玉树7．1级地震前后波速比变化特征分析

利用玉树、曲玛莱、杂多地震台观测到的数字震相资料,研究玉树Ms7．1级地震前后波速比时间演化特征。研究发现：3个台站平均波速比、波速比标准偏差在地震前后变化不相同,Ms4．7级前震发生时3个台站波速比都出现较明显的高值回返现象,其中玉树地震台波速比数值高达2．032。     

2012年新疆新源—和静M_S6.6地震极震区地质灾害特征研究

通过叙述2012年6月30日新源—和静MS6.6地震极震区内地震崩塌、滑坡、地裂缝和碎石流4种地震地质灾害规模、分布特征,结合震前极震区内地质灾害分布类型和特征,将震前与震后的地质灾害特征进行对比分析,认为虽然此次地震极震区烈度仅为Ⅷ度,但发生的地震裂缝与地震崩塌等地震地质灾害具有独特性,应与该地区的地貌、地层岩性有关。     

2014年云南鲁甸M_S6.5地震人员死亡年龄分布特征

通过收集到鲁甸地震分县(区)地震人员死亡统计表,对死亡人员的年龄、性别、死亡原因、死亡地点等情况进行分类分析,得到鲁甸地震人员死亡类型和死亡人员年龄总体分布特征。并分别对因房屋倒塌、因崩塌滑坡、因抢救无效致死人员年龄分布特征,性别—年龄分布特征等地震人员死亡年龄分布特征进行总结分析。同时与国内同类研究相比,鲁甸地震造成的人员死亡具备地震人员死亡的普遍特征,同时具有山区、经济欠发达地区地震人员死亡的特性。     

2014年新疆于田M_S7.3地震的地壳构造变形背景

利用2011~2013年的流动GNSS观测资料及处理结果,获得了2014年于田MS7.3地震区域水平形变场。结果显示:(1)于田MS7.3地震发生在构造活动较强烈的阿尔金断裂带西端,其两侧的形变差异运动为8~9 mm/a,左旋运动是差异运动的主要成份;(2)发震区域的主应变是全区最突出的区域,张压大小相对均等,主张方向为南东东—北西西;(3)该地震发生在左旋形变的高梯度带上,其北部的塔里木盆地为较弱的右旋形变,其南部约150 km以外几乎无旋形变;(4)地震发生的部位为面应变性质转变的过渡带,其西为面膨胀区,其东为面收缩区。     

遥感技术在川西甲基卡大型锂矿基地找矿填图中的应用

四川甲基卡矿田是中国乃至于世界上锂矿资源最集中的地区之一,目前运用遥感技术开展甲基卡型锂矿的研究工作尚较为薄弱,文章运用遥感技术在甲基卡特殊地貌区开展找矿填图应用研究,建立了研究区典型岩石及矿物的波谱数据库,总结了研究区黑云母片岩、十字石片岩、十字石堇青石片岩、角岩、二云母花岗岩、含锂辉石伟晶岩、无矿伟晶岩、石英脉、长石斑晶、锂辉石单晶、云母、绿柱石的波谱特征;之后分别基于中等分辨率遥感数据Landsat 8和高空间分辨率遥感数据Geoeye-1进行图像处理和信息提取,开展了地质填图应用初步研究。研究结果表明遥感技术作为一种新兴的技术手段,对甲基卡型锂矿的填图及找矿具有重要的指导意义,可以作为今后地质找矿工作的"先头兵"。     

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Discussion on the Abnormally Low Active Fault Slip Rate of the M_S 8. 0 Wenchuan Earthquake

Based on the collection of active fault slip rate data of large intra-continental shallow thrust earthquakes occurring in the triangular seismic region of the East Asia continent,a preliminary analysis has been performed with results showing that the Wenchuan,Sichuan, China earthquake ( MS = 8. 0) of May 12,2008 occurred on the Longmenshan Mountain active fault with an abnormally low slip rate.     

2003年青海德令哈6.6级地震前地震活动和前兆异常特征

2003年4月17日青海省德令哈市西北发生6.6级地震。该地震发生在具有强烈活动特征的大柴旦—宗务隆山断裂带上,震前地震活动表现出明显的大面积ML4级地震平静,而震中附近则同时出现了高频次、高GL值异常以及ML3级地震平静—活跃、ML4级地震平静等异常现象。对省内及甘肃省前兆观测资料进行追踪分析,认为震前有4项前兆测项呈现出中期和短期异常特征。     

New insights on the origin of troctolites from the breakaway area of the Godzilla Megamullion (Parece Vela back‐arc basin): The role of melt‐mantle interaction on the composition of the lower crust

The troctolites and olivine‐gabbros from the Dive 6 K‐1147 represent the most primitive gabbroic rocks collected at the Godzilla Megamullion, a giant oceanic core complex formed at an extinct spreading segment of the Parece Vela back‐arc basin (Philippine Sea). Previous investigations have shown that these rocks have textural and major elements mineral compositions consistent with a formation through multistage interaction between mantle‐derived melts and a pre‐existing ultramafic matrix. New investigations on trace element mineral compositions basically agree with this hypothesis. Clinopyroxenes and plagioclase have incompatible element signatures similar to that of typical‐MORB. However, the clinopyroxenes show very high Cr contents (similar to those of mantle clinopyroxene) and rim having sharply higher Zr/REE ratios with respect to the core. These features are in contrast with an evolution constrained by fractional crystallization processes, and suggest that the clinopyroxene compositions are controlled by melt‐rock interaction processes. The plagioclase anorthite versus clinopyroxene Mg#[Mg/(Mg + Fe^Tot)] correlation of the Dive 6 K‐1147 rocks shows a trend much steeper than those depicted by other oceanic gabbroic sections. Using a thermodynamic model, we show that this trend is reproducible by fractionation of melts assimilating 1 g of mantle peridotite per 1 °C of cooling. This model predicts the early crystallization of high Mg# clinopyroxene, consistent with our petrological observation. The melt‐peridotite interaction process produces Na‐rich melts causing the crystallization of plagioclase with low anorthite component, typically characterizing the evolved gabbros from Godzilla Megamullion.     

Silicate‐oxide mineral chemistry of mafic–ultramafic rocks as an indicator of the roots of an island arc: The Chilas Complex,Kohistan (Pakistan)

The Chilas Complex is a major lower crustal component of the Cretaceous Kohistan island arc and one of the largest exposed slices of arc magma chamber in the world. Covering more than 8000 km², it reaches a current tectonic width of around 40 km. It was emplaced at 85 Ma during rifting of the arc soon after the collision of the arc with the Karakoram plate. Over 85% of the Complex comprises homogeneous, olivine‐free gabbronorite and subordinate orthopyroxene–quartz diorite association (MGNA), which contains bodies of up to 30 km² of ultramafic–mafic–anorthositic association (UMAA) rocks. Primary cumulate textures, igneous layering, and sedimentary structures are well preserved in layered parts of the UMAA in spite of pervasive granulite facies metamorphism. Mineral analyses show that the UMAA is characterized by more magnesian and more aluminous pyroxene and more calcic plagioclase than those in the MGNA. High modal abundances of orthopyroxene, magnetite and ilmenite (in MGNA), general Mg–Fe–Al spatial variations, and an MFA plot of whole‐rock analyses suggest a calc‐alkaline origin for the Complex. Projection of the pyroxene compositions on the Wo–En–Fs face is akin to those of pyroxenes from island arcs gabbros. The presence of highly calcic plagioclase and hornblende in UMAA is indicative of hydrous parental arc magma. The complex may be a product of two‐stage partial melting of a rising mantle diaper. The MGNA rocks represent the earlier phase melting, whereas the UMAA magma resulted from the melting of the same source depleted by the extraction of the earlier melt phase. Some of the massive peridotites in the UMAA may either be cumulates or represent metasomatized and remobilized upper mantle. The Chilas Complex shows similarities with many other (supra)subduction‐related mafic–ultramafic complexes worldwide.