Magma Mixing Genesis of the Mafic Enclaves and Related Granitoids in the Kan Granite-Gneiss Complex of Central Côte d’Ivoire: Evidence from Geology, Petrology and Geochemistry

The mafic enclaves from Paleoproterozoic domain are considered to be the results of large-scale crust-mantle interaction and magma mixing. In this paper, petrography, mineralogy and geochemistry were jointly used to determine the origin of the mafic enclaves and their relationship with the host granitoids of the Kan granite-gneiss complex. This study also provides new information on crust-mantle interactions. The mafic enclaves of the Kan vary in shape and size and have intermediate chemical compositions. The diagrams used show a number of similarities in the major elements (and often in the trace elements) between the mafic enclaves and the host granitoids. Geochemical show that the Kan rock are metaluminous, enriched in silica, medium to high-K calc-alkaline I-type granite. The similarities reflect a mixing of basic and acid magma. Mafic enclaves have a typical magmatic structure, which is characterized by magma mixing. The genesis of these rocks is associated with the context of subduction. They result from the mixing of a mafic magma originating from the mantle and linked to subduction, and a granitic magma (type I granite) that arises from the partial melting of the crust.

Peraluminous A-type granites formed through synchronous fractionation,magma mixing,mingling,and undercooling:evidence from microgranular enclaves and host Mesoproterozoic Kanigiri granite pluton,Nellore Schist Belt,southeast India

The field and microstructural features coupled with mineral chemical data from microgranular enclave(ME)and host Mesoproterozoic Kanigiri granite(KG)pluton of Nellore Schist Belt(NSB),Southeastern India,have been documented in order to infer the likely processes responsible for the origin and evolution of ME and host KG magma.The ME and host KG bear the same mineral assemblages barring the KG which does not contain amphibole;however,they are modally disequilibrated.The ME in KG is originated due to multiple intrusions of ME magmas into the crystallizing host KG magma chamber.Field and textural features indicate the dynamic magma flow,mingling,and undercooling of the ME against a relatively cooler surface of host KG magma.The presence of NSB country rock xenoliths and its diffuse boundaries suggest the intrusive relation and marginal assimilation by the intruding KG magma.The occasional cumulate texture in the ME appears to have formed by the accumulation of early-formed minerals that crystallized rapidly in the ME magma globules.The ME shows the magmatically deform features developed due to the flowage and erosion by the subsequent intrusions of ME magma pulses into the crystallizing host KG magma chamber.The ME amphiboles show unusual composition as ferro-edenitic hornblende to potassian-hastingsitic hornblende,that crystallized in the subalkaline-alkaline transition,low fO_(2)(reducing to mildly oxidizing)magma.The unusual extremely low Mg/Mg+Fe^(t)=0.015(avg.)of ME amphiboles may be related to the changing physico-chemical(P,T,fO_(2),and H_(2)O)condition of the ME magma or they might have crystallized in equilibrium with more evolved KG magma.The KG(FeOt/MgO=37.04,avg.)and ME(FeO~t/MgO=77.72,avg.)biotites are siderophyllite,and buffered between QFM and NNO syn-crystallizing in the water undersaturated(H_(2O)≈3.58 wt.%in KG;≈3.53wt.%in ME),alkaline anorogenic(A-type)host magmas that were emplaced at mid-crustal(4–5 kbar;17 km)depth.Field,microtextural and mineral chemical evidences suggest that the alkaline KG magma originated from crustal source and evolved through synchronous fractionation,mixing,and mingling with coeval ME magmas in the KG magma chamber.

Mineral Chemistry,Trace Elements,Isotopic Analysis and Zircon U-Pb Dating in the Hesar Pluton,Northern UDMA,Iran:Implications for Pre-Collisional Magma Mixing

The Hesar pluton in the northern Urumieh-Dokhtar magmatic arc hosts numerous mafic-microgranular enclaves(MMEs).Whole rock geochemistry,mineral chemistry,zircon U-Pb and Sr-Nd isotopes were measured.It is suggested that the rocks are metaluminous(A/CNK=1.32-1.45),subduction-related I-type calc-alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures.The host rocks yielded an U-Pb crystallization age of 37.3±0.4 Ma for gabbro-diorite.MMEs have relatively low SiO_(2) contents(52.9-56.6 wt%)and high Mg^(#)(49.8-58.7),probably reflecting a mantle-derived origin.Chondrite-and mantle-normalized trace element patterns are characterized by LREE and LILE enrichment,HREE and HFSE depletion with slight negative Eu anomalies(Eu/Eu^(*)=0.86-1.03).The host rocks yield(^(87)Sr/^(86)Sr)_(i) ratios of 0.70492-0.70510,positive ε_(Nd)(t)values of+1.55-+2.06 and T_(DM2)of 707-736 Ma,which is consistent with the associated mafic microgranular enclaves((^(87)Sr/^(86)Sr)_(i)=0.705014,ε_(Nd)(t)=+1.75,T_(DM2)=729 Ma).All data suggest magma-mixing for enclave and host rock formation,showing a complete equilibration between mixed-mafic and felsic magmas,followed by rapid diffusion.The T_(DM1)(Nd)and T_(DM2)(Nd)model ages and U-Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantlederived magmas in a pre-collisional setting of Arabian-Eurasian plates.Clinopyroxene composition indicates a crystallization temperature of~1000℃ and a depth of~9 km.

Geochemical studies of hybrid granite from Madugulapalli area, Eastern Dharwar Craton, Southern India: Implications for crustal mixing

Magma produced by melting of continental crust and mantle at the Archean-Proterozoic boundary are compositionally variable and chemical compositions provide evidence for the mixing of two sources. Understanding the composition of hybrid magma is essential for determining the comparative infl uence of crust and mantle sources during orogenesis. The hybrid granites are less documented in Indian cratons, especially less in Dharwar Craton. Here we present petrographic and whole-rock geochemical data of Madgulapalli granitic rocks situated in the NE part of the Eastern Dharwar Craton(EDC), to elucidate their petrogenesis and role in crust formation. The Madugulapalli granites(MPG) are composed chiefl y of plagioclase, quartz, and alkali feldspar with associated biotite showing alteration and inter-granular textures. Geochemically, they are metaluminous to peraluminous in nature with calc-alkaline hybrid granite. The hybrid granites exhibit both negative and positive europium anomalies;the lower Rb/Sr, Rb, Sr, and higher Sr/Y,(Dy/Yb)N ratios suggest that the interaction of older rocks with residual garnet source melted at high pressures. We hypothesize that hybrid granites are formed by interaction(e.g., metasomatism, mingling, or mixing) between parental magmas and pre-existing rocks with the infl uence of sanukitoid melts(heat source) in a subduction environment. The genesis of the hybrid granites demonstrates the mixing coupled with diff erentiation in the petrogeny’s residue system in a syn-collision setting followed by continental crust stability in EDC during the Neoarchean period.

Magma source and tectonic setting of the Dunde granite in the Western Tianshan:constraints from geochronology,geochemistry,and Sr–Nd–Hf isotopes

The Dunde iron-zinc polymetallic deposit is one of large iron deposits occurred in the Awulale Metallogenetic Belt,Western Tianshan(NW-China).This study reports new geochronology and geochemistry for granite in the Dunde mining area in order to constrain the tectonicmagmatic activities and metallogenesis of this region.Granites in the southwest of Dunde mining area are mainly syenogranites intruded into volcanics of the Dahalajunshan Formation in the Early Carboniferous,and they are far from the area where ore bodies and mineralized altered rocks are widely developed.LA-ICP-MS U–Pb zircon dating indicates that Dunde syenogranite was at 306.8±1.0 Ma,which could constrain the upper limit of metallogenic age for this deposit.The Dunde granites are high SiO_(2)(73.41–80.07 wt%),high differentiation index(D.I.=89.7–95.0),weakly peraluminous to metaluminous(A/CNK=0.94–1.08),and they are enriched in LILE and LREE and depleted in Eu,Ba,Sr and P_(2)O_(5),indicating that they belong to highly fractionated Ⅰ-type granite.Based on εHf values(+9.2 to+10.5)for zircon and high εNd(-t)values(+4.7 to+5.8)for whole-rock,and the two-stage model ages for 601–735 Ma,suggest that the magma source could be the juvenile lower crust.Combined with regional geological setting,the 306.8 Ma Dunde granites are formed in post-collision extensional tectonic setting.

Petrogenesis and tectonic implications of Indosinian granitoids from Western Qinling Orogen,China:Products of magma-mixing and fractionation

The Western Qinling Orogen(WQO) is characterized by voluminous distribution of Indosinian granitoids,the formation of which provides an important window to unravel the geochemical and geodynamic evolution and associated metallogeny.Here we investigate a group of intrusions termed "Five Golden Flowers" based on petrological,geochemical,zircon U-Pb geochronological and Lu-Hf isotopic studies on the granitoids and their mafic microgranular enclaves(MMEs).Our results show that these intrusions are genetically divided into two types,namely,magma-mixing and highly fractionated.The Jiaochangba,Lujing,Zhongchuan,and Luchuba granitoids are biotite monzogranites(220±0.8 Ma to 217±2.6 Ma) with abundant coeval MMEs(220±.1 Ma to 217±2.7 Ma).The rocks contain moderate to high SiO2,high MgO,Rb,Sr,Ba,and Th contents,but low TiO2,P2 O5,and Sc values,A/CNK of <1.1,and a range of εHf(t) values of-11.7 to +2.23 with corresponding TDM2values of 1967-1228 Ma.The MMEs possess K-feldspar megacrysts,abundant acicular apatites,and show lopsided textures.They have lower SiO2,Al2 O3,and Th contents,but higher MgO,TiO2,and Sc,with εHf(t) values of-18.0 to +3.18 and TDM1 of 849-720 Ma.The data indicate that the MMEs were derived from a magma sourced from the enriched lithospheric mantle.We suggest that these host granitoids were produced by partial melting of latePaleoproterozoic to early-Mesoproterozoic lower crust with the involvement of Neoproterozoic SCLM-derived mafic magmas.The Baijiazhuang pluton is dominantly composed of leucogranite(muscovite granite and twomica monzogranite,216±1.5 Ma) without MMEs.The rocks are peraluminous with high A/CNK(1.06-1.27).Compared with the other four granitoids,the Baijiazhuang leucogranite shows higher SiO2 content,markedly lower concentrations of TiO2,MgO,Al2 O3,CaO,and Fe2 O3T,and lower LREE/HREE and(La/Yb)N values.These leucogranites are also rich in Rb,Th,and U,and display marked depletions in Ba,Sr,Ti,and Eu,indicating that they experienced significant fractionation.Zircon εHf(t) values(-10.2 to-3.27) and TDM2(1868-1424 Ma),as well as the Nb/Ta and K2 O/Na2 O values are similar to the other four granitoids,indicating that they are likely to have been derived from a similar source;with sediments playing only a minor role in the magma generation.The low contents of Yb and Y suggest that their partial melting was controlled by garnets and micrographic texture of K-feldspar reflects high-temperature melting through undercooling.Based on the above features,we infer that the Baijiazhuang leucogranite likely represents the product of high degree fractionation of the I-type biotite monzogranite magma which generated the other four granitoids at relatively high temperatures,within magma chambers at mid-crust depths.We propose that the granitoid suite was formed in the transitional setting from synto post-collision during the collisional orogeny between the SCB and NCB,following break-off of the subducted South China Block lithosphere during 220-216 Ma.

Magma Mixing and Mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt

The East Kunlun Orogenic Belt(EKOB)in northeast margin of the Qinghai-Tibetan Plateau is an important part of the Central Orogenic System(COS).During the long-time geological evolution,complicated tectono

Petrology,geochemistry,and crystal size distribution of the basaltic andesite-dacite association at Mt.Sumbing,Central Java,Indonesia:Insights to magma reservoir dynamics and petrogenesis

Ten rock samples consisting of one pyroclastic density current(PDC1)deposit,seven lava flows(LF1–7),and two summit lava domes(LD1,2)were studied to understand the petrogenesis and magma dynamics at Mt.Sumbing.The stratigraphy is arranged as LF1,PDC1,LF2,LF3,LF4,LF5,LF6,LF7,LD1,and LD2;furthermore,these rocks were divided into two types.TypeⅠ,observed in the oldest(LF1)sample,has poor MgO and high Ba/Nb,Th/Yb and Sr.The remaining samples(PDC1–LD2)represent typeⅡ,characterized by high MgO and low Ba/Nb,Th/Yb and Sr values.We suggest that type I is derived from AOC(altered oceanic crust)-rich melts that underwent significant crustal assimilation,while typeⅡoriginates from mantle-rich melts with less significant crustal assimilation.The early stage of typeⅡmagma(PDC1–LF3)was considered a closed system,evolving basaltic andesite into andesite(55.0–60.2 wt%SiO_(2))with a progressively increasing phenocryst(0.30–0.48φ_(PC))and decreasing crystal size distribution(CSD)slope(from-3.9 to-2.9).The evidence of fluctuating silica and phenocryst contents(between 55.9–59.7 wt%and 0.25–0.41φ_(PC),respectively),coupled with the kinked and steep(from-5.0 to-3.3)CSD curves imply the interchanging condition between open(i.e.,magma mixing)and closed magmatic systems during the middle stage(LF4–LF6).Finally,it underwent to closed system again during the final stage(LF7–LD2)because the magma reached dacitic composition(at most 68.9 wt%SiO_(2))with abundant phenocryst(0.38–0.45φ_(PC))and gentle CSD slope(from-4.1 to-1.2).

Source Enrichment Control on the Scale of Magmatic-Hydrothermal W-Sn Mineralization:Insights from Triassic and Jurassic Magma Reservoirs in the Continental Crust,Xitian,South China

There are two factors,source composition and magmatic differentiation,potentially controlling W-Sn mineralization.Which one is more important is widely debated and may need to be determined for each individual deposit.The Xitian granite batholith located in South China is a natural laboratory for investigating the above problem.It consists essentially of two separate components,formed in the Triassic at ca.226 Ma and Jurassic at ca.152 Ma,respectively.The Triassic and Jurassic rocks are both composed of porphyritic and fine-grained phases.The latter resulted from highlydifferentiated porphyritic ones but they have similar textural characteristics and mineral assemblages,indicating that they reached a similar degree of crystal fractionation.Although both fine-grained phases are highly differentiated with elevated rare metal contents,economic W–Sn mineralization is rare in the Triassic granitoids and this can be attributed to less fertile source materials than their Jurassic counterparts,with a slightly more enriched isotopic signature and whole-rockεNd(226 Ma)of−10.4 to−9.2(2σ=0.2)compared withεNd(152 Ma)of−9.2 to−8.2(2σ=0.2)for the Jurassic rocks.The initial W-Sn enrichment was derived from the metasedimentary rocks and strongly enhanced by reworking of the continental crust,culminating in the Jurassic.

Magma Mixing and Mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt

The Changning Menglian belt is an important area of research on the evolution of the Paleo Tethys ocean structure,the belt can be solved such as the Changning Menglianbeltposition;sequencestratigraphy;sedimentary environment;nature and its tectonic evolution history and tectonic domain and Gut Tis relationship;therefore,the research on Chang Ning Menglian zone have a great significance to solve many problems of the Sanjiang fold belt in Tethys and Himalaya tectonic area.'Hot spring'is located in the west margin of the southern Changning Menglian belt,studying Yunnan Fengqing hot spring group'geological and petrology characteristics roundly and in depth,concluding the metamorphism and deformation characteristics,clarifying the metamorphism effect and its stages,understanding the association its combination with the Changning Menglian belt between,therefore it has the great significance to solve the geological evolution history in the Sanjiang area,especially the paleo Tethyan tectonic belt,as well as Gondwana and Eurasia boundaries and other major problem.Through collect and read the literature data,measurement of field section,geological investigation,research and Study on rock sheet indoor,rock composition test,electron probe testing system,summarize the geological characteristics and petrological characteristics of'hot springs group',and through the discussion of the geochemical characteristics of rocks,explore its rock assemblages,characteristics of original rock and analysis of metamorphism and deformation stages,to provide basic data for regional geological evolution.The study shows that the main lithology is biotite quartz schist,mica schist and epimetamorphic sandstone interspersed with a small amount of phyllonite,granulite,silicalite,carbonaceous slate and phyllitic cataclasite that contains some pressure breccia.The metamorphic mineral paragenetic assemblage of the representative rock is:M1 biotite(Bi)+plagioclase(Pl)+quartz(Q),and M2 muscovite(Mus)+quartz(Q).The protolith is felsic rock and sedimentary rock that belongs to argiloid.On the basis of comparison,the stratigraphic sequence of the protolith is consistent with the type section of Wenquan formation.Along with the subduction(Hercynian)-subduction(Indosinian)-orogenic(Yanshan Himalayan period)process of Changning Menglian belt,hot springs group experienced two stages of metamorphism and three stages of deformation,metamorphic temperature at400-500℃,the pressure is foucs on 0.3-0.62Gpa,and shown the retrograde metamorphism of the low greenschist facies.Geological age of hot springs formation is early Devonian(survey team of Yunnan District three units,1980),sedimentary environment is mainly shallow and semi deep sea,observed Bouma sequence in rock slice,therefore,the depositional environment may be fan or basin of sea,the sedimentary formations are mainly clastic rocksiliceous rock formation,the upper coal—contained formation.With the Changning Meng Lian ocean expansion,ocean island begin to develop,material deposition continuing,appearing volcano material,the protolith may contain volcano matter through studying the thin section.To the Late Permian,Crust of Changning Menglian ocean begin to subduct to the east of the Yangtze block,ocean basin began to close,but it still has formation here at this time,mainly shallow carbonate formation,with proceeding of subduction,in the low temperature groove(7Km deep),due to changes in temperature and pressurer,appearing metamorphism(M1)and deformation(D1)for the first time,the shear effect produced by deformation lead to some cleavage,occurring regional foliation S1,major metamorphic minerals formed in metamorphism is long flake biotite.The main metamorphic mineral assemblages are biotite(Bi)+feldspar(Pl)+quartz(Q).Subsequently,crustal uplift,depositional break,because the Changning Meng Lianyang has closed during the Indosinian period,Baoshan-Zhenkang block in the west and the Yangtze block in the east knocked each other.In the Indosinian,under the action of faults,the hot spring formation clipping and retracing,back to a position about1-2Km depth,the position is still belongs to the low temperature groove,and occurring axial cleavage in the core of the fold,namely S2.That is,the emergence of the second metamorphism(M2)and deformation(D2).The deformation is affected by the strong pressure,so the rock have dewatered,so the second metamorphic deformation process is affected by temperature(T),pressure(Ps)and fluid(C).The main metamorphic minerals in the second generation of metamorphism is Muscovite,while there have some of biotite formed in same period,find that the first phase of biotite parallel growth of rock slice,namely S1 parallel S2,and we can see incomplete metamorphism biotite,so the the Muscovite is formed by the first stage of metamorphism and metamorphic biotite.The main mineral of the second stage metamorphism is Muscovite(Mus)+quartz(Q) Then,the crust continues to rise,the sedimentary break continues.In the Jurassic Cretaceous start orogeny,namely Yanshan period intracontinental orogeny,occurred third deformation(D3),under extrusion shearing,S3 emergencing,after Yanshan intracontinental orogenic period,in Himalayan period there have large-scale nappe structure and differential uplift and faulting.So the third deformation(D3)strengthened,with weak metamorphism,sericite emergencing.

Timing of Magma Mixing in the Gangdisê Magmatic Belt during the India-Asia Collision: Zircon SHRIMP U-Pb Dating

Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdise giant magmatic belt, within which the Qüxü batholith is the most typical MME-bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U-Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±l Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions.Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge-scale magma mixing in the Gangdise belt took place 15-20 million years after the initiation of the India-Asia continental collision, genetically related to the underplating of subduction-collision-induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass-energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.

Textures and melt-crystal-gas interactions in granites

Felsic intrusions present ubiquitous structures.They result from the differential interactions between the magma components(crystal,melt,gas phase) while it flows or when the flow is perturbed by a new magma injection.The most obvious structure consists in fabrics caused by the interactions of rotating grains in a flowing viscous melt.New magma inputs through dikes affect the buk massif flow,considered as global within each mineral facies.A review of the deformation and flow types developing in a magma chamber identifis the patterns that could be expected.It determines their controlling parameters and summarizes the tools for their quantification.Similarly,a brief review of the theology of a complex multiphase magma identifies and suggests interactions between the different components.The specific responses each component presents lead to instability development.In particular,the change in vorticity orientation,associated with the switch between monoclinic to triclinic flow is a cause of many instabilities.Those are preferentially local.Illustrations include fabric development,shear zones and flow banding.They depend of the underlying rheology of interacting magmas.Dikes,enclaves,schlieren and ladder dikes result from the interactions between the magma components and changing boundary conditions.Orbicules,pegmatites,unidirectional solidification textures and miarolitic cavities result from the interaction of the melt with a gaseous phase.The illustrations examine what is relevant to the bulk flow,local structures or boundary conditions.In each case a field observation illustrates the instability.The discussion reformulates instability observations,suggesting new trails for ther description and interpretation in terms of local departure to a bulk flow.A brief look at larger structures and at their evolution tries to relate these instabilities on a broader scale.The helical structures of the Ricany pluton,Czech Republic and by the multiple granitic intrusions of Dolbel,Niger illustrate such events.

Grain to outcrop-scale frozen moments of dynamic magma mixing in the syenite magma chamber,Yelagiri Alkaline Complex,South India

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 t K2O?5e 10 wt.%, Na2O/K2O ? 0.5e2, TiO2<0.7 wt.%) and metaluminous character. Systematic modal variation of plagioclase (An11e16 Ab82e88), K-feldspar (Or27e95 Ab5e61), diopside (En34e40Fs11e18Wo46e49), 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 ? 4e 5 wt.%, SiO2 ? 54e59 wt.%, K2O/Na2O ? 0.4e0.9) 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 injec-tion. 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 met-aluminous character;mineral chemistry, REE content, coherent geochemical variation in Harker diagram suggest that mixing of magma between similar composition. Outcrop-scale features of crystal accumu-lation 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.

Zircon Trace Element Constraints on U-Pb Dating:A Case Study of the Huayuangong A-type Granite in the Lower Yangtze Region,Eastern China

For magmatic rocks,it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample,which gives rise to large dating errors or even unrealistic dating results.As the trace element concentrations of zircon can reflect its equilibrated magma characteristics,they can be used to determine whether all the analytical spots on the zircons selected to calculate the weighted mean age are cogenetic and formed in a single magma chamber.This work utilizes the results of zircon trace element concentrations and U-Pb isotopic analyses to explore the screening of reasonable U-Pb ages,which can be used to determine a more accurate intrusion crystallization age.The late Mesozoic Huayuangong granitic pluton complex,which is located in the Lower Yangtze region,eastern China,was selected for a case study.The Huayuangong pluton comprises the central intrusion and the marginal intrusion.Two samples from the marginal intrusion yielded consistent zircon weighted mean 206 Pb/238 U ages of 124.6±2.0 Ma and 125.9±1.6 Ma.These analytical spots also exhibit Zr/Hf and Th/U ratios concordant with the evolution of a single magma,from which the dated zircons crystallized.However,for the central intrusion,the analytical spots on zircons from two samples all show a continuous distribution on the concordia line with a relatively large age span.For each sample from the central intrusion,the zircon Zr/Hf ratios do not conform to a single magma evolutionary trend,but rather can be divided into two groups.We propose that zircon Zr/Hf ratios can provide a new constraint on U-Pb zircon dating and zircon Th/U ratios can also be used as a supplementary indicator to constrain zircon dating and determine the origins of the zircons and whether magma mixing has occurred.By screening zircon analytical spots using these two indicators,the two samples from the central intrusion of the Huayuangong pluton produce results of 122.8±4.3 Ma and 122.9±2.2 Ma,which are consistent with the field observations that the central intrusion is slightly younger than the marginal intrusion.

Petrological Significance of Zoned Plagioclase in Eldjurti Granite and Mafic Microgranular Enclaves, North Caucasus, Russia

Plagioclase phenocrysts from mafic enclaves and plagioclase from its host granite possess a pat-tem of complex zonation. A plagioclase phenocryst can generally be divided into three parts : an oscillatory, locally patchy zoned core (An47-19), a ring with dusty, more calcic plagioclase (An64-20) and a normally zoned rim composed of sodic plagioclase (An22-3. 3). Majordiscontinuities in zoning coincide with resorption suffeces that are overgrown by the more calcic plagioclase. The cores of large plagioclase phenocrysts from mafic enclaves and host granite show similar zoning patterns and similar compositions, indicating their crystallization under the same conditions . Steep normal zoning of the rims of plagioclases both from host granite and mafic enclaves illustrates a drastic decrease in An content which is considered to have resulted from the continuous differentiation of hybrid magma and efficient heat loss because of the upward emplacement of the residual magma. Wide rims of plagioclases from the host granite against thc discrete rims of plagioclases from mafic enclaves indicate that differentiation and cooling lasted much longer in the host granite than in the mafic enclaves.

The Three End Members of Li-F Granites and Their Origin of Liquid Segregation

Li-F granites all over the world can be represented by three end members, i. e., theNa-rich ongonite (O), the K-rich xianghualingite (X) and the Si-rich topazite (T). Charac-ters and criteria are presented for these end-member rocks. Vertical zoning in Li-F granites, asreflected by increasing normative Q and C (corundum) and decreasing ALK (K2O + Na2O)with increasing content of fluorine, can be explained using the three-end-member scheme interms of petrochemistry and norms. Considering the difference in melt structure, viscosity anddensity between the end members, in couple with the reguarities that govern the Na-K and Si-ALK segregation known from field evidence and experiments, it is suggested that the three endmembers may have resulted from liquid segregation (immiscibility) rather than from crystalfractionation as commonly believed.

Petrogenesis of the microcrystalline-dioritic enclaves from Jiuling granitoids in the eastern segment of Jiangnan Orogen and constraints on magma source materials

Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids.Precise LAICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples,yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma,respectively.The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism.The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks,and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases.Furthermore,the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves.All of these petrographic features above imply magma mixing is involved in their diagenesis.The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids.Additionally,most of the zircons show extremely high εHf (t) with εHf (t) =3.54?11.94 from the southern samples,and εHf (t) =1.0?9.09 from the central region.Some zircons with the higher εHf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen.Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.

Magma Mixing as a Trigger of Unzen's Volcano Eruptions

Recent eruption in 1991-1995 years of Unzen Volcano(Kyushu Island,Japan)has caught attention of many volcanologists because of dramatical consequences of the previos eruption in 1792,when more than 15000 people were perished.So it is important to study this volcano and try to predict future eruptions and their possible damage.It is proved now,that magma hybridization processes

Petrogenetic Peculiarities of Rare-Metal Granite of Limu,Guangxi

Limu granite massif is a rather typical Mesozoic rare-metal granite in South China . Studying Limu granite massif has important petrological significance for understanding the genesis of rare-metal granites .This paper deals with the typical petrographic characteristics and peculiarity of REE in massif , and discusses the genesis of Limu granite massif in terms of analysis of these characteristics . It is suggested that Limu granite massif is derivative product of a high ordered superimposed -remelting granitic magma .

Detecting Magma Mixing Processes Using Scanning Electron Microscopy Method

This review work explains some of the most important techniques to detect the occurrence of magma mixing phenomena in the volcanic rocks by using SEM （scanning electron microscope）. In particular, the most useful methods related to the different types of mixing are reviewed： complete mixing （blending） or incomplete mixing （mingling）. For blending, backscattered electron images and EDS （energy dispersive spectroscopy） are the most accurate methods： an example taken from a sample of ash of the 2007 Stromboli volcano eruption was used. For mingling, the best method is given by X-ray elemental mapping （in particular of Ca and Si）, as explained through the example taken from a sample of the 2003 explosive eruption of Soufriere Hills volcano. The aim of this work was to establish whereas would be useful to use backscattered eletron images, EDS, or X-ray elemental mapping techniques, according to the different types of mixing that occur very often in magmatic systems.