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.     

用于裂变径迹技术刻度的铀标准玻璃的研制

监测中子积分通量是裂变径迹技术的重要组成部分。铀玻璃监测中子积分通量是国际裂变径迹定年标准化工作组推荐的重要方法之一，铀玻璃测定法还普遍用于测定样品中的铀含量及其空间分布。本文介绍的铀标准玻璃，经过多家实验室定值测定，表明其稳定性、均匀性均达到国家一级标准物质的要求，抗酸性能达到Ⅰ级光学玻璃水平，抗潮性能达到Ⅱ级光学玻璃水平。其它性能指标均达到或超过美国国家标准局的同类产品。     

Modelling the formation of fission tracks in apatite minerals using molecular dynamics simulations

We introduce a simple method to simulate the “ion explosion spike” mechanism of fission track formation within the framework of classical molecular dynamics. The method is applied to six apatite compositions and the resulting tracks are compared with each other as well as with the damage produced by another mechanism—the “Displacement spike”. In contrast to experimentally observed tracks, the radii of simulated tracks are not dependent on their direction in the crystal. Since the simulations model accurately the elastic response of apatites, this suggests that the experimentally observed difference in track radii for tracks along different crystal directions is not entirely caused by anisotropy in the elasticity of apatite. We suggest that anisotropy in the interactions between the electric fields of fission fragments and the crystal ions is a major factor in the final radii of fission tracks. In fluorapatite, the simulations also reveal the formation of small clusters of fluorite-like material in the core of the fission track, a phenomenon which has yet to be confirmed experimentally.

用裂变径迹法研究断层活动年龄的初步探讨

裂变径迹年代测定是研究断层活动年龄的新方法,它基于磷灰石中裂变径迹的退火效应。本文报导了取自郯庐断裂带等地区12个磷灰石和一个榍石的裂变径迹年龄,结果表明,在断裂带中磷灰石裂变径迹的退火效应非常明显,效应随离断层带的距离增加而减弱。结合断层带的活动特点和原岩的年龄,对断层带中磷灰石裂变径迹年龄的解释及今后的研究方向作了探讨     

Cenozoic Magmatism and Tectonic Framework of Western Yunnan, China: Constrained from Geochemistry, Sr–Nd–Pb Isotopes and Fission Track Dating

Western Yunnan is composed of several extruded continental microblocks that were generated by the oblique collision between the Indian and Asian continents during the Cenozoic. In this study, the magmatic and tectonic frameworks of western Yunnan in the Cenozoic were analyzed based on geochemistry, Sr–Nd–Pb isotopes, and apatite/zircon fission track dating. Magmatism during the Cenozoic in western Yunnan was then divided into three distinctive episodes: alkali granite rocks produced from 55 to 46 Ma were derived from the anatexis of crustal materials; bimodal igneous rocks formed between 37 and 24 Ma were possibly derived from an EMII mantle with a contribution from continental materials; and intermediate–basic volcanic rocks produced in the Tengchong microblocks since ~16 Ma are considered to be generated by the partial melting of the upper mantle that was induced by the pulling apart of the dextral Gaoligong strike–slip fault system. Moreover, fission track analysis of apatite and zircon indicates that the regional crustal uplift in western Yunnan possibly began at ~34 Ma, with accelerated annealing occurring at ~24 Ma, ~13 Ma, and ~4 Ma. During the past 24 Ma, the average denudation rate was ~0.32 mm/yr for the faulted block controlled by the Chongshan–Lancang River fault. However, crustal uplift has been relatively gentle in places lacking influence from strike–slip shear zones, with an average denudation rate of ~0.2 mm/yr. Combined with strike–slip shear and block rotation in the Cenozoic, the tectonic evolution of western Yunnan since ~45 Ma can thus be divided into four stages occurring at 45–37 Ma, 37–24 Ma, 24–13 Ma, and 13–0 Ma.     

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。     

Fission track ages of Hymalayan muscovites (Kathmandu Valley,Nepal)

Summary Himalayan muscovites from pegmatites of Kathmandu Valley, Nepal yield an age of 2–23 m. y. by fission track (f.t.) method. The uranium concentration is estimated to be 10^–10 atom/atom.     

Tracing sediment pathways by zircon fission track analysis: Oligocene marine connections in Central Europe

In this study, we use contrasting zircon fission track age signatures of Alpine detritus and detritus derived from the Variscan realm to trace sediment pathways in Central Europe. Our data show that the Molasse Basin was connected with the Rhine Graben Sea during the Mid-Oligocene, thus joining the North Sea to the Paratethys. Within the Rhine Graben Sea, fairly strong south–north directed currents existed, transporting sand-sized Alpine detritus nearly 300 km towards the north. A connection between the Rhône-Bresse Graben and the Rhine Graben and/or the French Molasse Basin and the Swiss Molasse Basin, by contrast, is not supported by the fission track data. This may be explained by the existence of submarine rises that hampered the transport of sand-sized sediment towards the north/northeast.     

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.     

中、上扬子白垩纪以来的剥蚀过程及构造意义——低温年代学数据约束

通过对磷灰石裂变径迹（AFT）数据系统的对比,本文从整体上分析了中、上扬子区块各地质单元在晚中生代、新生带抬升冷却特征,并初步构建了区域上中-新生代构造活动与内陆变形的时空关系.它们的构造活动在空间上具有分区性和连续性特征,在时间上具有幕式性特征.空间上的分区性与连续性主要表现在各地质单元隆升特征的差异性,即中扬子北缘江汉盆地、黄陵隆起最早开始冷却到大巴山逆冲带、米仓山-汉南隆起晚侏罗世自北（东）向南（西）的隆升与江南-雪峰山隆起、湘鄂西褶皱带、川东褶皱带及川东北地区自南东向北西依次递进逆冲褶皱变形的差异;构造活动时间上的幕式特征主要表现在阶段性的快速冷却及其相间的缓慢冷却过程.中、上扬子北缘大巴山逆冲带、米仓山-汉南隆起磷灰石裂变径迹年龄从北（东）向南（西）逐渐变小,它们在晚中生代、新生代处于秦岭-大别造山带向扬子地块逆冲挤压变形的动力学背景;而湘鄂西褶皱带、川东褶皱带及川东北地区磷灰石裂变径迹年龄自南东向北西方向减小的趋势主要受控于太平洋板块的俯冲挤压效应.中、上扬子喜山晚期的快速冷却主要是青藏高原隆升及其向东与南东方向构造逃逸挤压作用及亚洲季风等气候变化的响应.磷灰石裂变径迹的系统分析为中、上扬子递进扩展构造变形提供了年代学约束.