|
|
|
题名
|
作者
|
年代
|
出处
|
被引量
|
| 1 | Micro-textures in plagioclase from 1994-1995 eruption, Barren Island Volcano: Evidence of dynamic magma plumbing system in the Andaman subduction zone显示文摘A systematic account of micro-textures and a few compositional profles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995,from Barren Island Volcano,NE India ocean,are presented for the frst time.The identifed micro-textures can be grouped into two categories:(i)Growth related textures in the form of coarse/fne-sieve morphology,fne-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fuctuated due to change in temperature or H2O or pressure or composition of the crystallizing melt;and(ii)morphological texture,like glomerocryst,synneusis,swallow-tailed crystal,microlite and broken crystals,formed by the infuence of dynamic behavior of the crystallizing magma(convection,turbulence,degassing,etc.).Each micro-texture has developed in a specifc magmatic environment,accordingly,a frst order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit.Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth.Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective selfmixing environment.Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit.Intermittent degassing and eruption related decompression have also played a major role in the fnal stage of crystallization dynamics. | M.L.Renjith | 2014 | Geoscience Frontiers2014，5，1： | 4 |
| 2 | Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber,Yelagiri Alkaline Complex,South India显示文摘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 Complex,South India.Yelagiri syenite is a reversely zoned massif with shoshonitic(Na2O+K2O=5-10 wt.%,Na2O/K2 O=0.5-2,TiO2<0.7 wt.%) and metaluminous character.Systematic modal variation of plagioclase(An11-16Ab82-88),K-feldspar(Or27-95Ab5-61),diopside(En34-40Fs11-18Wo46-49),biotite,and Ca-amphibole(edenite) build up three syenite facies within it and imply the role of in-situ fractional crystallization(FC).Evidences such as(1) disequilibrium micro-textures in feldspars,(2) microgranular mafic enclaves(MME) and(3) synplutonic dykes signify mixing of shoshonitic mafic magma(MgO=4-5 wt.%,SiO2=54-59 wt.%,K2O/Na2 O=0.4-0.9) with syenite.Molecular-scale mixing of mafic magma resulted disequilibrium growth of feldspars in syenite.Physical entity of mafic magma preserved as MME due to high thermal-rheological contrast with syenite magma show various hybridization through chemical exchange,mechanical dilution enhanced by chaotic advection and phenocryst migration.In synplutonic dykes,disaggregation and mixing of mafic magma was confined within the conduit of injection.Major-oxides mass balance test quantified that approximately 0.6 portions of mafic magma had interacted with most evolved syenite magma and generated most hybridized MME and dyke samples.It is unique that all the rock types(syenite,MME and synplutonic dykes) share similar shoshonitic and metaluminous character; mineral chemistry,REE content,coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition.Outcrop-scale features of crystal accumulation and flow fabrics also significant along with MME and synplutonic dykes in syenite suggesting that Yelagiri syenite magma chamber had evolved through multiple physical processes like convection,shear flow,crystal accumulation and magma mixing. | M.L.Renjith S.N.Charan D.V.Subbarao E.V.S.S.K.Babu V.B.Rajashekhar | 2014 | Geoscience Frontiers2014，5，6： | 2 |
| 3 | Petrogenesis of carbonatitic lamproitic dykes from Sidhi gneissic complex,Central India显示文摘Petrographic, mineral chemical and whole-rock geochemical characteristics of two newly discovered lamproitic dykes(Dyke 1 and Dyke 2) from the Sidhi Gneissic Complex(SGC), Central India are presented here. Both these dykes have almost similar sequence of mineral-textural patterns indicative of:(1) an early cumulate forming event in a deeper magma chamber where megacrystic/large size phenocrysts of phlogopites have crystallized along with subordinate amount of olivine and clinopyroxene;(2) crystallization at shallow crustal levels promoted fine-grained phlogopite, K-feldspar, calcite and Fe-Ti oxides in the groundmass;(3) dyke emplacement related quench texture(plumose K-feldspar, acicular phlogopites) and finally(4) post emplacement autometasomatism by hydrothermal fluids which percolated as micro-veins and altered the mafic phases. Phlogopite phenocrysts often display resorption textures together with growth zoning indicating that during their crystallization equilibrium at the crystal-melt interface fluctuated multiple times probably due to incremental addition or chaotic dynamic self mixing of the lamproitic magma. Carbonate aggregates as late stage melt segregation are common in both these dykes, however their micro-xenolithic forms suggest that assimilation with a plutonic carbonatite body also played a key role in enhancing the carbonatitic nature of these dykes. Geochemically both dykes are ultrapotassic(K_2 O/Na_2 O: 3.0-9.4) with low CaO, Al_2 O_3 and Na_2 O content and high SiO_2(53.3-55.6 wt.%)and K_2 O/Al_2 O_3 ratio(0.51-0.89) characterizing them as high-silica lamproites. Inspite of these similarities, many other features indicate that both these dykes have evolved independently from two distinct magmas. In dyke 1, phlogopite composition has evolved towards the minette trend(Al-enrichment) from a differentiated parental magma having low MgO, Ni and Cr content; whereas in dyke 2, phlogopite composition shows an evolutionary affinity towards the lamproite trend(Al-depletion) and crystallized from a more primitive magma having high MgO, Ni and Cr content. Whole-rock trace-elements signatures like enriched LREE, LILE, negative Nb-Ta and positive Pb anomalies; high Rb/Sr, Th/La, Ba/Nb, and low Ba/Rb, Sm/La, Nb/U ratios in both dykes indicate that their pareintal magmas were sourced from a subduction modified garnet facies mantle containing phlogopite. From various evidences it is proposed that the petrogenesis of studied lamproitic dykes stand out to be an example for the lamproite magma which attained a carbonatitic character and undergone diverse chemical evolution in response to parental melt composition, storage at deep crustal level and autometasomatism. | M.Satyanarayanan D.V.Subba Rao M.L.Renjith S.P.Singh E.V.S.S.K.Babu M.M.Korakoppa | 2018 | Geoscience Frontiers2018，9，2： | 0 |
您所在的机构暂未开通此部分的功能，请联系管理员