Origin of “paired” aseismic rises: Ceará and Sierra Leone rises in the equatorial, and the Rio Grande Rise and Walvis Ridge in the South Atlantic

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.     

Evaporite deposition in the Aptian South Atlantic Ocean

The Aptian salt deposits of the South Atlantic Ocean extend for 250 km offshore and underlie the continental rise off Brazil and Angola in 4000 m water depth. These salt deposits do not occur south of the Walvis Ridge and Rio Grande Rise, and apparently lie on oceanic and continental crust. Geological evidence and an Aptian-Middle Barremian reconstruction of the South Atlantic suggests the pre-Aptian South Atlantic was closed at both ends, thus favouring widespread salt deposition on oceanic and continental crust. Three models of halite deposition are discussed briefly.     

Modification and pathways of Southern Ocean Deep Waters in the Scotia Sea

An unprecedented high-quality, quasi-synoptic hydrographic data set collected during the ALBATROSS cruise along the rim of the Scotia Sea is examined to describe the pathways of the deep water masses flowing through the region, and to quantify changes in their properties as they cross the sea. Owing to sparse sampling of the northern and southern boundaries of the basin, the modification and pathways of deep water masses in the Scotia Sea had remained poorly documented despite their global significance.Weddell Sea Deep Water (WSDW) of two distinct types is observed spilling over the South Scotia Ridge to the west and east of the western edge of the Orkney Passage. The colder and fresher type in the west, recently ventilated in the northern Antarctic Peninsula, flows westward to Drake Passage along the southern margin of the Scotia Sea while mixing intensely with eastward-flowing Circumpolar Deep Water (CDW) of the antarctic circumpolar current (ACC). Although a small fraction of the other WSDW type also spreads westward to Drake Passage, the greater part escapes the Scotia Sea eastward through the Georgia Passage and flows into the Malvinas Chasm via a deep gap northeast of South Georgia. A more saline WSDW variety from the South Sandwich Trench may leak into the eastern Scotia Sea through Georgia Passage, but mainly flows around the Northeast Georgia Rise to the northern Georgia Basin.In Drake Passage, the inflowing CDW displays a previously unreported bimodal property distribution, with CDW at the Subantarctic Front receiving a contribution of deep water from the subtropical Pacific. This bimodality is eroded away in the Scotia Sea by vigorous mixing with WSDW and CDW from the Weddell Gyre. The extent of ventilation follows a zonation that can be related to the CDW pathways and the frontal anatomy of the ACC. Between the Southern Boundary of the ACC and the Southern ACC Front, CDW cools by 0.15°C and freshens by 0.015 along isopycnals. The body of CDW in the region of the Polar Front splits after overflowing the North Scotia Ridge, with a fraction following the front south of the Falkland Plateau and another spilling over the plateau near 49.5°W. Its cooling (by 0.07°C) and freshening (by 0.008) in crossing the Scotia Sea is counteracted locally by NADW entraining southward near the Maurice Ewing Bank. CDW also overflows the North Scotia Ridge by following the Subantarctic Front through a passage just east of Burdwood Bank, and spills over the Falkland Plateau near 53°W with decreased potential temperature (by 0.03°C) and salinity (by 0.004). As a result of ventilation by Weddell Sea waters, the signature of the Southeast Pacific Deep Water (SPDW) fraction of CDW is largely erased in the Scotia Sea. A modified form of SPDW is detected escaping the sea via two distinct routes only: following the Southern ACC Front through Georgia Passage; and skirting the eastern end of the Falkland Plateau after flowing through Shag Rocks Passage.     

Seismic refraction observations in the Transkei Basin and adjacent areas

Some seismic refraction observations undertaken during the IGY are reported here together with a summary of other refraction studies carried out within the Transkei Basin, the Mozambique Ridge and the South African continental shelf area.A 2.5 km section of Cretaceous and younger rocks is associated with profiles observed on the continental shelf; directly below this group are rocks with velocities in the range 4.0–5.5 km s^-1, probably representatives of the Karroo and Cape supergroups. The basement material velocity variations were from 5.3 to 6.5 with an average of 5.9 km s^-1, and is correlated with granite or Malmesbury Formation plus granite. This crustal structure is similar to that found on the eastern continental shelf of southern South America.The profiles in the Transkei Basin show a thick layer of sediment with velocity range 1.50 to 3.50 km s^-1, underlain by a refracting layer in which the average velocity is 4.5 km s^-1. The velocity of 6.6 km s^-1 obtained for the oceanic layer is similar to the velocities of the crustal layer measured in the Argentine Basin. The mantle velocity (8.1 km s^-1) is consistent with the average mantle velocity for the Indian Ocean but significantly lower than the Pacific Ocean average of 8.20 km s^-1. The depth to Moho is about 12.0 km and the crustal section is typical oceanic. A plate tectonic model of the early opening of the South Atlantic is used to describe the evolution of the Transkei Basin.On the Mozambique Ridge the thin sediments (0.7 km) are underlain by rocks with velocities averaging 5.6 km s^-1. This is more than 1.0 km s^-1 faster than the velocity for layer 2 from the Transkei Basin and the Agulhas Plateau, indicating rocks of a younger age or of a different type. Moreover the crustal section of the Ridge has a thickness in excess of 22 km and is in isostatic equilibrium when compared with the adjacent Transkei Basin and Agulhas Plateau. DSDP site 249, situated on the Ridge, penetrated basalt at a depth of 0.4 km. Whether this is continental or oceanic basalt is not known; when this site 249 basalt was compared to the cored basalts of the adjacent Mozambique Basin, inconclusive results were obtained. The essential constitution of the Mozambique Ridge remains an enigma, but solution of this problem is vital for the proper understanding of the Mesozoic history of this oceanic region.     

Mesozoic break-up of SW Gondwana: implications for regional hydrocarbon potential of the southern South Atlantic

This work provides new palinspastic palaeofacies reconstructions of SW Gondwana incorporating rotation of a Falkland/Malvinas microplate. We discuss the implications of this for the tectonic evolution of the southern South Atlantic and hence for the regional hydrocarbon potential.Existing Gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents. In most continental reconstructions, the Falkland/Malvinas Plateau was assumed to be a rigid fragment of pre-Permian South American crust. However, it has been suggested, on the basis of palaeomagnetic data, that the Falkland/Malvinas Islands were rotated by ∼180° after 190 Ma. This rotation hypothesis has been successfully tested on the basis of Devonian stratigraphy and palaeontology, Permian stratigraphy and sedimentology and Late Palaeozoic and Early Mesozoic structure, making it unlikely that the plateau behaved as a rigid structure during breakup. We have explored the consequences of accepting this hypothesis for the tectonic evolution of SW Gondwana by compiling new palaeogeographic maps for the Permian–Cretaceous of the southern Atlantic area. To achieve a realistic close fit, we have devised a pre-rift proxy for the ocean–continent boundary for the South Atlantic. In order to produce the best fit, it is necessary to subdivide South America into four plates. The consequences of this are far-reaching. Our work suggests that although sedimentary basins were initiated at different times, three major tectonic phases can be recognised; in regional terms these can be thought of as pre-, syn- and post-rift.During the pre-rift time (until the Late Triassic), the area was dominated by compressional tectonism and formed part of the Gondwana foreland. The Falkland/Malvinas Islands lay east of Africa, the Falkland/Malvinas Plateau was ∼33% shorter and Patagonia was displaced east with respect to the rest of South America, in part along the line of the Gastre Fault System. Potential source facies are dominantly post-glacial black shales of Late Permian age deposited in lacustrine or hyposaline marine environments; these rocks would also be an effective regional seal. Sandstones deposited in the Late Permian would be dominantly volcaniclastic with poor reservoir qualities; Triassic sandstones tend to be more mature.There was significant extension from about 210 Ma (end-Triassic) until the South Atlantic opened at about 130 Ma (Early Cretaceous). In the early syn-rift phase, extension was accompanied by strike-slip faulting and block rotation; later extension was accompanied by extrusion of large volumes of lava. Early opening of the South Atlantic was oblique, which created basins at high angle to the trend of the ocean on the Argentine margin, and resulted in microplate rotation in NE Brazil. Intermittent physical barriers controlled deposition of Upper Jurassic–Cretaceous anoxic sediments during breakup; some of these mudrock units are effective seals with likely regional extent. During crustal reorganisation, clastic sediments changed from a uniform volcaniclastic provenance to local derivation, with variable reservoir quality.In the late rift and early post-rift phase, continental extension changed from oblique to normal and basins developed parallel to the continental margins of the South Atlantic. This change coincides with the main rifting in the Equatorial basins of Brazil and the early impact of the Santa Helena Plume. It resulted in widespread development of unconformities, the abandonment of the Recôncavo–Tucano–Jatoba rift and the end of NE Brazil plate rotation, which remained attached to South America. There was extensive deposition of evaporites, concentrated in (but not restricted to) the area north of the Rio Grande Rise/Walvis Ridge.Widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements. Our main conclusion is that the regional hydrocarbon potential of the southern South Atlantic has been constrained by the tectonic evolution.     

Establishment and closure of the directed Florida whiting (Menticirrhus americanus) fishery and implications for North Atlantic right whale (Eubalaena glacialis) conservation and management

Today, ocean and coastal marine resource management is extremely complex. Marine resource managers are charged with conserving and managing many diverse species. Southern kingfish (Menticirrhus americanus), commonly known as whiting, are found from southern New England to Florida. During the fall through winter, western North Atlantic right whales (Eubalaena glacialis) are primarily found in the coastal nearshore waters off South Carolina, Georgia, and Florida, overlapping the whiting's range and habitat.     

The deep waters from the Southern Ocean at the entry to the Argentine Basin

Hydrographic data from the World Ocean Circulation Experiment (WOCE) and South Atlantic Ventilation Experiment (SAVE) in the region of transition between the Scotia Sea and the Argentine Basin are examined to determine the composition of the deep water from the Southern Ocean that enters the Atlantic, and to describe the pathways of its constituents. The deep current that flows westward against the Falkland Escarpment is formed of several superposed velocity cores that convey waters of different origins: Lower Circumpolar Deep Water (LCDW), Southeast Pacific Deep Water (SPDW), and Weddell Sea Deep Water (WSDW).Different routes followed by the WSDW upstream of, and through, the Georgia Basin, lead to distinctions between the Lower-WSDW (σ₄>46.09) and the Upper-WSDW (46.04<σ₄ <46.09). The Lower-WSDW flows along the South Sandwich Trench, then cyclonically in the main trough of the Georgia Basin. Although a fraction escapes northward to the Argentine Basin, a comparison of the WOCE data with those from previous programmes shows that this component had disappeared from the southwestern Argentine Basin in 1993/1994. This corroborates previous results using SAVE and pre-SAVE data. A part of the Upper-WSDW, recognizable from different θ–S characteristics, flows through the Scotia Sea, then in the Georgia Basin along the southern front of the Antarctic Circumpolar Current. Northward leakage at this front is expected to feed the Argentine Basin through the northern Georgia Basin. The SPDW is originally found to the south of the Polar Front (PF) in Drake Passage. The northward veering of this front allows this water to cross the North Scotia Ridge at Shag Rocks Passage. It proceeds northward to the Argentine Basin around the Maurice Ewing Bank. The LCDW at the Falkland Escarpment is itself subdivided in two cores, of which only the denser one eventually underrides the North Atlantic Deep Water (NADW) in the Atlantic Ocean. This fraction is from the poleward side of the PF in Drake Passage. It also crosses the North Scotia Ridge at Shag Rocks Passage, then flows over the Falkland Plateau into the Atlantic. The lighter variety, from the northern side of the PF, is thought to cross the North Scotia Ridge at a passage around 55°W. It enters the Argentine Basin in the density range of the NADW.     

Contribution of global potential field data to the tectonic reconstruction of the Rio Grande Rise in the South Atlantic

The application of advanced enhancement techniques for geophysical anomalies to global gravity (WGM2012) and magnetic (EMAG2) models sheds light on the complex tectonic evolution of the Rio Grande Rise (RGR) in the southern South Atlantic. Long wavelength Bouguer gravity lows indicate a thicker crust beneath of the ridge, whose nature can be related to a microcontinent or an excess of volcanism within the oceanic realm. Recently dredged continental rocks reinforce the hypothesis of a microcontinent or, at least, slivers of continental crust. However, the reserval magnetic pattern of the processed magnetic anomalies provide no evidence of aborted spreading center similar to the well-studied Jan Mayen microcontinent and the surrounding (inactive) Aegir and (active) Kolbeinsey ridges in the North Atlantic Ocean. The reversal magnetic anomalies show a series N-S trending parallel stripes roughly follow the current South American coastline and segmented by E-W oriented oceanic fracture zones (FZs). The magnetic stripes are bended eastwards at the RGR, showing a more complex magnetic pattern similar to that in the Iceland. The aborted Cruzeiro do Sul Rift (CSR) and the Jean Charcot Chain (JCC) are structures that cross the RGR and contribute to the understanding of the tectonic evolution of the South Atlantic Ocean. NW-SE oriented extensive gravity lows and bathymetric valleys, which mark the CSR, are segmented by E-W trending magnetic lineaments related to FZs. This structural configuration suggests that the extensional event, which formed the rift and the seamounts chain, was replaced by strike-slip movements along the FZs. In addition, we constructed a plate kinematic model for the evolution of the RGR based on bathymetric, free-air and Bouguer gravity and magnetic data. Our model comprises five main stages of the RGR formation and evolution between late Cretaceous and Paleocene (ca. 95 - 60 Ma), separated by published seafloor isochrones. The proposed model suggests that the RGR was built at the mid-Atlantic ridge by increased magmatism probably related to the Tristan da Cunha hotspot.     

Tectonic control of the oil-rich large igneous-carbonate-salt province of the South Atlantic rift

The Early Cretaceous South Atlantic Magmatic Province (SAMP), which includes the Paraná-Etendeka LIP, produced about 8 million km³ of tholeiitic basalt and diabase over an area of 4 million km². Huge pre-salt oil reserves, discovered in 2007 by Petrobras in non-marine carbonates, are estimated at more than 45 billion barrels. Here we show the close causal relationship of the southward increasing width of the wedge-shaped South Atlantic rift with the similarly southward increase in igneous activity, in the thicknesses of non-marine carbonate and salt, and in the size of oil reserves, all controlled mainly by South America’s early clockwise rotation away from Africa about a pole in its northeast. Large diabase dike swarms transversal to the rift witness to South America’s rotation that opened in its wake the southward widening South Atlantic rift. Westward increasing pressure on the Equatorial margin by South America’s clockwise rotation forced open the Benue trough and created pre-late-Aptian folds in the Demerara Plateau and in Brazil’s Solimões (Upper Amazonas) basin. Prerift and synrift volcanic activity increases southward, culminating in the Parana-Etendeka LIP and in the offshore volcanic SDRSs that continue southward to the Cape Basin. Berriasian-Valanginian rift sediments deposited from about 145 Ma, 10 Ma before the flood basalts of the Parana-Etendeka LIP. The largest transversal dike swarm continued in the proto-Walvis Ridge that separated the central South Atlantic endorheic rift basin from the sea in the south; erosion and leaching of basalts supplied Ca, Mg, and SiO₂ to the endorheic basin for the deposition of non-marine carbonates and authigenic clays. Basalt flows intercalated with carbonates nearly until salt deposition about 113 Ma. Hypogenic leaching of carbonates by mantle-derived CO₂ created optimal reservoirs. Supergiant oil deposits occur where the widest endorheic basin and the volcanic province overlap.     

Magnetic susceptibility and ice-rafted debris in surface sediments of the Atlantic sector of the Southern Ocean

Spatial distribution of magnetic susceptibility and the gravel fraction in surface sediments in the Atlantic sector of the Southern Ocean were investigated to reconstruct source areas and recent transport pathways of magnetominerals and ice-rafted debris. Maxima of magnetic susceptibility were observed offshore from areas where mafic source rocks occur, e.g. Queen Maud Land and the northern Antarctic Peninsula. The glacigenic input of debris and subsequent redeposition of fine material by bottom and turbidity currents on the continental margins result in regional variations of the gravel and susceptibility values. In the deep sea, however, the mixing of ice-rafted debris and turbidites from distal source areas causes a homogenous distribution of the susceptibility signal. On submarine elevations such as Maud Rise and Astrid Ridge, dust input may be an additional source for magnetominerals.     

南马里亚纳海槽岩石学特征

南马里亚纳海槽岩性比较复杂：有玄武岩，根据标准矿物组合，进一步划分为碱性玄武岩，橄揽拉斑玄武岩和石英拉斑玄武岩；火山碎屑岩，包括凝灰岩和角砾凝灰岩；以及方辉橄榄岩．大部分玄武岩样品是距今五百万年以后形成的，个别岩石样品的形成年龄为八百万年左右．不同类型的玄武岩是含Ｈ２Ｏ的地幔岩块在底辟上升过程中，局部熔融、分离的产物；火山碎屑岩是火山喷发的火山灰、火山砾被水化学分解的物质胶结而成；方辉橄榄岩是地幔岩浆底辟上升直接侵入结晶的产物．     

Age of the Floors of the Protector and Dove Basins (Scotia Sea)

The tectonic evolution of the transition zone from the Pacific Ocean to the Atlantic Ocean is closely linked with the destruction of the American–Antarctic continental bridge in the Scotia Sea. The western segment of the bridge combines the Terror, Pirie, and Bruce banks, as well as the Protector and Dove basins between them. Modeling—primarily based on original geological and geophysical materials—of linear magnetic anomalies and calculation of the floor kinematics in these basins have made it possible for the first time to reveal that the collapse of the western segment of the American–Antarctic continental bridge occurred 18–25 Ma ago via a two-stage separation of the Pirie Rise from the Bruce Rise with the formation of the Dove Basin and a two stage separation of the Terror Rise from the Pirie Rise with the formation of the Protector Basin.     

Relation between sea surface temperature anomaly in the Atlantic and summer precipitation over the Northeast China

1 IwrRoDUcrIowln recen l00 years. mateorolQgi8ts have paid mu0h aneation to impact of ocean onlong-range weather process. Because fram view POillt of space and tAne scale condition,ocean is one of very important phySical factor for the evolotion of thespheric circulation.The scientific research cooperation grOup (l979) first found that SST in the equatorialeastern Pacific reversely correlates with summer tempendre aver Nowheast China. Pan etal (1981) discussed re1atfon between heating of…     

南海北部冷泉区深水珊瑚的发现及其特征

冷水珊瑚也称为深水珊瑚, 在生物多样性、生态资源和科研价值等方面具有重要意义。文章对采自南海北部冷泉区的冷水珊瑚骨骼碎屑进行测定, 鉴定出冷水珊瑚2个种(Crispatotrochus sp.1和Crispatotrochus sp.2), 以及4个属[Balanophyllia (Balanophyllia)、Balanophyllia (Eupsammia)、Lochmaeotrochus和Enallopsammia]。测定的冷水珊瑚的δ¹³C为-7.36‰~-1.15‰, δ¹⁸O为-1.38‰~3.67‰, 与全球冷水珊瑚碳氧同位素组成相似, 但明显不同于南海暖水珊瑚、冷泉碳酸盐岩及低温热液成因碳酸盐岩的碳氧同位素组成。     

南海北部及邻区岩石圈地幔特征与深部作用过程初探

对新生代火山活动携带到地表的超镁铁岩捕虏体岩石的主元素、微量元素和同位素特征的研究表明，南海北部及邻区岩石圈地幔组成和空间变化与大地构造分区有密切联系；区域上的岩石圈地幔经历过多重地幔交代作用，而与南海北部陆缘活化和陆缘扩张更为密切相关的地幔交代作用可能主要为高温型富Ｆｅ－Ｔｉ交代作用；软流圈热物质上升是引起大陆地壳活化的重要的深部作用因素。     

Potassium-argon/argon-40-argon-39 geochronology of Cenozoic alkali basalts from the South China Sea

Based on the isotopic chronologic results of Cenozoic alkali basalts from the South China Sea, the characteristics of volcanic activi- ty of the South China Sea after spreading were studied. The potassium - argon ages of eight alkali basalt samples from the South China Sea, and the argon - argon ages of two samples among them are reported. Apparent ages of the whole rock are 3.80 to 7. 91 Ma with an average value of 5.43 Ma （potassium- argon, whole rock）, and there is little difference among samples at the same location, e. g. , 4. 76 - 5.78 Ma for location S（M-12. The argon - argon ages for the two samples are 6.06 and 4. 71 Ma, which lie within the age scope of potassium - argon method. The dating results indicate that rock-forming age is from late Miocene to Pliocene, which is consistent with erupting event for alkali basalts from adjacent regions of the South China Sea. Volcanic activities occur after the cessation of spreading of the South China Sea, which are controlled by lithospheric fault and the spreading center formed during the spreading period of the South China Sea. These dating results, combined with geochemical characteristics of these basalts, the published chronological data for the South China Sea and its adjacent regions, and the updated geophysical data near Hainan Island, suggest that after the cessation of spreading of the South China Sea, there occur widely distributing magmatic activities which primarily is alkali basalt, and the volcanic activity continues to Quaternary. The activity may be relative to Hainan mantle plume originated from core/mantle boundary.     

Petrology, Geochemistry and Nd-Sr-Pb Isotopic Properties of Volcanic Rocks in Daheishan Island, Penglai, Shandong Province

The major elements, trace elements, K-Ar age and Sr-Nd-Pb isotopic systems of the Cenozoic volcanic rocks in Daheishan Island and Cishan, Penglai, Shandong Province are measured. The volcanic rocks ( olivine-nephelinite and nepheline-basanite ) in DaheishanIsland erupted periodically in an interval of 0.32 Ma, from 8.72 Mm 8.39 Ma, 8.08 Ma to 7.73Ma. The volcanic rocks are all rich in light REEs. They are similar to the OIB-type alkali basalt in the trace elements normalized model by primordial mantle: rich in high field elements such as Nb and Ta, and imcompatible elements such as Cs, Rb, Ba, Th, U. The volcanic rocks show a depletion of K and Rb elements. It is suggested by the trace elements that the olivine-nephelinite in Daheishan Island is originated fi‘om deep resources under the continental mantle, ε Nd (0) values of the volcanic rocks in Daheishan Island and Cishan are 5.31 - 8.51 and 7.33 respectively, suggesting that the volcanic rocks are from the depleted mantle resources, which have higher Sm/Nd ratios than the CHUR. ^143Nd /^144Nd ratios of Daheishan Island olivine-nephelinite and Cishan alkali basalts are 0.512 910 - 0.513 074 and 0.513 014 resoeetivelv. The ^87Sr /^86Sr of Daheishan lsland volcanic rocks are lower than that of Cishan, 0.703 427 - 0.703 482 and 0.703 895 respectively. The Daheishan Island olivinenephelinite has the Pb isotopic values as follows: ^206Pb /^204pb= 18.028 9 ～17.972 8,^207Pb /^204Pb= 15,435 8 - 15.402 2 and ^208Pb /^204Pb=38.087 6 - 37.997 5, lower than those of Cishan basanite. The Cishan basanite has ^206Pb / ^204Pb = 18.240 1, ^208Pb /^204Pb = 15.564 5 and ^208Pb /^204Pb=38.535. The authors suggest that the olivine-nephelinite in Daheishan Island is similar to the E-type MORB or Hawaii OIB, and the alkali basalts in Cishan similar to the Kerguelen OIB. The dominant mantle components of DM PREMA and perhaps DM( Dupal type ) are the dominant mantle components for volcanic rocks in Daheishan Island and Cishan. The PREMA component plays an important role.     

白垩纪以来太平洋上地幔组成和温度变化

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.     

Transport of Antarctic krill (Euphausia superba) across the Scotia Sea. Part I: Circulation and particle tracking simulations

The Harvard Ocean Prediction System (HOPS) is configured to simulate the circulation of the Scotia Sea and environs. This is part of a study designed to test the hypothesis that Antarctic krill (Euphausia superba) populations at South Georgia in the eastern Scotia Sea are sustained by import of individuals from upstream regions, such as the western Antarctic Peninsula. Comparison of the simulated circulation fields obtained from HOPS with observations showed good agreement. The surface circulation, particularly through the Drake Passage and across the Scotia Sea, matches observations, with its northeastward flow characterized by three high-speed fronts. Also, the Weddell Sea and the Brazil Current, and their associated transports match observations. In addition, mesoscale variability, an important component of the flow in this region, is found in the simulated circulation and the model is overall well suited to model krill transport. Drifter simulations conducted with HOPS showed that krill spawned in areas coinciding with known krill spawning sites along the west Antarctic Peninsula continental shelf can be entrained into the Southern Antarctic Circumpolar Current Front (SACCF). They are transported across the Scotia Sea to South Georgia in 10 months or less. Drifters originating on the continental shelf of the Weddell Sea can reach South Georgia as well; however, transport from this region averages about 20 months. Additional simulations show that such transport is sensitive to changes in wind stress and the location of the SACCF. The results of this study show that krill populations along the Antarctic Peninsula and the Weddell Sea are possible source populations that can provide krill to the South Georgia population. However, successful transport of krill to South Georgia is shown to depend on a multitude of factors, such as the location of the spawning area and timing of spawning, and variations in the location of the SACCF. Therefore, this study provides insight into which environmental factors control the successful transport of krill across the Scotia Sea and with it a better understanding of krill distribution in the region.