Petrology and Geochemistry of West Philippine Basin Basalts and Early Palau-Kyushu Arc Volcanic Clasts from ODP Leg 195, Site 1201D: Implications for the Early History of the Izu-Bonin-Mariana Arc

Site 1201D of Ocean Drilling Program Leg 195 recovered basalticand volcaniclastic units from the West Philippine Basin thatdocument the earliest history of the Izu–Bonin–Marianaconvergent margin. The stratigraphic section recovered at Site1201D includes 90 m of pillow basalts, representing the WestPhilippine Basin basement, overlain by 459 m of volcaniclasticturbidites that formed from detritus shed from the Eocene–Oligoceneproto-Izu–Bonin–Mariana island arc. Basement basaltsare normal mid-ocean ridge basalt (N-MORB), based on their abundancesof immobile trace elements, although fluid-mobile elements areenriched, similar to back-arc basin basalts (BABB). Sr, Nd,Pb and Hf isotopic compositions of the basement basalts aresimilar to those of basalts from other West Philippine Basinlocations, and show an overall Indian Ocean MORB signature,marked by high ²⁰⁸Pb/²⁰⁴Pb for a given ²⁰⁶Pb/²⁰⁴Pb and high¹⁷⁶Hf/¹⁷⁷Hf for a given ¹⁴³Nd/¹⁴⁴Nd. Trace element and isotopicdifferences between the basement and overlying arc-derived volcaniclasticsare best explained by the addition of subducted sediment orsediment melt, together with hydrous fluids from subducted oceaniccrust, into the mantle source of the arc lavas. In contrastto tectonic models suggesting that a mantle hotspot was a sourceof heat for the early Izu–Bonin–Mariana arc magmatism,the geochemical data do not support an enriched, ocean islandbasalt (OIB)-like source for either the basement basalts orthe arc volcanic section. KEY WORDS: back-arc basalts; Izu–Bonin–Marianas; Philippine Sea; subduction initiation; Ocean Drilling Program Leg 195     

The oxygen isotopic composition and temperature of Southern Ocean bottom waters during the last glacial maximum

We provide two new determinations of the oxygen isotopic composition of seawater during the last glacial maximum (LGM). High-resolution oxygen isotopic measurements were made on interstitial waters from Ocean Drilling Program (ODP) Sites 1168 and 1170 in the southeast Indian Ocean sector of the Southern Ocean. We use a diffusion-advection numerical model to calculate the glacial-interglacial change in bottom-water δ¹⁸O_sw from the pore water δ¹⁸O profiles; the first such determinations from this part of the oceans. Statistical analyses of the model runs indicate that Circumpolar Deep Water (CDW) δ¹⁸O_sw changed by 1.0-1.1±0.15‰ since the last glacial maximum (LGM). Our results are consistent with a previous calculation from a South Atlantic Southern Ocean location (ODP Site 1093) also situated within CDW. The new values determined in this study, together with previous estimates, are converging on a global average Δδ¹⁸O_sw of 1.0-1.1‰.Using the calculated bottom-water δ¹⁸O_sw, we have extracted the temperature component from the benthic foraminiferal δ¹⁸O record at Sites 1168 and 1170. Since the LGM, bottom waters at these two sites warmed by 2.6 and 1.9°C, respectively. The absolute temperature estimates for the LGM (−0.5°C [Θ=−0.6°C] at Site 1168 and −0.2°C [Θ=−0.4°C] at Site 1170) are slightly warmer than those reported from previous studies using the same technique, but are consistent with more homogenous deep-ocean temperatures during the LGM relative to the modern.     

哥斯达黎加地震起源计划——IODP334航次介绍

2011年3月13日至4月13日哥斯达黎加地震起源计划IODP334航次在中美洲哥斯达黎加俯冲带大陆边缘斜坡带实施。该航次的主要科学目标是研究俯冲剥蚀控制的俯冲带大地震的聚集和破裂过程。在1个月的钻探时间内,总共在4个站位、8个钻孔中获得1492．88m的岩芯,获得许多中新世到现代的火山灰层,初步确定上覆板块内沉积物和...     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.     

云南泸西县云鹏水电站坝基基础工程处理

大坝基础帷幕灌浆工程中采用新技术、新工艺，使工程质量大幅提高，也使这些新技也能在实践中得到发展和完善，为工程良好的质量和效益打下了坚实的基础。     

New evidence for age variation and scale effects of permeabilities of young oceanic crust from borehole thermal and pressure measurements

In 1996, long-term sealed-hole hydrological observatories with subseafloor temperature and pressure sensors were installed in four cased holes drilled by the Ocean Drilling Program into sedimented young oceanic crust east of the Juan de Fuca Ridge. Data recovered over a year later showed that all four holes displayed temperature profiles indicative of vertical fluid flow immediately prior to their being sealed. Warm water was being produced from basement in two cases, and cool ocean bottom water was being drawn into basement at the others. Linear flow rates of 60–200 m/h were estimated from the perturbation of the temperature profiles relative to undisturbed geothermal gradients at the sites. The pressure differentials driving the flow were also measured at the time of the observatory installations, allowing estimates of permeabilities of the upper crustal sections penetrated by the holes. Estimated permeabilities vary systematically with age, ranging from about 10⁻¹⁰ m² in the youngest site (0.9 Ma) to 10⁻¹² m² in the oldest site (3.6 Ma), confirming an apparent reduction of permeability with age determined with packer experiments at three of the same sites. Combined with other estimates of permeabilities in the same holes using methods with different scales of investigation, the new permeability estimates also provide evidence for a significant scale dependence of permeability in the upper oceanic crust.     

中国大陆科学钻探工程主孔石榴石单辉橄榄岩的岩石化学研究

中国大陆科学钻探工程主孔石榴石橄榄岩产出于603.20～683.53m之间,主要为石榴石单辉橄榄岩,内部还见有巨晶状角闪石岩(曾经是岩脉)和榴辉岩与橄榄岩之间厘米级的方辉辉石岩.石榴石橄榄岩多数含有钛斜硅镁石.从其内部所夹的榴辉岩条带可知,橄榄岩发生过褶皱等构造变形作用.其围岩和内部夹层榴辉岩中的锆石中舍柯石英的事实可能表明岩体经历过超高压变质作用.石榴石橄榄岩的主要造岩矿物橄榄石的Fo端员低(0.82～0.86)、全岩岩石化学的低Mg#值(77.26～85.07)和高易熔元素以及低于典型阿尔卑斯型橄榄岩的(Mg Ni)/(Fe Mn)比值,意味着该石榴石橄榄岩体的原岩为岩浆固结成因.石榴石橄榄岩的稀土元素总量低,配分型式有LREE富集型((La/Lu)N比值为9～16.6)、LREE适度富集型((La/Lu)N比值为1.47～8.22)和LREE亏损型或平坦型((La/Lu)N比值为0.62、1.19～1.92)三种,并构成从亏损或平坦型到富集型的韵律,反映了结晶分异的特点.微量元素蛛网图上,石榴单辉橄榄岩微量元素的丰度总体上低于N-MOBB的丰度.Cu、Ni和MgO的判别图表明,石榴石橄榄岩的原岩岩浆的固结成岩时期主要为镁铁质矿物的分离结晶作用而硫化物不是重要的矿物相.Ti和P的剧烈变化表明了有磁铁矿和磷灰石的堆积作用.微量元素判别图表明岩体受到了明显的地壳物质混染作用.铂族元素丰度总量低,其丰度分布型式图表明原岩岩浆的部分熔融程度高,而且元素的判别图表明岩浆具有S不饱和特点.硫化物残留在地幔中而使得岩浆中PGE相对Cu、Ni亏损,在Ni-PGE-Cu图上呈总体上的凹形分布.同属PPGE的Pt比Pd所显示的更高的相容性也表明了岩浆中S的不饱和特点.而Ir的负异常可能说明原始岩浆在侵入前的分离结晶作用其间发生了Ir的结晶析出,或者是在地幔部分熔融时Ir残留在地幔残留体中.因此,主孔石榴石橄榄岩的原始岩浆是上地幔适当部分熔融程度的产物((Pd/Ir)N≥1),可能在源区有硫化物的残余而造成了PGE相对Cu、Ni亏损而在Ni-PGE-Cu图上呈总体上的凹形分布.后S不饱和的岩浆经历分离结晶作用而造成了Pt相时于Pd亏损的特点.     

水平定向钻无套管双管回托工艺研究

本文结合单根管道水平定向钻穿越回托力计算,对无套管双管回托力计算方法进行了理论分析,并通过工程实例对计算公式进行了修正,得出了无套管双管回托力计算方法,以期为同类工程实践提供理论参考。     

Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of Calofornia—hydrothermal effects on unconsolidated diatom ooze

The effects of intrusive thermal stress have been studied on a number of Pleistocene sediment samples obtained from Leg 64 of the DSDP-IPOD program in the Gulf of California. Samples were selected from Sites 477, 478 and 481 where the organic matter was subjected to thermal stress from sill intrusions. For comparison purposes, samples from Sites 474 and 479 were selected as representative of unaltered material.The GC and GC-MS data show that lipids of the thermally unaltered samples were derived from microbial and terrestrial higher-plant detritus. Samples from sill proximities were found to contain thermally-derived distillates and those adjacent to sills contained essentially no lipids. Curie point pyrolysis combined with GC and GC-MS was used to show that kerogens from the unaltered samples reflected their predominantly autochthonous microbial origin. Pyrograms of the altered kerogens were much less complex than the unaltered samples, reflecting the thermal effects. The kerogens adjacent to the sills produce little or no pyrolysis products since these intrusions into unconsolidated, wet sediments resulted in in situ pyrolysis of the organic matter.Examination of the kerogens by ESR showed that spin density and line width pass through a maximum during the course of alteration but ESR g-values show no correlation with maturity. Stable carbon isotope (δ¹³C) values of kerogens decrease by 1–1.5‰ near the sills at Sites 477 and 481 and the atomic N/C decreases slightly with proximity to a smaller sill at Site 478. Differences in maturation behavior between Site 477 and 481 and Site 478 are attributed to dissimilarities in thermal stress and to chemical and isotopic heterogeneity of Guaymas Basin protokerogen.     

大洋钻探与深海热液作用

在ＤＳＤＰ／ＯＤＰ的２６年钻探中，有近２０个航次钻遇到的热液作用踪迹或热液产物。强调了深海热液作用作为研究海底扩张，地幔物质上涌，新生洋壳生成及火山活动所构成的地壳演化过程，已经成了大洋钻探计划的核心内容之一，并由此在若干重大理论问题上，获得了突破性的发展。