大别造山带南界襄樊—广济断裂带的演化规律与构造意义

自中三叠世扬子与华北板块发生碰撞—深俯冲作用以来,大别造山带南界上的襄樊—广济断裂带主要经历过两次变形事件: 1)早期变形事件发生在中三叠世末—晚三叠世初的造山带折返阶段,表现为造山带南边界上的韧性剪切带。这期北西—南东走向的剪切带向南西陡倾,发育北西—南东向的矿物拉伸线理,主要为右行走滑的运动性质,属于造山带斜向折返的侧边界走滑剪切带。造山带折返过程中将前陆褶断带北缘原先东西向褶皱改造为北西—南东走向。2)晚期变形事件发生在晚侏罗世,表现为脆性逆冲断层,使得前陆褶断带向北东逆冲在造山带南缘之上,同时在前陆上形成了一系列的逆冲断层。该断裂带的晚期逆冲活动与郯庐断裂带左行平移同时发生,代表了滨太平洋构造活动的开始。     

肥东花岗质岩脉的变形及年代学特征对郯庐断裂带早白垩世构造活动的指示

郯庐断裂带肥东段位于大别造山带与苏鲁造山带之间。在肥东段西韦采石场内发育了大规模的北北东向左行走滑韧性剪切带和一条低角度的韧性滑脱正断层。走滑韧性剪切带为郯庐断裂带走滑活动的产物,低角度滑脱正断层则代表了伸展背景下的构造活动。低角度滑脱正断层上、下盘发育未变形和变形的岩脉,走滑韧性剪切带内外也发育有受剪切带活动而变形的岩脉。对采石场内岩脉的构造和同位素年代学研究表明,低角度韧性滑脱正断层在129~126Ma之间发生过剪切活动,走滑韧性剪切带的活动时间在125Ma之后。综合研究认为,郯庐断裂带的伸展活动可能开始于早白垩世早期(130Ma),但在早白垩世并非一直处于伸展活动之中,125Ma之后的左行走滑活动很可能发生在早白垩世的晚期。     

Crustal thinning during Mesozoic extensional detachment faulting in the Yiwulüshan region,eastern North China Craton

Two stages of extension affected the Yiwulüshan area, forming the Yiwulü High-Temperature Extensional Ductile Shear Zone (YHED) and the Waziyu Low-Temperature Extensional Ductile Shear Zone (WLED) during the Middle–Late Jurassic and Early Cretaceous, respectively. The YHED and WLED are characterized by elongation strain and plane strain, respectively. Kinematic vorticity values (W_k ), estimated from polar Mohr diagrams, suggest that pure shear-dominated and thinning-related shearing generated the YHED, whereas simple and pure shearing created the WLED during crustal thinning. From the thickness (H) and the thinning rate (μ) of the ductile shear zones, the reduced crustal thickness due to ductile shearing was estimated to be approximately 3.72 km. Based on structural analysis, contact relationships, and geochronological data, we propose that intense extensional detachment contributed to the stratigraphic gap along a Middle–Late Jurassic ductile detachment shear zone at the contact between Palaeo-Mesoproterozoic metasedimentary rocks and the Archaean basement. Furthermore, this ductile detachment shear zone was reactivated in the Early Cretaceous and lasted for 7.48 million years. After correlating the stratigraphy of the Yiwulüshan area with regions adjacent to it, we conclude that a 1.46–1.69 km-thick section of Proterozoic and Archaean basement is missing along the ductile detachment shear zone. We estimate that the crustal thickness in the Yiwulüshan region has been reduced by more than 5.41 km because of extension-related shearing and this stratigraphic gap. In addition, numerous Mesozoic extensional structures occur throughout the northeastern North China Craton, and crustal thinning has been accommodated along all of them. Our findings highlight the importance of extensional detachments and crustal thinning to lithospheric thinning.     

祁连山东南段加里东造山期构造变形年代的精确限定及其意义

祁连山东南段呈北西-南东向展布着加里东期中祁连造山带和拉脊山造山带, 其基底为前加里东变质岩系, 在该变质结晶基底岩系中发育着菱形网格状韧性剪切带, 共轭韧性剪切带面对缩短方向的夹角为104°~114°, 其最大主应力方位为SW210°左右.在中祁连地块金沙峡和化隆地块科却两处韧性剪切带中的糜棱岩化岩石, 获取变质矿物白云母40Ar-39Ar坪年龄分别为(405.1±2.4) Ma和(418.3±2.8) Ma.这一年代学结果不仅确定了加里东基底变质岩系中韧性剪切带是加里东造山作用过程中形成, 更重要的是通过对基底韧性剪切带中变质变形岩石的年代学研究, 精确地限定了祁连山东南段的早古生代火山盆地(或岛弧盆地)、拉脊山小洋盆关闭的构造年代.这为造山带构造演化过程中盆地关闭时间的确定开辟了新的途径.      

赤峰—开源断裂在赤峰西部地段的构造形迹及其演化特征

为研究赤峰—开源断裂在赤峰西部地段的性质,笔者在1∶5万朝阳地幅、姜家营子幅区调工作中,利用岩石学、岩石地球化学、LA—ICP—MS锆石U—Pb测年等方法,对构造控制的多期次侵入岩进行构造环境研究。结果表明,晚泥盆世二长花岗岩年龄为382. 8±2. 1 Ma,形成于同碰撞挤压环境;晚泥盆世超基性岩年龄为378. 4±3. 2 Ma,形成于碰撞后裂谷拉张环境;早二叠世二长花岗岩、石英闪长岩年龄分别为280. 1±1. 5 Ma、275. 7±1. 8 Ma,形成于同碰撞挤压环境;晚三叠世、早白垩世花岗斑岩年龄分别为206±25 Ma和128. 8±1. 3 Ma,形成于非造山伸展拉张环境。构造带上带状构造的野外地质调查发现构造带经历了3期韧性和1期脆性变形,分别为晚泥盆世至晚石炭世北东东向右行正斜滑韧脆性剪切(构造内花岗斑岩脉年龄374. 2±2. 6 Ma),早二叠世北东东向左行正斜滑韧性剪切(构造内花岗斑岩脉年龄270. 3±1. 7 Ma),晚三叠世北西西向左行正斜滑韧脆性剪切(构造内辉长岩年龄247. 53±7. 4 Ma)和中侏罗世至早白垩世北东和北西向脆性断裂。显示赤峰—开源断裂在赤峰西部地段表现为多期次挤压、间歇伸展,并以挤压造山为主的构造-岩浆岩带。     

青藏高原东北缘宗务隆韧性剪切带40Ar/39Ar年代学及对印支期造山时限的制约

青藏高原东北缘的宗务隆构造带位于柴达木地块与南祁连地块之间,位置极为重要,其中发育的韧性剪切带变形特征和形成时代对于理解该构造带的构造属性具有重要的制约意义。详细的野外构造解析,显微构造解析与年代学研究表明,宗务隆剪切带发育走向NWW-SEE向糜棱面理,其上发育NWW-SEE向缓倾的拉伸线理,指示该剪切带逆冲-走滑剪切的特征。宏观尺度上可见由于剪切作用形成的不对称褶皱、旋转碎斑、构造透镜体及褶劈理等变形形迹;显微镜下可观察到云母鱼、S-C组构、σ型残斑及石英动态重结晶、拔丝构造等变形现象,指示该韧性剪切变形的温度在300~400℃。对剪切带同构造变形的白云母和黑云母进行了⁴⁰Ar/³⁹Ar同位素年代学分析,2个样品的坪年龄分别为(245.8±1.7)Ma、(238.5±2.6)Ma,指示了该剪切变形发生在早—中三叠世期间。结合对区域地质、岩石学等资料的综合分析,该期韧性剪切变形年龄代表了宗务隆构造带印支期造山作用的时间,这期造山活动可能与宗务隆有限洋盆闭合后,南祁连地块与欧龙布鲁克地块的斜向碰撞有关。     

东昆仑左行走滑韧性剪切带形成时代的锆石U-Pb年龄证据

巴颜咯拉—松潘甘孜地体与东昆仑南地体晚三叠纪斜向碰撞形成大规模的东昆仑左行走滑韧性剪切带,新生代时期韧性剪切转为脆性左旋走滑并构成青藏高原向东逃逸的北部边界。为了确定早期韧性剪切变形时代,对剪切带上2个同构造花岗斑岩脉进行了激光探针(LA-MC-ICP MS)测年研究,获得了196.4 ± 2.3 Ma和195.1 ± 1.6 Ma的锆石206Pb/238U加权平均年龄,表明东昆仑左行走滑韧性剪切带形成于燕山早期。      

Shear structures in the Serra do Azeite shear zone,southeastern Brazil: Transtensional deformation during regional transpression in the central Mantiqueira province (Ribeira belt)

The Serra do Azeite shear zone (SASZ) is a northeast-trending regional structure in southeastern Brazil. Kinematic analysis carried out in the SASZ suggests a ductile sinistral transtensional regime in amphibolite facies conditions. Constrictional, flattened, and simple-shear strain domains occur in mylonites with stretching lineation plunging to the east–southeast. Kinematic indicators suggest oblique top–down-to-the-east–southeast and sinistral strike-slip components along variably oriented shear planes. Results of the simple geometrical construction applied to the shear-zone pattern, coupled with field data and kinematic analysis, suggest that sinistral transtensional shearing resulted from east–northeast-directed crustal extension and sinistral strike-slip displacement, accompanied by north–northeast/south–southwest contraction and vertical thinning. The K/Ar and Ar/Ar cooling ages match the proposed interval for crustal extension in the central Mantiqueira province (0.6–0.58/0.57 Ga) based on ages of alkaline granitoids and volcanic rocks. These data indicate types-I and -S granite magmatism, as well as metamorphism and dextral transpressional deformation along the Ribeira belt. Therefore, we interpret the transtensional regime as a result of southwest-directed lateral extrusion and uplift crustal slices (overall oblique extrusion) during an orogenic-scale partitioned transpressional regime. Our results suggest this regime was coeval with a phase of regional stretching subparallel to the Ribeira belt, which would explain the coexistence of extensional and compressional structures during overall plate convergence.     

华南板块南缘早中生代的逆冲推覆构造及其相关的动力学背景

作为理解华南构造演化的关键地区,在华南板块南缘的云开地体和越北的Song Chay地体发育了早中生代的向北东逆冲推覆的韧性变形.在云开地体,经历角闪岩相和绿片岩相变质的矿物指示了产状平缓的面理上发育明显的北东-南西向矿物拉伸线理.沿着这些矿物拉伸线理,具有上部指向北东的剪切变形.同位素年代学的定年结果指示了变形事件发生...     

New Zircon U-Pb Geochronology of the Post-kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan-Red River Shear Zone and Its Geological Implications

<正>The Ailao Shan-Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest.It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian-Eurasian collision.Diancang Shan(DCS) high-grade metamorphic complex,located at the northwest extension along the Ailao Shan-Red River(ASRR) shear zone,is a representative metamorphic complex of the ASRR tectonic belt.Structural and microstructural analysis of sheared rocks in the high-grade metamorphic rocks reveals that they are coherent with solid-state high-temperature ductile deformation,which is attributed to left-lateral shearing along the ASRR shear zone.New LA-ICP-MS zircon U-Pb geochronological and microstructural studies of the post-kinematic granitic plutons provide a straightforward time constraint on the termination ductile left-lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone.It is suggested that the left-lateral shearing along the ASRR shear zone ended at ca.21 Ma at relative lower-temperature or decreasing temperature conditions.During or after the emplacement of the young dikes at ca.21 Ma,rapid brittle deformation event occurred,which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.     

Carboniferous convergence and subsequent crustal extension in the southern Schwarzwald (SW Germany)

Abstract

Detailed structural analysis in the southwestern part of the Variscan Sehwarzwald Massif (SW Germany) indicates polyphase, synmetamorphic deformation in ductile shear zones. The tectono-melainnrphir evolution is characterized by orogenic crustal shortening and subsequent late- orogenic crustal extension in Carboniferous times. Convergence is responsible for an KSK trending, north dipping thrust zone with intense deformation in orthogneissic S-C type mylonites Superposed on schistose and folded metasediments presumably lower Carboniferous in age. Southeastward thrust-’“g parallel to pervasive stretching lineation, similar to the pre-dominant oblique convergent structures ill the central part of the massif, is related to crustal stacking. Relations of early granite intrusions with the outlasting retrograde tectonics Point to a Lower Carboniferous (Late-Visean) age of shortening.

Subsequent crustal extension is indicated by a broad N-S trending and west dipping ductile shear zone within high grade meetamorphic (I1T7LP) gneisses. Retrograde stretching lineatone marked by sillimanite to chlorite anr consistent with a top-to-the-west shearing on the western flank of a large progressively warping domai structure. Intensely sheared and boudinaged granitic rocks are syn-tectonic and seal the age of extension at about 325 Ma (Lower/ Upper Carboniferous boundary). During progressively cataclastic stages of tectonic denudation the still active detachment controlled formation of an adjacent late Paleozoic (Stephano-Pcrniian) continental basin supersedding high-grade gneiss. As elsewhere in the Varisean belt, the late extensional process in the tectono-”“‘tainorphie evolution of the southern Sehwarzwald is related rapid uplift, exhumation and thinning by a gravitational collaps of a previously thickened crust.     

黑龙江嫩江地区三合屯金矿区糜棱岩锆石LA-ICP-MS U-Pb年龄与成矿的关系

三合屯金矿位于黑龙江省嫩江县境内,普遍认为其是韧性剪切带型金矿.本次对采自韧性剪切带中花岗质糜棱岩样品进行了锆石LA-ICP-MS U-Pb定年,以约束剪切带的活动时代,并为金矿化事件提供依据,获得糜棱岩中热液锆石增生边加权平均年龄为162 Ma.因此,矿区在燕山期晚侏罗世经历剪切变形,并且这期变形事件与前人研究的科洛...     

Late Mesozoic compressional to extensional tectonics in the Yiwulüshan massif,NE China and their bearing on the Yinshan–Yanshan orogenic belt: Part II: Anisotropy of magnetic susceptibility and gravity modeling

Granitoids play an important role in deciphering both crustal growth and tectonic evolution of Earth. In the eastern end of the Yinshan–Yanshan belt of North China Craton, the Yiwulüshan massif is a typical region that presents the tectonic evolution features of this belt. Our field work on the host rocks has demonstrated two phases of opposite tectonics: compressional and extensional, however, the deformation is almost invisible in the intrusive rocks. To improve the understanding of the tectonic evolution of the Yiwulüshan massif and the Late Mesozoic tectonics of East Asia, a multidisciplinary study has been carried out. In this study, anisotropy of magnetic susceptibility (AMS) and gravity modeling have been applied on these Jurassic plutons (Lüshan, Jishilazi and Guanyindong), which intrude into the Yiwulüshan massif. According to laboratory measurements and microscopic observations on thin sections, the AMS of the Yiwulüshan massif is characterized by secondary fabrics, indicating that the intensive post solidus deformation has reset the (primary) magmatic magnetic fabrics. A relatively gentle NW dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of N34°E and N335°E orientations, namely L_M1 and L_M2, relatively. Gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif. Integrating all results from structural observation, geochronological investigation, AMS measurement and gravity modeling, two tectonic phases have been identified in the Yiwulüshan massif, posterior to the Jurassic (180–160 Ma) magmatism in the Yinshan–Yanshan area. The early one concerns a Late Jurassic–Early Cretaceous (~ 141 Ma) compressional event with a top-to-the-south to southwest sense of shear. The second one shows an Early Cretaceous (~ 126 Ma) NW–SE ductile extensional shearing. At that time, sedimentary basins widened and Jurassic plutons started to be deformed under post solidus conditions. In fact, the NW–SE trend of the maximum stretching direction is a general feature of East Asian continent during Late Mesozoic.     

Oligo-Miocene shearing along the Ailao Shan–Red River shear zone: Constraints from structural analysis and zircon U/Pb geochronology of magmatic rocks in the Diancang Shan massif, SE Tibet, China

The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and post-collisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31 Ma, culminated between ca. 27 and 21 Ma resulting in high-temperature metamorphic conditions and slowed down at ca. 20 Ma at relatively low-temperatures.     

Precise Timing of Caledonian Structural Deformation Chronology and Its Implications in Southeast Qilian Mountains, China

The middle Qilian orogenic belt and Lajishan orogenic belt, both of which were formed in the Caledonian, strike NW-SE direction across southeast Qilian Mountains and their basement consists of pre-Caledonian metamorphic rocks with lozenge-shaped ductile shear zones in the crystalline base- ment. The blunt angle between the conjugated ductile shear zones ranges from 104° to 114°, indicating approximate 210° of the maximum principal stress. The plateau ages of muscovite 40Ar/39Ar obtained from the mylonitized rocks in the ductile shear zones of Jinshaxia-Hualong-Keque massif within the middle Qilian massif are (405.1±2.4) Ma and (418.3±2.8) Ma, respectively. The chronology data confirm the formation of ductile shear zones in the Caledonian basement metamorphic rocks during the Cale- donian orogeny. Furthermore, on the basis of basement rock study, precise timing for the closing of the Late Paleozoic volcanic basin (or island-arc basin) and Lajishan ocean basin is determined. This pro- vides us a new insight into the closing of ocean basin in the structural evolution of orogenic belt.     

西秦岭地区造山型与卡林型金矿床

西秦岭金矿床分为卡林型和造山型两类。卡林型金矿床麇集于南秦岭和松潘—甘孜造山带的东北部。三叠纪和早侏罗世的同构造花岗闪长岩广泛分布于西秦岭中部和南部、松潘—甘孜盆地以及扬子克拉通边缘。造山型脉状金矿床主要分布于西秦岭造山带中的脆韧性剪切带内。大部分粗粒金主要赋存在网格状石英细脉和角砾状围岩中的黄铁矿、磁黄铁矿、毒砂和少量贱金属硫化物中和以分散状分布在蚀变围岩中。同位素资料表明晚三叠世 -中侏罗世与扬子克拉通俯冲有关的作用控制了造山型金矿床的形成。     

郯庐断裂带肥东段早白垩世中期走滑运动的年代学证据

郯庐断裂带肥东段西韦地区和桃花源地区出露了大规模的北北东向韧性剪切带。桃花源地区韧性剪切带显示出2期构造变形的叠加。野外构造和显微构造分析皆指示为左行走滑韧性剪切带。糜棱岩中石英与长石的变形行为指示其变形温度分别为400~450℃和500℃。通过对这两处走滑剪切带内糜棱岩化花岗岩脉的锆石LA-ICP-MS定年,获得了3个样品的侵位年龄分别为(133.2±1.9)Ma,(131.3±2.0)Ma,(130.3±2.0)Ma。再结合已有的研究成果,认为在128~124Ma(早白垩世中期)郯庐断裂带发生过左行走滑活动。综合分析表明,郯庐断裂带在晚侏罗世和早白垩世中期分别经历了2期左行走滑活动,而期间和之后的早白垩世则处于伸展活动之中。伸展活动持续较长,控制发育了西侧的合肥盆地及断裂带内一系列岩浆活动;而区域挤压背景下出现的走滑活动则相对短暂。这些演化规律显示该断裂带在晚侏罗世—早白垩世呈现为交替式的走滑和伸展活动。新发现的早白垩世中期走滑活动,与太平洋区伊泽纳崎板块板块运动方向的调整相对应,是大洋板块运动方向短暂调整的构造响应。     

Syn-collisional transform faulting of the Tan-Lu fault zone,East China

Origin of the continental-scale Tan-Lu fault zone (TLFZ), East China, remains controversial. About 550 km sinistral offset of the Dabie orogenic belt (DOB) and Sulu orogenic belt (SOB) is shown along the NE-NNE-striking TLFZ. Syn-collisional, sinistral ductile shear belts in the TLFZ have been identified. Thirteen phengite bulk separates from the mylonites were dated by the ⁴⁰Ar/³⁹Ar method. They gave cooling ages of the 198–181 Ma for the shear belts along the eastern margin of the DOB and 221–210 Ma from the western margin of the SOB. Distribution of the foreland basin deposits suggests that sinistral offset of the DOB and SOB by the TLFZ took place prior to deposition of the Upper Triassic strata. The marginal structures around the DOB and SOB support syn-collisional faulting, and indicate anticlockwise rotation of the DOB during the displacement. The folding and thrust faulting related to crustal subduction, coeval with the Tan-Lu faulting, is older than the foreland basin deposition related to the orogenic exhumation. Several lines of evidence demonstrate that the TLFZ was developed as a syn-collisional transform fault during latest Middle to earliest Late Triassic time when the DOB and SOB experienced crustal subduction of the South China Block (SCB). Eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting.     

Polyphase structural evolution of the southwestern Argentine Precordillera

The western and southwestern parts of the Argentine Precordillera display complex geometries which are not consistent with those of a typical high-level fold-and-thrust belt. They are the result of a polyphase structural evolution which spans the Early Paleozoic to Late Tertiary period. After an Early Paleozoic folding and shearing event under a greenschist facies metamorphism, uplift, erosion, and deposition of Late Carboniferous to Early Permian clastics were accompanied by extensional faulting. This was followed by a Permian folding and faulting event which led to a partial inversion of the Late Carboniferous-Early Permian graben fill. Permian to Triassic crustal extension was combined with block faulting and the deposition of a thick volcanic sequence. The subsequent Late Tertiary crustal shortening partly reactivated older fault lines. Excluding folds, a few thrusts, and reverse faults, the crustal shortening within the older blocks was accommodated by a dominant sinistral strike-slip faulting under a W-E compressive regime. Above a major décollement, the entire sequence of faulted and folded blocks was carried from west to east towards its present position. The regional situation indicates that this southern part of the orogen was transferred further to the east with respect to the central thin-skinned parts. The movements are interpreted to be related to an important thrust fault which obliquely cuts through the fold-and-thrust belt.     

朝鲜半岛古生代中期-中生代早期构造格局

古生代中期─中生代早期朝鲜半岛发生了两次主要构造事件, 即古生代中期朝鲜半岛中部临津江构造带的活动和古生代晚期-中生代早期朝鲜半岛北部豆满江造山带(咸北地块) 的碰撞拼接事件。临津江带的地层、化石和构造等特征研究表明临津江带形成于志留纪末-泥盆纪初, 结束于中生代三叠纪松林期; 根据咸北地块沉积地层的岩浆岩岩石学、年代学资料, 认为豆满江造山带的碰撞拼接时期可能是二叠纪-三叠纪。黄海地球物理、地震研究, 朝鲜半岛大地构造和沉积盖层研究结果表明苏2鲁高压变质带没有延伸到临津江带, 而是被近南北向纵贯朝鲜西海的断裂右行错移到了济洲岛以南; 咸北地块和输城川断裂带的地质特征研究表明, 咸北地块可能与佳木斯地块相连接, 输城川断裂带可能与牡丹江断裂带相连接。