华北克拉通东部地块和大别—苏鲁造山带印支期褶皱-逆冲构造与动力学背景

大别-苏鲁造山带不同岩片(块)经历了不同的褶皱变形.榴辉岩块(或透镜体)和硬玉石英岩片经历了高压-超高压背景下的两幕褶皱变形之后,在区域性第一幕变形期间主要发生透镜化为主,后期与围岩共同经历紧闭同斜第二幕褶皱.而其它岩片主要经历了现今野外可见的区域性三幕褶皱,其中区域性第一幕褶皱为片内残留褶皱,在斜长角闪岩透镜体中多见,宏观规律不明.区域性第二幕褶皱在露头尺度多见,轴面为折劈理,局部强烈置换成片理化带(复合片理或第二期片理),恢复第三幕褶皱改造作用后,揭示出各种岩片中的各级尺度的第二幕褶皱都为轴面北西倾南东倒、轴迹走向为NNE向的紧闭不对称褶皱,不对称性一致反映其指向与各种岩片向南东的逆冲运动有关.第三幕褶皱为以片理或折劈理为变形面的宽缓褶皱,轴迹走向NWW,枢纽向西倾伏.韧性剪切带为非透入性构造,分早晚两期,早期为韧性逆冲,新县穹隆以南,运动学标志指示向北逆冲,错切第二幕褶皱,结合新县穹隆北部向南的逆冲特征,反映这些韧性逆冲断层多数为第二幕大型褶皱翼部的次级逆冲断层;晚期为韧性滑脱带,其发育局限于几个岩性差异较大的接触带,带内伸展型折劈理发育,并对挤压构造样式有重要的改造作用.华北克拉通东部地块是华北克拉通的重要组成,其盖层古生界和三叠系在印支运动期间经历了一幕宽缓褶皱作用,其轴迹方向主体也为NWW向.这一褶皱构造明显在变形时间、变形样式和展布方向上都和大别-苏鲁造山带中的第三幕褶皱非常一致,说明它们具有动力学上的必然联系.同时,研究表明在华北克拉通东部地块中没有经历大别-苏鲁造山带中区域性第一、第二幕褶皱变形的记录,故本文认为印支期这两幕变形主要发生在华北板块东南缘的边界上,并没有波及到板内,而且从东向西高压-超高压岩石剥露具有穿时性.只有当华北板块和华南板块在第二幕变形之后构成了统一块体后,第三幕变形才波及华北板内.     

雪峰山西侧贵州地区中生代构造特征及其演化

贵州中生代变形主要发生在燕山期,发育三幕褶皱变形、两幕逆冲和三幕走滑。根据区域对比、卷入褶皱的地层和褶皱间的叠加关系,判断三期褶皱的形成顺序依次为近东西向、北东向和南北向,时限在J_3—K_2之间。逆冲推覆构造主要由向北西或西逆冲的近南北向逆冲断层组成,大体与南北向褶皱同时形成;自雪峰构造带西缘向西,依次划分出根部带、中部带和前锋带。但是,在根部带识别出两幕逆冲推覆,其它两带各识别出一幕。走滑断层也有3个方向:东西向、北东向和近南北向。东西向走滑断层呈现出右行压扭的运动学特征,而大多数北东向走滑断层是左行张扭性质的。依据各个方向断层间的切割和限制关系,推测东西向走滑断层最早形成,其次是南北向逆冲断层,北东向走滑断层最晚活动。这些断裂和褶皱特征,总体表现出贵州多重多种复合联合的构造特征,最后,探讨了本区的构造成因模式。     

青海湖北岸原生砂楔的发现及其古气候意义

青海湖北岸刚察县城东与泉吉乡西发现原生砂楔群, 楔内充填物均为中细粒砂, 楔体底部中细粒砂ESR测年数据表明, 刚察县城东3个原生砂楔发育时代分别为(774±70) ka、(773±70) ka和(229±20) ka, 泉吉乡西1个原生砂楔形成时代为(197±18) ka, 反映该区至少发育两期原生砂楔, 其形成时代分别对应昆仑冰期和倒数第二次冰期. 基于原生砂楔的特殊形成环境, 估算青海湖盆地在昆仑冰期早期的年均温不高于-7.5~-10 ℃, 比现今至少低9.2~11.7 ℃, 中更新世早期青海湖盆地发育多年冻土, 青藏高原东北部可能已经进入冰冻圈; 倒数第二次冰期的年均温不高于-9.5~-10 ℃, 比现今低11 ℃以上.     

地下采煤的缓倾边坡变形机制

通过某地边坡变形的环境条件和多年监测资料,提出地下采煤的缓倾边坡变形机制,即由地下采煤产生的岩层弯曲下沉侧推效应和央体松动扩容侧推效应,以及地下水作用产生的空隙水压效应导致的边坡变形,并对边坡变形机制进行了验证。     

雪峰山西侧贵州地区中生代构造特征及其演化

贵州中生代变形主要发生在燕山期,发育三幕褶皱变形、两幕逆冲和三幕走滑。根据区域对比、卷入褶皱的地层和褶皱间的叠加关系,判断三期褶皱的形成顺序依次为近东西向、北东向和南北向,时限在J3—K2之间。逆冲推覆构造主要由向北西或西逆冲的近南北向逆冲断层组成,大体与南北向褶皱同时形成; 自雪峰构造带西缘向西,依次划分出根部带、中部带和前锋带。但是,在根部带识别出两幕逆冲推覆,其它两带各识别出一幕。走滑断层也有3个方向：东西向、北东向和近南北向。东西向走滑断层呈现出右行压扭的运动学特征,而大多数北东向走滑断层是左行张扭性质的。依据各个方向断层间的切割和限制关系,推测东西向走滑断层最早形成,其次是南北向逆冲断层,北东向走滑断层最晚活动。这些断裂和褶皱特征,总体表现出贵州多重多种复合联合的构造特征,最后,探讨了本区的构造成因模式。     

湘西花垣—张家界逆冲断裂带地质特征及其控矿意义

湘西花垣－张家界断裂带显逆冲压扭性、与其分枝断裂古丈－张家界断裂带关系密切,平面上在张家界市后坪复合、具有类似的地质特征。形成时代较古丈－张家界断裂带晚,时间上有先后及生成关系,向上呈叠瓦状、深部收敛在一起。具有明显的控矿作用。     

外部构造系统对松辽残留地台构造的干扰与改造

松辽残留地台区中的构造型相与伊陕,四川残留地台区的构造型相比较,既有稳定区构造型相的同一性,又有较大的特殊性,其特殊性在于局部地区系统性较强,并出现了较多的逆冲断层。通过运用＂壳体＂构造理论分析,作者初步认为它是外部构造系统干扰和改造的产物。据此对松辽地北部地段的油气远景评价提出了一些新的看法和建议。     

Deciphering thrust fault nucleation and propagation and the importance of footwall synclines

In this paper, we analyze small scale examples of thrust faults and related folding in outcrops of the Cretaceous Boquillas Formation within Big Bend National Park in west Texas to develop detailed understanding of the fault nucleation and propagation that may aid in the interpretation of larger thrust system structure. Thrust faults in the outcrop have maximum displacements ranging from 0.5 cm to 9 cm within competent limestone beds, and these displacements diminish both upward into anticlines and downward into synclines within the interbedded and weaker mudrock layers. We interpret the faults as having nucleated within the competent units and partially propagated into the less competent units without developing floor or roof thrusts. Faults that continued to propagate resulted in hanging wall anticlines above upwardly propagating fault tips, and footwall synclines beneath downwardly propagating fault tips. The observed structural style may provide insights in the nucleation of faults at the formation scale and the structural development at the mountain-range scale. Décollement or detachment layers may be a consequence rather than cause of thrust ramps through competent units and could be over interpreted from seismic data.     

Aspects of the structural and late thermal evolution of the Redbank Thrust system,central Australia: Constraints from the Speares Metamorphics

We present new data on the field geology and late thermal evolution of the Redbank Thrust system in the Arunta Block of central Australia. Geochronological and field data from the Speares Metamorphics are also used to relate the thermal evolution of the Redbank Thrust system to the structural evolution of the region. We show that several stages in the evolution might be discerned. An originally sedimentary sequence was intruded by mafic intrusions and then deformed during partial melting to form the principal foliation observed in the region (D1). This sequence was then folded during D2 into upright folds with north‐ to northeast‐plunging fold axes. These events are likely to correlate with the Strangways and/or Argilke and Chewings Orogenies known from previous studies. Subsequently, the Redbank Thrust was initiated during D3. This event is recognised by deflection of the host rocks into the shear zone and might therefore have been associated with a component of strike‐slip motion. It occurred probably at or before 1500–1400 Ma. Subsequent north‐over‐south thrust motion in the Redbank Thrust formed the intense mylonitic fabric and folded the mylonitic fabric during D4 into asymmetric folds with shallow fold axes. New ⁴⁰Ar/³⁹Ar K‐feldspar ages from three samples collected from variably deformed branches of the Redbank Thrust and undeformed rocks in the Speares Metamorphics suggest that most parts of the Redbank Thrust system cooled relatively slowly after metamorphism and deformation in the Mesoproterozoic so that the D4 thrusting might have been very long‐lived. Minimum ages of the K‐feldspar age spectra show that the entire region cooled below 200°C by approximately 300 Ma. Apatite fission track ages from nine samples show that cooling through the apatite partial annealing zone occurred during Cretaceous time (ca 150–70 Ma) and modelled cooling histories are consistent with the cooling rates obtained from the K‐feldspar data. They indicate that final exhumation of the Redbank Thrust system occurred probably in response to erosion, possibly driven by rifting around the margins of Australia.