医巫闾山变质核杂岩早白垩世伸展变形

对瓦子峪拆离断层带及下盘韧性剪切带中的构造岩进行构造变形及石英组构优选方位分析,这些构造岩的变形特点及分布规律显示伸展活动具有从高绿片岩相的脆-韧性变形向低绿片岩相的脆性变形演化的特点,展示了由浅部地壳向地表抬升的过程.上盘同伸展断陷盆地中地层发育特点和韧性剪切带中构造岩的同位素年代学数据显示早白垩世伸展作用随着时间的演化具有逐渐减弱和剪切带北部伸展作用持续时间比南部长的特点,此次伸展作用主要发生在132 ～ 117Ma.对比早白垩世与中、晚侏罗世的伸展方向并结合太平洋板块与依泽纳奇板块中生代的运动特点,推断医巫闾山地区中生代的伸展变形受到西太平洋地区板块活动的制约.     

扬子板块西北缘碧口地块变形变质作用序列——松潘—甘孜造山带伸展垮塌事件的意义

碧口地块位于秦岭—大别、松潘—甘孜造山带与扬子板块的交汇部位。根据碧口地区各套地层构造变形样式的不同,将地层自下而上划分为三个构造地层单元:①新元古界基底杂岩,主要由新元古界碧口群火山岩系和横丹群浊积岩系组成,杂岩体核部变形较弱,边部发育韧性剪切变形,并以一条由超糜棱岩带组成的基底拆离断层为顶界,与上覆地层分隔。基底杂岩经历了蓝片岩相到硬柱石-钠长石-绿泥石相的变质作用。②古生界中间韧性流变层,由志留系—泥盆系的糜棱岩或千糜岩组成,岩层中发育多期构造面理(S1、S2、S3)和典型的固态流变构造,变质程度普遍达中绿片岩相。③中生界沉积盖层,包括碧口地块以北的三叠系关家沟组和小面积出露的侏罗系—白垩系,以脆性破碎带和小型脆性断层构造为主。拆离断层与各套构造地层中的韧性剪切和流变构造一同反映了区域性上盘向SSE剪切的几何学和运动学特征,证实了碧口地区中生代206~154Ma伸展垮塌事件的存在,从而建立了碧口地块的隆升模式。研究结果表明,松潘—甘孜在中生代造山作用后的区域伸展作用下形成了拆离断层和中地壳韧性流变层,造成了地层缺失和地壳减薄,基底杂岩在造山带的腹陆隆升并露出地表。     

福建泉州晚中生代伸展构造变形特征与年代学制约

晚中生代福建沿海地区发育多期与古太平洋板块俯冲有关的岩浆活动和构造变形.福建泉州地区伸展构造变形主要表现为高角度正断层和低角度正断层或拆离断层, 古构造应力场反演指示其形成于NW-SE向伸展环境.锆石U-Pb年代学指示泉州地区发育4期岩浆活动, 分别为晚侏罗世(~155 Ma)、早白垩世中期(130~125 Ma)、早白垩世末期(~109 Ma)以及晚白垩世早期(~100 Ma之后).结合构造变形的切割关系和岩浆岩年代学, 长乐-南澳剪切带左旋韧性走滑形成于130~120 Ma, 而右旋脆性剪切形成于120~100 Ma之间.古太平洋板块向华南大陆之下的俯冲角度变化导致福建沿海地区发育晚中生代造山带.造山作用开始于早白垩世之初, 结束于早白垩世末期, 以大规模NW-SE向伸展构造发育为标志, 其从同造山挤压到后造山伸展的转换发生于~120 Ma.      

福建泉州晚中生代伸展构造变形特征与年代学制约

晚中生代福建沿海地区发育多期与古太平洋板块俯冲有关的岩浆活动和构造变形.福建泉州地区伸展构造变形主要表现为高角度正断层和低角度正断层或拆离断层,古构造应力场反演指示其形成于NW-SE向伸展环境.锆石U-Pb年代学指示泉州地区发育4期岩浆活动,分别为晚侏罗世(~155Ma)、早白垩世中期(130~125Ma)、早白垩世末期(~109Ma)以及晚白垩世早期(~100Ma之后).结合构造变形的切割关系和岩浆岩年代学,长乐-南澳剪切带左旋韧性走滑形成于130~120Ma,而右旋脆性剪切形成于120~100Ma之间.古太平洋板块向华南大陆之下的俯冲角度变化导致福建沿海地区发育晚中生代造山带.造山作用开始于早白垩世之初,结束于早白垩世末期,以大规模NW-SE向伸展构造发育为标志,其从同造山挤压到后造山伸展的转换发生于~120Ma.     

庐山变质核杂岩东侧拆离带两期构造性质转换:锆石U-Pb年代学证据

庐山变质核杂岩东侧的星子牛屎墩地区广泛岀露伸展拆离、韧性流变的构造现象,拆离方位为南东方向。该区还岀露一期NNE向左行走滑韧性剪切构造,推测是与郯庐断裂同期变形的构造产物,为郯庐断裂系的一部分。这两期构造运动反映了中生代太平洋构造体制下挤压应力向伸展应力的转换,对伸展滑脱层内同构造的伟晶岩脉及长英质脉的锆石U-Pb年代学测试,结合野外构造现象,以探究该区两期构造性质的转换时限和构造背景。新生变质流体结晶的锆石得到135~140Ma的庐山变质核杂岩拆离带的伸展年龄,内部受热液溶蚀作用的残余锆石得到150.5Ma和153.9Ma的左行剪切变形的年龄。受太平洋构造体制控制,晚侏罗世,该区受板块俯冲作用而处于挤压应力的构造背景,表现为左行剪切构造;早白垩世,在区域性的伸展、减薄作用下,挤压应力向伸展应力转换,庐山变质核杂岩得以形成,其伸展拆离构造是在早期左行剪切构造上的改造与叠加。     

印度／亚洲碰撞——南北向和东西向拆离构造与现代喜马拉雅造山机制再讨论

印度/亚洲碰撞形成的喜马拉雅增生地体由特提斯-喜马拉雅(THM)、高喜马拉雅(GHM)、低喜马拉雅(LHM)和次喜马拉雅(SHM)亚地体组成.通过喜马拉雅增生地体中变质基底和盖层的组成、变质演化、变形机制与形成时代的对比,确定高喜马拉雅(GHM)亚地体北缘的藏南拆离断裂(STD)向北延伸于特提斯-喜马拉雅(THM)亚地体之下,与形成在大于650℃温度、具有自南向北剪切滑移性质的康马-拉轨岗日拆离带(KLD)相连,深部地壳局部熔融、物质上涌造成的花岗岩侵位,使康马-拉轨岗日拆离带隆起,形成康马-拉轨岗日穹隆带.在高喜马拉雅(GHM)亚地体北部(普兰-吉隆-聂拉木-亚东一带)的变质基底与盖层之间发现EW向近水平的高喜马拉雅韧性拆离构造(GHD),以发育EW向拉伸线理、缓倾的糜棱面理及具有自西向东水平滑移为特征;而在GHM南部靠近主中央冲断裂(MCT)北侧发育具有挤压转换性质的韧性走滑-逆冲断层.高喜马拉雅亚地体从南到北具有由逆冲→斜向逆冲→EW向伸展→斜向伸展→SN向伸展的连续变形和转换的特征,是在现代喜马拉雅垂向挤出和侧向挤出的耦合造山机制下综合变形的响应.喜马拉雅地体中的东西向和南北向拆离构造的存在为喜马拉雅现代造山机制再讨论提供了基础.     

印度/亚洲碰撞——南北向和东西向拆离构造与现代喜马拉雅造山机制再讨论

印度/亚洲碰撞形成的喜马拉雅增生地体由特提斯-喜马拉雅(THM)、高喜马拉雅(GHM)、低喜马拉雅(LHM)和次喜马拉雅(SHM)亚地体组成。通过喜马拉雅增生地体中变质基底和盖层的组成、变质演化、变形机制与形成时代的对比,确定高喜马拉雅(GHM)亚地体北缘的藏南拆离断裂(STD)向北延伸于特提斯-喜马拉雅(THM)亚地体之下,与形成在大于650°C温度、具有自南向北剪切滑移性质的康马-拉轨岗日拆离带(KLD)相连,深部地壳局部熔融、物质上涌造成的花岗岩侵位,使康马-拉轨岗日拆离带隆起,形成康马-拉轨岗日穹隆带。在高喜马拉雅(GHM)亚地体北部(普兰-吉隆-聂拉木-亚东一带)的变质基底与盖层之间发现EW向近水平的高喜马拉雅韧性拆离构造(GHD),以发育EW向拉伸线理、缓倾的糜棱面理及具有自西向东水平滑移为特征;而在GHM南部靠近主中央冲断裂(MCT)北侧发育具有挤压转换性质的韧性走滑-逆冲断层。高喜马拉雅亚地体从南到北具有由逆冲→斜向逆冲→EW向伸展→斜向伸展→SN向伸展的连续变形和转换的特征,是在现代喜马拉雅垂向挤出和侧向挤出的耦合造山机制下综合变形的响应。喜马拉雅地体中的东西向和南北向拆离构造的存在为喜马拉雅现代造山机制再讨论提供了基础。     

印度/亚洲碰撞——南北向和东西向拆离构造与现代喜马拉雅造山机制再讨论

印度/亚洲碰撞形成的喜马拉雅增生地体由特提斯-喜马拉雅(THM)、高喜马拉雅(GHM)、低喜马拉雅(LHM)和次喜马拉雅(SHM)亚地体组成.通过喜马拉雅增生地体中变质基底和盖层的组成、变质演化、变形机制与形成时代的对比,确定高喜马拉雅(GHM)亚地体北缘的藏南拆离断裂(STD)向北延伸于特提斯-喜马拉雅(THM)亚地体之下,与形成在大于650℃温度、具有自南向北剪切滑移性质的康马-拉轨岗日拆离带(KLD)相连,深部地壳局部熔融、物质上涌造成的花岗岩侵位,使康马-拉轨岗日拆离带隆起,形成康马-拉轨岗日穹隆带.在高喜马拉雅(GHM)亚地体北部(普兰-吉隆-聂拉木-亚东一带)的变质基底与盖层之间发现EW向近水平的高喜马拉雅韧性拆离构造(GHD),以发育EW向拉伸线理、缓倾的糜棱面理及具有自西向东水平滑移为特征;而在GHM南部靠近主中央冲断裂(MCT)北侧发育具有挤压转换性质的韧性走滑-逆冲断层.高喜马拉雅亚地体从南到北具有由逆冲→斜向逆冲→EW向伸展→斜向伸展→SN向伸展的连续变形和转换的特征,是在现代喜马拉雅垂向挤出和侧向挤出的耦合造山机制下综合变形的响应.喜马拉雅地体中的东西向和南北向拆离构造的存在为喜马拉雅现代造山机制再讨论提供了基础.     

辽西医巫闾山变质核杂岩的形成过程与晚侏罗世伸展事件

根据野外详细调查,本文系统分析了医巫闾山地区的伸展构造,认为区内瓦子峪伸展韧性剪切带发育之前就出现了变质核杂岩.该核杂岩具有典型的三层结构,其拆离韧性剪切带出现在变质基底内,但西侧被晚期早白垩世瓦子峪韧性剪切带切割,呈不完整的长环形带状展布.露头构造、显微构造及石英C组构皆指示核杂岩的下盘、拆离韧性剪切带及上盘底部具有...     

太行山山前中—新生代伸展拆离构造和年代学

太行山山前中-新生代伸展滑脱的主拆离构造出现在早前寒武纪变质结晶基底和中元古代以后的沉积盖层之间.卷入拆离带中的变形岩石以断层碎裂岩为主,局部形成大规模由基底和盖层岩石碎片组成的构造混杂岩带,结晶基底顶部未见典型的糜棱岩,拆离过程表现为准塑性-脆性变形机制,形成深度应小于10 km.太行山山前拆离滑脱带沿走向分为阜平、赞皇两个独立的区段.拆离带中变形岩石的锆石、磷灰石裂变径迹年龄主要集中在68～52Ma和23～18Ma.结合太行山区夷平面年代和相邻盆地构造分析结果,华北大陆地壳的加厚作用可能发生在白垩纪中期(134±9Ma～92±4Ma),主要的伸展滑脱开始于白垩纪末(68Ma前).     

胶莱盆地及其邻区白垩纪－古新世沉积构造演化历史及其区域动力学意义

基于野外和钻孔测井资料分析、火山岩同位素年代学分析 (40Ar-39Ar and SHRIMP U-Pb)、地震剖面的构造解释、断层运动学的野外分析结果,综合研究了胶莱盆地及其邻区白垩纪－古新世沉积构造演化历史。岩性地层分析表明,胶莱断陷盆地由三套地层单元所充填：早白垩世莱阳群和青山群、晚白垩世－古新世王氏群。青山群火山岩的同位素年代学测试结果给出了该火山岩的喷发时代在120～105 Ma。地震剖面的构造解译结果揭示胶莱盆地伸展构造受到深部两个拆离构造系统控制：一个发育于盆地南部地区,拆离断面位于深部8~10 km,向南缓倾于苏鲁造山带之下;另一个拆离系统由一系列北倾的犁式断层组成、分布于宽阔的胶莱盆地北部地区,主拆离面向北倾。这两个拆离系统分别形成于早白垩世莱阳群和晚白垩世-古新世王氏群沉积阶段。通过对不同地层单元断层滑动矢量的野外测量和古构造应力场反演,以及地层时代和同位素年代学测试结果的制约,建立了白垩纪－古新世构造应力场演替的年代序列。结果表明,胶莱盆地在白垩纪-古新世之间经历了伸展－挤压应力体制的交替演化。早白垩世伸展作用经历了两个不同的阶段：早期NW-SE向伸展和晚期近W-E向伸展。在早白垩世末期至晚白垩世初期,盆地遭受NW-SE向挤压,导致了胶莱盆地的缩短变形和郯庐断裂带的左旋走滑活动。晚白垩世－古新世时期,构造应力场转变为N-S向伸展,直到古新世末期,构造应力场转换为NE－SW向挤压。胶莱盆地和沂沭裂谷系白垩纪－古新世沉积构造演化历史对华北地区岩石圈减薄过程的动力学背景提供了重要的构造地质学制约。笔者推断,早白垩世两期引张应力作用是分别对华北地区增厚地壳或岩石圈的重力垮塌和岩石圈拆沉的响应,而早白垩世末期NW-SE向挤压记录了古太平洋板块与亚洲陆缘俯冲碰撞产生的远程效应。晚白垩世-古新世的引张伸展作用完全不同于早白垩世伸展构造,它指示了沿NNE向郯庐断裂带的右旋走滑活动及其拉分作用,在动力学上受到青藏地区块体的陆－陆碰撞产生的远程效应和古太平洋板块向亚洲大陆俯冲作用的联合应力场控制。     

辽南变质核杂岩饮马湾山和赵房岩体锆石SHRIMP U-Pb年龄及其地质意义

辽南变质核杂岩形成于晚中生代华北岩石圈伸展和减薄背景下,其演化过程分为三个阶段：第一阶段（约130Ma）,在伸展作用下辽南地区发育拆离断层及其下伏韧性剪切带;第二阶段（130~120Ma）,同构造花岗质岩体的主动侵位影响了拆离断层的演化;同时在124Ma变质核杂岩的构造-岩浆活动达到峰值;第三阶段（113Ma之后）花岗质岩体在较浅层次侵位于停止活动的拆离断层带。辽南变质核杂岩发育与演化过程在年代学意义上揭示了华北板块晚中生代时期的区域性岩石圈伸展与减薄过程。本文认为由伸展后期侵位的赵房岩体所记录的拆离断层停止的时限（113Ma）可以作为华北岩石圈强烈构造岩浆活动的转捩点,113Ma之前华北板块广泛发育变质核杂岩、拉分盆地等一系列伸展构造,之后则以平稳的隆升和冷却过程为主。     

Mylonitization in the lower plate of the Buckskin-Rawhide detachment fault,west-central Arizona: Implications for the geometric evolution of metamorphic core complexes

In metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down-dip continuation of a detachment fault, or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault. Detailed microstructural, fabric, and strain data from mylonites in the Buckskin-Rawhide metamorphic core complex, west-central Arizona, constrain the structural development of the lower plate shear zone. Widespread exposures of ∼22–21 Ma granitoids of the Swansea Plutonic Suite enable us to separate Miocene strain coeval with core complex extension from older deformation. Mylonites across the lower plate consistently record top-to-the-NE-directed shear. Miocene quartz and feldspar deformation/recrystallization mechanisms indicate ∼450–500 °C mylonitization temperatures that were relatively uniform across a distance of ∼35 km in the extension direction. Quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction. Strain recorded in the Swansea Plutonic Suite is also relatively uniform in the extension direction, which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault. Altogether these data suggest the mylonitic shear zone initiated with a ≤4° dip and was unroofed by a more steeply dipping detachment fault system. Lower plate mylonites in the Buckskin-Rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down-dip continuation of a detachment fault.     

Ductile crust exhumation and extensional detachments in the central Aegean (Cyclades and Evvia Islands).

Abstract

The Aegean continental domain is known to be the site of widespread “back-arc” extension since at least 13 Ma, on the basis of seismotectonic, stratigraphic and fault analysis studies. This extension is documented to overprint structures related to the Mesozoic-Cenozoic Hellenic orogeny. Features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered HP/LT metamorphism across the Aegean. This study presents a structural analysis of the central Aegean area (Cyclades and Evvia Islands), examining in particular the relationship between ductile and brittle deformation, both in the field and on a regional scale. Extension appears to be responsible for most of the ductile deformation within HP rock units that have experienced penetrative greenschist facies and higher grade metamorphic over-printing. On each studied island, progressive extensional deformation has occurred through the development of a major normal-sense detachment zone down to depths of about 18-25 km. Large displacement along the detachment zone accounts for rapid cooling and exhumation of ductile lower crust to form a local metamorphic dome or core complex. Structural and stratigraphic features support a progressive migration of normal faulting away from the dome axis, and a rotation of previously active faults toward low dips, as in kinematic models recently suggested for the development of extensional detachment systems. All the studied domes, except that seen on los Island, show a dominant top-to-the north or north-east sense of shear, while on the southern flank of many of them, an opposite sense of shear is observed, displaying the same progressive evolution from ductile to brittle rock behaviour. This opposite sense of shear is thought not to result from shearing along a major conjugate detachment zone, as in some recent models, but from the accommodation in the ductile crust of upward bending of the brittle upper crust in the footwall of the north-dipping detachment. Available radiometric and stratigraphie data indicate an early minimum age (22-19 Ma) for the onset of extension. The relationship between early metamorphic domes and shallow-dipping detachments, on one hand, and Messinian-Quaternary steep normal faults and grabens, on the other hand, is best explained with the progressive and continuous development of new normal faults away from the domes axes, rather than with a two-stage evolutionary model (core-complex stage, then Basin-and-Range stage) of the type invoked for the North American Cordillera.     

Multi-level Detachments and Petroleum Potential of the Tarim Basin

Four detachment systems have been found in the Tarim Basin. They are made up of the Proterozoic,Palaeozoic, Mesozoic-Eogene and Neogene-Quaternary, respectively. The shallow-level detachments are char-acterized by the occurrence of fold-thrust belts in the Meso-Cenozoic. The mid-level detachments are markedby nappes, decollement folds and drag anticlines in the Palaeozoic. The deep-level detachments are representedby ductile shear belts in the basement. Mid-and deep-level detachments mainly occur in the Northern, Centraland Southern Uplifts which are major hydrocarbon accumulation belts of large-scale oil fields. Shallow-leveldetachments mainly exist in the Kuqa, Southwestern and Southeastern Depressions, which are favourable beltsfor finding medium- and small-sized oil-gas fields.     

张八岭隆起早白垩世变质核杂岩的厘定——对郯庐断裂带的制约及其与成矿作用关系

张八岭隆起广泛分布的平缓韧性剪切带与郯庐断裂带平移作用形成的陡立韧性剪切带明显不同。通过对平缓韧性剪切带的几何学、运动学分析,结合早白垩世盆地特征、中国东部变质核杂岩伸展拆离断层和同构造岩浆岩同位素定年结果,厘定出张八岭隆起早白垩世变质核杂岩。该变质核杂岩上盘由南华纪-奥陶纪沉积地层和早白垩世盆地组成,下盘为新元古代浅变质碎屑沉积岩、变海相火山岩（基底）以及早白垩世侵入岩,上下盘之间被一条主伸展拆离断层所分隔。变质核杂岩长轴为NE-SW向,指示构造反映上盘向SE剪切滑动,与中国东部变质核杂岩的伸展方向完全一致。通过本次变质核杂岩的厘定,结合野外地质事实,笔者认为管店-马厂断裂是郯庐断裂带的次级断裂,是对郯庐断裂带早白垩世末第三次左行平移的响应。在综合研究的基础上,建立了区域构造-岩浆-成矿关系模型,揭示了张八岭隆起早白垩世经历了早期伸展（变质核杂岩阶段）-挤压走滑（管店-马厂断裂形成阶段）-晚期伸展（闪长质脉岩侵位阶段）3个构造阶段,多期构造、岩浆的叠加作用下,形成了本区的金多金属矿产。     

Evolution and time of formation of the Hohhot metamorphic core complex,North China: new structural and geochronologic evidence

The Hohhot metamorphic core complex (MCC) is one of the typical MCCs in the North China craton. Its fault systems consist of the master Hohhot detachment zone (HHDZ) on the southern flank of the Daqing Shan, and the lowermost and uppermost northern detachment zones on the northern flank. Ductile deformation temperatures of three zones were estimated as 500 ± 50°C, 650 ± 50°C, and 400 ± 50°C, respectively, by analysis of microstructures of minerals and quartz [c] crystallographic axis fabrics using electron backscattered diffraction. These measurements suggest that previous ⁴⁰Ar/³⁹Ar ages could not represent the time of the high-temperature (>500°C) ductile deformations. Therefore, we used U-Pb zircon ages of mylonitized and non-mylonitized granitic intrusions to constrain the timing of the early high-temperature shearing. Strongly mylonitized granites and weakly mylonitized granites in the lowermost northern detachment zone yielded zircon U-Pb ages of 148 ± 1 and 140 ± 1 million years respectively. A syn-kinematic pluton in the lower plate of the MCC gave a U-Pb age of 142 ± 1 million years. These allow us to speculate on the possibility that SE-directed, early tangential, high-temperature ductile shearing probably was initiated during ca. 148–140 Ma (or ca. 142 Ma) at depth, with the thrust events occurring at shallow levels. A strongly mylonitized granitic dike and a non-mylonitized pluton in the master HHDZ yielded ages of 142 ± 1 and 132 ± 2 million years respectively. A non-mylonitized pluton intrusive into the uppermost northern detachment zone was dated at 131 ± 1 Ma. All these suggest that major extensional ductile shearing along the detachment zones took place during ca. 140–132 Ma. Using these new U-Pb ages, combined with previously published ⁴⁰Ar/³⁹Ar cooling ages that range from 127 Ma to 119 million years for the master HHDZ and supradetachment basins, we discuss and derive the time of formation process of the MCC. This is one of only a few cases of detailed study of timing for the development of an MCC from earlier deep-level shearing to later thermal uplifting (doming).     

Tectonic evolution of Cretaceous extensional basins in Zhejiang Province,eastern South China: structural and geochronological constraints

Widespread Cretaceous volcanic basins are common in eastern South China and are crucial to understanding how the Circum-Pacific and Tethyan plate boundaries evolved and interacted with one another in controlling the tectonic evolution of South China. Lithostratigraphic units in these basins are grouped, in ascending order, into the Early Cretaceous volcanic suite (K_1V), the Yongkang Group (K_1-2), and the Jinqu Group (K₂). SHRIMP U-Pb zircon geochronological results indicate that (1) the Early Cretaceous volcanic suite (K_1V) erupted at 136–129 Ma, (2) the Yongkang Group (K_1-2) was deposited from 129 Ma to 91 Ma, and (3) the deposition of the Jinqu Group (K₂) post-dated 91 Ma. Structural analyses of fault-slip data from these rock units delineate a four-stage tectonic evolution of the basins during Cretaceous to Palaeogene time. The first stage (Early to middle Cretaceous time, 136–91 Ma) was dominated by NW–SE extension, as manifested by voluminous volcanism, initial opening of NE-trending basins, and deposition of the Yongkang Group. This extension was followed during Late Cretaceous time by NW–SE compression that inverted previous rift basins. During the third stage in Late Cretaceous time, possibly since 78.5 Ma, the tectonic stress changed to N–S extension, which led to basin opening and deposition of the Jinqu Group along E-trending faults. This extension probably lasted until early Palaeogene time and was terminated by the latest NE–SW compressional deformation that caused basin inversion again. Geodynamically, the NW–SE-oriented stress fields were associated with plate kinematics along the Circum-Pacific plate boundary, and the extension–compression alternation is interpreted as resulting from variations of the subducted slab dynamics. A drastic change in the tectonic stress field from NW–SE to N–S implies that the Pacific subduction-dominated back-arc extension and shortening were completed in the Late Cretaceous, and simultaneously, that Neo-Tethyan subduction became dominant and exerted a new force on South China. The ongoing Neo-Tethyan subduction might provide plausible geodynamic interpretations for the Late Cretaceous N–S extension-dominated basin rifting, and the subsequent Cenozoic India–Asia collision might explain the early Palaeogene NE–SW compression-dominated basin inversion.     

陕西小秦岭华阳川韧性剪切带的特征 及其区域构造意义

陕西小秦岭华阳川韧性剪切带发育在新太古界太华群之中,野外调研和显微构造观察结果表明,该韧性剪切带是由构造片岩、眼球状片麻岩组成的深层次韧性剪切带,具有逆冲兼左行走滑的斜冲特征。对韧性剪切带构造片岩黑云母进行^40Ar／^39Ar同位素定年,获得坪年龄为419M±0．6Ma,反等时线年龄为417Ma±0．8Ma。认为华阳川韧性剪切带及其相应的小秦岭区域主导构造变形是发生于419Ma左右的秦岭加里东事件的结果。     

The Keisarhjelmen detachment records Silurian–Devonian extensional collapse in Northern Svalbard

At the junction of the Atlantic and Arctic margins, the crustal‐scale Keisarhjelmen detachment of north‐west Svalbard records previously unrecognised magnitudes of extension. The detachment separates a corrugated metamorphic core complex in the footwall from a mantling Devonian supradetachment basin in the hangingwall. The detachment has a top‐N displacement of more than 50 km, which is aligned with the map‐scale corrugations, and an upwards ductile to brittle transition with shear related footwall retrogression. This configuration has striking similarities to extensional collapse detachments in the paired Scandinavian–Greenland Caledonides, but orientation and position link the detachment with the Ellesmerian orogen.