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1.
人们对超慢速扩张洋中脊深部岩浆过程的了解至今仍十分模糊。我们对西南印度洋洋中脊(Southwest Indian Ridge,SWIR) 63. 9°E处采集到的斜长石超斑状玄武岩(Plagioclase Ultra-Phyric Basalt,PUB)进行了岩石学和地球化学研究。样品具有以下几个特征:斜长石斑晶的体积分数高达～25%,而橄榄石斑晶的体积分数约1%;尽管该样品中玻璃的成分与同一洋脊段玄武岩的成分基本一致,但高Fo橄榄石斑晶与玻璃基质的成分不平衡;不同类型的斜长石晶体之间存在成分差异,单个斜长石大斑晶中的An值也呈现出与正常的结晶分异过程不符的环带;斜长石斑晶中发育溶蚀、筛状等不平衡结构。因此,我们认为,斜长石超斑状玄武岩经历了多期次熔体的作用,是由通过密度分选聚集在岩浆房顶部的斜长石斑晶被之后的火山喷发带出海底形成。尽管斜长石超斑状玄武岩与同一洋脊段的非斑状玄武岩之间并不存在母熔体成分上的差别,但超斑状玄武岩的出现进一步反映了超慢速扩张洋壳岩浆活动的多样性。 相似文献
2.
慢速—超慢速扩张西南印度洋中脊研究进展 总被引：5，自引：0，他引：5
西南印度洋中脊具有慢速—超慢速扩张速率和斜向扩张的特征,是全球洋中脊系统研究的热点之一,也是研究海底构造环境、热液活动、地幔深部过程及其动力学机制的重要区域。在前人工作的基础上较为详细地介绍了西南印度洋中脊的研究历史、地形划分、扩张速率及其构造特征,归纳了西南印度洋中脊热液活动及岩石地球化学特征,探讨了超慢速扩张洋脊和超镁铁质岩系热液系统的特殊性,并认为超慢速扩张洋脊广泛暴露的地幔岩及其蛇纹石化作用、超镁铁质岩系热液系统以及热液硫化物成矿作用是西南印度洋中脊今后研究的重要内容。 相似文献
3.
西南印度洋中脊地质构造对地幔部分熔融的影响:深海橄榄岩尖晶石成分证据 总被引：2，自引：0，他引：2
慢速-超慢速扩张西南印度洋中脊普遍发育转换断层,洋脊分段性明显,是研究地质构造与地幔部分熔融关系的理想场所。对西南印度洋中脊(52°20′53°30′E)Gallieni转换断层与Gazelle转换断层之间洋脊段6个站位的深海橄榄岩研究发现:尖晶石Cr#的变化范围为0.194～0.329,对应的地幔部分熔融程度为7.6%～13.0%,反映全球洋中脊系统中低程度的地幔部分熔融,并且离转换断层近的地幔部分熔融程度低于洋脊分段中心,这种差异除了受转换断层的冷却作用影响外,还可能与洋脊分段中心更强的岩浆抽提作用有关。将研究区与全球其他洋脊对比发现,尖晶石Cr#及对应的地幔部分熔融程度随洋脊扩张速率的降低而降低,在探讨地幔部分熔融程度与洋脊扩张速率的相关性时,通过对转换断层效应的校正,能够更准确地反映地幔部分熔融程度随洋脊扩张速率的变化趋势。 相似文献
4.
对近年来我国"大洋一号"科考船在西南印度洋中脊(SWIR)多金属硫化物调查区4个站位所获得的玄武岩进行了岩石学及元素地球化学研究。其岩相学特征为以斑状结构为主,斑晶矿物主要由斜长石、辉石和橄榄石组成。基质以间隐结构为主,主要由斜长石、橄榄石和辉石微晶组成。全岩元素地球化学分析结果表明样品属于亏损型洋中脊玄武岩。矿物化学成分表明斜长石主要为倍长石和拉长石,橄榄石为贵橄榄石。研究区玄武岩具低的Na8、K/Ti比值和LREE/HREE以及较高的Fe8值,可整体归入SWIR 49°E-70°E区指示岩浆熔融程度最高、熔融深度最深的区域内。本次研究为探索SWIR洋脊玄武岩和岩浆熔融等相关研究提供了49.6°E和50.5°E区的新资料,也指示了区内岩浆活动或成矿围岩物质来源的复杂性。 相似文献
5.
藏东类乌齐地区辉长岩:冈瓦纳大陆北缘晚古生代裂解的记录 总被引：1，自引：0，他引：1
青藏高原处于冈瓦纳大陆与劳亚大陆的交汇部位,是研究冈瓦纳大陆裂解与聚合过程的关键地区。晚古生代伴随着特提斯洋的打开与扩张,冈瓦纳大陆北缘发生了广泛的裂解作用。大陆板内岩浆作用是超大陆裂解的重要证据。在青藏高原内部已有二叠纪大陆板内特征基性岩的报道,它们是该裂解事件的记录。然而,根据目前的相关报道,这些岩石主要出露在青藏高原的西部,以羌塘和潘伽地区为主,在其他地区尚无相关报道。首次报道的藏东类乌齐地区早二叠世辉长岩LA-ICP-MS锆石U-Pb定年结果显示,辉长岩的形成年龄为280±2Ma。全岩地球化学资料表明,辉长岩具有与典型大陆板内玄武岩类似的地球特征。辉长岩具有明显正的锆石εHf(t)值(5.1~11.5),暗示其岩浆起源于亏损的地幔源区。结合区域地质资料,认为类乌齐辉长岩是冈瓦纳大陆北缘早二叠世裂解的产物。因此,早二叠世大陆板内基性岩浆作用在青藏高原东部也有出露,它们是在羌塘-潘伽地幔柱活动的作用下,冈瓦纳大陆北缘裂解与班公湖-怒江洋打开和扩张的结果。 相似文献
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揭示洋中脊与地幔柱(脊- 柱)之间的可能联系为认识地球深部物质组成与深部地幔动力学过程提供了重要窗口，也是过去40多年以来固体地球科学研究领域的前沿与热点。在绵延八万多千米的全球洋中脊系统中，部分洋脊片段会受到地幔柱作用不同程度的影响。研究显示，大西洋的形成演化与地幔柱作用之间具有密切联系，尤其在南大西洋的裂解、打开演化过程中，南大西洋中脊系统始终与其周围地幔柱（如圣赫勒拿、阿森松、特里斯坦、高夫、发现等地幔柱）之间具有不同程度的相互作用关系，导致沿脊出露玄武岩在地球化学组成上呈现出明显的不均一性特征。本文在系统性总结脊- 柱相互作用研究现状与南大西洋地区地质构造演化特征的基础上，详细阐述了南大西洋中脊13. 2°S~24. 2°S地区玄武岩的岩石地球化学特征；揭示了南大西洋中脊研究区的岩浆演化、地幔源区性质；指示出圣赫勒拿地幔柱物质向南大西洋中脊系统传播的主要方向；圈定了圣赫勒拿地幔柱对南大西洋中脊系统地幔源区性质在沿脊方向的影响范围（14. 2°S~20. 4°S）；同时推测了南大西洋中脊系统与圣赫勒拿地幔柱之间受地幔柱影响的软流圈地幔物质在大洋岩石圈底部的空间展布。最后本文提出了关于南大西洋地区脊- 柱相互作用领域现存的科学问题与未来的研究方向。 相似文献
8.
西北印度洋的洋脊系统目前以"中印度洋脊"和"卡尔斯伯格脊"分别指示南北两段,两者的分界点被认为是澳大利亚板块与印度板块的板块边界与洋脊的交点,但具体分布位置不明确.基于已有的地质、地球物理和地球化学等多方面特征,认为卡尔斯伯格脊和中印度洋脊可以统一称为"西北印度洋脊",从罗德里格斯三联点一直延伸到欧文断裂带.新的洋脊厘定将有助于更全面地了解整个西北印度洋的洋脊演化和地球动力学过程.西北印度洋脊地形上南北两端断裂较少,中间断层密集,形似吸管的弯折部位,调节洋脊的转向.重力异常显示沿脊轴方向两端高中间低的特征,表明两端岩浆供给相对充足,而中间断层密集区岩浆量少.磁异常特征显示清晰的分带性,指示多阶段的洋脊扩张历史.岩石地球化学特征显示南北两个同位素相对富集洋脊段,可能与热点作用相关,或与残留岩石圈或地壳物质对亏损软流圈地幔的富集改造有关. 相似文献
9.
红海是地球上最年轻的大洋,其板块构造活动正处于威尔逊旋回的幼年期。红海南北两端分别连接着威尔逊旋回的胚胎期和终结期,即东非大裂谷和地中海。这一独特的地理位置和构造部位使其成为板块构造理论研究的圣地。本文通过对已有的地质、地球物理和地球化学资料进行综合分析,了解了红海地区的地形、重磁异常和沿脊的玄武岩地球化学组成等地质构造特征,探讨了红海裂谷的洋壳分布、地幔源区不均一性以及扩张演化历史等问题。红海地形中间深、南北两端浅,可以分为北、中北、中南、南等四段。重磁异常的条带主要出现在中南段,其他段不明显,因而限制了以往对红海扩张历史的认识。目前认为红海全段存在洋壳,红海两岸的沿岸悬崖是共轭扩张陆缘,呈向南开口的喇叭型扩张,而非对应红海岸线的梭子型。红海裂谷沿脊的地幔源区具有明显的不均一性,南段玄武岩显示E-MORB特征,表现为阿法尔地幔柱的影响。红海的发育经历了裂谷前火山作用(31~29Ma)、大陆张裂(29~13Ma)和洋底扩张(<13Ma)三个主要阶段。红海裂谷的形成演化与非洲大陆的裂解、阿法尔地幔柱的活动、新特提斯洋的闭合等密切相关,了解红海的地球动力学过程将为揭示区域大地构造演化以及板块运动规律提供依据。 相似文献
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N. M. Sushchevskaya V. S. Kamenetsky B. V. Belyatsky A. V. Artamonov 《Geochemistry International》2013,51(8):599-622
A comparison of new and published geochemical characteristics of magmatism in the western and eastern Indian Ocean at the initial and recent stages of its evolution revealed several important differences between the mantle sources of basaltic melts from this ocean.
- The sources of basalts, from ancient rises and from flanks of the modern Central Indian Ridge within the western Indian Ocean contain an enriched component similar in composition to the source of the Réunion basalts (with radiogenic Pb and Sr and unradiogenic Nd), except for basalts from the Comores Islands, which exhibit a contribution from an enriched HIMU-like component.
- The modern rift lavas of spreading ridges display generally similar geochemical compositions. Several local isotopic anomalies are characterized by the presence of an EM2-like component. However, two anomalous areas with distinctly different enriched mantle sources were recognized in the westernmost part of the Southwestern Indian Ridge (SWIR). The enriched mantle source of the western SWIR tholeiites in the vicinity of the Bouvet Triple Junction has the isotopic ratios indicating a mixture of HIMU + EM2 in the source. The rift anomaly distinguished at 40° E displays the EM1 signature in the mantle source, which is characterized by relatively low 206Pb/204Pb (up to 17.0) and high 207Pb/204Pb, 208Pb/204Pb and 87Sr/86Sr. This source may be due to mixing with material from the continental lithosphere of the ancient continent Gondwana. The material from this source can be distinguished in magmas related to the Mesozoic plume activity in Antarctica, as well as in basalts from the eastern Indian Ocean rises, which were formed by the Kerguelen plume at 100–90 Ma.
- The geochemical heterogeneities identified in the ancient and present-day magmatic products from the western and eastern Indian Ocean are thought to reflect the geodynamic evolution of the region. In the eastern part of the ocean, the interaction of the evolving Kerguelen plume with the rift zones produced magmas with specific geochemical characteristics during the early opening of the ocean; such a dispersion of magma composition was not recognized in the western part of the ocean.
12.
《International Geology Review》2012,54(14):1691-1719
This study investigates the formation of lower oceanic crust and geochemical variations of basalts along the Central Indian Ridge (CIR, lat. 7°45′–17°10′ S). Harzburgites, various gabbroic cumulates, medium- to fine-grained oxide gabbros, diabases, and pillow basalts were recovered by dredging from segment ends such as ridge-transform intersections (RTIs), non-transform discontinuities (NTDs), and transform offset areas. The occurrence of both harzburgites and gabbroic rocks with minor basalts at all segments ends, and leucogabbro intrusive into harzburgite at the 12°45′ S NTD indicates that oceanic crust at segment ends exposes mantle-derived harzburgites and gabbroic intrusions with a thin basaltic cover due to sparse magmatic activity. Basalts collected along the entire ridge show wide compositional variations between N (normal)- and E (enriched)-mid-ocean ridge basalt (MORB). T (transitional)-MORBs with enriched affinities are more prominent than N-MORBs. There is no tendency of enrichment towards specific directions. (La/Sm)N variations in MORB along the CIR (8°–21°S) fluctuates at a regional scale with local high positive anomalies reflecting compositional heterogeneity of the sub-CIR mantle domain. 相似文献
13.
Hafnium isotope and incompatible trace element data are presentedfor a suite of mid-ocean ridge basalts (MORB) from 13 to 47°Eon the Southwest Indian Ridge (SWIR), one of the slowest spreadingand most isotopically heterogeneous mid-ocean ridges. Variationsin Nd–Hf isotope compositions and Lu/Hf ratios clearlydistinguish an Atlantic–Pacific-type MORB source, presentwest of 26°E, characterized by relatively low Hf valuesfor a given Nd relative to the regression line through all Nd–Hfisotope data for oceanic basalts (termed the ‘Nd–Hfmantle array line’; the deviation from this line is termedHf) and low Lu/Hf ratios, from an Indian Ocean-type MORB signature,present east of 32°E, characterized by relatively high Hfvalues and Lu/Hf ratios. Additionally, two localized, isotopicallyanomalous areas, at 13–15°E and 39–41°E,are characterized by distinctly low negative and high positiveHf values, respectively. The low Hf MORB from 13 to 15°Eappear to reflect contamination by HIMU-type mantle from thenearby Bouvet mantle plume, whereas the trace element and isotopiccompositions of MORB from 39 to 41°E are most consistentwith contamination by metasomatized Archean continental lithosphericmantle. Relatively small source-melt fractionation of Lu/Hfrelative to Sm/Nd, compared with MORB from faster-spreadingridges, argues against a significant role for garnet pyroxenitein the generation of most central SWIR MORB. Correlations betweenHf and Sr and Pb isotopic and trace element ratios clearly delineatea high-Hf ‘Indian Ocean mantle component’ that canexplain the isotope composition of most Indian Ocean MORB asmixtures between this component and a heterogeneous Atlantic–Pacific-typeMORB source. The Hf, Nd and Sr isotope compositions of IndianOcean MORB appear to be most consistent with the hypothesisthat this component represents fragments of subduction-modifiedlithospheric mantle beneath Proterozoic orogenic belts thatfoundered into the nascent Indian Ocean upper mantle duringthe Mesozoic breakup of Gondwana. KEY WORDS: mid-ocean ridge basalt; isotopes; incompatible elements; Indian Ocean 相似文献
14.
Source characteristics of the basement rocks from the Sulu and Celebes Basins (Western Pacific): chemical and isotopic evidence 总被引：4，自引：0，他引：4
P. Spadea Massimo D’Antonio Matthew F. Thirlwall 《Contributions to Mineralogy and Petrology》1996,123(2):159-176
New Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged
Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu
Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes
Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacific, subsequently
developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision
phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between 87Sr/86Sr and 143Nd/144Nd show that the seafloor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean
ridge basalts (MORB), and distinct from East Pacific Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics
are different, in that they have distinctly lower ɛNd(T) for a given ɛSr(T), compared to Sulu and Celebes basalts. In the 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high
Δ7/4 Pb (5.3–9.3) and D8/4 Pb (46.3–68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through
Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features
of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type (“normal”)
mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was
slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan
Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental
characteristics and low Nd(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc
basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western
Pacific region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland,
when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources.
Received: 23 May 1995/Accepted: 12 October 1995 相似文献
15.
N. M. Sushchevskaya O. V. Levchenko E. P. Dubinin B. V. Belyatsky 《Geochemistry International》2016,54(3):237-256
The study of magmatism and tectonic structure of the East Indian or Ninetyeast Ridge (NER) reveals the geochemical similarity of mantle sources for the NER and Kerguelen Plateau melts. Magmas related to the Kerguelen plume were derived from an enriched mantle source, whereas the NER tholeiitic basalts originated from a source contaminated by a depleted material. While, depleted basalt varieties were not found within the NER basalts. It was shown that magmatic rocks forming the NER were generated by high degrees (30%) of partial melting within the ancient Wharton spreading ridge due to the activity of the Kerguelen plume, which was located at this time in the vicinity of the ridge. The most significant impact of the plume on the NER structures was recorded at 70–50 Ma ago. 相似文献
16.
K. M. Haase Colin W. Devey Dieter F. Mertz Peter Stoffers Dieter Garbe-Schönberg 《Contributions to Mineralogy and Petrology》1996,123(3):223-237
Mohns Ridge lavas between 71 and 72°30′N (∼360 km) have heterogeneous compositions varying between alkali basalts and incompatible-element-depleted
tholeiites. On a large scale there is a continuity of incompatible element and isotopic compositions between the alkali basalts
from the island Jan Mayen and Mohns Ridge tholeiites. The variation in isotopes suggests a heterogeneous mantle which appears
to be tapped preferentially by low degree melts (∼5%) close to Jan Mayen but also shows its signature much further north on
Mohns Ridge. Three lava types with different incompatible element compositions [e.g. chondrite-normalized (La/Sm)N<1 to >2] occur in the area at 72°N and were generated from this heterogeneous mantle. The relatively depleted tholeiitic
melts were mixed with a small degree melt from an enriched source. The elements Ba, Rb and K of the enriched melt were probably
buffered in the mantle by residual amphibole or phlogopite. That such a residual phase is stable in this region of oceanic
mantle suggests both high water contents and low mantle temperatures, at odds with a hotspot origin for Jan Mayen. Instead
we suggest that the melting may be induced by the lowered solidus temperature of a “wet” mantle. Mohns MORB (mid ocean ridge
basalt) and Jan Mayen area alkali basalts have high contents of Ba and Rb compared to other incompatible elements (e.g. Ba/La >10).
These ratios reflect the signature of the mantle source. Ratios of Ce/Pb and Rb/Cs are normal MORB mantle ratios of 25 and
80, respectively, thus the enrichments of Ba and Rb are not indicative of a sedimentary component added to the mantle source
but were probably generated by the influence of a metasomatizing fluid, as supported by the presence of hydrous phases during
the petrogenesis of the alkali basalts. Geophysical and petrological models suggest that Jan Mayen is not the product of hotspot
activity above a mantle plume, and suggest instead that it owes its existence to the unique juxtaposition of a continental
fragment, a fracture zone and a spreading axis in this part of the North Atlantic.
Received: 3 May 1995 / Accepted: 6 November 1995 相似文献
17.
Melt inclusion and host glass compositions from the easternend of the Southwest Indian Ridge show a progressive depletionin light rare earth elements (LREE), Na8 and (La/Sm)n, but anincrease in Fe8, from the NE (64°E) towards the SW (49°E).These changes indicate an increase in the degree of mantle meltingtowards the SW and correlate with a shallowing of the ridgeaxial depth and increase in crustal thickness. In addition,LREE enrichment in both melt inclusions and host glasses fromthe NE end of the ridge are compatible with re-fertilizationof a depleted mantle source. The large compositional variations(e.g. P2O5 and K2O) of the melt inclusions from the NE end ofthe ridge (64°E), coupled with low Fe8 values, suggest thatmelts from the NE correspond to a variety of different batchesof melts generated at shallow levels in the mantle melting column.In contrast, the progressively more depleted compositions andhigher Fe8 values of the olivine- and plagioclase-hosted meltinclusions at the SW end of the studied region (49°E), suggestthat these melt inclusions represent batches of melt generatedby higher degrees of melting at greater mean depths in the mantlemelting column. Systematic differences in Fe8 values betweenthe plagioclase- and the olivine-hosted melt inclusions in theSW end (49°E) of the studied ridge area, suggest that theplagioclase-hosted melt inclusions represent final batches ofmelt generated at the top of the mantle melting column, whereasthe olivine-hosted melt inclusions correspond to melts generatedfrom less depleted, more fertile mantle at greater depths. KEY WORDS: basalt; melt inclusions; olivine; plagioclase; Southwest Indian Ridge 相似文献