Structure of the Wollaston Lake Reflector (Trans-Hudson Orogen, Canada) from reflection AVO analysis: Fractured diabase intrusion, fluids, or silicified shear zone?     

Jinfeng Ma  Igor B. Morozov   《Tectonophysics》2007,441(1-4):97-114

A nearly 160-km long Wollaston Lake Reflector (WLR) observed in seismic reflection profile S2b of the 1994 Lithoprobe Trans-Hudson Orogen transect (THOT) in northern Saskatchewan (Canada) is among the most spectacular and well-recorded features imaged within the crystalline crust. Based on modeling of its normal-incidence reflectivity, the observed bright spot reflector was originally interpreted as a series of tabular diabase intrusions. In order to further elucidate its structure, we reprocessed line S2b and analysed the WLR for the Amplitude Variations with Offset (AVO). By contrast to conventional (approximate) AVO analysis, we used the exact Zoeppritz equations and considered a thin-layer (mixed positive and negative polarities) reflectivity. The results suggest two possible interpretations of the WLR: 1) the reflector caused by a massive mafic intrusion as suggested earlier, in which case the intruded rocks should have anomalous Poisson's ratios of σ ≥ 0.33, and 2) the WLR represents a silicified shear zone, with only moderate (e.g.,  5–10%) alteration of the host rock and σ ≈ 0.2. Although both of these models may to some extent co-exist within the WLR, its brightness, sharpness, great lateral extent and smooth shape favour the second interpretation.In both models, a fractured fluid-filled zone within a major crustal detachment should have played a key role in the formation of the WLR. The association of the reflector with laterally- and depth-migrating fluids is also supported by magneto-telluric measurements of crustal conductivity beneath the WLR. Analogies from the studies of the Kola Superdeep Borehole (Russia), where free or metamorphic fluids were found at comparable depths, also suggest that fluids may contribute to WLR structure and formation.  相似文献   

河南省济源盆地下侏罗统鞍腰组重力流沉积特征及其构造意义^*          下载免费PDF全文

杨文涛  吴蒙  杨旅涵  史飞  梁厅 《古地理学报》2017,19(3):433-444

在详细野外剖面工作的基础上,通过岩性特征、沉积构造及沉积序列等的系统观察研究,发现济源盆地下侏罗统鞍腰组重力流沉积由滑塌沉积、砂质碎屑流沉积和浊流沉积构成。滑塌沉积以砂岩和泥岩的混杂、岩层的滑动变形以及泥岩呈碎块被卷入砂岩层中为特征;砂质碎屑流沉积常呈厚层块状,颗粒分选和磨圆较差,杂基较多,可见漂浮于层内的石灰岩砾石;常见的浊流沉积分为2种类型: 具有明显正粒序结构的浊流沉积和砂泥岩薄互层的浊流沉积,可用鲍马序列来描述。鞍腰组重力流沉积可划分为3个沉积序列: 序列A记录了滑塌沉积→砂质碎屑流沉积→浊流沉积→深湖沉积的转换过程;序列B表现为砂质碎屑流与浊流沉积的叠覆;序列C由浊流及湖泊沉积构成,并经历了由序列A→序列B→序列C的沉积演化过程。重力流的形成受秦岭造山带于早侏罗世沿三门峡—鲁山—舞阳断裂发生逆冲推覆作用的控制,其沉积演化指示了秦岭造山带造山作用由强到弱的过程。  相似文献   

秦祁结合部位宝鸡地区早泥盆世香泉A型正长花岗岩年龄、地球化学特征及其构造意义     

徐通  陈清敏  郭岐明  张拴厚  毛友亮  王强 《地质通报》2017,36(7):1118-1128

对秦祁结合部位宝鸡地区香泉正长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究。结果显示,锆石~(206)Pb/~(238)Pb年龄加权平均值为410±5Ma(MSWD=0.20,n=18),限定该岩体的形成时代为早泥盆世。香泉正长花岗岩具有高硅(SiO_2=69.63%~73.94%)、富钾(K_2O=4.24%~4.88%,K_2O/Na_2O=1.23~1.44)、富铁(TFe_2O_3=2.10%~3.70%,TFe_2O_3/MgO=3.88~6.84)、低镁(MgO=0.31%~0.94%)、低磷(P_2O_5=0.08%~0.21%)的特征,属准铝质、高钾钙碱性系列。香泉正长花岗岩稀土元素含量较高(318×10~(-6)~499×10~(-6)),表现出明显的负Eu异常(δ Eu=0.37~0.46),富集Rb、Th、Zr、Sm、Ga(10000×Ga/Al=2.59~2.93)等微量元素,贫Ba、Nb、Ta、Sr,整体表现出A型花岗岩特征。结合区域资料认为,香泉正长花岗岩形成于造山后环境,为低压环境下长英质地壳物质部分熔融成因。  相似文献   

江南-雪峰隆起北缘海相油气富集主控因素和破坏机制     

邓大飞  梅廉夫  沈传波  刘昭茜  汤济广  凡元芳 《吉林大学学报(地球科学版)》2014,44(5):1466-1477

全球油气巨量富集带主要发育于被动大陆边缘、活动大陆边缘及大陆裂谷系中,而江南-雪峰隆起北缘具有区别于这3类的陆内坳陷斜坡带和古隆起边缘斜坡带的大地构造背景。通过对江南-雪峰隆起北缘（扬子南缘）海相油气陆内巨量富集的主控因素和破坏机制的研究,对比全球油气聚集带（区）发育的主要原因,试图建立海相油气富集和破坏的相关模式。类似于江南-雪峰隆起北缘的陆内坳陷斜坡带与古隆起边缘斜坡带的叠合斜坡带,是大陆块体内一种新的油气富集单元。通过研究,认为下寒武统和下志留统两套优质烃源岩、加里东旋回中-晚期和晚印支期-早燕山旋回早期两期良好的成藏时空匹配关系是海相油气富集的主控因素,而加里东旋回末期和晚印支期-早燕山旋回晚期两个关键破坏期,通过隆升剥蚀、断裂开启和岩浆活动等方式导致了海相油气的破坏。时空匹配的叠合斜坡带既是油气聚集的有利场所,又是油气改造的活跃区域。  相似文献   

造山动力学定量研究--理论与方法     

刘洁  刘启元  宋惠珍  童晓光 《地球科学进展》2005,20(5):533-540

造山动力学定量研究近10年来取得了重要进展,形成了较完整的理论技术体系,并获得了大量有说服力的实例分析结果,成为当前大陆变形研究的热点之一。造山动力学定量研究采用数值方法求解控制方程,获得造山带演化动态过程的图像,了解不同因素对该过程的影响作用,从力学解析的角度确定造山动力学模型的合理性。研究造山演化过程需要耦合固体力学、流体力学和热力学方程进行描述。造山演化过程中发生的强烈大位移、大应变（几何非线性）使得数值求解过程更复杂。对于强烈大应变可能需要采用重分网格技术。断裂的发生、运动与变形涉及岩石破裂准则与内部边界处理。同时,还必须综合分析地表剥蚀与沉积、重力均衡等作用。  相似文献   

Granitoids of the Ufalei block (South Urals): Sr-Nd isotope systematics, geodynamic position and genetic reconstructions     

Yu. L. Ronkin  G. Yu. Shardakova  A. V. Maslov  E. S. Shagalov  O. P. Lepikhina 《Stratigraphy and Geological Correlation》2009,17(2):137-145

Petrogeochemical and isotopic-geochronological signatures in granitoids developed in structures with complex geological history represent an important feature for reconstructing paleogeodynamic settings. Granitoids are widespread in the western slope of the Urals, where the Uralian Orogen contacts via a collage of different-age blocks of the east European Platform. The Ufalei block located in the Central Urals megazone at the junction between the South and Middle Urals’ segments represents one such boundary structure with multistage geological evolution. The isotopic ages obtained by different methods for acid igneous rocks range from 1290 to 245 Ma. We determined close Rb-Sr and Sm-Nd ages (317 Ma) for granites of the Nizhnii Ufalei Massif. By their petrochemical parameters, granitoids and host granite-gneisses differ principally from each other: the former are close to subduction-related, while the latter, to continental-riftogenic varieties. The primary ratio (⁸⁷Sr/8⁶Sr)₀ = 0.70428 and ?_Nd ≈ +4 values indicate significant contribution of oceanic (island-arc?) material to the substrate, which served as a source for granites of the Nizhnii Ufalei Massif. Model Nd ages of granites vary from 641 to 550 Ma. Distinct oceanic rocks and varieties with such ages are missing from the surrounding structures. New isotopic dates obtained for ultramafic and mafic rocks from different zones of the Urals related to the Cadomian cycle imply development of unexposed Upper Riphean-Vendian “oceanic” rocks in the central part of the Ufalei block, which played a substantial role in the formation of the Nizhnii Ufalei granitoids. Such rocks could be represented, for example, by fragments of the Precambrian Timanide-type ophiolite association. The analysis of original materials combined with published data point to the heterogeneous composition and structure of the Ufalei block and a significant part of the western segment of the Central Uralian Uplift and extremely complex geological history of the region coupling the Uralian Orogen with the East European Platform in the present-day structure.  相似文献   

江南古陆变质基底地层年代的修正和武陵运动构造意义   总被引：1，自引：0，他引：1  

高林志  丁孝忠  张传恒  陆松年  刘燕学  庞维华 《火山地质与矿产》2012,(2):71-76

江南古陆变质基底的研究中,最突出的基础地质问题依然是地层年代的精确标定。地层年代标定涉及到成矿地层的划分和对比及其构造演化的时限,也直接影响层控矿床找矿中涉及的基础地质问题。在最新的中国地层年表中,前寒武纪地层对比和构造背景解释已发生重大变化。本文依据扬子块体和华夏块体新元古代地层中最新的系列锆石U—Pb测年结果,初步揭示“江南古陆”变质基底地层火山事件和分布范围。结合全球格林威尔造山运动基本特征,对江南古陆变质基底地层年代的修正将有利于重新厘定江南造山带的成矿背景,提供层控矿床基础年代地层资料,为新的矿产资源大调查服务。  相似文献   

北祁连山银灿铜矿矿床地质特征及成因   总被引：2，自引：2，他引：0       下载免费PDF全文

郭周平  赵辛敏  白赟 《中国地质调查》2015,2(3):54-58

银灿铜矿地处于北祁连走廊南山北坡—冷龙岭岛弧带中,矿区出露一套具双峰式火山岩特征的火山沉积建造,矿体主要赋存在石英角斑岩中并存在明显分带,上部为铜矿体向下部变为锌矿体,矿石类型属黄铁矿型多金属矿石,成矿作用过程直接或间接与火山活动有关,是北祁连地区早古生代典型的海相火山岩型块状硫化物矿床。  相似文献   

南秦岭旬阳盆地东部晚泥盆世岩浆成因钠长岩及其构造意义     

罗金海  周亚军  徐欢  尤佳  李亦飞  车自成 《地质学报》2017,91(2):302-314

南秦岭旬阳盆地的钠长岩此前被认为是热水沉积或热液交代作用的产物。本文对南秦岭旬阳盆地东端黄石板地区侵入于下志留统梅子亚组浅变质岩中的钠长岩体进行了地球化学和锆石U-Pb LA-ICP-MS年代学研究,结果表明钠长岩具有富钠贫钾、铝不饱和、亏损大离子亲石元素K和Rb、高场强元素(Nb、Ta、Th、Hf)显著富集的地球化学特点,主体属于钙碱性系列岩石,反映幔源成因的特征。钠长岩中获得最年轻的锆石U-Pb年龄为364~376Ma,该年龄代表岩体的形成年龄,反映晚泥盆世时南秦岭旬阳盆地处于强烈的伸展构造环境。此项研究结果表明,在旬阳盆地的志留系中,岩浆成因与热水沉积成因的钠长岩可能是共存的。黄石板岩浆成因钠长岩岩体中含有大量前寒武纪和早古生代的捕获锆石,在捕获锆石中测得迄今为止在研究区及其邻区获得的最古老的锆石U-Pb年龄(3291Ma)。这些捕获锆石的测年数据说明,研究区所在的南秦岭地区可能从古太古代开始就与扬子地块具有明显的亲缘性。  相似文献   

Paleogene magmatism and gold metallogeny of the Jinping terrane in the Ailaoshan ore belt,Sanjiang Tethyan Orogen (SW China): Geology,deposit type and tectonic setting     

《Ore Geology Reviews》2017

The Jinping terrane is situated in the southern segment of the Ailaoshan ore belt, Sanjiang Tethyan Orogen (SW China). The Paleogene intrusions in Jinping consist of syenite porphyry, fine-grained syenite and biotite granite stocks/dikes, and contain relatively low TiO₂ (0.21–0.38 wt%), P₂O₅ (0.01–0.35 wt%), and high Na₂O (2.00–4.62 wt%) and K₂O (4.48–7.06 wt%), belonging to high-K alkaline series. Paleogene gold mineralization in Jinping comprises four genetic types, i.e., orogenic, alkali-rich intrusion-related, porphyry and supergene laterite. The NW–NNW-trending faults and their subsidiaries are the major ore-controlling structures. The orogenic Au mineralization, dominated by polymetallic sulfide-quartz veins, occurs in the diorite and minor in Silurian-Devonian sedimentary rocks. It contains a CO₂-rich mesothermal fluid system generated from the mixing of mantle-derived fluids with crustal-derived metamorphic fluids, and the ore-forming materials were upper crustal- or orogenic-derived. The alkali-rich intrusion-related Au mineralization is hosted in the Ordovician-Silurian sedimentary rocks and minor in the Paleogene alkaline intrusions, and the Au orebodies occur predominantly in the alteration halos. It contains a CO₂-bearing, largely metamorphic-sourced mesothermal fluid system, and the ore-forming materials were derived from the ore-hosting rocks and minor from the alkali-rich intrusions. The porphyry Cu-Mo-Au mineralization occurs in the granite/syenite porphyries and/or along their contact skarn, with the mineralizing fluids being magmatic-hydrothermal in origin. The former two hypogene Au mineralization types in Jinping were mainly formed in the late Eocene (ca. 34–33 Ma) and slightly after the porphyry Cu-Mo-Au mineralization (ca. 35–34 Ma), which is coeval with the regional Himalayan orogenic event. Subsequent weathering produced the laterite Au mineralization above or near the hypogene Au orebodies.  相似文献