http://www.sciencedirect.com/science/article/pii/S1674987113001151   总被引：1，自引：0，他引：1  

M.L. Renjith  S.N. Charan  D.V. Subbarao  E.V.S.S.K. Babu  V.B. Rajashekhar 《地学前缘(英文版)》2014,5(6)

Magma mixing process is unusual in the petrogenesis of felsic rocks associated with alkaline complex worldwide. Here we present a rare example of magma mixing in syenite from the Yelagiri Alkaline Comp...  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113001345     

B. Goswami  C. Bhattacharyya 《地学前缘(英文版)》2014,5(6):821-843

Many elongated, lenticular plutons of porphyritic granitoids are distributed mainly near the southern and northern margin of the Chhotanagpur Gneissic Complex （CGC） which belongs to the EW to ENE-WSW tending 1500 km long Proterozoic orogenic belt amalgamat ng the North and South Indian cratonic blocks. The late Grenvillian （1071 ±64 Ma） Raghunathpur porphyritic granitoid gneiss （PGG） batholith comprising alkali feldspar granite, granite, granodiorite, tonalite, quartz syenite and quartz monzonite intruded into the granitoid gneisses of southeastern part of CGC in the Purulia district, West Bengal and is aligned with ENE-WSW trending North Purulia sr~ear zone, Mineral chemistry, geochemistry, physical condition of crystallization and petrogenetic model of Raghunathpur PGG have been discussed for the first time. The petrographic and geochemical features （including major and trace- elements, mineral chemistry and S7Sr/S6Sr ratio） suggest these granitoids to be classified as the shosh- onitic type. Raghunathpur batholith was emplaced at around 800 ~C and at 6 kbar pressure tectonic discrimination diagrams reveal a post-collision tectonic setting while structural studies reveal its emplacement in the extensional fissure of North Purulia shear zone. l＇he Raghunathpur granitoid is compared with some similar granitoids of Europe and China to draw its petrogenetic model. Hybridi- zation of mantle-generated enriched mafic magma and crustal magma at lower crust and later fractional crystallization is proposed for the petrogenesis of this PGG. Mafic magma generated in a post-collisional extension possibly because of delamination of subducting slab. Raghunathpur batholith had emplaced in the CGC during the final amalgamation （~ 1.0 Ga） of the North and South Indian cratonic blocks. Granitoid magma, after its generation at depth, was transported to its present level along megadyke channel, ways within shear zones.  相似文献   

Petrology and phase equilibrium modeling of sapphirine ＋ quartz assemblage from the Napier Complex,East Antarctica： Diagnostic evidence for Neoarchean ultrahigh-temperature metamorphism     

Hisako Shimizu  Toshiaki Tsunogae  M. Santosh 《地学前缘(英文版)》2013,4(6):655-666

A synthesis of the petrological characters of granulite facies rocks that contain equilibrium sapphirine ＋ quartz assemblage from two localities （Tonagh Island （TI） and Priestley Peak （PP）） in the Napier Complex,East Antarctica,provides unequivocal evidence for extreme crustal metamorphism possibly associated with the collisional orogeny during Neoarchean.The reaction microstructures associated with sapphirine ＋ quartz vary among the samples,probably suggesting different tectonic conditions during the metamorphic evolution.Sapphirine and quartz in TI sample were probably in equilibrium at the peak stage,but now separated by corona of Grt ＋ Sil ＋ Opx suggesting near isobaric cooling after the peak metamorphism,whereas the Spr ＋ Qtz ＋ Sil ＋ Crd ＋ Spl assemblage replaces garnet in PP sample suggesting post-peak decompression.The application of mineral equilibrium modeling in NCKFMASHTO system demonstrated that Spr ＋ Qtz stability is lowered down to 930 ℃ due to small Fe3＋ contents in the rocks （mole Fe2O3/（FeO ＋ Fe2O3） =0.02）.The TI sample yields a peak p-T range of 950-1100 ℃ and 7.5-11 kbar,followed by cooling toward a retrograde stage of 800-950 ℃ and 8-10 kbar,possibly along a counterclockwise p-T path.In contrast,the peak condition of the PP sample shows 1000-1050 ℃ and ＞12 kbar,which was followed by the formation ofSpr ＋ Qtz corona around garnet at 930-970 ℃ and 6.7-7.7 kbar,suggesting decompression possibly along a clockwise p-T trajectory.Such contrasting p-T paths are consistent with a recent model on the structural framework of the Napier Complex that correlates the two areas to different crustal blocks.The different p-T paths obtained from the two localities might reflect the difference in the tectonic framework of these rocks within a complex Neoarchean subduction/collision belt.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113000315   总被引：2，自引：0，他引：2  

Clement Ganino  Nicholas T.Arndt  Catherine Chauvel  Alexandre Jean  Charlotte Athurion 《地学前缘(英文版)》2013,4(5):535-546

The Panzhihua gabbroic intrusion,part of the plumbing system of the Emeishan large igneous province, intruded late-Proterozoic dolomites and marls about～263 Ma ago.The dolomites in the contact aureole were converted to brucite marbles and a diverse suite of forsterite,diopside and garnet skarns.The variation in mineralogy is explained in part by differences in the composition of the protolith,particularly the proportion of silica minerals and clay,and in part by transfer of elements from intruding magmas.The trace element compositions of most marbles and skarns are very similar to those of unmetamorphosed dolomites and marls,but some contain high Si,Ti,and Fe contents that are interpreted to have come from a magmatic source.Three brucite marbles sampled～10 m from the contact of the intrusion and named "enriched brucite marble" have trace element compositions very different from their dolomitic protolith:their rare earth elements are strongly enriched whereas levels of Nb-Ta,Zr-Hf and Ti are very low.These characteristics resemble those of carbonate liquid in equilibrium with silicate liquid or more probably with silicate minerals in the case of Panzhihua,a similarity we take to indicate that the sample underwent partial melting.Samples taken up to 300 m from the contact contain brucite indicating that high temperatures persisted well into the country rocks.However,other samples collected only tens of metres from the contact are only slightly recrystallized indicating that conditions in the aureole were highly variable.We suggest that temperatures within the aureole were controlled by conduction of heat from the main intrusion and by supply of additional heat from abundant small dykes within the aureole.Circulation of fluids derived from deeper levels in the aureole flushed the carbon dioxide from the dolomite,lowering temperature needed to partially melt carbonate to the temperatures attained near the intrusion.Irregular but extensive heating destabilized the carbonates of the aureole and decarbonation reactions associated with carbonate breakdown and melting emitted a large volume of CO₂,with potential impact on global climate.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987112001053     

Nicholas Arndt 《地学前缘(英文版)》2013,4(2):195-198

Massif anorthosites form when basaltic magma differentiates in crustal magma chambers to form low-density plagioclase and a residual liquid whose density was greater than that of enclosing crustal rocks. The plagioclase and minor pyroxene crystallized in-situ on the floor of the magma chamber to produce the anorthosite complex, and the residual liquid migrated downwards, eventually to solidify as dense Fe-rich cumulates some of which were removed to the mantle. These movements were facilitated by high temperatures in Proterozoic continental crust, thus explaining the restriction of large anorthosite massifs to this period in Earth history.  相似文献   

月球雨海地区玄武质岩浆充填活动期次的重新厘定及地质意义     

王庆龙  刘建忠  籍进柱  郭弟均  刘敬稳 《岩石学报》2016,32(1):29-42

雨海盆地是月球上研究程度最高的多环结构盆地,月球上古老的和年轻的玄武岩在盆地中均有分布,因此雨海是研究月海玄武岩岩浆活动的理想区域。为了更合理的厘定雨海地区的玄武质岩浆演化历史,本文主要结合岩石学、年代学等工作对本区玄武岩的充填期次进行重新划分。利用嫦娥一号IIM光谱数据进行岩石类型分布图编制,初步划分了5类不同钛含量的月海玄武岩;基于高分辨率100m LRO宽视角影像数据通过撞击坑尺寸-频率定年法(CSFD)对本区玄武岩单元模式年龄进行厘定,共划分35个玄武岩单元,发现本区在3.49~2.23Ga均有玄武质岩浆充填活动,具有多期次性。在建立不同类别玄武岩、形貌特征与模式年龄的对应关系基础上,将玄武岩充填划分为4个期次:极低钛玄武岩(3.49~3.20Ga)、低钛玄武岩(3.29~2.83Ga)、中钛玄武岩(3.13~2.52Ga)、(极)高钛玄武岩(2.92~2.23Ga)。本区地形地貌高程特征与不同表面年龄的玄武岩单元之间总体上呈现出一定的负相关性。因此在本区玄武质岩浆期次划分考虑上,不仅要考虑玄武岩的成分特征,更要考虑结合与玄武岩演化密切相关的年代学及形貌学特征,利用形貌、成分数据和年代学信息来共同约束玄武质岩浆期次划分及演化历史。  相似文献   

Petrology and geochemistry of diamondiferous Mesoproterozoic kimberlites from Wajrakarur kimberlite field,Eastern Dharwar craton,southern India: genesis and constraints on mantle source regions   总被引：1，自引：0，他引：1  

N. V. Chalapathi Rao  Rajesh K. Srivastava 《Contributions to Mineralogy and Petrology》2009,157(2):245-265

The petrology and geochemistry of some new occurrences of Mesoproterozoic diamondiferous hypabyssal-facies kimberlites from the Chigicherla, Wajrakarur-Lattavaram and Kalyandurg clusters of the Wajrakarur kimberlite field (WKF), Eastern Dharwar craton (EDC), southern India, are reported. The kimberlites contain two generations of olivine, and multiple groundmass phases including phlogopite, spinel, calcite, dolomite, apatite, perovskite, apatite and rare titanite, and xenocrysts of eclogitic garnet and picro-ilmenite. Since many of the silicate minerals in these kimberlites have been subjected to carbonisation and alteration, the compositions of the groundmass oxide minerals play a crucial role in their characterisation and in understanding melt compositions. While there is no evidence for significant crustal contamination in these kimberlites, some limited effects of ilmenite entrainment are evident in samples from the Kalyandurg cluster. Geochemical studies reveal that the WKF kimberlites are less differentiated and more primitive than those from the Narayanpet kimberlite field (NKF), Eastern Dharwar craton. Highly fractionated (La/Yb = 108–145) chondrite-normalised distribution patterns with La abundances of 500–1,000 × chondrite and low heavy rare earth elements (HREE) abundances of 5–10 × chondrite are characteristic of these rocks. Metasomatism by percolating melts from the convecting mantle, rather than by subduction-related processes, is inferred to have occurred in their source regions based on incompatible element signatures. While the majority of the Eastern Dharwar craton kimberlites are similar to the Group I kimberlites of southern Africa in terms of petrology, geochemistry and Sr–Nd isotope systematics, others show the geochemical traits of Group II kimberlites or an overlap between Group I and II kimberlites. Rare earth element (REE)-based semi-quantitative forward modelling of batch melting of southern African Group I and II kimberlite source compositions involving a metasomatised garnet lherzolite and very low degrees of partial melting demonstrate that (1) WKF and NKF kimberlites display a relatively far greater range in the degree of melting than those from the on-craton occurrences from southern Africa and are similar to that of world-wide melilitites, (2) different degrees of partial melting of a common source cannot account for the genesis of all the EDC kimberlites, (3) multiple and highly heterogeneous kimberlite sources involve in the sub-continental lithospheric mantle (SCLM) in the Eastern Dharwar craton and (4) WKF and NKF kimberlites generation is a resultant of complex interplay between the heterogeneous sources and their different degrees of partial melting. These observations are consistent with the recent results obtained from inversion modelling of REE concentrations from EDC kimberlites in that both the forward as wells as inverse melting models necessitate a dominantly lithospheric, and not asthenospheric, mantle source regions. The invading metasomatic (enriching) melts percolating from the convecting (asthenosphere) mantle impart an OIB-like isotopic signature to the final melt products.  相似文献   

云南峨眉山高钛和低钛玄武岩的岩石成因   总被引：4，自引：4，他引：0  

姜寒冰  姜常义  钱壮志  朱士飞  张蓬勃  唐冬梅 《岩石学报》2009,25(5):1117-1134

峨眉山玄武岩主要的岩石类型是低钛玄武岩和高钛玄武岩,并有少量的苦橄岩。它们不同程度地富集大离子亲石元素和轻稀土元素,相对亏损重稀土元素,稀土元素分馏明显或比较明显,相容元素（Co、V、Cr、Ni）显著亏损。低钛玄武岩浆受到陆壳物质的明显混染,高钛玄武岩浆也受到混染,但混染程度弱于低钛玄武岩浆。同化混染对Sr同位素和大离子亲石元素的影响程度大于对稀土元素和Nd同位素的影响程度。混染物是下地壳变质岩,也有少量上地壳物质。未受混染的样品具有适度亏损的Nd、Sr同位素。高钛玄武岩在岩浆演化过程中主要分离结晶相/堆晶相是单斜辉石,并有少量的斜长石。低钛玄武岩中,单斜辉石和斜长石的分离结晶作用是最主要的因素。低钛玄武岩的主体部分是在尖晶石稳定域与石榴石稳定域之间的过渡带熔融的;高钛玄武岩的主体部分是在石榴石稳定域内熔融的,极少部分是在尖晶石稳定域内熔融的。  相似文献   

Petrology and geochemistry of REE-rich Mafé banded iron formations (Bafia group,Cameroon)     

Charles Nkoumbou  Fuh Calistus Gentry  Jacqueline Tchakounte Numbem  Yolande Vanessa Belle Ekwe Lobé  Christin Steve Nwagoum Keyamfé 《Comptes Rendus Geoscience》2017,349(4):165-174

Archaean–Paleoproterozoic foliated amphibole-gneisses and migmatites interstratified with amphibolites, pyroxeno-amphibolites and REE-rich banded-iron formations outcrop at Mafé, Ndikinimeki area. The foliation is nearly vertical due to tight folds. Flat-lying quartz-rich mica schists and quartzites, likely of Pan-African age, partly cover the formations. Among the Mafé BIFs, the oxide BIF facies shows white layers of quartz and black layers of magnetite and accessory hematite, whereas the silicate BIF facies is made up of thin discontinuous quartz layers alternating with larger garnet (almandine–spessartine) + chamosite + ilmenite ± Fe-talc layers. REE-rich oxide BIFs compositions are close to the East Pacific Rise (EPR) hydrothermal deposit; silicate BIFs plot midway between EPR and the associated amphibolite, accounting for a contamination by volcanic materials, in addition to the hydrothermal influence during their oceanic deposition. The association of an oceanic setting with alkaline and tholeiitic magmatism is typical of the Algoma-type BIF deposit. The REE-rich BIFs indices recorded at Mafé are interpreted as resulting from an Archaean–Paleoproterozoic mineralization.  相似文献   

Lithological interpretation of crustal composition in the Fennoscandian Shield with seismic velocity data     

M. Kuusisto  I.T. Kukkonen  P. Heikkinen  L.J. Pesonen 《Tectonophysics》2006,420(1-2):283

In this study, we report the results of an investigation of lithological interpretation of the crust in the central Fennoscandian Shield (in Finland) using seismic wide-angle velocity models and laboratory measurements on P- and S-wave velocities of different rock types. The velocities adopted from wide-angle velocity models were compared with laboratory velocities of different rock types corrected for the crustal PT conditions in the study area. The wide-angle velocity models indicate that the P-wave velocity does not only increase step-wise at boundaries of major crustal layers, but there is also gradual increase of velocity within the layers. On the other hand, the laboratory measurements of velocities indicate that no single rock type is able to provide the gradual downward increasing trends. Thus, there must be gradual vertical changes in rock composition. The downward increase of velocities indicates that the composition of the crust becomes gradually more mafic with increasing depth. We have calculated vertical velocity profiles for a range of possible crustal lithological compositions. The Finnish crustal velocity profiles require a more mafic composition than an average global continental model would suggest. For instance, on the SVEKA'81 transect, the calculated models suggest that the crustal velocity profiles can be simulated with rock type mixtures where the upper crust consists of felsic gneisses and granitic–granodioritic rocks with a minor contribution of amphibolite and diabase. In the middle crust, the amphibolite proportion increases. The lower crust consists of tonalitic gneiss, mafic garnet granulite, hornblendite, pyroxenite and minor mafic eclogite. Assuming that these rock types are present in sufficiently extensive and thick layers, they would also have sufficiently high acoustic reflection coefficients for generating the generally well-developed reflectivity in the crust in the central part of the shield. Density profiles calculated from the lithological models suggest that there is practically no density contrast at Moho in areas of the high-velocity lower crust. Comparison of reflectors from FIRE-1 and FIRE-3 transects and the velocity model from SVEKA'81 wide-angle transect indicated that the reflectors correlate with velocity layering, but the three-dimensional structures of the crust complicate such comparisons.  相似文献