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1.
Jong-Sun Kim Moon Son Byoung-Hoon Hwang Ki-Cheol Shin Hyeongseong Cho Young Kwan Sohn 《Mineralogy and Petrology》2014,108(2):207-229
Petrographic and geochemical features of the Cretaceous Yucheon granites and their mafic microgranular/magmatic enclaves (MMEs), SE Korea, reveal that the MMEs originated from magma mixing. Mesoscopic and microscopic features indicate that mechanical mixing operated heterogeneously to produce the MMEs with a wide range of sizes and textures. Chemical compositions of amphibole, biotite, and plagioclase rims of both the MMEs and host granites are almost identical, indicating that chemical homogenization took place to some extent after the mechanical mixing. Plagioclase cores, however, have various compositions depending on the host rocks and/or sampling locations, suggesting their sluggish re-equilibration. The MMEs are divided into Type A (low TiO2, very fine-grained, chilled margins) and Type B (high TiO2, fine- to medium-grained, no chilled margins). The lower TiO2 MMEs cooled more rapidly and interacted with granitic magma for a shorter period of time than the higher TiO2 MMEs. Additionally, the former are less enriched in HREEs than the latter. Zoned plagioclase has two zones of increased An content. These features are indicative of double injection events of mafic magma. A previous model explains the magma mixing as resulting from the generation of a slab window due to Kula-Pacific ridge subduction. The model cannot, however, explain the eastward younging of the granites in Korea, necessitating a new, more elaborate model of Cretaceous geodynamics and magmatism in East Asia. 相似文献
2.
3.
Andesite and dacite from Barren and Narcondam volcanic islands of Andaman subduction zone are composed of plagioclase, orthopyroxene,
clinopyroxene, olivine, titanomagnetite, magnesio-hornblende and rare quartz grains. In this study, we use the results of
mineral chemical analyses of the calc-alkaline rock suite of rocks as proxies for magma mixing and mingling processes. Plagioclase,
the most dominant mineral, shows zoning which includes oscillatory, patchy, multiple and repetitive zonation and ‘fritted’
or ‘sieve’ textures. Zoning patterns in plagioclase phenocrysts and abrupt fluctuations in An content record different melt
conditions in a dynamic magma chamber. ‘Fritted’ zones (An55) are frequently overgrown by thin calcic (An72) plagioclase rims over well-developed dissolution surfaces. These features have probably resulted from mixing of a more silicic
magma with the host andesite. Olivine and orthopyroxene with reaction and overgrowth rims (corona) suggest magma mixing processes.
We conclude that hybrid magma formed from the mixing of mafic and felsic magma by two-stage processes – initial intrusion
of hotter mafic melt (andesitic) followed by cooler acidic melt at later stage. 相似文献
4.
《International Geology Review》2012,54(9):854-867
The Agacoren Intrusive Suite is exposed as a large intrusive body over ～500 km2 east of Lake Tuz in central Anatolia and consists of the Cokumkaya gabbro, the Agacoren granitoid, and young dikes. The Agacoren granitoid is the predominant lithology of the Agacoren Intrusive Suite, and is differentiated into several subunits ranging in composition from monzonite, through granite, to alkali feldspar granite. The Cokumkaya gabbro occurs as stocks enclosed in the Agacoren granitoid; individual bodies range in size from 10 m × 20 m to 7 km × 3 km. Young dikes cut both the Cokumkaya gabbro and the Agacoren granitoid, and are particularly abundant in the central part of the intrusive body. Centimeter- to meter-size mafic microgranular enclaves (MME) are enclosed in the Agacoren granitoid. The enclaves are diorite, quartz diorite, and monzodiorite in composition, and represent blobs of mafic magma injected into a felsic host magma. The MME have a mineral assemblage (plagioclase + amphibole + biotite ± quartz ± K-feldspar) almost identical to that of host granitoid, but with different mineral proportions. The characteristic petrographic features of the MME are the presence of acicular apatite, blade-shaped biotite, quartz ocelli, and K-feldspar poikilitically enclosing mafic minerals. Microprobe analyses performed on amphibole and plagioclase reveal similar mineral chemistries for both the MME and the host granitoid. The anorthite contents of the plagioclases show an increase from rim to core in both the MME and the host granitoid. The rims of the MME plagioclase have compositions ranging from An5 to An40, whereas those of the host granitoid vary from An0 to An42. The cores, on the other hand, range from An30 to An90 and An20 to An90 in the MME and the host, respectively. Amphiboles are essentially of ferro-hornblende composition in the MME, and of ferro- to magnesiohornblende composition in the host granitoid. The similarity in mineral compositions reflects chemical equilibrium attained through the magma-mixing process. 相似文献
5.
Rocks of the Late Cretaceous Dagbasi Pluton (88-83 Ma), located in the eastern Pontides, include mafic microgranular enclaves (MMEs) ranging from a few centimetres to metres in size, and from ellipsoidal to ovoid in shape. The MMEs are composed of gabbroic diorite, diorite and tonalite, whereas the felsic host rocks comprise mainly tonalite, granodiorite and monzogranite based on both mineralogical and chemical compositions. MMEs are characterized by a fine-grained, equigranular and hypidiomorphic texture. The common texture of felsic host rocks is equigranular and also reveals some special types of microscopic textures, e.g., oscillatory-zoned plagioclase, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures and rounded plagioclase megacrysts in MMEs. Compositions of plagioclases (An33-An60), hornblendes (Mg#=0.77-1.0) and biotites (Mg#=0.61-0.63) of MMEs are slightly distinct or similar to those of host rocks (An12-57; hbl Mg#=0.63-1.0; Bi Mg#=0.50-0.69), which suggest partial to complete equilibration during mafic-felsic magma interactions.The felsic host rocks have SiO2 between 60 and 76 wt% and display low to slightly medium-K tholeiitic to calc-alkaline and peraluminous to slightly metaluminous characteristics. Chondrite-normalized rare-earth element (REE) patterns are fractionated (Lacn/Lucn=1.5-7.3) with pronounced negative Eu anomalies (Eu/Eu*=0.46-1.1). Initial εNd(i) values vary between −3.1 and 1.6, initial 87Sr/86Sr values between 0.7056 and 0.7067.Compared with the host rocks, the MMEs are characterized by relatively high Mg-number of 22-52, low contents of SiO2 (53-63 wt%), low ASI (0.7-1.1) and low to medium-K tholeiitic to calc-alkaline, metaluminous to peraluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn=1.4-3.9; (Tb/Yb)cn=0.9-1.5] and show small negative Eu anomalies (Eu/Eu*=0.63-1.01). Isotope signatures of these rocks (87Sr/86Sr(i)=0.7054-0.7055; εNd(i)=-1.0 to 1.9) are largely similar to the host rocks. Gabbroic diorite enclaves have relatively low contents of SiO2, ASI; high Mg#, CaO, Al2O3, TiO2, P2O5, Sr and Nb concentrations compared to dioritic and tonalitic enclaves.The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, interacted with a crustal melt that originated from dehydration melting of the mafic lower crust at deep crustal levels. The existence of compositional and textural disequilibrium and the nature of chemical and isotopic variation in these rock types indicate that magma mixing/mingling between an evolved mafic and a granitic magma was involved in their genesis. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched lithospheric mantle source. Al-in-amphibole estimates the pluton emplacement at ca. 0.3-3.8 kbar, and therefore, magma mixing and mingling must have occurred at 3.8 kbar or below this level. 相似文献
6.
西秦岭金厂石英闪长岩的岩浆混合成因：岩相学和锆石U-Pb年代学证据及其构造意义 总被引：7，自引：0，他引：7
位于西秦岭南部的金厂石英闪长岩岩体内含有大量镁铁质暗色微粒包体,包体大多呈浑圆状和水滴状,部分呈不规则拉长状,与寄主岩的接触界线截然或呈渐变过渡关系。石英闪长岩中的磷灰石呈短柱状,而包体中的磷灰石则呈细长针状,反映基性岩浆的快速冷凝结晶。石英闪长岩中的斜长石发育振荡环带,核部的斜长石An低,而边部斜长石An先急剧上升,复又下降;核部与边部之间存在明显的间断,同时斜长石边部包裹有暗色矿物,指示其形成时可能有更基性的岩浆注入。寄主岩中的角闪石大多为普通角闪石和镁普通角闪石,属SiO2饱和型,而包体中角闪石一部分为镁普通角闪石,属SiO2饱和型,一部分为韭闪石、韭闪石质普通角闪石,属SiO2不饱和类型。包体中的角闪石自核部到边部,Al2O3与TiO2含量急剧下降,说明核部和幔部相对于边部形成于更高温的环境。寄主岩中黑云母部分为铁质黑云母,部分为镁质黑云母,而包体中黑云母均为镁质黑云母,在∑FeO/(∑FeO+MgO)对MgO图解上寄主岩与包体中黑云母均落入壳-幔混源区。寄主岩和包体中的锆石均为典型的岩浆锆石,LA-ICP-MS锆石U-Pb定年表明它们的形成年龄分别为212±2Ma及215±1Ma(2σ),在误差范围内基本一致,证明二者同时形成。综合以上岩相学和年代学证据认为,金厂石英闪长岩和镁铁质暗色微粒包体是幔源基性岩浆和壳源酸性岩浆混合作用的产物,形成于秦岭造山带中三叠世造山后伸展环境。结合区域上的研究结果认为,中—晚三叠世时期的幔源岩浆底侵和下地壳部分熔融在西秦岭广泛存在。 相似文献
7.
《International Geology Review》2012,54(6):657-691
The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au–Bi–Cu–As deposit, Revenue Au ± Cu and Stoddart Cu–Mo ± W mineral occurrences, and Laforma Au–Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4–91% Or), whereas plagioclase spans a wide range (4.4–70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu–Mo ± W, Laforma Au–Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au–Bi–Cu–As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10–13 and 10–11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8–7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6–2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520–780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu–Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au–Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization. 相似文献
8.
西藏冈底斯尼木后碰撞花岗岩的岩浆混合作用:显微结构证据 总被引：4，自引：3，他引：1
岩浆混合过程中不同熔体之间的相互作用会影响晶体的成核与生长,形成矿物内部复杂的成分变化,以及矿物之间的不平衡结构。尼木二长花岗岩位于冈底斯岩浆岩带中部,是代表性的形成于后碰撞构造演化时期的花岗岩体。本文对其中的斜长石与角闪石颗粒进行了详细的结构和成分分析,揭示了斜长石中的港湾状、浑圆状、筛孔状熔蚀结构以及斜长石成分的突然变化和角闪石包裹黑云母的不平衡结构,并探讨了它们的成因以及相关的岩浆混合作用。分析结果显示,斜长石中突变环带的An含量为37.6~40.6,熔蚀环带的An含量为48.2~59.5,均高于两侧斜长石的An含量(18.4~26.4),表明在形成这些结构时有外来基性岩浆的混合使得岩浆成分发生了突变。样品中的部分黑云母被自形的角闪石包裹,黑云母呈浑圆状并且具有港湾状的熔蚀边,这可能是基性岩浆的混合作用使得岩浆的温度升高导致黑云母发生部分熔融,混合后的岩浆在黑云母周围继续结晶形成角闪石。这些显微结构为揭示冈底斯岩浆岩带的岩浆混合作用提供了新证据。 相似文献
9.
Sabah Yilmaz ahin 《Chemie der Erde / Geochemistry》2008,68(1):81-92
Rocks of the Late Cretaceous Tamdere Quartz Monzonite, constituting a part of the Eastern Pontide plutonism, include mafic microgranular enclaves (MMEs) ranging from spheroidal to ellipsoidal in shape, and from a few centimeters to decimeters in size. The MMEs are composed of diorite, monzodiorite and quartz diorite, whereas the felsic host rocks comprise mainly quartz monzonite, granodiorite and rarely monzogranite on the basis of both mineralogical and chemical compositions. The common texture of felsic host rocks is equigranular. MMEs are characterized by a microgranular texture and also reveal some special types of microscopic textures, e.g. antirapakivi, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures.
The distribution of major, trace and RE elements apparently reflect exchange between the MMEs and the felsic host rocks mainly due to thermal, mechanical and chemical interactions between coeval felsic host magma and mafic magma. The most evident major element transfer from felsic host magma to mafic magma blob is that of alkalis such as Na and K. LILEs such as Rb, Sr, Ba and some HFSEs such as Nb, Y, Zr and Th have been migrated from felsic host magma to MMEs. Apart from these major and trace elements, the other element transfer from felsic host magma to mafic one concerns REE contents. Such a transfer of REEs has evidently increased the LREE contents of MMEs. Enrichments in alkalis, LILEs, HFSEs and REEs could have been achieved by diffusional processes during the solidification of magma sources. The felsic and mafic magma sources behave as Newtonian and visco-plastic materials. In such an interaction, small MMEs behave as a closed system due to immediate rapid cooling, whereas the bigger MMEs suffer greater diffusion from the Newtonian felsic host magma due to slow cooling. 相似文献
10.
《International Geology Review》2012,54(13):1522-1558
The Melrose Stock in the Dolly Varden Mountains of east-central Nevada is one of the many Mesozoic intrusion s in the Basin and Range Province. It consists of monzonites, quartz monzonites, granodiorites, and granites sharply intruding Mississippian to Triassic units. Phenocrysts of plagioclase (An38–An24) with oscillatory zoning and albitic rims, hornblende ± diopside, and biotite are common. Coexisting phases include orthoclase, quartz and accessory magnetite, apatite, titanite, ilmenite, and allanite. Mineral compositions suggest that the intrusion was emplaced at ～720 ± 40°C and 1.8–2.3 kbar. All rocks are metaluminous to slightly peraluminous, defining a calcalkalic trend in which the monzonites and syenites are shoshonitic. Rare earth element patterns indicate that all studied rock types are comagmatic. Harker plots show curvilinear trends with some kinks consistent with fractionation, and mixing/assimilation. Major-element modelling and petrographic evidence suggest three stages of fractionation/mixing: Stage 1 marked by the fractionation of diopside and plagioclase; Stage 2 by fractionation of plagioclase, hornblende ± orthoclase ± biotite, accompanied by mixing through convection; and Stage 3 by fractionation of biotite, hornblende, plagioclase, and orthoclase. Mineralogic, petrographic, and major- and trace-element data demonstrate that all rocks are I-type granitoids, suggesting a significant mantle contribution. Spider diagrams show troughs for Ti, P, and Nb, indicating magma genesis in a subduction-zone setting. Discrimination diagrams classify all rocks as late orogenic. Magma was therefore generated from mantle metasomatized by subduction, differentiated to a monzonitic magma, and emplaced in the thinned continental crust during a period of extension late in the cycle of Elko orogeny. 相似文献
11.
Chemical and structural zoning in plagioclase can develop in response to a number of different magmatic processes. We examine plagioclase zonation formed during the transfer of plagioclase from a granodioritic host to a monzodioritic enclave to understand the development of different zonation patterns caused by this relatively simple magma mixing process. The transferred plagioclase records two stages of evolution: crystallization of oscillatory plagioclase in the host granodioritic magma and crystallization of high An zones and low An rims in the hybrid enclave magma. High An zones (up to An72) are formed only in the hybrid enclaves after plagioclase transfer. Plagioclase from a primitive enclave, showing no or only minimal interaction with the host, is An30–43. The implication is that high An zones crystallize only from the hybrid magma and not from the primitive one, probably because of an increase in water content in the hybrid magma. Complex interactions between the two magmas are also recorded in Sr content in plagioclase, which indicates an initial increase in Sr concentration in the melt upon transfer. This is contrary to what is expected from the mixing of low Sr enclave magma with a high Sr granodiorite one. Such Sr distribution in the plagioclase implies that the transfer of the plagioclase took place before the onset of plagioclase crystallization in the enclave magma. Therefore, the mixing between high Sr granodiorite magma and low Sr enclave magma was recorded only in plagioclase rims and not in the high An zones. 相似文献
12.
《Chemie der Erde / Geochemistry》2021,81(2):125713
Mafic microgranular enclaves (MMEs) in host granitoids can provide important constraints on the deep magmatic processes. The Oligocene-Miocene granitoid plutons of the NW Anatolia contain abundant MMEs. This paper presents new hornblende Ar-Ar ages and whole-rock chemical and Sr-Nd isotope data of the MMEs from these granitic rocks. Petrographically, the MMEs are finer-grained than their host granites and contain the same minerals as their host rocks (amphibole + plagioclase + biotite + quartz + K-feldspar), but in different proportions. The Ar-Ar ages of the MMEs range from 27.9 ± 0.09 Ma to 19.3 ± 0.01 Ma and are within error of their respective host granitoids. The MMEs are metaluminous and calc-alkaline, similar to I-type granites. The Sr-Nd isotopes of MMEs are 0.7057 to 0.7101 for 87Sr/86Sr and 0.5123 to 0.5125 for 143Nd/144Nd, and are similar to their respective host granitoids. These lithological, petrochemical and isotopic characteristics suggest that the MMEs in this present study represent chilled early formed cogenetic hydrous magmas produced during a period of post-collisional lithospheric extension in NW Anatolia. The parental magma for MMEs and host granitoids might be derived from partial melting of underplated mafic materials in a normally thickened lower crust in a post-collisional extensional environment beneath the NW Anatolia. Delamination or convective removal of lithospheric mantle generated asthenospheric upwelling, providing heat and magma to induce hydrous re-melting of underplated mafic materials in the lower crust. 相似文献
13.
义敦岛弧措交玛岩体岩浆混合成因:镁铁质微粒包体的证据 总被引：2，自引：0，他引：2
义敦岛弧北部的措交玛岩基岩体主要由黑云母二长花岗岩和边部的花岗闪长岩组成。在黑云母二长花岗岩中存在有少量镁铁质微粒包体,其成分为闪长质,与寄主岩石接触关系从渐变到截然。在包体周围的寄主岩石中存在黑云母、角闪石自身的包含结构,角闪石包含黑云母,斜长石发育明显的溶蚀结构,核部斜长石被溶蚀成筛状,边部环带状斜长石溶蚀不明显,是基性岩浆注入到酸性岩浆中导致岩浆混合的结果。黑云母二长花岗岩具有更高的轻重稀土分异系数,闪长质包体轻重稀土分异系数较低,黑云母二长花岗岩和暗色闪长质微粒包体具有明显相似性的微量元素特征。寄主岩黑云母二长花岗岩锆石U-Pb年龄为236±1.9Ma,闪长质包体为235±3.9Ma,二者形成年代在误差范围内基本一致,可能为甘孜-理塘洋向西俯冲过程中,俯冲洋壳部分熔融形成的玄武质岩浆上涌底侵于壳-幔边界导致地壳的部分熔融形成酸性的黑云母二长花岗岩岩基。 相似文献
14.
Ikizdere Pluton consists of granite, granodiorite, tonalite, monzonite, quartz monzonite containing pinkish colored K-feldspar megacrysts (KFMs). The crystal sizes of the KFMs range from 1 to 4 cm. The lath-shaped megacrysts are uniformly (i.e., randomly) distributed in the host plutonic rocks and have mafic and felsic inclusions whose crystal sizes are smaller than 1 mm. The crystal inclusions are biotite, slightly annitic in composition with XMg[=Fetot/(Fetot+Mg)]=0.50-0.58, amphibole (magnesio-hornblende, XMg[=Mg/(Mg+Fetot)]=0.70-0.79), iron-titanium oxide (low titanium magnetit and ilmenite), plagioclase (Ab75−25An65−35) and as minor quartz. The compositions of the KFMs range from Or95Ab5An0 to Or82Ab17An1. BaO contents of the megacrysts increase from core to rim. The mafic and felsic inclusions are compositionally similar those of the host rocks.The chemical and textural features of K-feldspar are typical for megacrysts that grew as phenocrysts in dynamic granitoidic magma systems. The overgrowth of KFMs and mafic magma injections (magma mixing) may be related to temperature, pressure and compositional fluctuations in the magma chamber. Remnant of earlier formed K-feldspar crystals remain in the felsic magma system, while the mafic injection can decompose some earlier precipitated KFMs. The remnant of K-feldspar remaining after mafic injection are overgrown by rapid diffusion of Ba, K and Na elements in liquid phase, during the later stages of crystallization of the host magma. 相似文献
15.
Michael J. Dorais Neil D. MacRae T. Grove 《Contributions to Mineralogy and Petrology》1994,117(1):76-86
The Garland Peak Syenite (GPS) of the Red Hill complex, New Hampshire, consists predominantly of amphibole, oligoclase, perthite, and quartz; amphiboles have homogeneous kaersutite cores with strongly zoned rims ranging in composition from pargasite to hastingsite to hornblende. The thin section scale association of kaersutite, an amphibole that typically crystallizes in silica-undersaturated magmas, with quartz suggests that the GPS magma experienced substanital changes in magmatic composition, including silica activity, during its crystallization history. Kaersutite-bearing camptonites are also associated with the Red Hill complex. The camptonite amphiboles are very similar in composition to the core kaersutites in the GPS, suggesting that the earliest GPS liquid may have had camptonitic affinities. In order to elucidate the process where-by silica-undersaturated magmas differentiate to saturation, amphiboles in these rocks were analyzed by electron and ion microprobe techniques. Amphiboles show a progressive increase in REE abundances from the camptonites to the GPS kaersutite cores to the GPS pargasite/hastingsite/hornblende rims. The systematic change in REE concentrations, and the variations in V, Ti, Sr versus Zr, Eu/Eu0 and La/Yb versus Ce, suggest a possible differentiation relationship for the amphiboles and imply that the GPS was derived from magmas similar to camptonites. Rimward depletions in Sr, Ti, V, and Eu/Eu0, and the increase in La/Yb values suggest that parental camptonites fractionated plagioclase, magnetite, and amphibole to produce the silica-oversaturated GPS. Bulk-rock modelling agrees with the trace element record preserved in the amphiboles, that plagioclase, magnetite, and amphibole fractionation caused silica saturation. Minor pegmatitic patches occur in the GPS. Ferrohornblendes in the pegmatites have REE abundances distinct from the other GPS amphiboles, and this difference may be due to open system processes. 相似文献
16.
东昆仑沟里地区暗色包体及其寄主岩石地球化学特征及成因 总被引：2，自引：0，他引：2
通过青海东昆仑东部沟里地区阿斯哈岩体中寄主闪长岩和暗色微粒包体的岩相学、全岩地球化学研究,确定了岩石成因及其构造属性。阿斯哈岩体中暗色包体广泛分布,包体岩性主要为角闪辉长岩。包体具有岩浆结构,部分包体具有塑性流变特征,包体中可见寄主岩石矿物的捕掳晶和针状磷灰石,表现出岩浆混合的岩相学特征。主岩及暗色包体同属准铝质、高钾钙碱性-钾玄岩系列过渡岩石,主量元素在Harker图解及Al2O3/K2O-CaO/K2O和SiO2/CaO-K2O/CaO的共分母协变图上具良好的线性关系,反映两者成分的变化与岩浆混合作用有关。两者的稀土元素配分模式总体一致,显示二者密切的成因联系。两者都富含大离子亲石元素（Rb、K）,相对亏损高场强元素（Nb、Ta、P、Ti）。暗色包体具有贫硅（w(SiO2)=50.70%~53.88%）和富镁、铁、钙的地球化学特征,其Mg#值较高（Mg#=0.52~0.59）,暗示其来源于俯冲带流体交代地幔楔的部分熔融。主岩的Rb/Sr值为0.22~0.27,接近地壳平均值,Nb/Ta值为14.5~15.2,介于地幔平均值与地壳平均值之间,表明寄主岩石岩浆具有壳源岩浆的性质并经历了幔源岩浆的混合作用。结合区域构造演化及构造判别,认为阿斯哈岩体形成于安第斯型活动大陆边缘的构造环境。早三叠世,阿尼玛卿洋向北俯冲,俯冲带流体交代地幔楔,导致其部分熔融形成基性岩浆,底侵的幔源基性岩浆诱发下地壳部分熔融并与之发生混合形成本区闪长岩,而其中的暗色包体为幔源岩浆混合不彻底的产物。 相似文献
17.
Dissolution kinetics of plagioclase in the melt of the system diopside-albite-anorthite,and origin of dusty plagioclase in andesites 总被引：9，自引：5，他引：9
Akira Tsuchiyama 《Contributions to Mineralogy and Petrology》1985,89(1):1-16
The textures and kinetics of reaction between plagioclase and melts have been investigated experimentally, and origin of dusty plagioclase in andesites has been discussed. In the experiments plagioclase of different compositions (An96, An61, An54, An23, and An22) surrounded by glasses of six different compositions in the system diopside-albite-anorthite was heated at temperatures ranging from 1,200 to 1,410° C for 30 min to 88 h. Textures were closely related to temperature and chemical compositions. A crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt (glass) and remained its original euhedral shape below the liquidus. Whatever the temperature, the crystal-melt interface became rough and often more complicated (sieve-like texture composed of plagioclase-melt mixture in the scale of a few m was developed from the surface of the crystal inward; formation of mantled plagioclase) if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt, and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase. From these results the following two types of dissolution have been recognized; (1) a crystal simply dissolves in the melt which is undersaturated with respect to the phase (simple dissolution), and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt (partial dissolution). The amount of a crystal dissolved and reacted increased proportional to the square root of time. This suggests that these processes are controlled by diffusion, probably in the crystal.Mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so-called resorbed plagioclase in igneous rocks. Chemical compositions and textures of plagioclase phenocrysts in island-arc andesites of magma mixing origin have been examined. Cores of clear and dusty plagioclase were clacic (about An90) and sodic (about An50), respectively. This result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing. 相似文献
18.
Petrologic constraints for eoalpine eclogite facies metamorphism in the austroalpine Ötztal basement
Metabasites of the southern Ötztal basement hitherto mapped as amphibolites, were identified as eclogites. Primary mineral parageneses are tschermakitic to pargasitic green amphiboles, omphacite (Jd40), garnet II (Gr20–30) Py10), phengite (Si3.5), zoisite, rutile and quartz. Al—pargasite (20 wt% Al2O3) rims between garnet and omphacite are interpreted as retrograde reaction products.Retrogression of the eclogite parageneses reflecting decreasing pressure and increasing temperature conditions are: Symplectites of diopside and plagioclase after omphacite, Al-and Na-poor green amphiboles, grossularite-poor garnet III surrounding garnet II partly with atoll textures and symplectites of biotite and plagioclase replacing phengite. Continuation of retrogression with decreasing temperature conditions is indicated by actinolitic amphiboles and albite-rims between amphibole II and quartz. 相似文献
19.
JIANG Hu ZHANG Dayu WANG Shiwei FU Xiang YE Longxiang Noel C. WHITE ZHOU Taofa 《《地质学报》英文版》2021,95(3):761-779
Magmatic microgranular enclaves (MMEs) are widely developed in the Shaocunwu granodiorite at the northeast margin of the eastern Jiangnan orogenic belt.Field geology showed that the MMEs occur as irregular ellipsoids near the edge of the intrusion,and consist of diorite,dominantly composed of amphibole,biotite,and plagioclase grains,with minor acicular apatite.Zircon U-Pb dating showed the ages of the host granodiorites and MMEs are 145.9±1.1 Ma and 145.6±2.5 Ma,respectively,indicating both originated during coeval late Jurassic magmatism.Whole-rock geochemical results show that the host granodiorite and MMEs have similar rare earth and trace element partition curves in spider grams,and similar ~(87)Sr/~(86)Sr,and ~(147)Nd/~(144)Nd isotope ratios,and their zircon ~(177)Hf/~(176)Hf isotopic ratios are similar.Geochemical studies indicate that both the host granodiorite and MMEs formed by mixing of coeval magma.Zircon Ti thermometers and oxygen fugacity of the host granodiorite and the MMEs show high oxygen fugacity,similar to that of W-Cu (Mo) mineralized granitoids in the eastern Jiangnan orogenic belt.A similar magma mixing process was probably one of the mechanisms that generated the W-Cu (Mo) fertile melts. 相似文献
20.
The Zhoukoudian pluton in the North China craton is a circular granodiorite intrusion containing porphyritic diorite dykes (PDDs), porphyritic granodiorite dykes (PGDs) and abundant mafic microgranular enclaves (MMEs), which provide an excellent opportunity to study fractional crystallization and magma mixing. The PDDs and PGDs are located in the western part of the pluton with the PDDs intruded by the PGDs. The dykes have similar mineral assemblages although plagioclase in the PDDs has higher anorthite content than the PGDs. Linear relationships between the SiO2 and most major and trace element contents, as well as a positive trend of initial 87Sr/86Sr ratios and a negative trend of epsilon Nd values with increasing SiO2 contents for the dykes suggest that both types were formed by assimilation and fractional crystallization of a common parental magma. Major oxide mass balance and trace element Rayleigh fractionation modeling points to early separation of garnet (11 %), clinopyroxene (27 %), orthopyroxene (16 %), plagioclase (25 %), biotite (19 %), and apatite (2 %) and late fractionation of hornblende (25 %), plagioclase (46 %), biotite (25 %), apatite (1 %), and magnetite (3 %). Most MMEs occur within the transitional granodiorite of the Zhoukoudian pluton. Zoned MMEs, dyke-like MME swarms, local presence of concave margins, veins and enclaves of host granodiorite within some MMEs, and several MMEs surrounded by the biotite-rich granodiorite support their formation by multiple magma mixing events, which finally resulted in different whole-rock major oxides and compatible elements, but homogeneous mineral major oxides (except zoned plagioclase), whole-rock incompatible elements and Sr-Nd isotopes between the MMEs and their host granodiorite. We suggest that multiple magma mixing events might also cause complexly zoned plagioclase in the Zhoukoudian pluton. Relative calcic, irregular or patchy cores and dusty zoned mantles from the zoned plagioclase crystals and their relatively low anorthite content indicate multiple mixing events between mafic/intermediate and felsic magmas. The mafic/intermediate end-members could be represented by the diabase dykes and the PDDs. Therefore, the dykes and MMEs in the Zhoukoudian pluton are genetically linked. 相似文献