南大西洋洋中脊附近沉积物中烃类分布和组成研究

我们利用气相色谱-质谱联用仪(GC-MS)测试了南大西洋洋中脊附近采集的沉积物样品中烃类的分布和组成。通过分析发现,样品中烃类表现出明显的双峰分布,同时明显的富集3-甲基烷烃、8-甲基烷烃以及2,4,(n-1)-三甲基烷烃,这可能是海底微生物代谢作用的结果。样品中也富集萜烷、藿烷和甾烷等生物标志物,这也支持样品中烃类主要为微生物来源的观点。样品中沥青和烃类显示出距离热液区近的2V-TVG10和26V-TVG05站位含量高,而距离热液区远的22IV-TVG01、22V-TVG11和22V-TVG14站位含量低的趋势,暗示出样品中沥青以及烃类的分布和组成可能受到海底热液活动的影响。     

Tectonic implications of the subduction of the Kyushu-Palau Ridge beneath the Kyushu,southwest Japan

The Kyushu-Palau Ridge(KPR), a remnant arc on the Philippine Sea Plate(PSP), is subducting beneath the Kyushu, southwest Japan. Influenced by the subducting KPR, the Kyushu subduction zone corresponding to the KPR is significantly different from Shikoku subduction zone in terms of gravity anomalies, seismicity, the stress state, and the subducting slab morphology. Significant negative free-air and Bouguer gravity anomalies are observed in a prolonged area of KPR, southeast of the Miyazaki Plain, indicating that this is where KPR overlaps the overriding plate. The gravity anomaly in this area is much lower than that in other areas where the inferred KPR extends, suggesting that the subduction of the buoyant KPR may cause the lower mantle density to decrease.More earthquakes have occurred in Hyuga-nada region where the KPR subducts than in Shikoku forearc and other areas in the Kyushu forearc, indicating that the subduction of the KPR enhances the local coupling between the subducting and overriding plates. The centroid moment tensor(CMT) mechanism of earthquakes shows that stress is concentrated in the accumulated crust beneath the Kyushu forearc corresponding to the KPR, and the shallow thrusting events in the obducting plate are caused by the KPR subduction. The buoyant KPR, with a large volume of low-density sediments, was responsible for the differences of the subduction depth and dip angle of the subducting Philippine Sea(PS) slab between northern Kyushu and Shikoku. The seismic gaps and the sudden change of the dipping angle of the subducting PS slab indicate that slab tear may have occurred along the west side of the KPR beneath southwest Kyushu. A two-tear model was proposed, and the subduction of the buoyant KPR was believed to play an important role in the slab tear.     

夏季西太平洋副热带高压的客观定量化预测及其对汛期降水的指示

基于动力统计相似预报原理,将模式误差动力统计预报方案应用于西太平洋副热带高压的客观定量化预测,通过交叉检验距平相关系数,筛选出对副热带高压区域的500 hPa高度场模式预报结果订正较好的因子作为前期关键因子集.对2003-2010年的副热带高压区域的500 hPa高度场进行了回报检验,结果显示该方案在数值模式预报结果基础上有了进一步提高,显示出较高的预测水平.在此基础上,从高度场预测结果中提取出与中国降水关系最为密切的两个典型副热带高压特征指数(脊线指数与西伸脊点指数),将其投影在二维平面上,并根据不同类型的副热带高压特征下对应的雨型分类特征得到预报年副热带高压所属类型下中国夏季降水的分布类型,多年检验结果表明,预测的投影类型所对应的降水合成分布与实况的降水具有较好的一致性,进一步验证此种副热带高压与雨型分类的合理性,达到通过副热带高压的定量化预测对夏季的旱涝分布形式进行预测的目的,为进一步提高汛期降水预测水平提供一种可能的思路.     

西南印度洋中脊49.6°E和50.5°E区玄武岩岩石学及元素地球化学特征

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。     

海洋环境甲烷水合物溶解度及其对水合物发育特征的控制

除合适的温度和压力条件外,甲烷水合物的形成还需要有充足的甲烷供给,沉积物孔隙水中的甲烷浓度必须大于甲烷水合物的溶解度.本文建立了水合物－水－游离气三相体系、水合物－水二相体系、气－水二相体系的甲烷溶解度计算优选方法,计算确定了水合物系统的甲烷溶解度-深度相图,依此划分出游离气、溶解气、水-水合物、水-水合物-游离气四个甲烷不同相态分布区.对水合物脊ODP1249和1250钻位、布莱克海台ODP997钻位稳定带甲烷水合物含量和稳定带之下游离气含量进行了计算.ODP1249浅部13.5～72.4 mbsf(mbsf表示海底以下深度)的甲烷水合物是沉积物孔隙体积的10%～61%,ODP1250钻位35～1065 mbsf的甲烷水合物约为孔隙体积的0.7%～1.9%,水合物层之下游离气层厚约22 m,游离气含量约占孔隙的4%.布莱克海台ODP997钻位的浅部146.9 mbsf处无水合物发育,202.4～433.3 mbsf之间水合物占孔隙体积的约5%～7%,水合物层之下游离气层厚约80 m,游离甲烷含量为孔隙的0.2%～28%.     

Quality Evaluation of Offshore Data in the Earth Magnetic Anomaly Grid（2-arc-Minute Resolution）：Taking the Southern Section of the Kolbeinsey Ridge in the Arctic Region as an Example

In order to evaluate the quality of the offshore magnetic data in the Earth Magnetic Anomaly Grid (2-arc-minute resolution)(EMAG2), the authors chose the aeromagnetic data at 1∶500 000 and 1∶1 000 000 scales of the southern section of the Kolbeinsey Ridge with a total area of 193 500 km² to compare and analyze. Based on the EMAG2 data, the authors obtained the EMAG2 (downward continuation 4 km) and the aeromagnetic anomaly (upward continuation 4 km) using the analytical continuation method. Then, the correlation coefficients between the aeromagnetic anomaly (upward continuation 4 km) and the EMAG2, and the aeromagnetic anomaly and the EMAG2 (downward continuation 4 km) were calculated by the correlation analysis method. Finally, through comprehensive analysis of the features of these correlation coefficients and differences, the quality of the magnetic data of the southern section of the Kolbeinsey Ridge was evaluated in the database EMAG2. The results showed that the EMAG2 integrated a large number of the airborne or offshore magnetic data. The quality of the offshore magnetic data is relatively high in the offshore areas with dense lines. However, the quality of the offshore magnetic data is relatively low if the EMAG2 data at 4 km altitude is converted to the anomaly data at sea level.     

Numerical modeling of the effects of water flow,sediment transport and vegetation growth on the spatiotemporal patterning of the ridge and slough landscape of the Everglades wetland

A numerical model has been developed to simulate the spatiotemporal patterning of the ridge and slough landscape in wetlands, characterized by crests (ridges) and valleys (sloughs) that are elongated parallel to the direction of water flow. The model formulation consists of governing equations for integrated surface water and groundwater flow, sediment transport, and soil accretion, as well as litter production by vegetation growth. The model simulations show how the spatial pattern self-organizes over time with the generation of ridges and sloughs through sediment deposition and erosion driven by the water flow field. The spatial and temporal distributions of the water depth, flow rates and sediment transport processes are caused by differential flow due to vegetation and topography heterogeneities. The model was parameterized with values that are representative of the Everglades wetland in the southern portion of the Florida peninsula in the USA. Model simulation sensitivity was tested with respect to numerical grid size, lateral vegetation growth and the rate of litter production. The characteristic wavelengths of the pattern in the directions along and perpendicular to flow that are simulated with this model develop over time into ridge and slough shapes that resemble field observations. Also, the simulated elevation differences between the ridges and sloughs are of the same order of those typically found in the field. The width of ridges and sloughs was found to be controlled by a lateral vegetation growth distance parameter in a simplified formulation of vegetation growth, which complements earlier modeling results in which a differential peat accretion mechanism alone did not reproduce observations of ridge and slough lateral wavelengths. The results of this work suggest that ridge and slough patterning occurs as a result of vegetation's ability to grow laterally, enhancing sediment deposition in ridge areas, balanced by increased sediment erosion in slough areas to satisfy flow continuity. The interplay between sediment transport, water flow and vegetation and soil dynamic processes needs to be explored further through detailed field experiments, using a model formulation such as the one developed in this work to guide data collection and interpretation. This should be one of the focus areas of future investigations of pattern formation and stability in ridge and slough areas.     

国产I-4C型OBS在西南印度洋中脊的试验

介绍了在DY115-21航次第6航段西南印度洋中脊构造调查中,中国科学院地质与地球物理研究所研制的5台I-4C型海底地震仪（OBS）的试验情况.在不同的水深点（2370～3534 m）共投放OBS 6个台次,全部投放和回收成功.OBS内置电化学式和外置机械式两种上浮释放系统都成功动作,取得了船载气枪震源的地震数据.但仍存在三个主要问题：第一,上浮后的GPS应答搜寻系统无效果;第二,夜间回收时所需的灯光明亮度较差;第三,外在结构不利于海面上的姿态控制和打捞.     

Petrology and geochemistry of South Mid-Atlantic Ridge (19°S) lava flows: Implications for magmatic processes and possible plume-ridge interactions

The South Mid-Atlantic Ridge (SMAR) 19°S segment, approximately located along the line of Saint Helena volcanic chain (created by Saint Helena mantle plume), is an ideal place to investigate the issue whether the ridge-hotpot interaction process affected the whole MAR. In this study, we present major and trace elemental compositions and Sr-Nd-Pb isotopic ratios of twenty fresh lava samples concentrated in a relatively small area in the SMAR 19°S segment. Major oxides compositions show that all samples are tholeiite. Low contents of compatible trace elements (e.g., Ni ​= ​239–594 ​ppm and Cr ​= ​456–1010 ​ppm) and low Fe/Mn (54–67) and Ce/Yb (0.65–1.5) ratios of these lavas show that their parental magmas are partially melted by a spinel lherzolite mantle source. Using software PRIMELT3, this study obtained mantle potential temperatures (T_p) beneath the segment of 1321–1348 ​°C, which is lower relative to those ridges influenced by mantle plumes. The asthenospheric mantle beneath the SMAR 19°S segment starts melting at a depth of ~63 ​km and ceases melting at ~43 ​km with a final melting temperature of ~1265 ​°C. The extent of partial melting is up to 16%–17.6% with an average adiabatic decompression value of 2.6%/kbar. The correlations of major oxides (CaO/Al₂O₃) and trace elements (Cr, Co, V) with MgO and Zr show that the parental magma experienced olivine and plagioclase fractional crystallization during its ascent to the surface.⁸⁷Sr/⁸⁶Sr (0.702398–0.702996), ¹⁴³Nd/¹⁴⁴Nd (0.513017–0.513177) and ²⁰⁶Pb/²⁰⁴Pb (18.444–19.477) ratios of these lavas indicate the mantle source beneath the SMAR 19°S segment is composed of a three-component mixture of depleted MORB mantle, PREMA mantle, and HIMU mantle materials. The simple, binary mixing results among components from plume-free SMAR MORB, Saint Helena plume and Tristan plume show that asthenospheric mantle beneath the SMAR 19°S segment may be polluted by both Saint Helena and Tristan plume enriched materials. The abovementioned mantle potential temperatures, together with the low Saint Helena (<10%) and Tristan (<5%) components remaining in the asthenospheric mantle at present, show that the physically ridge-hotspot interactions at SMAR 19°S segment may have ceased. However, the trace element and Sr-Nd-Pb isotopically binary mixing calculation results imply that these lavas tapped some enriched pockets left when Saint Helena and/or Tristan plume were once on the SMAR during earlier Atlantic rifted history.     

板块俯冲与斑岩铜金成矿

绝大多数斑岩铜金矿床分布在汇聚板块边缘。研究表明高氧逸度和洋壳部分熔融是控制斑岩铜金矿床形成的两个关键因素。作为亲硫元素,铜金的性质主要受还原态的硫(S~(2-))控制,而硫的价态和性质则强烈受氧逸度的影响。矿床学家很早就发现氧逸度ΔFMQ+2是斑岩铜金矿床成矿的魔幻数字。研究发现其原因是硫的性质在此氧逸度附近发生巨变,在低氧逸度时,硫主要以硫化物的形式存在,但是当氧逸度在ΔFMQ+1. 5以上时,硫主要以硫酸根的形式存在。硫酸盐在岩浆中的溶解度通常是硫化物的10倍左右,因此在部分熔融过程中,高氧逸度可以大幅度提高硫在岩浆中的溶解度,有利于源区硫化物被破坏,以硫酸根的形式被熔出,从而大幅度提高初始岩浆中的铜(金)含量;与此同时,硫化物在岩浆演化过程中可以保持不饱和状态,有利于作为中度不相容元素的铜(金)通过岩浆演化进一步富集。在磁铁矿结晶等过程中,岩浆体系的氧逸度降低,硫酸根被还原,还原态的硫(S~(2-))将岩浆中的铜金萃取,富集到流体相,从而形成斑岩铜金矿床。这种高氧逸度岩浆通常出现在汇聚板块边缘。由于洋壳铜、金、硫含量远高于陆壳和地幔,而且俯冲带氧逸度高出地幔和下地壳约2个数量级,因此俯冲洋壳部分熔融形成岩浆的初始铜、金、硫含量远高于陆内岩浆,有利于成矿。年轻洋脊的俯冲因其高热量是显生宙以来最容易发生俯冲洋壳部分熔融的地质过程,且同时具有高氧逸度,因此洋脊俯冲是形成大型、超大型斑岩铜金矿床的最佳途径。统计结果显示,全球主要超大型斑岩铜金矿床均与洋脊俯冲有关。