Calcite precipitation and Recrystallization fabrics—their significance in Jurassic Limestones of Europe

Many fabrics in Corallian (Upper Jurassic) carbonates in England, France and Switzerland are bigenetic, forming by solution/precipitation and recrystallization processes. Early precipitated cements are non‐ferroan, whereas those formed later are decidedly ferroan. Mossbauer spectroscopy has shown that the iron in the carbonates is largely divalent, substituting for calcium in the calcite lattice. The cements may be subdivided into those forming in an oxidizing environment, and those forming in a reducing environment. Fabric evidence indicates that a solution period separates the two cement phases. The diagenetic history is linked with the sedimentation pattern. Thus, under progressive build up of sediments into shallow‐water or supratidal conditions, the first‐phase cement probably precipitated from non‐marine, partially oxygenated vadose water. Subsequent subsidence and sedimentation resulted in the depression of partially cemented sediments into zones within the sedimentary pile conducive first to pyrite precipitation, and then to ferroan calcite precipitation. Fabrics can therefore be used to interpret the diagenetic environment of regressive sedimentary associations.     

Geology and age of the Glikson impact structure,Western Australia

The Glikson structure is an aeromagnetic and structural anomaly located in the Little Sandy Desert of Western Australia (23°59'S, 121°34′E). Shatter cones and planar microstructures in quartz grains are present in a highly deformed central region, suggesting an impact origin. Circumferential shortening folds and chaotically disposed bedding define a 19 km-diameter area of deformation. Glikson is located in the northwestern Officer Basin in otherwise nearly flat-lying sandstone, siltstone and conglomerate of the Neoproterozoic Mundadjini Formation, intruded by dolerite sills. The structure would not have been detected if not for its strong ring-shaped aeromagnetic anomaly, which has a 10 km inner diameter and a 14 km outer diameter. We interpret the circular magnetic signature as the product of truncation and folding of mafic sills into a ring syncline. The sills most likely correlate with dolerites that intrude the Boondawari Formation ～25 km to the north, for which we report a SHRIMP U?–?Pb baddeleyite and zircon age of 508?±?5 Ma, providing a precise older limit for the impact event that formed the Glikson structure.     

Distribution of the crustal magnetic anomaly and geological structure in Xinjiang,China

Based on the high-order crustal magnetic field model NGDC-720-V3, we investigate the distribution of crustal magnetic anomaly, the decay characteristics of the anomaly, and the relationship between the magnetic anomaly and geological structure in Xinjiang, China. Topography of the magnetic layer basement is studied through Curie isothermal surface using the power spectrum method. It is found that south Tarim Basin, Junggar Basin, and Turpan–Hami Basin have strong positive magnetic anomaly, whereas west Kunlun Mountain, Altun Mountain, Tianshan Mountain, and Altai Mountain have weak or negative anomaly. The magnetic anomaly well reflects the regional tectonic structure, i.e., three alternating mountains intervened by two basins. The magnetic anomaly on the ground surface in Tarim Basin is well corresponding to the mafic dykes. The decay of the magnetic anomaly with altitude indicates that Xinjiang is a large massif composed of several magnetic blocks with different sizes in different directions. The Curie surface presents a feature of being shallow under mountains whereas being deep under basins, roughly having an anti-mirror correspondence with the Moho depth.     

大兴安岭东南部油气资源勘查区重磁异常初步解释

区域重磁异常的初步解释表明,西拉木伦河以北的松辽盆地外围地区存在诸多中、新生代盆地,发育3条NW向深大断裂和近NEE向的弧形构造.1∶20万重力异常显示,本区中、新生代盆地边界具有较明显的梯度异常特征,1∶5万航磁异常可较为清晰地勾画中新生代火成岩的分布.重、磁、电剖面联合反演揭示,中生代地层厚度1～4km,古生界规模宏大,厚度可达4～6km,是本区寻找油气的重要层位;古生界含油气盆地基底为志留系及更老地层;大兴安岭NE向展布的花岗岩具有蘑菇状侵入特征.通过重、磁异常联合反演,消除火成岩影响,得出突泉和扎鲁特地区的中生代基底深度1.5～4km,古生代的基底深度为2～6km.     

综合物探在会东航磁异常查证中的应用

根据会东航磁异常的基本特征,判断其异常为深部多个磁性体的综合反映.采用地面高精度磁测和音频大地电磁测深法,并结合区域重力勘探资料对异常区开展了综合物探调查.通过对区域重力、高精度磁法资料和音频大地电磁测深数据开展综合解释,初步确定了异常体在深部的空间展布特征,为在该区实施进一步的勘查工作提供了重要找矿线索.     

建立磁化率快速预测白马钒钛磁铁矿含量模型

根据白马钒钛磁铁矿区试验钻孔井壁岩矿石磁化率与钒钛磁铁矿含量的关系,矿区岩矿石磁化率与钒钛磁铁矿含量的相关性,建立了磁化率与钒钛磁铁矿含量的回归方程。通过此方程的应用可以快速判断井壁岩矿体的钒钛磁铁矿含量,指导采样布设。     

磁法在云南武定地区铁铜矿勘查中的应用

矿产资源远景调查目的主要就是圈定找矿靶区及寻找隐伏矿体,磁法勘探对于寻找铁铜矿有较大的优势。在云南武定地区开展的1：5万磁法测量工作,共圈出了四个异常区块（A、B、C、D异常区）。在B异常区块进行1：1万高精度磁测,解析延拓显示位于该区块东南部的三度体异常具有深源性,规模较大,并出现较大的磁异常梯度带,且处于主控矿构造断裂带上,划定为该区域的重点勘探远景区。     

近50年来全球海温异常对我国东部地区冬季温度异常影响的诊断研究

利用1951－1997年全球海温、风场月平均资料和我国东部地区100个测站的冬季地面气温等资料，分析了我国东部地区冬季温度异常的时空特征和变化规律，探讨了全球海温异常与我国东部地区冬季温度异常的关系。发现赤道印度洋、赤道东太平洋、黑潮区是影响我国东部地区冬季温度异常的关键海区。前期夏、秋季赤道印度泣、赤道东太平洋海温异常与我国东部地区冬季温度异常有较好的相关关系，对预测我国东部地区冬季温度异常有一定的前兆意义。且不同关键海区的海温异常在不同季节对我国东部地区冬季温度异常产生影响的区域不同。     

1997/1998年ENSO过程与热带大气季节内振荡

根据珠江口气象站风速与潮汐站潮位资料,对1955～1998年12次El Nino过程的珠江口季风强度与海平面变化特点进行合成分析,结果表明,El Nino发生前一年冬季,珠江口冬季平均风速较常年值大0.4 m/s,El Nino发生当年,月平均风速也普遍大于常年,而月平均海平面则普遍较常年偏低,其中10与11月份负距平为6 cm左右。东亚地区的季风异常对珠江口海平面异常有着重大的影响。     

东亚副热带夏季风环流指数及其与中国气候的关系

采用大气环流正、斜压分解方法，从东亚副热带夏季风为正、斜压混合型季风观点出发，定义并计算了1958-1997年东亚副热带夏季风环流指数。该环流指数与1961-1995年中国160站夏季降水、气温的相关分析表明，它与中国东部夏季降水和气温的关系密切：强季风年，以河套地区为中心的黄河流域及华北地区多雨，长江流域少雨，华南和东南沿海多雨，以长江流域为中心的全国绝大部分地区气温偏高。弱季风年情况相反。此外，还将该环流指数与目前常用的4种东亚夏季风指数进行了对比分析。