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71.
72.
熔体包裹体对长白山天池火山千年大喷发的指示意义 总被引:2,自引:2,他引:0
长白山天池火山在全新世曾有过几次喷发,其中距今约1000年发生过大规模布里尼式爆炸喷发(即“千年大喷发”),其喷发产物——灰白色碱流质浮岩和喷发柱垮塌形成的火山碎屑流分布范围极广,除长白山区外,在朝鲜半岛和日本北部也有大量浮岩降落和堆积。根据野外较大范围的系统采样、镜下观察和测试分析,在天池火山千年大喷发产物的碱性长石晶屑中发现了两组颜色、形态、化学成分迥异的“火口组”和“圆池组”熔体包裹体,对揭示天池火山千年大喷发的成因具有重要意义。根据电子探针分析结果,“火口组”熔体包裹体成分为英安岩和粗面英安岩,寄主晶多为透长石;“圆池组”熔体包裹体成分为粗面英安岩和流纹岩,寄主晶为歪长石。相对“火口组”熔体包裹体,“圆池组”包裹体具有高SiO2、高H2O和高Cl含量的特点,化学成分也更为演化,可能是天池火山千年大喷发时岩浆结晶分异后期的产物。两组包裹体的存在为千年大喷发前的层状地壳岩浆房和成分并非单一提供了证据,它们可能是在同次大喷发的不同序列中喷出的。由于地幔岩浆注入地壳岩浆房,导致不同层位岩浆的扰动和混合作用,因挥发分出溶在岩浆房最顶部形成挥发分梯度和过饱和,最终触发了天池火山的千年大喷发,对当时的气候环境造成过较大影响。 相似文献
73.
ZHANG Shanwen 《《地质学报》英文版》2008,82(3)
Inspired from the anomaly of low pressure in the middle and deep reservoir of the Paleogene in the Jiyang depression, this paper theoritically discusses"waterconsumption"of the principal mineral alteration during the diagenetic stage. The preliminary research result shows that "water consumption" of mineral alteration in the diagenetic stage can make formation water greatly decrease. Relevant formations will be in the stage of low pressure without supply of exterior liquid. Pressure differences between the relevant formations and wall rocks make hydrocarbons enter easily to form the effective reservoir. 相似文献
74.
75.
Dense, CO2‐rich fluid inclusions hosted by plagioclases, An45 to An54, of the O.‐v.‐Gruber‐ Anorthosite body, central Dronning Maud Land, East Antarctica, contain varying amounts of small calcite, paragonite and pyrophyllite crystals detected by Raman microspectroscopy. These crystals are reaction products that have formed during cooling of the host and the original CO2‐rich H2O‐bearing enclosed fluid. Variable amounts of these reaction products illustrates that the reaction did not take place uniformly in all fluid inclusions, possibly due to differences in kinetics as caused by differences in shape and size, or due to compositional variation in the originally trapped fluid. The reaction albite + 2anorthite + 2H2O + 2CO2 = pyrophyllite + paragonite + 2calcite was thermodynamically modelled with consideration of different original fluid compositions. Although free H2O is not detectable in most fluid inclusions, the occurrence of OH‐bearing sheet silicates indicates that the original fluid was not pure CO2, but contained significant amounts of H2O. Compared to an actual fluid inclusion it is obvious, that volume estimations of solid phases can be used as a starting point to reverse the retrograde reaction and recalculate the compositional and volumetrical properties of the original fluid. Isochores for an unmodified inclusion can thus be reconstructed, leading to a more realistic estimation of P–T conditions during earlier metamorphic stages or fluid capturing. 相似文献
76.
D. NAKAMURA 《Journal of Metamorphic Geology》2009,27(7):495-508
Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet–clinopyroxene geothermometer based on 333 garnet–clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe3+ content of clinopyroxene. For the calibration, a published subregular‐solution model was adopted to express the non‐ideality of garnet. The magnitude of the Fe–Mg excess interaction parameter for clinopyroxene (WFeMgCpx), and differences in enthalpy and entropy of the Fe–Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe–Mg excess interaction parameter of clinopyroxene (WFeMgCpx = ? 3843 J mol?1). The pressure correction is simply treated as linear, and the difference in volume of the Fe–Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be ?120.72 (J kbar?1 mol?1). The regressed and obtained thermometer formulation is as follows: where T = temperature, P = pressure (kbar), A = 0.5 Xgrs (Xprp ? Xalm ? Xsps), B = 0.5 Xgrs (Xprp ? Xalm + Xsps), C = 0.5 (Xgrs + Xsps) (Xprp ? Xalm), Xprp = Mg/(Fe2+ + Mn + Mg + Ca)Grt, Xalm = Fe/(Fe2+ + Mn + Mg + Ca)Grt, Xsps = Mn/(Fe2+ + Mn + Mg + Ca)Grt, Xgrs = Ca/(Fe2+ + Mn + Mg + Ca)Grt, XMgCpx = Mg/(Al + Fetotal + Mg)Cpx, XFeCpx = Fe2+/(Al + Fetotal + Mg)Cpx, KD = (Fe2+/Mg)Grt/(Fe2+/Mg)Cpx, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800–1820 °C), with a standard deviation (1 sigma) of 74 °C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100 °C at >1300 °C and overestimate by 100–200 °C at <1300 °C. In addition, they tend to overestimate temperatures for high‐Ca garnet (Xgrs ≈ 0.30–0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20–100 °C lower than previous formulations. 相似文献
77.
杭州河上地区是浙西北上元古界上墅组火山岩发育的典型地区,同时还发育新元古代辉绿岩和碱长花岗岩板状复合浅成侵入体。火山岩与侵入岩在空间上密切共生,形成时间相近,皆为晋宁晚期构造岩浆活动的产物。火山喷发并伴随的岩浆侵入经历了两个阶段,每个阶段的火山岩与侵入岩在岩石类型、岩石化学和地球化学方面具有相似性或一致性,稀土元素分布型式基本一致,说明每个阶段的火山岩与侵入岩来源于同一岩浆源,均是同源岩浆活动的产物。第一阶段上墅组基性火山岩与次坞辉绿岩体起源于亏损程度较低的地幔,或来源于亏损地幔的岩浆受到陆壳物质的混染;第二阶段上墅组酸性火山岩与道林山碱长花岗岩体可能起源于地壳中既含有基性地壳组分和又含有酸性地壳组分的源区的部分熔融。 相似文献
78.
79.
Munetake Sasaki Koichiro Fujimoto Takayuki Sawaki Hitoshi Tsukamoto Osamu Kato Ryo Komatsu Nobuo Doi Masakatsu Sasada 《Journal of Volcanology and Geothermal Research》2003,121(3-4):247-269
A 3729-m-deep geothermal research well, WD-1a, provides us with a unique opportunity to study initial petrographic features of a high-temperature granite just after solidification of magma. The well succeeded in collecting three spot-cores of the Kakkonda Granite that is a pluton emplaced at a shallow depth and regarded as a heat source of the active Kakkonda geothermal system. The core samples were collected at the present formation temperatures of 370, 410 and over 500°C. These samples are granodiorite to tonalite consisting mainly of plagioclase, quartz, hornblende, biotite and K-feldspar. A sample collected at a formation temperature of over 500°C possesses the following remarkable petrographic features compared to the other two samples. Interstitial spaces are not completely sealed. K-feldspar exhibits no perthite by the exsolution of albite lamella. Quartz includes glassy melt inclusions without devitrification. Hornblende is less intensively altered to actinolite, and biotite is not altered. This study directly confirmed that perthite in K-feldspar is a recrystallization texture formed at 410–500°C based on a comparison of the in situ temperatures of the samples. Chemical compositions of minerals were analyzed to compare temperatures determined from geothermometers in several publications to the in situ temperatures of the samples. 相似文献
80.
一种刚玉夕线钾长片麻岩的岩石学矿物学特征及形成环境 总被引:3,自引:0,他引:3
刚玉夕线钾长片麻岩是产于新太古代迭布斯格岩群中的一种低Si、高Al、高K的特殊岩石,主要包括刚玉钾长金红石片麻岩、黑云夕线钾长金红石片麻岩2种岩石组合,呈互层状产出。刚玉、夕线石和钾长石是通过白云母的变质分解和白云母 SiO2的变质反应而生成的。形成温度约为720—760℃,压力约为0.6-0.8GPa。由于温度和压力稍高,岩石中已开始出现重熔钾长石细脉。环带状次生白云母的出现属退变质反应。变质程度为区域中高温变质作用,达高角闪岩相,与围岩的变质程度一致。其原岩是在较短的稳定条件下由富K、富Al的花岗质岩石经强烈风化搬运进入大陆边缘沉积盆地,再经化学分解和沉积作用而形成的不同的原岩组合。 相似文献