Geochemistry of mafic microgranular enclaves in the Tamdere Quartz Monzonite, south of Dereli/Giresun, Eastern Pontides, Turkey

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.     

西藏冈底斯带始新世曲水岩基的岩浆混合作用:来自斜长石阴极发光特征和成分变化的证据

斜长石作为主要造岩矿物,是研究岩石成因、示踪岩浆演化和岩浆混合过程的有效工具.对冈底斯带曲水岩基始新世花岗闪长岩、二长花岗岩、闪长岩脉和暗色包体中的斜长石进行了阴极发光图像结构特征、电子探针主量元素和LA-ICP-MS微量元素成分的分析,揭示了斜长石复杂环带的成因和相关的岩浆过程.该区斜长石的阴极发光图像呈现出多种颜色且与其An值相对应,随着An值降低依次为绿色、蓝色和暗灰色或暗红色等,并发育补丁状环带、筛状环带、韵律环带等.花岗闪长岩、二长花岗岩中斜长石的An值具有相似的变化范围(20~55),而闪长岩脉和暗色包体中An值的变化范围较大(25~85),表明曲水岩基经历了复杂的开放过程.微量元素结果表明:花岗闪长岩与闪长岩脉和暗色微粒包体具有相同的Sr含量范围(600×10^-6~1 100×10^-6);而二长花岗岩的Sr含量(1 000×10^-6~2 400×10^-6)整体高于前者.以上研究表明,花岗闪长岩中阴极发光呈现绿色的核部或幔部是偏中性岩浆注入寄主岩岩浆混合的结果;具有高Sr含量的二长花岗岩认为是高Sr含量的岩浆结晶形成的;闪长岩脉和暗色微粒包体中的筛状结构斜长石为寄主岩捕掳晶.     

Interaction between crustal-derived felsic and mantle-derived mafic magmas in the Oberkirch Pluton (European Variscides, Schwarzwald, Germany)

The composite Oberkirch pluton consists of three compositionally different units of peraluminous biotite granite. The northern unit is relatively mafic (SiO₂∼64%) and lacks cordierite. The more felsic central and southern units (SiO₂=67.8 to 70.4%) can only be distinguished from each other by the occurrence of cordierite in the former. Mafic microgranular enclaves of variable composition, texture and size occur in each of these units and are concentrated in their central domains. Most abundant are large (dm to m) hornblende-bearing enclaves with dioritic to tonalitic compositions (SiO₂=50.8 to 56.3 wt%; Mg#=63 to 41) and fine grained doleritic textures that suggest chilling against the host granite magma. Some of these enclaves are mantled by hybrid zones. Less common are microtonalitic enclaves containing biotite as the only primary mafic phase (SiO₂=53.7 to 64.4%) and small hybrid tonalitic to granodioritic enclaves and schlieren. Synplutonic dioritic dikes (up to 6 m thick) with hybrid transition zones to the host granite occur in the southern unit of the pluton. In chemical variation diagrams, samples from unmodified hornblende-bearing mafic enclaves and dikes form continuous trends that are compatible with an origin by fractionation of olivine, clinopyroxene, hornblende and plagioclase. Chemical and initial isotopic signatures (e.g. high Mg#, low Na₂O, ɛ_Nd=−1.2 to −5.1, ⁸⁷Sr/⁸⁶Sr=0.7055 to 0.7080, δ¹⁸O=8.0 to 8.8‰) exclude an origin by partial melting from a mafic meta-igneous source but favour derivation from a heterogeneous enriched lithospheric mantle. Samples from the granitic host rocks do not follow the chemical variation trends defined by the diorites but display large scatter. In addition, their initial isotopic characteristics (ɛ_Nd=−4.5 to −6.8, ⁸⁷Sr/⁸⁶Sr=0.7071 to 0.7115, δ¹⁸O=9.9 to 11.9‰) show little overlap with those of the diorites. Most probably, the granitic magmas were derived from metapelitic sources characterized by variable amounts of garnet and plagioclase. This is suggested by relatively high molar ratios of Al₂O₃/(MgO+FeO_tot) and K₂O/Na₂O, in combination with low ratios of CaO/(MgO+FeO_tot), variable values of Sr/Nd, Eu/Eu*[=Eu_cn/(Sm_cn × Gd_cn)^0.5] and (Tb/Yb)_cn (cn=chondrite-normalized) as well as variable abundances of Sc and Y. Whole-rock initial isotopic signatures of mafic microtonalitic enclaves (ɛ_Nd=−4.6 to −5.2; ⁸⁷Sr/⁸⁶Sr=0.7060 to 0.7073; δ¹⁸O ∼8.1‰) are similar to those of the low ɛ_Nd diorites. Plagioclase concentrates from a granite sample and a mafic microtonalitic enclave are characterized by initial ⁸⁷Sr/⁸⁶Sr ratios that are significantly higher than those of their bulk rock systems suggesting incorporation of high ⁸⁷Sr/⁸⁶Sr crustal material into the magmas. Field relationships and petrographic evidence suggest that the Oberkirch pluton originated by at least three pulses of granitic magma containing mafic magma globules. In-situ hybridization between the different magmas was limited. Late injection of dioritic magma into the almost solidified granitic southern unit resulted in the formation of more or less continuous synplutonic dikes surrounded by relatively thin hybrid zones. Received: 30 April 1999 / Accepted: 6 August 1999     

Petrogenesis of Middle-Eocene granitoids and their Mafic microgranular enclaves in central Urmia-Dokhtar Magmatic Arc (Iran): Evidence for interaction between felsic and mafic magmas

Whole rock major and trace element geochemistry together with zircon U-Pb ages and Sr-Nd isotope compositions for the Middle Eocene intrusive rocks in the Haji Abad region are presented. The granitoid hosts, including granodiorite and diorite, yielded zircon U-Pb ages with a weighted mean value of 40.0 ± 0.7 Ma for the granodiorite phase. Mafic microgranular enclaves(MMEs) are common in these plutons, and have relatively low SiO_2 contents(53.04-57.08 wt.%) and high Mg#(42.6-60.1), probably reflecting a mantle-derived origin. The host rocks are metaluminous(A/CNK = 0.69-1.03), arc-related calc-alkaline, and I-type in composition, possessing higher SiO_2 contents(59.7-66.77 wt.%) and lower Mg#(38.6-52.2); they are considered a product of partial melting of the mafic lower crust. Chondritenormalized REE patterns of the MMEs and granitoid hosts are characterized by LREE enrichment and show slight negative Eu anomalies(Eu/Eu* = 0.60-0.93). The host granodiorite samples yield(⁸⁷Sr/⁸⁶Sr);ratios ranging from 0.70498 to 0.70591,positive eNd(t) values varying from +0.21 to +2.3, and TDM2 ranging from 760 to 909 Ma, which is consistent with that of associated mafic microgranular enclaves(⁸⁷Sr/⁸⁶Sr)i = 0.705111-0.705113, ε_Nd(t)= +2.14 to +2.16, T_DM2 = 697-785 Ma). Petrographic and geochemical characterization together with bulk rock Nd-Sr isotopic data suggest that host rocks and associated enclaves originated by interaction between basaltic lower crust-derived felsic and mantlederived mafic magmas in an active continental margin arc environment.     

Zircon U–Pb geochronology,major-trace elements and Sr–Nd isotope geochemistry of Mashhad granodiorites (NE Iran) and their mafic microgranular enclaves: evidence for magma mixing and mingling

ABSTRACT

Mashhad granitoids and associated mafic microgranular enclaves (MMEs), in NE Iran record late early Mesozoic magmatism, was related to the Palaeo-Tethys closure and Iran-Eurasia collision. These represent ideal rocks to explore magmatic processes associated with Late Triassic closure of the Palaeo-Tethyan ocean and post-collisional magmatism. In this study, new geochronological data, whole-rock geochemistry, and Sr–Nd isotope data are presented for Mashhad granitoids and MMEs. LA–ICP–MS U–Pb dating of zircon yields crystallization ages of 205.0 ± 1.3 Ma for the MMEs, indicating their formation during the Late Triassic. This age is similar to the host granitoids. Our results including the major and trace elements discrimination diagrams, in combination with field and petrographic observations (such as ellipsoidal MMEs with feldspar megacrysts, disequilibrium textures of plagioclase), as well as mineral chemistry, suggest that MMEs formed by mixing of mafic and felsic magmas. The host granodiorite is a felsic, high K calc-alkaline I-type granitoid, with SiO₂ = 67.5–69.4 wt%, high K₂O (2.4–4.2 wt%), and low Mg# (42.5–50.5). Normalized abundances of LREEs and LILEs are enriched relative to HREEs and HFSEs (e.g. Nb, Ti). Negative values of whole-rock εNd_(t) (?3 to ?2.3) from granitoids indicate that the precursor magma was generated by partial melting of enriched lithospheric mantle with some contributions from old lower continental crust. In the MMEs, SiO₂ (53.4–58.2 wt%) is lower and Ni (3.9–49.7 ppm), Cr (0.8–93.9 ppm), Mg# (42.81–62.84), and εNd_(t) (?2.3 to +1.4) are higher than those in the host granodiorite, suggesting a greater contribution of mantle-derived mafic melts in the genesis of MMEs.     

Petrogenesis of mafic microgranular enclaves (MMEs) in the oligocene-miocene granitoid plutons from northwest Anatolia,Turkey

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.     

Fractional crystallization and magma mixing: evidence from porphyritic diorite-granodiorite dykes and mafic microgranular enclaves within the Zhoukoudian pluton,Beijing

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.     

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

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。     

江西九瑞矿集区东雷湾矿区中酸性侵入岩及其铁镁质包体的成因:锆石U-Pb年代学、地球化学与Sr-Nd-Pb-Hf同位素制约

九瑞矿集区成矿与燕山期中酸性侵入岩体关系密切,但对该区东雷湾矿床的地质地球化学研究还相对较少.对东雷湾矿区中酸性侵入岩(花岗闪长斑岩、石英闪长玢岩)及其铁镁质包体进行了系统的锆石U-Pb年代学、矿物化学、岩石地球化学和Sr-Nd-Pb-Hf同位素研究,探讨其岩石成因.锆石LA-ICP-MS U-Pb定年表明:东雷湾中酸性侵入岩的成岩年龄为144.3~148.7 Ma,铁镁质包体的年龄为146.4~147.1 Ma,与寄主侵入岩花岗闪长斑岩的年龄一致.东雷湾侵入岩属准铝质范围,岩石的Mg#较高(42.5~68.0,平均56.0),并具有较高的相容元素含量,富集轻稀土,Eu异常不明显,富集大离子亲石元素,亏损高场强元素.暗色铁镁质包体呈细粒结构,常见针状磷灰石和钾长石斑晶.东雷湾样品的Sr-Nd同位素组成变化范围较小,初始87Sr/86Sr比值位于0.706 4 ~ 0.707 9,ε_Nd(t)值变化于-5.80~-3.31,t_2DM(Nd)为1.2~1.4 Ga,锆石ε_Hf(t)值为-15.9~-3.6.样品的206Pb/204Pb(t)、207Pb/204Pb(t)、208Pb/204Pb(t)值分别变化于17.333 3~18.260 0、15.513 5~15.621 0、37.404 1~38.395 4之间.详尽的元素和同位素地球化学特征表明,东雷湾铁镁质包体是由拆沉的加厚下地壳发生部分熔融,并在其上升过程中与地幔物质发生相互作用,进而与花岗质岩浆混合过冷结晶形成的.该区侵入岩的形成很可能是因为加厚下地壳拆沉入软流圈地幔后发生部分熔融,熔体与地幔橄榄岩相互作用后在上侵的过程分别形成了铁镁质岩石和花岗质岩石.      

周口店岩体矿物学、年代学、地球化学特征及其岩浆起源与演化

周口店岩体由三次侵入的中酸性岩石组成, 本次测得石英闪长岩锆石U-Pb年龄为131.6±2.1 Ma, 闪长玢岩锆石U-Pb年龄为128.1±1.4 Ma.周口店岩体各种类型岩石属高钾钙碱性系列、偏铝质, Mg#较高, 重稀土元素和Ta、Nb、P以及Ti明显亏损, 轻稀土元素和Ba、K以及Sr相对富集, Eu没有异常, Yb元素含量小于2×10-6, (La/Yb)_N和Sr/Y比值较高.斜长石复杂环带能谱线扫描表明, 花岗闪长岩中的斜长石核部牌号高, 完整的幔部由内向外由反环带和正环带组成, 微粒包体中的斜长石核部牌号低, 幔部以尘状环带开始, 然后演变为正环带, 这揭示存在多期基性岩浆的注入作用, 结合暗色微粒包体的形态、大小、数量、反向脉、矿物含量统计、矿物成分、地球化学和各类环带包体、岩墙状包体群等特征, 说明暗色微粒包体是在花岗闪长岩浆冷凝过程的不同阶段, 多期幔源基性岩浆注入并与酸性岩浆在围绕包体周缘的局部范围内发生不均一机械混合作用的结果.周口店中酸性岩石体现埃达克质岩的地球化学特征, 岩浆成分主要受源区控制, 形成于加厚下地壳环境.由石英闪长岩-花岗闪长岩至中酸性岩脉, 岩石(Er/Lu)_N和Nb/Ta比值升高, 说明源区残留相矿物组合由角闪石+石榴石向石榴石+金红石变化, 岩浆源区不断变深.      

Eocene tonalite–granodiorite from the Havza (Samsun) area,northern Turkey: adakite-like melts of lithospheric mantle and crust generated in a post-collisional setting

ABSTRACT

Eocene intermediate to felsic plutons of different sizes and compositions are widespread in the Eastern Pontides Orogenic Belt in northern Turkey. Of these, the Ta?l?k Tepe pluton in the Havza (Samsun) area is fine-to-medium-grained, with granular, porphyritic, and micrographic textures, and include mafic microgranular enclaves (MMEs). LA-ICP-MS U-Pb zircon dating yielded emplacement ages of 42.9 (± 1.4) and 40.5 (± 1.3) Ma for the host granodioritic pluton and the dioritic MMEs, respectively. Petrochemically, the host pluton has I-type, high-K calc-alkaline, and metaluminous-to-slightly peraluminous features (A/CNK = 0.95–1.06). The host pluton also shows geochemical features of adakite-like rocks with high SiO₂ (67–68 wt%) and Al₂O₃ (15.5–16.0 wt%) content and Ba/La (17–23), Sr/Y (40.7–61.6), and La_N/Yb_N (14.4–23.7) ratios and low Y (8.2–9.9 ppm) and Yb_N (3.1–4.4) contents. Whole-rock major and trace element variations suggest that fractional crystallisation played a significant role in the pluton evolution. The N-MORB normalised trace element patterns of the pluton are similar to those of MMEs with enrichment in large-ion lithophile elements, Th and Ce, and negative Nb and Ti anomalies. Chondrite-normalised rare earth element plots show moderate-to-highly enriched concave patterns (La_N/Lu_N = 14.2–21.6) with insignificant negative Eu anomalies (Eu_N/Eu* = 0.86–1.14), all of which imply hornblende fractionation during magmatic evolution. The pluton samples have ⁸⁷Sr/⁸⁶Sr ratios of 0.704767 to 0.704927, ¹⁴³Nd/¹⁴⁴Nd ratios of 0.512767–0.512774, εNd values of (+2.52) – (+2.65), and δ¹⁸O values of 7.9–9.7‰. The isotopic compositions of the host pluton and MMEs are similar to I-type granitoids derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. Combined with regional studies, these new data suggest that the parental magma of the studied adakite-like pluton was generated from the lithospheric mantle and then modified by fractional crystallisation and assimilation in a post-collisional setting.     

Oligocene subduction-related plutonism in the Nodoushan area,Urumieh-Dokhtar magmatic belt: Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Geochemical data and Sr–Nd isotopes of the host rocks and magmatic microgranular enclaves (MMEs) collected from the Oligocene Nodoushan Plutonic Complex (NPC) in the central part of the Urumieh–Dokhtar Magmatic Belt (UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U–Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene (middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene (latest Chattian) for granodioritic and diorite porphyry units, respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite (SiO₂ = 47.73–57.36 wt.%; Mg# = 42.15–53.04); the host intrusions are mainly granite, granodiorite and diorite porphyry (SiO₂ = 56.51–72.35 wt.%; Mg# = 26.29–50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements (LILEs, e.g. Rb, Ba, Sr) and light rare earth elements (LREEs) relative to high field strength elements (HFSEs) and heavy rare earth elements (HREEs). These features, combined with a relative depletion in Nb, Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display I_Sr = 0.705045–0.707959, ε_Nd(t) = −3.23 to +3.80, and the Nd model ages (T_DM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with I_Sr ranging from 0.705513 to 0.707275 and ε_Nd(t) from −1.46 to 4.62. The MMEs have T_DM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust- and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle (SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr–Nd isotope data indicate that ∼50% to 90% of the lower crust-derived melt and ∼10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast, ∼45%–65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma (∼35%–55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.     

西秦岭德乌鲁岩体成因及地质意义——来自岩石地球化学的证据

西秦岭德乌鲁岩体位于夏河-合作断裂和力士山-围当山断裂之间,寄主岩石以花岗闪长岩为主,石英闪长岩和石英二长闪长岩次之,并含有大量暗色微粒包体(MMEs)。对德乌鲁岩体开展了年代学研究,获得的花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为225.9±1.3 Ma,表明该岩体形成于晚三叠世早期,可能与扬子板块与华北板块陆陆碰撞有关。岩石地球化学研究表明,寄主岩石具有高K2O,低Y、MgO的特点,而暗色微细粒包体(MMEs)具低K2O,高Y、MgO的特点,在微量元素蛛网图解和稀土元素配分模式上它们具有类似的曲线,在Al_2O_3/MgOSiO_2/MgO图上呈现明显的线性关系,表明这些岩石之间发生了明显的物质交换,说明德乌鲁岩体中的石英闪长岩、石英二长闪长岩和花岗闪长岩是由镁铁质岩浆和长英质岩浆混合产生的,可能与扬子板块和华北板块陆陆碰撞后伸展环境下发生的强烈壳-幔相互作用有关。MMEs可能是镁铁质岩浆的残余物,地球化学特征显示可能有幔源物质的加入,并带来了Au、Cu等成矿元素,在岩体形成演化过程中生成富含Cu和Au的含矿热液,从而在德乌鲁岩体中形成了热液型铜金矿床。     

西藏曲水碰撞花岗岩的混合成因：来自成因矿物学证据

西藏曲水碰撞花岗岩地处冈底斯构造-岩浆带中部,呈东西向平行雅鲁藏布缝合带分布.该岩体以花岗闪长岩、石英闪长岩为主,其次为石英二长闪长岩.岩体内普遍发育微粒镁铁质包体.对花岗闪长岩、石英闪长岩及微粒镁铁质包体的成因矿物学研究结果显示：（1）斜长石发育环带且边缘和核部偏基性,幔部酸性;（2）斜长石斑晶边缘常含有角闪石、黑云母等暗色矿物包体;（3）钾长石X射线结构分析显示自核部向边缘温度呈现逐渐升高的特点;（4）长石矿物中普遍含有较高的Cr、Ni、Co元素,明显不同于壳熔花岗岩;（5）角闪石、黑云母矿物MgO含量高于典型壳熔花岗岩;（6）包体中发育针状磷灰石和角闪石,显示为岩浆淬冷的结果.上述特征不可能用正常岩浆分异作用来解释,而更可能是壳-幔岩浆混合作用的结果.采用矿物温压计所得到的结果也符合混合后的岩浆演化特征.     

内蒙古解放营子花岗闪长岩岩浆混合机制——来自斜长石和角闪石的矿物化学证据

为揭示华北克拉通北缘中晚三叠世解放营子花岗闪长岩的岩浆混合机制,对寄主岩石和镁铁质包体中斜长石和角闪石开展了电子探针分析.分析结果显示,多斑和少斑包体边部的斜长石斑晶发育An值增加的突变环带,环带的An值为32～46,明显高于核部和边部斜长石的An值(18～31),而核部的An值与寄主岩石中斜长石的An值一致,该特征指...     

Magma mixing origin for the post-collisional adakitic monzogranite of the Triassic Yangba pluton, Northwestern margin of the South China block: geochemistry, Sr–Nd isotopic, zircon U–Pb dating and Hf isotopic evidences

Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively. The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element and evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.707069–0.707138, and ε_Nd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive ε_Hf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90), suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.7041–0.7061, and ε_Nd(t) = −3.1 to −4.3] and high contents of K₂O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55), Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite show negative ε_Hf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive ε_Hf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains the Neoproterozoic juvenile crust that has the positive ε_Hf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks.     

西准噶尔克拉玛依岩体的成因:年代学、岩石学和地球化学证据

西准噶尔地区克拉玛依岩体主要由闪长岩和花岗岩组成,锆石SHRIMP法给出的岩体结晶年龄为(315.5±2.8)Ma,为晚石炭世侵入岩.克拉玛依岩体具岛弧岩石的元素地球化学特征:总体上岩石富钠.A/CNK=0.57～0.84,富集LREE,(La/Yb)N=4.7～6.1,Eu显示弱负异常(δEu=0.76～0.91),...     

粤西晚侏罗世花岗质岩体及其暗色微粒包体的成因及意义:年代学、矿物学和地球化学约束

粤西阳江市八二花岗质岩体中广泛发育似斑状细粒闪长质暗色微粒包体,这些暗色微粒包体形态多样,与寄主岩具相似的矿物组合,对研究花岗岩成因和壳-幔相互作用具有十分重要的意义.为了探讨它们的岩石成因及构造属性,对寄主岩和暗色微粒包体开展了系统的岩相学、年代学和地球化学研究.LA-ICP-MS锆石U-Pb定年结果表明,寄主岩年龄为160.0±1.0 Ma,暗色微粒包体年龄为159.3±1.1 Ma,均为晚侏罗世的产物.全岩地球化学特征显示,寄主岩属于富钾的准铝质I型花岗岩,寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素,亏损重稀土元素和Nb、Ta、Ti等高场强元素.此外,两者具相似的Sr-Nd同位素组成,寄主岩的ε_Nd（t）值为-5.73~-5.67,（87Sr/86Sr）_i值为0.707 63~0.707 67;而暗色微粒包体的ε_Nd（t）值为-5.81~-4.35,（87Sr/86Sr）_i值为0.707 04~0.707 74.锆石饱和温度计和角闪石全铝压力计表明八二花岗质岩体结晶于730~754℃和19.8~20.6 km.综合寄主岩及其暗色微粒包体的岩石学、地球化学、同位素特征,晚侏罗世八二花岗质岩体可能形成于陆内伸展背景,由于软流圈物质上涌底侵,导致中下地壳变基性岩为主的源岩部分熔融,并且源区有少量幔源物质的加入,局部可能存在岩浆混合作用;暗色微粒包体是由镁铁质岩浆与长英质岩浆混合形成的.      

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

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。     

Eocene I-type magmatism in the Eastern Pontides,NE Turkey: insights into magma genesis and magma-tectonic evolution from whole-rock geochemistry,geochronology and isotope systematics

ABSTRACT

The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikda??, Ayd?ntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by signi?cant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (⁸⁷Sr/⁸⁶Sr_(i) = 0.70502 to 0.70560; εNd_(i) = +0.9 to – 1.4; δ¹⁸O = +5.0 to +8.7‰, εHf_(i) = – 2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (⁸⁷Sr/⁸⁶Sr_(i) = 0.70508 to 0.70542; εNd_(i) = +0.9 to ?1.1; δ¹⁸O = +5.8 to +8.0, εHf_(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers.