Oxygen Isotope Evidence for Chemical Interaction of Ki lauea Historical Magmas with Basement Rocks

Klauea historical summit lavas have a wide range in matrix ¹⁸O_VSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, ¹⁸O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine ¹⁸O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma ¹⁸O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine ¹⁸O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination     

Japan-equator XBT sections in late November 1989 and in early December 1991

A comparison between Japan-equator XBT sections along 150°E in late November 1989 and along 140°E in early December 1991 is made. The warmest surface water above 29°C diminished to the south of 2–4°N and the surface mixed layer noticeably decreased in thickness in the equatorial region in December 1991; besides, the North Equatorial Countercurrent was intensified. This is considered to be a manifestation of changes in the surface layer of the western equatorial Pacific in the mature phase of El Niño.     

Risk assessment of TBT in the Japanese short-neck clam (Ruditapes philippinarum) of Tokyo Bay using a chemical fate model

A risk assessment of Tributyltin (TBT) in Tokyo Bay was conducted using the Margin of Exposure (MOE) method at the species level using the Japanese short-neck clam, Ruditapes philippinarum. The assessment endpoint was defined to protect R. philippinarum in Tokyo Bay from TBT (growth effects). A No Observed Effect Concentration (NOEC) for this species with respect to growth reduction induced by TBT was estimated from experimental results published in the scientific literature. Sources of TBT in this study were assumed to be commercial vessels in harbors and navigation routes. Concentrations of TBT in Tokyo Bay were estimated using a three-dimensional hydrodynamic model, an ecosystem model and a chemical fate model. MOEs for this species were estimated for the years 1990, 2000, and 2007. Estimated MOEs for R. philippinarum for 1990, 2000, and 2007 were approximately 1–3, 10, and 100, respectively, indicating a declining temporal trend in the probability of adverse growth effects.A simplified software package called RAMTB was developed by incorporating the chemical fate model and the databases of seasonal flow fields and distributions of organic substances (phytoplankton and detritus) in Tokyo Bay, simulated by the hydrodynamic and ecological model, respectively.     

The characteristic distribution of silica over the East China Sea shelf slope

The localized near-bottom water with silica content higher than that in the adjacent shelf water was observed to exist at the eastern margins of the East China Sea continental shelf. The core of the high silica water possessed the silica content corresponding to that in the Kuroshio at depths greater than on the shelf. The mixing analysis of water masses using temperature (T) and silica (Si) showed that the core water can be produced through the vertical mixing of intermediate water of the Kuroshio deeper than 100 m. This study provides us a conclusion that the intermediate water of the Kuroshio is strongly mixed on the shelf slope and then upwelled to form the ridge-like distribution of water masses with low temperature and high silica content at the shelf edge.     

U-Pb Age Determination for Seven Standard Zircons using Inductively Coupled Plasma–Mass Spectrometry Coupled with Frequency Quintupled Nd-YAG (λ = 213 nm) Laser Ablation System: Comparison with LA-ICP-MS Zircon Analyses with a NIST Glass Reference Material

This paper evaluates the analytical precision, accuracy and long‐term reliability of the U‐Pb age data obtained using inductively coupled plasma–mass spectrometry (ICP‐MS) with a frequency quintupled Nd‐YAG (λ = 213nm) laser ablation system. The U‐Pb age data for seven standard zircons of various ages, from 28 Ma to 2400 Ma (FCT, SL13, 91500, AS3, FC1, QGNG and PMA7) were obtained with an ablation pit size of 30 μm diameter. For ²⁰⁷Pb/²⁰⁶Pb ratio measurement, the mean isotopic ratio obtained on National Institute of Standards and Technology (NIST) SRM610 over 4 months was 0.9105 ± 0.0014 (n = 280, 95% confidence), which agrees well with the published value of 0.9096. The time‐profile of Pb/U ratios during single spot ablation showed no significant difference in shape from NIST SRM610 and 91500 zircon standards. These results encouraged the use of the glass standard as a calibration standard for the Pb/U ratio determination for zircons with shorter wavelength (λ = 213 nm) laser ablation. But ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U ages obtained by this method for seven zircon standards are systematically younger than the published U‐Pb ages obtained by both isotope dilution–thermal ionization mass spectrometry (ID‐TIMS) and sensitive high‐resolution ion‐microprobe (SHRIMP). Greater discrepancies (3–4% younger ages) were found for the ²⁰⁶Pb/²³⁸U ages for SL13, AS3 and 91500 zircons. The origin of the differences could be heterogeneity in Pb/U ratio on SRM610 between the different disks, but a matrix effect accuracy either in the ICP ion source or in the ablation‐transport processes of the sample aerosols cannot be neglected. When the ²⁰⁶Pb/²³⁸U (= 0.2302) newly defined in the present study is used, the measured ²⁰⁶Pb/²³⁸U and ²⁰⁷Pb/²³⁵U ages for the seven zircon standards are in good agreement with those from ID‐TIMS and SHRIMP within ±2%. This suggests that SRM610 glass standard is suitable for ICP‐MS with laser ablation sampling (LA‐ICP‐MS) zircon analysis, but it is necessary to determine the correction factor for ²⁰⁶Pb/²³⁸U by measuring several zircon standards in individual laboratories.     

Numerical simulation of migration–accumulation of oil resources

Numerical simulation of oil migration and accumulation is to describe the history of oil migration and accumulation in basin evolution. It is of great value to the evaluation of oil resources and to the determination of the location and amount of oil deposits. This thesis discusses the characteristics of petroleum geology and permeation fluid mechanics. For the three-dimensional problems of Dongying hollow of Shengli Petroleum Oil Field, it puts forward a new model and a kind of modified method of upwind finite difference fractional steps implicit interactive scheme. For the famous hydraulic experiment of secondary migration–accumulation, the numerical simulation test has been done, and both the computational and experimental results are basically identical. For the actual problem of Dongying hollow, the numerical simulation test and the actual conditions are basically coincident. Thus, the well-known problem has been solved.     

An experimental study on seismic responses of multifunctional vibration‐absorption reinforced concrete megaframe structures

Two models are tested on a shake‐table. One of the models is a normal reinforced concrete megaframe structure and the other is a multifunctional vibration‐absorption reinforced concrete megaframe structure in which the laminated rubber bearings are placed between the major frame and the minor frames. Two earthquake motions (the El Centro wave and the Taft wave) are used during the test. This paper presents the dynamic characteristic, the seismic responses and the failure mechanism of these two models under varying peak acceleration levels for each of the earthquake motions. The test results demonstrate that the aseismic behavior of a multifunctional vibration‐absorption reinforced concrete megaframe structure is much better than that of a normal reinforced concrete megaframe structure. Copyright © 2003 John Wiley & Sons, Ltd.     

A study of microearthquake seismicity and focal mechanisms within the Sea of Marmara (NW Turkey) using ocean bottom seismometers (OBSs)

We have carried out seismological observations within the Sea of Marmara (NW Turkey) in order to investigate the seismicity induced after Gölcük–İzmit (Kocaeli) earthquake (M_w 7.4) of August 17, 1999, using ocean bottom seismometers (OBSs). High-resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this Marmara Sea OBS project involving deployment of 10 OBSs within the Çınarcık (eastern Marmara Sea) and Central-Tekirdağ (western Marmara Sea) basins during April–July 2000. Little was known about microearthquake activity and their source mechanisms in the Marmara Sea. We have detected numerous microearthquakes within the main basins of the Sea of Marmara along the imaged strands of the North Anatolian Fault (NAF). We obtained more than 350 well-constrained hypocenters and nine composite focal mechanisms during 70 days of observation. Microseismicity mainly occurred along the Main Marmara Fault (MMF) in the Marmara Sea. There are a few events along the Southern Shelf. Seismic activity along the Main Marmara Fault is quite high, and focal depth distribution was shallower than 20 km along the western part of this fault, and shallower than 15 km along its eastern part. From high-resolution relative relocation studies of some of the microearthquake clusters, we suggest that the western Main Marmara Fault is subvertical and the eastern Main Marmara Fault dips to south at 45°. Composite focal mechanisms show a strike-slip regime on the western Main Marmara Fault and complex faulting (strike-slip and normal faulting) on the eastern Main Marmara Fault.     

西藏班戈县东嘎花岗岩体特征及锡找矿前景分析

东嘎花岗岩体位于冈底斯一念青唐古拉板片北缘、班公错一怒江结合带中段班戈一崩错板片。岩体时代为燕山晚期,属印度一欧亚板块碰撞造山构造环境。岩石属富钠、硅铝过饱和类型,该岩体位于斑戈一嘉黎一波密一察隅锡成矿远景带内,岩浆分异程度高,具有S型花岗岩体的典型特征,与滇西、川西含锡花岗岩体特征相似,成矿条件有利。区域化探资料显示锡异常明显,异常为Sn、Rb、Y、u、Nb、Ag、w、Th、Pb等多元素组合。sn元素的强度高、规模大。据区域地质、岩石化学及地球化学特征及区域成矿资料,东嘎花岗岩体具有良好的锡成矿前景。