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1.
洋中脊玄武岩（MORB）的微量元素成分和同位素比值具有变化范围大的特点，这些变化很难简单地用地幔部分熔融和结晶分异等岩浆演化过程来解释。传统观点认为洋中脊玄武岩的地球化学成分的多样性是由其下部地幔成分的大尺度不均一性决定的。这种地幔不均一性则是外来物质的加入造成的，如再循环的地壳物质、下大陆岩石圈、交代的岩石圈和外地核等成分加入到上地幔中。在本研究中，我们对大西洋洋中脊的玄武岩展开研究工作，评估了玄武岩源区的温压条件并综合对比了微量元素和同位素比值。靠近地幔柱的洋中脊玄武岩的地球化学和同位素成分具有较大的变化。地幔柱对洋中脊地区的影响范围可以达到1400公里，但并不是每个地幔柱都能够影响其周围1400km范围内的所有洋中脊脊段。未受地幔柱影响的洋中脊玄武岩成分和地幔潜在温度均没有异常表现。我们认为上述现象是由于地幔柱柱头形状不同造成的。地幔柱的流动形状可以分为管状和饼状两种，饼状地幔柱影响其周围的地幔是没有方向性的，而管状地幔柱对其周围地幔的影响在方向上具有选择性。沿着大西洋中脊的玄武岩的元素和同位素比值变化较大，暗示其源区具有较高的不均一性。我们认为该地区地幔不均一性主要是由于上地幔中加入了俯冲板片和拆沉下地壳造成的。另外，地幔柱的活动也不容忽视，它们影响了其周围部分洋脊段的成分变化。 相似文献
2.
《热带海洋学报》2017,(6)
近年来对西南印度洋中脊的研究显示,超慢速扩张(全扩张率:12~18mm·yr~(-1))的西南印度洋中脊包含岩浆增生型和非岩浆增生型两种截然不同的地壳结构。岩浆增生型中脊段表现为轴向的海底隆起,通常具有较低的地幔布格重力异常和较强的磁性,地壳厚度较大;非岩浆增生型中脊段通常水深较深,缺乏转换断层,发育拆离断层和高角度正断层,具有较高的地幔布格重力异常和微弱的磁性,大量蛇纹石化的地幔橄榄岩出露海底,火成岩地壳较薄甚至不存在。南海西南次海盆具有较慢速扩张率(全扩张率:50~35mm·yr~(-1)),其接近消亡洋中脊中央部分的地壳厚度也较薄,也有可能存在蛇纹石化地幔,具有超慢速扩张脊非岩浆增生段的特点。 相似文献
3.
洋中脊与地幔柱热点相互作用研究进展 总被引：8，自引：0，他引：8
地表热点是认识地幔柱假说以及地幔柱动力学的窗口,发生在洋脊与热点之间的相互作用则是了解地球上两大动力系统(板块构造和地幔柱)的直接联系的最有利地区。研究洋脊-热点之间的相互作用对于揭示地幔动力学、热点附近洋壳构造的演变以及与热点密切相关的洋中脊处的岩浆热液活动具有重要的意义。在肯定地幔柱假说的基础上,对洋脊-地幔柱(热点)的模拟实验以及三大洋中不同扩张脊与热点相互作用的最新研究作了系统的介绍和评述,指出室内模拟实验以及地质学、岩石学、地球化学和地球物理学(特别是高分辨率的地震技术)的结合研究将是本领域研究的发展趋势。 相似文献
4.
本文利用卫星重力数据和海底地形数据对大塔穆火山开展详细的重力导纳分析。结果显示大塔穆火山的岩石圈有效弹性厚度是1～3 km,指示火山形成于洋中脊之上,符合低重力异常和洋中脊三联点的构造背景。Airy均衡模型和岩石圈挠曲均衡模型推算的大塔穆火山的平均地壳厚度是11～17 km,最厚处拥有一个约30 km的地壳根,与实际地震观测结果基本一致。大塔穆火山的超厚洋壳不同于正常洋中脊,目前地幔柱与洋中脊相互作用是比较合理的成因模式。研究还发现大塔穆火山底下存在一个质量缺失的低密度区,这个区域可能是残留岩浆房造成的结果,与火山中心的地球化学特征、地震波速异常以及广泛的后期火山活动相吻合。另外,这个低密度区提供浮力支撑火山中心隆起,可能导致火山侧翼因差异性沉降而产生正断层。 相似文献
5.
东南印度洋脊(Southeast Indian Ridge, 简称SEIR)是中速扩张洋中脊, 在其中的108°—134°E区域的全扩张速率为72~76 mm·a -1。但在接近澳大利亚-南极洲不整合带(Australian-Antarctic Discordance, 简称AAD)区内, 海底地貌沿洋中脊的变化强烈, 其变化范围涵盖了从慢速到快速扩张洋中脊上常见的例子, 且出现了明显的地球物理与地球化学异常, 说明洋中脊在AAD区附近的岩浆供应量极不均匀。文章定量分析了高精度多波束测深数据, 计算了洋中脊不同段的地形坡度、断层比例以及平面与剖面的岩浆参数M值, 结合研究区内剩余地幔布格重力异常以及洋中脊轴部地球化学指标Na8.0、Fe8.0等资料, 分析与讨论了研究区的断层构造与岩浆活动特征的关系。研究发现, 东南印度洋脊108°—134°E区域的B区(在AAD区内)及C5段(在AAD区外西侧)发育有大量的海洋核杂岩, 而且B区的海洋核杂岩单体规模更大, 其中最大的位于B3区, 沿洋中脊扩张方向延伸约50km。研究结果首次系统性地显示, 相比东南印度洋的其他区域, B和C5异常区具有偏低的平面与剖面M值、偏高的断层比例、偏正的地幔布格重力异常以及偏高的Na8.0值与偏低的Fe8.0值, 这些异常特征可能反映了B区和C5段的岩浆初始熔融深度较浅以及岩浆熔融程度较低, 因此导致其岩浆供应量异常少, 形成较薄的地壳。研究结果同时表明, 在岩浆供应量极少的洋中脊, 构造伸展作用有利于海洋核杂岩的发育, 导致地壳进一步减薄。 相似文献
6.
三大洋中脊的重力异常及构造意义 总被引：1，自引：0，他引：1
本文根据中国第三次南极考察暨首次环球重力调查实测的重力资料,对太平洋、大西洋和印度洋三大洋中脊的重力异常特征及构造意义进行了较深入的研究和探讨。结果表明,构造活动强烈的世界三大洋中脊系,其活动的强大外力来源为地幔的热动力。其地壳虽新,但活动历史却很久远,且已达到热动力平衡状态。洋中脊处的低幅度、短波长变化的空间异常,不能一般近似地视为均衡异常,更不能由此断定洋中脊已处于均衡状态。在洋中脊之下,海底、莫氏面及软流层界面均发生了不同程度的拍升,是影响重力异常的主要原因。 相似文献
7.
本文研究了亚丁-欧文-卡尔斯伯格脊(AOC)三联点邻近洋脊的玄武岩样品在主量、微量元素和Pb-Sr-Nd同位素特征上的差异和联系并分析其原因。结果表明,AOC附近卡尔斯伯格脊和希巴洋脊的玄武岩均为正常型洋脊玄武岩(N-MORB),起源自亏损地幔,其中卡尔斯伯格脊的样品较希巴洋脊样品更亏损;欧文洋脊玄武岩样品为洋岛玄武岩(OIB)特征,其地幔源区可能有残余陆块物质的混染;亚丁洋脊玄武岩样品类型包括N-MORB、E-MORB和可能的大陆玄武岩,与洋壳形成过程中大陆岩石圈物质的贡献程度有关。除了卡尔斯伯格脊外,阿法热点对各洋脊的岩浆均有一定程度的影响。 相似文献
8.
《海洋地质与第四纪地质》2021,41(5)
作为超慢速扩张脊的代表,西南印度洋中脊(SWIR)因其独一无二的地形地貌特征、洋壳结构、洋壳增生机制、岩浆和热液活动以及深部动力学过程,近30年来成为国内外研究的热点区域。基于近年来对SWIR玄武岩、辉长岩及橄榄岩的岩石学和地球化学研究成果总结,重点探讨了沿SWIR轴向(大尺度)以及单个洋脊分段(小尺度)的岩石地球化学变化特征及其影响因素,阐述了SWIR的岩浆供应及洋壳增生模式。其中,在9°～16°E斜向扩张脊,以构造作用为主的洋脊扩张模式导致了更宽的洋壳增生带和显著的地球化学异常;而在50°～51°E脊段,发育了强烈的火山活动,其成因机制包括克洛泽热点与洋中脊相互作用、微热点、古老熔融事件的残留地幔再熔融等几种观点。此外,西南印度洋中脊龙旂热液区(～49.7°E)的最新研究表明,其热液循环路径与拆离断层的发育密不可分,热液流体循环最深可达莫霍面以下6 km。因此,在今后的一段时间,应进一步加强SWIR不同空间尺度地幔源区性质、洋中脊构造与岩浆作用过程、热点-洋中脊相互作用和岩浆-热液活动与成矿等主要科学问题的研究。 相似文献
9.
《热带海洋学报》2017,(6)
文章利用高精度船载多波束测深及重力数据研究了超慢速西南印度洋脊14°E—25°E区域洋壳增生的构造与岩浆特征。首先采用滤波的方法将原始地形数据分为短波长地形(波长小于20km)和长波长地形(波长大于20km)。然后利用长波长地形剖面获得洋中脊裂谷的深度,利用短波长地形剖面和坡度来识别正断层,并计算出岩浆作用在整个扩张过程中所占的比例,即M值。同时从自由空气重力异常中去除海底地形、参考莫霍面以及板块冷却等重力效应,获取能够表征相对洋壳厚度的剩余地幔布格重力异常(Residual Mantle Bouguer Anomaly,RMBA)。最后在垂直于洋脊的剖面上以10km宽的窗口计算出一系列窗口内的M值、平均RMBA值以及断层的垂直断距,并探讨它们之间的相关性。研究发现在超慢速扩张的西南印度洋脊14°E—25°E区域,岩浆率M值随时间和空间变化明显,裂谷深度呈现较强的两翼不对称性,裂谷深度在一定程度上反映了脊轴附近的平均M值。区域性的平均构造拉伸率(即1-M)处于20%~50%之间,南翼整体处于较强的拉伸状态。统计结果表明,在岩浆作用较强的时期,M值偏大,通常产生较厚的洋壳以及断距较小的断层。 相似文献
10.
为了理解古今地幔动力学及地幔与地壳的相互作用,必须确定地幔的结构和组成。一些学者认为,在大部分的地球历史时期内,部分地幔已经从地幔对流圈中分离出来,而仅在地幔柱中保存有原始成分。支持这种观点的证据主要来自于稀有气体,因为地幔柱衍生的岩浆其放射成因同位素与原生同位素的比率通常低于洋中脊玄武岩（ＭＯＲＢｓ）。不同意见来自于地球物理、实验及地球化学证据,这些证据认为,部分俯冲板块沉入６７０ｋｍ深的地震不连续面以下,意味着地球存在全球性扰动。浅地幔的Ｎ同位素组成相对于空气组成的千分比偏差（以δ１５Ｎ表示）大约为… 相似文献
11.
白垩纪以来太平洋上地幔组成和温度变化 总被引：1，自引：0，他引：1
张国良 《海洋学报(英文版)》2016,35(4):19-25
The geological evolution of the Earth during the mid-Cretaceous were shown to be anomalous, e.g., the pause of the geomagnetic field, the global sea level rise, and increased intra-plate volcanic activities, which could be attributed to deep mantle processes. As the anomalous volcanic activities occurred mainly in the Cretaceous Pacific, here we use basalt chemical compositions from the oceanic drilling(DSDP/ODP/IODP) sites to investigate their mantle sources and melting conditions. Based on locations relative to the Pacific plateaus, we classified these sites as oceanic plateau basalts, normal mid-ocean ridge basalts, and near-plateau seafloor basalts. This study shows that those normal mid-ocean ridge basalts formed during mid-Cretaceous are broadly similar in average Na8, La/Sm and Sm/Yb ratios and Sr-Nd isotopic compositions to modern Pacific spreading ridge(the East Pacific Rise). The Ontong Java plateau(125–90 Ma) basalts have distinctly lower Na8 and143Nd/144 Nd, and higher La/Sm and 87Sr/86 Sr than normal seafloor basalts, whereas those for the near-plateau seafloor basalts are similar to the plateau basalts, indicating influences from the Ontong Java mantle source. The super mantle plume activity that might have formed the Ontong Java plateau influenced the mantle source of the simultaneously formed large areas of seafloor basalts. Based on the chemical data from normal seafloor basalts, I propose that the mantle compositions and melting conditions of the normal mid-ocean ridges during the Cretaceous are similar to the fast spreading East Pacific Rise. Slight variations of mid-Cretaceous normal seafloor basalts in melting conditions could be related to the local mantle source and spreading rate. 相似文献
12.
太平洋洋底虽然有大规模的洋底高原和大量大大小小的海山,但西北太平洋的Shatsky海隆不管在构造位置上,还是在理解洋底高原成因所特有的重要证据上,都是独一无二的,对研究太平洋各隆起形成的机制有重要参考价值.目前,对Shatsky海隆的形成有3种主要假说:(1)地幔柱头假说;(2)洋中脊假说;(3)陨星撞击假说.这些假说... 相似文献
13.
Rhett Butler 《Marine Geophysical Researches》1986,8(1):27-38
P-waves recorded on Ponape Island at the northern end of the Ontong Java plateau have been investigated. Different modes of
propagation in the distance range 12° to 17° Δ between paths from Melanesian earthquakes across the Ontong Java plateau and
paths from Mariana earthquakes across the eastern Mariana basin suggest that the mantle underlying the regions is not homogeneous.
Travel-times of P-waves beneath the Ontong Java plateau are slower than for paths beneath the east Mariana basin. The frequency
content of the first-arriving P-waves is lower for paths across the Ontong Java plateau than for the east Mariana basin. The
disparate crustal thicknesses of the Ontong Java plateau and east Mariana basin may influence the relative amplitude of oceanic
Pn, with smaller amplitudes corresponding to a thicker crust. Pn-P differential times for the Ontong Java plateau show a general
decrease with the depth of earthquake focus but no comparable trend is seen in the Mariana data, possibly because of the scatter.
The observation of high-frequency oceanic Pn propagation across the Ontong Java Plateau is suggestive that the plateau is
not of continental origin. 相似文献
14.
The Solomon arc lacks subduction-associated volcanism in its eastern part. This anomalous absence arose from the collision
of the submarine Ontong Java Plateau with the Solomon arc about 8 m.y. ago and a consequent flip in subduction. Collision
was most forceful over the eastern half, so that the new, north-plunging slab of Indo-Australian plate remained in collisional
contact with the thick oceanic crust (>40 km) and lithosphere of the Ontong Java Plateau along a face of cooled depleted refractory
mantle; there is no intervening asthenospheric wedge, and therefore no magma production. 相似文献
15.
Some of the islets in the eastern Beibu Gulf are covered by Quaternary volcano strata. The rock samples from these islets mainly consist of quartz tholeiites （at Shenjiandao）, olivine tholeiites （at Linshidao and Xieyang- dao） and alkali basalts （at Yangpubi and Jianshidao）, and basically represent four periods of the Quaternary volcanism of Hainan Island and its adjacent regions. Except for the samples from Shenjiandao, most of the Quaternary volcanics of these islets belong to alkali magma series. The trace element characteristics of all of these samples show they are OIB （oceanic island basalt） -like, which implies that their deep geodynamic setting may be related to a mantle plume. The Sr-Nd-Pb isotopic compositions show that the mantle source beneath the Quaternary strata can be regarded as a result of binary mixing between a depleted, DMM （de- pleted MORB mantle）-like source and an enriched mantle type 2 （EM2）. The EM2 may be originated from the Hainan mantle plume, and has been metasomatized by carbonaceous fluids released from ancient re- cycled oceanic crust at an asthenospheric mantle level. These features, together with typical trace element ratios, reflect that the parent magma was not subjected to crustal contamination during its ascent to the surface. This study provides further petrological and geochemical evidence for the existence of the Hainan mantle plume. 相似文献
16.
超慢速扩张洋中脊具有不同于其他扩张速率洋中脊的特征，表现为剧烈变化的洋壳厚度和典型的非岩浆段。本文对前人研究的洋中脊岩浆形成关键因素和迁移聚集模式进行综合分析，结合实际地球物理和地球化学的观测数据，探讨了超慢速扩张洋中脊岩浆从地幔源区形成、迁移汇聚、形成洋壳的整个地质过程，进一步指出了影响洋壳结构的关键控制因素。研究结果表明，超慢速扩张洋中脊沿轴洋壳厚度的变化受岩浆补给量和迁移汇聚的共同制约。其中，岩浆补给量受控于洋中脊的地幔潜热、地幔成分和扩张速率的变化；岩浆迁移和汇聚过程则与超慢速扩张洋中脊密集的分段特征和阻渗层的空间结构密切相关。 相似文献
17.
The detailed seismic refraction investigation of the oceanic crust south of Shatsky Rise in the Northwestern Pacific revealed
a low velocity zone (LVZ) with an average compressional wave velocity of 6.3 km/s within layer 3. This conclusion is based
on the shadow zone for refractions on the travel time curves in their first arrivals from the M discontinuity. The LVZ may
be composed of oceanic plagiogranites because serpentinization of peridotites would probably lead to an increase in crustal
block volume with a concomitent decrease in density and thereby thickening and upwelling at the place of now “overdeepened”
ocean would be expected. 相似文献
18.
In the equatorial Atlantic the Ceará and Sierra Leone rises lie on opposing sides of the mid-ocean ridge and are equidistant from its axis. The northern and southern boundaries respectively, of the two rises are formed by the same fracture zones. The area of shallowest acoustic basement under the Ceará Rise coincides with the presence of a 1–2 km thick seismic layer (velocity: 3.5 km/sec) lying over the oceanic layer 2. This 3.5 km/sec layer is interpreted as a sequence of volcanics which began erupting about 80 m.y. ago when the sites of the two rises lay at the ridge axis. As the “abnormal” volcanic activity ceased, the breakup of this volcanic pile into two pieces has formed the Ceará and Sierra Leone rises.
In the South Atlantic, the northern and southern boundaries of the Rio Grande Rise are also formed by fracture zones and an approximately 1 km thick layer with a velocity of 3.5 km/sec exists also under this rise. The same fracture zones appear to bound the Walvis Ridge. Drilling data suggests that both the Rio Grande Rise and Walvis Ridge have subsided continuously since their creation. The igneous rocks recovered from both rises consist of alkalic basaltic suites typical of oceanic volcanic islands. The existing data favor a model in which “excessive” volcanism along the same segment of the Mid-Atlantic Ridge created both the South Atlantic aseismic rises between 100 and 80 m.y. ago. In both the examples, the northern and southern boundaries of the rises are formed by the same fracture zones which originally bounded the abnormally active segment of the ridge axis. 相似文献
19.
Jinchang Zhang William W. Sager William J. Durkin 《Marine Geophysical Researches》2017,38(1-2):169-185
Newly collected, high resolution multi-beam sonar data are combined with previous bathymetry data to produce an improved bathymetric map of Shatsky Rise oceanic plateau. Bathymetry data show that two massifs within Shatsky Rise are immense central volcanoes with gentle flank slopes declining from a central summit. Tamu Massif is a slightly elongated, dome-like volcanic edifice; Ori Massif is square shaped and smaller in area. Several down-to-basin normal faults are observed on the western flank of the massifs but they do not parallel the magnetic lineations, indicating that these faults are probably not related to spreading ridge faulting. Moreover, the faults are observed only on one side of the massifs, which is contrary to expectations from a mechanism of differential subsidence around the massif center. Multi-beam data show many small secondary cones with different shapes and sizes that are widely-distributed on Shatsky Rise massifs, which imply small late-stage magma sources scattered across the surface of the volcanoes in the form of lava flows or explosive volcanism. Erosional channels occur on the flanks of Shatsky Rise volcanoes due to mass wasting and display evidence of down-slope sediment movement. These channels are likely formed by sediments spalling off the edges of summit sediment cap. 相似文献
20.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献