Geochemistry of volcanic glass from Oligocene detrital sediments at DSDP Site 296, Kyushu Palau Ridge: Interpreting the magmatic evolution of the early northern Izu–Bonin–Mariana Island Arc

Understanding the petrologic and geochemical evolution of island arcs is important for interpreting the timing and impacts of subduction and processes leading to the formation of a continental crust. The Izu–Bonin–Mariana (IBM) Arc, western Pacific, is an outstanding location to study arc evolution. The IBM first arc (45–25 Ma) followed a period of forearc basalt and boninite formation associated with subduction initiation (52–45 Ma). In this study, we present new major and trace element data for the IBM first arc from detrital glass shards and clasts from DSDP Site 296, located on the northernmost Kyushu Palau Ridge (KPR). We synthesize these data with published literature for contemporaneous airfall ash and tephra from the Izu–Bonin forearc, dredge and piston core samples from the KPR, and plutonic rocks from the rifted eastern KPR escarpment, locations which lie within or correlate with KPR Segment 1 of Ishizuka, Taylor, Yuasa, and Ohara (2011). Our objective is to test ways in which petrologic and chemical data for diverse igneous materials can be used to construct a complete picture of this section of the Oligocene first arc and to draw conclusions about its evolution. Important findings reveal that widely varying primary magmas formed and differentiated at various depths at this location during this period. Changes in key trace element ratios such as La/Sm, Nb/Yb, and Ba/Th show that mantle sources varied in fertility and in the inputs of subducted sediment and fluids over time and space. Plutonic rocks appear to be related to early K‐poor dacitic liquids represented by glasses sampled both in the forearc and volcanic fronts. An interesting observation is that the variation in magma compositions in this relatively small segment encompasses that inferred for the IBM Arc as a whole, suggesting that sampling is a key factor in inferring temporal, across‐arc, and along‐strike geochemical trends.     

西南印度洋中脊49.5°E离轴地壳结构

超慢速扩张西南印度洋中脊岩浆的集中供给在空间维度上表现为岩浆扩张段（NVR）与相邻的非转换断层不连续带（NTD）地壳结构的差异,而在时间维度上表现为离轴与沿轴地壳结构的差异.为了进一步揭示岩浆集中供给的时空分布特征,本文选取西南印度洋中脊热液区2010年海底地震仪深部探测中平行于洋中脊距轴部偏北约10 km的离轴测线d0d10,使用射线追踪正演和反演的方法,得到了NVR和NTD北侧离轴区域的地壳及上地幔P波速度结构,并与轴部速度结构进行了对比分析.研究结果表明：（1）NTD北侧离轴区域的地壳厚度约5.2 km,其厚度明显大于轴部NTD下方地壳厚度（~3.2 km）,由此推测洋脊轴部NTD区域形成的地壳在不断减薄;（2）NVR北侧离轴区域的地壳厚度约7.0 km,其厚度亦大于轴部NVR地壳厚度（~5.8 km）,表明在洋中脊演化过程中洋脊轴区域的岩浆供给在不断减少,其活动性在不断减弱.     

春末环贝加尔湖地区环流的年际和年代际变化及与中国温度和降水的关系

本文利用1951~2011年的再分析资料及观测资料,探讨了春末环贝加尔湖地区环流的年际和年代际变化特征及其与中国温度、降水的关系,主要结论如下:(1)春末贝加尔湖脊(简称贝脊)在1951~1979年间较弱,但在1980~1999年期间显著增强。进入21世纪后,春末贝脊呈显著减弱的趋势;(2)强(弱)贝脊使我国北方地区的温度显著升高(降低),使西南地区的温度降低(升高)。贝脊的强弱变化,对北方地区温度的影响在1951~1979年期间最为显著,对西南地区温度的影响在1980~2011年期间显著。在1951~1999年期间,贝脊的强弱变化与长江下游的降水量存在明显的反位相变化关系。进入21世纪后,贝脊的强弱变化与西南地区降水量之间存在较为显著的正相关关系(99%置信度);(3)强贝脊与由北大西洋/欧洲上空向东传播的定常行星波密切相关,而弱贝脊主要与欧亚大陆次极区纬向伸展的行星尺度脊相联系。在不同的年代际时段,与贝脊强弱变化相联系的北半球异常环流特征也存在一定的差异;(4)5月份的强贝脊环流以前期的北大西洋涛动、东大西洋型以及弱东亚大槽环流为前兆信号。同年3月乌拉尔山气旋式异常环流为5月份贝脊弱的前兆信号。     

Evaluation and modelling of Tertiary source rocks in the central Arctic Ocean

With the recently recovered organic-rich sediments of early Tertiary age from the Lomonosov Ridge by the Integrated Ocean Drilling Program (IODP) Expedition 302, the first data collection directly from source rocks of the central basins of the Arctic Ocean is now available. Using the results of seismic interpretations and published sedimentological and organic geochemical data from Expedition 302, the framework for the first quantitative assessment of source-rock quality and distribution of the Palaeogene sediments was modelled in the central Arctic Ocean. The modelling results suggest that an approximately 100-m-thick Early to Middle Eocene sedimentary sequence of good to very good source rocks exists along a 75 km long transect across the Lomonosov Ridge. In-situ generation of hydrocarbons is unlikely because the overburden (200–250 m) and consequently the thermal maturity are too low. Burial history and thermal modelling reveal that an additional overburden of at least 1000 m is necessary to start hydrocarbon generation along the ridge. However, source-rock modelling results show that good source-rock potential may exist in correlative units in the adjacent Amundsen Basin. Simulated organic carbon contents of 1.5–5%, coupled with an overburden of 1000–1200 m, and heat flow anomalies (117 and 100 mW m⁻²) due to the vicinity to the Gakkel Ridge spreading centre indicate that necessary conditions for hydrocarbon expulsion are already reached, and point to viability of a potential petroleum system. Our results support the hypothesis that deposition of a potentially good hydrocarbon source rock occurred across the entire Arctic Basin and adjacent margins during the early Tertiary.     

Regional study on potential CO2 geosequestration in the Collie Basin and the Southern Perth Basin of Western Australia

Coal-fired power stations in Collie, Western Australia emit 10 million tonnes of CO₂ per year. This study assesses the potential opportunities of geological storage of CO₂ both within the Collie Basin and the onshore part of the adjacent Southern Perth Basin of Western Australia within 50 km of Collie town site through a desktop evaluation of existing data. The aquifers and coal formations within both basins have been evaluated for their suitability for storage based on geological, geographical and environmental criteria related to storage capacity, injectivity, proximity to sources of CO₂, location of other natural resources and containment security. The study has concluded that there is limited scope for large-scale storage of CO₂ within the Collie Basin. In addition the potential for storage within coals of either basin is not a viable solution. This assessment is based on published criteria for CO₂ storage in sedimentary basins and coal-bearing formations.     

Preliminary study on the erratic exposure ages of Grove Mountains, East Antarctica

The first study of erratic boulder exposure ages in the Grove Mountains,interior Antarctica,indicates the two erratic boulders(060131-1 and 060131-2,collected from a typical nunataks,Zakharoff Ridge in the Grove Mountains) have 10Be minimum exposure ages of 1.24±0.11 Ma,1.37±0.12 Ma,and 26Al ages of 0.90±0.12 Ma,0.44±0.04 Ma,respectively.Meanwhile,another erratic boulder sample 060131-4,coming from vicinal ice surface,has 10Be and 26Al minimum exposure ages of 0.47±0.3 Ma and 0.44±0.04 Ma,respectively.The e...     

大洋中脊海底热液系统的演化特征及其成矿意义

大洋中脊海底热液系统的演化与成矿是复杂、综合的地质过程.归纳、分析了前人研究的资料认为,热源供给和热液活动构造体系是控制热液系统演化与成矿的关键因素.在快速扩张洋中脊热液系统中,岩浆的供给充裕,构造体系渗透性极好,演化时间较短,海底的热液循环输出过程可分为发生、持续和衰退3个阶段;在慢速扩张洋中脊热液系统中,岩浆的供给...     

Evolution of the Grenada and Tobago basins and implications for arc migration

The tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood. This paper presents an integrated stratigraphic and tectonic evolution of Late Cretaceous to Recent volcanic arcs and associated basins in the southeastern Caribbean Sea using seismic reflection data, wide-angle seismic refraction data, well data, and onland geologic data. We propose a new tectonic model for the opening of the Grenada and Tobago basins and the 50-250-km eastward jump of arc volcanism from the Late Cretaceous Aves Ridge to the Miocene to Recent Lesser Antilles arc in the southeast Caribbean based on the mapping of three seismic megasequences. The striking similarity of the half-graben structure of the Grenada and Tobago basins that flank the Lesser Antilles arc, their similar smooth basement character, their similar deep-marine seismic facies, and their similar Paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single, saucer-shaped, oceanic crust Paleogene forearc basin adjacent to the now dormant Aves Ridge. This single forearc basin continued to extend and widen through flexural subsidence during the early to middle Eocene probably because of slow rollback of the subducting Atlantic oceanic slab. Rollback may have been accelerated by oblique collision of the southern Aves Ridge and southern Lesser Antilles arc with the South American continent. Uplift and growth of the southern Lesser Antilles arc divided the Grenada and Tobago basins by early to middle Miocene time. Inversion of normal faults and uplift effects along both edges of the Lesser Antilles arc are most pronounced in its southern zone of arc collision with the South American continent. The late Miocene to Recent depositional histories of the Grenada and Tobago basins are distinct because of isolation of the Grenada basin by growth and uplift of the Neogene Lesser Antilles volcanic ridge.     

Dampier Ridge,Tasman Sea,as a stranded continental fragment∗

Dredging of the Dampier Ridge recovered small fragments of granite, gabbro and sandstone. Dating of the igneous samples by the U‐Pb, K‐Ar and Rb‐Sr methods yielded precise ages mainly in the range 250 to 270 Ma, mid‐Permian. An imprecise Sm‐Nd mineral age of ～ 310 Ma might reflect slightly earlier emplacement of the gabbro. A granitic fragment has a composition approximating that of a minimum melt. Taken together with the Late Palaeozoic emplacement ages and other geochemical and geophysical data, the evidence strongly supports the conclusion that the Dampier Ridge is a continental fragment, formerly part of eastern Australia, with its present location a consequence of continental rifting and opening of the Tasman Basin by sea‐floor spreading.