Contact Partial Melting of Granitic Country Rock, Melt Segregation, and Re-injection as Dikes into Ferrar Dolerite Sills, McMurdo Dry Valleys, Antarctica     

Hersum  Taber G.; Marsh  Bruce D.; Simon  Adam C. 《Journal of Petrology》2007,48(11):2125-2148

Numerous, interconnected, granitic dikes (<30 cm in widthand hundeds of meters in length) cut Ferrar dolerite sills ofthe McMurdo Dry Valleys, Antarctica. The source of the graniticdikes is partial melting of granitic country rock, which tookplace in the crust at a depth of about 2–3 km adjacentto contacts with dolerite sills. Sustained flow of doleriticmagma through the sill generated a partial melting front thatpropagated into the granitic country rock. Granitic partialmelts segregated and collected at the contact in a melt-rich,nearly crystal-free reservoir adjacent to the initial doleritechilled margin. This dolerite chilled margin was subsequentlyfractured open in the fashion of a trapdoor by the graniticmelt, evacuating the reservoir to form an extensive complexof granitic dikes within the dolerite sills. At the time ofdike injection the dolerite was nearly solidified. Unusuallycomplete exposures allow the full physical and chemical processesof partial melting, segregation, and dike formation to be examinedin great detail. The compositions of the granitic dikes andthe textures of partially melted granitic wall rock suggestthat partial melting was characterized by disequilibrium mineraldissolution of dominantly quartz and alkali feldspar ratherthan by equilibrium melting. It is also unlikely that meltingoccurred under water-saturated conditions. The protolith granitecontains only 7 vol.% biotite and estimated contact temperaturesof 900–950°C suggest that melting was possible ina dry system. Granite partial melting, under closed conditions,extended tens of meters away from the dolerite sill, yet meltsegregation occurred only over less than one-half a meter fromthe dolerite chilled margin where the degree of partial meltingwas of the order of 50 vol.%. This segregation distance is consistentwith calculated length scales expected in a compaction-drivenprocess. We suggest that the driving force for compaction wasdifferential stress generated by a combination of volume expansionas a result of granite partial melting, contraction during doleritesolidification, and relaxation of the overpressure driving doleriteemplacement. On a purely chemical basis, the extent of meltsegregation necessary under fractional and batch melting tomatch the Rb concentrations between melt and parent rock isa maximum of 48 and 83 vol.% melt, respectively. KEY WORDS: Antarctica; dike injection; disequilibrium; granite partial melting; silicic melt segregation  相似文献   

共生黑钨矿与石英等多种矿物中流体包裹体的红外显微测温对比研究——以江西西华山石英脉钨矿床为例   总被引：3，自引：0，他引：3  

黄惠兰  常海亮  谭靖  李芳  张春红  周云 《岩石学报》2015,31(4):925-940

西华山钨矿床是一个产于燕山期花岗岩中的大脉型钨矿床。已有百余年的开采史。但在矿床成矿条件和成矿流体性质等方面一直存在不同认识。作者利用红外显微镜及其它相关设备,对西华山矿床不同中段样品中的黑钨矿、锡石、绿柱石、黄铁矿、闪锌矿、石英和萤石中的流体包裹体进行了详细对比研究。结果显示,蚀变花岗岩中造岩石英只见次生气液包裹体,晶洞水晶中只有原生包裹体,而云英岩石英中原生、次生包裹体均较发育。黑钨矿中以原生气液包裹体为主,在早期结晶的黑钨矿中还有较多的硅酸盐熔融包裹体,而晶洞中的黑钨矿和水晶一样——只有原生气液包裹体。绿柱石中除了硅酸盐包裹体外,主要是气液包裹体(多为次生)。其它锡石、黄铁矿、闪锌矿和萤石等都只有气液包裹体(原生或次生)。研究结果表明,西华山钨矿床的初始成矿流体是一种岩浆——热液过渡性流体,尔后才演变成单一的热水溶液,在这一过程中黑钨矿、黄铁矿、闪锌矿、萤石和石英等矿物不断晶出。矿床总的成矿温度大致为700~200℃,压力约为160~200MPa。各种气液包裹体的盐度主要为5.0%~10%Na Cleqv。文中还对这些数据的地质意义以及对脉钨矿床流体包裹体研究和数据解释中的某些问题进行了较深入的讨论。  相似文献   

Chemical dynamics of N-containing ionic species in a boreal forest snowcover during the spring melt period     

H. G. Jones  C. Deblois 《水文研究》1987,1(3):271-282

A study of the changes in the ionic loads of NO, NH, SO and H⁺ in a boreal forest snowpack at Lake Laflamme, Québec was carried out using hydrological and chemical data from field lysimeters. The results showed that depletion of the N-containing species occurs periodically in the snowpack during meltwater discharge. Rain-on-snow events led to in-pack losses of NO and NH at a rate of 130 μeq m^?2 day^?1 and 101·3 μeq m^?2day^?1 respectively. On dry days, however, dry deposition and deposition of organic debris from the canopy resulted in increases of 183·3 μeq m^?2day^?1 for NO and 4·5 μeq m^?2day^?1 for NH in the pack. In contrast, SO₄^2? showed continual in-pack increases due to deposition of 5·0 μeq m^?2day^?1 for wet days and 92·6 μeq m^?2day^?1 for dry days. The depletion of NO and NH is due to microbiological uptake of these nutrients during periods when the free water content of the pack is high. Controlled melts in a laboratory snowmelt simulator containing snow and organic matter from the forest canopy at Lake Laflamme showed losses of NO and NH similar to those observed in the field. As the microbiological uptake proceeds at a rate comparable to that of ionic load increases in the pack by dry deposition, models of the chemical dynamics of snowmelt should take the former into account in any system where organic content of the snowpack is appreciable.  相似文献   

Melt inclusion analysis of the Unzen 1991–1995 dacite: implications for crystallization processes of dacite magma     

Koshi Nishimura  Tatsuhiko Kawamoto  Tetsuo Kobayashi  Takeshi Sugimoto  Shigeru Yamashita 《Bulletin of Volcanology》2005,67(7):648-662

Dacitic magma, a mixture of high-temperature (T) aphyric magma and low-T crystal-rich magma, was erupted during the 1991–1995 Mount Unzen eruptive cycle. Here, the crystallization processes of the low-T magma were examined on the basis of melt inclusion analysis and phase relationships. Variation in water content of the melt inclusions (5.1–7.2 wt% H₂O) reflected the degassing history of the low-T magma ascending from deeper levels (250 MPa) to a shallow magma chamber (140 MPa). The ascent rate of the low-T magma decreased markedly towards the emplacement level as crystal content increased. Cooling of magma as well as degassing-induced undercooling drove crystallization. With the decreasing ascent rate, degassing-induced undercooling decreased in importance, and cooling became more instrumental in crystallization, causing local and rapid crystallization along the margin of the magma body. Some crystals contain scores of melt inclusions, whereas there are some crystals without any inclusions. This heterogeneous distribution suggests the variation in the crystallization rate within the magma body; it also suggests that cooling was dominant cause for melt entrapment. Numerical calculations of the cooling magma body suggest that cooling caused rapid crystal growth and enhanced melt entrapment once the magma became a crystal-rich mush with evolved interstitial melt. The rhyolitic composition of melt inclusions is consistent with this model.Editorial responsibility: H Shinohara  相似文献   

Decompression and H<Subscript>2</Subscript>O exsolution driven crystallization and fractionation: development of a new model for low-pressure fractional crystallization in calc-alkaline magmatic systems     

James Gerald Brophy 《Contributions to Mineralogy and Petrology》2009,157(6):797-811

Magma ascent, decompression-induced H₂O exsolution and crystallization is now recognized as an important process in hydrous subduction zone magmas. During the course of such a process calculations suggest that the ascent rate of a degassing and crystallizing mafic magma will be greater than crystal settling velocities. Thus, any crystals formed as a consequence of volatile exsolution will remain suspended in the magma. If the magma erupts before the percentage of suspended crystals reaches the critical crystallinity value for mafic magma (~55 vol.%) it will produce the commonly observed crystal rich island arc basalt lava. If the magma reaches its critical crystallinity before it erupts then it will stall within the crust. Extension of compaction experiments on a 55 vol.% sand-Karo syrup suspension at different temperatures (and liquid viscosities) to the likely viscosities of interstitial andesitic to dacitic liquid within such a stalled magma suggest that small amounts (up to ~10%) can be expelled on a time scale of 1–10 years. The expelled liquid can create a new intermediate to silicic body of magma that is related to the original mafic magma via fractional crystallization. The short time scale for liquid expulsion indicate that decompression-induced H₂O exsolution and crystallization can be an important mechanism for fractional crystallization. Based on this assumption a general model of decompression-induced crystallization and fractionation is proposed that explains many of the compositional, mineralogical and textural features of Aleutian (and other andesites).  相似文献   

Apatite as a monitor of late-stage magmatic processes at Volcán Irazú, Costa Rica   总被引：1，自引：1，他引：0  

Jeremy W. Boyce  Richard L. Hervig 《Contributions to Mineralogy and Petrology》2009,157(2):135-145

Apatite phenocrysts from the 1963 and 1723 eruptions of Irazú volcano (Costa Rica) record a volatile evolution history that confirms previous melt inclusion studies, and provides additional information concerning the relative and absolute timing of subvolcanic magmatic events. Measurements of H, Cl, and F by secondary ion mass spectrometry reveal multiple populations of apatite in both 1723 and 1963 magmas. Assuming nominal apatite/melt partition coefficients allows us to compare the pattern of melt inclusions and apatites in ternary space, demonstrating the fidelity of the record preserved in apatite, and revealing a complex history of magma mixing with at least two components. The preservation of heterogeneous populations of apatite and of internally heterogeneous crystals requires short timescales (days to years) for these magmatic processes to occur.  相似文献   

Combined Sr isotope and trace element analysis of melt inclusions at sub-ng levels using micro-milling, TIMS and ICPMS   总被引：1，自引：0，他引：1  

R. Harlou  D.G. Pearson  G.M. Nowell  C.J. Ottley  J.P. Davidson 《Chemical Geology》2009,260(3-4):254-268

This paper describes a technique, which allows precise and accurate Sr isotope measurement combined with trace element analysis of individual melt inclusions, of sample sizes  1 ng of Sr. The technique involves sampling by micro-milling, chemical dissolution, micro Sr column chemistry, TIMS, and ICPMS analyses. A 10% aliquot of each sample solution is used for trace element analysis by double focusing magnetic sector field ICPMS, while Sr is chemically separated from the remaining 90% and used for ⁸⁷Sr/⁸⁶Sr determinations by TIMS.During the development of the technique outlined above, we documented in detail the potential sources of blank contributions and their magnitude. The average size and Sr isotope composition of our laboratory total procedural blank during this study was 5.4 pg ± 0.3 pg Sr (n = 21) with an ⁸⁷Sr/⁸⁶Sr of 0.7111 ± 0.0002 (2SE, n = 3). The total procedural Rb blank was 1.9 ± 0.7 pg (n = 21). The total procedural blank was found to have minimal effect (< 150 ppm shift) on the ⁸⁷Sr/⁸⁶Sr of sample material containing down to  250 pg Sr. Applying a blank correction allows ‘in house’ standards of this size to be corrected back to within 175 ppm of their accepted values. By applying blank corrections we can confidently measure the Sr isotope composition on sample sizes down to  25 pg Sr to an accuracy better than 400 ppm.The utility of the technique is illustrated by application to a suite of melt inclusions from NW Iceland and their host olivines. It is shown that the effect of a small amount of entrainment of the host olivine during sampling of 50 μm melt inclusions has a negligible effect on the measured Sr isotope and trace element composition. Furthermore, where melt inclusions are < 50 μm it is possible to obtain Sr isotope and trace element data on multiple melt inclusions hosted in a single olivine. This provides similar information to that of the single melt inclusions.  相似文献   

扬子地块北缘新元古代望江山层状岩体矿物成分和铂族元素特征:对岩浆演化过程和构造环境的制约   总被引：1，自引：1，他引：0  

王岩  王梦玺  焦建刚 《地质力学学报》2019,25(2):267-285

望江山层状岩体位于扬子地块北缘新元古代汉南杂岩带中,岩体从底部到顶部由超镁铁质岩过渡为中性岩:底部主要由辉石岩和橄长岩组成;中部为辉长苏长岩和辉长岩;上部为辉长岩和闪长岩。研究以中部岩相带橄榄辉长苏长岩、辉长苏长岩和辉长岩为对象,通过主要矿物的主微量元素和全岩主微量元素的分析,查明望江山岩体来源于尖晶石二辉橄榄岩组成的大陆下岩石圈地幔,并且地幔源区受到了来自俯冲板片流体的交代,岩体中部带的母岩浆为拉斑玄武质岩浆。钛铁矿—磁铁矿矿物对成分计算表明,母岩浆在形成时具有较高氧逸度。通过单斜辉石压力计得到岩体的侵位深度约为12.9~18 km。对岩体母岩浆橄榄石分离结晶过程的模拟计算表明,中部带橄榄石为母岩浆经过~28%分离结晶的产物。此外,铂族元素（PGE）组成暗示岩体并未经历过大规模的硫化物熔离,可能与缺乏地壳物质混染有关。岩体中单斜辉石与岛弧环境堆晶岩中单斜辉石成分相似,不同于裂谷环境中堆晶单斜辉石的成分;同时,全岩Th/Yb和Nb/Yb比值也与岛弧玄武岩比值相似,因此矿物和全岩成分均说明望江山层状岩体应形成于岛弧环境。研究认为扬子北缘在新元古代长期的俯冲过程中,大洋板片断离导致软流圈上涌,提供热源使交代大陆下岩石圈地幔部分熔融形成具有岛弧特征的镁铁质岩浆,在局部伸展环境中上升侵位形成汉南杂岩带中镁铁—超镁铁质层状岩体。   相似文献   

Unraveling the multi-scalar residential segregation and socio-spatial differentiation in China: A comparative study based on Nanjing and Hangzhou   总被引：1，自引：0，他引：1  

SONG Weixuan  HUANG Qinshi  GU Yue  HE Ge 《地理学报(英文版)》2021,31(12):1757-1774

Residential segregation is a dual process of socio-spatial differentiation in residents and spatio-temporal heterogeneity in dwelling.However,most of the existing studies are es-tablished from the single perspective of urban residents based on demographic data,which is difficult to reveal the dynamics and complex spatial reconstruction within and between cities.With the characteristics of both stability and timeliness,the rapidly changing housing market is one of the processes and results of socio-spatial reconfiguration,and it is undoubtedly a better lens to observe residential segregation.This paper adopts methods such as multi-group segregation index,multi-scalar segregation profiles,and decomposition of segregation index,with Nanjing and Hangzhou as case cities,and establishes multi-scalar segregation profiles and comparative models based on three geographical scales of census tract,block and grid,and different residential types.A quantitative study was conducted on the degree and pattern of multi-scalar residential segregation in Nanjing and Hangzhou from 2009 to 2018.The pa-per found that the spatial segregation index is an improvement of the non-spatial segregation index.There are differences between Nanjing and Hangzhou in the evolution process of residential segregation.Nanjing has a higher degree of spatial differentiation as a whole,among which spatial components have a more significant impact.  相似文献   

非户籍与户籍人口居住空间分异的多维度解析——以深圳为例   总被引：4，自引：3，他引：1  

张瑜  仝德  IanMacLACHLAN 《地理研究》2018,37(12):2567-2575

在居住空间相异指数基础上,构建了集聚—分散度、中心—边缘度和极化—均质度指数,进一步挖掘由于人口聚居形态、居住区位和居住质量等方面差异导致的居住空间分异的多维内涵,及其所揭示出的社会经济空间现象、成因及空间治理重点。利用全国第六次人口普查数据开展深圳实证研究,在计算全市及各区分维指数的基础上,分析深圳人口居住空间相异指数特征及空间尺度差异,多维居住空间分异格局特征及成因,并通过聚类分析将深圳非户籍与户籍人口居住空间分异类型划分为三类,分类提出空间治理政策建议。从而为深入理解中国大城市日益出现的居住分异现象及机制提供新鲜视角和多样化测度方法,为解决其带来的社会及空间治理问题提供更有针对性的政策建议。  相似文献