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1.
中晚元古代碧口群海相火山岩分布于扬子古板块西北缘,本文通过火山岩岩相学及微量元素研究,对该群火山岩的岩浆系列,岩浆作用以及产出地质构造环境等一系列问题进行了论述。碧口群海相火山岩由火山相细碧岩、角斑岩、石英角斑岩及次火山相的钠质辉绿岩组成,岩相学资料表明本区细碧-角斑岩系是由偏富钠的细碧岩浆直接结晶形成,可借用“海底热卤水与岩浆混染”成因模式来说明细碧岩浆成因。火山相细碧角斑岩属钙碱岩浆系列,次火山相钠质辉绿岩属拉斑玄武岩浆系列,它们与产于火山岩系中的超基性岩组成蛇绿岩套,产于岛弧环境,按都城(1975)分类属I类蛇绿岩。该蛇绿岩组合为橄榄拉斑玄武岩浆深部分异序次喷发-侵入的产物。 相似文献
2.
长江中下游地区繁昌火山盆地在早白垩世先后发育3个喷发旋回:中分村旋回、赤沙旋回和蝌蚪山旋回。其中蝌蚪山旋回下段以凝灰质粉砂岩为主,中段为玄武岩和流纹质凝灰岩互层,上段以流纹岩为主。蝌蚪山玄武岩中的辉石既存在斑晶中也存在于基质中,这两种辉石在成分上有明显的差异,从斑晶辉石的核部到边部再到基质的核部,化学成分由富镁向富铁演化,显示出拉斑玄武岩系列的特点,辉石成因的判别图解表明其寄主岩浆为板内拉斑玄武岩,但其化学成分的变化趋势又表明岩浆在结晶分异的过程中向着碱性系列演化。根据单斜辉石与熔体平衡原理计算出玄武岩形成时的温度约为1 100℃,压力约为400MPa,相应的深度约为15km,证明岩浆在地壳中有过短暂的停留,并在上地壳部位发生分离结晶作用后喷出地表快速冷凝形成蝌蚪山玄武岩。 相似文献
3.
南秦岭碧口群海相火山岩岩石学研究 总被引：2，自引：0，他引：2
中晚元古代碧口群海相火山岩分布于扬子古板块西北缘,本文通过火山岩岩相学及微量元素研究,对该群火山岩的岩浆系列,岩浆作用以及产出地质构造环境等一系列问题进行了论述。碧口群海相火山岩由火山相细碧岩、角斑岩、石英角斑岩及次火山相的钠质辉绿岩组成,岩相学资料表明本区细碧-角斑岩系是由偏富钠的细碧岩浆直接结晶形成,可借用“海底热卤水与岩浆混染”成因模式来说明细碧岩浆成因。火山相细碧角斑岩属钙碱岩浆系列,次火山相钠质辉绿岩属拉斑玄武岩浆系列,它们与产于火山岩系中的超基性岩组成蛇绿岩套,产于岛弧环境,按都城(1975)分类属I类蛇绿岩。该蛇绿岩组合为橄榄拉斑玄武岩浆深部分异序次喷发-侵入的产物。 相似文献
4.
哀牢山蛇绿岩带两种玄武岩的成因探讨 总被引：1，自引：0，他引：1
《沉积与特提斯地质》1999,(1)
哀牢山蛇绿岩带位于横断山脉南缘,东临扬子地块,西接太忠-李仙江弧火山岩带(图1),是我国乃至世界上著名的蛇绿岩带。自段新华等(1981)报道了该蛇绿岩带以来,不少学者在此做过卓有成效的工作。但目前对该蛇绿岩带中两种玄武岩即辉石玄武岩和斜长玄武岩的成因机制尚缺乏系统... 相似文献
5.
延边地区中生代火山岩的岩浆源区:来自Sr-Nd同位素和深源捕虏体(晶)的证据 总被引：6，自引：0，他引：6
延边地区中侏罗世和早白垩世火山岩中包含有较多的辉石岩捕虏体和角闪石捕虏晶,前者为普通辉石变种,其化学成分类似于中国东部新生代玄武岩中单斜辉石巨晶的成分,具有岩浆堆积成因特征;后者为韭闪石和镁质绿钠闪石变种,其成分类似于中生代晚期玄武岩中角闪二辉石岩包体里的角闪石和新生代玄武岩中的角闪石巨晶.矿物温压计算结果显示,它们形成深度介于25～37km.延边地区中生代火山岩的(87Sr/86Sr)i值介于0.704 3～0.705 0,εNd(t)值介于2.33～4.71,表明岩浆源区应是一套具有亏损性质的新增生的地幔物质.综合上述结果,可以判定延边地区中生代火山岩的原始岩浆应来源于新增生的壳幔过渡带物质的部分熔融,地壳增生事件的时间为新元古代. 相似文献
6.
长白山地区新生代火山岩主要为玄武岩类、粗面岩类和碱性流纹岩类。其中奶头山期碱性玄武岩中含有幔源的尖晶石二辉橄榄岩包体和辉石岩包体。幔源包体及不同期次火山岩的主要矿物是橄榄石、单斜辉石、斜方辉石、尖晶石、斜长石、碱性长石。不同寄主岩石中的矿物组成及其化学成分具有一定的变化，反映了岩浆分异演化的特征；矿物及火山熔岩中的包裹体成分及玻璃熔体结构的激光拉曼光谱分析结果表明，地下深处的岩浆含有较多的挥发分，岩浆上升过程中发生了强烈的出溶作用；岩浆由起源经分异演化上升到地壳浅部直至喷发，幔源的挥发分减少，而浅成或壳源的挥发分增多，特别是在岩浆喷发过程中，地下水或大气成分起了重要作用 相似文献
7.
长白山地区新生代火山岩主要为玄武岩类、粗面岩类和碱性流纹岩类。其中奶头山期碱性玄武岩中含有幔源的尖晶石二辉橄榄岩包体和辉石岩包体。幔源包体及不同期次火山岩的主要矿物是橄榄石、单斜辉石、斜方辉石、尖晶石、斜长石、碱性长石。不同寄主岩石中的矿物组成及其化学成分具有一定的变化，反映了岩浆分异演化的特征；矿物及火山熔岩中的包裹体成分及玻璃熔体结构的激光拉曼光谱分析结果表明，地下深处的岩浆含有较多的挥发分，岩浆上升过程中发生了强烈的出溶作用；岩浆由起源经分异演化上升到地壳浅部直至喷发，幔源的挥发分减少，而浅成或壳源的挥发分增多，特别是在岩浆喷发过程中，地下水或大气成分起了重要作用。 相似文献
8.
洪古勒楞蛇绿岩层序出露较齐全,在岩石中保存了比较新鲜的造岩矿物。本文以电子探针分析数据为基础,讨论了其中辉石的化学成分特征,证明辉石化学成分受寄主岩石类型的制约:但在同一寄主岩石中,单斜辉石比斜方辉石富含较多的TiO_2、MnO和Cr_2O_3。统计分析表明,从蛇绿岩的底部到顶部,二种辉石的化学成分有相同的变化趋势:从富Cr_2O→MgO→Na_2O、K_2O→NiO→FeO→TiO_2、MnO。根据辉石的化学成分特征提出堆积岩可能为岩浆堆积成因的观点。 相似文献
9.
《矿物岩石地球化学通报》2018,(6)
本文通过研究峨眉山大火成岩省白马层状岩体和二滩高钛玄武岩中单斜辉石的主量和微量元素组成,反演与单斜辉石平衡的熔体成分,以查明层状岩体和高钛玄武岩之间的成因联系。结果显示,不同岩石中单斜辉石的稀土配分型式基本相似,在微量元素配分图解中均表现出Sr、Zr、Hf、Ti、Zn、Co和Ni负异常。二滩高钛玄武岩中单斜辉石斑晶环带核部的成分与高钛苦橄岩中单斜辉石斑晶的成分类似。模拟结果显示,白马岩体中与单斜辉石平衡的熔体成分与峨眉山高钛玄武岩成分类似,单斜辉石的Zr-Hf负异常与Zr和Hf在单斜辉石和熔体之间的分配系数较低有关。因此,高钛玄武岩和白马岩体分别代表深部岩浆房高钛苦橄质岩浆经分离结晶作用产生的高钛玄武质岩浆的喷出和侵入产物。 相似文献
10.
弗林弗隆变质火山岩带中的火山成因块状硫化物矿床，产在包括岛弧拉班玄武岩以及撤榄玄粗岩组合的早元古代岛弧环境中。在马尼托巴的弗林弗隆镇附近，这些火山岩组合在构造上并置于一个构造单元中。弗林弗隆地区几乎所有的火山成因块状硫化物矿床与岛弧拉斑玄武岩组合伴生，共产在代表火山构造和前岩浆弧中火山内盆地的复杂地层层序内。弗林弗隆带的背弧或洋底玄武岩仅赋存有小量的小型富铜块状硫化物矿床。在岛弧拉斑玄武岩组合内，火山成因块状硫化物矿床产在长奖质火山岩单位的组合内，即产在火山岩带的主要地层和成分的突变处。这些突变… 相似文献
11.
辽东地区早元古代火山岩特征及其形成的动力学背景 总被引：3，自引：0，他引：3
辽东地区早元古代火山岩是下元古界辽河群地层的重要组成部分,它们由酸性和基性两套火山岩组成。前者形成于辽河裂谷发育早期的拉张裂陷阶段,属于壳源岩浆成因;后者形成于辽河裂谷发育中晚期的强烈拉张裂陷阶段,属于幔源岩浆成因。重点讨论了基性火山岩的岩石学、矿物学、岩石化学和地球化学特征,结果表明,这些基性火山岩主要为一套海底喷发的基性枕状熔岩,具有大陆拉斑玄武岩和大洋拉斑玄武岩的双重特征,是辽河裂谷由大陆壳向大洋壳演化过程中的产物。火山岩形成的动力学背景与早元古代时期热地幔对流形式的出现以及郯-庐断裂带发生右旋平移剪切活动密切相关。 相似文献
12.
元古代蛇绿岩及铬铁矿 总被引：2，自引：1，他引：1
本文总结了国外典型元古代蛇绿岩的岩石组合、野外产状、地球化学资料以及成矿特征,并与显生宙蛇绿岩进行了对比,继而探讨元古代板块构造演化和铬铁矿成因。资料表明,早元古代和中-新元古代均有蛇绿岩的存在,但前者较少,仅见于Canadian地盾的Cape Smith Belt中的Prutuniq蛇绿岩(2. 05～2. 0Ga)和芬兰Fennoscandian地盾的Outokumpu和Jormua蛇绿岩(时代为1. 97～1. 96Ga),而中-新元古代的蛇绿岩则见于世界许多地区,如埃及东部沙漠区(～750Ma)和非洲东北部地区(ca.900～800Ma)等。与显生宙蛇绿岩相比,这些老蛇绿岩具如下特征:(1)它们均为被肢解的蛇绿岩,大多与"弧火山岩"和(或)混杂岩伴生,经历不同程度的变形和变质(具绿片岩相-角闪岩相组合);(2)岩石组合大多较齐全,壳层组合发育,以镁铁-超镁铁岩(堆晶岩)、辉长岩、镁铁质席状岩床(墙)杂岩、火山岩为代表;层状镁铁-超镁铁岩的韵律层以及矿物的隐晶变化等均提示了岩浆多期次活动及开放岩浆房的特征;(3)元古代蛇绿岩中既有高铝型铬铁矿,也有高铬型铬铁矿,且主要寄主于纯橄岩(或蛇纹岩)中;高铝型和高铬型直接受控于熔体的熔融程度及含水流体的参与,反映了铬铁矿形成于俯冲带演化的不同阶段;铬铁矿规模均较小,且均以低TiO 2为特征,均为岩浆分异作用的产物,明显区别于显生宙熔融残余成因的豆荚状铬铁矿;(4)元古代蛇绿岩常伴有硫化物Cu-Co-Zn-Au矿,且铬铁矿含Zn较高(Zn=0. 11%～0. 18%)(如芬兰Outokumpu蛇绿岩);橄榄岩及铬铁矿中常含较高的MnO (高达1. 79%,如埃及东部的Wizer蛇绿岩);(5)元古代蛇绿岩具多种成因:主要为俯冲带成因(如埃及蛇绿岩、北东非蛇绿岩、芬兰Outokumpu蛇绿岩),少量为洋中脊成因(加拿大Purtuniq蛇绿岩)及裂谷成因(芬兰Jormua蛇绿岩)等。 相似文献
13.
Nicholas Arndt 《地学前缘(英文版)》2013,4(2):195-198
Massif anorthosites form when basaltic magma differentiates in crustal magma chambers to form low-density plagioclase and a residual liquid whose density was greater than that of enclosing crustal rocks. The plagioclase and minor pyroxene crystallized in-situ on the floor of the magma chamber to produce the anorthosite complex, and the residual liquid migrated downwards, eventually to solidify as dense Fe-rich cumulates some of which were removed to the mantle. These movements were facilitated by high temperatures in Proterozoic continental crust, thus explaining the restriction of large anorthosite massifs to this period in Earth history. 相似文献
14.
On the western and southern margins of the sickle shaped Vindhyan basin of north Indian shield, there are basal Vindhyan mafic volcanic rocks referred to as Khairmalia volcanics and Jungel volcanics respectively. These volcanics vary in composition from low-Ti tholeiite to high-Ti alkali basalt showing close affinity with continental flood basalts (CFB) and ocean island basalts (OIB) respectively. The parental magmas of Khairmalia and Jungel alkali basalts were formed by different degrees of partial melting of a garnet lherzolite. The magma of Khairmalia tholeiites was generated by a relatively higher degrees of partial melting of a garnet + spinel lherzolite. The geochemical data coupled with available geological and geophysical data favour a rift type origin of this basin which evolved as a peripheral basin showing many similarities with Paleogene Himalayan foreland basin. The existing radiometric age data suggest that the origin of Vindhyan basin is linked with Aravalli–Satpura orogeny. At about 1800–1600 Ma collision occurred along the Aravalli-Delhi fold belt (ADFB) and Central Indian Tectonic Zone (CITZ) with west and south subduction respectively. During this process the subducting lithosphere suffered extensional deformation on its convex side and some pre-existing large faults in the already thin leading edge of subducted plate also reactivated and tapped magma generated by decompressional melting of the subcontinental mantle. The simultaneous processes such as flexural subsidence, reactivation of pre-existing faults, heating, thermal cooling and contraction during volcanism, resulted in the formation of curvilinear warp parallel to the emerging mountain front. The Lower Vindhyan volcano–sedimentary succession was deformed and exposed to erosion before the deposition of Upper Vindhyan rocks. The orogenic forces were active intermittently throughout the Vindhyan sedimentation. 相似文献
15.
The very low-grade metamorphic sequence of volcano-sedimentary rocks, sandwiched between the platform sediments of the Vindhyan Supergroup to the east and the Banded Gneissic Complex (BGC) to the west, in the eastern fringe of the Aravalli-Delhi orogenic belt, has remained a stratigraphic enigma in the Precambrian geology of Rajasthan. This sequence known earlier as the Gwalior ‘series’ and in contemporary literature as the Hindoli Group, has been considered by several workers as a Proterozoic supracrustal unit and by some others, as an Archean secondary greenstone belt, based purely on geological considerations. U-Pb zircon geochronology was conducted to find an answer to this controversy on samples of felsic volcanics, conformably intercalated with the Hindoli sediments and hence, considered contemporaneous with them. Zircons from a sample of massive rhyodacite gave a concordia age of 1854k7 Ma though zircons from a sample of felsic tuff gave a wide range of ages between 3259-1877 Ma. Careful consideration of the nature of the samples and their constituent zircons suggests that the Hindoli Group rocks represent a low-grade Proterozoic supracrustal cover sequence in the eastern part of the Bhilwara belt, broadly synchronous to the Aravalli-Bhilwara sedimentation around 1.8 Ga. 相似文献
16.
《Gondwana Research》2001,4(3):509-518
The Proterozoic Bandal mafic rocks, exposed in Kullu-Rampur window, Lesser Himalaya, Himachal Pradesh, indicate two distinct (high-Ti and low-Ti) magma types. The high-Ti basalts are characterised by high-TiO2 (> 2 wt%), Ti/Y, Ti/Zr, TiO2/K2O and low Rb/Sr ratios. They are enriched in high field strength (HFS) elements (Nb, Zr, Ti) relative to low field strength (LFS) incompatible elements (K, Rb). The low-Ti basalts are charactersied by low TiO2 (< 2 wt%), Ti/Y, Ti/Zr and high Rb/Sr and Rb/Ba ratios. Quartz-normative composition, continental tholeiite characteristics with Nb/La less than 1 are some of the common factors of the two groups of the Bandal mafic rocks. The trace element concentrations and their ratios of the two groups of the basalts indicate that they have been derived from the asthenosphere at different depths, low-Ti at shallow and high-Ti at deeper levels. Some of the chemical features like low Mg #, Cr, Ni, high incompatible element concentrations (especially Ba), light rare earth element (LREE) enriched patterns point towards assimilation and fractional crystallisation (AFC) process which may have played a significant role in the generation of these basalts.Furthermore, the Bandal mafic rocks, apart from field settings, are geochemically similar to other Proterozoic mafic bodies like the Rampur volcanics, Mandi-Darla volcanics, Garhwal volcanics and Bhimtal-Bhowlai volcanics of the Lesser Himalaya. This widespread Proterozoic continental tholeiitic magmatism over an area of 170,000 km2 in the Lesser Himalaya provides an evidence of plume activity in the region. 相似文献
17.
Tectonic Development of the Proterozoic Continental Margins in East Qinling and Adjacent Regions 总被引：2，自引：0，他引：2
Wang Hongzhen 《中国地质大学学报(英文版)》1990,(1)
The East Qinling and adjacent cratonic regions belong to two geotectonicunits,the Sinokorean Subdomain including the Sinokorean Platform and itssouthern continental margin the North Qinling Belt,and the YangtzeanSubdomain comprising the Yangtze Platform and its northern continental mar-gin the South Qinling Belt.The Qinling region may thus be subdivided into twocontinental margin belts separated from each other by the Proterozoic Qinlingmarine realm,which did not disappear until Late Triassic.The convergentcrustal consumption zone,the megasuture between the two belts,lies betweenthe Fengxian-Shangnan line in the north and the Shanyang-Xijia line in thesouth and was much deformed and displaced through Mesozoic intracratoniccollision and compression.In the northern subdomain the Lower Proterozoic is representedby protoaulacogen volcano-sediments,the inner Tiedonggou Group and theouter marginal Qinling Group,which were folded and metamorphosed in theLuliangian orogeny,a general process of aggregation and s 相似文献
18.
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
19.
Abstract Two unconformity‐bound groups of volcanic rocks and associated sediments (El Sherana and Edith River Groups) separate the older Pine Creek Geosyncline metasediments from platform cover of the McArthur Basin. Dominated by intersecting NW and ENE rift systems, the volcanics are genetically related to an extensional tectonic system which was also active during deposition of the Pine Creek Geosyncline sequence. In contrast, the younger platform cover was deposited in a relatively stable environment. The rift valleys were filled with rhyolite flows, ignimbrite and ill‐sorted arenite and rudite, and flyschoid sediments spread onto adjacent lands. Following tight upright folding, granite intrusion and erosion, an extensive ignimbrite sheet (=6000 km2) spread from a centre probably at the intercept of the two rifts. Microgranite at this intersection was possibly emplaced in the evacuated magma chamber. The volcanic sequences were deeply eroded and weathered before platform cover deposition began. The platform sediments, represented in the area by the Kombolgie Formation, were deposited from about 1690 Ma to 1650 Ma, and their base is taken as the closest stratigraphic indicator of the boundary between the Early and Middle Proterozoic. 相似文献
20.
The Parnell Quartz Monzonite in the Pilbara Block of Western Australia is a Proterozoic (1731 ± 14 Ma) pluton characterized by high modal K‐feldspar and a greater abundance of hornblende relative to biotite, as is typical of Phanerozoic monzonitic rocks in eastern Australia. The only geochemical features reflecting its setting in an Archaean terrain are high Na2O, Ni and Cr. The pluton is zoned, with an increase in K‐feldspar, quartz and biotite and a decrease in plagioclase and hornblende from margin to core. Chemically, this zoning is reflected by systematic variation of CaO, K2O, Na2O, Sr and Rb, but ferromagnesian elements have irregular trends, implying preferential extraction of feldspars relative to mafic minerals during differentiation of the magma. The unusual geochemical trends are explained by a model involving ‘in situ’ feldspar fractionation of a K‐rich residual liquid from a mafic crystalline mush. A parent magma similar to the average rock composition of the pluton is deduced because high ferromagnesian trace element abundances preclude extensive fractionation of mafic minerals. Geochemical and isotopic constraints suggest that the ultimate source was chemically similar to a shoshonitic basaltic andesite, that must have been emplaced beneath the eastern margin of the Pilbara Block in the Early Proterozoic. Subsequent partial melting of this postulated underplated source at ～ 1700 Ma to produce the Parnell Quartz Monzonite was probably associated with tectonism in the Gregory Range Complex. 相似文献