the shallow lithosphere and led to enrichments in LREE with minor enrichments in HFSE. An intermediate metasomatic style, possibly a signature of volatile-rich silicate melts, is also recognised. These metasomatic styles may be related through modification of a single melt during progressive interaction with the mantle. This metasomatism is suggested to have occurred during Paleoproterozoic rifting of the Buffalo Head Terrane from the neighbouring Rae Province and may be responsible for the evolution of some samples toward unradiogenic Nd and Hf isotopic compositions. Disturbed Re–Os isotope systematics, evident in implausible model ages, were obtained in situ for sulfides in several spinel lherzolites and suggest that many sulfides are secondary (metasomatic) or mixtures of primary and secondary sulfides. Sulfide in one peridotite has unradiogenic 187Os/188Os and gives a model age of 1.89±0.38 Ga. This age coincides with the inferred emplacement of mafic sheets in the crust and suggests that the melts parental to the intrusions interacted with the lithospheric mantle. A younger metasomatic event is indicated by the occurrence of sulfide-rich melt patches, unequilibrated mineral compositions and overgrowths on spinel that are Ti-, Cr- and Fe-rich but Zn-poor. Subsequent cooling is recorded by fine exsolution lamellae in the pyroxenes and by arrested mineral reactions. If the lithosphere beneath the Buffalo Head Terrane was formed in the Archaean, any unambiguous signatures of this ancient origin may have been obliterated during these multiple events. 相似文献
14.
Small-scale seismic heterogeneity exists at different levels in the lower mantle, and is detected by methods that analyze scattered–not direct–energy from natural and artificial sources. Its vertical distribution, association with subduction, and its ≤ 10-km characteristic scale length strongly suggest that it is chemical/petrological in nature and originally created by melting and differentiation during mid-ocean ridge formation. What is of interest is that the scale lengths of both upper and lower mantle seismic heterogeneity are similar, which supports the view of a common origin explored here. Unlike the lower mantle however, which is broadly homogeneous in structure, the upper mantle contains things that trap and impede the dispersal and re-mixing of heterogeneity: continental crust, lithosphere and cratonic roots. These probably control the depths, the longevity and the age of heterogeneities at shallow mantle levels, and suggest that heterogeneities observed in continental mantle lithosphere are probably old, trapped by the process that grows continental roots. Alternatively, if crustal heterogeneity is controlled by the details of a magmatic process, it must either be somehow continually renewed, for which there is no recognizable surface expression, or it must be depleted over time and the present is a time when, by luck, we may still witness it. 相似文献
15.
Continental cratons overlie thick, high-viscosity, thermal and chemical boundary layers, where the chemical boundary layers are less dense than they would be due to thermal effects alone, perhaps because they are depleted in basaltic constituents. If the continental tectosphere is the same age as the overlying Archaean crust, then the continental tectosphere must be able to survive for several billion years without undergoing a convective instability, despite being both cold and thick. Since platforms and shields correlate only weakly with Earth's gravity and geoid anomalies, acceptable models of the continental tectosphere must also satisfy this gravity constraint. We investigate the long-term stability of the continental tectosphere by carrying out a number of numerical convection experiments within a two-dimensional Cartesian domain. We initiate our experiments with a tectosphere (thermal and chemical boundary layers) immersed in a region of uniform composition, temperature, and viscosity, and consider the effects on the stability of the tectosphere of (1) activation energy (used to define the temperature dependence of viscosity), (2) compositional buoyancy, and (3) linear or non-linear rheology. The large lateral thermal gradients required to match oceanic and tectosphere structures initiate the dominant instability, a “drip” which develops at the side of the tectosphere and moves to beneath its center. High activation energies and high background viscosities restrict the amount and rate of entrainment. Compositional buoyancy does not significantly change the flow pattern. Rather, compositional buoyancy slows the destruction process somewhat and reduces the stress within the tectosphere. With a non-Newtonian rheology, this reduction in stress helps to stiffen the tectosphere. In these experiments, dynamical systems that adequately model the present ocean-continent structures have activation energy E*≥180 kJ mole −1 — a value about one third the estimate of activation energy for olivine, E*≈520 kJ mole −1. Although for E*≈520 kJ mole −1, compositional buoyancy is not required for the tectosphere to survive, the joint application of longevity and gravity constraints allows us to reject all models not containing compositional buoyancy, and to predict that the ratio of compositional to thermal buoyancy within the continental tectosphere is approximately unity. 相似文献
16.
The assembly of supercontinents should impact mantle flow fields significantly, affecting the distribution of subduction, upwelling plumes, lower mantle chemical heterogeneities, and thus plausibly contributing to voluminous volcanism that is often associated with their breakup. Alternative explanations for this volcanism include insulation by the continent and thus elevated subcontinental mantle temperatures. Here we model the thermal and dynamic impact of supercontinents on Earth-like mobile-lid convecting systems. We confirm that insulating supercontinents (over 3000 km extent) can impact mantle temperatures, but show the scale of temperature anomaly is significantly less for systems with strongly temperature-dependent viscosities and mobile continents. Additionally, for continents over 8000 km, mantle temperatures are modulated by the development of small-scale convecting systems under the continent, which arise due to inefficient lateral convection of heat at these scales. We demonstrate a statistically robust association between rising plumes supercontinental interiors for a variety of continental configurations, driven largely by the tendency of subducting slabs to lock onto continental margins. The distribution of slabs also affects the spatial positioning of deep mantle thermochemical anomalies, which demonstrate stable configurations in either the sub-supercontinent or intraoceanic domains. We find externally forced rifting scenarios unable to generate significant melt rates, and thus the ultimate cause of supercontinent breakup related volcanism is probably related to dynamic continental rifting in response to mantle reconfiguration events. 相似文献
17.
有关地幔交代作用的研究始于７０年代早期。近２０年来研究工作的贡献是使人们对与地幔演化和不均一性有关的地幔交代作用特征和交代作用机制有了更多的了解。地幔交代作用很复杂，它取决于交代作用发生的时间、构造环境、交代介质的种类以及与不同深度地幔内各种地质事件有关的流体的组成。进一步深入开展有关交代作用成因、机制及其与各种地质事件关系的研究，对于深入认识岩石圈地幔的演化和不均一特征具有十分重要的意义。对不同构造环境中的不同包体类型进行深入研究，为地幔交代作用提供广泛约束。将传统的地质学、岩石学的研究与地球化学、地球物理学以及现代测试技术相结合，很可能为解决交代作用成因、机制及交代作用与岩浆作用之间的时间先后问题，交代作用与地质事件的关系问题提供有效的方法和途径。 相似文献
18.
Spinel lherzolite xenoliths from Tertiary basaltic host magmas at Allyn River, eastern Australia reveal two distinct petrographic and geochemical types. One group is distinguished by xenoliths with undeformed, equilibrated microstructures and interstitial melt patches; The second group shows deformation and contains abundant fluid inclusions but no melt patches. Trace-element signatures of clinopyroxene in these xenoliths provide evidence for metasomatism by a silicate agent with hydrous component and by a carbonate-rich agent respectively. Melt patches in the undeformed xenoliths contain secondary minerals including clinopyroxene, olivine, feldspar, Mg- and Ca-rich carbonate, apatite, ilmenite and spinel. They are interpreted to represent volatile-rich melt captured shortly prior to entrainment in the host basalt. Sulfide globules, now recrystallised to discrete sulfide phases but inferred to be molten at lithospheric mantle T and P, are closely associated with the melt patches. The close association between sulfide and highly mobile, volatile-bearing fluid has important implications for the mobility of Re and Os, the use of their isotopes in dating mantle events, and the possible effect of volatile-bearing metasomatic agents on their composition. 相似文献
19.
有关地幔交代作用的研究始于７０年代早期。近２０年来研究工作的贡献是使人们对与地幔演化和不均一性有关的地幔交代作用特征和交代作用机制有了更多的了解，地幔交作用很复杂，它取决于交代作用发生的时间、构造环境、交代介质的种类以及与不同深度地幔内各种地质事件有关的流体的组成。进一步深入开发有关交代作用成因、机制及其与各种地质事件关系的研究，对于深入认识岩石圈地幔的演化和不均一特征具有十分重要的意义。对不同构 相似文献
20.
The oxidation state, reflected in the oxygen fugacity ( fO 2), of the subcratonic lithospheric mantle is laterally and vertically heterogeneous. In the garnet stability field, the Kaapvaal
lithospheric mantle becomes progressively more reducing with increasing depth from Δlog fO 2 FMQ-2 at 110 km to FMQ-4 at 210 km. Oxidation accompanying metasomatism has obscured this crystal-chemical controlled depth- fO 2 trend in the mantle beneath Kimberley, South Africa. Chondrite normalized REE patterns for garnets, preserve evidence of
a range in metasomatic enrichment from mild metasomatism in harzburgites to extensive metasomatism by LREE-enriched fluids
and melts with fairly unfractionated LREE/HREE ratios in phlogopite-bearing lherzolites. The metasomatized xenoliths record
redox conditions extending up to Δlog fO 2 = FMQ, sufficiently oxidized that magnesite would be the stable host of carbon in the most metasomatized samples. The most
oxidized lherzolites, those in or near the carbonate stability field, have the greatest modal abundance of phlogopite and
clinopyroxene. Clinopyroxene is modally less abundant or absent in the most reduced peridotite samples. The infiltration of
metasomatic fluids/melts into diamondiferous lithospheric mantle beneath the Kaapvaal craton converted reduced, anhydrous
harzburgite into variably oxidized phlogopite-bearing lherzolite. Locally, portions of the lithospheric mantle were metasomatized
and oxidized to an extent that conversion of diamond into carbonate should have occurred.
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