On statistical estimation in fission track dating

Statistical methodology is described for obtaining point and interval estimates of age in fission track dating experiments, particularly for (a) the external detector method, which is reviewed briefly, and (b) the population method, which is considered in more detail. Some mathematical background to models, based on the underlying physical process, is given. This is used to suggest appropriate statistical methods, to assess them and to help understand sources of variation in the data. For the external detector method, a model is required for numbers of tracks given the amount of uranium; the usual Poisson model is derived as a consequence of independent thinning of a bivariate point process. For the population method, uranium heterogeneity does not necessarily invalidate the estimate but does represent a source of variation that must be allowed for in its error; thus an interval estimate of age might be relatively uninformative.     

Consolidation and Break-up of the South American Platform in Southeastern Brazil: Tectonothermal and Denudation Histories

The different tectonic stages that occurred at the end of the Proterozoic and during the Phanerozoic have an important bearing on the tectonothermal history of the South American Platform and its consolidation. Geochronological data (U/Pb monazite, ⁴⁰Ar/³⁹Ar whole rock) and apatite fission-track analysis, from Precambrian rocks of the southeastern Brazilian coastline, permit the modeling of a long-term thermal history of the crust and constrain variable denudation rates.Using these data, a temperature-time diagram reflects a period of accelerated exhumation during the end of the Brasiliano Orogeny, followed by long stability and reactivation of the platform during the Rifting Phase of the South Atlantic Ocean.U/Pb zircon and monazite (blocking temperature of ca. 650° C) data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 Ma. During the following escape tectonics, between 610 and 590 Ma the exhumation process indicates cooling rates of ca. 12°C/Ma. ⁴⁰Ar/³⁹Ar biotite ages between 540 and 510 Ma (ca. 300°C) and a corrected fission-track age on apatites (100°C) of 480 Ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones.A long stabilization phase, with low exhumation, and cooling rate around 0.25°C/Ma was recorded from the Cambro/Ordovician to the Mesozoic. At 65 Ma an acceleration of the exhumation through denudation and reworking of the South American surface with cooling rate of 1.5°C/Ma is observed.The uplift of the Mantiqueira and Serra do Mar mountain ranges along the southeast Brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long-term scarp retreat, combined with intense, but progressive denudation towards the continent. A denudation of 2.5 to 4 km was calculated for such processes. This lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast Brazil.     

The thermal history of the eastern Officer Basin (South Australia): evidence from apatite fission track analysis and organic maturity data

The eastern Officer Basin in South Australia contains a Neoproterozoic to Devonian succession overlain by relatively thin (<500 m) Permian, Mesozoic and Tertiary deposits. Within the basin fill, there are several major unconformities representing uncertain amounts of erosion. Three of these surfaces are associated with regional deformational events. Regional unconformities formed between 560 and 540 Ma (Petermann Ranges Orogeny), approximately 510–490 Ma (Delamerian Orogeny), 370–300 Ma (Alice Springs Orogeny), 260–150 Ma; and 95–40 Ma. AFTA® results from 13 samples of Neoproterozoic, Cambrian and Permian sedimentary rocks in five wells (Giles-1, Manya-2, -5 and -6 and Lake Maurice West-1) show clear evidence for a number of distinct thermal episodes. Results from all samples are consistent with cooling from the most recent thermal episode beginning at some time between 70 and 20 Ma (Maastrichtian–Miocene). AFTA results from Giles-1 indicate at least two pre-Cretaceous thermal episodes with cooling beginning between 350 and 250 Ma (Carboniferous–Permian) and between 210 and 110 Ma (Late Triassic–Albian). Results from Manya-2, -5 and -6 and Lake Maurice West-1 show evidence for at least one earlier higher temperature event, with cooling from elevated paleotemperatures beginning between 270 and 200 Ma (Late Permian to Late Triassic). These episodes can be correlated with other cooling/erosional events outside the study area, and the AFTA-derived paleotemperatures are consistent with kilometre-scale erosion for each of the episodes identified. Integration of the AFTA data with organic thermal maturation indicators (MPI) in the Manya and Giles-1 wells suggests that the Cambrian and Neoproterozoic successions in the northern part of the study area reached peak maturation prior to the Permian, while limited data from Lake Maurice West-1 allows peak maturation to have occurred as young as the Late Permian to Late Triassic thermal episode revealed by AFTA. The approach outlined in this study is relevant to all ancient basins as it emphasises the importance of understanding events associated with neighbouring regions. The thermal history of the Officer Basin, as with most other ancient basins, has been strongly affected by significant tectonic events throughout its history, even though younger deposits are not preserved in the basin itself. The recognition of these younger events, and the implications of these events for the depositional history, is important as it allows identification of the best regions for preservation of early generated hydrocarbons, and in some cases, suggests areas where generation of hydrocarbons could have occurred more recently than previously thought.     

热带气旋运动曲率的数学模型与路径异常的月尖突变判据

采用运动曲率数学模型，研究热带气旋异常路径的成因，得到的主要结果是：热带气旋路径曲率及其变化与科氏力参数、环境场气压分布、热带气旋的移速及涡旋动力结构、下垫面摩擦力等因子有关；当各类影响因子渐变至满足月尖突变判据时，出现演变曲线的折叠区，随着外源参数变化，一旦解移出折叠区，热带气旋便可发生移间突变，出现各类异常轨迹。     

SPECTRUM-90时期大气10—20天准周期振荡对热带气旋转向路径的影响

本文研究了SPECTRUM-90时期，大气10—20天周期振荡对西北太平洋转向台风路径的影响，结果表明，这种影响是显著的。在SPECTRUM-90时期，10—20天周期振荡比较活跃，西北太平洋副热带高压的周期性退缩现象是来自中、高纬和热带的10—20天周期低压扰动共同影响所致，这也是导致热带气旋转向运动的一个重要原因。进一步研究还发现，在SPECTRUM-90时期，存在着一支源于热带西北太平洋上呈经向排列的纬向风波列，热带波动沿此波列向北传播，在一定程度上，可以推动热带气旋北上转向。     

On statistical models for fission track counts

The statistical basis for the usual analysis of fission track counts obtained by the external detector method is discussed and illustrated with examples. A consequence is that if any observed correlation between counts of spontaneous and induced tracks is due to heterogeneity in the density of uranium, then the model proposed by McGee and Johnson (1979)for assessing the experimental error is inappropriate and results based on it could be misleading. The same remark applies to the method proposed by Johnson, McGee, and Naeser (1979).     

用裂变径迹法研究云贵高原洱海和南明河中铀含量

为确定云贵高原洱海和南明河中铀的含量及污染程度,从洱海和南明河中污染程度不同的地段采集两类水样,在核反应堆中经热中子辐照,使铀裂变碎片在固体径迹探测器上产生径迹,并用NaOH蚀刻.通过光学显微镜观测径迹数,结果表明:南明河水中铀含量远大于洱海.通过南明河与国内外其它河流的对比,讨论了铀污染的情况.     

跟踪国外大地震的震情分析资料库

该项研究为应急跟踪国外灾害地震，提供基础性背景资料的一种快速反应措施，它包括资料库和检索应用软件两部分。资料部分包括以下三个方面的内容：全球灾害性地震活动区的地震地质构造背景；灾害性历史地震目录和活动性数据；各国地震管理和观测研究机构概况以及与之配套的资料检索应用软件等．     

裂变径迹定年法中国际标样的年龄测定

第６届国际裂变径迹测定地质年代学术讨论会上推荐标准化刻度裂变径迹定年法，并推荐了几种定年标样。本文通过标准铀玻璃刻度系数定出值，利用外探测器法测定了国际标样中的３种桔石和两种磷灰石的年龄（ＦＣＴ２７．７±０．８Ｍａ，ＢＭ１６．１±０．５Ｍａ，ＴＲ６０．０±３．ＯＭａ，Ｄｕｒａｎｇｏ３０．８±１．９Ｍａ），在误差范围内与参考年龄一致。