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1.
《Russian Geology and Geophysics》2014,55(8):929-940
Petrological and geochemical studies performed with invoking data on the compositions of clinopyroxenes have clarified the conditions of formation of Vendian-Cambrian basaltic complexes in the Dzhida zone of the Paleoasian Ocean (northern Mongolia and southwestern Transbaikalia). The research was based on a comparative analysis with reference igneous basaltic associations. Of special importance are our microprobe data on trace and rare-earth elements in clinopyroxenes from igneous rocks of different present-day geodynamic settings, namely, N-MORB (Mid-Atlantic Ridge, Central Atlantic), OIB (Bouvet Island, South Atlantic), WPB (within-plate tholeiitic plateau basalts of the Siberian Platform), and boninites of ensimatic arcs (Izu-Bonin island arc, Pacific). The studies have shown that the paleo-oceanic structures in the district of the Urgol guyot formed during geodynamic processes under the impact of mantle plumes on oceanic spreading crust, which resulted in oceanic basaltic plateaus and within-plate oceanic islands. All these structures were later superposed by typical island-arc structure-lithologic associations. Formation of basalt complexes in the Dzhidot guyot district proceeded with a stronger effect of enriched plume melts of within-plate oceanic islands as compared with the Urgol guyot. This is evidenced from petrochemical and geochemical data showing the development of OIB-type magmatic systems on the oceanic basement. Data on clinopyroxenes confirm the participation of mantle plume in this process, which led to the evolution of magmas from typical oceanic basalts (MORB) to plateau basalts and OIB. 相似文献
2.
In this paper, the concept of a geochemical structure (Yaroshevskii, 2004) was applied to describe chemical variations in the Early Carboniferous volcanic complexes and their distribution over the tectonic zones of the Southern Urals and Transuralian region in order to clarify the geodynamic settings of their formation. The cluster analysis of a geochemical dataset including 325 analyses of volcanic rocks from the Magnitogorsk, Southern Ural, Transuralian, and Valer’yanovskii tectonic zones allowed us to reduce the geochemical diversity of rocks to eight large geochemical groups. Based on average compositions, these geochemical groups (clusters) can be classed with the following rocks: (1) low-K tholeiitic basalts, (2) high-Ti subalkaline basalts, (3) high-Al subalkaline basalts, (4) subalkaline andesites, (5) subalkaline rhyolites, (6) Na subalkaline rhyolites, (7) potassic subalkaline rhyolites, and (8) high-Al potassic trachyandesibasalts. The distribution of these clusters in tectonic zones of the Southern Urals and Transuralian makes it possible to organize these complexes into four groups. The first group includes a differentiated series from high-Ti subalkaline basalts to sodic subalkaline rhyolites with the predominance of aluminous subalkaline basalts and subalkaline andesites. This group is most widespread in the Magnitogorsk and Valer’yanovskii zones. The second group corresponds to a differentiated series from low-K basalts to Na subalkaline rhyolites with a strong prevalence of high-Ti subalkaline basalts and less abundant aluminous subalkaline basalts. This group is widespread in the Eastern Ural zone. The third group includes subalkaline andesites and rhyolites with subordinate ultrapotassic rhyolites and trachyandesibasalts, which compose the Uya-Novoorenburg suture. The fourth group comprises high-Ti subalkaline basalts occurring in the Transuralian zone. Such a distinct distribution of the geochemical types of volcanic rocks is well consistent with concepts on the formation of the Southern Ural volcanic belts at the East European paleocontinent margin in a Californian-type setting. The Valer’yanovskii belt was formed at the active margin of the Kazakhstan paleocontinent. 相似文献
3.
New mineralogical, geochemical, and isotope data in combination with numerical modeling were used to reconstruct the physicochemical and geodynamic conditions of the formation of Pleistocene basalts of Kunashir Island. Although they are petrologically close to the Holocene basalts of Tyatya Volcano, their eruption occurred during a brief period of island arc extension, which was accompanied by the high degree melting of mantle wedge asthenosphere. Numerous geological, petrological, and paleogeographical data testify that Pleistocene is an important stage in the geodynamic reorganization of the Kuril island arc. This stage was responsible for uplifting of the southern islands above sea level accompanied by catastrophic endogenous events, deformation, topographic reorganization of the large area of the Sea of Japan and adjacent land, and final folding stage in the West Sakhalin Mountains. 相似文献
4.
S.I. Shkol'nik L.Z. Reznitskii V.G. Belichenko I.G. Barash 《Russian Geology and Geophysics》2009,50(9):779-788
The geochemical composition of metavolcanics (metabasalts and metaandesites) of the Tunka terrane is considered. They are differently enriched in incompatible elements relative to N-MORB. The geochemical features of the basalts (LILE and LREE enrichment, Zr and Hf negative anomalies) point to the suprasubductional nature of synsedimentary volcanism; at the same time, the rocks lack negative Nb, Ta, and Ti anomalies. Comparison of the Tunka metavolcanics with those of modern geodynamic settings shows their analogy to back-arc basin basalts. 相似文献
5.
A. A. Vorontsov V. V. Yarmolyuk G. S. Fedoseev A. V. Nikiforov G. P. Sandimirova 《Petrology》2010,18(6):596-609
Based on the systematic investigation of the geochemical and isotopic (Sr and Nd) characteristics of basic rocks from various
volcanic areas of the Devonian Altai-Sayan rift system, the compositions of mantle magma sources were characterized, and the
geodynamic scenarios of their entrainment into rifting processes were reconstructed. It was found that the titanium-rich basic
rocks (2.5 < TiO2 < 4.2 wt %) of this region are enriched in lithophile trace elements, including the rare earth elements, compared with N-MORB
and are similar in composition to intraplate subalkali basalts of the OIB type. In contrast, moderate-titanium basic rocks
(1.1 < TiO2 < 2.5 wt %) are mainly depleted in the highly charged incompatible elements Th, U, Nb, and Ta (La/Yb = 1.2−2.2) and, to a
lesser extent, in Zr, Hf, and LREE ((La/Yb)N < 7), but are enriched in Ba. With respect to these characteristics, the moderate-titanium basites are similar to rocks formed
in subduction environments. The geochemical parameters of the basites are strongly variable, which probably reflects the heterogeneity
of the mantle sources that contributed to the formation of the rift system. In particular, the most notable variations in
rock composition related to an increase in the contribution of an OIB-type source to magma composition were observed in the
eastern direction, i.e., inland from the paleocontinent margin. The isotopic composition of the basites is relatively stable
within individual rift zones and significantly variable at a comparison of rocks from different zones of the region. Based
on the isotopic characteristics of the rocks, three melt sources were identified. One of them is chemically similar to the
PREMA and is a common component in all observed trends of isotopic variations, irrespective of the position of the particular
assemblage in the structure of the region. This component dominates the composition of the titaniumrich basalts with geochemical
signatures of the derivatives of enriched mantle reservoirs of the E-MORB and OIB types and is considered as a plume source.
Two other isotopic melt sources are related to subduction processes, which is indicated by their dominance during the formation
of the moderate-titanium basalts showing the geochemical signatures (primarily, Ta-Nb depletion) of typical volcanic-arc rocks.
These differences are consistent with the formation of the Altai-Sayan rift system in a complex geodynamic setting, which
developed under the influence of intraplate magma sources (mantle plume) on the region of melt generation in an active continental
margin (subduction zone). 相似文献
6.
《Geodinamica Acta》2013,26(5):349-361
The most widespread blocks within the Cretaceous ophiolitic mélange (North Anatolian ophiolitic mélange) in Central Anatolia (Turkey) are pillow basalts, radiolarites, other ophiolitic fragments and Jurassic-Cretaceous carbonate blocks. The pillow basalts crop out as discrete blocks in close relation to radiolarites and ophiolitic units in Cretaceous ophiolitic mélange. The geochemical results suggest that analyzed pillow basalts are within-plate ocean island alkali basalts. The enrichment of incompatible elements (Nb, Ta, Light REE, Th, U, Cs, Rb, Ba, K) demonstrates the ocean island environment (both tholeiites and alkali basalts) and enriched MORB. Dated calcareous intrafills and biodetrital carbonates reveal an age span of Callovian—Early Aptian. The thin-shelled protoglobigerinids, belonging to the genus Globuligerina, in the calcareous intrafills between pillow basalt lobes indicates a Callovian—Barremian age interval, most probably, Valanginian to Late Barremian. The volcanic and radiolarite detritus-bearing orbitolinid—Baccinella biodetrital carbonates dated as Late Barremian-Early Aptian in age, were probably deposited around atolls and have a close relationship with the ocean island pillow basalts. The results collectively support the presence of a seamount on the Neo-Tethyan oceanic crust during the Valanginian—Late Barremian and atolls during the Late Barremian-Early Aptian interval. The presence of an oceanic crust older than that seamount along the Northern Branch of Neo-Tethys is conformable with the geodynamic evolution of the Tethys. 相似文献
7.
B. Coira M. Koukharsky S. Ribeiro Guevara C.E. Cisterna 《Journal of South American Earth Sciences》2009,27(1):24-35
Geochemical characteristics of Ordovician basic volcanic rocks help to define the evolving tectonic setting of the Argentine Puna and northern Chile. Four spatially distinct magmatic groups are defined on geological, petrographical, geochemical and isotopic bases, each associated with particular geodynamic environments.The Tremadoc western group of subalkaline low K tholeiites with arc and modified MORB like signatures represent early stages of a back-arc basin, where spreading was incipient.The Arenig western group, medium K calc-alkaline basalts to andesites have volcanic arc in transition to back-arc signatures.The Tremadoc subalkaline basalts of the eastern group have REE patterns similar to E-MORB and at the same time weak subduction characteristics suggesting a rather mature supra-subduction zone (SSZ) basin. In contrast, the Late Tremadocian-Arenig basalts of the same group have intra-plate signatures, interpreted as magmas that ascended along pull apart regions associated with a transtensional regime.The geochemical patterns were applied to correlate basic sequences of doubtful geological setting. So, basalts from Chile were related to the Tremadocian western group, where they represent a slightly more mature stage of spreading of the basin. Basic rocks from Pocitos and part of Calalaste represent pre-Ordovician records of a back-arc system similar to that of the Tremadoc western group. Clearly similar arc patterns to those of the Arenig western group allow extending the arc environment to the southern Puna. The Tremadocian basalts from the eastern group were related to metabasites from the southern Puna, as part of a back-arc environment at that time. 相似文献
8.
西秦岭地处青藏高原东北缘,是古亚洲构造域、特提斯构造域和滨太平洋构造域的交接转换带,也是分野中国大陆东、西部地理与地质构造的关键部位。该区广泛分布了大量中生代火山岩。由于该区基础地质研究程度很低,特别是缺少可靠的年代学和地球化学资料,对该区中生代火山岩的成因及地球动力学背景一直存在争议,影响了人们对西秦岭大地构造属性及发展演化历史的全面认识。文中提供了甘肃西秦岭夏河县麻当乡红墙村中生代玄武岩的岩相学、地球化学和同位素年代学研究资料和数据,对火山岩的成因与动力学条件进行了初步讨论。红墙玄武岩中分离出的锆石LA-ICP-MS U-Pb定年结果表明,该玄武岩形成于(104.8±0.99)Ma(MSWD=0.63),与野外观察结果一致,证明红墙玄武岩是早白垩世火山作用产物。岩相学和地球化学的观察和研究显示,该套岩石以出现斜长石斑晶、基质中出现大量斜长石微晶或微斑晶为特征,岩石具有较高的SiO2、Al2O3、Na2O和较低的CaO,属于钠质碱性玄武岩,而不同于该研究区东部礼县—宕昌一带新生代超钾质火山岩。红墙玄武岩在地球化学方面具有富集轻稀土和部分高场强元素(如Nb、Ta、Zr、Hf、Ti等),亏损大离子亲石元素(Rb、K等),正的εNd(t)=5.9～7.5和低的87Sr/86Sr(t)=0.703 3～0.705 6以及206Pb/204Pb(t)=17.707～18.319、207Pb/204Pb(t)=15.398～15.626和208Pb/204Pb(t)=37.266～38.454等特征。所有这些特征一致表明,红墙早白垩世玄武岩具有与大陆OIB相似的地球化学特征,其源区可能具有DMM和PREMA端员混合的特点,推测其主要来自亏损的软流圈地幔。结合对火山岩产出大地构造背景的综合分析及与礼县—宕昌新生代超钾质火山岩的对比,提出红墙早白垩世钠质碱性玄武岩是大陆裂谷岩浆作用的产物,其成因和动力学背景与自中生代以来南北构造带的裂谷性质及其发展演化有关。西秦岭东、西两段新生代与早白垩世火山岩在岩相学、全岩化学以及岩石系列和类型方面的差异,可能与不同时期软流圈地幔源区的演化、岩浆起源深度和部分熔融程度等有关。 相似文献
9.
A. N. Filippov G. I. Govorov A. A. Chashchin T. A. Punina 《Russian Journal of Pacific Geology》2010,4(4):289-303
This paper reports new data on the mineralogical-petrographical composition, genetic types of sedimentary rocks, and geochemical
features of the volcanic rocks of the Snarsky area of the Nizhneussuriisk segment of the Kiselevka-Manoma accretionary complex,
which is developed on the right bank of the lower reaches of the Ussuri River. The Middle Jurassic-Aptian sedimentary rocks
of the area are represented by pelagic radiolarian cherts, semipelagic siliceous-clayey deposits, subordinate shallow limestones,
volcanomictic conglomerates, and turbidite sandstones. The basalts of the area are represented by alkaline basalts resembling
within-plate ocean-island basalts and N-MORB-type tholeiitic basalts. Rock associations of two physicogeographical and geodynamic
settings are distinguished: the pelagic setting with within-plate alkaline volcanic rocks and the hemipelagic one with volcanic
edifices of spreading basalts. 相似文献
10.
It is generally believed that andesite–dacite–rhyolite suites and contemporary porphyry Cu deposits are related to subduction in active continental margin settings. However, it is still unclear which tectonic events result in the generation of porphyry Cu deposits and whether asthenospheric mantle material is involved in this process. Widespread andesitic–dacitic felsic intrusions associated with porphyry Cu deposits and rarer basalts have been identified in the Late Triassic southern Yidun arc (SYA) of eastern Tibet. However, few geochronological and geochemical data are available for these basalts, thereby hampering the development of geodynamic models for this magmatic event and the formation of related porphyry Cu deposits in the region. Here we present the first geochemical and SIMS (secondary ion mass spectrometry) zircon U–Pb data of Xiaxiaoliu basalts in the SYA. The age of the Late Triassic Xiaxiaoliu basalts (216.1 ± 2.8 Ma) is consistent with the timing of emplacement of voluminous porphyritic intrusions and the formation of Cu deposits within the SYA (peaking at 215–217 Ma). The Xiaxiaoliu basalts have E-MORB-like trace element patterns that are free of negative Nb–Ta anomalies, and have high 143Nd/144Nd(t) values, suggesting they were sourced from asthenospheric mantle without any arc-type influence. These observations, combined with the fact that some Late Triassic mineralized porphyritic intrusions within the SYA have adakitic affinities, suggest that the basalts and other igneous rocks and associated porphyry Cu deposits within the SYA were produced by tearing of a westward-dipping slab, triggering the upwelling of asthenospheric mantle material during subduction of the Garze–Litang Ocean crust. 相似文献
11.
New geochemical and isotopic-geochronological data are reported on the intrusive association from one of the largest and relatively poorly studied Cretaceous (Aptian-Cenomanian) magmatic zones of the Sikhote-Alin accretionary fold system. The new results and previously published studies were interpreted using concepts of a blocked (terrane) structure of the region and the different geodynamic nature of the magmatic complexes. It was shown that the “transitional” geochemical and geodynamic characteristics of the studied intrusive rocks can be explained in terms of magmatism along the transform continental margin. Additional complicating factors are the composition of the terrane rocks and the change in the geodynamic setting during the formation of the considered magmatic area (114-90 Ma). 相似文献
12.
R.A. Shelepaev V.V. Egorova A.E. Izokh R. Seltmann 《Russian Geology and Geophysics》2018,59(5):525-540
We consider geochemical features of mafic magmatism manifested during the evolution of a complex nappe-folded structure in Western Sangilen, resulted from the Cambrian-Ordovician collisional tectogenesis. There are abundant ultramafic-mafic and mafic associations of different types in this region: layered low-Ti low-alkali ultramafic-mafic intrusions, high-Ti medium-alkali gabbroids, gabbro-monzodiorite intrusions, and alkali basalts. Isotope-geochronological data showed that these complexes formed over a wide time interval, from 570 to 440 Ma. At this time, the geodynamic setting in Western Sangilen changed from an island-arc one via a collision one to an intercontinental rift setting. At the early and late stages of the evolution of Western Sangilen, the geochemical features of mafites were typical of their geodynamic settings. The properties of mafites that formed synchronously with the collision are of particular interest. The studies have shown that the chemical composition of collisional mafites of Western Sangilen changed with time. They became richer in alkalies, titanium, and incompatible elements. This fact indicates a change in the type of mantle source from suprasubductional in the Cambrian to enriched deeper-level one in the Ordovician. 相似文献
13.
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
14.
Geochemical evidence for arc-type volcanism in the Aegean Sea: the blueschist unit of Siphnos, Cyclades (Greece) 总被引：2，自引：0，他引：2
Blueschists, eclogites, chlorite–actinolite rocks and jadeite-gneisses of the blueschist unit of Siphnos have been investigated for their geochemical composition. Their protolith nature is characterised and a geodynamic model for the pre-metamorphic evolution of these metavolcanic rocks is proposed on the basis of immobile elements, especially trace elements and rare earth elements (REE).
The protoliths of the eclogites are characterised as calc-alkaline basalts, andesites and Fe-rich tholeiites evolving in an island-arc setting. Trace element data indicate that subducted marine sediments were assimilated in the magma chamber, enriching the protoliths in LILE and Pb. Produced in the early stage of back-arc basin opening, a protolith with affinities to both island-arc and MORB formed the precursor of the chlorite–actinolite rocks. They were created by low degrees of partial melting of very primitive magmas, akin to spinel-peridotites and have affinities to boninites, probably through melting of the peridotitic mantle wedge. Tholeiitic basalts and andesites with N-MORB affinity, especially in their REE-patterns, were then produced by partial melting, possibly in an embryonic back-arc basin. These rocks were the protoliths of the blueschists of Siphnos. Their enrichment in some LILE and Pb indicates a N-MORB source contaminated by marine sediments, probably shales or other Pb-rich sediments. Because the jadeite-gneisses show affinities to MOR-granites and volcanic arc granites, intrusion of their protoliths in a back-arc environment is likely. The protoliths of the quartz-jadeite gneisses are rhyodacites/dacites and rhyolites, those of the glaucophane-jadeite gneisses were andesites.
The proposed geodynamic model, solely based on geochemical data, is consistent with geochemical data from neighbouring islands, though those rock units show much higher chemical variability. Consistent with geotectonic models, which are based on structural and geophysical data, the volcanic protoliths of the Siphnos blueschist unit reflect the transition from subduction to spreading environment and record in detail: subduction, formation of an island-arc, and the evolution of a back-arc basin. 相似文献
15.
北祁连九个泉蛇绿岩及其上覆岩系的岩石地球化学特征和地球动力学意义 总被引：3，自引：1，他引：2
本文通过对北祁连九个泉蛇绿岩及其上覆岩系的详细的野外、岩石学和地球化学的研究表明：该区火山岩由多个火山角砾岩—块状玄武岩—凝灰岩的旋回所组成;蛇绿岩之上整合覆盖着一套火山岩—沉积岩组合（蛇绿岩的上覆岩系）。蛇绿岩中玄武岩为典型的N-MORB,其上覆岩系中玄武岩为E-MORB。剖面从下到上,玄武岩中LREE,HFSE含量递增。火山岩的地球化学和沉积岩的岩相学反映了洋壳从扩张中脊向大陆方向迁移的动力学过程,蛇绿岩从形成到侵位的时间间隔较短。 相似文献
16.
The geodynamic nature of the Late Neoproterozoic island-arc dacites (691 ± 8.8 Ma) and rift basalts (572 ± 6.5 Ma) of the Kiselikhinskaya Formation, Kutukasskaya Group, in the Isakovskii terrane is inferred from geochemical data and U–Pb zircon (SHRIMP-II) dates. The volcanic rocks were produced during the late evolutionary history of the Yenisei Range, starting at the origin of oceanic crustal fragments and their accretion to the Siberian craton to the postaccretionary crustal extension and the onset of the Caledonian orogenesis. The reproduced sequence of geological processes marks the early evolution of the Paleo- Asian Ocean in its junction zone with the Siberian craton. The data refine the composition and age of volcanic rocks in the trans-Angara part of the Yenisei Range and specifics of the Neoproterozoic evolution of the Sayan–Yenisei accretionary belt. 相似文献
17.
N. M. Sushchevskaya B. V. Belyatsky E. P. Dubinin O. V. Levchenko 《Geochemistry International》2017,55(9):775-791
Petrological–geochemical study showed that the alkaline-ultramafics of the Jetty Oasis (rift zone of the Lambert glacier, East Antarctica) are similar in the age (117–110 Ma) and geochemistry to the ultrapotassic alkali basalts of eastern India (Jharia and Raniganj intrusions). Alkaline magmatism in India and Antarctica is related to the activity of the Kerguelen plume, which significantly affected the evolution of the entire eastern Indian Ocean, in particular, determined geodynamic peculiarities of the ocean opening (existence of non-spreading blocks, fragments of the Gondwana lithosphere in oceanic areas) and geochemical characteristics of erupted tholeiitic magmas. Enriched magma sources related to the Kerguelen plume were formed by melting of ancient Gondwana-derived continental fragments, which experienced multiple transformations during its evolution up to the formation of metasomatized mantle under the impact of the Kerguelen plume on the Antarctic and India margins. 相似文献
18.
《International Geology Review》2012,54(14):1791-1805
Newly discovered basalts in the Dabure area (central Qiangtang block, northern Tibet) were subjected to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb zircon dating, geochemical analyses, and zircon Hf isotope analyses. Dating of magmatic zircons from three basalt samples indicates that the Dabure basalts formed during the late Ediacaran (~550 Ma). Xenocrystic zircons yield ages of 700–1150 Ma, providing evidence of the Cryogenian crust in the Tibet block. The Dabure basalts are alkaline, rich in Ti and Fe, and are strongly enriched in light rare earth elements without Eu anomalies. The basalts are geochemically similar to within-plate basalts but are relatively depleted in Nb and Ta. Although the analysed zircons show differences in their Hf isotope compositions, the geochemical data suggest that the Dabure basalts were derived from enriched mantle and that the source magmas were contaminated by the continental crust. The basalts may have erupted during rifting at ~550 Ma (from the dating of magmatic zircons), and may have been a product of the initial breakup of Gondwanaland. 相似文献
19.
《Russian Geology and Geophysics》2016,57(8):1119-1134
Study of Late Triassic volcanic, subvolcanic, and volcanosedimentary rocks of the Chukchi Peninsula (Vel’may terrane) has shown their different geochemical types. Basalts, dolerites, and tuffs of the lower-middle strata of the Upper Triassic section bear evidence for their formation in suprasubductional geodynamic setting. Basalts and dolerites of the upper strata of this section correspond in composition to within-plate rocks and are similar to Middle-Late Triassic oceanic-plateau basalts and dolerites. U-Pb dating of magmatic zircons from tuffs of the lower-middle strata and from dolerites of the upper strata shows the almost synchronous magmatic activity in the suprasubductional (206 ± 5 Ma) and within-plate (212 ± 4 Ma) geodynamic settings. 相似文献
20.
东巧蛇绿岩出露于班公湖-怒江缝合带中段,是蛇绿岩组合单元出露较完整的地区。微量(稀土)元素分析结果表明,蛇绿岩中的玄武岩具有轻稀土元素(LREE)显著富集的右倾稀土元素配分模式。(La/Yb)N=7.05~12.02,Th、Nb、Ta、Zr和Hf略具有正异常的微量元素组成特征,属于典型的洋岛玄武岩(OIB),与洋中脊玄武岩(MORB)和板块汇聚环境下的岛弧玄武岩(IAB)存在明显差异。通过对其构造环境的判别,并结合蛇绿岩与相邻地质体的关系分析,认为东巧蛇绿岩中的玄武岩形成于大洋板内岩石圈上隆减压的洋岛环境,代表班公湖-怒江洋盆形成和发展阶段洋岛环境的大洋岩石圈残片。 相似文献