Temperature dependent grain boundary migration in deformed-then-annealed material: Observations from experimentally deformed synthetic rocksalt

Grain boundary migration between strained, substructured grains and newly appearing, strain free grains has been observed during static in-situ annealing of pre-deformed rocksalt in the SEM. With increasing temperature (T) the migration velocity increases and the character of grain boundary migration changes. As temperature increases there is an increase in the length of individual migrating boundary segments that move at similar rates. In addition, the frequency of migrating boundaries that form traces of a {100} boundary plane of at least one of the crystals involved increases, and moving grain boundaries between new and old grains change from highly irregular to smooth, straight boundaries. At the same time there is a decrease in the influence of the substructure of pre-existing strained grains on the grain boundary movement. Resultant microstructures reflect these changes. At  325–350 °C, the deformed-then-annealed microstructure is characterized by very irregular grain boundaries, a high abundance of 5–50 m scale remnants of old, substructured grains within new grains, giving a poikilitic microstructure. At  350–400 °C, grain boundaries often exhibit elongate embayments into the strained grains and most remnants of old, strained grains are located at former grain boundaries. At > 400 °C, grain boundaries between new and old, strained grains are straight to smoothly curved.The grain boundary velocity observations are explained by the effect of temperature on mobility coupled with local driving force variations. Additionally, at low annealing temperature, impurity (solute) drag and driving-force variations are influential, while at high temperature the anisotropy in grain boundary energy with crystallographic orientation becomes more important. Transferring the knowledge from our experiments to geological samples enables us to recognize and interpret similar microstructures in rocks, thereby making it is possible to relate microstructural characteristics to the pre-annealing and post-deformational annealing history.     

波阻抗遗传算法反演方法的研究及应用

作者介绍的遗传算法是在自然界生物遗传过程优选和进化原理的基础上，针对波阻抗反演的实际问题，对标准的遗传算法进行了改进，引入了模拟退火算法中的热槽法控制初始群体的产生，用逐位迭代的交换方式代替传统的杂交方式即随机选择杂交点进行交换。使用改进的遗传算法对地震波阻抗进行反演，可很好地提高反演的精度。在文中最后，作者通过理论模型和实例验证了上述的思想。     

Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb–Sr and fission-track ages of gneissose granitoid and numerical modeling

Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb–Sr whole-rock–mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb–Sr ages fall in a range of ca 89–87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1σ error), respectively. Combining the newly obtained ages with previously reported (Th–)U–Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is ≥ 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1–0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis.     

改进的模拟退火方法及其在电阻率图像重建中的应用

实际中的大量地球物理反演都是一个多参数、非线性优化问题,以往的局部方法只是利用有限的信息来改进初始模型,因此对初始模型有很大的依赖性,难以得到全局最优解。针对这一问题,本文选择全局反演方法中的模拟退火和单纯形的组合算法,改进了模拟退火和单纯形算法的匹配技术,并将它引入到电阻成像反演问题中。     

New age constraints on the cooling and unroofing history of the Trans-Himalayan Ladakh Batholith (Kargil area), N. W. India

Thermotectonic history of the Trans-Himalayan Ladakh Batholith in the Kargil area, N. W. India, is inferred from new age data obtained here in conjunction with previously published ages. Fission-track (FT) ages on apatite fall around 20±2 Ma recording cooling through temperatures of ∼100°C and indicating an unroofing of 4 km of the Ladakh Range since the Early Miocene. Coexisting apatite and zircon FT ages from two samples in Kargil show the rocks to have cooled at an average rate of 5–6°C/Ma in the past 40 Ma. Zircon FT ages together with mica K−Ar cooling ages from the Ladakh Batholith cluster around 40–50 Ma, probably indicating an Eocene phase of uplift and erosion that affected the bulk of the batholith after the continental collision of India with the Ladakh arc at 55 Ma. Components of the granitoids in Upper Eocene-Lower Oligocene sediments of the Indus Molasse in Ladakh supports this idea. Three hornblende K−Ar ages of 90 Ma, 55 Ma, and 35 Ma are also reported; these distinctly different ages probably reflect cooling through 500–550°C of three phases of I-type plutonism in Ladakh also evidenced by other available radiometric data: 102 Ma (mid-Cretaceous), 60 Ma (Palaeocene), and 40 Ma (Late Eocene); the last phase being localised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.     

断层物质测年的热释光研究

断层物质ＴＬ测年的关键，是断裂运动产生的温压效应能否使断裂带内某些矿物原贮存的ＴＬ能量完全释放而“归零”。为此，进行了不同条件的高温、高压和位移速率变化等的模拟断裂运动的实验。结果表明，断裂运动产生的摩擦增温是使断层面上矿物ＴＬ强度减弱的主要因素。讨论了摩擦增温值与断裂运动时剪应力大小、断层泥厚度和断层位移间的关系，并得到了野外断层面上实际测试的证实。据此研究成果，还对小湾坝区Ｆ＿７断裂的活动时代进行了测定     

Long-term landscape evolution of the northeastern margin of the Bohemian Massif: apatite fission-track data from the Erzgebirge (Germany)

To study the relative and absolute timing of post-Variscan cooling and denudation processes in the Erzgebirge of the Mid-European Variscides, eight samples for apatite fission-track (AFT) analysis were collected from a ~1,300 m drill-core. The fission-track data reveal two stages of accelerated cooling through the apatite partial annealing zone (APAZ; i.e., 110±10–60 °C) in the Late Jurassic-Late Cretaceous and in the late Cenozoic, respectively. Late Jurassic-Late Cretaceous cooling corresponding to denudation of 1.5–5.9 km has been related to wrench tectonics along the Elbe Zone during Triassic-Jurassic Pangea breakup. Late Cenozoic exhumation of 2.1–5.6 km, and the increase of the geothermal gradient from 17±5 °C km^–1 (Oligocene/Miocene) to 25–27 °C km^–1 (recent) is likely connected to the formation of the Eger Graben starting from the Oligocene, as a result of the late Alpine orogenic phases.     

人工神经网络及其在短期气候预测中的应用

从业务实际出发，提出了面向短期气候预测的神经网络。选用主分量作为网络的输入和输出，大大减少了输入输出节点数，重点突出了大尺度影响变化关系，提高了实际预报的稳定性；用全局寻优的SA算法取代经典BP算法，使网络学习训练更充分，知识获取更全面；针对业务实际设计代价函数，保证了网络学习训练能适应短期气候预测业务的要求，学习目的更明确，针对性更强。     

陕西省数字地震台下方壳幔速度结构研究

利用广义反、透射系数的传递矩阵计算理论地震图，用快速模拟退火法搜索最佳模型，通过与地震台站实际记录的P波波形进行拟合对比，反演了陕西省13个数字地震台下方的P波速度结构。台站分布区域涉及到秦岭造山带、渭河盆地及鄂尔多斯地台三个构造区域。结果显示，3个构造区的地下速度结构差异明显，呈现了各自的构造特点。其中秦岭造山带上地壳乃至地表速度高，中下地壳出现多个低速层，可能与岩石脱水、构造滑脱带等有关；渭河盆地内上中地壳高低速度层交替出现，反映了断层活动在浅部的影响；鄂尔多斯地台有部分台站保持稳定的匀速构造。反映了古老地台地层稳定发展的特性，部分台站受到后期改造，低速层位增多。因为变化剧烈的台站分布在盆地的南部和西部。而且震源机制解显示该区主应力场方向为近东西向，可以说秦岭北缘的断裂作用以及后来来自青藏高原的挤压应力是导致渭河盆地形成和发展的主要因素。最后我们讨论了速度结构与强震、地震分布以及不同构造演化的关系。     

Geology of the summit limestone of Mount Qomolangma (Everest) and cooling history of the Yellow Band under the Qomolangma detachment

Abstract   Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The ⁴⁰Ar–³⁹Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock ⁸⁷Rb–⁸⁶Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma).