An Overview on the REE-Mineralized Alkaline Granites in Egypt, with Special Reference to the Abu Khruq and Gara El Hamra Bodies

Abstract. The REE-mineralized alkaline granites in Egypt are divided into the following three classes: (1) Mesozoic, anorogenic nepheline syenite ring complexes with REE amounting up to 1.3 %, particularly in their fenitized parts (e.g. Abu Khruq), (2) an orogenic peralkaline syenite-granite, composed of i) Zr, Nb, - REE, and Th-enriched peralkaline granite-syenite complexes with REE amounting up to 0.5 % (e.g. Um Hibal, Tarbite North and South, Gharib, and Zarget Naam) and ii) Y, Th, HREE, and P-enriched post-Cretaceous peralkaline complexes that intrude the Phanerozoic rocks of the Southwestern Desert with REE amounting up to 2 % (e.g. Gara El Hamra), and (3) upper Proterozoic, post-orogenic siderophyllite alkali feldspar granite with REE amounting up to 0.8 %, particularly in their apical miarolitic pegmatites and albitized zones (e.g. Kadabora-Abu Dob and Um Naggat). Special attention is given to the Abu Khruq and Gara El Hamra granitic bodies.     

Late Proterozoic older granitoids from the North Eastern desert of Egypt: petrogenesis and geodynamic implications

Major, trace, and REE data for three localities of calc?Calkaline older granitoid rocks exposed in the north Eastern Desert of Egypt are presented. These rocks were selected to cover wide compositional spectrum of the Egyptian older granitoid varieties. They are petrographically represented by granodiorite, tonalite, quartz?Cdiorite, and quartz?Cmonzodiorite. The rocks are comparable with the peraluminous, unfractionated calc?Calkaline suites and fall within the volcanic arc and I-type granite fields. So, they can be regarded as belonging to the volcanic arc collision stage (665?C614?Ma). The granitoids are geochemically similar to other rocks recorded from continental margin arc-systems being exhibit light-REE enriched patterns with variable but chiefly positive Eu anomaly. The latter has reverse relationship with the ??REE, which was attributed to the fractionation of hornblende during partial melting. These patterns are comparable with models involving partial melting of amphibolitic source. This source must represent basalts, gabbros, or volcanics of an island arc system that were transformed to the level of the island arc crust during continental growth where the P?CT conditions are suitable for partial melting. Thus, it is plausible that the studied rocks were derived by partial melting of LREE-enriched, garnet-free, and amphibole-bearing (i.e., hydrated) mafic source. Wadi Milaha granitoids are consistent with the derivation by a high degree of partial melting (30?C40%) of amphibolite protolith in the deep crust. However, the two other localities (Wadi Umm Anab and West Gharib) are matching with 20?C30% partial melting. Within each locality, variation in rock types from granodiorite to tonalite is said to be dominated by variable degree of restite separation during magma ascent. The high water and volatile contents in Wadi Milaha granitoids allowed higher degree of partial melting (30?C40%). Moreover, the lower volatile contents in the other two localities (Wadi Umm Anab and West Gharib) gave lower degrees of partial melting (20?C30%). These processes may resemble important geodynamic features of the Arabo-Nubian Shield evolution in the north Eastern Desert of Egypt.     

Geochemistry and fluid inclusions study of highly fractionated garnet-bearing granite of Gabal Abu Diab, central Eastern Desert of Egypt

The Neoproterozoic granite of Gabal Abu Diab, central Eastern Desert of Egypt, comprises mainly garnet-bearing granite and alkali feldspar granite intruded into calc-alkaline granodiorite–tonalite and metagabbro–diorite complexes. The garnet-bearing granite is composed mainly of plagioclase, K-feldspar, quartz, garnet and primary muscovite ± biotite. The presence of garnet and primary muscovite of Abu-Diab granite suggests its highly fractionated character. Geochemically, the garnet-bearing granite is highly fractionated as indicated from the high contents of SiO₂ (74.85–77.5%), alkalis (8.27 to 9.2%, Na₂O+K₂O) and the trace elements association: Ga, Zn, Zr, Nb and Y. This granite is depleted in CaO, MgO, P₂O₅, Sr and Ba. The alumina saturation (Shand Index, molar ratio A/CNK) of 1.0 to 1.1 indicates the weak peraluminous nature of this garnet-bearing granite. The geochemical characteristics of the Abu Diab garnet-bearing granite are consistent with either the average I-type or A-type granite and also suggest post-orogenic or anorogenic setting. A fluid inclusions study reveals the presence of three fluid generations trapped into the studied granite. The earlier is a complex CO₂–H₂O fluid trapped in primary fluid inclusions with CO₂ contents >?60 vol.%. These inclusions were probably trapped at minimum temperature >?400°C and minimum pressure >?2 kb. The second is immiscible water–CO₂ fluid trapped in secondary and/or pseudo-secondary inclusions. The trapping conditions were estimated at temperature between 400°C and 170°C and pressure between 900 and 2000 bar. The latest fluid is low-salinity aqueous fluid trapped in secondary two-phase and mono-phase inclusions. The trapping conditions were estimated at temperature between 90°C and 160°C and pressure <?900 bar. The origin of the early fluid generation is magmatic fluid while the second and third fluids are of hydrothermal and meteoric origin, respectively.     

Geochemistry and petrogenesis of a peralkaline granite complex from the Midian Mountains, Saudi Arabia

A zoned intrusion with a biotite granodiorite core and arfvedsonite granite rim represents the source magma for an albitised granite plug near its eastern margin and radioactive siliceous veins along its western margin. A study of selected REE and trace elements of samples from this complex reveals that the albitised granite plug has at least a tenfold enrichment in Zr, Hf, Nb, Ta, Y, Th, U and Sr, and a greatly enhanced heavy/light REE ratio compared with the peralkaline granite. The siliceous veins have even stronger enrichment of these trace elements, but a heavy/light REE ratio and negative eu anomaly similar to the peralkaline granite. It is suggested that the veins were formed from acidic volatile activity and the plug from a combination of highly fractionated magma and co-existing alkaline volatile phase. The granodiorite core intrudes the peralkaline granite and has similar trace element geochemistry. The peralkaline granite is probably derived from the partial melting of the lower crust in the presence of halide-rich volatiles, and the granodiorite from further partial melting under volatile-free conditions.     

Geochemistry and petrogenesis of post-collisional alkaline and peralkaline granites of the Arabian-Nubian Shield: a case study from the southern tip of Sinai Peninsula,Egypt

The southern Sinai Peninsula, underlain by the northernmost extension of the Arabian-Nubian Shield, exposes post-collisional calc-alkaline and alkaline granites that represent the youngest phase of late Neoproterozoic igneous activity. We report a petrographic, mineralogical and geochemical investigation of post-collisional plutons of alkaline and, in some cases, peralkaline granite. These granites intrude metamorphosed country rocks as well as syn- and post-collisional calc-alkaline granitoids. The alkaline and peralkaline granites of the southern tip of Sinai divide into three subgroups: syenogranite, alkali feldspar granite and riebeckite granite. The rocks of these subgroups essentially consist of alkali feldspar and quartz with variable amounts of plagioclase and mafic minerals. The syenogranite and alkali feldspar granite contain small amounts of calcic amphibole and biotite, often less than 3%, while the riebeckite granite is distinguished by sodic amphibole (5–10%). These plutons have geochemical signatures typical of post-collisional A-type granites and were most likely emplaced during a transition between orogenic and anorogenic settings. The parental mafic magma may be linked to lithospheric delamination and upwelling of asthenospheric mantle material. Differentiation of the underplated basaltic magma with contributions from the juvenile crust eventually yielded the post-collisional alkaline granites. Petrogenetic modelling of the studied granitic suite shows that pure fractional crystallization cannot quantitatively explain chemical variations with the observed suite, with both major oxides and several trace elements displaying trends opposite to those required by the equilibrium phase assemblage. Instead, we show that compositional variation from syenogranite through alkali feldspar granite to riebeckite granite is dominated by mixing between a low-SiO₂ liquid as primitive or more primitive than the lowest-SiO₂ syenogranite and an evolved, high-SiO₂ liquid that might be a high-degree partial melt of lower crust.     

Post-orogenic and anorogenic A-type fluorite-bearing granitoids, Eastern Desert, Egypt: Petrogenetic and geotectonic implications

The present study focuses on four A-type fluorite-bearing granitic plutons in the Eastern Desert of Egypt which are classified into post-orogenic subsolvus (Homrit Waggat, 535 Ma; Homer Akarem, 541 Ma and Ineigi, 571 Ma) and anorogenic hypersolvus (Gabal Gharib, 476 Ma) granites. All the granites are Si- and alkali-rich and MgCaTi poor. Whereas both granite types appear relatively homogeneous in terms of most of their major and trace elements, they differ in that the subsolvus granites are depleted in TiO₂, FeO^*, Ba, Sr and Zr and enriched in Rb and Y with respect to the hypersolvus granites. The two granite types, however, can be distinguished more easily by their rare-earth element (REE) patterns. Chondrite-normalized REE patterns of the hypersolvus granite display a gull-wing shape, characterized by a large negative Eu anomaly and moderate-to-high LREE contents. Relative to the hypersolvus granite, subsolvus granite is depleted in LREE and more enriched in HREE contents. The increase of HREE in the subsolvus granite is presumably caused by F complexing during the late stage of its evolution. This is supported by the abundance of fluorite veins cross-cutting the subsolvus granite. The negative Eu anomalies in the subsolvus granite point to the role of feldspars as residual phase in the source, and as a crystallizing phase during magmatic differentiation.Field relations, textural, mineralogical and geochemical data of the post-orogenic subsolvus granite are consistent with its derivation from a parental basic magma through crystal-liquid fractionation of alkali feldspar, plagioclase, amphibole, FeTi oxides, titanite, zircon, monazite and allanite. Crystallization occurred in a water-enriched and rather oxidizing environment, as a result of which the entire suite has a transitional character between that of a post-orogenic and an anorogenic setting. On the other hand, the most credible mechanism for the origin of the anorogenic hypersolvus granite is partial melting of I-type granodiorite-monzogranite source rocks in the study area.     

新疆富蕴县恰库尔特—带碱性花岗岩的基本特征及形成的大地构造背景

恰库尔特一带的碱性花岗岩按侵入顺序和岩性可分为:晶洞(霓石)钾长花岗岩、(霓石)碱长花岗斑岩、霓石花岗岩.这些岩石大都含碱性暗色矿物.发育指示浅成特点的晶洞构造及文象结构,从矿物组合看岩石具贫水特征;岩石化学方面以高硅、高碱或过碱,贫铝、镁、钙为主要特征;岩石通常具有高的∑REE,其中以过碱性的霓石花岗岩为最高;轻稀土较重稀土富集,并具有强的负Eu异常;微量元素地球化学图谱表明,岩石相当于洋脊花岗岩,具有高钾、铷、钍的含量,而钡、钽、铌的富集程度相对较低.以上特征和区域构造分析表明,恰库尔特一带的碱性花岗岩为阿尔泰造山带造山作用结束以后于中晚三叠世的非造山环境下形成的A型花岗岩.     

Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting

In the Tifnoute Valley, three plutonic units have been defined: the Askaoun intrusion, the Imourkhssen intrusion and the Ougougane group of small intrusions. They are made of quartz diorite, granodiorite and granite and all contain abundant mafic microgranular enclaves (MME). The Askaoun granodiorite and the Imourkhssen granite have been dated by LA-ICP-MS on zircon at 558?±?2 Ma and 561?±?3 Ma, respectively. These granitic intrusions are subcontemporaneous to the widespread volcanic and volcano-detrital rocks from the Ouarzazate Group (580–545 Ma), marking the post-collisional transtensional period in the Anti-Atlas and which evolved towards alkaline and tholeiitic lavas in minor volume at the beginning of the Cambrian anorogenic intraplate extensional period. Geochemically, the Tifnoute Valley granitoids belong to an alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta negative anomalies and no alkaline affinities. Granitoids and enclaves display positive ε_Nd-560Ma (+0.8 to +3.5) with young Nd-T_DM between 800 and 1200 Ma and relatively low ⁸⁷Sr/⁸⁶Sr initial ratios (Sr_i: 0.7034 and 0.7065). These values indicate a mainly juvenile source corresponding to a Pan-African metasomatized lithospheric mantle partly mixed with an old crustal component from the underlying West African Craton (WAC). Preservation in the Anti-Atlas of pre-Pan-African lithologies (c. 2.03 Ga basement, c. 800 Ma passive margin greenschist-facies sediments, allochthonous 750–700 Ma ophiolitic sequences) indicates that the Anti-Atlas lithosphere has not been thickened and was never an active margin during the Neoproterozoic. After a transpressive period, the late Ediacaran period (580–545 Ma) is marked by movement on near vertical transtensional faults, synchronous with the emplacement of the huge Ouarzazate Group and the Tifnoute Valley granitoids. We propose here a geodynamical model where the Tifnoute Valley granitoids as well as the Ouarzazate Group were generated during the post-collisional metacratonic evolution of the northern boundary of the West African craton. The convergence with the peri-Gondwanan active margin produced brittle fracturing of the cratonic boundary without thickening, allowing rising of magmas. The Tifnoute Valley granitoids display a metasomatized lithospheric mantle source mixed with a minor ancient (2 Ga) continental crust component from the underlying WAC.     

Sequence of magmatic events in the Late Paleozoic of Transbaikalia,Russia (U-Pb isotope data)

The Late Paleozoic intrusive rocks, mostly granitoids, totally occupy more than 200,000 km² on the territory of Transbaikalia. Isotopic U-Pb zircon dating (about 30 samples from the most typical plutons) shows that the Late Paleozoic magmatic cycle lasted for 55–60 m.y., from ~330 Ma to ~275 Ma. During this time span, five intrusive suites were emplaced throughout the region. The earliest are high-K calc-alkaline granites (330–310 Ma) making up the Angara–Vitim batholith of 150,000 km² in area. At later stages, formation of geochemically distinct intrusive suites occurred with total or partial overlap in time. In the interval of 305–285 Ma two suites were emplaced: calc-alkaline granitoids with decreased SiO₂ content (the Chivyrkui suite of quartz monzonite and granodiorite) and the Zaza suite comprising transitional from calc-alkaline to alkaline granite and quartz syenite. At the next stage, in the interval of 285–278 Ma the shoshonitic Low Selenga suite made up of monzonite, syenite and alkali rich microgabbro was formed; this suite was followed, with significant overlap in time (281–276 Ma), by emplacement of Early Kunalei suite of alkaline (alkali feldspar) and peralkaline syenite and granite. Concurrent emplacement of distinct plutonic suites suggests simultaneous magma generation at different depth and, possibly, from different sources. Despite complex sequence of formation of Late Paleozoic intrusive suites, a general trend from high-K calc-alkaline to alkaline and peralkaline granitoids, is clearly recognized. New data on the isotopic U-Pb zircon age support the Rb-Sr isotope data suggesting that emplacement of large volumes of peralkaline and alkaline (alkali feldspar) syenites and granites occurred in two separate stages: Early Permian (281–278 Ma) and Late Triassic (230–210 Ma). Large volumes and specific compositions of granitoids suggest that the Late Paleozoic magmatism in Transbaikalia occurred successively in the post-collisional (330–310 Ma), transitional (305–285 Ma) and intraplate (285–275 Ma) setting.     

The miarolitic pegmatites from the K?nigshain: a contribution to understanding the genesis of pegmatites

In this paper, we show that the crystallization of miarolitic pegmatites at K?nigshain started at about 700°C, in melts containing up to 30 mass% water. Such high water concentration at low pressures (1–3 kbar) is only possible if the melts are peralkaline. Such peralkaline melts are highly corrosive, and reacted with the wall rock—here the granite host—forming the graphic granite zone, in part via a magmatic–metasomatic reaction. With cooling, the water concentration in some melt fractions increased up to 50 mass% H₂O. The melt-dominated system ends below 600°C and passes into a fluid-dominated system, the beginning of which is characterized by strong pressure fluctuations, caused by the change of OH and CO₃ ²⁻ in the melt, to molecular water and CO₂. We note two generations of smoky quartz, one crystallized above the β–α-transition of quartz (≈573°C), and one below, both of which contain melt inclusions. This indicates that some melt fraction remains during at least the higher-temperature portion of the growth of minerals into the miarolitic cavity, contradicting the view that minerals growing into a pegmatite chamber only do so from aqueous fluids. We show that the K?nigshain miarolitic pegmatites are part of the broad spectrum of pegmatite types, and the processes active at K?nigshain are representative of processes found in most granitic pegmatites, and are thus instructive in the understanding of pegmatite formation in general, and constraining the composition and characteristics of pegmatite-forming melts. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

班公湖-怒江缝合带西段阿翁错地区中酸性侵入岩的成因及其对区域构造演化的指示

班公湖-怒江缝合带西段出露大量中酸性侵入岩,为特提斯洋俯冲、拉萨地块与羌塘地块碰撞造山过程中岩浆响应的重要组成部分。本文对该缝合带西段阿翁错地区的闪长岩、花岗闪长岩和花岗岩进行了详细的岩石地球化学和锆石U-Pb年代学研究。锆石LA-ICP-MS U-Pb定年结果表明闪长岩、花岗闪长岩、花岗岩成岩年龄分别为119.3±1.8 Ma、114.7±1.4 Ma和103.2±1.3 Ma。岩石地球化学特征显示中酸性侵入岩属高钾钙碱性系列,具准铝质-弱过铝质I型花岗岩特征;其LREE分馏程度较高,而HREE近于平坦,存在Eu负异常;富集Rb、La等大离子亲石元素和Th、Zr、Hf等高场强元素,亏损Nb、Ta、P、Ti等高场强元素,具有岛弧岩浆岩的特征。研究结果表明在早白垩世晚期(103.0±1.3 Ma)班公湖-怒江特提斯洋壳仍在向北俯冲于南羌塘地块之下,随着俯冲深度增加,大洋板片发生大规模脱水,释放的流体交代地幔楔并引发其部分熔融,产生的幔源岩浆向上运移,与下地壳物质不同比例混合形成了闪长岩和花岗闪长岩;而花岗岩主要由古老下地壳物质部分熔融形成,并有少量地幔物质的参与。     

东昆仑东段清水泉中酸性侵入岩地球化学特征及成因讨论

清水泉侵入体位于青海省沟里地区的北部,处于东昆南造山带的东段,为东昆仑岩浆岩带的组成部分.该侵入体主要为花岗闪长岩和斜长花岗岩,次为闪长岩.不同岩性之间具有清楚的接触界线,花岗闪长岩和斜长花岗岩中含有暗色闪长质包体.岩石化学特征显示,侵入体为富钙中钾的钙碱性系列岩石,是岩浆成因的Ⅰ型花岗岩,形成于与岛弧、大陆弧有关的大...     

The Mount Gharib A-type granite,Nubian Shield: petrogenesis and role of metasomatism at the source

The Mount Gharib peralkaline A-type complex (476±2 Ma), located in the Nubian Shield of Egypt, contains sodic-calcic to sodic amphiboles, accessory astrophyllite, zircon, fluorite, apatite, allanite, aenigmatite, elpidite(?) and ilmenite. This “within plate” hypersolvus suite is enriched in large-ion lithophile (LIL) and high field-strength (HFS) elements, and characterized by a fractionated REE pattern (Ce/Yb=49) and a significant negative Eu anomaly. A fine-grained acicular-amphibole-bearing roof facies shows further enrichment in the LIL and HFS elements. The suite was emplaced in a Pan-African granodiorite-adamellite host, which it locally metasomatized. The affected rocks contain hydrothermal albite, end-member arfvedsonite, astrophyllite, and levels of the LIL and HFS elements intermediate between those in the peralkaline granite and the roof facies. Trace element and isotopic modeling of this A-type granite, with its high initial ⁸⁷Sr/⁸⁶Sr value (0.7110), documents an active role of the lithosphere in magma generation. Lithospheric extension, expressed by regional dyke-swarms, was caused by cooling, fracturing and relaxation of the thin, newly formed Pan-African crust. Localized partial melting took place in an open system, possibly as a result of an influx of alkali-rich fluid derived from a sublithospheric source. Metasomatic reactions similar to those observed in the metasomatized wallrocks are considered to have played an important role just prior to the onset of anatexis and generation of the A-type melt.     

崂山花岗岩岩石地球化学与成因

崂山花岗岩是中国东部晚中生代较典型的由钙碱性岩碱和碱性岩套构成的复合花岗岩体，可划分石英二长岩、黑云二长花岗岩、正长花岗岩和碱性花岗同夺四个单元，结晶年龄分别为１４６．８、１２６．２、１１３．０和１１０．８Ｍａ。岩石地球化学研究表明：钙碱性岩套自石英二长岩→黑云二长花岗岩→正长花岗岩 呈现向富硅、富碱、低铝、低钙、低镁方向的演化特征；碱性花岗岩总体呈现出高硅、高碱、低铝、低钙、低镁的特征，其大离子亲石元素和高场强元素Ga、Nb、Hf、Zr、Y及Ga／Al、F／Cl比值等明显偏高，与国内外典型的A型花岗岩成分相当。同位泰示踪及成岩机理研究揭示出崂山花岗岩起源于下地壳基底变质岩的部分熔融。两套岩石分别与两次熔融事件有关，钙碱性岩套各单元是岩浆不同分离结晶程度的产物，而碱性花岗岩可能起源于经先前熔融事件(形成钙碱性岩套)萃取过的残留源岩，其形成与AFC过程有关。基于一系列地球化学图解的判别，结合区域构造演化，指出崂山花岗岩是胶北地体－胶南地体陆－陆碰撞剪切造山带构造发展演化至特定阶段的产物，钙碱性岩套形成于造山晚期压性或压性向张性转化的应力环境，而碱性花岗岩则形成千造山期后的剪切张性(transtension)构造环境．后者成为苏北－胶南地区燕山晚期造山作用结束的标志。     

Geochemical constraints on the genesis of the Sarıcakaya intrusive rocks,Turkey: Late Paleozoic crustal melting in the central Sakarya Zone

The Sakarya Zone is intruded by several Late Paleozoic granitoids, of which the Sar?cakaya intrusive rocks in the central Sakarya (Eski?ehir) region, is the least-studied. The Sar?cakaya intrusive rocks consist mainly of quartz diorite-granodiorite, granodiorite and granite. They are, geochemically, divided into two groups: diorites and granites. The former is medium-K and calc-alkaline (mainly I-type), whereas the latter is high-K to shoshonite and calcic (I-type). Typical minerals for both rock types are plagioclase, K-feldspar, quartz, biotite, hornblende and Fe–Ti oxides. Chondrite-normalized REE patterns for the Sar?cakaya intrusive rocks are moderately fractionated and have small negative Eu anomalies. They are enriched in LILE and LREE relative to HFSE showing characteristics of arc-related granitoids. Geochemical characteristics of the Sar?cakaya intrusive rocks indicate a hybrid origin through partial melting of lower crustal source rocks.     

青海泽多桌肉地区花岗闪长岩与暗色包体地球化学特征及成因

青海泽多桌肉地区花岗闪长岩中发育大量暗色闪长质包体。通过对花岗闪长岩(寄主岩石)与暗色包体的地球化学研究发现,花岗闪长岩(寄主岩石)的SiO_2含量为w(SiO_2)=61.61%~68.80%,A/CNK=0.91~0.99,属于偏铝质钙碱性花岗岩特征;暗色包体中发育针状磷灰石,暗色包体的SiO_2含量为w(SiO_2)=52.66%~66.99%,碱度率AR=2.08~2.26(大于1),里特曼指数σ=1.89~8.67,固结指数SI=16~24.74,属过铝质钙碱性花岗岩。稀土元素分析显示,花岗闪长岩稀土总量w(ΣREE)=117.44×10~(-6)~265.68×10~(-6);暗色包体稀土总量w(ΣREE)=184.05×10~(-6)~342.11×10~(-6),总量高于寄主岩石;暗色包体和寄主花岗岩有着相似的稀土元素配分模式,显示轻稀土富集,重稀土亏损,轻重稀土元素分馏明显的特征。微量元素分析显示,暗色包体微量元素的分布型式与寄主岩微量元素特征基本一致,大离子亲石元素K、Rb、Ba相对富集,高场强元素Nb、Ta、Zr、Hf相对亏损,反映了岩浆混合作用的特征。在花岗闪长岩中获得LA-ICP-MS锆石U-Pb年龄为202.49 Ma±0.63 Ma,属晚三叠世。表明泽多桌肉花岗闪长岩属于晚三叠世以来的造山带伸展崩塌造成岩石圈较快速减薄以及幔源岩浆底侵作用的发生,并导致地壳岩石接近熔融温度产生壳源岩浆而成岩。     

西天山喇嘛苏岩体年代学、地球化学及成矿意义

文中主要对西天山喇嘛苏岩体进行SHRIMP锆石U-Pb年龄、主微量及Sr-Nd-Pb同位素测定,阐明岩体成因及形成构造背景。喇嘛苏岩体主要由石英二长闪长岩、花岗闪长斑岩和英云闪长斑岩组成。其中,石英二长闪长岩形成于(394.8±4.9)Ma,花岗闪长斑岩和英云闪长斑岩形成于(380.9±3.9)Ma,略晚于石英二长闪长岩。岩体具有埃达克质岩的特征,且显示从钙碱性向高钾钙碱性演化的趋势,稀土元素配分曲线显示相对富集轻稀土((La/Yb)N:3.55～15.52)及中等的负或正Eu异常(δEu:0.53～1.12)。岩体具有较高的Sr含量((322～808)×10-6)和较低的Y含量((12.90～18.86)×10-6)。微量元素特征显示岩体富集LILE亏损HFSE,并具有Nb、Ta和Ti负异常。岩体初始Sr-Nd同位素组成为εNd(t)=-4.29～+0.75和ISr=0.706 052～0.708 263,Nd模式年龄为1.03～1.46Ga。花岗闪长斑岩和英云闪长斑岩的铅同位素特征为206Pb/204Pb=18.500～19.044,207Pb/204Pb=15.575～15.626,208Pb/204Pb=38.443～38.864;石英二长闪长岩为206Pb/204Pb=18.694～18.711,207Pb/204Pb=15.622～15.630,208Pb/204Pb=38.648～38.660。所有地球化学特征显示喇嘛苏岩体是俯冲洋壳部分熔融形成的熔体,上升过程中与受俯冲带沉积物交代的地幔楔相互作用,且有少量古老地壳的混染而形成。岩体形成于晚泥盆世准噶尔残余洋盆向伊犁—中天山地块俯冲的大陆弧背景,与该区Cu(Au)矿化有较密切的联系。     

新疆北部阿尔泰山东段泥盆纪岩浆活动及侵位方式的探讨

新疆北部阿尔泰山东段发育大量的岩浆岩,对取自阿德尔石英闪长斑岩和乔拉克萨依花岗闪长岩的样品进行了LA-ICP-MS锆石U-Pb同位素年龄测定,获得了(415.7±4.0) Ma和(413.5±3.0) Ma的年龄值。据此将其形成时代厘定为早泥盆世。两组样品主量元素差异明显,稀土、微量元素特征基本一致。石英闪长斑岩具有中钾-低钾钙碱性、过铝质花岗岩岩石特征,而花岗闪长岩具有高钾钙碱性、准铝质系列特征。两者轻稀土富集、重稀土相对亏损,中等-弱负Eu异常;微量元素Rb、Th、U等LILE富集,具有明显的“峰”,Nb、Ta、Ti等HFSE强烈亏损,呈明显“TNT”负异常,显示了与俯冲作用有关的岩浆岩特征。综合区域地质资料分析,阿尔泰造山带东段泥盆纪早期岩浆活动剧烈,成因复杂,侵位方式多样,形成了多种火成岩构造组合,可能是热幔-热壳结构下的产物,具有形成超大型矿床的潜力。     

西藏鸡公村钼矿区中酸性岩体的时代、岩石地球化学特征及构造背景

鸡公村钼矿位于冈底斯下察隅晚燕山—喜山期岩浆弧带南缘。文中以矿区广泛分布的中酸性岩体为研究对象,从野外地质调查、岩石学、LA-ICP-MS锆石U-Pb定年、岩石地球化学成分特征等方面对其进行了系统的探讨。研究结果显示：鸡公村中酸性岩体的岩石类型主要为石英闪长岩和少量的花岗闪长岩;中酸性岩体的LA-ICP-MS锆石U-Pb年龄为(51.8±0.5) Ma,表明其形成于始新世(E2)时期;中酸性岩具低K(w(K2O)为1.66%~2.44%)、高Na(w(Na2O)为3.58%~4.06%)的特点,属钙碱性高钾钙碱性系列,具准铝质弱过铝质的特征;稀土总量(ΣREE)变化范围较大((53.6~117)×10-6),稀土元素配分模式表现为轻稀土富集的右倾斜型,其(La/Yb)N值为3.90~7.31,铈、铕异常不明显(Ce/Ce*=0.92~1.17,Eu/Eu*=0.96~1.15);微量元素比值蛛网图上显示出Rb、Th、U、K等元素的正异常和Ba、Nb、Ta、P、Ti等元素的负异常;鸡公村中酸性岩属I型花岗岩,是变玄武岩质下地壳部分熔融的产物;鸡公村中酸性岩体形成于印度欧亚板块俯冲碰撞环境,起源于地壳加厚导致的源区物质的部分熔融。     

Hingganite-(Y) from a small aplite vein in granodiorite from Oppach,Lusatian Mts., E-Germany

Mineralogy and Petrology - Crystals of hingganite-(Y) occur co-trapped in quartz crystals from miarolitic cavities in an aplite vein in the Cadomian granodiorite from Oppach/Lusatian, Germany. We...