Fractal analysis of the fracture strength of lava dome material based on the grain size distribution of block-and-ash flow deposits at Unzen Volcano, Japan     

Keiko Suzuki-Kamata  Takashi Kusano  Kazuhito Yamasaki 《Sedimentary Geology》2009,220(3-4):162

A fractal theory of rock fragmentation is applied to block-and-ash flow deposits from the Fugendake dome, Unzen Volcano, Kyushu, Japan, in order to analyze the material strength and the energy required for size reduction of the source lava dome. Two fractal dimensions h and D_s, which are mutually interchangeable, represent the relative strength and energy for particles reduced to a given size. They can be theoretically estimated from the power relations of a reference grain size to the cumulative mass and number of fragments smaller than that size. The Unzen–Fugendake block-and-ash flow deposits have been further modified by size sorting and secondary fragmentation that occurred during flowage, so that the h value decreases (or D_s value increases) with increasing distance from the source. Coarse, reversely graded deposits are, however, found to retain the original size population relatively well. The D_s values estimated from deposits of this type are compatible with those previously reported from decompression–fragmentation experiments conducted on the same dome material. The employed fractal approach could thus give insights into the potential mode of dome collapse that generates block-and-ash flows.  相似文献   

辽东古元古代造山带花岗片麻岩穹窿:热造山带典型构造样式   总被引：1，自引：1，他引：0  

张程  杨洪祥  冯嘉  刘俊来 《岩石学报》2019,35(9):2926-2942

中下地壳的底辟上升是地壳中物质运移和热传递的一种重要机制,由这种机制产生的一系列穹窿构造不仅为揭示区域构造环境和构造演化提供了重要的线索,而且还提供了一个了解地壳深部物质流动的窗口。辽东半岛的古元古代造山带内就发育有这样一套花岗片麻岩穹窿构造,为了深入理解这套花岗片麻岩穹窿的成因以及对造山带演化的影响,本文对其不同构造层次进行了详细的构造特点和变形演化研究。结果显示,典型的花岗片麻岩穹窿可分为三层结构:混合岩化的花岗岩内核、发育顺层韧性剪切带的幔部以及含大型构造透镜体的外壳。其中核部花岗岩塑性流动变形发育,并具有明显的交代现象。顺层韧性剪切带的变形环境由靠近岩体的角闪岩相到远离岩体的低绿片岩相,并且没有明显的退化变质特点,拉伸线理具有统一的NW-SE方向。根据年代学数据与区域构造分析,花岗片麻岩穹窿构造是在区域收缩体制下花岗岩底辟形成的产物,其出现标志着辽东古元古代造山带变为一个由垂向和横向对流作用为主导的热造山带。  相似文献   

激电测深在江西某矿集区穹隆构造勘查中的应用          下载免费PDF全文

冯天勇  刘永涛  邹华敏 《地质找矿论丛》2017,32(4):648-653

文章简述了激电测深在江西某矿集区穹隆构造勘查中的应用。通过在穹隆构造上布设剖面,开展大功率对称四极激电测深,结合矿集区岩矿石标本的电参数以及地质资料,对测深剖面进行了电阻率/极化率2.5维反演与推断解释,根据不同电性特征,成果大致反映了该区的地电结构分层情况,对该穹隆构造的地层单元界线划分有所体现,激电异常对深部寻找隐伏岩体具有一定地质指示意义。  相似文献   

北喜马拉雅错那洞穹隆:片麻岩穹隆新成员与穹隆控矿新命题   总被引：3，自引：0，他引：3  

张志  张林奎  李光明  梁维  夏祥标  付建刚  董随亮  马国桃 《地球学报》2017,38(5):754-766

错那洞片麻岩穹隆位于特提斯喜马拉雅南侧,靠近藏南拆离系,是北喜马拉雅片麻岩穹隆带(NHGD)中最新发现的新成员。本文在详实的野外地质调查基础上,首次全面介绍了错那洞片麻岩穹隆的结构组成,同时进行了片麻岩的年代学研究。结果表明,错那洞片麻岩穹隆由核-幔-边三部分组成,核部由花岗片麻岩及淡色花岗岩组成,并可见大量伟晶岩脉穿插;幔部为一套强变质变形的二云母片岩,从内至外具有夕线石+石榴石→蓝晶石+石榴石→十字石+石榴石→石榴石+十字石+堇青石→堇青石+石榴石的变质分带特征;边部主要为浅变质沉积岩系,可见较多因穹隆隆升而形成的A型褶皱。花岗片麻岩LA-ICP-MS锆石U-Pb年龄为(499.7±3.4)Ma(MSWD=0.025),与NHGD其它穹隆核部片麻岩时代基本一致,均为泛非—早古生代造山活动的产物。在本次野外地质调查过程中,在错那洞片麻岩穹隆中发现了矽卡岩型钨锡铍工业矿体以及铜金矿化体,同时在伟晶岩中还存在着大量的绿柱石等宝石矿产,这样的成矿作用与矿化组合在NHGD中尚属首次发现,基于此本文提出了北喜马拉雅片麻岩穹隆控矿新命题。  相似文献   

川西地区甲基卡穹隆的构造变形特征     

武文辉  詹涵钰  秦宇龙  李峥  徐云峰  申伟 《沉积与特提斯地质》2017,37(4):84-90

甲基卡穹隆因其丰富的锂辉石资源而闻名,在华北、扬子和羌塘3个板块之间的南北向和东西向双向收缩背景下,形成了其复杂的变形特征。穹隆顶部地层平缓,向外逐渐变陡,总体为同心圆状向外倾的复式背斜。顶部发育有A型等斜平卧褶皱、肠状石英脉及对称型压力影;翼部变质矿物多被拉伸旋转而呈不对称状,表现出向穹隆周围的正向剪切运动;穹隆外围地层产状较陡,多发育直立紧闭褶皱及倒转褶皱。总体来说,甲基卡穹隆岩浆底辟作用前,先后经历了南北向及东西向的挤压,成穹后再一次经历南北和东西向挤压的两期构造运动,属于构造变形与岩浆作用的共同产物。  相似文献   

白垩纪以来米仓山-汉南穹窿剥蚀过程及其构造意义：磷灰石裂变径迹的证据   总被引：9，自引：4，他引：5       下载免费PDF全文

田云涛  朱传庆  徐明  饶松  Barry P.Kohn  胡圣标 《地球物理学报》2010,53(4):920-930

报道了米仓山-汉南穹窿一带磷灰石裂变径迹分析结果,以制约该区白垩纪以来的剥蚀-演化历史.露头样品磷灰石裂变径迹年龄分布显示从汉南穹窿南部的核部地区向南至四川盆地北部裂变径迹的年龄逐渐变新,这与米仓山地区逆冲断裂以背驮式扩展的构造样式从汉南穹窿向南经米仓山褶皱-逆冲带发育到四川盆地北缘的构造模式相吻合.热模拟的结果显示米仓山-汉南穹窿经历了两期快速的剥蚀,其分别发生在白垩纪（约90 Ma之前）和15 Ma以来.研究区白垩纪的快速剥蚀反映了秦岭-大别造山带白垩纪的区域性剥蚀事件,这可能是对临区诸多构造事件（如西伯利亚-蒙古-中朝板块的碰撞,拉萨-羌塘-思茅-印支块体的碰撞,太平洋板块向欧亚板块的俯冲及其相关的岩浆活动）远场效应的响应;约15 Ma以来的快速剥蚀是对青藏高原隆升向东北方向传递的响应.  相似文献   

Seismic hybrid swarm precursory to a major lava dome collapse: 9–12 July 2003, Soufriere Hills Volcano,Montserrat     

L. Ottemöller 《Journal of Volcanology and Geothermal Research》2008

A swarm of ≈ 9500 hybrid earthquakes preceded the 12–13 July 2003 dome collapse at Soufriere Hills Volcano, Montserrat. Most events had nearly identical waveforms and cross-correlation was applied to measure inter-event periods as well as phase arrival times to determine accurate relative location. Hypocenter depths were shallow (< 3 km), and relative locations were confined to a radius of < 150 m. This small source volume is consistent with the observed waveform similarity. Changes in inter-event periods and energy release, measured from the seismic records, showed that the volcano evolved through several energetic states, possibly linked to cyclic magma movement. Shorter inter-event periods were linked to higher energy release rates and possibly reflect increased pressurization during periods of low extrusion rates.  相似文献   

矾山岩浆型磷(铁)矿床地质、地球物理、遥感影象特征及其找矿模型   总被引：1，自引：1，他引：0  

黄富荣  东野脉兴 《化工矿产地质》1999,21(3):149-153

矾山磷 (铁 )矿床为一隐伏矿床 ,赋存在印支期碱性 超基性杂岩体中。矿床地处中朝准地台燕山台褶带 ,该处莫霍面深 39～ 40km ,并由陡变缓 ,矿床还处于张宣幔枝外围拆离滑脱带上。不同方向的深大断裂在矿床附近交叉通过 ,区域褶皱是印支期开阔宽缓的复式背向斜。赋矿的碱性 超基性杂岩体生成于 2 0 3～ 2 48Ma ,产状为岩盆 ,由三期侵入岩和一期脉岩组成 ,具层状岩系特征和韵律结构。矿体产于第一期岩石辉石岩带中。杂岩体航磁异常最高达36 0 0nT ,形态规则 ,地表剖面磁异常最高达 45 0 0nT ,剩余重力异常达 0 .2× 10 -4 m/s2 。在遥感影象图中 ,杂岩体与深部相连的同期岩体共同组成复合环状构造 ,并受北东向断裂和更大的环形断裂控制。据此建立了找矿模型。  相似文献   

The role of visual saliency in the automation of seismic interpretation          下载免费PDF全文

Muhammad Amir Shafiq  Tariq Alshawi  Zhiling Long  Ghassan AlRegib 《Geophysical Prospecting》2018,66(Z1):132-143

In this paper, we propose a workflow based on SalSi for the detection and delineation of geological structures such as salt domes. SalSi is a seismic attribute designed based on the modelling of human visual system that detects the salient features and captures the spatial correlation within seismic volumes for delineating seismic structures. Using this attribute we cannot only highlight the neighbouring regions of salt domes to assist a seismic interpreter but also delineate such structures using a region growing method and post‐processing. The proposed delineation workflow detects the salt‐dome boundary with very good precision and accuracy. Experimental results show the effectiveness of the proposed workflow on a real seismic dataset acquired from the North Sea, F3 block. For the subjective evaluation of the results of different salt‐dome delineation algorithms, we have used a reference salt‐dome boundary interpreted by a geophysicist. For the objective evaluation of results, we have used five different metrics based on pixels, shape, and curvedness to establish the effectiveness of the proposed workflow. The proposed workflow is not only fast but also yields better results as compared with other salt‐dome delineation algorithms and shows a promising potential in seismic interpretation.  相似文献   

Reconstruction of the eruptive history of Usu volcano,Hokkaido, Japan,inferred from petrological correlation between tephras and dome lavas     

Akiko Matsumoto  Mitsuhiro Nakagawa 《Island Arc》2019,28(3)

Usu volcano has erupted nine times since 1663. Most eruptive events started with an explosive eruption, which was followed by the formation of lava domes. However, the ages of several summit lava domes and craters remain uncertain. The petrological features of tephra deposits erupted from 1663 to 1853 are known to change systematically. In this study, we correlated lavas with tephras under the assumption that lava and tephra samples from the same event would have similar petrological features. Although the initial explosive eruption in 1663 was not accompanied by lava effusion, lava dome or cryptodome formation was associated with subsequent explosive eruptions. We inferred the location of the vent associated with each event from the location of the associated lava dome and the pyroclastic flow deposit distribution and found that the position of the active vent within the summit caldera differed for each eruption from the late 17th through the 19th century. Moreover, we identified a previously unrecognized lava dome produced by a late 17th century eruption; this dome was largely destroyed by an explosive eruption in 1822 and was replaced by a new lava dome during a later stage of the 1822 event at nearly the same place as the destroyed dome. This new interpretation of the sequence of events is consistent with historical sketches and documents. Our results show that petrological correlation, together with geological evidence, is useful not only for reconstructing volcanic eruption sequences but also for gaining insight into future potential disasters.  相似文献