Magnetic field intensity study of the 1960 Kilauea lava flow, Hawaii, using the microwave palaeointensity technique   总被引：1，自引：0，他引：1  

Mimi J. Hill  & John Shaw 《Geophysical Journal International》2000,142(2):487-504

It is extremely valuable to study historic lava flows where the geomagnetic field at their time of extrusion is well known. In this study, two vertical sections, 16 m apart, have been sampled from the approximately 1 m thick 1960 Kilauea lava flow, Hawaii. Variations are seen in the rock-magnetic and palaeomagnetic properties between and within the two sections, indicating that there are small-scale lateral and vertical variations in the lava flow. The two sections showed different responses to microwave palaeointensity analysis. Section H6001 generally gave ideal linear behaviour on plots of natural remanent magnetization (NRM) lost against microwave-induced thermoremanent magnetization (T_M RM) gained, whilst the majority of samples from H6002 showed anomalous two-slope behaviour. When all plots were interpreted by taking the best-fitting line through all points, the flow mean intensity for H6001 was 31.6 ± 3.6 μT and that for H6002 was 37.1 ± 6.4 μT, compared with the expected intensity of 36 μT. Additional historic flows need to be studied in order to ascertain whether this behaviour is typical of all lava, and whether it is best to always interpret NRM lost/T_M RM gained plots by taking the line of best fit regardless of shape.  相似文献   

Historical eruptions of Merapi Volcano, Central Java, Indonesia, 1768–1998     

B. Voight  E. K. Constantine  S. Siswowidjoyo  R. Torley 《Journal of Volcanology and Geothermal Research》2000,100(1-4)

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山东临朐-昌乐地区新生代火山岩研究     

张春池  杨恩秀  李秀章  任天龙  朱继托  宁振国 《上海国土资源》2010,31(Z1)

山东临朐-昌乐地区新生代火山岩是新近纪中新世-上新世火山活动产生的大陆溢流玄武岩,分为牛山期、山旺期和尧山期,主喷发期为牛山期和尧山期,属于碱性玄武岩系列。火山岩化学成分由早至晚向富碱、钛、钙,贫硅、镁、锰的方向演化,岩浆分异程度晚期较早期高。岩石内有大量二辉橄榄岩、方辉橄榄岩等幔源包体和透长石、普通辉石、尖晶石等巨晶。玄武岩K-Ar年龄为4.34～18.87Ma。火山岩岩浆来源于上地幔。  相似文献   

The Petrology and Geochemistry of Oto-Zan Composite Lava Flow on Shodo-Shima Island, SW Japan: Remelting of a Solidified High-Mg Andesite Magma   总被引：1，自引：0，他引：1  

TATSUMI  Y.; SUZUKI  T.; KAWABATA  H.; SATO  K.; MIYAZAKI  T.; CHANG  Q.; TAKAHASHI  T.; TANI  K.; SHIBATA  T.; YOSHIKAWA  M. 《Journal of Petrology》2006,47(3):595-629

The Oto-Zan lava in the Setouchi volcanic belt is composed ofphenocryst-poor, sparsely plagioclase-phyric andesites (sanukitoids)and forms a composite lava flow. The phenocryst assemblagesand element abundances change but Sr–Nd–Pb isotopiccompositions are constant throughout the lava flow. The sanukitoidat the base is a high-Mg andesite (HMA) and contains Mg- andNi-rich olivine and Cr-rich chromite, suggesting the emplacementof a mantle-derived hydrous (7 wt % H₂O) HMA magma. However,Oto-Zan sanukitoids contain little H₂O and are phenocryst-poor.The liquid lines of descent obtained for an Oto-Zan HMA at 0·3GPa in the presence of 0·7–2·1 wt % H₂Osuggest that mixing of an HMA magma with a differentiated felsicmelt can reasonably explain the petrographical and chemicalcharacteristics of Oto-Zan sanukitoids. We propose a model wherebya hydrous HMA magma crystallizes extensively within the crust,resulting in the formation of an HMA pluton and causing liberationof H₂O from the magma system. The HMA pluton, in which interstitialrhyolitic melts still remain, is then heated from the base byintrusion of a high-T basalt magma, forming an H₂O-deficientHMA magma at the base of the pluton. During ascent, this secondaryHMA magma entrains the overlying interstitial rhyolitic melt,resulting in variable self-mixing and formation of a zoned magmareservoir, comprising more felsic magmas upwards. More effectiveupwelling of more mafic, and hence less viscous, magmas througha propagated vent finally results in the emplacement of thecomposite lava flow. KEY WORDS: high-Mg andesite; sanukitoid; composite lava; solidification; remelting  相似文献   

云南龙脖河铜矿区东矿带成矿条件、控矿规律研究   总被引：2，自引：1，他引：1  

高俊  崔银亮 《地质与勘探》2004,40(5):33-38

云南金平龙脖河铜矿区, 除铜外还伴有金、铁矿化,东矿带目前累计估算铜资源量已达100万t,具有矿床埋藏较浅、规模大、品位高、矿石质量好、交通便利、容易开采的特点,矿床受地层岩性、构造、海相中基性火山岩等因素控制特征明显,属海相火山块状硫化物型铜矿床,是云南三江南段找矿有较大突破的区带.  相似文献   

Melting of eclogite facies sedimentary rocks in the Belomorian Eclogite Province,Russia          下载免费PDF全文

K. A. Dokukina  M. V. Mints  A. N. Konilov 《Journal of Metamorphic Geology》2017,35(4):435-451

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香港国家地质公园粮船湾组火山岩岩石学研究   总被引：2，自引：0，他引：2       下载免费PDF全文

邢光福吴振扬陶奎元伍世良  陈荣 姜杨 李龙明  余明刚 《中国地质》2011,38(4):1079-1093

在香港国家地质公园西贡火山岩园区,核心地质景观是白垩纪粮船湾组(Kkh)火山岩优美的六方形石柱(柱状节理),它们的岩石类型长期存在熔岩和火山碎屑岩之争。笔者等经野外调查和薄片岩石学研究,确认粮船湾组火山岩实属一种特殊的熔岩——流纹质碎斑熔岩,以普遍的柱状节理、斑晶具有碎斑结构和珠边结构、基质发育霏细结构和流动构造为特征;它们不仅代表了香港地区中生代最晚期火山喷发的产物,而且构成了西贡破火山机构的中央侵出相岩穹。推断粮船湾组火山岩石柱是地球上已知面积最大的流纹质碎斑熔岩石柱群(～150 km2),目前所见的火山岩石柱仅是长期剥蚀后的残余部分。  相似文献   

Direct ascent to the surface of asthenospheric magma in a region of convex lithospheric flexure     

Yuki Sato  Naoto Hirano  Shiki Machida  Junji Yamamoto  Masao Nakanishi  Teruaki Ishii 《International Geology Review》2018,60(10):1231-1243

The stress field of oceanic lithosphere controls the distribution of submarine petit-spot volcanoes. However, the eruption sites of these petit-spot volcanoes are considered to be limited to concavely flexed regions of lithosphere off the outer rise. Here, we present new data for a recently identified petit-spot lava field on a convexly flexed section of the lithosphere adjacent to the subduction zone offshore of northeast Japan in an area containing more than 80 volcanoes. This area is marked by strongly alkaline lavas that were erupted on the convexly flexed region. As for the concavely flexed region where the petit-spots previously reported, the base of the lithosphere beneath the eruption sites is under extension, whereas the upper part of the lithosphere is under compression. This change in the stress field, from the lower to upper lithosphere, causes ascending dikes to stall in the mid-lithosphere, leading to metasomatic interaction with the surrounding peridotite. The new geochemical data of rocks and xenocrysts presented in this study indicate that strongly alkaline magmas erupted on the convexly flexed region would have ascended more rapidly through the mid-depth of lithosphere because of the extensional regime of the upper lithosphere and decreasing the degree of metasomatic reaction with the surrounding mantle peridotite. The results indicate that the degree of metasomatism and the compositional variations of petit-spot magmas are controlled mainly by the stress field of the lithosphere.  相似文献   

关于赣中相山矿田相山“碎斑熔岩”   总被引：5，自引：0，他引：5  

张万良  李子颖 《地质论评》2015,61(2):367-375

赣中相山矿田相山杂岩体的主体岩石——"碎斑熔岩"的成因和命名,长期看法不一,主要观点有火山喷发成因、火山溢流成因、火山侵出成因、潜火山侵入成因等,本文通过综述"碎斑熔岩"的岩石学和相带特征,结合剥蚀程度、密度垂向变化研究成果,论述了"碎斑熔岩"不是火山岩而是侵入岩的成因观点。同时,对相山是否存在潜火山岩提出了质疑,探讨了相山"碎斑熔岩"的形成深度问题。认为"碎斑熔岩"命名为碎斑花岗斑岩更符合其侵入成因特点。  相似文献   

The anisotropy of magnetic susceptibility of lava flows: an experimental approach     

E. Can-Tapia  H. Pinkerton 《Journal of Volcanology and Geothermal Research》2000,98(1-4)

Measurements of the anisotropy of magnetic susceptibility (AMS) of natural lavas have shown that AMS varies with depth within a lava flow. We have investigated the reasons for such variation by studying the effects of temperature and strain rate on the AMS of recent lava in the laboratory. Samples of lava from Kilauea were melted and subjected to a range of strain rate and cooling histories. The results show that the degree of anisotropy is a function of both the thermal and shearing history of a sample. High degrees of anisotropy were found only in samples that were deformed at temperatures close to those encountered during eruption and then rapidly quenched. Lavas subjected to similar shear stresses at high temperatures had low degrees of anisotropy if allowed to cool down slowly without further deformation. Additionally, lava subjected to complex shearing yield a lower degree of anisotropy even when high strain rates were imposed on it. These results lead to the conclusion that only the last phase of deformation is detectable using AMS and that high strain rates will not result in high degrees of anisotropy if either deformation ends while lava is still fluid or if the orientation of the maximum shear stress varies with time. The relation between the orientation of the principal susceptibilities and that of shear is less sensitive to variation on shear with time. Consequently, flow directions can be inferred confidently with this type of measurements.  相似文献