U–Pb dating of zircon in hydrothermally altered rocks as a correlation tool: Application to the Mangakino geothermal field,New Zealand

Recognition and correlation of rock units within geothermal fields is often hampered by high degrees of alteration that obscure primary mineralogies and lithological boundaries, and preclude direct dating by radiometric techniques. Magmatic zircons are commonly present in silicic volcanic rocks, where zircon saturation was achieved and zircons crystallized up to the point of eruption. Young zircons are highly resistant to hydrothermal alteration and can yield a record of their crystallization ages in otherwise heavily altered rocks. Zircon crystallization-age spectra have been obtained by SIMS techniques (SHRIMP-RG) from three samples of cuttings and a core sample from ignimbrite penetrated in 3 drillholes up to ~ 3.2 km deep at the Mangakino geothermal field in New Zealand. The crystallization ages are similar between the drillcore and cutting samples, indicating that downhole mixing of cuttings has not been important, and showing collectively that volcanic units of closely similar ages are represented between ~ 1.4 and ~ 3.2 km depth. This is despite apparent changes in the inferred primary volcanic lithology that had led to earlier inferences that multiple ignimbrites of contrasting age were present in this depth interval. Comparisons of zircon crystallization-age spectra and inferred primary mineralogical characteristics from the drillhole samples with surficial ignimbrites that crop out west of Mangakino suggest that the boreholes have entered a > 1.8-km-thick intracaldera fill of ignimbrite generated in the closely-spaced Kidnappers and Rocky Hill eruptions at ~ 1 Ma.     

The issue of trust and its influence on risk communication during a volcanic crisis

This paper investigates trust in the scientists, government authorities and wider risk management team during the ongoing volcanic crisis in Montserrat, WI. Identifying the most trusted communicator and how trust in information can be enhanced are considered important for improving the efficacy of volcanic risk communication. Qualitative interviews, participant observations and a quantitative survey were utilised to investigate the views and attitudes of the public, authorities and scientists. Trust was found to be dynamic, influenced by political factors made more complex by the colonial nature of Montserrat’s governance and the changing level of volcanic activity. The scientists were viewed by the authorities as a highly trusted expert source of volcanic information. Mistrust among some of the local authorities towards the scientists and British Governor was founded in the uncertainty of the volcanic situation and influenced by differences in levels of acceptable risk and suspicions about integrity (e.g. as a consequence of employment by the British Government). The public viewed friends and relatives as the most trusted source for volcanic information. High trust in this source allowed competing messages to reinforce beliefs of lower risk than were officially being described. The scientists were the second most trusted group by the public and considered significantly more competent, reliable, caring, fair and open than the authorities. The world press was the least trusted, preceded closely by the British Governor’s Office and Montserratian Government officials. These results tally well with other empirical findings suggesting that government ministers and departments are typically distrusted as sources of risk-related information. These findings have implications for risk communication on Montserrat and other volcanic crises. The importance and potential effectiveness of scientists as communicators, because of, and despite, the existence of political, cultural and institutional barriers, is exemplified by this study.

Geophysical imaging of buried volcanic structures within a continental back-arc basin: The Central Volcanic Region, North Island, New Zealand

Hidden beneath the ~ 2 km thick low-velocity volcaniclastics on the western margin of the Central Volcanic Region, North Island, New Zealand, are two structures that represent the early history of volcanic activity in a continental back-arc. These ~ 20 × 20 km structures, at Tokoroa and Mangakino, form an adjacent gravity high and low, respectively. Interpretations from seismic refraction arrivals and gravity modelling indicate the − 65 mgal Mangakino residual gravity anomaly can be modelled, in part, by two low-density bodies that reach depths of ~ 6.5 km, whereas the Tokoroa gravity anomaly is due to a higher density rock coming, at most, to within ~ 650 m of the surface. The Mangakino anomaly is interpreted to be due to the remnants of magma chambers that fed large ignimbrite eruptions from about 1.2 Ma. An andesite volcano or complex volcanic structure is the preferred interpretation for the Tokoroa gravity high. The size of the putative volcanic structure is comparable to the presently active Tongariro Volcanic Complex in the centre of North Island.     

An automatic procedure to forecast tephra fallout

Tephra fallout constitutes a serious threat to communities around active volcanoes. Reliable short-term forecasts represent a valuable aid for scientists and civil authorities to mitigate the effects of fallout on the surrounding areas during an episode of crisis. We present a platform-independent automatic procedure with the aim to daily forecast transport and deposition of volcanic particles. The procedure builds on a series of programs and interfaces that automate the data flow and the execution and subsequent postprocess of fallout models. Firstly, the procedure downloads regional meteorological forecasts for the area and time interval of interest, filters and converts data from its native format, and runs the CALMET diagnostic model to obtain the wind field and other micro-meteorological variables on a finer local-scale 3-D grid defined by the user. Secondly, it assesses the distribution of mass along the eruptive column, commonly by means of the radial averaged buoyant plume equations depending on the prognostic wind field and on the conditions at the vent (granulometry, mass eruption rate, etc). All these data serve as input for the fallout models. The initial version of the procedure includes only two Eulerian models, HAZMAP and FALL3D, the latter available as serial and parallel implementations. However, the procedure is designed to incorporate easily other models in a near future with minor modifications on the model source code. The last step is to postprocess the outcomes of models to obtain maps written in standard file formats. These maps contain plots of relevant quantities such as predicted ground load, expected deposit thickness and, for the case of or 3-D models, concentration on air or flight safety concentration thresholds.     

应力腐蚀开裂的一种概率竞争机制

１９９８年１月,采用极化曲线,慢应变速率及扫描电镜等试验技术,研究了奥氏体不锈钢的应力腐蚀开裂。结果表明,奥氏体不锈钢在酸性氯离子溶液中处于活性阳极溶解状态,但去发生应力腐蚀开裂,其断口形貌具有解理特征。这种ＳＣＣ无法用钝化膜破裂一再钝化理论和氢脆理论解释。本文以阳极溶解和表变的相互作用,激光散斑干涉术对裂纹尖端应变行为的测量,断口形貌观察等实验结果为基础,结合韧性和脆性断裂概率竞争的观点,提出了     

江苏苏05井、苏06井水温近年来典型异常特征分析及其机理讨论

近10年历史震例的分析表明,江苏苏05井、苏06井水温观测资料异常与江苏及邻省中等地震有很好的对应关系。本文对2010年后两口井的观测数据进行分析,总结了苏05井、苏06井水温测项在震前的典型异常特征:①异常表现为打破上升趋势的下降变化;②震前异常持续时间为2-3个月左右,映震范围在300km左右;③两口井的震前异常幅度在0.003℃左右。根据总结的异常特征并结合水温与井孔结构关系、水温与水位的关系、不同层位水温观测原理以及水化分析结果等,对异常可能的成因进行了初步探讨。     

The role of the Polochic Fault as part of the North American and Caribbean Plate boundary: Insights from the infill of the Lake Izabal Basin

The Lake Izabal Basin in Guatemala is a major pull-apart basin along the sinistral Polochic Fault, which is part of the North American and Caribbean plate boundary. The basin infill contains information about the tectonic and sedimentological processes that have imparted a significant control on its sedimentary section. The inception of the basin has been linked to the relative importance of the Polochic Fault in the tectonic history of the plate boundary; yet, its sedimentological record and its inception age have been poorly documented. This study integrates diverse datasets, including industry reports, well logs and reports, well cuttings, vintage seismic data, outcrop observations and geochronological data to constrain the initial infill and age of inception of the basin. The integrated data show that during the Oligocene–Miocene, a marine carbonate platform was established in the region which was later uplifted and eroded in the early Miocene. The fluvial–lacustrine deposits above this carbonate platform are part of the initial infill of the basin and are constrained with zircon weighted-mean ²⁰⁶Pb/²³⁸U ages of 12.060 ± 0.008 from a volcanic tuff ~30 m above the unconformity. Sandstone, mudstone and coal dominate the interval from 12 to 4 Ma, with an increase in conglomerate correlating to the uplift of the Mico Mountains and San Gil Hill at 4 Ma. Fault switch activity between the Polochic and Motagua faults has been hypothesized to explain total offset along the Polochic Fault and the geologic and geodetic slip rates along the two faults. The 12 Ma age determined for the initial infill of the basin confirms this hypothesis. Consequently, our study confirms that at ~12 Ma the Polochic Fault served as the main fault of the plate boundary with inferred slip rates ranging from 13 to 21 mm/yr with a strong possibility that the Polochic Fault was, at some point between 15 Ma and 7 Ma, the only active fault of the plate boundary. The results of this study show that tectonic records preserved in sediments of strike-slip basins improve the understanding of the relative significance of individual faults and the implications with respect to strain partitioning throughout its tectonic history.     

新生代地磁漂移研究若干进展

地磁漂移事件的成因及发生规律是地学研究热点,是古地磁学科在这个世纪可能为地球科学贡献新理论的一个突破口。在回顾地磁漂移研究历史的基础上,对新生代地磁漂移记录及其时代进行了概述,从地磁漂移的成因、地磁漂移事件与地磁场强度的关系、地磁场漂移期间地磁场形态学研究等几个方面对过去的研究进行了总结。最后,提出未来研究需关注沉积速率较高的河湖相沉积物,通过多种手段生成不同地理位置的可靠地磁漂移记录,利用轨道调谐手段准确限定时代等,才能获得对新生代地磁漂移规律的全面认识。     

欧洲海洋调查船运作组织及其对我国 海洋调查船协同机制的启示

海洋调查船是了解认知与开发利用海洋的关键基础设施。欧洲海洋调查船运作组织(ERVO)推动这一关键基础设施协同的努力颇具代表性。它面对欧洲海洋调查船多元化且无权威主体的境地,通过会员制构建协同平台,明晰了业务主导、可持续发展的协作目标;它通过年会聚焦海洋调查船及相关仪器装备,交流运行管理,研讨技术创新、改造更新以及与海洋调查船相关的共性话题,以促进欧洲海洋调查船和相关装备具有最佳的运行成效;它与相关海洋调查与研究组织机构联动,跻身于欧洲海洋调查船发展战略层,推动欧洲海洋调查船在项目层面组队共享。文章解析了欧洲海洋调查船运作组织的背景和运作模式,同时针对我国海洋调查船协作多头发力缺乏合纵连横的状况,提议发起中国海洋调查船协同论坛,组建联合工作组做好长期务实的基础性工作,筹划中国及关系国调查船协调计划,以建立我国海洋调查船协同机制并逐步跻身国际海洋调查船战略协同层。     

The farnacht formation along the south side of the clew bay fault zone,Western Ireland: Its chemistry and age of metamorphism

The tectonically isolated Farnacht Formation consists of calc-alkaline dacitic-andesitic lavas of volcanic arc affinity. It is situated immediately to the south of the Clew Bay Fault Zone (western continuation of the Highland Boundary Fault Zone of Scotland) in the northeast corner of the Lower Palaeozoic South Mayo Trough in northwest Ireland. It has been metamorphosed to biotite grade greenschist facies following the development of a pervasive, c-s composite muscovite, quartz, and feldspar schistosity. The Farnacht Formation may comprise a terrane that is directly unrelated to nearby Ordovician and Silurian rocks; its present position was fixed largely by Wenlock times. The age of the Farnacht Formation and the deformational event(s) that produced the schistosity are not known. ⁴⁰Ar/³⁹ Ar step heating from four specimens have dated the crystallization of biotite at from 422 ± 2 to 405 ± 14 Ma with a mean age of 413 Ma. These ages date either the post-D2, pre-D3 metamorphic peak, or a hornfelsing of the same structural age related to an unseen thermal source, and provide a minimum age for the end Silurian - early Devonian Caledonian tectonothermal activity in the northeast part of the South Mayo Trough.