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1.
Geochemical data indicate that the protoliths of the overwhelming majority of the metamorphic rocks composing the Fedorov Complex in the Aldan granulite megacomplex were volcanic rocks of three groups, which occur in different proportions in the complex: (i) volumetrically predominant (no less than 90%) continuous differentiated island-arc basalt-andesite-dacite-rhyolite series, (ii) within-plate basalts, whose composition was similar to that of low-Ti traps, and (iii) basalts of composition similar to that of continentalrift basalts. The U-Pb zircon crystallization age of the metamorphosed basaltic andesites of the Fedorov Complex was estimated at 2006 ± 3 Ma, which testifies, when considered together with preexisting geochronological data, that the complex was produced during a time span of no longer than 25 m.y. A model is proposed according to which the complex was produced within the geodynamic system of the active continental margin of the Olekma-Aldan continental microplate and the Fedorov island arc.  相似文献   

2.
Part II of this paper reports geochemical and Nd isotope characteristics of the volcanogenic and siliceous-terrigenous complexes of the Lake zone of the Central Asian Caledonides and associating granitoids of various ages. Geological, geochronological, geochemical, and isotopic data were synthesized with application to the problems of the sources and main mechanisms of continental crust formation and evolution for the Caledonides of the Central Asian orogenic belt. It was found that the juvenile sialic crust of the Lake zone was formed during the Vendian-Cambrian (approximately 570–490 Ma) in an environment of intraoceanic island arcs and oceanic islands from depleted mantle sources with the entrainment of sedimentary crustal materials into subduction zones and owing to the accretion processes of the amalgamation of paleoceanic and island arc complexes and Precambrian microcontinents, which terminated by ∼490 Ma. The source of primary melts for the low-Ti basalts, andesites, and dacites of the Lake zone ophiolites and island arc complexes was mainly the depleted mantle wedge above a subduction zone. In addition, an enriched plume source contributed to the genesis of the high-Ti basalts and gabbroids of oceanic plateaus. The source of terrigenous rocks associating with the volcanics was composed of materials similar in composition to the country rocks at a minor and varying role of ancient crustal materials introduced into the ocean basin owing to the erosion of Precambrian microcontinents. The sedimentary rocks of the accretionary prism were derived by the erosion of mainly juvenile island arc sources with a minor contribution of rocks of the mature continental crust. The island arc and accretion stages of the development of the Lake zone (∼540–590 Ma) were accompanied by the development of high- and low-alumina sodic granitoids through the melting at various depths of depleted mantle reservoirs (metabasites of a subducted oceanic slab and a mantle wedge) and at the base of the island arc at the subordinate role of ancient crustal rocks. The melts of the postaccretion granitoids of the Central Asian Caledonides were derived mainly from the rocks of the juvenile Caledonian crust at an increasing input of an ancient crustal component owing to the tectonic mixing of the rocks of ophiolitic and island arc complexes and microcontinents. The obtained results indicate that the Vendian-Early Paleozoic stage of the evolution of the Central Asian orogenic belt was characterized by the extensive growth of juvenile continental crust and allow us to distinguish a corresponding stage of juvenile crust formation.  相似文献   

3.
Based on structure, mineralogy, petrography, and geodynamic setting of sedimentation, Barremian(?)-Albian terrigenous rocks in the Kema terrane (Eastern Sikhote Alin) are interpreted as back-arc rocks of the Moneron-Samarga island-arc system. The composition of terrigenous rocks indicates that an ensialic volcanic island arc, the basement of which was composed of the oceanward-advancing continental crust fragment, served as the main source of clastic material. Genetic features of rocks suggest their formation in the lower zone and near the foothill of submarine slope, as well as in adjacent areas of the basin plain. Accumulation of the thick gravitational sequence in the rear zone of the island arc was accompanied by active volcanic processes.  相似文献   

4.
田原  陈灵  唐立梅  高鹏  方银霞 《地球科学》2021,46(3):840-852
俯冲带地幔演化与岩浆作用是地球各固体圈层之间发生物质和能量交换的重要地质过程.西太平洋雅浦海沟因其极短的沟-弧距离和洋脊碰撞等独特的地质构造特征成为研究复杂条件下俯冲带演化的理想场所.为了探究雅浦海沟地幔演化与岩浆作用,本文将前人对雅浦海沟火成岩的研究数据进行整合,分析了雅浦海沟火成岩的成因,并根据火成岩形成的制约条件,对卡罗琳板块俯冲到菲律宾海板块的地幔演化与岩浆作用过程进行了讨论.结果显示雅浦海沟火成岩均具有与俯冲相关火成岩的典型特征.橄榄岩地球化学特征指示雅浦海沟地幔熔融程度为20%~25%,地幔在部分熔融过程中受到了流体与熔体的双重交代作用.Re-Os同位素特征指示雅浦海沟地幔中存在约1.16 Ga非常古老的残余地幔,表明地幔可能经历过多期熔融事件,从而导致雅浦海沟地幔非常亏损.雅浦岛弧成因至今仍存争议,主要包括:(1)现今雅浦岛弧为帕里希维拉海盆洋壳的一部分,在中新世因卡罗琳洋脊的碰撞导致帕里希维拉海盆洋壳逆冲到原雅浦岛弧之上.(2)雅浦岛弧在不同构造时期经历过多期岛弧岩浆作用,包括俯冲初始阶段(~52 Ma)的弧前玄武岩、俯冲开始后的岛弧玄武岩(~25 Ma)、与卡罗琳洋脊碰撞(21 Ma)后的岛弧拉斑玄武岩(7~11 Ma).其中7~11 Ma的岛弧拉斑玄武岩指示雅浦岛弧岩浆活动并未因卡罗琳洋脊的碰撞完全停止,很有可能在晚中新世短暂恢复活动.   相似文献   

5.
国坤  翟世奎  于增慧  蔡宗伟  张侠 《地球科学》2016,41(10):1655-1664
冲绳海槽是一个处于弧后扩张作用早期的年轻的弧后盆地,是研究弧后扩张作用早期盆地演化和壳幔过程的天然实验室.随着调查研究工作的逐步展开和深入,也发现了一些新的、重要的、亟待解决的科学问题,而火山岩岩石系列归属的厘定又是其他研究工作的基础.在系统收集和整理迄今已有冲绳海槽火山岩资料的基础上,结合近期分析测试数据, 对冲绳海槽火山岩的岩石系列归属进行了重新厘定,探讨了火山岩的构造环境指示意义和浮岩与玄武岩之间的成因联系.研究结果表明:冲绳海槽火山岩分布具有以基性玄武岩和酸性(流纹)英安岩为主的双峰式特征,中性火山岩稀少,基性的玄武岩属于亚碱性系列的橄榄拉斑玄武岩,酸性浮岩可归属为亚碱性岩系的流纹英安岩或流纹岩;在构造环境判别上,冲绳海槽玄武岩表现出大洋中脊和岛弧构造环境的特点,既有别于大洋中脊扩张中心,也有别于成熟型弧后盆地,呈现出弧后早期扩张阶段盆地独特的构造环境特征;广泛分布于冲绳海槽的酸性浮岩表现出一定的岛弧环境的特点;酸性浮岩与玄武岩具有同源性,酸性岩是基性的玄武质岩浆经不同程度结晶分异和同化混染作用的产物.   相似文献   

6.
尹滔  张伟  尹显科  裴亚伦 《地球科学》2020,45(11):4128-4142
目前对班公湖-怒江蛇绿混杂岩带的中酸性侵入岩的报道相对较少,对其成因和形成机制的研究有助于揭示班公湖-怒江特提斯洋构造带的岩浆作用过程和动力学背景.对西藏班公湖-怒江蛇绿混杂岩带江玛地区的闪长玢岩进行了年龄分析、岩石地球化学研究.闪长玢岩的LA-ICP-MS锆石U-Pb年龄为121±1 Ma,表明其形成于早白垩世晚期.岩石地球化学特征表明,闪长玢岩具高Al2O3含量（18.2%~19.3%）,属高铝玄武岩,岩石富集轻稀土元素和大离子亲石元素Rb、K等,亏损高场强元素Nb、Ta、Ti,属典型的岛弧玄武岩.综合区域地质资料认为,江玛地区闪长玢岩可能形成于俯冲带前缘增生的岛弧环境,是早白垩世期班公湖-怒江特提斯洋壳岩石圈南向俯冲消减背景下,板片脱水形成的流体与地幔楔橄榄岩发生交代作用的产物.   相似文献   

7.
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   

8.
洋岛类型的海山和洋底高原类型的海山主要由玄武岩组成, 中酸性岩出露很少, 因此很少引起学术界的关注。 我们认为即便中酸性岩很少, 研究他们也是很有意义的, 因为这些中酸性岩不仅可能与洋岛和洋底高原玄武岩的构造背景有关, 也可能与洋岛和洋底高原在形成中酸性岩时的温度和压力变化有关, 这对正确认识洋岛和洋底高原形成的地球动力学背景是很有意义的。 本次研究收集了 GEOROC 数据库中的数据总量为 44 404 个, 经过清洗留下有效数据 3 908 个, 分为洋岛中酸性岩（OIG）、洋底高原中酸性岩（OPG）和洋底高原中酸性岩中的岛弧部分（OPAG）3 类。 学术界通常认为, 洋岛代表热点, 洋底高原温度相对较低, 属于大火成岩省。 然而, 本文对全球洋岛和洋底高原的中酸性岩浆岩的研究表明, 分布在洋岛和洋底高原的中酸性岩主要是板内环境的富碱性的粗面岩和碱性流纹岩, 洋底高原边缘可能受俯冲带的影响, 部分中酸性岩具有岛弧的地球化学特征。 按照中酸性岩的 Sr-Yb 分类, 可知洋岛中酸性岩大多属于南岭型和广西型, 洋底高原海山中酸性岩主要属于南岭型, 广西型很少, 指示洋底高原中酸性岩形成的深度比洋岛浅, 温度也比洋岛低, 同时表明中酸性岩大多形成的压力较低而温度很高, 指示伴有高热中酸性岩的洋岛和洋底高原是地球上的热点。 本文认为, 洋岛和洋底高原中酸性岩并非学术界普遍认为的是玄武岩和碧玄岩分离结晶形成的, 因为洋岛和洋底高原岩浆岩如果是双峰式分布的话, 则不大可能是分离结晶的, 其中的酸性岩部分可能是玄武岩部分熔融形成的。 同时有些岩浆演化的关系表明, 中酸性岩在哈克图解中与玄武岩受不同因素制约, 说明并非演化的关系。  相似文献   

9.
In this paper, a new discrimination diagram using absolute measures of Th and Nb is applied to post-Archean ophiolites to best discriminate a large number of different ophiolitic basalts. This diagram ...  相似文献   

10.
全球幔源岩Pb-Sr-Nd同位素体系   总被引：5，自引：0，他引：5  
朱炳泉 《地学前缘》2007,14(2):24-36
根据各种同位素数据库得到的3万多个晚古生代以来的幔源岩(包括洋中脊玄武岩、洋岛玄武岩、岛弧火山岩、大陆与大洋溢流玄武岩以及大陆板内玄武岩)Pb-Sr-Nd同位素资料和图解分析,对各类火山岩的源区以及地幔的垂向与横向不均一性问题作了进一步讨论。笔者认为不存在具有公共性质的EM1、EM2和HIMU地幔端员,它们的源区可能来自上、下地幔过渡带,只在局部地区出现,独一无二。PREMA(FOZO)则是洋岛玄武岩和溢流玄武岩公共端员。DUAPAL异常现象不只是在洋中脊玄武岩中出现,在洋岛玄武岩、岛弧火山岩和大洋溢流玄武岩中也存在同步的地球化学分区现象。溢流玄武岩的同位素体系特征表明它们的源区涉及再循环地幔的壳幔混合、岩石圈减压熔融、上—下地幔过渡带和似原始-略亏损的下地幔。Pb同位素体系为鉴别俯冲带的存在提供了更严格的证据,这种鉴别表明,安第斯弧火山作用不是洋陆俯冲带产生的。  相似文献   

11.
全球新生代安山岩构造环境有关问题探讨   总被引：6，自引：0，他引：6       下载免费PDF全文
20世纪70～80年代,以Pearce为代表的一批科学家先后提出了玄武岩和花岗岩的构造环境判别图,将构造环境与岩石地球化学特征有机地结合起来,为岩浆岩大地构造环境研究开辟了新途径。但学术界对全球广布的安山岩构造环境及相关地球化学特征问题的讨论则相对不足。本文利用GEOROC 和PetDB 两个数据库对全球新生代安山岩进行数据挖掘,讨论了它们的地球化学特征及形成环境。初步将全球新生代安山岩归属为12个形成构造环境,其中67.71%产出于岛弧、陆缘弧等汇聚板块边缘环境,其余安山岩则形成于大陆板内、大陆溢流、洋岛、大陆裂谷、洋中脊等构造环境。研究表明,常用的玄武岩微量元素判别图以及LILE/HFSE 玄武岩判别图均在一定程度上可用于安山岩成因及环境判别, 暗示安山岩地球化学成分也可用于构造环境的判定。采用大数据思维,探索洋岛安山岩（OIA）和岛弧安山岩（IAA）中地球化学元素的关联关系,从获得的近20 000 个OIA-IAA 判别图中选出lg（Cs/Ta）-lg（Cu/Ta）、lg（CaO/Nb）-lg（Cs/Zr）和lg（Cu/Ta）-lg（Co/Nb）等6个图解,能有效限定它们的构造环境,为安山岩成因及形成环境研究提供了新的思路。这些初步成果说明科学大数据的研究方法可成为岩浆岩构造环境及地球化学研究中的重要有效手段。  相似文献   

12.
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   

13.
The Vohibory Block of south‐western Madagascar is part of the East African Orogen, the formation of which is related to the assembly of the Gondwana supercontinent. It is dominated by metabasic rocks, which have chemical compositions similar to those of recent basalts from a mid‐ocean ridge, back‐arc setting and island‐arc setting. The age of formation of protolith basalts has been dated at 850–700 Ma by U–Pb SHRIMP analysis of magmatic cores in zircon, pointing to an origin related to the Neoproterozoic Mozambique Ocean. The metabasic rocks are interpreted as representing components of an island arc with an associated back‐arc basin. In the early stage of the Pan‐African orogeny, these rocks experienced high‐pressure amphibolite to granulite facies metamorphism (9–12 kbar, 750–880 °C), dated at 612 ± 5 Ma from metamorphic rims in zircon. The metamorphism was most likely related to accretion of the arc terrane to the margin of the Azania microcontinent (Proto‐Madagascar) and closure of the back‐arc basin. The main metamorphism is significantly older than high‐temperature metamorphism in other tectonic units of southern Madagascar, indicating a distinct tectono‐metamorphic history.  相似文献   

14.
The variations of petrogenic oxides and trace elements have been studied in the Cretaceous volcanic rocks recovered by a deep borehole from the depth interval of 1253–4011 m on Moneron Island. The volcanic section is subdivided into two complexes: the Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous Complex occur below 1500 m. Chemically, they belong to low-potassium island arc tholeiites, and their trace element distribution suggests their formation in a suprasubduction mantle wedge under the influence of water fluids that were subsequently released from subducted sediments and oceanic plate during the dehydration of subducted sedimentary rocks and oceanic basalts and, finally, mainly from basalts. The Early Cretaceous basalts from the borehole are interpreted as ascribing to the frontal part of the Moneron-Samarga island arc system. The volcanic rocks of the Late Cretaceous Complex are situated at depths above 1500 m. They also were formed in a suprasubduction setting, but already within the East Sikhote-Alin continental-margin volcanic belt that was initiated after the accretion of the Moneron-Samarga island arc system to the Asian continent. The island-arc section of the Moneron borehole contains basaltic andesite dikes, which are geochemically comparable with the Early-Middle Miocene volcanic rocks of Southwestern Sakhalin.  相似文献   

15.
A continent-oceanic island arc collision model was proposed as a new geodynamic scenario for the evolution of the Cretaceous Central Anatolian granitoids in the Central Anatolian crystalline complex (CACC) by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb–206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust, Turkey. Journal of Asian Earth Sciences 31, 71–86]. The key aspects of this model include an intra-oceanic subduction in the Neotethyan Izmir-Ankara Ocean, formation of an island arc and its subsequent collision with the northern margin of the Tauride–Anatolide Platform. The identical scenario was initially proposed by Göncüoglu et al. (1992) [Göncüoglu, M.C., Erler, A., Toprak, V., Yalınız, K., Olgun, E., Rojay, B., 1992. Geology of the western Central Anatolian Massif, Part II: Central Areas. TPAO Report No: 3155, 76 p] . Moreover, the weighted mean values of the reported 207Pb–206Pb single-zircon evaporation ages by Boztug et al. (2007b) [Boztug, D., Tichomirowa, M., Bombach, K., 2007b. 207Pb–206Pb single-zircon evaporation ages of some granitoid rocks reveal continent-oceanic island arc collision during the Cretaceous geodynamic evolution of the central Anatolian crust: Turkey. Journal of Asian Earth Sciences 31, 71–86] from A-type granitoids in the CACC seem to be miscalculated and contrast with the field data.  相似文献   

16.
新疆东昆仑木孜塔格蛇绿混杂岩中发现富Nb玄武岩   总被引：4，自引：2，他引：4  
富Nb 玄武岩以相对高的TiO2 含量、低的LILE/HFSE和LREE/HFSE比值以及(La/Nb)MN＜2为特征,是岛弧环境的典型产物。首次报道发现于新疆东昆仑木孜塔格蛇绿混杂岩中的富Nb玄武岩,并分析了它们的典型地球化学特征和构造环境,表明了它们形成在岛弧环境。  相似文献   

17.
This work presents new data on the composition of volcanics, developed within the Alazeya Plateau of the Kolyma–Indigirka fold area (Northeast Russia), which indicate essential differences in their composition and, accordingly, different geodynamic settings of the formation of rocks. The studied igneous rocks are subdivided into two groups. Volcanics of the first group of the Late Cretaceous age, which are represented by differentiated volcanic rock series (from andesitobasalts to dacites and rhyolites), were formed under island arc conditions in the continent–ocean transition zone. Volcanics of the second group are ascribed to the tholeiitic series and were formed under the other geodynamic setting, which is associated with the regime of extension and riftogenesis, manifested in the studied area probably at the later stage.  相似文献   

18.
The zoned composition changes of the massive sulfide deposits in the major massive sulfide zone of the Southern Urals such as the Magnitogorsk Megasynclinorium are considered. The zoning is expressed as the trend of Ni–Co–Cu → Zn–Cu → Cu–Zn → Au–Ba–Pb–Cu–Zn. This trend is related to two basic factors: (1) the subduction process with the slab’s eastward subsidence preconditioned the formation (from the west to the east) of the following massive sulfide zones: accretionary prism, frontal island arc, developed island arc, inter-arc spreading zone, split back arc, and back-arc spreading; (2) the longitudinal zoning of the massive sulfide paleovolcanic belts related to changes in the thickness of the crust’s basaltic layer and an inclination of the subducting plate in transverse blocks of the belt. The first factor affects the general paleovolcanic and metallogenic latitudinal zoning of the studied region, while the second factor defines the local meridional zoning. The composition of ore-bearing solutions is dependent on the formation depth of the subduction fluids, magma differentiation type, and the ratio of deep fluids to solutions of near-surface convective cells. The combination of the geodynamic factors expressed in the composition of ore-bearing volcanic complexes and the specific geological settings defines the massive sulfide mineralization composition and productivity criteria. The most productive structures include the frontal island-arc and inter-arc spreading zones and within them, the central-type volcanic edifices whose basalts are referred to as the island-arc tholeiite series and are characterized by the minimum TiO2 and Zr content and low La/Yb ratios.  相似文献   

19.
The geotectonic setting refers to the three-dimensional space and related events based on which a metallogenic system is formed and an ore-forming process takes place. This paper discusses the tectonic evolution of the southwestern margin of the North China paleocontinent and related geotectonic settings in which large or superlarge deposits are formed. Emphasis is put on the geodynamic conditions of the Jinchuan nickel-copper deposit, the Baiyin copper-polymetallic deposit and the Hanshan gold deposit. It is significant that the three deposits occur together as a "trinity" on the same paleocontinental margin. The Jinchuan nickel-copper deposit was formed during the early stage of rifting of the paleocontinental margin; the Baiyin copper-polymetallic deposit was formed during the splitting stage of a continental-margin arc. The continental-margin arc spitting resulted in an "island arc rift" in the early stage of evolution. The Hanshan gold deposit was formed within the Altun sinistral strike-slip fault  相似文献   

20.
It has been established that volcanic rocks of the Schmidt, Rymnik, and Terpeniya terranes are fragments of the compound Early to Late Cretaceous-Paleogene East Sakhalin island arc system of the Sea of Okhotsk region. This island arc paleosystem was composed of back-arc volcano-plutonic belt, frontal volcanic island arc, fore-arc, inter-arc, and back-arc basins, and the Sakhalin marginal paleobasin. The continental volcanic rocks dominate in the back-arc volcano-plutonic belt and frontal volcanic island arc. The petrochemical composition of basalts, basaltic andesites, andesites, and trachytes from the frontal island arc formed in submarine conditions are typical of oceanic island arc or marginal sea rocks (IAB). The petrochemical composition of volcanic rocks from the island arc structures indicates its formation on the heterogeneous basement including the continental and oceanic blocks.  相似文献   

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