Age and impacts of the caldera-forming Aniakchak II eruption in western Alaska

The mid-Holocene eruption of Aniakchak volcano (Aniakchak II) in southwest Alaska was among the largest eruptions globally in the last 10,000 years (VEI-6). Despite evidence for possible impacts on global climate, the precise age of the eruption is not well-constrained and little is known about regional environmental impacts. A closely spaced sequence of radiocarbon dates at a peatland site over 1000 km from the volcano show that peat accumulation was greatly reduced with a hiatus of approximately 90–120 yr following tephra deposition. During this inferred hiatus no paleoenvironmental data are available but once vegetation returned the flora changed from a Cyperaceae-dominated assemblage to a Poaceae-dominated vegetation cover, suggesting a drier and/or more nutrient-rich ecosystem. Oribatid mites are extremely abundant in the peat at the depth of the ash, and show a longer-term, increasingly wet peat surface across the tephra layer. The radiocarbon sample immediately below the tephra gave a date of 1636–1446 cal yr BC suggesting that the eruption might be younger than previously thought. Our findings suggest that the eruption may have led to a widespread reduction in peatland carbon sequestration and that the impacts on ecosystem functioning were profound and long-lasting.     

Historical measurements of the Earth's magnetic field compared with remanence directions from lava flows in Italy over the last four centuries

Direct measurements of the Earth's magnetic field in Italy since 1640 a.d. have been used to check the remanence directions derived from historically dated volcanic rocks of Etna and Vesuvius. Direct measurements consist of the records of L’Aquila and Pola geomagnetic observatories, the repeat stations of the Italian Magnetic Network and the data base of the Historical Italian Geomagnetic Data Catalogue. All have been relocated to the same reference site (Viterbo — lat. 42.45°N, long. 12.03°E) in order to draw a reference secular variation (SV) curve. The direction of the Earth's field at Viterbo has also been calculated from the historical records (2000-1600) of ref. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Phil. Trans. R. Soc. London, Ser. A 358, 957-990] database. The remanence directions from Etna show a general agreement with the trend of the SV curve, although their inclination is usually lower than that from the direct measurement. The directions from Vesuvius are more scattered. Large discrepancies occur at both volcanoes and in some cases have been ascribed in the literature to poor geographic information, making it difficult to identify the flows actually emplaced during the eruptions reported in the chronicles. Closer examination shows that the great majority of the best-defined remanence directions (semi-angle of confidence α₉₅ < 2.5°) deviate significantly from the geomagnetic direction measured at the time of the emplacement, the angle between the two directions being larger than the α₉₅ value. The value of 2.5-3.0° can thus be regarded as a conservative evaluation of the error when dealing with dating Etna and Vesuvius lava flows older than 17th century, even when the accuracy attained in remanence measurements is higher. In default of a SV curve for Italy derived from archaeological artefacts, a further error in dating is introduced when reference is made to SV curves of other countries, even if well-established, as these are from regions too far from Italy (>600 km) to confidently relocate magnetic directions.     

越南兰龙盆地白虎油田储集层特征及成藏模式探讨

基于岩心、钻测井、三维地震和沉积相资料,对越南兰龙盆地白虎油田的碎屑岩、基岩储集层特征以及对应的两种成藏模式进行综合分析。结果表明,白虎油田发育两类岩性储集层,即碎屑岩(砂岩)、花岗岩基岩储集层,其中碎屑岩储层在兰龙盆地基底地垒构造格架下沉积,受大地构造运动、海平面变化控制,以冲积扇、扇三角洲和河流相为主,在渐新统泥岩供烃的条件下形成了具有自生自储、下生上储特征的岩性、构造油藏。花岗岩的基岩裂缝、孔洞发育,具备优势的储集空间、储层规模大,成为最主力的储集层,成因为基底演化过程中的断裂活动、热液岩熔等作用。在花岗岩基岩储层中形成了两种成藏模式：一种以花岗岩无机成因自身含烃表现出原地成藏的特征;另一种上覆渐新统泥岩为富油烃源岩,沿断层、不整合面等侧向运移至基底顶部晚期聚集成藏,最终在基底中广泛发育裂缝、缝洞型基岩油藏。     

滇西墨江西部石炭、二叠纪火山岩

墨江西部出露有石炭纪和晚二叠世两套火山岩,它们呈平行的两条带分布。石炭纪火山岩以拉斑玄武岩为主,少量流纹岩,它们是由上地幔源区10%部分熔融形成的原始岩浆,经橄榄石、辉石和斜长石不同程度结晶分异作用形成。其喷发环境可能是一个发育在大陆边缘的张性海盆地。晚二叠世火山岩较为复杂,熔岩与火山碎屑岩交互发育,熔岩主要属于拉斑系列,还含有少量钙碱性系列岩石;形成于陆缘火山弧环境。     

场地类别分类方案研究

基于性能的抗震设计,要求工程师设计出具有预期抗震性能的结构,一个关键因素是地震作用的确定,这在很大程度上取决于局部场地条件。通过收集和分析北京、苏州和唐山城区956个钻孔资料,建立地表20 m和30 m深土层走时平均剪切波速VS20和VS30的关系式;现场钻探获取北京城区深105 m的典型钻孔原状土样,试验给出各类土体动剪切模量和阻尼比曲线;建立北京城区170个钻孔的场地反应计算模型,采用Nakamura提出的HVSR法和陈国兴等提出的弱震法估算场地基本周期TS值,结合国内外现行抗震规范的场地分类及一些学者对场地分类的研究成果,提出两种新的场地分类建议方案：基于等效剪切波速VSE和覆盖土层厚度H（地表至剪切波速VS ≥ 500 m/s的基岩深度）的双指标场地分类方案及基于VSE、H和TS的三指标场地分类方案。提出的场地分类方案对我国现行抗震规范场地分类方法的改进有参考价值。     

Geochemical and isotope data from the Acatlán Volcanic Field, western Trans-Mexican Volcanic Belt: Origin and evolution

The Quaternary Acatlán Volcanic Field (AVF) is located at the western edge of the Trans-Mexican Volcanic Belt (TMVB). This region is related to the subduction of the Pacific Cocos and Rivera plates beneath the North American plate since the late Miocene. AVF rocks are products of Pleistocene volcanic activity and include lava flows, domes, erupted basaltic andesite, trachyandesite, trachydacite, and rhyolite of calc–alkaline affinity. Most rocks show depletion in high field-strength elements and enrichment in large ion lithophile elements and light rare earth elements as is typical for magmas in subduction-related volcanic arcs. ⁸⁷Sr/⁸⁶Sr values range from 0.70361 to 0.70412, while Nd values vary from +2.3 to +5.2. Sr–Nd isotopic data plot along the mantle array. On the other hand, lead isotope compositions (²⁰⁶Pb/²⁰⁴Pb=18.62–18.75, ²⁰⁷Pb/²⁰⁴Pb=15.57–15.64, and ²⁰⁸Pb/²⁰⁴Pb=38.37–38.67) give evidence for combined influences of the upper mantle, fluxes derived from subducted sediments, and the upper continental crust involved in magma genesis at AVF. Additionally δ¹⁸O whole rock analyses range from +6.35‰ in black pumice to +10.9‰ in white pumice of the Acatlán Ignimbrite. A fairly good correlation is displayed between Sr as well as O isotopes and SiO₂ emphasizing the effects of crustal contamination. Compositional and isotopic data suggest that the different AVF series derived from distinct parental magmas, which were generated by partial melting of a heterogeneous mantle source.     

云南景东文玉火山热液型铜矿

铜矿赋存在三叠系上统小定西组火山岩系中,岩浆期后热液对矿质的运移、改造、叠加起重要作用。矿床具中低温火山热液蚀变特征。     

塔里木溢流玄武岩火山通道的三维结构及其热成因气体释放

塔里木上奥陶统-志留系沉积地层中广泛发育早二叠世溢流玄武岩的火山通道相岩床-岩墙网络。三维地震数据解释结果显示,这些火山通道以平行围岩地层的岩床和斜切围岩地层的"碟状岩床"为主要特征。在玄武岩喷发过程中,火山通道岩浆的热量可以导致沉积围岩发生热接触变质并将沉积围岩中的有机质转化为"热成因气体"。在塔北英买2井区火山通道烘烤沉积围岩模型基础上,利用有限元热模拟方法确定了该区早二叠世玄武岩喷发时火山通道热烘烤影响范围随时间的变化。基于沉积围岩有机质丰度估算,该区热烘烤成因甲烷释放量可达11.3Gt(即113亿吨)。如果整个塔里木溢流玄武岩省具有与英买2地区相同的释放强度,则塔里木溢流玄武岩省活动期间释放的甲烷总量可达7062.5Gt,必然导致非常显著的环境效应。同时,玄武岩火山通道岩浆引起的热接触变质作用对已存在的油藏具有明显的破坏作用,塔里木盆地古生界总量约8~10Gt的油藏破坏和大量沥青的形成可能与此有关。     

中国东北新生代火山区CO2释放规模与成因

板片俯冲过程将地表碳带入地球内部,火山作用将深部碳输送至地球外部圈层,两者构成了地球深部碳循环的主要方式,进而影响了地史时期的气候变化.我国东北新生代火山活动被认为是太平洋板片深俯冲作用的产物,板片俯冲导致岩浆源区强烈的碳酸盐组分交代作用,进而使东北亚上地幔成为一个新生代时期的巨型深部碳库,它的活动和释放将会对全球的气...     

空气潜孔锤钻进技术在舜皇山基岩地热深井的应用

空气潜孔锤钻进技术不仅可以提高钻探效率,而且不损害地热储层,因此在地热井中的应用十分广泛,但是仍受到钻探深度和出水量的限制。在湖南永州舜皇山基岩地热深井钻探过程中,常规牙轮钻进与泥浆钻进工艺存在钻进效率低、堵塞储层、影响出水量的可能。应用空气潜孔锤钻进技术实现了钻探深度的突破,钻探深度达到1820 m,实际出水量400 m³/d,出水温度43 ℃,符合设计指标。本文总结了相应的钻进工艺措施,以期促进对该技术在地热深井中的推广应用。