岩体结构面各向异性变异系数的尺寸效应研究     

洪陈杰  黄曼  夏才初  罗战友  杜时贵 《岩土力学》2020,41(6):2098-2109

岩体结构面的各向异性与尺寸效应特征对其力学性质影响较大，综合考虑两者之间的相互关系对工程岩体稳定性评价具有重要意义。全面分析不同尺度结构面的各向异性分布，提出考虑正交方向三维形貌参数的各向异性变异系数AVC3D。通过渐进覆盖法统计4组天然岩体结构面10种不同采样尺寸的各向异性变异系数及其尺寸效应规律。结果表明：各向异性变异系数均随结构面尺寸增大而减小至定值，其与结构面尺寸具有较好的负对数函数关系；通过归一化处理，各向异性变异系数与结构面尺寸呈现较好的线性函数关系，表明各向异性变异系数具有分形结构，分维数D可以实现其尺寸效应的规律统计。该方法揭示了影响结构面形貌特征方向性变化的最大有效倾角 和粗糙系数C的增长幅度会随采样尺寸增大趋于稳定的变化机制，体现了当结构面达到各向异性尺寸效应的阈值后，会呈现出稳定的各向异性规律。  相似文献   

Sedimentary and geochemical characterization of Middle–Late Miocene formations in the Neogene Tsugaru Basin,Japan by means of DTH27‐1 well sediment analysis     

Paolo Martizzi  Shun Chiyonobu  Hiroyuki Arato 《Island Arc》2020,29(1)

Middle–Late Miocene age siliceous formations outcropping along the northwestern side of Honshu Island are considered prospective source rocks for hydrocarbons. An analysis of geophysical, sedimentological, and geochemical properties is essential to evaluate the formations' source potential, and to understand the factors that determined the accumulation and preservation of organic matter. This study investigates the Middle–Late Miocene geological record of the Tsugaru back‐arc basin, located in the western part of Aomori prefecture, through an analysis of a 200 m long portion of a core from the DTH27‐1 well; this core is composed of the diatomaceous siltstones of the Akaishi Formation and the siliceous mudstones of the Odoji Formation. Sedimentological and geophysical characterization showed that the Akaishi Formation's diatomaceous siltstones are mostly massive and bioturbated, have low magnetic susceptibility, and demonstrate moderate natural radioactivity. Although the Odoji Formation's siliceous mudstones are massive, they have exceedingly low magnetic susceptibility and high natural radioactivity. Geochemical data from a Rock‐Eval Pyrolysis such as total organic carbon and generative potential (S1 + S2) revealed that, in the Tsugaru area, only the Odoji Formation is a likely prospective source rock for hydrocarbons. On the other hand, T_max values indicate that both the formations are thermally immature for generating hydrocarbons. The difference between the Akaishi and Odoji Formation in the sedimentological facies, in terms of the degree of bioturbation and the organic carbon content, indicates variations in lithological properties, such as porosity and grain size; moreover, this difference indicates a variation in the paleo‐oxygenation of bottom waters, with the transition from oxygen‐deficient conditions in the Middle Miocene to the more oxygenated conditions in the Late Miocene. Both the lithological and paleo‐environmental factors possibly influenced the organic richness in the two formations.  相似文献   

勉略构造带新元古代洋盆俯冲作用：来自略阳地区纸房沟岩片火山岩锆石U- Pb年龄和Lu- Hf同位素的证据     

徐通  张晓团  焦建刚  张红强  贾力 《地质学报》2020,94(12):3607-3624

纸房沟岩片位于勉略构造带略阳地区。通过细致的岩石学和地球化学研究，将纸房沟岩片内的火山岩分为拉斑玄武岩系列（Ⅰ类）和钙碱性火山岩系列（Ⅱ类）。Ⅰ类火山岩稀土配分曲线左倾，富Na贫P，整体具有N- MORB特点，形成于洋脊构造环境。相比Ⅰ类火山岩，Ⅱ类火山岩具有更高的SiO2(49.02％~61.86％)和K2O(0.32％~1.55％)含量，相对亏损Nb、Ta、P和Ti，形成于陆缘弧构造环境。Ⅱ类火山岩锆石Lu- Hf同位素测试结果显示，εHf(t)值主体为负值，介于-8.01~+0.77，表明其主要为古老地壳物质熔融成因。Ⅱ类火山岩LA- ICP- MS锆石U- Pb测年结果为854±3Ma(MSWD=0.12, n=30)、844±4Ma (MSWD=0.03, n=15)，表明纸房沟岩片火山岩结晶时代为新元古代早中期。综合前人成果认为，纸房沟岩片火山岩为新元古代勉略洋盆俯冲的产物，俯冲作用一直持续到800Ma左右，该俯冲过程很可能是对全球性Rodinia超大陆聚合事件的响应。  相似文献   

Late Quaternary paleo sea level geomorphological markers of opposite vertical movements at Salina volcanic island (Aeolian Arc)     

F. Lucchi  A. Ricchi  C. Romagnoli  D. Casalbore  R. Quartau 《地球表面变化过程与地形》2019,44(12):2377-2395

Raised marine terraces and submerged insular shelves are used through an integrated approach as markers of relative sea level changes along the flanks of the Salina volcanic island (Aeolian Arc, southern Italy) for the purpose of evaluating its crustal vertical deformation pattern through time. Paleo sea level positions are estimated for the terrace inner margins exposed subaerially at different elevations and the erosive shelf edges recognized offshore at different depths. Compared with the eustatic sea levels at the main highstands (for the terraces) and lowstands (for the shelf edges) derived from the literature, these paleo sea level markers allowed us to reconstruct the interplay among different processes shaping the flanks of the island and, in particular, to quantify the pattern, magnitudes and rates of vertical movements affecting the different sectors of Salina since the time of their formation. A uniform uplift process at rates of 0.35 m ka⁻¹ during the Last Interglacial is estimated for Salina (extended to most of the Aeolian Arc) as evidence of a regional (tectonic) vertical deformation affecting the sub-volcanic basement in a subduction-related geodynamic context. Before that, a dominant subsidence at rates of 0.39–0.56 m ka⁻¹ is instead suggested for the time interval between 465 ka (MIS 12) and the onset of the Last Interglacial (MIS 5.5, 124 ka). By matching the insular shelf edges with the main lowstands of the sea level curve, a relative age attribution is provided for the (mostly) submerged volcanic centres on which the deepest (and oldest) insular shelves were carved, with insights on the chronological development of the older stages of Salina and the early emergence of the island. The shift from subsidence to uplift at the Last Interglacial suggests a major geodynamic change and variation of the stress regime acting on the Aeolian sub-volcanic basement. © 2019 John Wiley & Sons, Ltd.  相似文献   

腾冲火山及周边地区双差层析成像          下载免费PDF全文

华雨淋  吕彦 《地球物理学报》2019,62(8):2982-2990

利用云南腾冲火山地区15个固定台站记录到的7923次地震的P波到时资料，采用双差层析成像方法，反演得到腾冲火山及周边地区地壳及上地幔顶部三维P波速度结构和地震重定位结果.研究发现，腾冲火山区域地壳内存在明显的地震波低速区，P波速度低于整个区域地壳速度平均值超过15%，上地幔顶部存在规模较大的低速异常区.推测腾冲火山地区存在较大规模的地幔热物质上涌以及向地壳的侵入，热物质在地壳内以岩浆囊形式存储，并且壳内岩浆囊之间可能存在岩浆通道.通过联合反演获得的地震重定位结果显示，丛集地震位置更加集中，其展布特征与断裂构造具有显著的对应关系，表明研究区域断裂构造比较活跃.获得的高分辨率三维P波层析成像结果，为进一步认识火山地区岩浆存储特征以及地震分布与区域构造之间的关系提供了新的地震学依据.  相似文献   

Cretaceous tectonic evolution of the Neo-Tethys in Central Iran:Evidence from petrology and age of the Nain-Ashin ophiolitic basalts     

Tahmineh Pirnia  Emilio Saccani  Ghodrat Torabi  Marco Chiari  Spela Gorican  Edoardo Barbero 《地学前缘(英文版)》2020,11(1):57-81

The Nain and Ashin ophiolites consist of Mesozoic melange units that were emplaced in the Late Cretaceous onto the continental basement of the Central-East Iran microcontinent(CEIM).They largely consist of serpentinized peridotites slices;nonetheless,minor tectonic slices of sheeted dykes and pillow lavas-locally stratigraphically associated with radiolarian cherts-can be found in these ophiolitic melanges.Based on their whole rock geochemistry and mineral chemistry,these rocks can be divided into two geochemical groups.The sheeted dykes and most of the pillow lavas show island arc tholeiitic(IAT)affinity,whereas a few pillow lavas from the Nain ophiolites show calc-alkaline(CA)affinity.Petrogenetic modeling based on trace elements composition indicates that both IAT and CA rocks derived from partial melting of depleted mantle sources that underwent enrichment in subduction-derived components prior to melting.Petrogenetic modeling shows that these components were represented by pure aqueous fluids,or sediment melts,or a combination of both,suggesting that the studied rocks were formed in an arc-forearc tectonic setting.Our new biostratigraphic data indicate this arc-forearc setting was active in the Early Cretaceous.Previous tectonic interpretations suggested that the Nain ophiolites formed,in a Late Cretaceous backarc basin located in the south of the CEIM(the so-called Nain-Baft basin).However,recent studies showed that the CEIM underwent a counter-clockwise rotation in the Cenozoic,which displaced the Nain and Ashin ophiolites in their present day position from an original northeastward location.This evidence combined with our new data and a comparison of the chemical features of volcanic rocks from different ophiolites around the CEIM allow us to suggest that the Nain-Ashin volcanic rocks and dykes were formed in a volcanic arc that developed on the northern margin of the CEIM during the Early Cretaceous in association with the subduction,below the CEIM,of a Neo-Tethys oceanic branch that was existing between the CEIM and the southern margin of Eurasia.As a major conclusion of this paper,a new geodynamic model for the Cretaceous evolution of the CEIM and surrounding Neo-Tethyan oceanic basins is proposed.  相似文献   

大兴安岭南部二叠系—三叠系界线及沉积环境演化     

陈树旺  郑月娟  张健  张海华  张德军  苏飞  黄欣  公繁浩  甄甄 《中国地质》2020,47(3):821-838

北方陆相二叠系—三叠系界线研究是界线地层研究的重要问题之一,对采自内蒙古巴林右旗幸福之路组二段建组剖面的安山质岩屑晶屑凝灰岩开展锆石LA-ICP-MS U-Pb测年,结果为(255.5±1.1)Ma,火山岩上部多个层位粉砂质泥岩中发现孢粉化石,计17属20种,时代为晚二叠世—早三叠世,推断幸福之路组的时代为晚二叠世—早三叠世,大兴安岭地区二叠系—三叠系界线在幸福之路组内部,二者为整合接触。幸福之路组以红层做为划分标志,岩性为正常沉积碎屑岩夹火山岩,见大量泥灰岩夹层、钙质结核及干裂现象,反映了炎热、干燥及强氧化条件的气候环境,大兴安岭地区晚二叠世晚期(幸福之路组二段下部)就已出现反映干旱气候的红层沉积,与相邻的华北及新疆准噶尔盆地相似。  相似文献   

Geochemical characteristics of a pre-Middle Jurassic oceanic crust fragment from the Central Pontides in northern Turkey: Geodynamic implications on intra-oceanic subduction initiation     

《Chemie der Erde / Geochemistry》2020,80(1):125535

The Central Pontides (northern Turkey) is one of the key localities to understand the geodynamic evolution of the Palaeo- and Neotethyan oceans. It consists of the pre-Jurassic basement units, the Early Jurassic and the Early Cretaceous accretionary complexes, the widespread Middle Jurassic continental arc magmatics and the Late Jurassic to Tertiary cover units. The Early Cretaceous accretionary complex is represented by the Central Pontide Structural Complex and includes the Middle Jurassic oceanic units, which were metamorphosed during the Early Cretaceous. Apart from these oceanic units, a few metaophiolite and serpentinite fragments have been recognized within the basement units, which may represent the remnants of an older ocean. The pre-Middle Jurassic Devrekani Metaophiolite is the largest oceanic fragment and tectonically intercalated within/between the Devrekani Metamorphics and the Çangaldağ Metamorphic Complex. It is mainly composed of harzburgites, dunites with chromite veins and metagabbros, and cut by metabasaltic andesites and metadacites. Petrographically, the gabbro consists mainly of plagioclase and clinopyroxene, and displays phaneritic/porphyritic texture. In contrast, the metabasaltic andesite includes plagioclase and mica phenocrysts within a fine-grained groundmass. Also, the metadacite is composed predominantly of quartz, plagioclase, and mica minerals. Two different magmatic groups belonging to completely different tectono-magmatic settings have been geochemically determined based on the immobile trace element systematics. The metadacites and metabasaltic andesites are akin to continental arc magmatics and characterized by negative Nb and Ta anomalies and depleted HFSE relative to Th and La contents. However, the metagabbro samples display the geochemical signatures of boninitic rocks and characterized by highly depletion in HFSEs and REEs relative to N-MORB. The Devrekani Metaophiolite in the Central Pontides may represent another remnant of pre-Middle Jurassic oceanic crust generation and can be north-eastward continuation of the Permian-aged Almacık complex and the Boğazköy Metaophiolite fragment in the western Sakarya Composite Terrane. It may have been cut by intrusions of the extensive Middle Jurassic continental arc magmatism after its imbrication within the basement unit. The presence of pre-Middle Jurassic oceanic units may indicate that the Paleozoic ocean may have survived as the Jurassic Intra-Pontide Ocean between the Scythian Platform and Sakarya Composite Terrane during the Mesozoic time. Thus, the Intra-Pontide Suture may normally include the Palaeozoic and Mesozoic remnants of the long-lived northward subducting Tethyan ocean.  相似文献   

利用偏光显微镜反射光系统观察黑色生油岩电子探针薄片中的生烃母质特征     

郑庆华  刘行军  刘乔  梁秀玲  张小龙  左琴  杨开艳  马婷  许锋 《岩矿测试》2020,39(3):442-450

鄂尔多斯盆地上三叠统延长组长7油层组的黑色泥岩、油页岩等黑色生油岩薄片中的生烃母质,因黑色石油、沥青等黑色有机质的覆盖或不透明,导致其在偏光显微镜透射光系统下观察常局部或整体呈现为黑色。因此,建立一种黑色生油岩薄片中生烃母质有效观察的方法,对致密油、页岩油的生烃研究具有重要的理论和实际意义。本文提出了一种利用电子探针薄片和偏光显微镜的反射光系统观察黑色生油岩中生烃母质特征的方法。该方法能够克服黑色生油岩薄片中生烃母质因被黑色有机质覆盖或不透明,而在偏光显微镜的透射光系统下局部或整体呈黑色的弊端,能够对生烃母质的大小、形态、结构、分布和物质成分等特征进行整体且清晰的观察。实践表明,本文提出的利用偏光显微镜反射光系统观察黑色生油岩电子探针薄片中生烃母质特征的方法,简单有效,易在致密油、页岩油的生烃研究领域推广使用。  相似文献   

祁连山冻土区天然气水合物地球化学迁移机理探讨     

张富贵  秦爱华  祝有海  孙忠军  张舜尧  王惠艳  杨志斌  周亚龙 《矿床地质》2020,39(2):326-336

陆域冻土区天然气水合物成矿机制较为复杂,水合物横向难以对比,形成机理不清楚,急需对天然气水合物迁移机理进行研究。文章根据祁连山冻土区天然气水合物发现区钻井揭示的地质和地球化学资料以及岩芯样品分析测试结果进行了综合分析。结果显示,研究区中侏罗统和上三叠统均为较好烃源岩,天然水合物气源以热解气为主,主要由上三叠烃源岩迁移和中侏罗统木里组烃源岩扩散提供,显示了多源多期次的特点。根据地质和地球化学分析,祁连山天然气水合物的形成经历了晚侏罗世—早白垩世的气体运移与聚集、中新世中晚期—上新世整体抬升、第四纪游离气体转化成天然气水合物矿藏3个阶段,经历了"先聚集-再抬升-后成藏"等过程,是构造-气候耦合作用的结果,初步建立了祁连山冻土区天然气水合物迁移机理。  相似文献