火山区基本压力源模型及应用

通过简要介绍火山区不同压力源模型引起的垂直形变与水平形变特征,总结不同模型引起的最大水平位移与最大垂直位移的比值R,得到膨胀模型产生的地表形变多以中心为对称,R小于0.5;腔状模型产生的地表形变多为轴对称,可得到更高的R比值;这些结论为模拟分析火山区压力源参数选用模型时提供依据.最后利用所得结果,分析了长白山天池火山可...     

利用垂直形变资料分析龙岗火山的活动性

首先分析了龙岗火山区及其附近20多年来5条水准路线所反映的垂直形变背景场情况,发现相对于长春基准点,长白山区东部和北部地区主要表现为大面积下沉运动,而龙岗火山区则表现为相对上升运动;然后分析了龙岗火山区主要隆起区垂直形变场变化以及剪切和张裂变形率变化,所得结果均反映了长抚线发生了较明显的活动;最后运用改进的Mogi模型,采用L曲线法反演了主要隆起区可能的压力源参数.结果表明,龙岗火山区岩浆的位置在42.1°N,126.5°E附近,与深地震测深研究结果近似.相对于长白山天池火山,压力源等效半径变化较大,达到183 m左右,源的深度在30 km左右,相对较深.     

应用形变和重力资料分析腾冲火山区岩浆的活动特征

文中对腾冲火山区1998—2004年水准及重力观测资料进行了分析,发现垂直形变量大多在±10mm之内,重力变化为几十μGal,火山锥体和断层附近点位活动异常较大,可综合应用多源mogi模型和断层模型解释,断层的活动可使相邻测点的形变方向相反;垂直形变和重力的逐年变化表明火山岩浆处于一种活动状态。将火山区点位各时间段的重力梯度展布在形变-重力关系解释图中,发现数据主要落在Ⅰ、Ⅱ、Ⅳ和Ⅴ区,结合形变量对压力源等效体积的估算,初步认为火山区岩浆目前活动程度较低,暂没有喷发的危险     

以垂直形变资料反演腾冲火山区岩浆活动性的初步研究

根据腾冲火山区67个精密水准测点的4期实测垂直形变资料,和对该火山区已有的地质和地球物理工作的分析,参考了由层析成像推测的腾冲火山岩浆系统动力模型,利用Mogi模型对岩浆房的大小和空间位置进行了最小二乘法反演的初步研究。对4期资料分别进行了形变差的反演计算,所得初步结果表明岩浆活动源比较分散,可能存在3个表示岩浆流入引起地面上升的上升源,和2个表示岩浆流出到断层中引起地面下降的下降源。上升源位置大致沿北东走向的断层分布。而下降源位置则在测区东南一侧,等效岩浆源的深度在6～4km之间,与小震震源的深度大致相符。4年来岩浆活动量约为10^6m^3,量级与国外已喷发的火山相比处于较低活动水平．     

成层自重弹性-粘弹性半空间内膨胀源引起的地表形变和重力变化s

研究了两个弹性层覆盖于一个Maxwell半空间模型内膨胀源(Mogi模型)引起的地表形变和重力变化．着重研究了数值计算方法和Maxwell半空间介质流变特性对地表垂直位移和重力的影响．研究结果表明，Maxwell半空间介质流变特性对地表垂直位移和重力的空间分布和量级都有影响，尤其当源处于岩石层的地壳以下时，介质流变特性对位移和重力有较大影响；当膨胀和岩浆侵入地壳内时，半空间流变特性的影响较小．并且，地表重力与垂直位移的比值不是常数，而是随时间变化．本文的模型和数值方法，可以用于模拟火山区、地壳隆起区、地震区和地热场等长期地表形变和重力观测结果．      

中国大陆火山监测研究进展

在过去几年里，长白山天池火山观测到了明显的地震活动增加、地表抬升和膨胀以及多种流体化学异常。地震学研究和形变模拟表明，长白山天池火山近年来的活动可能是由其下方的岩浆活动引起的。1993年以来，腾冲火山出现强烈的水热活动。地球化学参数的变化表明，气体源区的深度逐渐增加。火山区存在的震群活动、部分台站观测到的S波阴影区以及地表的缓慢抬升等，指示火山区存在一个岩浆系统。监测研究结果表明，目前我国大陆其他火山的活动性较弱。     

腾冲火山区形变分析

腾冲火山群是我国目前仍具喷发危险的火山群。本文首先对火山区的地壳运动背景进行了总结分析,然后介绍了火山区的形变监测情况,再依据1998～2004年的水准测量及2002～2004年GPS观测成果,参考重力变化及其它观测资料分析火山区岩浆的活动特征,最后得出主要结论:相对欧亚板块,腾冲火山区总体具有向西南的顺时针旋转运动;火山区的形变变化受岩浆和断层活动两方面控制;火山区西南部发生了较强烈的下沉运动,可能由于岩浆和水的流失及放气等原因引起;以固东—腾冲断裂的西支为界,水平位移在断层两侧分别向东西两个方向运动,2002～2003年运动更剧烈些,断层活动表现为明显的拉张特征。综合各种资料表明火山目前活动量较小,近期喷发的危险性不大。     

空间大地测量技术在火山形变监测中的应用

岩浆活动的不同阶段引起地表变化不同。地表形变受压力源大小、形状、深度及岩浆运移速率等影响；另外火山类型不同，地形不同，形变特征也不同。地表形变幅度范围很大，为1×10-7—1米量级。火山区形变监测可以了解火山活动状态，有助于进行喷发危险性的预测预报。形变监测从20世纪60年代的传统技术逐渐过渡到20世纪90年代发展起来的GNSS和InSAR等大地测量新技术，火山区形变时空监测能力得到提高，同时缩短了预测时间。我国火山形变监测开始较晚，现已在长白山天池、腾冲以及海南等主要火山区开展监测。传统的连续测量以地倾斜观测为主；新技术主要以流动GNSS监测为主，连续观测站少，InSAR技术研究时间密度不够；目前形变监测还不能实现很好的时空覆盖。     

各向同性膨胀点源模拟长白山火山区岩浆囊压力变形源

2002～2003年长白山火山区的水平运动缺乏中心对称性分布特征,本文采用同一深度沿三个互相垂直方向拉张的点源模式模拟了长白山火山区的岩浆囊压力变形源. 在介质参数为V_p＝6.700 km/s,V_s＝3.8700 km/s,ρ＝2900 kg/m³的均匀弹性半空间中, 联合利用2002～2003年长白山火山区的GPS观测数据和水准数据, 结合PSGRN/PSCMP代码和遗传算法反演长白山火山区的压力变形源特征. 反演结果表明,由三个垂直的不等量扩张方向确定的椭球状点源模型可以较好地模拟长白山火山区岩浆囊压力变形源. 岩浆囊深处9.2 km,在走向为34.4°,倾角为82.2°的断层面的法向方向体积扩张量最大,达到7000000 m³;在走向为3028°,倾角为78.5°的断层面的法向方向体积扩张量次之,达到6598071 m³;在走向为337.7°,倾角为14.0°的断层面的法向方向体积扩张量最小,达到5220160 m³.     

粘弹性半空间内膨胀引起的地表垂直位移和重力变化

研究了粘弹性空间内膨胀（Ｍｏｇｉ模型）引起的地表垂直位移和重力变化，推导了Ｍａｘｗｅｌｌ半空间模型的解析计算公式。数值结果表明，地表垂直位移，重力变化以及重力变化与地表垂直位移之比受介质流变特性的影响很大，因此，在解释和模拟火山区，地壳隆地区，地热场等长期地表形变和重力观测时需考虑介质的流变特性影响。     

Caldera-scale inflation of the Lazufre volcanic area, South America: Evidence from InSAR

Collapsed calderas are the structural surface expression of the largest volcanic eruptions on Earth and may reach diameters of tens of kilometres while erupting volumes larger than 1000 km³. Remnants of collapse calderas can be found along the South American volcanic arc and are thought to be inactive. However, this study shows that systems of such dimension may become active in a relatively short period of time without attracting much attention. Using satellite-based InSAR data, a 45 km wide elongated area of ground deformation was observed in the Lazufre volcanic region (Chile), where no deformation was detected 10 years ago. The deformation signal shows an uplift of up to ~ 3 cm yr^− 1 during 2003–2006, affecting an area of about 1100 km², comparable in size to super-volcanoes such as Yellowstone or Long Valley. This deformation signal can be explained by an inflating magma body at about 10 km depth, expanding and propagating laterally at a velocity of up to 4 km per year. Although it is not clear whether this intrusion will lead to an eruption, its dimensions and the rapid deformation rate insinuate that a potentially large volcanic system is forming.     

Intra-arc opening and closure of a marginal sea: The case of the Guerrero Terrane (SW Mexico)

Abstract The pre-Oligocene structure of southwest Mexico, south of the trans-Mexico volcanic axis, is investigated from Taxco (Guerrero state, abbreviation: Gro) to the Pacific coast. Three volcano-sedimentary units are recognized; from east to west the calc-alkaline Teloloapan, tholeiitic Arcelia and calc-alkaline Zihuatanejo suites. Structural and stratigraphic data show that the Teloloapan volcanic arc, active during ?Late Jurassic and early Cretaceous, was built upon continental basement. The Teloloapan lavas are overlain by the Albian–Cenomanian Morelos platform carbonates and followed by the Upper Cretaceous Mexcala flysch. In contrast, the Arcelia pillow lavas are associated with sandstones and cherts of Albian-?Cenomanian age. The Zihuatanejo arc was also installed upon continental basement and its magmatic activity was in part coeval with Arcelia magmatism. Unlike the almost undeformed Zihuatanejo volcanic rocks, all the other volcanic units are involved in east-vergent thrusting and recumbent folding associated with ductile tectonics, as well as the Late Cretaceous Mexcala flysch overlying the Morelos platform carbonates. Contrasting with previous views, the present results do not support a major mid-Cretaceous thrusting event in the study area. The new geodynamic interpretation proposed here considers that the Arcelia rocks were formed in a marginal basin situated east of the Zihuatanejo arc. Closure of this basin in Paleocene times is responsible for the east vergent thrust tectonics in SW Mexico.     

2000-2007年期间长白山天池火山区地壳变形监测与分析

自2000年以来,在天池火山区附近布设了由2条精密水准路线、15个GPS测量点构成的地壳形变监测系统。文中详述了该系统的构成,并对近期长白山天池火山区地壳形变资料进行了分析研究。结果表明:2002—2005年,长白山天池火山区地面发生了明显的变形。在垂直方向上,水准路线高差3年累积变化达6.8cm,且越是靠近火山口,变形量越大。在水平方向上,以火山口为中心,各观测点总体位移出现放射状变化,最大可达38cm;山体出现明显的膨胀,最大面膨胀可达6×10-6/a。上述变化于2006年后逐步恢复为正常变化。在此期间,长白山天池火山区火山地震活动频繁,其它监测资料也出现了同步的异常变化。文中分析讨论了引起上述变化的可能原因,认为是天池火山一次最新的岩浆活动所致     

五大连池火山构造地震空间分布及其构造含义

在对五大连池地震台１９８３年以来观测到的五大连池火山区的地震记录复核的基础上，测定了火山构造地震的空间分布状态。研究结果表明该地区地震活动均为壳内地震。受火山构造环境影响，地震活动存在着外围边缘强，震源深度分布深；内部弱，震源深度分布浅的差异。火山区内部地震深度分布优势在５ｋｍ—８ｋｍ，有３个地震分布密集区，震中分布呈明显的沿火山构造断层成带分布特性。在地震条带交汇处，震源深度起伏变化大，是火山构造活动强烈部位     

徐家围子断陷火山机构叠置关系解析及其数字化模型参数建立

随着庆深气田勘探开发工作的不断深入,揭示出火山岩气藏以孤立火山机构控藏的特征,火山岩地层的非均质性特征非常明显,为提高火山岩气藏的综合研究程度,实现认识上的飞跃.在松辽盆地北部徐家围子断陷密井网-三维地震工区,开展了地质先验模型约束下的地震火山机构解剖.识别出层状、穹窿和漏斗形三种火山机构;它们的叠置方式有串珠、上叠和...     

河北沽源—多伦地区中生代含铀火山岩地球化学

沽源和多伦地区是燕辽多金属成矿带的重要组成部分，中生界主要发育上侏罗统白旗组、张家口组，下白垩统大北沟组和花吉营组。张家口组火山岩分布广、厚度大，是铀（钼）矿床的主要含矿主岩。中生代火山岩属于钙碱性系列，化学成分富硅、偏碱，δ值1.17-7.60。稀土元素特征反映火山岩有壳幔混合和壳源改造两种成因。火山岩形成于弱造山环境，其年龄与库拉—太平洋板块向亚洲板块俯冲的时间吻合。张家口组酸性火山岩具有我国相山产铀火山杂岩富硅、富钾，铕极亏损的地球化学特征。     

petrological and geochemical characteristics of quarternary volcanic rocks in haixing area,eastern north china

Field investigation and lab analysis on samples were carried out for Quaternary volcanoes, including Xiaoshan volcano, Dashan volcano and Bianzhuang hidden volcano, in Haixing area, east of North China. Results show that Xiaoshan volcano with the eruptive material of volcanic scoria, crystal fragments and volcanic ash is a maar volcano, the eruptive pattern is pheatomagmatic eruption, and the influence scope is near the crater. Dashan volcano exploded in the early stage, and then the magma intruded, forming the volcanic neck. The eruption strength and scale are limited, and the eruptive materials are scoria, volcanic agglomerate and dense lava neck. The volcanic rocks in Bianzhuang are porosity and dense volcanic rocks and volcanic breccia, reflecting the pattern of weak explosive eruption and lava flow, and the K-Ar age dating on volcanic rocks indicates that the eruption happened in early Pleistocene. Xiaoshan volcanic scoria and Bianzhuang hidden volcanic rocks are mainly basaltic, Dashan volcanic rocks with lower SiO₂ content are nephelinite in composition. Their oxide contents have no linear relationship, indicating that there is no magma evolution relationship between these magmas from the three places. Three volcanic rocks all have enrichment of light rare earth. The Bianzhuang volcanic rocks are rich in large ion lithophile elements, and have no high field strength elements Zr and Hf, Ti losses. The volcanic materials from Xiaoshan and Dashan are intensively rich in Th, U, Nb and Ta, and significantly poor in K and Ti. Although the magmas from these three places in Haixing area may all come from asthenosphere, the volcanic materials have different petrological and geochemical features, and relatively independent volcanic structures, therefore, they experienced different magma processes.     

Late Cretaceous-Early Cenozoic volcanism of Southern Mongolia: A trace of the South Khangai mantle hot spot

The Gobi-Tien Shan volcanic area (in Southern Mongolia) is part of the South Khangai volcanic region (SKVR). The formation of its lava fields was related to three stages of volcanic activity: the Late Cretaceous (88–71 Myr), Paleocene-Early Eocene (62–47 Myr), and Early Oligocene (37–30 Myr). Volcanic occurrences of different age are represented by trachybasalt, trachyandesitobasalt, basanite, and melanephelinite with similar geochemical characteristics, which are also close to the geochemical characteristics of OIB basalt. The isotope composition (Sr, Nd) of the rocks indicates that the magma sources were formed as a result of mixing of a moderately depleted PREMA mantle and an EM-I mantle enriched in neodymium.The patterns of migration of volcanic centers of different ages over the area of interest have been studied. The earliest (Late Cretaceous) volcanic occurrences were concentrated mainly in the south of the area, the Paleocene-Early Eocene eruptions took place at the center of the area, and the Early Oligocene volcanism occurred in the northern area. The observed migration of the volcanic activity centers is related to lithospheric plate motions relative to a localized source of hot mantle (the South Khangai mantle hot spot), which controlled volcanic activity within SKVR. In the lithospheric structure of this region, local asthenospheric high, reaching a depth of ～50 km, correspond to this hot spot.     

Earthquake Monitoring and Study in the Jingpohu Volcano Cluster Area

Seismicity in the Jingpohu volcanic area was investigated based on the seismic data recorded by the mobile seismic network consisting of 14 stations equipped with 24-bit broad-band 3- component seismographs around Crater Forest, Results show that there appears certain seismicity in Jingpohu and its adjacent areas with a low activity level and most of the recorded earthquakes are the volcanic-tectonic ones, The results of location indicate a dominant focal depth of 10km - 30kin, most of the earthquakes are smaller than ML2,0, and are concentrated in the area of ＂ Crater Forest＂ and on the Dunhua-Mishan fault which runs through the volcanic area. At station No. 2, which has better observation conditions, two types of events, likely associated to volcanism, were recorded; their waveform characteristics are somewhat similar to that of the long-period volcanic event and the volcanic tremor, but with different feature of frequencies.