Structural characteristics of the KPR-CBR triple-junction inferred from gravity and magnetic interpretations,Philippine Sea Plate

The intersection of the Kyushu-Palau Ridge (KPR) and the Central Basin Rift (CBR) of the West Philippine Basin (WPB) is a relic of a trench-trench-rift (TTR) type triple-junction, which preserves some pivotal information on the cessation of the seafloor spreading of the WPB, the emplacement and disintegration of the proto-Izu-Bonin-Mariana (IBM) Arc, and the transition from initial rifting to steady-state spreading of the Parece Vela Basin (PVB). However, the structural characteristics of this triple-junction have not been thoroughly understood. In this paper, using the newly acquired multi-beam bathymetric, gravity, and magnetic data obtained by the Qingdao Institute of Marine Geology, China Geological Survey, the authors depict the topographic, gravity, and magnetic characteristics of the triple-junction and adjacent region. Calculations including the upward continuations and total horizontal derivatives of gravity anomaly are also performed to highlight the major structural features and discontinuities. Based on these works, the morphological and structural features and their formation mechanisms are analyzed. The results show that the last episode amagmatic extension along the CBR led to the formation of a deep rift valley, which extends eastward and incised the KPR. The morphological and structural fabrics of the KPR near and to the south of the triple-junction are consistent with those of the western PVB, manifesting as a series of NNE-SSW- and N-S-trending ridges and troughs, which were produced by the extensional faults associated with the initial rifting of the PVB. The superposition of the above two reasons induced the prominent discontinuity of the KPR in deep and shallow crustal structures between 15°N–15°30′N and 13°30′N–14°N. Combined with previous authors’ results, we propose that the stress produced by the early spreading of the PVB transmitted westward and promoted the final stage amagmatic extension of the CBR. The eastward propagation of the CBR destroyed the KPR, of which the magmatism had decayed or ceased at that time. The destruction mechanism of the KPR associated with the rifting of the PVB varies along strike the KPR. Adjacent to the triple-junction, the KPR was destroyed mainly due to the oblique intersection of the PVB rifting center. Whereas south of the triple-junction, the KPR was destroyed by the E-W-directional extensional faulting on its whole width.©2021 China Geology Editorial Office.     

Analysis of the institutional and social responses to the eruption and the lahars of Mount Pinatubo volcano from 1991 to 1998 (Central Luzon, Philippines)

Mount Pinatubo volcano erupted in June 1991 in the main island of Luzon belonging to the Philippines archipelago. Huge economic losses and population exodus have followed. This major crisis has been relayed with other crises due to rain-fed lahars which have been supplied with eruption deposits. These lahars have occurred every year since 1991 during the rainy season. They will probably last until 2005. After a brief presentation of the Philippine official response system to disasters, this paper draws up a critical analysis of the different kinds of institutional and social responses deployed to manage the different crisis and post-crisis phases of this event. Based on three viewpoints: from population, media and other actors, this analysis attempts to point out the strengths and weaknesses of the official management system, especially by studying the efficiency and the range of the solutions taken. So, it appears that the management of the June 1991 main crisis (eruption) was a success. On the other hand, difficulties have occurred with lahars risk management. Indeed, these lahars have obliged the authorities to protect and relocate thousands of people. In spite of persistent problems, the management system (monitoring/warning/evacuation) of lahar crises improves year after year. Failures appear especially within the rehabilitation program (protection/rehousing). Many direct (lack of means, preparedness, coordination, dialog, etc.) and indirect (politico-administrative, socio-economic, cultural contexts) factors come together to lock the wheels of the institutional response system. They defer the socio-economic start of this vital northern Philippines area. This revised version was published online in July 2006 with corrections to the Cover Date.     

渤中凹陷中生界火山岩储层裂隙发育程度实验研究：以安山岩为例

渤海湾盆地中生界火山岩发育广泛,但含油气性横向变化较大,失利井较多,勘探风险大,了解火山岩潜山储层内部裂隙发育程度及规律可为中生界火山岩潜山勘探提供理论依据。本文选取中生界安山岩,开展不同构造环境下岩石微裂隙发育程度实验,分析安山岩在不同应力状态下微裂隙发育规模、频率以及微裂隙空间分布,探讨张性和压性构造应力环境下中生界火山岩微裂隙发育能力及空间展布规律。实验结果表明：安山岩在压性和张性环境下均有微裂隙发育;安山岩在较低的压应力作用下产生大量微裂隙,微裂隙发育规模不随应力增大而升高,其原因可能是安山岩本身含有大量先存构造缝、溶蚀缝和溶蚀孔,受较小的应力后“再活化”产生微裂隙;结合渤中凹陷的构造演化过程,安山岩经历了燕山早期北东向压扭、中期伸展, 燕山晚期右旋压扭及喜山期伸展,导致其内部裂隙较为发育,其运储能力提升,具备成为优质储层的基本条件。     

海洋围隔生态系中环境因子对长牡蛎的生态效应

本研究应用海洋围隔实验技术探索围隔生态系中环境因子对长牡蛎的生态效应。研究结果表明：牡蛎养殖密度与牡蛎体重增长呈负相关;养殖水体的Ｎ、Ｐ平均浓度分别达到２６．４和２．５μｍｏｌ／ｄｍ＾３的水平时牡蛎生物较佳;服物浓度过高会导致牡蛎死     

东天山晚古生代构造转折: 红山南-天木东地区岩浆岩年代学与地球化学的约束

东天山是中亚造山带的重要组成部分, 区内晚古生代岩浆活动与成矿作用强烈, 是理解中亚造山带构造演化与成矿作用的关键地区。然而, 前人对东天山构造带由俯冲向碰撞转变的时间和过程仍存在较大争议。本文对东天山红山南-天木东地区广泛出露的晚古生代岩浆岩开展了野外考察和岩相学鉴定, 进行了年代学和岩石地球化学分析, 以限定其形成时代、岩石成因和构造背景, 进而探讨晚古生代构造演化过程。红山南-天木东地区岩浆岩主要为早石炭世火山岩和侵入岩, 次为早二叠世侵入岩。早石炭世火山岩主要为安山岩(328.8±2.0Ma)和英安岩, 侵入岩主要为辉长闪长岩(328.7±1.8Ma); 早二叠世侵入岩为黑云母二长花岗岩(290.3±2.1Ma)和石英闪长岩(290.0±1.6Ma)。早石炭世岩浆岩富含角闪石和斜长石, 为钙碱性, 准铝质系列, 富Rb、Ba、Th、U和Pb等大离子亲石元素, 亏损Nb、Ta和Ti等高场强元素和Sr-Nd-Hf同位素, 具有岛弧岩浆岩特征, 是交代地幔楔部分熔融的产物。相对于早石炭世岩浆岩, 早二叠世侵入岩富含黑云母和碱性长石, 富集SiO₂、Na₂O和K₂O, 贫Al₂O₃、MgO、Fe₂O₃^T及CaO, 同位素更亏损, 为碰撞后背景下新生加厚地壳部分熔融的产物。总之, 红山南-天木东地区的早石炭世与早二叠世岩浆岩地球化学差异显著, 指示东天山构造背景从早石炭世大洋俯冲体制转变为早二叠世碰撞后造山体制, 即其构造转折时间为晚石炭世-早二叠世。

     

对雅鲁藏布江结合带形成演化的再探讨

通过1∶5万区域地质调查和收集相关资料的综合研究,本文对雅鲁藏布江结合带的形成演化作了进一步的探讨。雅鲁藏布江特提斯洋具有弧后扩张洋盆的性质,在早三叠世至中三叠世中期洋盆初步形成,中三叠世晚期至晚三叠世洋盆全面形成,从早侏罗世至晚白垩世洋盆逐步萎缩,到古新世至始新世关闭。南带的蛇绿岩主要为洋中脊扩张型(MORB型),形成于中三叠世晚期至晚三叠世。北带的蛇绿岩主要为与洋内俯冲相关的俯冲带上盘型(SSZ型),形成于早中侏罗世。带内侏罗纪至白垩纪其他岩浆岩主要为前弧玄武岩类(FAB型)。显示雅鲁藏布江特提斯洋从早侏罗世开始发生了洋内俯冲,并同步向北向冈底斯带之下主动俯冲消减和向南向喜马拉雅地块之下被动俯冲消减,持续发展到晚白垩世,在古新世至始新世俯冲碰撞消亡转化为结合带。     

青藏高原新生代火车头山碱性及钙碱性两套火山岩的地球化学特征及其物源讨论

藏北羌塘火车头山新生代火山岩可区分为钙碱性及碱性两个不同的系列.钙碱性火山岩主要岩石组合为玄武岩-安山岩-英安岩,其SiO2介于49%～70%之间,Al2O3＞10%,Na2O/K2O＞1;其中玄武岩具平坦型稀土配分型式,LREE/HREE为1.3～1.8,（La/Yb）N为2.87～4.45,无明显铕异常,δEu为0.96～1.09;该套岩石的Mg#与SiO2相关关系以及La/Sm-La等亲岩浆元素与超亲岩浆元素协变关系表明,它们应为幔源岩浆经分离结晶演化的产物,其岩石组合类型以及低的Sm/Yb值（Sm/Yb=1.53～5.35）表明它们的原始岩浆应来源于岩石圈地幔尖晶石二辉橄榄岩的局部熔融.本区碱性火山岩为一套典型的钾质岩石系列,主要岩石组合类型为碱玄岩-碱玄质响岩-响岩,其SiO2介于44%～59%之间,Al2O3＞14%,Na2O/K2O介于0.47～1.51之间;岩石轻稀土强烈富集,LREE/HREE为13.20～15.76,（La/Yb）N=50.44～91.99;其岩石组合类型以及Mg^#与SiO2相关关系以及La/Sm-La协变关系同样表明它们为共源岩浆分离结晶演化的产物;然而,其较高的Sm/Yb值（Sm/Yb=2.63～13.98）表明它们并非地幔橄榄岩直接局部熔融的产物,岩石弱的负Eu异常（δEu=0.77～0.85）以及Th、U的强烈富集和Nb、Ta的相对亏损,又反映了原始岩浆中有显著的地壳物质的贡献;该套钾质碱性系列岩石在La/Co-Th/Co同分母协变图上呈直线型分布,而在La/Co-Sc/Th异分母协变图上呈显著的双曲线分布,从而表明其源区为二源混合型,是青藏高原特殊的壳幔混合层局部熔融的产物,这些特征是新生代青藏高原壳幔层圈物质交换的重要岩石学证据.     

新疆喀拉通克Y1含矿岩体的岩石化学特征及其与成矿的关系

喀拉通克Ｙ１含矿岩体岩石类型属铁质基性岩类,岩体为单式岩体,具富镁、铁、碱、低钙贫铝的特点。组成岩体的各岩相是同一母岩浆结晶分异的产物。原始岩浆为来自上地幔的拉斑玄武岩浆。岩体锶初始比值约为０．７０３３,形成时代约为２９１Ｍａ。在岩浆结晶分异作用下,氧化物组分的变化使硫化物熔浆与硅酸盐熔浆发生分离,并在重力作用下聚积形成铜镍硫化物富矿。     

Origin and depositional environments of source rocks and crude oils from Niger Delta Basin: Carbon isotopic evidence

Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin, Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry. The bulk carbon isotopic values of the whole rock extracts, saturate and aromatic fractions range from –28.7‰ to –26.8‰, –29.2‰ to –27.2 ‰ and –28.5 ‰ to –26.7 ‰, respectively while the bulk carbon isotopic values of the whole oils, saturate and aromatic fractions range from –25.4 ‰ to –27.8 ‰, –25.9 ‰ to –28.4 ‰ and –23.5 ‰ to –26.9 ‰, respectively. The average carbon isotopic compositions of individual alkanes (nC₁₂-nC₃₃) in the rock samples range from –34.9‰ to –28.2‰ whereas the average isotopic values of individual n-alkanes in the oils range from –31.1‰ to –23.8‰. The δ¹³C isotope ratios of pristane and phytane in the rock samples range from –29.2 ‰ to –28.2 ‰ and –30.2 ‰ to –27.4 ‰ respectively while the pristane and phytane isotopic values range from –32.1‰ to –21.9‰ and –30.5‰ to –26.9‰, respectively. The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments. The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.     

基于南黄海盆地海相油气的海洋立体宽线地震勘探技术设想

南黄海盆地中—古生代海相碳酸盐岩具有良好的油气前景,由于埋藏深、厚度大、构造复杂等特殊地震地质条件的原因,地震原始资料品质差,严重地制约了勘探进程。综合常规宽线和上下缆勘探技术的优势,提出了海洋立体宽线(MTBL)地震勘探新技术设想,对其改善地震资料品质的作用和优势进行了分析,为南黄海海相油气地震的勘探工作者提供了参考。