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1.
Plate tectonic reconstructions assume a major inactive transform fault, the Davie Fracture Zone, in the West Somali Basin, along which Madagascar is thought to have migrated southwards following Gondwana breakup in the Mesozoic. Based on the interpretation of reflection seismic data, we show that the Walu Ridge offshore Kenya and the Kerimbas Basin offshore northern Mozambique are tectonically unrelated to the southward motion of Madagascar and correlate with Late Cretaceous volcanism and inversion in Kenya and the evolution of the East African Rift System respectively. Offshore Tanzania, geophysical data do not show basement structures indicating the presence of a major transform fault. These results challenge the commonly supported transform margin concept and imply a more southerly pre‐breakup position of Madagascar within Gondwana. Opening of the West Somali Basin by SW‐propagating oblique rifting and seafloor spreading is proposed.  相似文献   

2.
在《印度洋底大地构造图》的基础上,分析了印度洋盆构造格局和洋盆演化重大事件序列,并从印度洋盆初始裂解机制、扩张中心跃迁与热点作用、洋中脊扩展作用等方面讨论了印度洋盆的张开过程,提出以下几点认识:(1)现今印度洋洋中脊可分为两个系统:东南印度洋中脊-中印度洋中脊-卡斯伯格洋脊系统(东支)和西南印度洋中脊系统(西支),前者是太平洋洋中脊扩展作用的产物,后者是太平洋-东南印度洋中脊与大西洋中脊之间构造调节的产物;(2)印度洋盆最初裂解受地幔柱垂向挤压-水平伸展作用控制,沿前寒武造山带等地壳薄弱带发育;(3)印度洋盆经历两次扩张中心的跃迁,其趋向性跃迁方向与热点相对板块的运动方向具有一致性,显示两者存在内在联系。(4)大西洋和太平洋洋中脊在印度洋交汇,于古近纪连通,末端伴随陆块持续发生碎裂化、裂解化,可称为鱼尾构造模式,表明印度洋盆衔接和调节了三大洋盆的发育和演化过程,具有全球洋盆枢纽的关键意义。  相似文献   

3.
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   

4.
We have identified an extinct E–W spreading center in the northern Natal valley on the basis of magnetic anomalies which was active from chron M11 (133 Ma) to 125.3 Ma, just before chron M2 (124 Ma) in the Early Cretaceous. Seafloor spreading in the northern Natal valley accounts for approximately 170 km of north–south motion between the Mozambique Ridge and Africa. This extension resolves the predicted overlap of the continental (central and southern) Mozambique Ridge and Antarctica in the chron M2 to M11 reconstructions from Mesozoic finite rotation parameters for Africa and Antarctica. In addition, the magnetic data reveal that the Mozambique Ridge was an independent microplate from at least 133 to 125 Ma. The northern Natal valley extinct spreading center connects to the spreading center separating the Mozambique Basin and the Riiser-Larsen Sea to the east. It follows that the northern Mozambique Ridge was either formed after the emplacement of the surrounding oceanic crust or it is the product of a very robust spreading center. To the west the extinct spreading center connects to the spreading center separating the southern Natal valley and Georgia Basin via a transform fault. Prior to chron M11, there is still a problem with the overlap of Mozambique Ridge if it is assumed to be fixed with respect to either the African or Antarctic plates. Some of the overlap can be accounted for by Jurassic deformation of the Mozambique Ridge, Mozambique Basin, and Dronning Maud land. It appears though that the Mozambique Ridge was an independent microplate from the breakup of Gondwana, 160 Ma, until it became part of the African plate, 125 Ma.  相似文献   

5.
The study provides new understanding of magmatism at extinct and modern spreading zones around the western margin of East Antarctica from Bransfield Strait to the Bouvet Triple Junction (BTJ) in the Atlantic Ocean and reveals causes of geochemical heterogeneity of mantle magmatism during the early opening of the Southern Ocean. The results indicate the involvement of an enriched source component in the generation of parental melts, which was formed in several tectonic stages. The enriched (metasomatized) mantle generated at rift zones has geochemical characteristics typical of the western Gondwana lithosphere (with isotopic compositions similar to those inferred for the enriched HIMU and EM-2 sources). This mantle source may have been produced by the thermal erosion of the continental mantle during the early stages of the Karoo–Maud–Ferrar superplume activity. This enriched mantle generated in the apical parts of the plume (sub-oceanic) began to melt during tectonic displacement and fragmentation of Gondwana. The Bouvet Triple Junction, located along modern spreading zones between the Antarctic and South American plate, is characterized by a greater depth of melting and a higher degree of enrichment of primary tholeiitic magmas. The highest enrichment of magmas in this region is controlled by a contribution from a pyroxenite-rich component, which was also identified in the extinct spreading center in Powell Basin.  相似文献   

6.
Paleopositions of the African, Indian and Antarctic plates are used as an independant set of data to test various hypotheses, derived from geophysical data, on the origin, emplacement mechanism and evolution of five aseismic structures of the Western and Southern Indian Ocean (Crozet and Kerguelen plateaus, Marion Dufresne, Léna and Ob seamount chain, Madagascar and Mascarene ridges).Except for a continental fragment of very limited extent bearing the Seychelles Islands, these structures, together with the Madagascar and Mascarene ridges, are probably due to anomalous volcanic episodes at —or near— active plate boundaries, rather than to intraplate emplacement. Their creation processes are therefore mainly related to the relative motions between the Antarctic, African and Indian plates. The volcanic episodes are synchronous with major changes in the relative motions between these plates and thus substantiate the role played by frequent irregularities in the kinematic pattern of the Western and Southern Indian Ocean, such as ridge jumps, asymmetric spreading and rapid variations in spreading velocity or direction. Finally, we think that thermal anomalies, located not far from active spreading boundaries, may have played a role in the physical processes creating the aseismic ridges.  相似文献   

7.
Investigations of three plausible tectonic settings of the Kerguelen hotspot relative to the Wharton spreading center evoke the on-spreading-axis hotspot volcanism of Paleocene (60-54 Ma) age along the Ninetyeast Ridge. The hypothesis is consistent with magnetic lineations and abandoned spreading centers of the eastern Indian Ocean and seismic structure and radiometric dates of the Ninetyeast Ridge. Furthermore, it is supported by the occurrence of oceanic andesites at Deep Sea Drilling Project (DSDP) Site 214, isotopically heterogeneous basalts at Ocean Drilling Program (ODP) Site 757 of approximately the same age (59-58 Ma) at both sites. Intermix basalts generated by plume-mid-ocean ridge (MOR) interaction, exist between 11° and 17°S along the Ninetyeast Ridge. A comparison of age profile along the Ninetyeast Ridge between ODP Sites 758 (82 Ma) and 756 (43 Ma) with similarly aged oceanic crust in the Central Indian Basin and Wharton Basin reveals the existence of extra oceanic crust spanning 11° latitude beneath the Ninetyeast Ridge. The extra crust is attributed to the transfer of lithospheric blocks from the Antarctic plate to the Indian plate through a series of southward ridge jumps at about 65, 54 and 42 Ma. Emplacement of volcanic rocks on the extra crust resulted from rapid northward motion (absolute) of the Indian plate. The Ninetyeast Ridge was originated when the spreading centers of the Wharton Ridge were absolutely moving northward with respect to a relatively stationary Kerguelen hotspot with multiple southward ridge jumps. In the process, the spreading center coincided with the Kerguelen hotspot and took place on-spreading-axis volcanism along the Ninetyeast Ridge.  相似文献   

8.
The Perth Abyssal Plain (PAP), located offshore southwest Australia, formed at the centre of Mesozoic East Gondwana breakup and Kerguelen plume activity. Despite its importance as a direct and relatively undisturbed recorder of this early spreading history, sparse geophysical data sets and lack of geological sampling hamper our understanding of the evolution of the PAP. This study combines new bathymetric profiles across the PAP with petrographic and geochemical data from the first samples ever to be dredged from the flanks of the Dirck Hartog Ridge (DHR), a prominent linear bathymetric feature in the central PAP, to better constrain the formation of the early Indian Ocean floor and the influence of the Kerguelen plume. Seafloor spreading in the PAP initiated at ~ 136 Ma with spreading observed to occur at (half) rates of ~ 35 mm/yr. Changes in spreading rate are difficult to discern after the onset of the Cretaceous Quiet Zone at ~ 120 Ma, but an increase in seafloor roughness towards the centre of the PAP likely resulted from a half-spreading rate decrease from 35 mm/yr (based on magnetic reversals) to ~ 24 mm/yr at ~ 114 Ma. Exhumed gabbro dredged from the southernmost dredge site of the DHR supports a further slowdown of spreading immediately prior to full cessation at ~ 102 Ma. The DHR exhibits a high relief ridge axis and distinctive asymmetry that is unusual compared to most active or extinct spreading centres. The composition of mafic volcanic samples varies along the DHR, from sub-alkaline dolerites with incompatible element concentrations most similar to depleted-to-normal mid-ocean ridge basalts in the south, to alkali basalts similar to ocean island basalts in the north. Therefore, magma sources and degrees of partial melting varied in space and time. It is likely that the alkali basalts are a manifestation of later excess volcanism, subsequent to or during the cessation of spreading. In this case, enriched signatures may be attributed tectonic drivers and melting of a heterogeneous mantle, or to an episodic influence of the Kerguelen plume over distances greater than 1000 km. We also investigate possible scenarios to explain how lower crustal rocks were emplaced at the crest of the southern DHR. Our results demonstrate the significance of regional tectonic plate motions on the formation and deformation of young ocean crust, and provide insight into the unique DHR morphology.  相似文献   

9.
We provide an up-to-date compilation of Euler rotations that model the evolution of the Central and Northern Atlantic Ocean (Table 1). The data basis forms seafloor spreading magnetic anomalies of the Atlantic. We checked the published rotations and selected those that form a consistent model. The increments of the Euler rotations going back in time from magnetic anomaly to magnetic anomaly can be illustrated by chains of points on “drift lines” that are paths of motions from continent to continent. Along these paths, the continents bordering the Atlantic Ocean can be moved back to their Mesozoic position within Pangea. Other figures exhibit the early rifting of the North Atlantic, the drift of Iberia, and the evolution of the Greenland-Ellesmere region. The points on the drift lines do not correspond directly to the lines of magnetic anomalies or their “picks” displayed today symmetrically in the Atlantic Ocean. To acquire correspondence, symmetric “flow lines” are constructed analogous to the spreading procedure. But points on the flow lines constructed by half of the increments partially also deviate from the expected symmetric position and in this way quantify displacements or jumps of the axis of rifting or spreading. Most of the selected rotations are from the excellent analyses of previous work. Essential deviations from published rotations are the M 0 rotations of Eurasia and of the Porcupine unit with respect to North America (EUR-NAM and POR-NAM). They lead to a better coincidence between the back-rotated M 0 magnetic anomalies in the Bay of Biscay on the one side and a change of the first transform motions between Greenland and Svalbard on the other side. Through this explanation, an overlap in Pangea SW of Svalbard is avoided and transform motions instead of strong extension are predicted. Some additional data are needed to complete the model: the earliest part of the path of Iberia to North America (IBA-NAM) up to M 4 is calculated assuming that Iberia moved parallel to the African plate, though with slower spreading rates. The evolution of the Central and North Atlantic Ocean system is described in short. This model of the Central and North Atlantic was produced with the primary intention of clearing and fixing the positions of Africa, Iberia, and Eurasia as a framework for an improved reconstruction of the Western Tethys evolution.  相似文献   

10.
E. Honza  K. Fujioka 《Tectonophysics》2004,384(1-4):23-53
Results of the geological and geophysical surveys in the Daito ridges and basin in the northern West Philippine Basin suggest that the Daito Ridge was an arc facing toward the south from the Late Cretaceous to the Early Tertiary. The Late Cretaceous and Tertiary history of Southeast Asia is evaluated based on these data in the Daito ridges and basins and reconstructed based on overall plate kinematics that have operated in this area. During the Late Cretaceous, the Daito Ridge and the East Philippine Islands were positioned along the boundary between the Indian and Pacific Plates. The western half of the Philippines setting on the Indian Plate approached from the south and collided with the East Philippine–Daito Arc either during the latest Paleocene or the earliest Eocene. It is inferred that the bulk of the Philippine archipelago rotated clockwise and Borneo spun counterclockwise during the Tertiary.From the reconstruction, the formation of backarc basins and their spreading direction are assessed. As a result, some primary causes and significant characteristics are suggested for the opening of backarc basins in Southeast Asia. First, opening of some backarc basins commenced with or was triggered by collisions. Second, backarc basins opened approximately parallel to oceanic plate motion. Third, the formation of some backarc basins was triggered by the approach of a hot spreading center. Fourth, the spreading mode or direction of backarc basins was greatly affected by the configuration of the surrounding continent and was also rearranged to spread approximately parallel to oceanic plate motion.The formation of backarc basins and their spreading direction can be reasonably explained by plate kinematics. However, the generative force responsible for their formation is possibly within the subduction system, particularly to form horizontal tensional force in backarc side.  相似文献   

11.
Zvi Ben-Avraham   《Tectonophysics》1978,45(4):269-288
The structural elements on the shallow (Sunda Shelf) and deep seas of east and south—east Asia are interpreted as the result of past interaction between lithospheric plates. During the Mesozoic the western Pacific Ocean and the eastern Indian Ocean were parts of the Tethys Sea and were moving to the north relative to Antarctica. A Mesozoic ridge system trending east—west produced east—west trending magnetic anomalies throughout the entire area. The ridge system was bisected by large north—south transform faults which divided the eastern Indian Ocean—western Pacific Ocean into sub-plates traveling at different speeds. The Mesozoic evolution of the Sunda Shelf and the deep seas resulted from such horizontal differential movement in a north—south direction. During Late Cretaceous—Eocene the various segments of the spreading ridge gradually submerged beneath the deep sea trenches to the north, causing a gradual change in the direction of motion of the Pacific plate. The change in motion of the Pacific plate resulted in the separation between the Pacific and the eastern Indian Ocean plates, the formation of large northeast—southwest tectonic elements on the Sunda Shelf and elsewhere in south—east Asia, the formation of the western Philippine Basin and the rapid northward motion of Australia. The only remnant of the Mesozoic ridge system exists today at the western Philippine Basin.  相似文献   

12.
中国近海海域新生代成盆动力机制分析   总被引：1，自引：0，他引：1       下载免费PDF全文
任建业 《地球科学》2018,43(10):3337-3361
中国近海海域发育了渤海湾、东海和南海等10多个新生代富油气沉积盆地,其发育演化过程及动力学背景的异同需要在统一的研究思路和方法下进行系统的总结.以海域盆地油气勘探开发中积累的丰富的地质地球物理资料为基础,详细解释和分析了渤海、东海和南海三大海域新生代盆地的构造地层格架,进一步明确了渤海湾盆地斜向拉分盆地的演化阶段,证实了区域走滑断裂体系对盆地发育的重要控制作用;在东海陆架盆地划分出弧后前陆盆地的演化阶段,认识到区域挤压作用对该盆地的演化过程的重要性;在南海北部深水区发现了大型拆离断层及其所控制的拆离盆地,提出大型拆离断层作用是地壳薄化、地幔剥露和陆缘深水盆地形成演化的主要机制.研究揭示出中国近海海域盆地新生代期间在经历了古新世-中始新世期间分布全区的均一断陷作用之后,从晚始新世开始进入到区域构造的差异性演化阶段,其中渤海湾盆地进入斜向走滑拉分阶段,并持续到渐新世末期,随后是中新世的热沉降和上新世以来的加速沉降过程;东海陆架盆地则进入长期的弧后前陆盆地演化阶段,直到上新世开始才进入区域性的沉降过程;而南海则持续伸展形成深水拆离盆地,并最终在渐新世初期（32 Ma）发生岩石圈裂解,南海洋盆开始扩张,陆缘则进入被动大陆边缘演化阶段.区域板块运动学分析表明,晚始新世发生的全球板块运动重组事件导致了中国近海海域盆地构造的差异性演化.该事件发生之前,中国东部处于欧亚板块和太平洋板块相互作用构建的"双板块"动力体制之下,太平洋板块的俯冲后退作用导致了陆缘弧后伸展,形成了广布中国东部大陆边缘的盆岭式断陷盆地系.该事件之后,中国大陆处于印度板块、欧亚板块、太平洋板块和菲律宾海板块等构建的"多板块体制"之下,印度-欧亚大陆的碰撞、太平洋板块俯冲方向的转变、古南海的俯冲碰撞、菲律宾海板块的楔入及其与太平洋板块向西运移俯冲等产生了更为复杂的板块运动过程和多期次的运动重组事件导致了中国海域盆地成因类型的多样性和构造演化过程的差异性.海域盆地是我国重要的油气生产基地,本文的研究不仅进一步深化了中国海域盆地的形成演化过程和动力机制的认识,而且对于该区的油气勘探和开发也具有重要的实际应用价值.   相似文献   

13.
Airborne and marine magnetic observations in East Antarctica and adjacent seas of the Indian Ocean were compiled for a magnetic anomaly map of the Antarctic. For East Antarctica, over 260,000 line km of Russian reconnaissance magnetic data were used that had been collected since 1955 mainly at line spacings of about 5, 20 and 50 km. For the offshore areas, magnetic data from American, Australian, German, Japanese, and Russian marine expeditions were incorporated. Digitally recorded data and data digitized from published and unpublished maps and profiles were included in the compilation. Local grids of these data were developed and merged into a regional grid at an interval of 5 km. The prime product of this compilation is a shaded-relief map that shows the most complete and coherent perspective to date of the region's magnetic character. In combination with other types of data, the compilation provides new insight on the tectonic features and history of this largely inaccessible region of the world. It maps out approximately 4300 km of the Antarctic Continental Margin Magnetic Anomaly (ACMMA) related to Gondwana breakup, new cratons and mobile belts, and large submarine igneous provinces.  相似文献   

14.
A re-compilation of magnetic data in the Weddell Sea is presented and compared with the gravity field recently derived from retracked satellite altimetry. The previously informally named ‘Anomaly-T,’ an east–west trending linear positive magnetic and gravity anomaly lying at about 69°S, forms the southern boundary of the well-known Weddell Sea gravity herringbone. North of Anomaly-T, three major E–W linear magnetic lows are shown, and identified with anomalies c12r, c21–29(r) and c33r. On the basis of these, and following work by recent investigators, isochrons c13, c18, c20, c21, c30, c33 and c34 are identified and extended into the western Weddell Sea. Similarly, a linear magnetic low lying along the spine of the herringbone is shown and provisionally dated at 93–96 Ma. Anomaly-T is tentatively dated to be M5n, in agreement with recent tectonic models.Although current tectonic models are generally in good agreement to the north of T, to the south interpretations differ. Some plate tectonic models have only proposed essentially north–south spreading in the region, whilst others have suggested that a period of predominantly east–west motion (relative to present Antarctic geographic coordinates) occurred during the mid-Mesozoic spreading between East and West Gondwana. We identify an area immediately to the south of T which appears to be the southerly extent of N–S spreading in the herringbone. Following recent work, the extreme southerly extent of the N–S directed spreading of the herringbone is provisionally dated M9r/M10. In the oldest Weddell Sea, immediately to the north and east of the Antarctic shelf, we see subtle features in both the magnetic and gravity data that are consistent with predominantly N–S spreading in the Weddell Sea during the earliest opening of East and West Gondwana. In between, however, in a small region extending approximately from about 50 km south of T to about 70°S and from approximately 40° to 53°W, the magnetic and gravity data appear to suggest well-correlated linear marine magnetic anomalies (possible isochrons) perpendicular to T, bounded and offset by less well-defined steps and linear lows in the gravity (possible fracture zones). These magnetic and gravity data southwest of T suggest that the crust here may record an E–W spreading episode between the two-plate system of East and West Gondwana prior to the initiation of the three-plate spreading system of South America, Africa and Antarctica. The E–W spreading record to the east of about 35°W would then appear to have been cut off at about M10 time during the establishment of N–S three-plate spreading along the South American–Antarctic Ridge and then subducted under the Scotia Ridge.  相似文献   

15.
南海北部陆缘位于大华南地块洋陆过渡带南段的关键核心段落,曾处于特提斯洋构造域与（古）太平洋构造域交接地带,是印度洋构造动力系统与太平洋构造动力系统波及的共同地区。然而,以往研究和勘探程度较低,特提斯构造域与太平洋构造域交接转换区域的大地构造背景、过程、机制始终不够明确。基于南海北部陆缘地震剖面,不仅关注该区新生代盆地结构构造,以服务该区油气精准勘探,并且试图以此解剖、揭示该区中生代基底结构特征,进而探索新生代南海海盆打开、扩张、停滞到消亡过程的前生今世。对珠江口盆地地震剖面解析和华南陆缘野外构造研究表明:华南地块洋陆过渡带先后经历了中生代印支期碰撞造山、燕山早期增生造山、燕山晚期压扭造山三个过程;随后进入新生代,又经历了早期北东东—南西西走向正断层主控下的弥散性裂解成盆、中期北东—北北东走向张扭断裂主控下的右行走滑拉分成盆、晚期北西—北西西向张扭断裂主控下的左行走滑拉分成盆三期伸展构造叠加。总体上,该区特提斯洋构造体系向太平洋构造体系的转换过程经历了四个阶段:古特提斯洋构造体系向新特提斯洋构造体系转换、新特提斯洋构造体系向古太平洋构造体系转换、新特提斯洋构造体系向太平洋构造体系转换及古太平洋构造体系向太平洋构造体系的转换。东亚洋陆过渡带的构造转换折射出地球深浅部动力系统驱动“东亚大汇聚”的长期机制,即东南亚环形俯冲驱动体系、太平洋LLSVP和非洲LLSVP的深部动力系统（统称为海底“三极”）的重要性,其中,东南亚环形俯冲驱动体系是地球板块运动的重要动力引擎之一。   相似文献   

16.
In the early Paleozoic the Sino-Korean Craton (SKC) and South China Craton (SCC) were situated along the margin of east Gondwana. The SKC was connected to core Gondwana by an epeiric sea which was the site for deposition of lower Paleozoic sequences of SKC. The SKC and SCC may have drifted away from core Gondwana sometime during the mid-Paleozoic and would have been outboard microcontinents in the late Paleozoic, until they collided to form the East Asian continent in the Triassic. The breakup of SCC from Gondwana was suggested to have taken place at ∼380 Ma, while no reliable suggestions have hitherto been made for breakup of SKC from Gondwana. This study presents a convincing evidence for breakup of SKC from Gondwana, based on the recognition of Late Ordovician volcanism in Korea. New SHRIMP U–Pb zircon ages, 445.0 ± 3.7 Ma and 452.5 ± 3.2 Ma, are obtained from trachytic rocks of the Ongnyeobong Formation of Taebaeksan Basin in Korea which occupied the marginal part of the SKC in the early Paleozoic. This Late Ordovician volcanism along with previous records of Ordovician volcanic activities along the western margin of the SKC is interpreted indicating the development of an incipient oceanic ridge. The oceanic ridge uplifted the SKC including the epeiric sea, which subsequently resulted in terminating the early Paleozoic sedimentation of the epeiric sea. The paucity of lower Paleozoic volcanic rocks across much of the SKC however suggests that the oceanic ridge did not extend into the epeiric sea. Instead, spreading of oceanic ridge entailed dextral movement of associated transform faults, which may have played a major role in breakup of SKC from mainland Gondwana by the end of Ordovician.  相似文献   

17.
本文将全球洋中脊系统作为研究整体,根据洋中脊的全球分布、运动学特征及其初始形成时与泛大陆的构造几何关系,将全球现今的洋中脊系统划分为内、外支洋中脊。外支洋中脊为探索者洋中脊-太平洋洋隆-东南印度洋中脊-西北印度洋中脊,起源于泛大洋及冈瓦纳大陆内部;内支洋中脊为西南印度洋中脊-大西洋中脊-北冰洋加科尔洋中脊,起源于泛大陆内部。两者之间通过俯冲带、转换断层以及弥散性板块边界实现全球板块构造在运动上的平衡,并保持地球的球形几何形态恒定。外支洋中脊在全球板块构造上造成泛大洋缩减,并持续被太平洋取代,直接推动了环太平洋俯冲带的形成;内支洋中脊造成大西洋盆、印度洋盆中生代以来持续扩张。中生代以来,外支洋中脊和内支洋中脊共同作用引起非洲板块、印度澳大利亚板块向北运动,新特提斯洋盆关闭,形成特提斯(阿尔卑斯山-喀尔巴阡山-扎格罗斯山-喜马拉雅山)碰撞造山带,并通过洋中脊扩张平衡了相关的岩石圈缩短。  相似文献   

18.
The Lachlan Fold Belt of southeastern Australia developed along the Panthalassan margin of East Gondwana. Major silicic igneous activity and active tectonics with extensional, strike-slip and contractional deformation have been related to a continental backarc setting with a convergent margin to the east. In the Early Silurian (Benambran Orogeny), tectonic development was controlled by one or more subduction zones involved in collision and accretion of the Ordovician Macquarie Arc. Thermal instability in the Late Silurian to Middle Devonian interval was promoted by the presence of one or more shallow subducted slabs in the upper mantle and resulted in widespread silicic igneous activity. Extension dominated the Late Silurian in New South Wales and parts of eastern Victoria and led to formation of several sedimentary basins. Alternating episodes of contraction and extension, along with dispersed strike-slip faulting particularly in eastern Victoria, occurred in the Early Devonian culminating in the Middle Devonian contractional Tabberabberan Orogeny. Contractional deformation in modern systems, such as the central Andes, is driven by advance of the overriding plate, with highest strain developed at locations distant from plate edges. In the Ordovician to Early Devonian, it is inferred that East Gondwana was advancing towards Panthalassa. Extensional activity in the Lachlan backarc, although minor in comparison with backarc basins in the western Pacific Ocean, was driven by limited but continuous rollback of the subduction hinge. Alternation of contraction and extension reflects the delicate balance between plate motions with rollback being overtaken by advance of the upper plate intermittently in the Early to Middle Devonian resulting in contractional deformation in an otherwise dominantly extensional regime. A modern system that shows comparable behaviour is East Asia where rollback is considered responsible for widespread sedimentary basin development and basin inversion reflects advance of blocks driven by compression related to the Indian collision.  相似文献   

19.
Evidence for heterogenes primary MORB and mantle sources,NW Indian Ocean   总被引：1，自引：0，他引：1  
Basalts from 5 Deep Sea Drilling Project (DSDP) sites in the northwest Indian Ocean (Somali Basin and Arabian Sea) have general geochemical features consistent with a spreading origin at the ancient Carlsberg Ridge. However, compared to most MORBS from other oceans they have low normative olivine, TiO2, and Zr contents. There is no evidence that the mantle source of these northwest Indian Ocean basalts was enriched in incompatible elements relative to the Atlantic and Pacific ocean mantles. In detail, incompatible element abundances in these DSDP basalts establish that they evolved from several compositionally distinct parental magmas. In particular, basalts from site 236 in the Somali Basin have relatively high SiO2 and low Na, P, Ti, and Zr contents. These compositional features along with low normative olivine contents are similar to those proposed for melts derived by two-stage (or dynamic) melting. Published data also indicate there is no enrichment in incompatible elements at the southwest Indian Ocean triple junction, although southwest Indian Ocean basalts have slightly higher 87Sr/86Sr than normal Atlantic MORB. The data suggest that there are significant subtle geochemical variations in the Indian Ocean mantle sources, but are insufficient to show whether these variations have a systematic temporal or geographic distribution.  相似文献   

20.
East Asia plate tectonics since 15 Ma: constraints from the Taiwan region   总被引：4，自引：0，他引：4  
15 Ma ago, a major plate reorganization occurred in East Asia. Seafloor spreading ceased in the South China Sea, Japan Sea, Taiwan Sea, Sulu Sea, and Shikoku and Parece Vela basins. Simultaneously, shear motions also ceased along the Taiwan–Sinzi zone, the Gagua ridge and the Luzon–Ryukyu transform plate boundary. The complex system of thirteen plates suddenly evolved in a simple three-plate system (EU, PH and PA). Beneath the Manila accretionary prism and in the Huatung basin, we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations. These two patterns are rotated by 15°. They were formed by seafloor spreading before 15 Ma and belonged to the same ocean named the Taiwan Sea. Half-spreading rate in the Taiwan Sea was 2 cm/year from chron 23 to 20 (51 to 43 Ma) and 1 cm/year from chron 20 (43 Ma) to 5b (15 Ma). Five-plate kinematic reconstructions spanning from 15 Ma to Present show implications concerning the geodynamic evolution of East Asia. Amongst them, the 1000-km-long linear Gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the PH Sea plate; the formation of Taiwan was driven by two simple lithospheric motions: (i) the subduction of the PH Sea plate beneath Eurasia with a relative westward motion of the western end (A) of the Ryukyu subduction zone; (ii) the subduction of Eurasia beneath the Philippine Sea plate with a relative southwestward motion of the northern end (B) of the Manila subduction zone. The Luzon arc only formed south of B. The collision of the Luzon arc with Eurasia occurred between A and B. East of A, the Luzon arc probably accreted against the Ryukyu forearc.  相似文献   

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