The emplacement of pahoehoe lavas on Kilauea and in the Deccan Traps     

H. C. Sheth 《Journal of Earth System Science》2006,115(6):615-629

There is a growing interest in deciphering the emplacement and environmental impact of flood basalt provinces such as the Deccan, India. Observations of active volcanism lead to meaningful interpretations of now-extinct volcanic systems. Here, I illustrate and discuss the morphology and emplacement of the modern and active lava flows of Kilauea volcano in Hawaii, and based on them, interpret the compound pahoehoe lavas of the Deccan Traps. The latter are vastly larger (areally extensive and voluminous) than Kilauea flows, and yet, their internal architecture is the same as that of Kilauea flows, and even the sizes of individual flow units often identical. Many or most compound flows of the Deccan Traps were emplaced in a gentle, effusive, Kilauea-like fashion. Bulk eruption rates for the Deccan province are unknown, and were probably high, but the local eruption rates of the compound flows were no larger than Kilauea’s. Large (≥ 1000 km³) individual compound pahoehoe flows in the Deccan could have been emplaced at Kilauea-like local eruption rates (1 m³/sec per metre length of fissure) in a decade or less, given fissures of sufficient length (tens of kilometres), now exposed as dyke swarms in the province.  相似文献   

Characterisation of Tensile Damage in Rock Samples Induced by Different Stress Paths     

Patrick Ganne  André Vervoort 《Pure and Applied Geophysics》2006,163(10):2153-2170

Cracks, induced by different stress states, are studied systematically on thin slices of crinoidal limestone samples. Samples damaged by tension are compared to samples in which first damage is induced by compressive stresses, followed by tensile stresses. To quantify the effect of the compressive stresses, samples only damaged by compression are also studied. The tensile stresses cause the occurrence of an intergranular crack. When the sample is first damaged by compressive stresses, former induced damage influences the growth of this crack. It results in an intergranular crack with a zigzag profile. The average orientation of the intergranular crack is, however, the same as in the samples damaged by tension only.  相似文献   

Emplacement of subaerial pahoehoe lava sheet flows into water: 1990 Kūpaianaha flow of Kilauea volcano at Kaimū Bay, Hawai`i     

Susumu Umino  Miyuki Nonaka  Jim Kauahikaua 《Bulletin of Volcanology》2006,69(2):125-139

Episode 48 of the ongoing eruption of Kilauea, Hawai`i, began in July 1986 and continuously extruded lava for the next 5.5 years from a low shield, Kūpaianaha. The flows in March 1990 headed for Kalapana and inundated the entire town under 15–25 m of lava by the end of August. As the flows advanced eastward, they entered into Kaimū Bay, replacing it with a plain of lava that extends 300 m beyond the original shoreline. The focus of our study is the period from August 1 to October 31, 1990, when the lava buried almost 406,820 m² of the 5-m deep bay. When lava encountered the sea, it flowed along the shoreline as a narrow primary lobe up to 400 m long and 100 m wide, which in turn inflated to a thickness of 5–6 m. The flow direction of the primary lobes was controlled by the submerged delta below the lavas and by damming up lavas fed at low extrusion rates. Breakout flows through circumferential and axial inflation cracks on the inflating primary lobes formed smaller secondary lobes, burying the lows between the primary lobes and hiding their original outlines. Inflated flow lobes eventually ruptured at proximal and/or distal ends as well as mid-points between the two ends, feeding new primary lobes which were emplaced along and on the shore side of the previously inflated lobes. The flow lobes mapped with the aid of aerial photographs were correlated with daily observations of the growing flow field, and 30 primary flow lobes were dated. Excluding the two repose periods that intervened while the bay was filled, enlargement of the flow field took place at a rate of 2,440–22,640 square meters per day in the bay. Lobe thickness was estimated to be up to 11 m on the basis of cross sections of selected lobes measured using optical measurement tools, measuring tape and hand level. The total flow-lobe volume added in the bay during August 1–October 31 was approximately 3.95 million m³, giving an average supply rate of 0.86 m³/s.  相似文献   

Relationships between volcanic patterns and neotectonics in Eastern Anatolia from analysis of satellite images and DEM     

. Ad&#x;yaman  J. Chorowicz  O. Kse 《Journal of Volcanology and Geothermal Research》1998,85(1-4)

The late Neogene to Quaternary volcanism in Eastern Anatolia is related to the Arabia–Eurasia convergence but a clear deformation pattern has not yet been established in this region. We have used the distribution and shape of volcanoes and fault geometry as indicators of the tectonic regime. Volcanic edifices and related faults were analyzed in vertical view using SAR–ERS, Spot images and a Digital Elevation Model (DEM). In several places, adjacent volcanoes that form linear clusters or elongated volcanoes are clearly rooted on vertical tension fractures. These are compatible with horizontal σ₃ striking 90°N, associated with σ₁ horizontal (strike-slip regime) or vertical (extensional regime). We mapped the recent faults that are directly associated to volcanoes. Volcanic vents are related to tail-crack, horsetail or releasing bend structures. In this work, it has been possible to define the ESE-striking, 270-km-long Tutak–Hamur–Çaldiran fault that forms a releasing bend testifying to right-lateral motion. Extension is well documented for few places but no recent fold has been observed. Since 8 Ma, the tectonic system is principally strike-slip. Most of the tension fractures being 2 to 10 km in length, so we infer that they affect only part of the crust. Most strike-slip fault zones are of several tens to a few hundred kilometers long and thus not of lithospheric scale. Therefore, the channels used by the magma to reach the surface are crustal structures.  相似文献   

Characteristics and origins of coal cleat: A review   总被引：7，自引：0，他引：7  

S. E. Laubach  R. A. Marrett  J. E. Olson  A. R. Scott 《International Journal of Coal Geology》1998,35(1-4)

Cleats are natural opening-mode fractures in coal beds. They account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations. Because permeability and stimulation success are commonly limiting factors in gas well performance, knowledge of cleat characteristics and origins is essential for successful exploration and production. Although the coal–cleat literature spans at least 160 years, mining issues have been the principal focus, and quantitative data are almost exclusively limited to orientation and spacing information. Few data are available on apertures, heights, lengths, connectivity, and the relation of cleat formation to diagenesis, characteristics that are critical to permeability. Moreover, recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well-studied parameters can yield insight into coal permeability. More effective predictions of cleat patterns will come from advances in understanding cleat origins. Although cleat formation has been speculatively attributed to diagenetic and/or tectonic processes, a viable mechanical process for creating cleats has yet to be demonstrated. Progress in this area may come from recent developments in fracture mechanics and in coal geochemistry.  相似文献   

吉林省夹皮沟金矿成因研究   总被引：1，自引：0，他引：1  

李碧乐  金巍 《世界地质》1998,17(1):22-25

吉林省夹皮沟金矿区金矿赋存在夹皮沟北西向韧性带内,控矿构造为叠加在韧性剪切带之上的脆性构造。中生代中酸性脉岩为成矿期脉岩,且与黄泥河花岗岩岩基有着密切的成因联系。成矿物质主要来自岩浆分异,金丰度值高的暗色岩类提供部分矿质。  相似文献   

碎斑熔岩在黑矿型矿床成矿作用中的地位   总被引：2，自引：0，他引：2  

李智佩  彭礼贵 《西北地质科学》1998,19(1):59-67

白银矿田火山碎屑岩及赋矿岩石的深入研究表明,该地区存在一种长英质侵出相火山岩——碎斑熔岩。其主要特征是：①产于矿田酸性火山岩穹的火山活动中心或古火山喷口位置,代表中酸性火山作用晚期岩浆活动的产物,其典型者如折腰山石英角斑质碎斑熔岩体,规模为2×0．5km2,有次火山相石英钠长斑岩和各种火山碎屑岩如晶屑凝灰岩、集块岩及熔岩等分布在其四周;②碎斑熔岩中碎斑为长石和石英,具破而不碎、碎而不离或离而不远的特征,③基质具霏细结构,但多数已发生绢云母化、绿泥石化和黄铁矿化等;④岩石化学上同该地区喷出相石英角斑岩相当,SiO2均大于70ωB％,具有较高的Al2O3含量和Na2O／K2O值,分别为11．16～14．90和1．78～7．43,具I型与S型的混合型特征,⑤稀土元素配分型式具平坦型和富集型两种,分别与白银矿田东西两段酸性火山岩成因类型相对应,微量元素地球化学研究表明碎斑熔岩与区内石英角斑岩属同源岩浆的衍生物．海相火山岩中碎斑熔岩的确立,不仅增加了海相火山作用形式,即便出作用,而且因其占据火山活动中心或岩浆通道位置,在成岩或火山作用期后便成为海底热液对流循环成矿作用中心即热液喷流口．它既标志着黑矿型块状硫化物矿床成矿的相对时期,是在火山作用晚期侵出相碎斑熔  相似文献   

内蒙白旗地区火山碎斑熔岩矿物红外光谱特征研究   总被引：3，自引：0，他引：3  

赖绍聪  隆平 《西北地质》1997,18(3):1-7

正镶白旗碎斑熔岩和花岗斑岩中钾长石主要为高正长石和低透长石，有序度低，反映了白旗火山岩形成温度较高，钾长石有序度具明显的变化规律，反映了各相带岩石形成环境的差异性。各相带中石英的红外光谱反映了与钾长石相同的温度变化规律；岩石中锆石主要以晶质锆石为主；磁铁矿的红外光谱特征则表明碎斑熔岩形成于高氧化条件的侵出相环境。  相似文献   

Geologic hazards assessment of Cairo and vicinity     

A. F. Kamel  A. A. El Sokkary 《Natural Hazards》1996,13(3):253-274

The greater area from Cairo to west of Suez and a smaller area directly around Cairo are subjected to general and detailed analysis of hazard due to geological fractures. Fracture density contour maps and rose diagrams of the fracture trends are provided. Possible natural geologic hazards which might affect the area are discussed. These include landslides, block failure, earthquakes, maars, fumarolic activity, hot springs, caves and possible rejuvenation of old fault systems.  相似文献   

川西螺髻山冰川侵蚀地貌研究   总被引：2，自引：4，他引：2  

刘耕年 《冰川冻土》1989,(3)

定量分析发现影响该地区冰斗形态的因素有海洋性较强的气候,朝向北(极向),朝向东和较大的地形起伏四种。槽谷的横剖面可以公式化为Y=a·X~b,槽谷形态不对称由冰川差异侵蚀和冻融差异所致。发现两种冰川侵蚀裂痕,即挤压剪切裂痕和拉张剪切裂痕。  相似文献