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韧性剪切带是岩石圈在塑性状态下受构造作用的影响而连续变形所形成的狭长高应变带(Ramsay et al., 1970; Ramsay, 1980; Simpson et al., 1993),其广泛发育在造山带的中下地壳层次,带内岩石不同的流变学特征和变形机制对造山带的演化具有重要的制约作用 (Bercovici et al., 2012; Fossen et al., 2017)。在古造山带和现今汇聚板块边界,常发育具有纯剪和单剪分量的转换挤压韧性剪切带,通常被认为是板块斜向汇聚的产物,调节并记录板块间的相互作用 (Harland, 1971; Sanderson et al., 1984; Fossen et al., 1993; Means, 1995; Jiang et al., 2001)。
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柴达木盆地北缘构造带(简称柴北缘构造带)以其南侧发育早古生代高压-超高压(HP-UHP)变质带为特征 (Yang Jingsui et al., 2001; Song Shuguang et al., 2003, 2005; Zhang Jianxin et al., 2005, 2009, 2010; Liu Liang et al., 2012; Yu Shengyao et al., 2012),被认为是原特提斯洋俯冲、闭合及碰撞造山作用的产物 (Zhang Jianxin et al., 2015, 2019及相关文献)。在柴北缘构造带形成及后期构造演化过程中,由于俯冲和碰撞造山作用使得地壳变形遍及整个构造带内,并由于应变局部化形成了不同类型和时代的韧性剪切带 (Xu Zhiqin et al., 2002, 2006; 付建刚等, 2016)。然而已有的研究主要集中在柴北缘构造带中不同类型岩石的岩石学、地球化学及年代学研究,对其构造变形特别是与造山作用有关韧性变形的研究很少涉及,这也限制了对柴北缘构造带演化过程的全面认识。近期,在1:5万专题地质填图中,在柴北缘构造带东段乌兰北部察汗河地区,笔者识别出一系列韧性剪切带,分别具有左行走滑和右行转换挤压性质(图1b)。本文以其中NWW—SEE向展布的右行转换挤压韧性剪切带为研究对象,揭示了该剪切带的宏微观构造特征、石英c轴组构、运动学涡度和流变学特征,并结合锆石U-Pb定年限定了韧性剪切带的变形时代,在此基础上,简要探讨该剪切带对柴北缘构造带早古生代碰撞造山过程的启示意义。
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1 区域地质背景
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柴北缘构造带位于青藏高原东北缘,为祁连造山带和柴达木地块所夹持,西以阿尔金断裂带为界,东接西秦岭造山带。柴北缘构造带由南向北主要由柴北缘俯冲-碰撞杂岩带、欧龙布鲁克微陆块以及乌北地块(解体自欧龙布鲁克微陆块)(Wang Lu et al., 2016;Zhang Jianxin et al., 2021)组成(图1a)。
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柴北缘俯冲-碰撞杂岩带位于柴达木地块与欧龙布鲁克地块之间,西起塞什腾山,东至都兰北部沙柳河-阿尔茨托山,呈北西—南东向展布 (Zhang Jianxin et al., 2015)。柴北缘俯冲-碰撞杂岩带可进一步划分为南西侧的柴北缘高压-超高压变质带以及空间上与其伴生的滩间山群浅变质火山-沉积岩系。柴北缘高压-超高压变质岩主要分布于鱼卡-落凤坡、绿梁山、锡铁山、都兰沙柳河等地,主要由榴辉岩、正片麻岩、副片麻岩和少量石榴橄榄岩所组成 (Yang Jingsui et al., 2001; Song Shuguang et al., 2003, 2005; Zhang Jianxin et al., 2009, 2010, Liu Liang et al., 2012)。大量的锆石U-Pb同位素年代学数据显示柴达木盆地北缘超高压变质作用年龄集中在460~423Ma (Zhang Jianxin et al., 2005, 2008, 2009, 2010, 2011, 2015; Song Shuguang et al., 2005, 2006, 2014; Chen D L et al., 2009; Xiong Qing et al., 2011, 2012; Yu Shengyao et al., 2012)。这些岩石学证据和年代学数据共同表明早古生代柴达木盆地北缘大陆地壳曾经历过深俯冲作用。
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滩间山群浅变质火山-沉积岩系在柴北缘俯冲碰撞杂岩带内广泛分布,与超高压变质岩石呈断层接触(王惠初等,2003; 高晓峰等,2011;Zhang Jianxin et al., 2015)。其主要由早古生代浅变质的中性-基性火山岩及沉积岩组成,局部伴随有酸性和基性-超基性岩。滩间山群的形成时代及构造属性存在一定争议,早期部分学者将滩间山群及相伴生的超基性岩和辉长岩统归为蛇绿岩组合(如赖绍聪等, 1996),即古大洋岩石圈残片;而大部分学者则认为滩间山群归属于弧构造背景(袁桂邦等, 2002; 王惠初等, 2003; 史仁灯等, 2004)。此外,滩间山群及其相关的基性岩的年代学数据主要集中在535~440Ma(袁桂邦等, 2002; 史仁灯等, 2004; 高晓峰等,2011;朱小辉等, 2012; 2014;Sun Huashan et al., 2018),为大陆深俯冲之前原特提斯洋俯冲作用的产物。
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欧龙布鲁克微陆块(也称为全吉地块)位于柴北缘构造带的北部,被认为是与塔里木板块有亲缘性的大陆克拉通残片 (Chen Nengsong et al., 2012; Gong Songlin et al., 2012; Liao Fanxi et al., 2014)。其基底主要由中-高级变质程度的古元古代早期德令哈杂岩、古元古代中晚期的达肯大坂群和中元古代的万洞沟群组成,并被中—新元古代的全吉群和早古生代以来的沉积岩系不整合覆盖(陆松年等, 2002; Chen Nengsong et al., 2012; Gong Songlin et al., 2012; He Chuan et al., 2018; Sun Jiaopeng et al., 2019)。
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近年来,在柴北缘构造带东段乌兰北部原定为欧龙布鲁克微陆块变质基底中,识别出中元古代的副变质岩系和中—新元古代多期次的变质侵入岩,明显不同于以古元古代变质基底为特征的欧龙布鲁克微陆块,并依据其地理位置将其命名为“乌北地块”(Wang Lu et al., 2016)(图1a)。而根据其普遍遭受早古生代的变质作用和早古生代—中生代的岩浆侵入,也称之为乌兰北变质-岩浆杂岩带(Lu Zenglong et al., 2018)。其中的中元古代副变质岩系被新命名为中元古代察汗河岩群(未出版资料)(图1b),其经历了1.1Ga的高温变质作用和早古生代(505~450Ma)的低压-高温变质作用的叠加 (李秀财等, 2015; Lu Zenglong et al., 2018; Wang Qinyan et al., 2018; Li Xiucai et al., 2019; Yu Shengyao et al., 2019; Wang Chunyu et al., 2021),结合其早古生代侵入体具有弧岩浆岩性质 (Niu Manlan et al., 2021),推测乌兰地块在早古生代处于大陆弧-弧后的构造背景,是柴达木盆地北缘大陆深俯冲前的原特提斯洋向北俯冲的产物 (Lu Zenglong et al., 2018; Li Xiucai et al., 2019; Zhang Jianxin et al., 2021)。
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图1 柴北缘构造带与邻区大地构造位置图(a)(修改自路增龙等,2020)和柴北缘乌兰北部(乌北地块) 韧性剪切带分布及区域地质简图(b)
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Fig.1 Geological sketch map of the North Qaidam tectonic belt and adjacent area (modified after Lu Zenglong et al., 2020) (a), geological map showing distribution of ductile shear zones in North Wulan terrane of the North Qaidam tectonic belt (b)
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通过专题地质填图,发现乌北地块受到多期构造变形作用的叠加,以发育多条规模不等的韧性剪切带为特征,并于浅层次脆性域中受到一系列逆冲及走滑断层的叠加与改造(图1b)。这些韧性剪切带的几何展布、剪切方向、变形样式以及形成年代存在较大差异。在乌北地块的中部及北部发育有数条NWW—SEE走向的左行走滑韧性剪切带,其宽度从0.2~1km不等(图1b),具有中等角度倾斜的糜棱面理与近水平的拉伸线理,年代学数据指示其应形成于中生代 (笔者未发表数据),而本文的研究对象察汗河韧性剪切带分布在乌北地块南缘,为深变质的察汗河岩群与浅变质的滩间山群的界线(图1b)。
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2 察汗河韧性剪切带
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察汗河韧性剪切带呈NWW—SEE向沿乌兰北部的阿汗达勒寺-达尔登木特-察汗河村一带展布,剪切带宽约500m,在空间上与北向逆冲脆性断层共生(图2a)。该剪切带在东南段发育有良好的天然露头(图3),带内岩石类型由北向南主要包括察汗河岩群钙质变沉积岩、副片麻岩、滩间山群绿片岩以及闪长岩。本次研究所采集定向样品的岩性可见表1。其中察汗河岩群钙质变沉积岩主要由方解石(35%)、白云石(15%)、石英(15%)、斜长石(5%)和磁铁矿(2%)等矿物组成;副片麻岩的主要岩性为含石榴子石黑云斜长片麻岩,包括黑云母(20%)、白云母(5%)、斜长石(30%)、石英(25%)和石榴子石(5%)等矿物;滩间山群绿片岩主要由绿泥石(25%)、绿帘石(15%) 阳起石(10%)、钠长石(30%)、石英(25%)和黑云母(5%)等矿物组成;闪长岩的主要造岩矿物包括斜长石(50%)、角闪石(25%)、石英(15%)、辉石(3%)和黑云母(2%)等。带内的各类型岩石均遭受强烈的韧性剪切作用(图2c),并由此形成由云母鱼、缎带状石英、长石及角闪石旋转碎斑拖尾等韧性变形产物定向排列构成的糜棱面理和矿物拉伸线理(图3a、b)。糜棱面理走向与剪切带走向保持一致,倾向NNE或SSW,倾角为30°~90°,优势产状为184°∠ 76°(图2b)。在糜棱面理上发育的拉伸线理产状发生波动,从向SEE倾伏,倾伏角为5°~25°的缓倾斜线理变化为以中等倾伏角向NEE倾伏(图2b)。
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图2 乌北北部察汗河地区地质简图(a)、糜棱面理极轴与拉伸线理的极射赤平投影图 (等面积网,下半球投影)(b)和察汗河韧性剪切带观察剖面及采样位置(c)
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Fig.2 Geological sketch map of the Chahanhe area in the northern Wulan (a), stereographic projection of the pole to mylonitic foliations and the stretching lineations (equal-area net, lower hemisphere) (b) and section and sample locations for the Chahanhe ductile shear zone (c)
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察汗河韧性剪切带内岩石保留了不同尺度及性质的变形构造。带内的指示剪切运动方向的宏观不对称构造普遍存在,自北向南在剪切带东南段野外露头的X-Z面(由岩石变形最长轴方向及最短轴方向组成)上观察到C剪切面理和S面理,且两者都被伸展褶劈理C’所截切,形成典型的S-C-C’组构(图3c)、σ型旋转碎斑(图3e、f)和S-C组构(图3d),其共同指示了剪切带的右行走滑剪切分量。此外,垂直于剪切带走向方向上发育的σ型和δ型长英质旋转碎斑表明带内部分由北向南的垂向逆冲运动分量的存在(图3g~i)。
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在显微尺度上,自北向南在沿X-Z面制备的薄片上观察到一系列指示右行走滑剪切的不对称构造,如σ型石英旋转碎斑(图4a)、磁铁矿的书斜构造(图4a)、主要由黑云母和石英细小晶体颗粒集合体组成拖尾的δ型斜长石旋转碎斑(图4b)、由斜长石的旋转碎斑系所代表的S面理、富云母和石英的条带组成的C面理共同构成的S-C组构(图4c、d)以及被脆性变形所叠加的σ型角闪石旋转碎斑(图4e、f)等。石英主要以扁长状多晶集合体的形式存在,具有波状消光的特征,在其交织状晶界处发育有重结晶亚晶粒(图4a、c、e),这些显微构造表明石英发生了以亚颗粒旋转(SGR)和颗粒边界迁移(GBM)重结晶为主的动态重结晶机制。斜长石常发育有机械双晶和波状消光,其变形主晶常被其细小的亚晶粒集合体所环绕形成典型的核幔构造(图4c),是斜长石动态恢复和动态重结晶的共同产物。角闪石的波状消光和机械双晶亦普遍存在,并伴随着微破裂的发育,代表着角闪石脆—韧性转变的变形机制。
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图3 柴北缘构造带察汗河右行转换挤压韧性剪切带野外露头照片
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Fig.3 Field photographs of the Chahanhe dextral transpressional ductile shear zone in the North Qaidam tectonic belt
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(a)、(b)—糜棱面理及拉伸线理;(c)—X-Z面上观察到的S-C-C’组构;(d)—X-Z面上观察到的S-C组构;(e)、(f)—发育于X-Z面上的右行σ型旋转碎斑; (g)—垂直于剪切带走向方向上发育的σ型长英质旋转碎斑系;(h)—(g)中旋转碎斑系素描;(i)—垂直于剪切带走向方向上观察到的δ型长英质旋转碎斑拖尾;Qtz—石英;Pl—斜长石
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(a),(b)—Mylonitic foliations and the stretching lineations;(c)—S-C-C’ fabrics observed in X-Z plane;(d)—S-C fabrics observed in X-Z plane;(e),(f)—σ-type porphyroclasts in X-Z plane (g) —felsic σ-type porphyroclast system in direction of perpendicular to the strike of the shear zone;(h) —the sketch of porphyroclast system in (g);(i) —δ-type porphyroclasts observed in direction of perpendicular to the strike of the shear zone;Qtz—quartz;Pl—plagioclase
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图4 察汗河韧性剪切带显微构造及其剪切指向
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Fig.4 Microphotographs showing microstructures and shearing signatures of the Chahanhe dextral transpression ductile shear zone in the North Qaidam tectonic belt
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(a)—正交偏光下σ型石英旋转碎斑;(b)—单偏光下的δ型斜长石旋转碎斑;(c)—正交偏光下由云母、石英和斜长石构成的S-C组构;(d)—图(c)中电子背散射衍射(EBSD)的矿物分布图像;(e)、(f)—正交偏光及单偏光下的σ型角闪石旋转碎斑;(a)~(f)拍摄于X-Z面;Amp—角闪石;Qtz—石英;Pl—斜长石;Mag—磁铁矿;SGR—亚颗粒旋转重结晶;GBM—颗粒边界迁移重结晶
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(a)— σ-type quartz porphyroclasts (cross-polarized light);(b)—δ-type plagioclase porphyroclasts (plane-polarized light);(c) —S-C fabrics consist of mica, quartz and plagioclase under cross-polarized light;(d)—the mineral distribution map scan by electron backscatter diffraction ( EBSD) from (c);(e),(f)—σ-type amphibole porphyroclasts (e,cross-polarized;f,plane-polarized light); (a)~(f) are microphotographs for X-Z section of sample;Amp—amphibole;Qtz—quartz;Pl—plagioclase;Mag—magnetite;SGR—subgrain rotation recrystallisation;GBM—grain boundary migration recrystallisation
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3 石英c轴组构特征
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为了进一步获取察汗河韧性剪切带的剪切方向和变形机制等关键信息,笔者对带内的定向样品的X-Z面薄片进行了电子背散射衍射测试 (EBSD)。通过基于MATLAB开发的MTEX工具包(Bachmann et al., 2010)处理得到薄片内石英c轴的优选方位极图及其J、M指数(图5)(Bunge, 1982; Skemer et al., 2005)。为了避免石英颗粒大小对石英c轴极图结果的影响,笔者使用单个石英颗粒作为数据点构建极图 (One point per grain)。样品测定在自然资源部深地动力学实验室完成,使用了FEI Quanta450扫描电镜搭配Oxford Nordlys F+ EBSD高速探测器,并通过AztecSynergy软件完成图像采集,结合“Spline Filter”函数来完成数据降噪,具体测试流程见许志琴等(2009)。
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图5 柴北缘构造带察汗河韧性剪切带变形岩石的石英c轴组构
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Fig.5 The quartz c axis fabrics of deformed rocks in the Chahanhe dextral transpression ductile shear zone in the North Qaidam tectonic belt
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n —石英颗粒数量;J —组构强度J指数;M —组构强度M指数;β—石英c轴组构中心环带的法线和面理的夹角;OA—石英组构开角;T —石英开角温度计所得的变形温度
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n —Number of quartz grains; J —J-index for the texture strength; M —M-index for the texture strength; β—the angle between the perpendicular to the central girdle of the quartz c-axis diagram and the foliation; OA—opening-angle of quartz c-axis fabric; T —deformation temperatures calculated by opening-angle thermometer
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剪切带内样品X-Z面定向薄片的＜0001＞石英c轴极图的不对称性指示了右行走滑剪切作用(图5,图7b)。带内X-Z面的石英c轴极图＜0001＞面发育多种类型的极密,包括位于极图边缘偏离Z轴的点极密(AQ21-2-3.1),介于极图边缘和中心发育的交叉环带(D1007-1和AQ21-2-4.1a)以及位于中心Y轴的点极密(AQ21-2-4.1b和AQ21-2-4.2),分别对应着石英c轴组构的低温底面＜a＞滑移、中低温棱面＜a＞滑移和中高温柱面＜a＞滑移机制 (Stipp et al., 2002a; Passchier et al., 2005)。
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4 有限应变测量和涡度估算
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4.1 有限应变测量
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对构造岩石的有限应变测量能够揭示韧性剪切带内的应变程度 (如Hossack, 1968)。察汗河韧性剪切带内岩性多样,主要包括钙质变沉积岩、黑云斜长片麻岩和闪长岩,其中的造岩矿物从力学性质从弱到强依次为云母、方解石、石英、长石和角闪石。在这些矿物中选择可靠的应变标志体对提高有限应变测量结果的准确度有着重要影响 (Ramsay et al., 1970; Bailey et al., 1994)。本文挑选其中强度适中的石英和长石旋斑颗粒进行有限应变测量,这两种矿物所估算出的有限应变结果被认为接近全岩的真实应变 (Bailey et al., 2003)。由于带内岩石的应变特征并非典型的压扁应变, 且石英、长石和角闪石均发生了晶内塑性变形,故笔者的有限应变测量是建立在全岩没有体积损失的假设之上的 (Ramsay, 1967; Xypolias et al., 2001)。通过Fry法和直接测量法,笔者估算出了X-Z和Y-Z面上应变椭圆的轴率 (Fry, 1979),并分别使用弗林图解和许氏图解来表达三维应变椭球体的形态 (Flinn, 1962; Hsü, 1966)。
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通过以上方法所测定的弗林指数(K)值在0.69~0.99之间波动,八面体剪应变强度(εs)及Lode参数(V)的变化范围则分别为0.38~0.49和0.01~0.19(表1)。这些三维有限应变数据的投影多落于两图解的平面应变线附近,并含有一定量的压扁应变分量,归属于L=S构造岩类型(图6)。此外,通过Fry法和直接测量法测量的结果之间具有较好的一致性,这提高了测量结果的真实性和可信度。
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注:pq—初糜棱岩化石英岩;mm—糜棱岩化变沉积岩;mp—糜棱岩化副片麻岩;md—糜棱岩化闪长岩。
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4.2 运动学涡度
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运动学涡度(W k)是度量岩石内部在变形过程中的瞬时剪应变与瞬时应变速率之间关系的无量纲参数,亦能反映纯剪切和简单剪切分量在变形过程中所占的比例,即纯剪切的运动学涡度为0,简单剪切为1,一般剪切介于0到1之间 (Truesdell, 1953; Means, 1980; Bobyarchick, 1986)。在实际运用中,常使用实际可测的有限应变来取代不可测的瞬时应变,如此确定的运动学涡度即为某一变形事件的平均运动学涡度(W m)。目前已报道了多种方法来测量高应变带内岩石的平均运动学涡度,如极莫尔圆法 (Simpson et al.,1993; Zhang J et al., 1997)、RS/θ法 (Fossen et al., 1993;Tikoff et al., 1995)、石英c轴组构法 (Wallis, 1992, 1995)、临界形态因子法 (Passchier, 1987; Simpson et al., 1993;Wallis, 1995; Jessup et al.2007) 和β/δ 法 (Xypolias, 2009, 2010) 等。本文依据定向构造样品的具体特征分别采用R S/θ法、石英c轴组构法和临界形态因子法来对X-Z面上的平均运动学涡度进行估算,以获取察汗河韧性剪切带内单斜变形的共轴性特征。
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图6 柴北缘构造带察汗河右行转换挤压韧性剪切带中石英、长石颗粒形态弗林图解(a)及石英、长石颗粒形态许氏图解(b)
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Fig.6 The types of quartz and plagioclase grains on a Flinn diagram (a), the types of quartz and plagioclase grains on a Hsü diagram (b) for the Chahanhe dextral transpressional ductile shear zone in the North Qaidam tectonic belt
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K —弗林参数;εs—八面体剪应变强度;V —lode参数
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K —Flinn parameter;εs—octahedral strain intensity;V —Lode’s parameter
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图7 R S/θ法获取的柴北缘构造带察汗河韧性剪切带平均运动学涡度结果(a)(底图据Fossen et al.,1993) 和察汗河韧性剪切带石英c轴组构的野外空间方位示意图(b)
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Fig.7 The kinematic vorticity result of R S-θ method (a)(after Fossen et al.,1993) and spatial relationship between the field orientation and the quartz c axis fabrics (b) of the Chahanhe ductile shear zone in the North Qaidam tectonic belt
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R S/θ法,通过测量得到应变椭圆的轴率R S和应变椭圆长轴与高应变带边界的夹角θ,从而使用R S/θ关系图解来估算W m (Fossen et al., 1993)。本文在假设岩石体积损失为零的情况下,以发育于 X-Z面定向薄片上的σ型旋转碎斑和S-C-C’组构为测量依据,利用R S/θ法计算出带内糜棱岩在两个方向上的涡度值。计算结果显示,带内变形岩石在X-Z面的涡度值介于0.54~0.77(表2),在R S/θ图解中主要表现为纯剪切分量与简单剪切分量近相等的应变特征(图7a)。
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石英c轴组构法,Wallis (1992, 1995)提出石英c轴组构中心环带的法线和面理的夹角(β)等于压扁应变面和流变面之间的夹角,结合主应变轴比(R S)即可计算出平均运动学涡度(W m),三个参数间存在如下关系式:
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本次计算所使用的主应变轴比(Rs)数据来源于前文的Fry法有限应变测量结果(表1),结合由石英c轴组构测定的β值(图5)估算出X-Z面和Y-Z面的W m值。计算结果显示,X-Z面的运动学涡度值为0.57~0.79(表2)。
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临界形态因子法,是根据刚性体旋转方式和长轴取向在双曲线两侧的显著变化特征来确定临界形态因子(B *),等同于运动学涡度(W m)的投图估算方法,其投图方式包括Passchier图示 (Passchier, 1987)、双曲线网(PHD)图示(Simpson et al., 1993)、Waills图示 (Wallis, 1995)和刚性颗粒网(RGN)图示 (Jessup et al., 2007)等。其中刚性颗粒网(RGN)图示在Passchier图示的基础上引入了一系列双曲等值线来帮助提高涡度分析的准确度 (Jessup et al., 2007)。RGN图示的纵坐标为旋转碎斑长轴与剪切(C)面理的夹角(θ),横坐标是由旋转碎斑的长轴长度Mx和短轴长度Mn计算得到的B *,计算公式如下 (Passchier, 1987):
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为了避免人工测量所引起的误差,笔者通过基于GIS开发的Q-XRMA和Min-GSD分析工具 (Visalli, 2018; Ortolano et al., 2018, 2020),结合对薄片的光学扫描及X射线荧光光谱分析(XRF)得出三种不同岩性薄片中旋转碎斑的矢量化参数,包括长轴长度Mx、短轴长度Mn和长轴与剪切面的夹角(θ),并将所得数据投于RGN图示以求得X-Z面的W m值(图8)。从分析结果来看,在糜棱岩化变沉积岩(AQ21-2-3.1)中共识别出134个石英旋斑,W m值介于0.36~0.40之间;糜棱岩化副片麻岩(D1007-1)包含282个斜长石旋斑,W m值为0.43~0.50;糜棱岩化闪长岩(AQ21-2-4.1)中251个角闪石旋斑,W m值范围为0.58~0.62。
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5 变形温度与流变学
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5.1 石英开角温度计
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Kruhl (1998)通过对不同温度下变形石英的c轴组构的分析研究,发现了石英c轴大圆环带的开角(OA)和变形温度之间的正线性关系,以此为基础发展成一种变形温度计 (Morgan et al., 2004; Law, 2014)。除了变形温度以外,三维有限应变的几何形态、压力、流体和应变速率等因素对石英开角也有着一定的影响(Lister et al., 1980; Morgan et al., 2004; Law, 2014; Faleiros et al.2016)。在不考虑其他因素影响的条件下,笔者使用最新校正的石英开角温度计公式来计算察汗河韧性剪切带的变形温度(Faleiros et al., 2016):
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在糜棱岩化闪长岩(AQ21-2-4.1b)的石英c轴极图中,其OA角为73.2°,通过上述公式计算出带内变形温度为553±50℃(图5)。由于石英c轴组构开角受到上述多种因素的共同影响,因此该方法计算出的变形温度应与其他的变形温度标志相互验证。在该样品(AQ21-2-4.1)内的石英的SGR和GBM共存(图4e),以及石英c轴极图的柱面＜a＞滑移(图5)指示了其GBM I型重结晶机制,处于500~630℃的变形温度(Stipp et al., 2002a; Faleiros et al., 2010; Law, 2014),石英开角温度计所计算出的结果(553±50℃)与这一温度范围较为吻合,能够代表剪切带内的变形温度。
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图8 柴北缘构造带察汗河韧性剪切带内薄片光学扫描影像、矿物颗粒尺寸分布(Min-GSD)测量结果 (底图据Jessup et al.,2007)与刚性颗粒网(RGN)图示结果(底图据Jessup et al.,2007)
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Fig.8 Images of thin section optical scans, mineral-grainsize distribution (Min-GSD) (after Jessup et al., 2007)and the result of rigid grain net (RGN) (after Jessup et al., 2007)in the Chahanhe ductile shear zone, the North Qaidam tectonic belt
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n Qtz—石英旋转碎斑数量;n Pl—斜长石旋转碎斑数量;n Amp—角闪石旋转碎斑数量
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n Qtz—Number of quartz porphyroclasts;n Pl—number of plagioclase porphyroclasts;n Amp—number of amphibole porphyroclasts
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5.2 古差异应力与应变速率
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应变速率及其与所受应力和应变关系的确定是理解岩石圈流变学变化特征的关键环节 (Huntington et al., 2018)。对研究区内韧性剪切带不同部位的古差异应力和应变速率的测定能进一步加深对剪切带内的流变学及其应变局部化的空间变化特征的认识。
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前人通过实验岩石学的研究发现差异应力(σ)与中高温条件下以动态重结晶方式形成的新生石英颗粒的平均粒径(d)具有特定关系,并据此建立了古应力计 (Twiss, 1977; Stipp et al., 2003, 2010)。对新生石英颗粒的尺寸测量方式主要包括光学显微镜法和石英c轴集成法 (Heilbronner et al., 1993)。近期,Cross et al.(2017)提出了EBSD分离法,并对相关实验参数进行修正,即基于EBSD实验数据,通过MATLAB的MTEX工具包的数据处理 (Bachmann et al., 2010),以合成颗粒内部的取向散布程度来代表其晶内的位错密度,并以此来区分石英重结晶颗粒和残余颗粒的测量方式,其测量结果为所得石英重结晶颗粒尺寸的均方根(d RMS)。本文将使用该方法测定的d RMS(单位μm)及其修正的实验参数来估算察汗河韧性剪切带的古差异应力(σ)(MPa)(Cross et al., 2017):
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通过EBSD分离法,笔者识别出带内不同位置代表性样品的石英重结晶颗粒和残余颗粒及其尺寸分布频率(图9)。从高斯拟合曲线来看,石英重结晶颗粒的粒度分布普遍小于残余颗粒,所测得两个样品的 d RMS值分别为67.3 μm和72.2 μm(图9)。计算结果表明,自北向南带内变形岩石的差异应力分别为28.5MPa和30.0MPa(表3)。
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图9 EBSD分离法得出的石英重结晶颗粒和残余颗粒尺寸频率分布直方图以及高斯拟合曲线(d RMS为重结晶颗粒尺寸的均方根)
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Fig.9 The frequency distribution histogram and Gaussian fitting curve of the recrystallized and relict quartz grain size from the EBSD-based separation method (d RMS is the root mean square of the recrystallized grain)
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注:mp—糜棱岩化副片麻岩; md—糜棱岩化闪长岩;d RMS—石英重结晶颗粒尺寸的均方根。
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石英的流变学性质受到温度(T)、差异应力(σ)、水逸度()和应变速率(ε)等多种因素影响,在假定水逸度()不变的情况下,一般认为其流变学本构方程为 (Paterson et al., 1990; Hirth et al., 2001; Rutter et al., 2004; Boutonnet et al., 2013):
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式中:为应变速率(S-1),A为实验参数(MPa-n/s)、σ为差异应力(MPa),n为应力指数,d为重结晶颗粒尺寸(μm),m为颗粒指数,Q为活化能(kJ/mol),R为理想气体常数,T为绝对温度。
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本文应变速率计算选用Paterson et al.(1990)通过对岩石学实验以及与前人结果的对比所确定的适用于中低温变形的实验参数(A=6.5×10-8 MPa-n/s; Q=135kJ/mol; n=3.1; m=0)。根据带内样品的石英c轴组构开角与滑移系共同限定出的平均剪切变形温度(T),结合上文估算的古差异应力值(σ)计算出察汗河韧性剪切带自北向南的应变速率(表3)。估算结果显示,两个代表性样品的应变速率分别为1.59×10-12/s和7.15×10-12/s。
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6 锆石U-Pb定年结果
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为了限制察汗河韧性剪切带的变形时代,本文在剪切带南侧卷入剪切带的闪长岩体中采集了定年样品(D1393-1),该样品岩性为弱变形闪长岩,主要由斜长石(50%)、角闪石(25%)、石英(15%)和黑云母(3%)等矿物组成。具体取样位置见图2a,并对其进行了锆石U-Pb同位素测年。测定方法及流程见路增龙等(2017)。
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样品D1393-1中锆石阴极发光(CL)图像显示锆石主要呈碎片状,发育有板状环带,粒径100~130 μm,同时具有较高的Th/U比值(0.8~2.2),为典型基性岩岩浆中结晶锆石的特征。对该样品进行了30个测点的分析测试,排除6个测点年龄偏小且谐合度稍差的数据,其余24个测点获得的206Pb/238U年龄介于441~422Ma之间,加权平均年龄为432.1±2.5Ma(MSWD=1.2),应代表了弱变形闪长岩体的形成年龄。
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7 讨论
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7.1 察汗河韧性剪切带变形温度及应变速率
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石英的塑性变形温度较斜长石和角闪石低,常受到晚期构造事件的叠加和改造并予以记录(Passchier et al., 2005)。察汗河韧性剪切带内石英的SGR和GBM共存的重结晶机制以及石英c轴组构的底面＜a＞滑移向柱面＜a＞滑移过渡的滑移系应代表晚期中高温(~500℃)韧性剪切变形作用 (Stipp et al.2002a; Faleiros et al., 2010; Law, 2014)。而带内斜长石的核幔构造和角闪石脆—韧性转变变形机制等显微构造特征指示了较高温(650~700℃)的变形事件 (Simpson 1985; Cumbest et al., 1989; Yund et al., 1991; Skrotzki et al., 1992; Passchier et al., 2005)。考虑到乌北地块在早古生代早期(505~450Ma)经历了高温变质作用 (李秀财等, 2015; Lu Zenglong et al., 2018; Wang Qinyan et al., 2018; Li Xiucai et al., 2019; Yu Shengyao et al., 2019; Wang Chunyu et al., 2021),其可能也遭受过早古生代早期的高温变形作用,并保存在斜长石和角闪石等矿物中。带内样品的石英c轴组构的滑移系及石英组构开角温度计指示从北自南其变形温度由500℃逐步升高至553℃(表3)。在假定陆壳的平均地温梯度为30℃/km的条件下(汪集旸等,2001),估算出察汗河韧性剪切带应发育于16~18km的中地壳层次。
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图10 柴北缘构造带察汗河韧性剪切带内弱变形闪长岩代表性锆石的阴极发光(CL) 图像(a)和弱变形闪长岩的锆石U-Pb谐和图(b)
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Fig.10 Cathodoluminescent (CL) images of representative zircons from weakly deformed diorite in the Chahanhe dextral transpression ductile shear zone in the North Qaidam tectonic belt (a) and zircon U-Pb concordia diagrams of weakly deformed diorite (b)
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剪切带内样品重结晶石英颗粒粒度估算获得的古差异应力介于28.5~30.0MPa之间,从北自南总体表现出差异应力减小的趋势(表3)。带内样品的应变速率从剪切带北侧向南侧有增加的趋势,介于1.59×10-12~7.15×10-12/s之间,符合Stipp et al.(2002b)推测的中地壳层次变形温度(500~553℃)下石英的SGR和GBM重结晶机制的应变速率变化范围。该测量结果应代表了韧性剪切带内的局部应变速率(Gueydan et al., 2005; Cross et al., 2015)。
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7.2 察汗河韧性剪切带运动学涡度
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R S/θ法、石英c轴组构法和临界形态因子法获得X-Z面上的平均运动学涡度值分别为0.57~0.77、0.57~0.79和0.36~0.60,总体表现为简单剪切和纯剪切分量接近相等的变形特征(图11)。R S/θ法与石英c轴组构法的原理类似,所估算的运动学涡度值变化范围亦趋于一致,而临界形态因子法具有相对较小的涡度值,可能与变形过程中旋转碎斑长短轴比的减小有关(郑亚东等,2008)。这三种方法在X-Z面上所估算的平均运动学涡度数据有效地定量了带内应变过程中的非共轴变形组分,且表现出较为一致的变化趋势,即察汗河剪切带的南部较北部具有较高的简单剪切分量(图11)。
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7.3 转换挤压变形样式
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在察汗河韧性剪切带的X-Z面上发育的宏微观不对称剪切指向(图3、图4)和石英c轴组构(图5)均表明了其右行走滑的剪切方向,结合压扁型的三维应变椭球体形态(图6),共同指示了一个转换挤压(transpression)的变形样式,其同时具有纯剪切和简单剪切分量 (Harland, 1971; Sanderson et al., 1984)。运动学涡度测量结果表明察汗河剪切带内纯剪切分量和简单剪切分量占总体变形的比例相近(图11)。
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图11 柴北缘构造带察汗河右行转换挤压韧性剪切带运动学涡度(X-Z面)与应变速率对比趋势图
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Fig.11 The tendency chart of the kinematic vorticity (X-Z plane) and strain rate of the Chahanhe dextral transpressional ductile shear zone in the North Qaidam tectonic belt
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在古造山带和现今汇聚板块边界,常发育具有纯剪和单剪分量的转换挤压韧性剪切带,通常被认为是板块斜向汇聚的产物,调节并记录板块间的相互作用 (Harland, 1971; Sanderson et al., 1984; Fossen et al., 1993; Means, 1995; Jiang et al., 2001),察汗河韧性剪切带的转换挤压变形样式表明其形成于板块间斜向汇聚的动力学背景。此外,在露头尺度上垂直于剪切带走向方向上发育有σ型和δ型长英质旋转碎斑(图3g~i),指示出部分自北向南的垂向逆冲分量,其应为在转换挤压变形过程中斜向的走滑剪切作用在垂直于剪切带走向方向上表现出来的部分逆冲运动分量(图12)。
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7.4 察汗河韧性剪切带的韧性变形时限与区域构造意义
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厘清察汗河右行转换挤压韧性剪切带的变形时代对理解和重建柴北缘构造带东段的汇聚造山过程具有重要意义。察汗河韧性剪切带切割了带南侧的闪长岩体并使其发生强烈韧性变形,闪长岩体的锆石加权平均年龄为432.1±2.5Ma,代表了韧性剪切变形的下限年龄,该下限年龄在柴达木盆地北缘的UHP变质作用发生时代(460~423Ma)的变化范围内 (Song Shuguang et al., 2005, 2006, 2014; Zhang Jianxin et al., 2008, 2009, 2010, 2011, 2015; Chen D L et al., 2009; Xiong Qing et al., 2011, 2012)。Xu Zhiqin et al.(2006) 曾在柴北缘锡铁山和都兰北沙柳河的超高压变质带中识别出右行转换挤压韧性剪切带,并获得糜棱岩化岩石中白云母40Ar-39Ar坪年龄为406~402Ma;这些超高压变质带中的韧性剪切带被解释为斜向陆内汇聚的产物,并促使了超高压变质岩的斜向挤出和折返,而406Ma代表了超高压变质岩折返的完成时代 (Xu Zhiqin et al., 2006)。考虑到白云母40Ar-39Ar约405℃的封闭温度 (Harrison et al., 2009),这些韧性剪切带的形成时代应在406Ma之前。本文所厘定的察汗河韧性剪切带与超高压变质带中的韧性剪切带具有类似的右行转换挤压性质,它们可能形成于同一构造背景下。
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早古生代柴北缘构造带经历了原特提斯洋的俯冲、增生、闭合、大陆深俯冲及陆-陆碰撞和造山后垮塌伸展的演化过程 (Xiao Wenjiao et al., 2009; Yu Shengyao et al., 2012; Zhang Jianxin et al., 2015, 2019)。察汗河韧性剪切带的转换挤压变形样式指示其应形成于斜向汇聚造山过程 (Sanderson et al., 1984, Jones et al., 1997, 2004),即柴北缘超高压变质作用所代表的北向大陆深俯冲作用之后的陆-陆碰撞造山作用过程中。一些研究显示,柴北缘构造带在早—中泥盆世(400Ma左右)开始进入后碰撞伸展垮塌阶段,如王惠初等(2005)获得都兰地区具裂解性质的乌龙滩花岗岩的形成年龄为400Ma左右,以及绿梁山地区具板内产出背景的闪长岩锆石U-Pb年龄为396.2±6.8Ma;Wu Cailai et al.(2019) 认为柴北缘地区413~391Ma的花岗岩与板片断离(Slab break off)所引起的伸展构造背景有关。柴北缘构造带内的泥盆系牦牛山组被认为是造山后伸展垮塌阶段的产物(张春宇等, 2019;钱涛等, 2021)。杨张张等(2017)在石底泉地区牦牛山组上部火山岩段的安山岩中得到锆石U-Pb年龄为395.7±2.7Ma,与钱涛等(2021)在尕海南山牦牛山组顶底部凝灰岩中获得的锆石U-Pb年龄(396.6±2.4Ma和396.9±2.5Ma)高度一致。由此笔者推断,柴北缘构造带从挤压碰撞造山阶段进入造山后伸展垮塌阶段大约在早泥盆世末期(~396Ma),而具有转换挤压性质的韧性剪切带变形活动应早于这一时间。
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图12 柴北缘构造带察汗河韧性剪切带的构造模式示意图
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Fig.12 The schematic tectonic model for the Chahanhe ductile shear zone in the North Qaidam tectonic belt
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基于上述年代学数据和转换挤压变形样式,笔者认为在中志留世—早泥盆世(432~396Ma)时,位于早古生代柴北缘构造带弧-弧后大地构造位置的欧龙布鲁克微陆块和乌北地块(李秀财等, 2015; Wang Qinyan et al., 2018; Li Xiucai et al., 2019; Zhang Jianxin et al., 2019)受到大陆深俯冲之后挤压背景下的碰撞造山作用的影响,在两个地块边界处形成了转换挤压性质的韧性剪切带以调节斜向汇聚造山作用带来的应变量,同时剪切带的转换挤压变形样式也指示柴北缘构造带的斜向汇聚作用主要表现为以垂直于造山带的水平收缩和平行于造山带的侧向挤出的构造变形方式,伴随着部分由北向南的逆冲分量(图12)。
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8 结论
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(1)察汗河韧性剪切带内宏微观尺度上的不对称构造以及石英c轴组构均指示了一致的右行走滑剪切方向。剪切带内石英的重结晶机制、c轴组构滑移系以及其开角温度计指示其变形温度介于500~553℃之间。带内样品重结晶石英颗粒粒度估算获得的古差异应力为28.5~30.0MPa,应变速率为10-12/s,推测形成于16~18km的中地壳层次。
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(2)三维有限应变测量结果表明,察汗河韧性剪切带内的样品的均展示出靠近平面应变的压扁应变特征,归属于L=S构造岩类型。带内样品X-Z面上的平均运动学涡度值介于0.36~0.77之间。
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(3)察汗河韧性剪切带形成于一个典型的转换挤压构造背景,带内纯剪切和走滑分量近一致,其非水平的走滑剪切作用在垂向上表现为部分自北向南的逆冲变形分量。
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(4)基于锆石U-Pb定年和区域地质资料,笔者推断察汗河韧性剪切带的变形时代介于中志留世—早泥盆世之间(432~396Ma),形成于早古生代晚期柴北缘构造带碰撞造山的构造背景下,为欧龙布鲁克微陆块和乌北地块之间陆内斜向汇聚作用的产物。
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致谢:刘俊来教授和两位匿名审稿人对文章提出了建设性的修改意见,在此表示感谢!
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参考文献
-
Bachmann F, Hielscher R, Schaeben H. 2010. Texture analysis with MTEX-Free and open source software toolbox. Solid State Phenomena, 160: 63~68.
-
Bailey C M, Simpson C, De Paor D G. 1994. Volume loss and tectonic flattening strain in granitic mylonites from the Blue Ridge province, central Appalachians. Journal of Structural Geology, 16(10): 1403~1416.
-
Bailey C M, Eyster E L. 2003. General shear deformation in the Pinaleño Mountains metamorphic core complex, Arizona. Journal of Structural Geology, 25(11): 1883~1892.
-
Bercovici D, Ricard Y. 2012. Mechanisms for the generation of plate tectonics by two-phase grain-damage and pinning. Physics of the Earth and Planetary Interiors, 202-203: 27~55.
-
Bobyarchick A R. 1986. The eigenvalues of steady flow in Mohr space. Tectonophysics, 122(1): 35~51.
-
Boutonnet E, Leloup P H, Sassier C, Gardien V, Ricard Y. 2013. Ductile strain rate measurements document long-term strain localization in the continental crust. Geology, 41(8): 819~822.
-
Bunge H J. 1982. Texture Analysis in Materials Science: Mathematical Methods. London: Butterworths.
-
Chen D L, Liu L, Sun Y, Liou J G. 2009. Geochemistry and zircon U-Pb dating and its implications of the Yukahe HP/UHP terrane, the North Qaidam, NW China. Journal of Asian Earth Sciences, 35(3-4): 259~272.
-
Chen Nengsong, Zhang Lu, Sun Min, Wang Qinyan, Kusky T M. 2012. U-Pb and Hf isotopic compositions of detrital zircons from the paragneisses of the Quanji massif, NW China: implications for its early tectonic evolutionary history. Journal of Asian Earth Sciences, 54-55: 110~130.
-
Cross A J, Kidder S, Prior D J. 2015. Using microstructures and TitaniQ thermobarometry of quartz sheared around garnet porphyroclasts to evaluate microstructural evolution and constrain an Alpinefault zone geotherm. Journal of Structural Geology (75): 17~31.
-
Cross A J, Prior D J, Stipp M, Kidder S. 2017. The recrystallized grain size piezometer for quartz: an EBSD-based calibration: EBSD-based quartz grain size piezometer. Geophysical Research, 44(13): 6667~6674.
-
Cumbest R J, Drury M R, van Roermund H L M, Simpson C. 1989. Dynamic recrystallization and chemical evolution of clinoamphibole from Senja, Norway. Contributions to Mineralogy and Petrology, 101(3): 339~349.
-
Faleiros F M, Campanha G A C, Bello R M S, Fuzikawa K. 2010. Quartz recrystallization regimes, c-axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone (Ribeirashear zone, SE Brazil). Tectonophysics, 485(1-4): 193~214.
-
Faleiros F M, Moraes R, Pavan M, Campanha G A C. 2016. A new empirical calibration of the quartz c-axis fabric opening-angle deformation thermometer. Tectonophysics, 671: 173~182.
-
Flinn D. 1962. On folding during three-dimensional progressive deformation. Quarterly Journal of the Geological Society, 118(1-4): 385~428.
-
Fossen H, Tikoff B. 1993. The deformation matrix for simultaneous simple shearing, pure shearing and volume change, and its application to transpression-transtension tectonics. Journal of Structural Geology, 15(3-5): 413~422.
-
Fossen H, Cavalcante G C G. 2017. Shear zones—a review. Earth-Science Reviews, 171: 434~455.
-
Fry N. 1979. Random point distributions and strain measurement in rocks. Tectonophysics, 60(1-2): 89~105.
-
Fu Jiangang, Liang Xinquan, Wang Ce, Jiang Ying, Zhou Yun, Pan Chuanchu, Yang Yongqiang, Wang Zeli, Zhong Yongsheng. 2016. Characteristics and muscovite40Ar/39Ar age of ductile shear zone in the Xitieshan area, North Qaidam. Geotectonica et Metallogenia, 40(1): 14~28 (in Chinese with English abstract).
-
Gao Xiaofeng, Xiao Peixi, Jia Qunzi. 2011. Redetermination of the Tanjianshan Group: geochronological and geochemical evidence of Basalts from the margin of the Qaidam basin. Acta Geologica Sinica, 85(9): 1452~1463 (in Chinese with English abstract).
-
Gong Songlin, Chen Nengsong, Wang Qinyan, Kusky T M, Wang Lu, Zhang Lu, Ba Jin, Liao Fanxi. 2012. Early Paleoproterozoic magmatism in the Quanji massif, northeastern margin of the Qinghai-Tibet Plateau and its tectonic significance: LA-ICPMS U-Pb zircon geochronology and geochemistry. Gondwana Research, 21(1): 152~166.
-
Gueydan F, Mehl C, Parra T. 2005. Stress-strain rate history of a midcrustal shear zone and the onset of brittle deformation inferred from quartz recrystallized grain size. Geological Society, London, Special Publications, (243): 127~142.
-
Harland W B. 1971. Tectonic transpression in Caledonian Spitsbergen. Geological Magazine, 108(1): 27~41.
-
Harrison T M, Célérier J, Aikman A B, Hermann J, Heizler M T. 2009. Diffusion of 40Ar in muscovite. Geochimica et Cosmochimica Acta, 73(4): 1039~1051.
-
He Chuan, Gong Songlin, Wang Lu, Chen Nengsong, Santosh M, Wang Qinyan. 2018. Protracted post-collisional magmatism during plate subduction shutdown in early Paleoproterozoic: insights from post-collisional granitoid suite in NW China. Gondwana Research, 55: 92~111.
-
Heilbronner R P, Pauli C. 1993. Integrated spatial and orientation analysis of quartz c-axes by computer-aided microscopy. Journal of Structural Geology, 15(3-5): 369~382.
-
Hirth G, Teyssier C, Dunlap J W. 2001. An evaluation of quartzite flow laws based on comparisons between experimentally and naturally deformed rocks. International Journal of Earth Sciences, 90(1): 77~87.
-
Hossack J R. 1968. Pebble deformation and thrusting in the Bygdin area (Southern Norway). Tectonophysics, 5(4): 315~339.
-
Hsü T C. 1966. The characteristics of coaxial and non-coaxial strain paths. Journal of Strain Analysis, 1(3): 216~222.
-
Huntington K W, Klepeis K A. 2018. Challenges and opportunities for research in tectonics: understanding deformation and the processes that link earth systems, from geologic time to human time. A community vision document submitted to the U. S. National Science Foundation.
-
Jessup M J, Law R D, Frassi C. 2007. The Rigid Grain Net (RGN): an alternative method for estimating mean kinematic vorticity number (Wm). Journal of Structural Geology, 29(3): 411~421.
-
Jiang D, Lin S, Williams P F. 2001. Deformation path in high-strain zones, with reference to slip partitioning in transpressional plate-boundary regions. Journal of Structural Geology, 23(6-7): 991~1005.
-
Jones R R, Holdsworth R E, Bailey W, 1997. Lateral extrusion in transpression zones: the importance of boundary conditions. Journal of Structural Geology, 19(9): 1201~1217.
-
Jones R R, Holdsworth R E, Clegg P, McCaffrey K, Tavarnelli E. 2004. Inclined transpression. Journal of Structural Geology, 26(8): 1531~1548.
-
Kruhl J H. 1998. Prism-and basal-plane parallel subgrain boundaries in quartz: a microstructural geothermobarometer. Journal of Metamorphic Geology, 16, 142~146.
-
Lai shaocong, Deng Jinfu, Zhao Hailing. 1996. Paleozoic ophiolites and its tectonic significance on north margin of Qaidam basin. Geoscience, (1): 19~22 (in Chinese with English abstract).
-
Law R D. 2014. Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures: a review. Journal of Structural Geology, 66: 129~161.
-
Li Xiucai, Niu Manlan, Yan Zhen, Da Liangchao, Han Yu, Wang Yusong. 2015. LP/HT metamorphic rocks in Wulan County, Qinghai Province: an Early Paleozoic paired metamorphic belt on the northern Qaidam basin? Chinese Science Bulletin, 60(35): 3501~3513 (in Chinese with English abstract).
-
Li Xiucai, Niu Manlan, Yakymchuk C, Wu Qi, Fu Changlei. 2019. A paired metamorphic belt in a subduction‐to‐collision orogen: an example from the South Qilian-North Qaidam orogenic belt, NW China. Journal of Metamorphic Geology, 37(4): 479~508.
-
Liao Fanxi, Zhang Lu, Chen Nengsong, Sun Min, Santosh M, Wang Qinyan, Mustafa H A. 2014. Geochronology and geochemistry of meta-mafic dykes in the Quanji Massif, NW China: Paleoproterozoic evolution of the Tarimcraton and implications for the assembly of the Columbia supercontinent. Precambrian Research, 249: 33~56.
-
Lister G S, Hobbs B E. 1980. The simulation of fabric development during plastic deformation and its application to quartzite: the influence of deformation history. Journal of Structural Geology, 2(3): 355~370.
-
Liu Liang, Wang Chao, Cao Yuting, Chen Danling, Kang Lei, Yang Wenqiang, Zhu Xiaohui. 2012. Geochronology of multi-stage metamorphic events: constraints on episodic zircon growth from the UHP eclogite in the South Altyn, NW China. Lithos, 136-139: 10~26.
-
Lu Songnian, Yu Haifeng, Jin Wei, Li Huaikun, Zheng Jiankang. 2002. Microcontinents on the eastern margin of Tarim paleocontinent. Acta Petrologica Et Mineralogica, 21(4): 317~326 (in Chinese with English abstract).
-
Lu Zenglong, Zhang Jianxin, Mao Xiaohong, Zhou Guisheng, Peng Yinbiao. 2017. Paleoproterozoic mafic granulite in the eastern Oulongbuluke block of the North Qaidam Mountains: evidence from petrology, zircon U-Pb dating and Hf isotope. Acta Petrologica Sinica, 33(12): 3815~3828 (in Chinese with English abstract).
-
Lu Zenglong, Zhang Jianxin, Mattinson C. 2018. Tectonic erosion related to continental subduction: an example from the eastern North Qaidam Mountains, NW China. Journal of Metamorphic Geology, 36(5): 653~666.
-
Lu Zenglong, Zhang Jianxin, Mao Xiaohong, Zhou Guisheng, Teng Xia, Wu Yawei. 2020. Ordovician adakite-Nb-enriched basalt suite in the eastern North Qaidam Mountains: implications for oceanic subduction and crustal accretion prior to deep continental subduction. Acta Petrologica Sinica, 36(10): 2995~3017 (in Chinese with English abstract).
-
Means W D. 1995. Shear zones and rock history. Tectonophysics, 247(1): 157~160.
-
Means W D, Hobbs B E, Lister G S, Williams P F. 1980. Vorticity and non-coaxiality in progressive deformations. Journal of Structural Geology, 2(3): 371~378.
-
Morgan S S, Law R D. 2004. Unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the Eurekavalley-Joshua Flat-Beer Creek pluton, California: a case for anhydrous conditions created by decarbonation reactions. Tectonophysics, 384(1-4): 209~231.
-
Niu Manlan, Cai Qianru, Li Xiucai, Yakymchuk C, Wu Qi, Yuan Xiaoyu, Sun Yi. 2021. Early Paleozoic tectonic transition from oceanic to continental subduction in the North Qaidam tectonic belt: constraints from geochronology and geochemistry of syncollisional magmatic rocks. Gondwana Research, 91: 58~80.
-
Ortolano G, Visalli R, Godard G, Cirrincione R. 2018. Quantitativex-ray map analyser (Q-XRMA): a new GIS-based statistical approach to mineral image analysis. Computers and Geosciences, 115: 56~65.
-
Ortolano G, Fazio E, Visalli R, Alsop G I, Pagano M, Cirrincione R. 2020. Quantitative microstructural analysis of mylonites formed during Alpine tectonics in the western Mediterranean realm. Journal of Structural Geology, 131: 103956.
-
Passchier C W. 1987. Stable positions of rigid objects in non-coaxial flow—a study in vorticity analysis. Journal of Structural Geology, 9(5): 679~690.
-
Passchier C W, Trouw R A. 2005. Microtectonics. Berlin: Springer.
-
Paterson M S, Luan F C. 1990. Quartzite rheology under geological conditions. Geological Society, London, Special Publications, 54(1): 299~307.
-
Qian Tao, Li Wangpeng, Gao Wanli, Jiang Wan. 2021. A preliminary study on post-orogenesis of the North Qaidam tectonic belt during the Early Paleozoic by provenance analysis of the Devonian sediments. Acta Geologica Sinica, 10. 19762/j. cnki. dizhixuebao. 2021280 (in Chinese with English abstract).
-
Ramsay J G. 1967. Folding and Fracturing of Rocks. New York: McGraw Hill.
-
Ramsay J G. 1980. Shear zone geometry: a review. Journal of Structural Geology, 2(1-2): 83~99.
-
Ramsay J G, Graham R H. 1970. Strain variation in shear belts. Canadian Journal of Earth Sciences, 7(3): 786~813.
-
Rutter E H, Brodie K H. 2004. Experimental grain size-sensitive flow of hot-pressed Brazilian quartz aggregates. Journal of Structural Geology, 26(11): 2011~2023.
-
Sanderson D J, Marchini W R D. 1984. Transpression. Journal of Structural Geology, 6(5): 449~458.
-
Shi Rendeng, Yang Jingsui, Wu Cailai, Tsuyoshi Iizuka, Takafumi Hirata. 2004. Island arc volcanic rocks in the North Qaidam UHP metamorphic belt. Acta Geologica Sinica, 50(1): 52~64 (in Chinese with English abstract).
-
Simpson C. 1985. Deformation of granitic rocks across the brittle-ductile transition. Journal of Structural Geology, 7(5): 503~511.
-
Simpson C, De Paor D G. 1993. Strain and kinematic analysis in general shear zones. Journal of Structural Geology, 15(1): 1~20.
-
Skemer P, Katayama I, Jiang Z, Karato S. 2005. The misorientation index: development of a new method for calculating the strength of lattice-preferred orientation. Tectonophysics, 411(1-4): 157~167.
-
Skrotzki W. 1992. Defect structure and deformation mechanisms in naturally deformed hornblende. Physica Status Solidi (a), 131(2): 605~624.
-
Song S G, Yang J S, Xu Z Q, Liou J G, Shi R D. 2003. Metamorphic evolution of the coesite-bearing ultrahigh-pressure terrane in the North Qaidam, Northern Tibet, NW China. Journal of Metamorphic Geology, 21(6): 631~644.
-
Song Shuguang, Zhang Lifei, Niu Yaoling, Su Li, Jian Ping, Liu Dunyi. 2005. Geochronology of diamond-bearing zircons from garnet peridotite in the North Qaidam UHPM belt, northern Tibetan Plateau: a record of complex histories from oceanic lithosphere subduction to continental collision. Earth and Planetary Science Letters, 234(1-2): 99~118.
-
Song Shuguang, Zhang Lifei, Niu Yaoling, Su Li, Song Biao, Liu Dunyi. 2006. Evolution from oceanic subduction to continental collision: a case study from the northern Tibetan Plateau based on geochemical and geochronological data. Journal of Petrology, 47(3): 435~455.
-
Song Shuguang, Niu Yaoling, Su Li, Zhang Cong, Zhang Lifei. 2014. Continental orogenesis from ocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: the example of the North Qaidam UHPM belt, NW China. Earth-Science Reviews, 129: 59~84.
-
Stipp M, Stünitz H, Heilbronner R, Schmid S M, 2002a. The eastern Tonale fault zone: a ‘natural laboratory’ for crystal plastic deformation of quartz over a temperature range from 250 to 700°C. Journal of Structural Geology, 24(12): 1861~1884.
-
Stipp M, Stünitz H, Heilbronner R, Schmid S M, 2002b. Dynamic recrystallization of quartz: correlation between natural and experimental conditions. Geological Society, London, Special Publications, 200(1): 171~190.
-
Stipp M, Tullis J. 2003. The recrystallized grain size piezometer for quartz. Geophysical Research Letters, 30(21): 2088.
-
Stipp M, Tullis J, Scherwath M, Behrmann J H. 2010. A new perspective on paleopiezometry: dynamically recrystallized grain size distributions indicate mechanism changes. Geology, 38(8): 759~762.
-
Sun Huashan, Li Huan, Algeo T J, Gabo‐Ratio J A S, Yang Hui, Wu Jinghua, Wu Pan. 2018. Geochronology and geochemistry of volcanic rocks from the Tanjianshan Group, NW China: implications for the early Palaeozoic tectonic evolution of the North Qaidam Orogen. Geological Journal, 54(3): 1769~1796.
-
Sun Jiaopeng, Dong Yunpeng, Ma Licheng, Peng Yuan, Chen Shiyue, Du Jianjun, Jiang Wan. 2019. Late Paleoproterozoic tectonic evolution of the Olongbuluke Terrane, northern Qaidam, China: constraints from stratigraphy and detrital zircon geochronology. Precambrian Research, 331: 105349.
-
Tikoff B, Fossen H. 1995. The limitations of three-dimensional kinematic vorticity analysis. Journal of Structural Geology, 17(12): 1771~1784.
-
Truesdell C. 1953. Twomeasures of vorticity. Indiana University Mathematics Journal, 2(2): 173~217.
-
Twiss R J. 1977. Theory andapplicability of a recrystallized grain size paleopiezometer. In Stress in the Earth, Contributions to Current Research in Geophysics: 227~244.
-
Visalli R. 2018. Innovative numerical petrological methods for definition of metamorphic time scale events of southern European variscan relicts via thermodynamic and diffusion modelling of zoned garnets. Plinius, (44): 99~109.
-
Wallis S R. 1992. Vorticity analysis in a metachert from the Sanbagawabelt, SW Japan. Journal of Structural Geology, 14(3): 271~280.
-
Wallis S. 1995. Vorticity analysis and recognition of ductile extension in the Sanbagawa belt, SW Japan. Journal of Structural Geology, 17(8): 1077~1093.
-
Wang Chunyu, Yu Shengyao, Sun Deyou, Lv Pei, Feng Zhao, Wang Guan, Gou Jun. 2021. Mesoproterozoic tectonic-thermal events in the Oulongbuluke block, NW China: constraints on the transition from supercontinent Columbia to Rodinia. Precambrian Research, 352: 106010.
-
Wang Huichu, Lu Songnian, Yuan Guibang, Xin Houtian, Zhang Baohua, Wang Qinghai, Tian Qi. 2003. Tectonic setting and age of the “Tanjianshan Group” on the northern margin of the Qaidam basin. Regional Geology of China, (7): 487~493 (in Chinese with English abstract).
-
Wang Huichu, Lu Songnian, Mo Xuanxue, Li Huaikun, Xin Houtian. 2005. An Early Paleozoic collisional orogen on the northern margin of the Qaidam basin, northwestern China. Regional Geology of China, (7): 603~612 (in Chinese with English abstract).
-
Wang Lu, Wang Heng, He Chuan, Chen Nengsong, Santosh M, Sun Min, Wang Qinyan, Jin Lanlan, Liao Fanxi. 2016. Mesoproterozoic continental breakup in NW China: evidence from gray gneisses from the North Wulan terrane. Precambrian Research, 281: 521~536.
-
Wang Qinyan, Dong Yanjun, Pan Yuanming, Liao Fanxi, Guo Xiaowei. 2018. Early Paleozoic granulite-Facies metamorphism and magmatism in the northern Wulan terrane of the Quanji massif: implications for the evolution of the Proto-Tethys ocean in northwestern China. Journal of Earth Science, 29(5): 1081~1101.
-
Wu Cailai, Wu Di, Mattinson C, Lei Min, Chen Hongjie. 2019. Petrogenesis of granitoids in the Wulan area: magmatic activity and tectonic evolution in the North Qaidam, NW China. Gondwana Research, 67: 147~171.
-
Xiao Wenjiao, Windley B F, Yong Yong, Yan Zhen, Yuan Chao, Liu Chuanzhou, Li Jiliang. 2009. Early Paleozoic to Devonian multiple-accretionary model for the Qilian Shan, NW China. Journal of Asian Earth Sciences, 35(3-4): 323~333.
-
Xiong Qing, Zheng Jianping, Griffin W L, O’Reilly S Y, Zhao Junhong. 2011. Zircons in the Shenglikou ultrahigh-pressure garnet peridotite massif and its country rocks from the North Qaidam terrane (western China): Meso-Neoproterozoic crust-mantle coupling and early Paleozoic convergent plate-margin processes. Precambrian Research, 187(1-2): 33~57.
-
Xiong Qing, Zheng Jianping, Griffin W L, O’Reilly S Y, Pearson N J. 2012. Decoupling of U-Pb and Lu-Hf isotopes and trace elements in zircon from the UHP North Qaidam orogen, NE Tibet (China): tracing the deep subduction of continental blocks. Lithos, 155: 125~145.
-
Xu Zhiqin, Li Haibing, Chen Wen, Wu Cailai, Yang Jingsui, Ji Xiaochi, Cheng Fangyuan. 2002. Alarge ductile sinistral strike-slip shear zone and its movement timing in the south Qilian Mountains, western China. Acta Geologica Sinica (English Edition), 76(2): 183~193.
-
Xu Zhiqin, Yang Jingsui, Wu Cailai, Li Haibing, Zhang Jianxin, Qi Xuexiang, Song Shuguang, Qiu Haijun. 2006. Timing and mechanism of formation and exhumation of the northern Qaidam ultrahigh-pressure metamorphic belt. Journal of Asian Earth Sciences Journal of Asian Earth Sciences, 28(2-3): 160~173.
-
Xu Zhiqin, Wang Qin, Liang Fenghua, Chen Fangyuan, Xu Cuiping. 2009. Electron backscatter diffraction (EBSD) technique and its application to study of continental dynamics. Acta Petrologica Sinica, 25(7): 1721~1736 (in Chinese with English abstract).
-
Xypolias P. 2009. Some new aspects of kinematic vorticity analysis in naturally deformed quartzites. Journal of Structural Geology, 31(1): 3~10.
-
Xypolias P. 2010. Vorticity analysis in shear zones: a review of methods and applications. Journal of Structural Geology, 32(12): 2072~2092.
-
Xypolias P, Koukouvelas I K. 2001. Kinematic vorticity and strain rate patterns associated with ductile extrusion in the Chelmos Shear Zone (external Hellenides, Greece). Tectonophysics, 338(1): 59~77.
-
Yang Jingsui, Xu Zhiqin, Song Shuguang, Zhang Jianxin, Wu Cailai, Shi Rendeng, Li Haibing, Brunel M. 2001. Discovery of coesite in the North Qaidam Early Palaeozoic ultrahigh pressure (UHP) metamorphic belt, NW China. Earth and Planetary Science, 333(11): 719~724.
-
Yang Zhangzhang, Sun Jian, Zhao Xinke, Tian Zhen, Zhao Zhenying, Sun Dongliang, Li Dalei, Yang Benzhao, Yang Qiangsheng. 2017. LA-ICP-MS U-Pb age of the zircons from the volcanic rocks in Maoniushan Formation in Shidiquan area, Delingha, Qinghai, and its geological significance. Geological Review, 63(6): 1613~1623 (in Chinese with English abstract).
-
Yu Shengyao, Zhang Jianxin, Del Real P G. 2012. Geochemistry and zircon U-Pb ages of adakitic rocks from the Dulan area of the North Qaidam UHP terrane, north Tibet: constraints on the timing and nature of regional tectonothermal events associated with collisional orogeny. Gondwana Research, 21(1): 167~179.
-
Yu Shengyao, Li Sanzhong, Zhang Jianxin, Liu Yongjiang, Peng Yinbiao, Sun Deyou, Li Yunshuai. 2019. Grenvillian orogeny in the Oulongbuluke block, NW China: constraints from an ~1. 1 Ga Andean-type arc magmatism and metamorphism. Precambrian Research, 320: 424~437.
-
Yuan Guibang, Wang Huichu, Li Huiming, Hao Guojie, Xin Houtian, Zhang Baohua, Wang Qinghai, Tian Qi. 2002. Zircon U-Pb age of the Gabbros in Luliangshan area on the northern margin of Qaidam basin and its geological implication. Progress In Precambrian Research, (1): 36~38 (in Chinese with English abstract).
-
Yund R A, Tullis J. 1991. Compositional changes of minerals associated with dynamic recrystallizatin. Contributions to Mineralogy and Petrology, 108(3): 346~355.
-
Zhang Chunyu, Zhao Yue, Liu Jin, Dai Kun, Zheng Ce. 2019. Provenance analysis of the Maoniushan Formation in the North Qaidam basin and its tectonic significance. Acta Geologica Sinica, 93(3): 712~723 (in Chinese with English abstract).
-
Zhang Jianxin, Yang Jingsui, Mattinson C G, Xu Zhiqin, Meng Fancong, Shi Rendeng. 2005. Two contrasting eclogite cooling histories, North Qaidam HP/UHP terrane, western China: petrological and isotopic constraints. Lithos, 84(1-2): 51~76.
-
Zhang Jianxin, Mattinson C G, Meng Fancong, Wan Yusheng, Tung Kuoan. 2008. Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: evidence from zircon U-Pb geochronology. Geological Society of America Bulletin, 120(5-6): 732~749.
-
Zhang Jianxin, Mattinson C G, Meng Fancong, Yang Huaijen, Wan Yusheng. 2009. U-Pb geochronology of paragneisses and metabasite in the Xitieshan area, north Qaidam Mountains, western China: constraints on the exhumation of HP/UHP metamorphic rocks. Journal of Asian Earth Sciences, 35(3-4): 245~258.
-
Zhang J X, Mattinson C G, Yu S Y, Li J P, Meng F C. 2010. U-Pb zircon geochronology of coesite-bearing eclogites from the southern Dulan area of the North Qaidam UHP terrane, northwestern China: spatially and temporally extensive UHP metamorphism during continental subduction: extensive UHP metamorphism in North Qaidam. Journal of Metamorphic Geology, 28(9): 955~978.
-
Zhang Jianxin, Li Huaikun, Meng Fancong, Xiang Zhenqun, Yu Shengyao, Li Jinping. 2011. Polyphase tectonothermal events recorded in “metamorphic basement” from the Altyn Tagh, the southeastern margin of the Tarim basin, western China: constraint from U-Pb zircon geochronology. Acta Petrologica Sinica, 27 (1): 23~46 (in Chinese with English abstract).
-
Zhang Jianxin, Yu Shengyao, Li Yunshuai, Yu Xingxing, Lin Yihui, Mao Xiaohong. 2015. Subduction, accretion and closure of Proto-Tethyan ocean: early Paleozoic accretion/collision orogeny in the Altun-Qilian-North Qaidam orogenic system. Acta Petrologica Sinica, 31 (12): 3531~3554 (in Chinese with English abstract).
-
Zhang Jianxin, Mattinson C, Yu Shengyao, Li Yunshuai, Yu Xingxing, Mao Xiaohong, Lu Zenglong, Peng Yingbao. 2019. Two contrasting accretion v. collision orogenies: insights from Early Paleozoic polyphase metamorphism in the Altun-Qilian-North Qaidam orogenic system, NW China. Geological Society, London, Special Publications, 474(1): 153~181.
-
Zhang Jianxin, Lu Zenglong, Mao Xiaohong, Teng Xia, Zhou Guisheng, Wu Yawei, Guo Qi. 2021. Revisiting the Precambrian micro-continental blocks within the Early Paleozoic orogenic system of the northeastern Qinghai-Tibet Plateau: insight into the origin of ProtoTethyan ocean. Acta Petrologica Sinica, 37(1): 74~102 (in Chinese with English abstract).
-
Zhang J, Zheng Y. 1997. Polar Mohr constructions for strain analysis in general shear zones. Journal of Structural Geology, 19(5): 745~748.
-
Zheng Yadong, Wang Tao, Zhang Jinjiang. 2008. Theory and practice of kinematic vorticity (Wk). Earth Science Frontiers, (3): 209~220 (in Chinese with English abstract).
-
Zhu Xiaohui, Chen Danling, Liu Liang, Wang Chao, Yang Wenqiang, Cao Yuting, Kang Lei. 2012. Chronology and geochemistry of the mafic rocks in Xitieshan area, North Qaidam. Geological Bulletin of China, 31(12): 2079~2089 (in Chinese with English abstract).
-
Zhu Xiaohui, Chne Danling, Liu Liang, Zhao Jiao, Zhang Le. 2014. Geochronology, geochemistry and significance of the Early Paleozoic back-arc type ophiolite in Lvliangshan area, North Qaidam. Acta Petrologica Sinica, 30(3): 822~834 (in Chinese with English abstract).
-
付建刚, 梁新权, 王策, 蒋英, 周云, 潘传楚, 杨永强, 王泽利, 钟永生. 2016. 柴北缘锡铁山韧性剪切带的基本特征及其形成时代. 大地构造与成矿学, 40(1): 14~28.
-
高晓峰, 校培喜, 贾群子. 2011. 滩间山群的重新厘定——来自柴达木盆地周缘玄武岩年代学和地球化学证据. 地质学报, 85(9): 1452~1463.
-
赖绍聪, 邓晋福, 赵海玲. 1996. 柴达木北缘古生代蛇绿岩及其构造意义. 现代地质, (1): 19~22.
-
李秀财, 牛漫兰, 闫臻, 笪梁超, 韩雨, 王玉松. 2015. 青海省乌兰县早古生代低压高温变质岩: 柴北缘存在双变质带? 科学通报, 60(35): 3501~3513.
-
陆松年, 于海峰, 金巍, 李怀坤, 郑健康. 2002. 塔里木古大陆东缘的微大陆块体群. 岩石矿物学杂志, 21(4): 317~326.
-
路增龙, 张建新, 毛小红, 周桂生, 彭银彪. 2017. 柴北缘欧龙布鲁克地块东段古元古代基性麻粒岩: 岩石学、锆石U-Pb年代学和Lu-Hf同位素证据. 岩石学报, 33(12): 3815~3828.
-
路增龙, 张建新, 毛小红, 周桂生, 滕霞, 武亚威. 2020. 柴北缘东段奥陶纪埃达克岩-富Nb玄武岩: 对大陆深俯冲之前大洋俯冲及地壳增生的启示. 岩石学报, 36(10): 2995~3017.
-
钱涛, 李王鹏, 高万里, 江万. 2021. 柴北缘构造带早古生代造山后作用初探: 泥盆纪沉积物物源示踪. 地质学报, 10. 19762/j. cnki. dizhixuebao. 2021280.
-
史仁灯, 杨经绥, 吴才来, Tsuyoshi Iizuka, Takafumi Hirata. 2004. 柴达木北缘超高压变质带中的岛弧火山岩. 地质学报, 50(1): 52~64.
-
汪集旸, 胡圣标, 杨文采, 程本合, 程振炎, 李铁军. 2001. 中国大陆科学钻探先导孔地热测量. 科学通报, (10): 847~850.
-
王惠初, 陆松年, 袁桂邦, 辛后田, 张宝华. 2003. 柴达木盆地北缘滩间山群的构造属性及形成时代. 地质通报, (7): 487~493.
-
王惠初, 陆松年, 莫宣学, 李怀坤, 辛后田. 2005. 柴达木盆地北缘早古生代碰撞造山系统. 地质通报, (7): 603~612.
-
许志琴, 王勤, 梁凤华, 陈方远, 许翠萍. 2009. 电子背散射衍射(EBSD)技术在大陆动力学研究中的应用. 岩石学报, 25(7): 1721~1736.
-
杨张张, 孙健, 赵新科, 田振, 赵振英, 孙东亮, 李大磊, 杨本昭, 杨强晟. 2017. 青海德令哈石底泉地区牦牛山组火山岩LA-ICP-MS锆石U-Pb年龄及地质意义. 地质论评, 63(6): 1613~1623.
-
袁桂邦, 王惠初, 李惠民, 郝国杰, 辛后田, 张宝华, 王青海, 田琪. 2002. 柴北缘绿梁山地区辉长岩的锆石U-Pb年龄及意义. 前寒武纪研究进展, (1): 36~38.
-
张春宇, 赵越, 刘金, 代昆, 郑策. 2019. 柴达木盆地北缘牦牛山组物源分析及其构造意义. 地质学报, 93(3): 712~723.
-
张建新, 李怀坤, 孟繁聪, 相振群, 于胜尧, 李金平. 2011. 塔里木盆地东南缘(阿尔金山)“变质基底”记录的多期构造热事件: 锆石U-Pb年代学的制约. 岩石学报, 27(1): 23~46.
-
张建新, 于胜尧, 李云帅, 喻星星, 林宜慧, 毛小红. 2015. 原特提斯洋的俯冲、增生及闭合: 阿尔金-祁连-柴北缘造山系早古生代增生/碰撞造山作用. 岩石学报, 31(12): 3531~3554.
-
张建新, 路增龙, 毛小红, 滕霞, 周桂生, 武亚威, 郭祺. 2021. 青藏高原东北缘早古生代造山系中前寒武纪微陆块的再认识——兼谈原特提斯洋的起源. 岩石学报, 37(1): 74~102.
-
郑亚东, 王涛, 张进江. 2008. 运动学涡度的理论与实践. 地学前缘, (3): 209~220.
-
朱小辉, 陈丹玲, 刘良, 王超, 杨文强, 曹玉亭, 康磊. 2012. 柴北缘锡铁山地区镁铁质岩石的时代及地球化学特征. 地质通报, 31(12): 2079~2089.
-
朱小辉, 陈丹玲, 刘良, 赵姣, 张乐. 2014. 柴北缘绿梁山地区早古生代弧后盆地型蛇绿岩的年代学、地球化学及大地构造意义. 岩石学报, 30(3): 822~834.
-
摘要
转换挤压剪切带普遍发育在汇聚板块边界及碰撞造山带中,对调节造山过程中的增生、碰撞及物质侧向挤出等起重要作用。位于青藏高原东北缘的柴达木盆地北缘构造带(柴北缘构造带)被认为是早古生代原特提斯洋闭合、大陆深俯冲、陆-陆碰撞和造山后伸展垮塌作用的产物。最近,在柴北缘构造带东段乌兰北部察汗河地区,笔者新厘定出NWW—SEE向展布的右行转换挤压韧性剪切带。本文通过对该剪切带内宏微观构造特征、石英c轴组构、运动学涡度等研究,结合锆石U-Pb年代学数据,来探该讨剪切带的转换挤压样式及对柴达木盆地北缘早古生代造山作用的启示意义。察汗河韧性剪切带内X-Z面上发育的宏微观构造以及石英c轴组构共同指示了右行走滑剪切指向,结合糜棱岩的轻微压扁—压扁的应变椭球体形态,共同指示了其具有转换挤压的构造性质;估算的平均运动学涡度限定了其转换挤压变形样式。根据石英颗粒的重结晶机制、c轴组构滑移系以及其开角温度计,确定其变形温度为500~553℃,指示了中地壳变形层次,并结合剪切带内石英动态重结晶颗粒大小,估算其差异应力为28.5~30.0 MPa,古应变速率为10-12/s。通过锆石U-Pb定年,获得卷入韧性剪切变形的闪长岩时代为432±3 Ma,结合柴达木盆地北缘已有区域地质资料,推断韧性剪切作用的活动时代为中志留世—早泥盆世(432~396 Ma)。以上资料显示,察汗河韧性剪切带表现出垂直于造山带的水平收缩和平行于造山带的侧向挤出的构造变形样式,伴随着部分由北向南的逆冲分量,形成于柴达木盆地北缘早古生代晚期的碰撞造山阶段,并指示了其造山作用具有斜向汇聚及碰撞特征。
Abstract
The transpressional shear zone, commonly recognized in the convergence plate margins and collision orogens, has played a significant role for accommodating accretion, collision lateral extrusion parallel to orogens. The North Qaidam tectonic belt, which is located in northern Tibet, was regarded as resulting from closure of Proto-Tethys, continental deep subduction and post-orogenic extension collapse during early Paleozoic era. Recently, an NWW—SEE trending dextral transpression ductile shear zone was newly recognized in the Chahanhe area, eastern North Qaidam Mountains. In this contribution, we present macro-microstructural observations, quartz C-axis fabric analyses, quantitative structural data (including kinematic vorticity, paleo-stress and strain rate), and combine with zircon U-Pb dating data, to investigate the type of the transpression of the ductile shear zone and discuss its tectonic evolution. The macro-to micro-structural feature and quartz C-axis fabric in X-Z planes show that the Chahanhe ductile shear zone is characterized by dextral strike-slip shear sense. Finite strain and kinematic vorticity in deformed rocks indicate a slightly prolate ellipsoid near plane strain, suggesting a transpressional style. Mineral recrystallization mechanism, quartz c-axis fabrics slip system and opening-angle thermometer reveal that the Chahanhe ductile shear zone developed under 500 to 553 ℃, corresponding to a mid-crust level (16~18 km). Combining with dynamic recrystallization particle size of quartz, the differential stress and strain rate were estimated to be 29~30 MPa and 10-12/s, respectively. Zircon U-Pb dating of diorite involved in ductile shearing gave an age of 432±3 Ma. Combining with previously geological data suggests the timing of the ductile shearing deformation between middle Silurian and early Devonian (432~396 Ma). The integrated data indicate that the Chahanhe ductile shear zone is characterized by combination of horizontal contraction perpendicular to the orogenic belt and lateral extrusion parallel to the orogenic belt, accompanied by a part of top-to-the south thrust component, resulted from oblique convergence and collision during late early Paleozoic orogeny.
