岷县、漳县交界6.6级地震长波辐射异常分析

本文通过涡度方法、时频分析等方法,研究了岷县漳县6.6级地震前,震中区域(102.50°E~105.50°E,33.50°N~37.50°N)红外遥感OLR时空分布特征,结果显示:(1)岷县漳县6.6级地震前震中区域涡度场存在显著增强的异常现象;(2)震中区格点OLR涡度值时序曲线一般情况下随机波动,但在震前存在明显异常变化,其时频结果也显示在地震前存在能量密度增强现象,异常期间谱结构不断变化。     

2013年甘肃岷县漳县M_s6.6地震前地壳形变特征研究

基于2013年岷县漳县M6.6地震震源区及其邻区1999年以来的GPS观测资料,通过应变率动态特征分析、多期次GPS剖面分析和基线变形速率的分析讨论了地震的震前变形特征.GPS速度场和块体应变率表明,汶川地震的发生导致了柴达木地块运动与变形状态发生明显调整,但由于西秦岭北缘等深大断裂的存在,岷-秦地块对其响应不明显;GPS连续应变率显示,在汶川地震引起的区域地壳变形调整过程中岷县漳县地震震源区附近的应变积累速率有减缓的迹象;GPS剖面显示,平行于岷县漳县主破裂带的运动分量对汶川地震响应显著,汶川震后表现为剪切变形速率的增强,而垂直于主破裂带的运动分量则对汶川地震响应不明显;震中周边GPS基线变形速率表明,基线伸缩变化率总体呈现NW向拉张、NE向压缩状态,且拉张量明显小于压缩量.上述地壳变形动态特征表明西秦岭北缘断裂及其附近地区的应变积累水平和断层闭锁程度可能处于较高水平,在岷县漳县地震前该区表现出局部“硬化”迹象.     

青藏高原东北缘M_s≥6.0强震活动特征及未来形势研究

2013年7月22日甘肃岷县漳县6.6级地震打破了青藏高原东北缘地区自2003年以来近十年的6级平静,该地震的意义及该区未来震情发展受到了地震学家的关注.本文运用Morlet小波变换分析了1875-2013年青藏高原东北缘MS≥6.0强震活动的周期特征,结果表明该区强震存在2～3年、8～10年、25～30年等尺度的显著周期;1977年以来青藏高原东北缘地区强震活动频度虽然正常但活动强度处于一个相对较低的阶段.在讨论了岷县漳县6.6级地震的发震背景基础上,认为该地震在青藏高原东北缘强震活动长时间较弱的背景下发生,可能是该区强震活动强弱的一个拐点,未来该区强震活动的频度与强度有增加的趋势.研究结果对该区震情跟踪工作有一定的参考价值.     

Untangling the influence of in-lake productivity and terrestrial organic matter flux on 4,250 years of mercury accumulation in Lake Hambre, Southern Chile

There is ongoing debate about the relative influence of aquatic production, flux, and sedimentation of aquatic and terrestrial organic matter on mercury accumulation in lake sediments. In this study, lake sediments spanning the past 4,250 years, were collected from remote, organic-rich Lake Hambre, Patagonia (53° S) and investigated for changes in the accumulation of pre-anthropogenic mercury and organic matter of aquatic and terrestrial origin. Natural mercury accumulation varied by up to a factor of four, comparable to the recent anthropogenic forcing of the mercury cycle (factor 3–5). Hydrogen and Oxygen indices (HI and OI, Rock–Eval©) and nitrogen/carbon ratios of the organic matter, combined with multi-element sediment data, reveal intense changes in aquatic productivity as well as influx of terrestrial organic matter into the lake. Evaluation of the multi-element dataset using Principal Component Analysis shows clear covariation of mercury with other soil-derived elements such as copper and yttrium. This covariance reflects a common transport mechanism, i.e. leaching of trace-element-bearing organic matter complexes from catchment soils. Correlation between changes in aquatic productivity and mercury concentrations occurs in some sections of the record, but we do not suggest they are linked by a direct causal relationship. Mass balance approaches suggest that mercury scavenging and accumulation in this organic-rich lake is controlled by the supply of mercury from catchment soils rather than the amount of organic material produced within the water column. A common controlling mechanism, i.e. changing climate, however, is thought to independently drive variations in both the flux of terrestrial organic matter mercury complexes and aquatic productivity.     

北吕宋岛菲律宾活动带蛇绿岩及其上覆浊积岩的放射虫研究新进展

The basement of the Philippine Mobile Belt (PMB) is mainly composed of ophiolites that are mostly overlain by Paleogene to Miocene turbidites in central Luzon. To clarify the geological development of the PMB with respect to the initial stage of the arc volcanism (eg. Yumul et al., 2003, 2008; Dimalanta and Yumul, 2003; Suzuki et al., 2011), radiolarian dating was examined in siliceous sediments associated with the ophiolites and turbidites. The samples were collected from sites identified with the Zambales and Montalban ophiolites, basic tuff phyllites in NW Din-galan, and their overlying formations.     

The evolution of the hydrothermal IOCG system in the Mantoverde district,northern Chile: new evidence from microthermometry and stable isotope geochemistry

New microthermometric data combined with stable isotope geochemistry and paragenetic relationships support a previously suggested cooling–mixing model for the iron oxide–copper–gold mineralization in the Mantoverde district. Fluid inclusions show characteristics of a CO₂-bearing aqueous NaCl ± CaCl₂ salt system. The evolution of the Mantoverde hydrothermal system is characterized by (1) an early hypersaline, high to moderate temperature fluid; (2) a moderate saline, moderate temperature fluid; and (3) a low saline, moderate to low temperature fluid. Early magnetite formation took place at median temperatures of 435.0°C, whereas hematite formed at median temperatures of 334.4°C. The main sulfide mineralization texturally post-dates the iron oxides and occurred before late-stage calcite, which developed at a median temperature of 244.8°C. Boiling occurs only locally and is of no relevance for the ore formation. The microthermometric and stable isotope data are supportive for a fluid cooling and mixing model, and suggestive for a predominantly magmatic–hydrothermal fluid component during the iron oxide and main sulfide mineralization. Thereafter, the incursion of a nonmagmatic fluid of ultimately meteoric or seawater gains more importance.     

Talc mineralisation associated with soft hematite ore, Gongo Soco deposit, Minas Gerais, Brazil: petrography, mineral chemistry and boron-isotope composition of tourmaline

Talc mineralisation occurs as hematite–talc schist between soft hematite ore and dolomitic itabirite at Gongo Soco, Quadrilátero Ferrífero of Minas Gerais, Brazil. The hematite–talc schist and soft hematite have a prominent tectonic foliation of tabular hematite. Tabular hematite without preferential orientation is superimposed on the tectonic foliation. The talcose schist is enriched in F and has a constant Fe/S ratio. Electron-microprobe analyses indicate trace amounts of S in different generations of hematite. The whole-rock Fe/S ratio possibly represents sulfate S from hematite-hosted fluid inclusions. Fluid inclusions in foliation-overprinting hematite and chlorite geothermometry from talcose rocks suggest, respectively, temperatures from <200°C to ~300°C. Tourmaline, a rarely observed mineral in the hematite–talc schist, belongs to the alkali group and falls in the dravite compositional field. Boron-isotope determinations of tourmaline crystals, using secondary ion mass spectrometry, vary from −20‰ to −12‰ δ¹¹B. This compositional isotopic range and the tourmaline chemical composition suggest a meta-evaporitic origin. A non-marine evaporitic setting is the most likely source of acidic, highly oxidising fluids, which resulted in the abundant F-bearing talc and the presence of otherwise immobile Ti in hematite. Oxidising brines were channelled along shear zones and converted dolomitic itabirite into the Gongo Soco soft hematite and the talc mineralisation. The latter is envisaged as the hydrothermal wall-rock alteration of dolomitic itabirite, which gave rise to the soft hematite ore.     

A protoceratopsid skeleton with an associated track from the Upper Cretaceous of Mongolia

The Djadokhta Formation of the Gobi Desert is known for the number and diversity of dinosaur and other vertebrate bones and skeletons found there, but only theropod, hadrosaur and supposed ankylosaurid footprints have been reported from this stratum. Dinosaur footprints are also noted from the Nemegt Formation, and occur as typical dinosaur track accumulations (tracksites). An articulated protoceratopsid skeleton - specimen ZPAL Mg D-II/3 - was collected by the Polish-Mongolian Expedition of 1965 from the Djadokhta Formation of Flaming Cliffs in Mongolia. Recently, the natural cast of a tetradactyl digitigrade footprint was found underneath the pelvic girdle while the skeleton and matrix were being prepared. This is possibly the first find of a dinosaur track in close association with an articulated skeleton. Although Protoceratops is an extremely common dinosaur in Mongolia, its footprints have never previously been reported from the Late Cretaceous of the Gobi Desert.     

Geology and vein tin mineralization in the Dadoushan deposit,Gejiu district,SW China

Vein-type tin mineralization in the Dadoushan deposit, Laochang ore field, Gejiu district, SW China, is predominantly hosted in Triassic carbonate rocks (Gejiu Formation) over cupolas of the unexposed Laochang equigranular granite intrusion. The most common vein mineral is tourmaline, accompanied by skarn minerals (garnet, diopside, epidote, phlogopite) and beryl. The main ore mineral is cassiterite, accompanied by minor chalcopyrite, pyrrhotite, and pyrite, as well as scheelite. The tin ore grade varies with depth, with the highest grades (~1.2 % Sn) prevalent in the lower part of the vein zone. Muscovite ⁴⁰Ar–³⁹Ar dating yielded a plateau age of 82.7 ± 0.7 Ma which defines the age of the vein-type mineralization. Measured sulfur isotope compositions (δ ³⁴S = −4.1 to 3.9 ‰) of the sulfides (arsenopyrite, chalcopyrite, pyrite, and pyrrhotite) indicate that the sulfur in veins is mainly derived from a magmatic source. The sulfur isotope values of the ores are consistent with those from the underlying granite (Laochang equigranular granite, −3.7 to 0.1 ‰) but are different from the carbonate wall rocks of the Gejiu Formation (7.1 to 11.1 ‰). The calculated and measured oxygen and hydrogen isotope compositions of the ore-forming fluids (δ ¹⁸O_H2O = −2.4 to 5.5 ‰, δD = −86 to −77 ‰) suggest an initially magmatic fluid which gradually evolved towards meteoric water during tin mineralization.