Meso‐Cenozoic Tectonothermal History of Permian Strata,Southwestern Weibei Uplift: Insights from Thermochronology and Geothermometry

This study provides an integrated interpretation for the Mesozoic-Cenozoic tectonothermal evolutionary history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin. Apatite fission-track and apatite/zircon(U-Th)/He thermochronometry, bitumen reflectance, thermal conductivity of rocks, paleotemperature recovery, and basin modeling were used to restore the Meso-Cenozoic tectonothermal history of the Permian Strata. The Triassic AFT data have a pooled age of ～180±7 Ma with one age peak and P(χ2)=86%. The average value of corrected apatite(U-Th)/He age of two Permian sandstones is ～168±4 Ma and a zircon(U-Th)/He age from the Cambrian strata is ～231±14 Ma. Bitumen reflectance and maximum paleotemperature of two Ordovician mudstones are 1.81%, 1.57% and ～210°C, ～196°C respectively. After undergoing a rapid subsidence and increasing temperature in Triassic influenced by intrusive rocks in some areas, the Permian strata experienced four cooling-uplift stages after the time when the maximum paleotemperature reached in late Jurassic:(1) A cooling stage(～163 Ma to ～140 Ma) with temperatures ranging from ～132°C to ～53°C and a cooling rate of ～3°C/Ma, an erosion thickness of ～1900 m and an uplift rate of ～82 m/Ma;(2) A cooling stage(～140 Ma to ～52 Ma) with temperatures ranging from ～53°C to ～47°C and a cooling rate less than ～0.1°C/Ma, an erosion thickness of ～300 m and an uplift rate of ～3 m/Ma;(3)(～52 Ma to ～8 Ma) with ～47°C to ～43°C and ～0.1°C/Ma, an erosion thickness of ～500 m and an uplift rate of ～11 m/Ma;(3)(～8 Ma to present) with ～43°C to ～20°C and ～3°C/Ma, an erosion thickness of ～650 m and an uplift rate of ～81 m/Ma. The tectonothermal evolutionary history of the Qishan area in Triassic was influenced by the interaction of the Qinling Orogeny and the Weibei Uplift, and the south Qishan area had the earliest uplift-cooling time compared to other parts within the Weibei Uplift. The early Eocene at ～52 Ma and the late Miocene at ～8 Ma, as two significant turning points after which both the rate of uplift and the rate of temperature changed rapidly, were two key time for the uplift-cooling history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin.     

新疆及邻区Pn速度层析成像

利用新疆及邻区2万多条Pn射线的走时资料,采用层析成像的方法反演该地区上地幔顶部的Pn速度结构.主要结果是:①新疆地区平均h速度为.2km/s,高于中国大陆地区的平均值(.0km/s),速度变化量从-0.3km/s到0.2km/s.②准噶尔盆地是明显的高Pn速度区,高速区与地貌形状吻合较好,最大值达.4km/s;塔里木盆地整体上呈现高速异常二者都可能与盆地是稳定地块、构造活动和变形较弱有关.③在盆地与山脉的交接带即主要的构造活动带,存在较低的Pn速度,可达7.9km/s.④塔里木南缘中部存在一显著的低速区,可能与岩浆活动和构造活动较强有关.⑤上地幔顶部波速各向异性整体上盆地中心较弱,边缘地带较强.新疆南部波速的各向异性可能是因印度板块对欧亚大陆的碰撞使地幔物质向北蠕动的结果.     

由多个小震推断的青甘和川滇地区地壳应力场的方向特征

本文根据1975-1984年期间发生的多个小地震的P波初动方向数据,推断了青、甘、川、滇地区平均主应力轴的方向。结果表明,该地区压应力轴（P轴）和张应力轴（T轴）方向皆水平,但其方位由北到南呈现规则转动的趋势,即主压应力轴在北部青甘地区大致取NE-SW方向,到中部川西北地区转为近E-W方向,再到南部云南地区转为NNW-SSE或近N-S方向。形成应力轴方向这样特定分布图象的原因,可用印度板块向北对青藏高原的推挤和缅甸中源地震带地区下沉物质对云南地区的拖曳作用来解释。     

中国及邻区现代构造应力场的区域特征

本文根据我国及邻区40年来(1937—1977年)173次浅源地震的断层面解结果以及其他资料, 讨论了我国及邻区普遍存在着的以水平压应力为特征的现代构造应力场.其区域特征表现为:(1)华南地区以北西西走向的水平压应力为主;(2)华北以及朝鲜和西南日本是以北东东走向的水平压应力和北北西走向的水平张应力为其特点;(3)青藏高原的大部分直到蒙古西部均处在近南北到北东走向的水平压应力作用之下, 兰州amp;amp;mdash;察隅一线以东的压应力呈现有规则的向东南偏转.西天山地区具有北西向压应力.我国大陆板块内部的现代构造应力场与周围岩石圈板块运动和上地幔的物质运动有关.     

High-resolution assessment of retrogressive thaw slump susceptibility in the Qinghai-Tibet Engineering Corridor

Under the rapidly warming climate in the Arctic and high mountain areas, permafrost is thawing, leading to various hazards at a global scale. One common permafrost hazard termed retrogressive thaw slump(RTS) occurs extensively in ice-rich permafrost areas. Understanding the spatial and temporal distributive features of RTSs in a changing climate is crucial to assessing the damage to infrastructure and decision-making. To this end, we used a machine learning-based model to investigate the environ...     

Numerical Studies of Magnetic Reconnection and Heating Mechanisms for the Ellerman Bomb

An Ellerman Bomb(EB) is a kind of small scale reconnection event, which is ubiquitously formed in the upper photosphere or the lower chromosphere. The low temperature(<10,000 K) and high density(～1019–1022) plasma there makes the magnetic reconnection process strongly influenced by partially ionized effects and radiative cooling. This work studies the high β magnetic reconnection near the solar temperature minimum region based on high-resolution 2.5D magnetohydrodynamics simulations. The time...     

Serpentinisation is Required for the Magnetization of the Martian Crust

The remnant magnetism in the crust of Martian southern highland is associated with the magnetic sources at an average depth of ～32 km. In this work, we investigate the magnetization of Martian crust via 1-D parameterized model for the stagnant-lid mantle convection. According to our model, the magnetization of Martian crust is likely to take place in the top-down manner during 4.1–3.7 Ga. To reproduce the average depth of magnetic sources below the southern highland, magnetite and Mg-ferrite are...     

Molecular evolution of nitrogen-containing compounds in highly mature organic matter: Implications for the hydrocarbon generation potential

Evaluating the hydrocarbon generation potential of highly mature organic matter is a key and critically challenging area of research in petroleum geochemistry. To explore this issue, we used negative ion electrospray ionization-Fourier transform-ion cyclotron resonance-mass spectrometry to investigate the molecular evolution of N-containing compounds in Carboniferous-lower Permian source rocks with a range of maturities in the northwestern Junggar Basin, China. The N₁ compounds formed...     

Petrogenesis of Potassic Basalts from Northeast China: New Constraints from Trace Elements in Olivine

<正>This study used trace elements in olivine as a new petrogenetic indicator to further constrain the petrogenesis of potassic basalts from the Erkeshan-Wudalianchi-KeluoXiaogulihe potassic volcanic field(EWKX for short)in the Songliao Basin of NE China,with a combination of the previous olivine and whole-rock geochemical data.We     

地震烈度和建筑物破坏率

本文通过对现行三种地震烈度表的分析,认为现代地震烈度评定中存在一定问题,提出以房屋等建筑物的破坏率作为衡量地震烈度标志的方法,并指出该方法有助于将地震调查、震害预测和减灾对策结合起来。