共查询到20条相似文献，搜索用时 31 毫秒
1.
V. P. Simanenko A. N. Filippov A. A. Chashchin 《Russian Journal of Pacific Geology》2009,3(3):220-233
Basalts developed on the right bank of the Matai River belong to the Samarka terrane (Central Sikhote Alin), which is a fragment of the Jurassic accretionary prism. They associate with Carboniferous-Permian reef limestones, Permian pelagic cherts, Jurassic hemipelagic cherty-clayey deposits, and terrigenous rocks of the near-continental sedimentation area. The petrogeochemical features of the basalts provide insight into the character of the volcanism in different settings of the ancient Pantalassa ocean. In terms of chemistry, the Carboniferous-Permian basalts are similar to the within-plate ocean-island basalts related to plume mantle sources. They were presumably formed in an oceanic area with numerous islands and seamounts. The Permian basalts associated with cherts are tholeiitic in composition and were formed from depleted mantle in a spreading center located in the pelagic area. The Jurassic basalts are of plume origin and, in terms of geochemistry, occupy an intermediate position between OIB and E-MORB. They were presumably formed in a convergent zone in a geodynamic setting of rapid oblique subduction. 相似文献
2.
岛弧的形成和演化对于理解板块构造和大陆生长有重要意义.祁连山-西秦岭一带发育两条不同类型的弧岩浆岩带,其北侧为北祁连增生杂岩带,由蛇绿岩、高压变质岩和大陆型弧岩浆岩带组成,形成时代为520~440 Ma.岩浆岩以中酸性火山岩-侵入岩为主,部分地区发育典型双峰式火山岩.南侧为祁秦增生杂岩带,由寒武纪蛇绿岩（525~490 Ma）和奥陶纪IBM型洋内弧岩浆岩（470~440 Ma）组成,蛇绿岩以拉脊山-永靖洋底高原型蛇绿岩为代表,蛇绿岩的上部熔岩部分由夏威夷型苦橄岩、板内碱性玄武岩和板内拉斑玄武岩组成,为大洋板块内部地幔柱活动产物.洋内弧岩浆岩以高镁玄武岩、玄武安山岩、高铝安山岩、玻安岩为主,局部发育赞岐岩.祁秦增生杂岩带的蛇绿岩和弧火山岩组合很好地说明洋底高原与海沟碰撞和俯冲带阻塞是造成俯冲带起始和新的洋内弧形成和发展主要因素. 相似文献
3.
In the east of the Tuvinian trough within the Kropotkin Ridge, the formation of Devonian volcanic associations was intimately conjugate with rifting on the southwestern framing of the Siberian Platform. The associations include picrite-like basalts, trachybasalts, basaltic trachyandesites, trachyandesites, trachytes, trachyrhyodacites, trachyrhyolites, comendites, and subvolcanic dolerites. The basic and normal-basic rocks are subdivided into two groups by TiO2 contents: high-Ti (TiO2 ～ 2.2–4.2 wt.%) and medium-Ti (TiO2 ～ 1.3–2.0 wt.%). Compared with the high-Ti basites, the medium-Ti ones are depleted in K, Rb, REE, Nb, Ta, Th, and U and have features of magmatic series of active continental margins. The high-Ti rocks are similar in composition to within-plate basalts. But in the isotopic compositions of Sr and Nd the above groups of basites are similar and correspond to mantle sources forming enriched within-plate basalts of the OIB type. This combination of within-plate and continent-marginal geochemical features in the basites localized in the same structure-geologic conditions might indicate the formation of rock associations in the rift zone at the rear of active continental paleomargin during the evolution of their common plume source. Its interaction with the suprasubductional lithospheric mantle determined the geochemistry of rocks. 相似文献
4.
大陆玄武岩通常具有与洋岛玄武岩相似的地球化学成分,其中含有显著的壳源组分.对于洋岛玄武岩来说,虽然其中的壳源组分归咎于深俯冲大洋板片的再循环,但是对板片俯冲过程中的壳幔相互作用缺乏研究.对于大陆玄武岩来说,由于其形成与特定大洋板片在大陆边缘之下的俯冲有关,可以用来确定古大洋板片俯冲的地壳物质再循环.本文总结了我们对中国东部新生代玄武岩所进行的一系列地球化学研究,结果记录了古太平洋板片俯冲析出流体对地幔楔的化学交代作用.这些大陆玄武岩普遍具有与洋岛玄武岩类似的地球化学成分,在微量元素组成上表现为富集LILE和LREE、亏损HREE,但是不亏损HFSE的分布特点,在放射成因同位素组成上表现为亏损至弱富集的Sr-Nd同位素组成.在排除地壳混染效应之后,这些玄武岩的地球化学特征可以由其地幔源区中壳源组分的性质来解释.俯冲大洋地壳部分熔融产生的熔体提供了地幔源区中的壳源组分,其中包括洋壳镁铁质火成岩、海底沉积物和大陆下地壳三种组分.华北和华南新生代大陆玄武岩在Pb同位素组成上存在显著差异,反映它们地幔源区中的壳源组分有所区别.中国东部新生代玄武岩的地幔源区是古太平洋板片于中生代俯冲至亚欧大陆东部之下时,在>200 km的俯冲带深度发生壳幔相互作用的产物.在新生代期间,随着俯冲太平洋板片的回卷引起的中国东部大陆岩石圈拉张和软流圈地幔上涌,那些交代成因的地幔源区发生部分熔融,形成了现今所见的新生代玄武岩. 相似文献
5.
Two basalt groups corresponding to different geodynamic environments were distinguished based on results of additional geochemical studies of materials obtained during Cruise 15 of the R/V Akademik Kurchatov and literature data on the Charlie-Gibbs Fracture Zone: (1) predominantly low-Ti tholeiites that are most closely similar to spreading basalts generated during the initial opening of the North Atlantic (southeastern margin of Greenland and the Vöring and Rockall plateaus) and (2) high-Ti differentiated basalts of variable alkalinity, which are deep, low-volume partial melts likely derived with the participation of a mantle plume. Compositional variations in the basalts were studied in the active and passive parts of the fracture zone. Our results bridge the gap in detailed geochemical data on oceanic crustal rocks and can be used in reconstructions of ancient geodynamic environments. 相似文献
6.
A. I. Kiselev V. V. Yarmolyuk K. N. Egorov R. A. Chernyshov A. V. Nikiforov 《Petrology》2006,14(6):588-608
Middle Paleozoic magmatism at the eastern Siberian platform was related to riftogenic processes, which were most clearly expressed in the Vilyui Rift and led to the formation of rift depressions filled with sedimentary-volcanogenic rocks and extended basaltic dike belts in rift shoulders. Two fields of diamondiferous kimberlites were found along with basaltic dikes in the Vilyui-Markha dike belt surrounding rift in the northwest. Active subalkali basaltic magmatism predated the emplacement of kimberlite bodies, which occasionally (Nyurba pipe) are cut by dikes of potassium alkali basalts. Based on geochemical and Sr-Nd isotopic characteristics, deep-seated sources were determined for the intrusive and volcanic basalts of the northwestern shoulder of the Vilyui rift. The REE distribution patterns of the studied rocks normalized to the primitive mantle are close to that of OIB, except for somewhat higher HREE. In the diagrams of indicator ratios of trace and rare-earth elements, the basalts are also plotted in the OIB field, being located between the end member of plume composition (FOZO) and enriched mantle sources. The rocks have positive εSr (+3.5 and +28.6) and εNd (+1.3 and +5.3). In a diagram εNd(T)-εSr(T), two fields with distinct content of radiogenic Sr are distinguished, which can be regarded as derived by mixing of the moderately depleted PREMA-type mantle and a source enriched in radiogenic Sr. Available isotope-geochemical data confirm that OIB type basalts of the region were generated by plume activity. The geodynamic setting of Middle Paleozoic magmatism and rifting in the eastern part of the Siberian platform is considered in light of plume-lithosphere interaction. The sequence of tectonomagmatic events during evolution of the Vilyui rift is consistent with the model of plume-lithosphere interaction or the model of active rifting. 相似文献
7.
A GIS layout of the map of recent volcanism in North Eurasia is used to estimate the geodynamic setting of this volcanism.
The fields of recent volcanic activity surround the Russian and Siberian platforms—the largest ancient tectonic blocks of
Eurasia—from the arctic part of North Eurasia to the Russian Northeast and Far East and then via Central Asia to the Caucasus
and West Europe. Asymmetry in the spatial distribution of recent volcanics of North Eurasia is emphasized by compositional
variations and corresponding geodynamic settings. Recent volcanic rocks in the arctic part of North Eurasia comprise the within-plate
alkaline and subalkaline basic rocks on the islands of the Arctic Ocean and tholeiitic basalts of the mid-ocean Gakkel Ridge.
The southern, eastern, and western volcanic fields are characterized by a combination of within-plate alkaline and subalkaline
basic rocks, including carbonatites in Afghanistan, and island-arc or collision basalt-andesite-rhyolite associations. The
spatial distribution of recent volcanism is controlled by the thermal state of the mantle beneath North Eurasia. The enormous
mass of the oceanic lithosphere was subducted during the formation of the Pangea supercontinent primarily beneath Eurasia
(cold superplume) and cooled its mantle, having retained the North Pangea supercontinent almost unchanged for 200 Ma. Volcanic
activity was related to the development of various shallow-seated geodynamic settings and deep-seated within-plate processes.
Within-plate volcanism in eastern and southern North Eurasia is controlled, as a rule, by upper mantle plumes, which appeared
in zones of convergence of lithospheric plates in connection with ascending hot flows compensating submergence of cold lithospheric
slabs. After the breakdown of Pangea, which affected the northern hemisphere of the Earth insignificantly, marine basins with
oceanic crust started to form in the Cretaceous and Cenozoic in response to the subsequent breakdown of the supercontinent
in the northern hemisphere. In our opinion, the young Arctic Ocean that arose before the growth of the Gakkel Ridge and, probably,
the oceanic portion of the Amerasia Basin should be regarded as a typical intracontinental basin within the supercontinent
[48]. Most likely, this basin was formed under the effect of mantle plumes in the course of their propagation (expansion,
after Yu.M. Pushcharovsky) to the north of the Central Atlantic, including an inferred plume of the North Pole (HALIP). 相似文献
8.
V. A. Simonov E. A. Kudryashova V. V. Yarmolyuk S. V. Kovyazin A. V. Kotlyarov 《Petrology》2013,21(5):489-506
Data on melt inclusions in minerals provide direct information on the physicochemical petrogenetic parameters of Late Cenozoic basaltic complexes in the Southern Baikal and Southern Khangai Volcanic Areas (SBVA and SKVA, respectively) in Central Asia. Newly obtained data on inclusions in olivine reveal differences between the temperatures of the magmatic systems that produced basalts in SBVA and SKVA. The comparison of the experimentally determined homogenization temperatures and parameters calculated from data on the composition of glasses in the melt inclusions allowed us to realistically evaluate the temperatures of the petrogenetic processes that generated Late Cenozoic basaltic complexes in SBVA (1130–1160°C and 1175–1250°C) and SKVA (1145–1185°C, 1210–1270, and about 1300–1310°C). The analysis of fluid phases in the inclusions testifies that basaltic melts in SBVA were rich in carbon dioxide, which ensured elevated pressures (up to 5–6.6 kbar) during the crystallization of the minerals. Data on the composition of inclusions in the olivine highlight differences between the chemistries of magmatic systems in the two territories: elevated TiO2, Al2O3, and CaO concentrations at relatively low FeO and MgO contents in the SBVA melts as compared to analogous concentrations in the SKVA basaltic magmas. The petrochemical and geochemical parameters of the primary melt inclusions and the composition of the olivine generally testify that deep plume magmatic processes were actively involved in the generation of basalts in both SBVA and SKVA. Data on melt inclusions in olivine and the composition of the clinopyroxene reveal similarities between the geochemistry, mineralogy, and crystallization parameters of Late Cenozoic basalts in both SBVA and SKVA and Cretaceous-Paleogene basalts in the Tien Shan and their certain differences from the plume-related systems of the OIB type. These data suggest that the geodynamic environment of the Cenozoic and Late Mesozoic intraplate plume magmatism in Central Asia were different from the geodynamic environment of typical long-lived mantle plumes like that at Hawaii. 相似文献
9.
We present a new approach for recognizing the origin of accreted basaltic rocks based on ocean plate stratigraphy (OPS), and on the petrology and geochemistry of basalts from mid-oceanic ridges (MORB) and oceanic islands (OIB) using examples from four accretionary complexes (AC) in SW Japan: Akiyoshi, Mino–Tamba, Chichibu and Shimanto. The key to the problem is the model of OPS, which includes an association of igneous and sedimentary rocks that form on an oceanic plate during its travel from a mid-oceanic ridge to a subduction zone. We propose the reconstruction of the tectonic settings of basalts according to their relationships with associated OPS sediments, their petrogenesis and their geochemical features. Five types of OPS are recognized in the accretionary complexes of SW Japan: (1) sandstone/shale; (2) sandstone/shale and chert; (3) sandstone/shale, chert and MORB; (4) sandstone/shale, chert, MORB and gabbro (± peridotite); (5) seamount OPS including OIB, cap carbonates, slope clastics and basal shale/chert. The alkaline, tholeiitic or calc-alkaline composition of basaltic melts, which are typical of oceanic islands, mid-oceanic ridges and island-arcs, respectively, can be identified by the sequence in crystallization of their major phenocrysts, i.e. olivine (ol), clinopyroxene (cpx) and plagioclase (pl), and by their compositions. Alkaline and calc-alkaline mafic lavas are characterized by an ol → cpx → pl succession, whereas tholeiitic melts by their ol → pl ± cpx succession. Titanium-rich minerals, e.g., Ti–augite, kaersutite, Ti–biotite, are typical of alkaline lavas. The application of geochemistry-based tectonic discrimination diagrams is also a powerful tool, if not supported by geological and petrological data, may result in confusion due to magma contamination, post-magmatic alteration, and secular change of mantle thermal conditions. We propose that a direct comparison of normalized multi-element patterns and key binary plots from older volcanic rocks with their modern analogues provides a more viable and reliable method of basalt discrimination. Our OPS–petrology–geochemistry method allows us to confirm the above conclusions that the lavas of the Akiyoshi, Mino–Tamba and Southern Chichibu AC formed in oceanic islands, because they are associated with seamount OPS sediments, crystallized from ol to cpx and pl, contain Ti–augite and kaersutite and are enriched in TiO2, LREE and Nb. In this paper we present geochemical data from the Inuyama basalts of the Mino–Tamba AC and from the Toba complex in the huge Mikabu greenstone belt of the Chichibu AC. The Inuyama basalts are in contact with Jurassic pelagic cherts, but their geochemical features are confusing; they contain phenocrysts of ol, Ti–augite and kaersutite and therefore probably formed in seamounts. The Toba volcanic rocks are a part of the huge ophiolite belt; they have flat to slightly LREE-enriched REE patterns, are characterized by an ol → cpx succession of phenocrysts and they plot in the OIB field in binary plots suggesting they formed in an oceanic plateau. 相似文献
10.
对信阳地区商丹断裂带南侧龟山岩组新元古代变质玄武岩进行了岩石学、地球化学及Sr-Nd同位素研究,分析结果显示该套玄武岩为亚碱性拉斑玄武系列,分为低Ti及高Ti两种类型：低Ti型较富Mg,不相容元素富集程度及稀土分馏程度较低,具有E-MORB的微量元素地球化学特征,Sr-Nd同位素组成相对富集,可能来自地幔柱引发的岩石圈地幔的部分熔融,并受到一定程度的地壳混染;高Ti型较富Fe,强烈富集不相容元素,具有OIB的地球化学特征,Sr-Nd同位素组成较为亏损,可能来自地幔柱的部分熔融,并较少受到地壳物质的影响。综合构造判别显示该套玄武岩可能为地幔柱伸展背景下的岩浆活动产物,可能为区域上沿商丹断裂带分布的中—新元古代局部伸展背景岩浆活动产物的组成部分。 相似文献
11.
A. M. Larin 《Geology of Ore Deposits》2014,56(4):257-280
The paper systematizes and integrates the results of geological, isotopic geochronological, and geochemical studies of the igneous rocks that make up the Ulkan-Dzhugdzhur anorthosite-rapakivi granite-peralkaline granite association and related mineralization. This association is a typical example of anorogenic igneous rocks that formed in the within-plate geodynamic setting most likely under effect of the mantle superplume, which was active in the territory of the Siberian Craton 1.75–1.70 Ga ago. The igneous rock association formed in a discrete regime that reflected the pulsatory evolution of a sublithospheric mantle source. The prerift (1736–1727 Ma) and rift proper (1722–1705 Ma) stages and a number of substages are distinguished. All igneous rocks pertaining to this association have mixed mantle-crustal origin. Basic rocks crystallized from the OIB-type basaltic magma, which underwent crustal contamination at various depths. Felsic rocks are products of mantle and crustal magma mixing. The contribution of mantle component progressively increased in a time-dependent sequence: moderately alkaline subsolvus granite → moderately alkaline and alkaline hypersolvus granites → peralkaline hypersolvus granite. All endogenic deposits in the studied district are related to a single source represented by the mantle plume and its derivatives. The Fe-Ti-apatite deposits hosted in anorthosite formed as a result of intense lower crustal contamination of basaltic magma near the Moho discontinuity and two stages of fractional crystallization at lower and upper crustal depth levels. The rare-metal deposits are genetically related to peralkaline granite. Formation of uranium deposits was most likely caused by Middle Riphean rejuvenation of the region, which also involved rocks of the Ulkan-Dzhugdzhur association. 相似文献
12.
13.
东天山自然铜矿化带玄武岩的起源、演化及成岩构造背景 总被引：9，自引：5，他引：4
新疆东天山地区与玄武岩有关的自然铜矿化带位于东天山觉罗塔格构造带内,自西向东有十里坡、黑龙峰、长城山、东尖峰等主要矿(化)点,自然铜矿化主要发育在玄武岩、杏仁状玄武岩及凝灰岩夹层中。本文基于玄武岩的地球化学特征,研究东天山自然铜矿化带玄武岩是否与地幔柱有关、岩浆源区性质、岩浆演化、成岩构造背景等问题。研究显示,东天山自然铜矿化带玄武岩与地幔柱岩浆活动无直接关系,整个天山地区是否存在石炭-二叠纪地幔柱岩浆活动也需要进一步的研究; 玄武岩起源于亏损岩石圈地幔,是演化岩浆的产物; 演化的玄武质岩浆形成后,在岩浆房中或上升至地表的过程中没有发生明显的分离结晶作用,也没有受到明显的地壳物质混染; 与玄武岩对应的地幔橄榄岩平衡原生岩浆演化的高镁岩浆的产物,可能为东天山地区与铜镍硫化物成矿有关的基性-超基性岩,指示这些铜镍硫化物矿床可能与地幔柱岩浆活动也没有关系; 玄武岩形成于新疆北部后碰撞构造阶段的伸展期,是在拉张应力体制下,由于软流圈上涌导致岩石圈地幔部分熔融而形成。 相似文献
14.
Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust 总被引：61，自引：0，他引：61
Two geochemical proxies are particularly important for the identification and classification of oceanic basalts: the Th–Nb proxy for crustal input and hence for demonstrating an oceanic, non-subduction setting; and the Ti–Yb proxy for melting depth and hence for indicating mantle temperature and thickness of the conductive lithosphere. For the Th–Nb proxy, a Th/Yb–Nb/Yb projection demonstrates that almost all oceanic basalts lie within a diagonal MORB–OIB array with a principal axis of dispersion along the array. However, basalts erupted at continental margins and in subduction zones are commonly displaced above the MORB–OIB array and/or belong to suites with principal dispersion axes which are oblique to the array. Modelling of magma–crust interaction quantifies the sensitivity of the Th–Nb proxy to process and to magma and crustal compositions. For the Ti–Yb proxy, the equivalent Ti/Yb–Nb/Yb projection features a discriminant boundary between low Ti/Yb MORB and high Ti/Yb OIB that runs almost parallel to the Nb/Yb axis, reflecting the fact that OIB originate by melting beneath thicker lithosphere and hence by less melting and with residual garnet. In the case of volcanic-rifted margins and oceanic plume–ridge interactions (PRI), where hot mantle flows toward progressively thinner lithosphere (often becoming more depleted in the process), basalts follow diagonal trends from the OIB to the MORB field. Modelling of mantle melting quantifies the sensitivity of the Ti–Nb proxy to mantle potential temperature and lithospheric thickness and hence defines the petrogenetic basis by which magmas plot in the OIB or MORB fields. Oceanic plateau basalts lie mostly in the centre of the MORB part of that field, reflecting a high degree of melting of fertile mantle. Application of the proxies to some examples of MORB ophiolites helps them to be further classified as C (contaminated)-MORB, N (normal)-MORB, E (enriched)-MORB and P (plume)-MORB ophiolites, which may add a useful dimension to ophiolite classification. In the Archean, the hotter magmas, higher crustal geotherms and higher Th contents of contaminants all result in widespread crustal input that is easy to detect geochemically with the Th–Nb proxy. Application of this proxy to Archean greenstones demonstrates that almost all exhibit a crustal component even when reputedly oceanic. This indicates, either that some interpretations need to be re-examined or that intra-oceanic crustal input is important in the Archean making the proxy less effective in distinguishing oceanic from continental settings. The Ti–Yb proxy is not effective for fingerprinting Archean settings because higher mantle potential temperatures mean that lithospheric thickness is no longer the critical variable in determining the presence or absence of residual garnet. 相似文献
15.
在滇东南建水地区发现产于峨眉山玄武岩中的高镁火山岩包体,这对于地幔柱的形成演化具有重要研究意义.对这些包体进行了锆石U-Pb年代学、地球化学和岩矿分析.高镁火山岩包体具斑状结构,致密块状构造,斑晶主要为贵橄榄石和透辉石.13颗锆石U-Pb LA-ICP-MS加权平均年龄为259±2Ma(MSWD=1.9),显示与寄主岩石同期形成.包体岩石具有高镁(Mg~#=68～75)、低硅(SiO_2=45.11%～45.93%)特征,轻稀土元素(LREE)、高场强元素(HFSE)富集而重稀土元素(HREE)亏损,属于亚碱性、拉斑玄武岩系列,具有板内玄武岩(IPB)特征.火山岩包体的原始岩浆起源于石榴子石二辉橄榄岩低程度部分熔融的产物,岩浆演化过程中发生了橄榄石和单斜辉石的分离结晶作用,在侵位上升过程中未受明显的地壳混染作用.该高镁火山岩的存在,显示地幔柱除了垂直上升运动外,在地球深部不同的边界还有多次侧向扩展移动,表明滇东南晚二叠世存在峨眉山地幔柱的一个分支-地幔枝活动. 相似文献
16.
Liu Yongsheng Gao Shan Luo Tingchuan Faculty of Earth Sciences China University of Geosciences Wuhan 《中国地质大学学报(英文版)》1998,9(2)
ＩＮＴＲＯＤＵＣＴＩＯＮＡｌａｒｇｅｃｈａｎｇｅｉｎｃｈｅｍｉｃａｌｃｏｍｐｏｓｉｔｉｏｎｏｆｍａｎｔｌｅａｔｔｈｅＡｒｃｈｅａｎ－Ｐｒｏｔｅｒｏｚｏｉｃｔｒａｎｓｉｔｉｏｎ（Ａｒ－Ｐｔｂｏｕｎｄａｒｙ）ｏｆ２．５Ｇａｗａｓｓｕｇｇｅｓｔｅｄｂｙｍａ... 相似文献
17.
《International Geology Review》2012,54(9):1097-1121
The Coastal Accretionary Complex of central Chile constitutes the product of early Carboniferous to Late Triassic subduction at the rear of Chilenia, a continental terrane likely derived from Laurentia and accreted to southwestern margin of Gondwana during the Mid to Late Devonian. The complex contains basaltic metavolcanic sequences of the subducted oceanic lithosphere accreted to the active margin. In this paper, we address the tectonic setting of these rocks by means of a geochemical study in the coastal area of Pichilemu region, central Chile. The accreted fragments of oceanic crust occupy different structural levels, exhibit variable metamorphic grade, and have geochemical fingerprints that reveal a compositional heterogeneity of the subducted oceanic crust. The amphibolites have N to E-MORB compositions. Greenschist units include N-MORB and E-MORB transitional to OIB, and blueschists and greenschists interleaved within a single metavolcanosedimentary sequence have OIB signatures. Neodymium isotopic systematics indicate depleted and enriched mantle sources, whereas strontium isotopic systematics indicate seawater/rock interaction. The variety of rocks suggests formation in an oceanic setting characterized by shallow and deep mantle sources, such as plume-influenced ridge. Based on the geological, petrological, geochemical, and isotopic characteristics, we propose that the metavolcanic protoliths of the Pichilemu region formed relatively close to the western margin of the Chilenia terrane during the initial stage (late Cambrian–Early Devonian) of seafloor development and drifting of this continental block. Geochemical similarities with oceanic units accreted to the active margin south of the Pichilemu region indicate a regional pattern of the oceanic crust subducted under the Palaeozoic Chilean margin between, at least, 34°S and 39°S latitude, strongly supporting the activity of a mantle plume. This, in turn, can be correlated with the location of the Pacific plume generation zone in early Palaeozoic era, corroborating a Laurentian origin for the Chilenia terrane. 相似文献
18.
山东昌乐位于华北克拉通东部,郯庐断裂带中段,广泛出露挟裹幔源捕虏体的新生代碱性玄武岩.为深入了解华北克拉通演化,依据岩相学特征、矿物化学成分特征,把昌乐碱性玄武岩中单斜辉石主要分为三大类:第1类为幔源捕虏体中原生单斜辉石,其主、微量元素含量呈现趋势不一致的解耦现象,且LREE、HREE各异特征表明其经历了多期、不同程度的地幔富集交代和部分熔融作用（低于10%的尖晶石相部分熔融）,交代熔体包括地幔富碱（K）富Al硅酸盐熔/流体,可能有碳酸盐熔体的贡献;第2类为幔源捕虏体中筛状单斜辉石,是部分熔融和熔体交代作用的共同产物,从无筛孔部位到筛孔周围远离筛孔部位和紧挨着筛孔部位,呈现出受熔体作用逐渐加强趋势,离筛孔较远部位记录了玄武质熔浆作用之前的一次富碱（K）富Al熔体交代的特征,而紧挨着筛孔的部位受晚期玄武质熔浆作用的影响最强;第3类为幔源捕虏体中反应边单斜辉石及玄武岩中斑晶单斜辉石,两者的化学成分及形成条件相似,显示HFSE正异常,LILE负异常,受OIB特征寄主玄武岩浆强烈的影响.昌乐新生代碱性玄武岩地幔捕虏体中单斜辉石显示经历多期"熔体作用"和不同程度的部分熔融特征,是研究区岩石圈地幔不均一性的体现. 相似文献
19.
Cao Xiaobin Bao Huiming Gao Caihong Liu Yun Huang Fang Peng Yongbo Zhang Yining 《中国地球化学学报》2019,38(3):327-334
Understanding the origin of ocean island basalts (OIB) has important bearings on Earth’s deep mantle. Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB’s formation, its exact fraction in OIB’s mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. Here we show, through theoretical calculation, that unlike many known proxies, triple oxygen isotope compositions (i.e. Δ17O) in olivine samples are not affected by crystallization and partial melting. This unique feature, therefore, allows olivine Δ17O values to identify subducted oceanic crusts in OIB’s mantle source. Furthermore, the fractions of subducted ocean sediments and hydrothermally altered oceanic crust in OIB’s mantle source can be quantified using their characteristic Δ17O values. Based on published Δ17O data, we estimated the fraction of subducted oceanic crust to be as high as 22.3% in certain OIB, but the affected region in the respective mantle plume is likely to be limited.
相似文献20.
《International Geology Review》2012,54(14):1576-1592
Topographic uplifts in the central Sahara occur in the Hoggar-Aïr and Tibesti-Gharyan swells that consist of Precambrian rocks overlain by Cenozoic volcanic rocks. The swells and associated Cenozoic volcanism have been related either to mantle plumes or to asthenospheric upwelling and to partial melting due to rift-related delamination along pre-existing Pan-African mega-shears during the collision between Africa and Europe. The Cenozoic volcanic rocks in the Hoggar generally range from Oligocene tholeiitic/transitional plateau basalts, which occur in the centre of the dome, to Neogene alkali basalts characterized by a decrease in their degree of silica undersaturation and an increase in their La/Yb ratios. The alkali basaltic rocks occur mainly along the margins of the dome and typically have less radiogenic Nd and Sr isotopic ratios than the tholeiitic/transitional basalts. The geochemistry of the most primitive basaltic rocks resembles oceanic island basalt (OIB) tholeiitic – in particular high-U/Pb mantle (HIMU)-type – and is also similar to those of the Circum-Mediterranean Anorogenic Cenozoic Igneous (CiMACI) province. These characteristics are consistent with, but do not require, a mantle plume origin. Geophysical data suggest a combination of the two mechanisms resulting in a complex plumbing system consisting of (a) at depths of 250–200 km, an upper mantle plume (presently under the Aïr massif); (b) between 200 and 150 km, approximately 700 km northeastward deflection of plume-derived magma by drag at the base of the African Plate and by mantle convection; (c) at approximately 150 km, the magma continues upwards to the surface in the Tibesti swell; (d) at approximately 100 km depth, part of the magma is diverted into a low S-wave velocity corridor under the Sahara Basin; and (e) at approximately 80 km depth, the corridor is tapped by Cenozoic volcanism in the Hoggar and Aïr massifs that flowed southwards along reactivated Precambrian faults. 相似文献