南秦岭佛坪隆起的成因探讨——构造解析的证据

通过对佛坪隆起基底及其周围地区构造面理和线理的系统测量和统计,恢复其古应力场,揭示区域构造应力场的分布规律,进而探讨佛坪隆起的成因机制。研究结果表明,佛坪隆起主体及其北部龙草坪隆起区外围地层中的构造片理呈外倾的封闭环状展布,结合古构造应力场分析,证明佛坪基底抬升主要生成于穹状隆起,这种穹状隆升与该区岩浆侵入活动密切相关。综合区域构造解析与古应力场分析表明,佛坪穹隆是在早期近垂向的穹状隆升的基础上,叠加了后期南北向挤压构造才奠定了其基本构造面貌。     

佛坪自然保护区植物群落物种多样性与海拔梯度的关系

用多元统计分析方法研究了佛坪自然保护区植物群落多种性及群落各生长型多样性特征沿海拔梯度的变化。结果表明：1）植物群落的Shannon指数与Simpson指数及物种丰富度与海拔梯度均呈显著负相关关系;2）乔木层的物种多样性沿海拔梯度的变化则体现了“中国高度膨胀”的规律,即中等海拔高度上多样性高而低海拔和高海拔多样性较低;3）灌木层丰富度指数在1600-1700m之间有个很不明显的峰值,而其它4个指标沿海拔呈单调的下降趋势;4）草本层植物多样性呈先降后升的趋势,在中等海拔高度较低。     

论秦岭佛坪地区隆-滑构造

由基底片麻岩（内核）、剥离断层（接合面）及滑覆层状岩系（外壳）构成的佛坪穹隆构造,从其岩石组成、早期的运动学特征、变质变形改造和同位素测年资料综合分析,表明佛坪穹隆可能形成于印支期的主造山期前,并受印支期主造山期褶皱变形和燕山期逆冲、走滑作用的叠加改造。它经历了中元古代—前印支期隆－滑构造形成阶段,而与造山后期变质核杂岩明显不同,在造山带构造演化中具有重要意义。隆－滑构造发生的深部背景是造山带岩石圈垂向加积增生作用。该穹隆突出而重要地参与了秦岭造山带的形成与演化,具有重要的大陆动力学意义。     

南秦岭佛坪麻粒岩的矿物学和地球化学特征及其构造意义

采用电子探针、红外光谱和全岩化学分析方法,对佛坪麻粒岩开展了系统的矿物学和地球化学研究。研究结果表明本区麻粒岩以酸性岩为主,主要组成矿物为长石、石英、石榴子石、紫苏辉石及少量的黑云母和钙质角闪石。岩石富集轻稀土和大离子亲石元素,亏损高场强元素,具有强烈的Nb、Ta负异常,表明源岩在成因上与洋壳的俯冲消减作用有关。结合区域地质和测年资料,我们认为佛坪麻粒岩源岩的形成与勉略古洋壳向南秦岭地块之下的俯冲有关,是中—晚三叠世南秦岭与扬子地块的陆-陆碰撞所导致的麻粒岩相变质作用的产物。     

Structural Characteristics and Formation Mechanism in the Micangshan Foreland,South China

Lying at the junction of the Dabashan, Longmenshan and Qinling mountains, the Micangshan Orogenic Belt coupled with a basin is a duplex structure and back-thrust triangular belt with little horizontal displacement, small thrust faults and continuous sedimentary cover. On the basis of 3D seismic data, and through sedimentary and structural research, the Micangshan foreland can be divided into five subbelts, which from north to south are: basement thrust, frontal thrust, foreland depression-back-thrust triangle, foreland fold belt or anticline belt, and the Tongjiang Depression. Along the direction of strike from west to east, the arcuate structural belt of Micangshan can be divided into west, middle and east segments. During the collision between the Qinling and Yangtze plates, the Micangshan Orogenic Belt was subjected to the interaction of three rigid terranes: Bikou, Foping, and Fenghuangshan (a.k.a. Ziyang) terranes. The collision processes of rigid terranes controlled the structural development of the Micangshan foreland, which are: (a) the former collision between the Micangshan-Hannan and Bikou terranes forming the earlier rudiments of the structure; and (b) the later collision forming the main body of the structural belt. The formation processes of the Micangshan Orogenic Belt can be divided into four stages: (1) in the early stage of the Indosinian movement, the Micangshan-Hannan Rigid Terrane was jointed to the Qinling Plate by the clockwise subduction of the Yangtze Plate toward the Qinling Plate; (2) since the late Triassic, the earlier rudiments of the Tongnanba and Jiulongshan anticlines and corresponding syncline were formed by compression from different directions of the Bikou, Foping and Micangshan-Hannan terranes; (3) in the early stage of the Himalayan movement, the Micangshan-Hannan Terrane formed the Micangshan Nappe torwards the foreland basin and the compression stresses were mainly concentrated along both its flanks, whereas the Micangshan-Hannan Terrane wedged into the Qinling Orogenic Belt with force; (4) in the late stage of the Himalayan movement, the main collision of the Qinling Plate made the old basement rocks of the terrane uplift quickly, to form the Micangshan Orogenic Belt. The Micangshan foreland arcuate structure was formed due to the non-homogeneity of terrane movement.     

南秦岭佛坪地区地层格架与物源分析:变质沉积岩中碎屑锆石LA-ICP-MS U-Pb定年提供的制约

南秦岭佛坪地区位于东西秦岭交汇部位,以前寒武纪基底穹状隆升为主要特征,因其特殊的构造位置和变质变形特征而受到广泛关注。为了更好地揭示南秦岭构造带的性质及其在秦岭造山带构造演化中的作用,本文对佛坪地区的前寒武纪基底和沉积盖层进行了系统的碎屑锆石LA-ICP-MS U-Pb年代学研究。佛坪穹隆核部前寒武纪基底中碎屑锆石主要年龄峰值为600~820Ma、2021Ma和2467Ma,其中3个样品给出最年轻的年龄区间约为615~728Ma,沉积时代不早于新元古代,另外1个样品给出的最年轻的年龄峰值为1113Ma,沉积时代不早于中元古代,否定了关于认为其为太古代或古元古代的变质结晶基底的认识,其碎屑物质可能来源于南秦岭构造带和扬子陆块北缘。佛坪穹隆上覆盖层和外围南侧盖层给出了相似的年龄图谱,主要年龄峰值为410～450Ma、650～880Ma和910～950Ma,其中最年轻的年龄区间为344～416Ma,表明其沉积时代晚于泥盆纪,碎屑物质来源为北秦岭构造带和南秦岭构造带。上述研究结果表明,南秦岭构造带(前寒武纪基底)于新元古代已增生为扬子陆块北缘的重要组成部分,于晚古生代(泥盆纪)紧邻华北-北秦岭构造带南缘,并共同为南秦岭大面积的泥盆纪盆地提供碎屑物质。     

秦岭佛坪变质结晶岩系年龄和物质组成特征——SHRIMP锆英石U-Pb年代学和全岩Sm-Nd年代学数据

秦岭是长期多阶段发展的复杂大陆碰撞造山带。本文报道了位于造山带中部佛坪变质结晶杂岩系的SHRIMP锆英石U-Pb年龄和全岩Sm-Nd年龄同位素分析结果。变质岩SHRIMP锆英石U-Pb年龄十分复杂，除有少量太古宇形成的锆英石外，还存在大量元古宇至显生宇的锆英石。并在2000Ma，1200Ma，800Ma，400Ma，200Ma左右形成峰期。片麻岩Nd模式年龄tDM 1372～2081Ma。佛坪变质结晶岩系主体可能形成于古元古代，年龄2000Ma左右。在后期强烈地质作用中有少量地幔物质加入。岩系形成于新太古代的意见笔者没有得到证实。秦岭造山带中部可能存在或存在过太古宙结晶基底岩石。     

Structural Characteristics and Formation Mechanism in the Micangshan Foreland,South China

Lying at the junction of the Dabashan,Longmenshan and Qinling mountains,the Micangshan Orogenic Belt coupled with a basin is a duplex structure and back-thrust triangular belt with little horizontal displacement,small thrust faults and continuous sedimentary cover.On the basis of 3D seismic data,and through sedimentary and structural research,the Micangshan foreland can be divided into five subbelts,which from north to south are:basement thrust,frontal thrust,foreland depression-back-thrust triangle,fore...     

佛坪地区中元古代孔兹岩系地质特征

根据佛坪地区广泛出露的一套副变质岩系的岩石组合、矿物组合、变质相特征和岩石地球化学特征的分析,认为它们是一套中深变质的碎屑岩－泥质岩－碳酸盐岩建造。原岩形成于相对稳定的大陆边缘－微板块内的陆表海环境。经过角闪岩相区域变质作用,形成了佛坪地区较为完整的孔兹岩系