共查询到20条相似文献，搜索用时 156 毫秒
1.
M. A. Mishkin A. M. Lennikov G. M. Vovna Z. G. Badredinov R. A. Oktyabr’skii 《Geochemistry International》2007,45(6):546-560
The bottom of the stratigraphic sequence of the Dzhugdzhur deep-seated granulite complex was determined to consist of a stratified metabasite-enderbite association. The distributions of major and trace elements indicate that the protoliths of the association were volcanic rocks of the calc-alkaline, komatiite-tholeiite, and picrite series. The model assumed for the genesis of the protolithic volcanics of the metabasite-enderbite association includes two stages. The first of them was responsible for the decompression-induced partial melting of the material of an ascending mantle plume with the derivation of melts of the komatiite-tholeiite series. During the second stage, the volcanics of the calc-alkaline series were produced by the partial melting of the metabasite crust under the effect of the heat of the ascending mantle plume. The protoliths of the metabasite-enderbite association were formed in the Early Proterozoic. 相似文献
2.
The Kholodnikan Complex consists of two units: lower volcanic and upper volcanic-sedimentary. The distributions of major and
trace elements suggest that the protoliths of the lower unit were volcanics of the komatiite-tholeiite series (komatiite-basalt
association) and those of the upper unit were volcanics of the calc-alkaline series (andesite-dacite-rhyolite association).
The model assumed for the genesis of these associations involves two stages: (1) decompression-induced partial melting of
the material of an ascending mantle plume with the derivation of melts of the komatiite-basalt association and (2) derivation
of volcanic rocks of the andesite-dacite-rhyolite association via the partial melting of various rocks in the basement of
the Aldan Shield under the effect of the heat of the ascending mantle plume. The magmatic protoliths of the Kholodnikan Complex
were formed in the Paleoproterozoic at 2.41 Ga. 相似文献
3.
Early Archean sialic crust of the Siberian craton: Its composition and origin of magmatic protoliths
This study demonstrates that the base of the Archean deep-seated granulite complexes within the Siberian craton consists of
a metabasite-enderbite association. The major and trace element distribution patterns revealed that the protoliths of this
association are represented by calc-alkaline andesites and dacites, containing several minor sequences of komatiitic-tholeiitic
volcanic rocks. The origin of the primary volcanic rocks of the metabasite-enderbite association is inferred on the basis
of a model of mantle plume magmatism, which postulates that both andesitic and dacitic melts were derived from the primary
basitic crust at the expense of heat generated by ascending mantle plumes. The formation of the protoliths of the Archen metabasite-enderbite
association of the Siberian craton began at 3.4 Ga and continued until the late Archean. 相似文献
4.
A.P. Berzina V.O. Gimon I.V. Nikolaeva S.V. Palesskii A.V. Travin 《Russian Geology and Geophysics》2009,50(10):827-841
The Erdenetiyn-Ovoo magmatic center (EMC) with a porphyry Cu-Mo deposit includes the following intrusive complexes: Selenga, Shivota, ore-bearing porphyry, and post-ore dike. The EMC formed at 260–200 Ma. The geologic evolution of northern Mongolia in that period was much determined by the effect of a mantle plume, which showed two periods of activity: Late Paleozoic and Early Mesozoic. The long multistage evolution of the EMC was due to its localization on the periphery of the Late Paleozoic and Early Mesozoic areas of the plume’s influence. The Shivota and post-ore basites are considered to be comagmatic to the Late Permian–Early Triassic trachyandesite-basalt and Late Triassic–Early Jurassic trachyandesite series, respectively, which are similar to the products of Late Paleozoic and Early Mesozoic within-plate magmatism in northern Mongolia. The Selenga complex, which formed before the Shivota one, and the porphyry complex, which formed before the post-ore dike one, are differentiated gabbro-granite series. Gabbro-granitoid magmatism was initiated by the melting of rocks of continental lithosphere under the action of a plume. Later on, as the plume ascended to the surface and the lithosphere became thinner, the conditions were created favoring the lithosphere breakthrough and within-plate basaltoid magmatism.In geochemical features (high contents of LILE and LREE, low contents of HFSE and HREE) the studied basites are similar to the products of subduction magmatism. But this contradicts the geologic position of basites formed after the completion of subduction during the transition of the region to the rifting stage and during the rifting. The mantle metasomatized during the preceding subduction is regarded as the main source of basites. The high contents of alkalies and LREE in the volcanics of the post-ore dike complex and the REE patterns similar to the OIB ones evidence the influence of the plume on the magma formation. The high contents of incompatible trace elements and the Nd isotope composition corresponding to the weakly depleted mantle do not exclude a possible plume effect during the formation of the Selenga complex gabbroids. The geochemical features of the Shivota gabbros, comagmatic to volcanics produced during the Late Paleozoic within-plate activity, are partly transformed during the melt evolution in crustal chambers.The REE patterns of the EMC basites evidence that the evolution of ascending magma was accompanied by the fractionation of amphibole. During this process, ore elements were redistributed into mineral and concentrated in amphibole-containing rocks, from which metals were later mobilized by late melts and fluids. The evolution of basaltoid magmatism of the Selenga, Shivota, and porphyry complexes is regarded as a preliminary stage of ore formation, which was considerably responsible for the EMC productivity. 相似文献
5.
杭州河上地区是浙西北上元古界上墅组火山岩发育的典型地区,同时还发育新元古代辉绿岩和碱长花岗岩板状复合浅成侵入体。火山岩与侵入岩在空间上密切共生,形成时间相近,皆为晋宁晚期构造岩浆活动的产物。火山喷发并伴随的岩浆侵入经历了两个阶段,每个阶段的火山岩与侵入岩在岩石类型、岩石化学和地球化学方面具有相似性或一致性,稀土元素分布型式基本一致,说明每个阶段的火山岩与侵入岩来源于同一岩浆源,均是同源岩浆活动的产物。第一阶段上墅组基性火山岩与次坞辉绿岩体起源于亏损程度较低的地幔,或来源于亏损地幔的岩浆受到陆壳物质的混染;第二阶段上墅组酸性火山岩与道林山碱长花岗岩体可能起源于地壳中既含有基性地壳组分和又含有酸性地壳组分的源区的部分熔融。 相似文献
6.
T.V. Donskaya D.P. Gladkochub A.M. Mazukabzov B. De Waele S.L. Presnyakov 《Russian Geology and Geophysics》2012,53(1):22-36
The Kataev volcanoplutonic association has been recognized in western Transbaikalia. It unites the volcanosedimentary rocks of the Kataev Formation and associated granites localized within the lower plates of the Buteel-Nuur and Zagan metamorphic-core complexes. The rocks of the Kataev association are dynamometamorphosed to different degrees, which is due to the tectonic exposure of metamorphic-core complexes in the Early Cretaceous. The U-Pb zircon dating of the Kataev Formation rhyolites yielded an age of 226 ± 3 Ma. The U-Pb zircon age of the granites intruding the Kataev Formation rocks is 223.4 ± 5.0 Ma. The volcanics of the Kataev Formation belong to the subalkalic basalt-andesite-dacite-rhyolite series. The trachybasalts and trachyandesite-basalts of the Kataev Formation have geochemical characteristics of igneous rocks formed as a result of subduction, e.g., they show distinct negative Nb and Ti and positive Ba and Sr anomalies on multielemental patterns. The specific composition of mafic volcanics points to their formation through the melting of a mantle source resulted from the mixing of depleted mantle and subduction components. Trachyandesites have higher Th and U contents than basaltoids. They can result from the contamination of a mantle source, similar in composition to the Kataev Formation basaltoids, with crustal material. The felsic volcanics of the Kataev Formation and granites intruding them show nearly identical geochemical characteristics corresponding to both A-and I-type granites. These rocks might have formed through the melting of a moderately water-saturated magmatic source of diorite-tonalite composition at 742–833°C. We have established that the rocks of the Kataev volcanoplutonic association in western Transbaikalia and Northern Mongolia formed in the Late Triassic synchronously with the calc-alkaline granitoids of the Henteyn–Daurian batholith and the alkali granites and bimodal volcanic associations of the Kharitonovo and Tsagaan-Hurtey volcanoplutonic associations. The synchronous formation of volcanoplutonic associations of normal and high alkalinity agrees with the geodynamic setting of the Andean-type active continental margin existing in the area of present-day western Transbaikalia and Northern Mongolia in the Early Mesozoic. This setting was the result of the subduction of the Mongol-Okhotsk oceanic plate beneath the Siberian continent. 相似文献
7.
华南大陆构造与铀矿省 总被引：4，自引：3，他引：4
华南前震旦纪基底由江南、武夷、云开－南海和闽台等４个地块组成，它们自晚元古代起处在同一岩石图板块范围内。铅同位素研究揭示，该板块富铀、钍，从而为铀矿省的形成提供了必不可少的地质前提。元古代、加里东、印支和燕山等造山事件导致４个板块的融合及其最终与扬子克拉通连成一体，但运动发生在莫霍流变层垫托之上，属板内构造范畴；晚震旦一早寒武世、晚古生代含铀黑色岩系及中生代容矿花岗岩、火山岩分别产生在相应时代主造山隆起带的前陆地区。继三叠纪－早侏罗世地壳显著增厚和花岗岩基大规模侵位之后，构造体制从挤压松弛往侧向伸展方向发展，其间中始新世至渐新世发生过局部性挤压，但伸展仍居主导地位，绝大多数铀矿床正形成于这一准克拉通化过程中，即晚侏罗世至第三纪。华南地学断面显示，在福建大田、泉州一带壳下岩石圈出现薄化裂离而在湘中一带壳下岩石圈则呈现为漏斗状凹陷。据分析，前者起因于热地幔柱上涌，并可能是太平洋超级热幔柱的组成部分；后者则为冷地幔柱下降所在位置，处于亚洲超级冷幔柱范围内。文中突出强调花岗岩一火山区是寻找富大铀矿的主要目标区，后火山侵入体（富挥发份花岗质小岩体或斑岩体）控制富铀矿生成。 相似文献
8.
This paper addresses the composition, geochemistry, isotopic characteristics, and age of rocks from the Carter Seamount of
the Grimaldi seamount group at the eastern margin of the Central Atlantic. The age of the seamount was estimated as 57–58
Ma. Together with other seamounts of the Grimaldi system and the Nadir Seamount, it forms a “hot line” related to the Guinea
Fracture Zone, which was formed during the late Paleocene pulse of volcanism. The Carter Seamount is made up of olivine melilitites,
ankaramites, and analcime-bearing nepheline tephrites, which are differentiated products of the fractional crystallization
of melts similar to an alkaline ultramafic magma. The volcanics contain xenoliths entrained by melt at different depths from
the mantle, layer 3 of the oceanic crust, which was formed at 113–115 Ma, and earlier magma chambers. The rocks were altered
by low-temperature hydrothermal solutions. The parental melts of the volcanics of the Carter Seamount were derived at very
low degrees of mantle melting in the stability field of garnet lherzolite at depths of no less than 105 km. Anomalously high
Th, Nb, Ta, and La contents in the volcanics indicate that a metasomatized mantle reservoir contributed to the formation of
their primary melts. The Sr, Pb, and Nd isotopic systematics of the rocks show that the composition of the mantle source lies
on the mixing line between two mantle components. One of them is a mixture of prevailing HIMU and the depleted mantle, and
the other is an enriched EM2-type mantle reservoir. These data suggest that the formation of the Carter Seamount volcanics
was caused by extension-related decompression melting in the Guinea Fracture Zone of either (1) hot mantle plume material
(HIMU component) affected by carbonate metasomatism or (2) carbonated basic enclaves (eclogites) ubiquitous in the asthenosphere,
whose isotopic characteristics corresponded to the HIMU and EM2 components. In the former case, it is assumed that the melt
assimilated during ascent the material of the metasomatized subcontinental mantle (EM2 component), which was incorporated
into the oceanic lithospheric mantle during rifting and the breakup of Pangea. 相似文献
9.
华北古陆的形成与构造演化史 总被引：1，自引：0，他引：1
以华北古陆为例，论述了地球演化史中经历的三大阶段：（１）古陆的形成阶段（４６００～１８００Ｍａ）：地球形成早期，以地幔对流为主导作用，到早太古宙出现初始古陆核，地幔对流驱动的地体拼贴和板底垫托是陆壳形成的主要方式；中太古宙开始出现一定规模的坳陷盆地，发育了基性火山岩 碎屑岩 镁质碳酸盐岩等表壳岩，同时伴随着大量中基性、花岗质岩浆活动；晚太古宙和早元古宙是陆壳形成的主要时期，并已具现今板块活动特征。地幔热柱与板块构造共同控制着地壳运动。（２）古陆稳定发展阶段（１８００～２５０Ｍａ）：地幔热柱活动较弱，古陆主要表现为缓慢的升降运动（造陆运动）。（３）地球新活动时期（２５０Ｍａ至今）：地幔热柱活动进入一个新的活跃时期。岩石圈发生明显的热减薄，地幔热柱表现为多级演化，并导致盆岭系的形成。 相似文献
10.
大陆弧安山岩的形成是大洋板片向大陆边缘之下俯冲的结果,但是在具体形成机制上存在很大争议.针对这个问题,对长江中下游地区中生代安山质火山岩及其伴生的玄武质和英安质火山岩进行了系统的岩石地球化学研究,结果对大陆弧安山质火成岩的成因提出了新的机制.分析表明,这些岩石形成于早白垩世,它们不仅表现出典型的岛弧型微量元素分布特征,而且具有高度富集的Sr-Nd-Hf同位素和高的放射成因Pb以及高的氧同位素组成.通过全岩和矿物地球化学成分变化检查发现,地壳混染和岩浆混合作用对其成分的富集特征贡献有限,而其岩浆源区含有丰富的俯冲地壳衍生物质才是其成分富集的根本原因.虽然这些火山岩的喷发年龄为中生代,但是其岩浆源区形成于新元古代早期的华夏洋壳俯冲对扬子克拉通边缘之下地幔楔的交代作用.大陆弧安山岩地幔源区中含有大量俯冲洋壳沉积物部分熔融产生的含水熔体,显著区别于大洋弧玄武岩的地幔源区,其中只含有少量俯冲洋壳来源的富水溶液和含水熔体.正是这些含水熔体交代上覆地幔楔橄榄岩,形成了不同程度富集的超镁铁质-镁铁质地幔源区.在早白垩纪时期,古太平洋俯冲过程的远弧后拉张导致中国东部岩石圈发生部分熔融,其中超镁铁质地幔源区熔融形成玄武质火山岩,镁铁质地幔源区则熔融形成安山质火山岩.因此,大陆弧安山岩成因与大洋弧玄武岩一样,可分为源区形成和源区熔融两个阶段,其中第一阶段对应于俯冲带壳幔相互作用. 相似文献
11.
JIANG Changyi BAI Kaiyin HI Aizhi ZHAO Xiaoning ZHANG Hongbo Xi抋n Engineering College Xi抋n China 《Continental Dynamics》2001,(1)
1. Geological setting The terrane of Kuruktag lies in the north-eastern margin of the Tarim Basin and is a faulted marginal uplift of the basin. In the terrane, there occur extensively Dagelagebulake Group and Xinditage Group of Archaean-Paleoprotozoic metamorphic sequences overlain by Sinian-Cambrian sequences (Geological and mineral bureau of Xingjiang ulger atonomous region, 1993). The sedimentology of the Sinian-Cambrian strata have been studied (South Xinjiang petrollum exploratio… 相似文献
12.
The Archean greenstone belts of the Nyanzian System in western Kenya are composed principally of andesite with minor tholeiitic basalt and siliceous volcanics. The Nyanzian tholeiite is an intermediate-K tholeiite with a flat REE pattern. There are two chemically-distinct andesites: a low-K andesite (Andesite I) and a high-K andesite (Andesite II). The REE pattern of the Andesite II is enriched in light REE and depleted in heavy REE relative to Andesite I.Major and trace element calculations indicate an origin for the Nyanzian tholeiite by 35–40% equilibrium melting of a lherzolite source followed by 10% shallow fractional crystallization. Similar calculations best explain Andesite I and Andesite II by 20 and 5% melting, respectively, of an ecologite or garnet amphibolite source of Nyanzian tholeiite composition. The rhyolite may have formed either by 20–30% partial melting of a siliceous granulite or by 20–30% fractional crystallization of a granodiorite parent magma.With respect to total exposure areas, the Nyanzian volcanics have significantly less tholeiite and more Andesite and siliceous volcanics than other Archean greenstone belts. If these abundances are representative, two models are proposed to explain the anomalous abundances of Andesite and siliceous volcanics. The first model involves an Archaen upper mantle with a relatively low geothermal gradient beneath Kenya, while the second model involves a relatively cool mantle plume. Both models inhibit ascent of a significant amount of primary tholeiite to the surface and prevent formation of secondary tholeiite. Other Archean greenstone terranes with higher mantle geotherms or hotter mantle plumes would receive higher proportions of mafic and ultramafic magmas. 相似文献
13.
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
14.
Khromykh S. V. Semenova D. V. Kotler P. D. Gurova A. V. Mikheev E. I. Perfilova A. A. 《Geotectonics》2020,54(4):510-528
Studies of volcanic rocks in orogenic troughs of Eastern Kazakhstan were carried out. The troughs were formed at late-orogenic stages of evolution of Hercynian Altai collision system. Volcanic rocks are represented by basalts, andesites, dacites and rhyolites. Based on geochemical and isotopic data, the basalts and andesites derived from mafic magmas that formed as a result of partial melting of garnet peridotites in the upper mantle under the orogen. U–Pb zircon data prove two volcanic stages: more-scaled Middle Carboniferous (~311 Ma) and less-scaled Early Permian (297–290 Ma). Basalts and andesites in lower parts of the orogenic troughs and independent dacite-rhyolite structures were formed at the Middle Carboniferous stage. Parental mafic magmas were formed as a result of partial melting of mantle substrates in local transtensional zones along large shear faults. The formation of dacites and rhyolites could have been caused by partial melting of crustal substrates under effect of mafic magmas. Transtensional movements in the lithosphere of orogenic belts may indicate the beginning of collapse of orogens. A smaller volume of basalts and andesites formed at the Early Permian stage. Geochemical data prove the independent episode of partial melting in upper mantle. Synchronous basalts and andesites also appeared at wide territory in Tian Shan, Central Kazakhstan, and Central and Southern Mongolia. Early Permian volcanism indicates general extension of the lithosphere at the postorogenic stages. Large-scaled Early Permian mafic and granitoid magmatism in Central Asia has been interpreted in recent years as the Tarim Large Igneous Province caused by Tarim mantle plume activity. Thus, the extension of the lithosphere and associated volcanism in the Early Permian can be an indicator of the onset of the plume–lithosphere interaction process.
相似文献15.
Nickolay L. Dobretsov Alexey A. Kirdyashkin Anatoliy G. Kirdyashkin Valery A. Vernikovsky Igor N. Gladkov 《Lithos》2008,100(1-4):66-92
Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t1 between plume formation and eruption. These relationships are used to determine thermal power and time t1 for the Tunguska syneclise and the Siberian traps as a whole.
The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts. 相似文献
16.
桂北元宝山宝坛地区约825Ma镁铁-超镁铁岩的地球化学及其地质意义 总被引：13，自引：0，他引：13
镁铁－超镁铁岩的岩石学和地球化学特征表明，元宝山超镁铁岩中橄榄石的Fo为78－83，岩石具有明显的包橄结构，具有LREE亏损，低Th/Nb和La/Nb比值以及高（t)值（约＋5），是来源于亏损地幔低程度部分熔融的岩浆堆晶的产物；宝坛地区镁铁－超镁铁岩富集LREE，具有高的Th/Nb,La/Nb比值和低的（t)值（－0．45－7．01），是镁铁质岩浆上升，结晶过程中与地壳物质混染（AFC）的结果，超镁铁岩与澳大利亚Garidner岩脉群具有相似的不相容元素分布型式和Nd(t) 值，是导致新元古代Rodinia超大陆裂解的地幔柱熔融的产物。 相似文献
17.
Mihir K. Bose 《Journal of the Geological Society of India》2009,73(1):13-35
The Singhbhum craton has a chequred history of mafic magmatism spanning from early Archaean to Proterozoic. However, lack
of adequate isotopic age data put constraints on accurately establishing the history of spatial growth of the craton in which
mafic magmatism played a very significant role. Mafic magmatism in the craton spreads from ca.3.3 Ga (oldest “enclaves” of
orthoamphibolites) to about 0.1 Ga (‘Newer dolerite’ dyke swarms). Nearly contemporaneous amphibolite and intimately associated
tonalitic orthogneiss may represent Archaean bimodal magmatism. The metabasic enclaves are appreciably enriched and do not
fulfill the geochemical characteristics of worldwide known early Archaean (>3.0 Ga) mafic magmatism. The enclaves reveal compositional
spectrum from siliceous high-magnesian basalt (SHMB) to andesite. However, the occurrence of minor depleted boninitic type
within the assemblage has so far been overlooked. High magnesian basalt with boninitic character of Mesoarchaean age is also
reported in association with supracrustals from southern fringe of the granitoid cratonic nucleus. The subcontinental lithospheric
mantle (SCLM) below the craton is conjectured to have initiated during the early Archaean. Significantly, recurrence of depleted
magma types in the craton is observed during the whole span of mafic igneous activity which has been vaguely related to “mantle
heterogeneity”, although the alternative model of sequential mantle melting is also being explored.
The Singhbhum craton includes the Banded Iron Formation (BIF) associated mafic lavas, MORB-like basic and komatiitic ultrabasic
bimodal volcanism — documented as Dalma volcanics, Dhanjori lavas, and the Proterozoic Newer dolerite dykes. Three different
types of REE fractionation patterns are observed in the BIF-associated mafic lavas. These are the REE unfractionated type
is more depleted than N-MORB and some lavas with boninitic type of REE distribution. MORB-like basic and komatiitic ultrabasic
(Dalma volcanics) are emplaced within the Proterozoic Singhbhum Basin (PSB). The vista of magmatism in the basin was controlled
by a miniature spreading centre represented by the mid-basinal Dalma volcanic ridge. The volcano-sedimentary basinal domain
of Dhanjori emerged at the interface of two subprovinces (viz. the mobile volcano-sedimentary belt of PSB and rigid granite
platform) under unique stress environment related to extensional tectonic regime. Trace element distribution in Dhanjori lavas
is remarkably similar to that in PSB minor intrusions and lavas (except a Ta spike in the latter). The Proterozoic Newer dolerite
dykes within Singhbhum nucleus manifest an unusually wide spam of intrusive activity (ca 2100 Ma to 1100 Ma) and unexpectedly
uniform mantle melting behaviour. 相似文献
18.
Approximately 1650-Ma-old NW/SE and NE/SW-trending dolerite dykes in the Tiruvannamalai (TNM) area and approximately 1800-Ma-old NW/SE-trending dolerite dykes in the Dharmapuri (DP) area constitute major Proterozoic dyke swarms in the high-grade granulite region of Tamil nadu, southern India. The NW- and NE-trending TNM dykes are compositionally very similar and can be regarded as having been formed during a single magmatic episode. The DP dykes may relate to an earlier similar magmatic episode. The dolerites are Fe-rich tholeiites and most of the elemental variations can be explained in terms of fractional crystallisation. Clinopyroxene and olivine are the inferred ferromagnesian fractionation phases followed by plagioclase during the late fractionation stages. All the studied dykes have, similar to many continental flood basalts (CFB), large-ion lithophile element (LILE) and light rare-earth element (LREE) enrichment and Nb and Ta depletion. The incompatible element abundance patterns are comparable to the patterns of many other Proterozoic dykes in India and Antarctica, to the late Archaean (～2.72 Ga) Dominion volcanics in South Africa and to the early Proterozoic (～2.0 Ga) Scourie dykes of Scotland. The geochemical characteristics of the TNM and DP dykes cannot be explained by crustal contamination alone. Instead, they are consistent with derivation from an enriched lithospheric mantle source which appears to have been developed much earlier than the dyke intrusions during a major crustal building event in the Archaean. The dyke magmas may have been formed by dehydration melting induced by decompression and lithospheric attenuation or plume impingement at the base of the lithosphere. These magmas, compared with CFB, appear to be the minor partial melts from plume heads of smaller diameter and of shallow origin (650 km). Therefore, the Proterozoic thermal events could induce crustal attenuation and dyke intrusions in contrast to the extensive CFB volcanism and continental rifting generally associated with the Phanerozoic plumes of larger head diameter (>1000 km) and of deeper origin (at crust mantle boundary). 相似文献
19.
挪威中部Ｇｊｅｒｓｖｉｋ地区加里东造山带由一系列地体组成。Ｇｊｅｒｓｖｉｋ地体内的火山岩系具有明显的双峰态特征，主要由深色和浅色拉斑玄武质绿岩以及石英角斑质火山碎屑岩组成。火山活动分为三个阶段，各阶段火山活动特征与裂谷构造演化息息相关。地质和地球化学证据表明，裂谷演化早期形成来源于亏损地幔未分异型拉斑玄武岩，中期形成由玄武岩或辉长岩局部重熔产生的长英质火山岩，晚期则形成来源于更深部的富集地幔分异型拉斑玄武岩。Ｇｊｅｒｓｖｉｋ地体内已发现一系列的与火山活动有关、空间上与长英质火山碎屑岩紧密共生的块状硫化物矿床。 相似文献
20.
G. M. Vovna M. A. Mishkin A. M. Lennikov R. A. Oktyabrsky V. F. Polin Z. G. Badredinov T. A. Yasnygina 《Russian Journal of Pacific Geology》2014,8(1):56-64
Two series of volcanic rocks with different petrochemical affinities-calc-alkaline and komatiitetholeiitic series-were identified as protoliths for the Early Proterozoic metamorphic rocks of the Batomga granite-greenstone terrane. The metavolcanic rocks of the calc-alkaline series comprise metabasalts, metaandesites, metadacites, and metarhyolites. The distribution of the trace element abundances in the felsic metavolcanic rocks is similar to that of the Archean grey gneisses from the platform basements, thus suggesting a similar petrological mechanism for the formation of their protoliths. The protoliths for the komatiite-tholeiitic metavolcanic rocks include komatiite and tholeiite basalts. The chemical behavior of the tholeiites tends to support the fractionation of primary high-Mg basaltic magmas in a transient magma chamber at low pressures. The variations in the Nb, Y, and Zr contents of the metatoleiites indicate the derivation of their parental magmas from a plume-related source. 相似文献