Broadband seismic experiment at Merapi Volcano, Java, Indonesia: very-long-period pulses embedded in multiphase earthquakes

Multiphase (MP) and low frequency (LF) earthquakes with spectral peak amplitudes at 3–4 and 1 Hz, respectively, are two common types of shallow volcanic earthquakes previously recognized at Merapi Volcano. Their mechanisms are poorly understood but MPs have been temporally associated with lava dome growth. We conducted a seismic experiment in January–February 1998, using four broadband seismographs to investigate the nature of seismic activity associated with dome growth. During our experiment, Merapi experienced mild dome growth with low-level seismic activity. We compare our data to that recorded on a local short-period (SP) network, with the following preliminary results.MP and LF events as recorded and classified on the short-period network instruments were recognized on the broadband network. Frequency spectrograms revealed similar patterns in the near summit region at widely separated broadband stations. Higher frequency spectra than previously recognized were identified for both MP and LF events, and were strongly attenuated as a function of radial distance from the source. Thus the spectral characteristics of these events as recorded on far-field stations are not fully indicative of the source processes. In particular, many events classified as LF-type appear to have much high frequency energy near the source. This aspect of these so-called LF earthquakes, and their association with very-long-period (VLP) pulses, suggests that many events identified in the far-field as LF events are in actuality a variety of the MP event and involve similar source processes. Broadband records indicated that simple large-amplitude VLP pulses were embedded in MP and LF wavetrains. From event to event these pulses were similar in their waveforms and had periods of 4 s. VLP events embedded in LF and MP earthquakes were located using particle motions. The epicenters were clustered in a central region of the dome complex, and preliminary source depths were within about 100 m of the dome surface, suggesting a source region deep within the dome or the uppermost conduit. A similar source location was established by study of MP high-frequency onsets. Our broadband data suggests that we have recorded both elastic seismic waves and a simple embedded pulse that is interpreted to represent a surface tilt at the seismometer site. The inferred tilt indicates an inflation and subsequent deflation, possibly caused by a gas pressure pulse or episodic shallow magma transport with stick-slip movement of the conduit wall.     

数字钻孔摄像在小浪底帷幕灌浆检测孔中的应用

为了评价帷幕灌浆效果,将数字钻孔摄像技术应用到小浪底水利枢纽3号灌浆洞3个灌浆质量检查孔中。通过数字钻孔摄像得到的孔壁图像资料, 对钻孔内发育的节理裂隙、破碎带和砂浆充填情况进行了分析研究,结果表明：?灌浆时浆液在外压下,主要沿连通性较好、延伸较远的裂隙向孔外岩体渗透。与渗流路径相连通的裂隙或延伸较短的裂隙,被浆液直接充填凝固后形成水泥结石。与渗流路径没有连通的裂隙则被忽略,或在灌浆压力下劈裂而部分充填,造成全充填、半充填和砂浆流出等几种充填效果;?破碎带充填与否主要与破碎带的规模、性质和与灌浆洞连通性有关。小浪底水利枢纽3号灌浆洞内的灌浆效果是明显的;将数字钻孔摄像技术应用于检查帷幕灌浆质量,分析灌浆浆液渗流路径,也是可行的。     

提高锚杆锚固力方法研究

在总结大连地区15项工程76根锚杆抗拔试验时发现锚杆的锚固力是受多种因素影响的,其中主要因素是钻探成孔工艺(影响c,φ值)和锚杆注浆质量(影响k₀值).对于风化岩或土层灌浆锚杆建议采用风动成孔;对于中风化或微风化岩层灌浆锚杆建议采用风动成孔并进行清水洗孔;对于锚杆注浆建议采用膨胀砂浆,并建议锚杆抗拔试验同时进行钢筋应力测试.     

Evidence for microbial activity in British and Irish Ordovician pillow lavas

Pyrite is consistently found in modern seafloor vesicular basalts and has a sulphur isotopic composition consistent with microbial activity. We present S isotope data from pyrite in Ordovician pillow lavas at localities across the British Isles, which yield a range of δ³⁴S compositions consistent with two components of sulphur: groundmass pyrite (~0 ± 4‰) and ³²S‐enriched pyrite in the vesicles (−8‰ to −27‰). The latter are recorded from vesicular lavas in four different terranes, representing different settings at the margins of the Iapetus Ocean. Whereas a component of magmatic sulphate is recognized in the groundmass values, the isotopically light data in the vesicles are consistent with microbial reduction of seawater sulphate in sub‐seafloor lavas. This is consistent with modern examples and indicates considerable longevity for this sub‐seafloor microbial habitat. Copyright © 2014 John Wiley & Sons, Ltd.     

江西省广丰县李家膨润土矿床成因及找矿标志

广丰县李家膨润土矿床赋存于白垩系上统南雄组第二岩性段酸性火山岩的顶底部。膨润土的主要矿物成分为蒙脱石,矿石结构构造与成矿原岩有关。矿石化学成分与酸性熔岩相近,矿体形态及空间分布受酸性熔岩流相带的控制。因此认为,膨润土矿床成矿原岩为酸性玻质熔岩,矿床是由酸性玻璃质熔岩经水解脱玻化而形成,其成因类型为风化淋滤蚀变岩型矿床。膨润土可自然改型,由原来的钠基膨润土改型成钙基膨润土和偏镁的钙基膨润土。对时代较新的酸性火山岩,在玻质熔岩发育处都有可能找到有利用价值的膨润土矿。由于膨润土常由珍珠岩、沸石脱玻化形成,三者常共生出现,是很好的找矿标志。     

广西南部钦州地区早—中三叠世火山事件——台马碎斑熔岩

通过对前人划分的十万大山岩带的主要岩体——台马岩体的野外地质特征、岩石学特征的研究,认为原台马岩体主要由碎斑熔岩组成,是火山侵出相的产物而不是侵入相的花岗斑岩。结合台马碎斑熔岩与周边火山岩、侵入岩、地层的关系,认为它是早—中三叠世中心裂隙式火山构造中央部位侵出的穹状岩脊。因此,十万大山岩带是火山-侵入杂岩带,台马碎斑熔岩是该火山-侵入杂岩带的一个相。     

江西相山铀矿田燕山期岩浆活动的多阶段性及其意义

相山铀矿田是我国最大的火山岩型铀矿田,区域内主要出露有碎斑熔岩、流纹英安岩、花岗斑岩等火山岩—潜火山岩。前人对这三种岩浆岩进行了较为详尽的年代学研究。近年来随着相山西部深部钻探的开展,发现钻孔中由上至下出现‘碎斑熔岩—流纹英安岩—碎斑熔岩’的现象,现有的年代学结果还不能给予合理的解释。为此,我们对相山西部典型钻孔中的上下两层碎斑熔岩及其间的流纹英安岩,以及相山北部和西部钻孔中的三个花岗斑岩样品进行了详细的年代学研究,结果显示,流纹英安岩的锆石206Pb/238 U加权平均年龄为139.7±1.0Ma,碎斑熔岩（上层）的加权平均年龄为135.3±0.9Ma,碎斑熔岩（下层）的加权平均年龄为129.9±0.9Ma,不同地点的三个花岗斑岩样品的加权平均年龄分别为125.4±1.0Ma, 134.4±1.3Ma,148.8±2.3Ma,结合上下两层碎斑熔岩的镜下特征,认为下层碎斑熔岩是在上层碎斑熔岩形成后沿流纹英安岩之下的凝灰岩接触面超浅层侵入形成,从而在剖面上显示出“上老下新”的特征。这些结果表明相山燕山期岩浆活动持续时间较长（长达约24Ma）,为成矿有利因素,而不是前人认为的相山燕山期岩浆活动是一次短暂而集中的活动。对相山火山—侵入杂岩锆石的Hf同位素研究表明,各岩石样品的锆石εHf(t)值相近,分布在-10.6~-4.9之间,锆石的Hf模式年龄TDM2介于1478~1844Ma之间,本研究认为相山火山—侵入杂岩体可能起源于相山深部中元古代岩地壳所衍生的基底副变质岩部分熔融。     

Mantle heterogeneity,plume-lithosphere interaction at rift controlled ocean-continent transition zone: Evidence from trace-PGE geochemistry of Vempalle flows,Cuddapah Basin,India

This study reports major, trace, rare earth and platinum group element compositions of lava flows from the Vempalle Formation of Cuddapah Basin through an integrated petrological and geochemical approach to address mantle conditions, magma generation processes and tectonic regimes involved in their formation. Six flows have been identified on the basis of morphological features and systematic three-tier arrangement of vesicular-entablature-colonnade zones. Petrographically, the studied flows are porphyritic basalts with plagioclase and clinopyroxene representing dominant phenocrystal phases.Major and trace element characteristics reflect moderate magmatic differentiation and fractional crystallization of tholeiitic magmas. Chondrite-normalized REE patterns corroborate pronounced LREE/HREE fractionation with LREE enrichment over MREE and HREE. Primitive mantle normalized trace element abundances are marked by LILE-LREE enrichment with relative HFSE depletion collectively conforming to intraplate magmatism with contributions from sub-continental lithospheric mantle(SCLM) and extensive melt-crust interaction. PGE compositions of Vempalle lavas attest to early sulphur-saturated nature of magmas with pronounced sulphide fractionation, while PPGE enrichment over IPGE and higher Pd/Ir ratios accord to the role of a metasomatized lithospheric mantle in the genesis of the lava flows. HFSEREE-PGE systematics invoke heterogeneous mantle sources comprising depleted asthenospheric MORB type components combined with plume type melts. HFSE-REE variations account for polybaric melting at variable depths ranging from garnet to spinel lherzolite compositional domains of mantle. Intraplate tectonic setting for the Vempalle flows with P-MORB affinity is further substantiated by(i) their origin from a rising mantle plume trapping depleted asthenospheric MORB mantle during ascent,(ii) interaction between plume-derived melts and SCLM,(iii) their rift-controlled intrabasinal emplacement through Archeane Proterozoic cratonic blocks in a subduction-unrelated ocean-continent transition zone(OCTZ). The present study is significant in light of the evolution of Cuddapah basin in the global tectonic framework in terms of its association with Antarctica, plume incubation, lithospheric melting and thinning, asthenospheric infiltration collectively affecting the rifted margin of eastern Dharwar Craton and serving as precursors to supercontinent disintegration.     

膏盐层在矽卡岩型铁矿成矿中的作用

矽卡岩型铁矿是我国富铁矿的重要类型,约占全国富铁矿总储量的60%。虽然膏盐层与矽卡岩型铁矿的关系已引起部分矿床学家的关注,但膏盐层的控矿机制尚不清楚。本文以我国最重要的大冶式和邯邢式矽卡岩型铁矿为例,探讨了膏盐层在矽卡岩型铁矿成矿中的作用。膏盐层富含碳酸盐、石膏和石盐等,不仅可以为成矿提供大量Na⁺、Cl^-、CO3²⁺等矿化剂,使围岩发生钠长石化、方柱石化（氯化）和矽卡岩化等蚀变,使Fe²⁺以NaFe-Cl等络合物形式搬运,膏盐层还是地壳深处最重要的氧化障,能够将硅酸盐熔体和成矿溶液中的Fe²⁺氧化成Fe³⁺,富集形成铁矿床,是矽卡岩型铁矿成矿的关键因素。大冶地区的膏盐层属于中三叠统下部的嘉陵江组,邯邢地区的膏盐层属于中奥陶统马家沟组—峰峰组。大冶和邯邢式矽卡岩型铁矿中硫化物的δ³⁴S_V-CDT值异常高,计算结果表明矿床中约80%的硫来自膏盐层硫酸盐的还原,还原温度多在500℃以上,但硫化物的沉淀温度相对较低,就位时间稍晚;硫酸盐的δ³⁴S_V-CDT值和还原温度越高,硫化物的δ³⁴S_V-CDT值越高,原始岩浆硫所占比例越高,硫化物的δ³⁴S_V-CDT值越低。当炽热的岩浆与膏盐层（CaSO₄）发生同化混染时,SO₄^2-将硅酸盐熔体中的Fe²⁺氧化成Fe³⁺,Fe³⁺无法进入硅酸盐矿物晶格,而形成Fe₃O₄/Fe₂O₃进入熔体,铁氧化物在磷、氯化钠、水等挥发分和盐类物质的作用下在岩浆房中与硅酸盐熔体发生不混熔,形成铁矿浆,沿构造有利部位贯入,形成矿浆型铁矿床。在矽卡岩型铁矿床中,矿浆充填型和热液交代型矿体同时存在,二者在空间上具有一定的分带性,有时渐变过渡,矿浆充填型铁矿体通常位于深部靠近成矿岩体的部位,而热液交代型铁矿体位于成矿流体运移的前方。在SO₄^2-氧化Fe²⁺的同时自身被还原为S^2-,与Fe²⁺结合形成硫铁矿,分布在铁矿的上部或边部。     

新疆阿什库勒盆地大黑山火山地质及地球化学特征

大黑山火山是新疆阿什库勒火山群最大的火山,通过野外地质调查和遥感解译,火山锥体由渣锥、溅落锥和寄生火山锥组成。大黑山岩石类型分别为玄武粗安岩、粗面安山岩和粗面岩,钾玄岩系列。岩浆分离结晶特征明显,斜长石晶体析出导致残余熔体中δEu形成明显负异常。大黑山锥体南侧发育一套长约1.3km的碎屑熔岩。该套岩石显微薄片上表现为发育玻晶交织结构和溶蚀结构等熔岩结构特征,少许凝灰结构。碎屑主要为5~6cm的角砾,含少量的火山弹。角砾可能来自于大黑山火山较强的爆发,生成岩屑以及少量凝灰质碎屑。后期熔岩喷泉式喷发形成熔岩流,在流动过程中裹带大量的岩屑以及少量凝灰质碎屑。该套碎屑熔岩的发现,加深了对整个地区火山活动类型的了解。