The Petrological and Geochemical Evolution of Ediacaran Rare-Metal Bearing A-type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia

New fieldwork, mineralogical and geochemical data and interpretations are presented for the rare-metal bearing A-type granites of the Aja intrusive complex(AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring-shaped outcrops cut by later faulting. The A-type rocks of the AIC are late Neoproterozoic post-collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A-type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A-type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A-type granites consist of K-feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe-Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved(71.3–75.8 wt% SiO2) and display the typical geochemical characteristics of post-collisional, within-plate granites. They are rare-metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu-negative anomalies(Eu/Eu* = 0.17–0.37) of the A-type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interactions. The chemical characteristics indicate that the A-type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle contribution. Accumulation of residual volatile-rich melt and exsolved fluids in the late stage of the magma evolution produced pegmatite and quartz veins that cut the peripheries of the AIC. Post-magmatic alteration related to the final stages of the evolution of the A-type granitic magma, indicated by alterations of sodic amphibole and sodic pyroxene, hematitization and partial albitization.

Structural Setting and Kinematic Analysis of the Halaban Region,Eastern Arabian Shield,Saudi Arabia

The vorticity analysis technique was applied to measure the different lithological units,such as schist,metagranite and metavolcano-sedimentary rocks,which are present in the Halaban region.This work aims to interpret the relationship between the different lithologies and the tectonic setting,in order to elucidate the nature of kinematic analysis in the Halaban region.The kinematic analyses were applied to feldspar porphyroclasts,quartz and hornblende for twenty-six samples.The kinematic vorticity number(Wm)for deformed rocks in the study area ranged from~0.6 to 0.9.The direction of the long axes for finite strain data(X axes)revealed a WNW trend with shallow dipping.The direction of the short axes for finite strain data(Z axes)were represented by vertical with associated horizontal foliation.The results of the kinematic vorticity and strain analyses are characterized by simple shear with different degrees of deformation in the Halaban region.Furthermore,our finite strain data shows no significant volume change during deformation.The subhorizontal foliation was synchronized with thrusting and deformation.Furthermore,throughout the overlying nappes,the same attitudes of tectonic contacts are observable,the nappes in the orogens being formed from simple shear deformation.

Hydrogeology of Wadi Qudaid Area, Northeast Jeddah, West Central Arabian Shield, Saudi Arabia

The study area is a part of the Arabian Shield rocks of west central part of Saudi Arabia (150 km to the northeast of Jeddah). Geologically, the study area comprises five main geologic units i.e. 1) Layered basic volcanics and related volcaniclastics which are composed mainly from intercalated basalts and andesites and the related volcaniclastic derivatives, 2) Acidic volcanics and related volcaniclastics which are composed from layered and laminated dark and light acidic to intermediate igneous rocks, quartz and chert and marbles, 3) The Tertiary sedimentary succession which of volcaniclastic red beds and the intercalated clays;5) Tertiary volcanics of Harrart, and 4) The Quaternary wadi fill deposits which are composed from friable pebble supported conglomerates, sandstones and clays. Hydrogeologically, the groundwater aquifer of Wadi Qudaid is present mainly in two main horizons i.e. i) unconfined shallow aquifer (13 - 37 m) within the well porous and permeable conglomerates of the Quaternary Wadi deposits, ii) The deep confined aquifer of the bedded tuffaceous sandstones and mudstone of the Tertiary sedimentary succession of Ash Shumaysi Formation. The water samples are analyzed for major elements i.e. Ca, Mg, Na, Cl, SO4, HCO3 and the results show the normal content of these elements. The study related the addition and depletion of many elements during the running trip of the groundwater from the northeast (recharge area) to the southwest (downstream) area.

Measurements of Natural Radioactivity of Industrial Raw Materials from the West of Saudi Arabia (Arabian Shield)

Rock samples of industrial raw materials that are used in the building, from the West of Saudi Arabia (Arabian Shield), have been investigated using X-ray diffraction to identify the mineral chemical composition. The concentrations of Al%, Bi, Pb, Th, U, and K in ppm were measured by atomic absorption analysis. The activity concentrations in Bq/kg dry weight of 226Ra, 232Th and 40K were measured using gamma-ray spectrometry where the range and average were found to be (03.04 - 10.91) 07.90, (03.19 - 13.31) 09.14 and (95.59 - 361.52) 234.81 in Basalt, for Granite (33.81 - 89.13) 80.85, (28.42 - 112.77) 68.50 and (1260.13 - 1629.21) 1376.69, for Gold (00.78 - 11.84) 04.73, (01.48 - 4.69) 02.69 and (13.76 - 445.09) 197.58, for Andesite 05.72, 03.73 and 471.93, and for Marble 01.56, 01.38 and 10.15 respectively. Most results existing within the given values in building materials by UNSCEAR 1993 included Raeq (Bq/kg), D (nGy/h), Deff (mSv/y), Hex and Hin, which meant that it was safe for humans.

Geochemistry of island arc assemblage in the Eastern Desert of Egypt and the role of Pan-African magmatism in crustal growth of the Arabian–Nubian Shield:A review

Neoproterozoic island arc assemblage of the Arabian–Nubian Shield(ANS)in the Eastern Desert(ED)of Egypt comprises juvenile suites of metavolcanics(MV),large amounts of meta-sedimentary rocks(MS),and voluminous metagabbros-diorites(MGD)and syn-tectonic intrusions of older granitoids(OG).We report here the updates of these four rock units in terms of classification,distribution,chemical characteristics,geodynamic evolution,metamorphism,and ages.In addition,we discuss these integrated data to elucidate a reasonable and reliable model for crustal evolution in the ANS.The main features of these rock units indicate their relation to each other and the geodynamic environment dominated by early immature oceanic island arcs to primitive continental arcs.Integrated information of the island arc metavolcanic and plutonic rocks(gabbros,diorites,tonalites,and granodiorites)furnish evidence of the genetic relationships.These include proximity and a coeval nature in the field;all protolith magmas are subalkaline in nature following calc-alkaline series with minor tholeiitic affinities;common geochemical signature of the arc rocks and subduction-related magmatism;their similar enrichment in LREEs;and similar major element compositions with mafic melts derived from metasomatized mantle wedge.The volcano-sedimentary and the OG rocks underwent multiphase deformation events whereas the MGD complexes deformed slightly.Based on the magmatic,sedimentological,and metamorphic evolutions constrained by geochronological data as well as the progressive evolutionary trend from extensional to compressional regimes,a possible gradual decrease in the subducted slab dip angle is the most infl uential in any geodynamic model for arc assemblage in the ED of Egypt.

Geochemistry,Petrogenesis and Alteration of Rare-Metal-Bearing Granitoids and Mineralized Silexite of the Al-Ghurayyah Stock,Arabian Shield,Saudi Arabia

New data are presented for the rare-metal bearing A-type granitoids of the AlGhurayyah stock in the northwestern segment of the Arabian Shield, a composite pluton intruding metamorphosed volcano-sedimentary successions of the Silasia Formation. Metals in the granitoids are variably enriched, with up to 1 990 μg/g Zn, 7 680 μg/g Zr, 2 316 μg/g Nb, 232 μg/g Ta, 485 μg/g Hf, 670 μg/g Th, 137 μg/g U and 1 647 μg/g total rare earth elements(REE). The silexite is highly mineralized and yields higher maximum concentrations of several metals than the granitoids, including up to 1 860 μg/g Y, 9 400 μg/g Zr, 878 μg/g Hf, 1 000 μg/g Th, and 2 029 μg/g total REE. The Al-Ghurayyah stock has been assigned to an intraplate setting. Lithospheric delamination led to generation of mantle melts that supplied heat to melt the juvenile crust of the ANS. The fluorine and rare-metal enriched parental magma evolved by fractional crystallization. The quartz-rich silexite, distinct in character from ordinary hydrothermal vein quartz, is inferred to be co-genetic with the granitoids on the basis of their similar REE patterns;it is interpreted as a small volume of residual magma enriched in SiO2, volatiles, and trace metals. Mineralization took place both at the magmatic stage and later during a hydrothermal stage that concentrated these elements to economic grades.

Petrogenesis and Tectonic Implications of the Jabal Hadb Ad Dayheen Granitic Complex, Central Arabian Shield

The Jabal Hadb Ad Dayheen granitic complex in central Saudi Arabia is an alkaline granitic ring complex associated with a collapsed caldera. It mainly consists of monzogranite in the center, biotite-hornblende porphyritic granite, and biotite-aegirine-riebeckite granite, intruded by some felsic and mafic dikes. The petrological and geochemical characteristics show that the granitic suites consist of metalminous-peralkaline A-type granites. The secondary ion mass spectrometry(SIMS) zircon U-Pb analysis yielded ^(206)Pb/^(238)U ages of 613.3 ± 8.1 – 603.8 ± 3.8, 602.4 ± 3.8, 596 ± 5.6 Ma for biotitehornblende porphyritic granite, microgranite, and biotite-aegirine-riebeckite granite, respectively. The trace element characteristics and positive ε_(Hf)(t) values(3.2–12.2) indicate that the granitic rocks of the Dayheen Ring Complex are mainly derived from the juvenile crust with the involvement of mantlederived materials. Combined with the regional tectonic evolution, the formation of the Dayheen Ring Complex mainly covered four periods:(1) subduction initiation and formation of arc terranes(870–620 Ma)—volcanic craters formed during this period provided the channel for alkaline complex intrusion;(2) collision between East and West Gondwana continents and formation of the north East African Orogen(640–613 Ma)—monzogranite stock at the center of the ring complex emplaced during this period;(3) post-collision extension and collapse(613–602 Ma)—red metaluminous biotite-hornblende porphyritic granite and microgranite sheets in the rim of the Dayheen Ring Complex emplaced during this period;(4) within-plate extension(602 – 545 Ma) —white peralkaline biotite-aegirine-riebeckite granite and plenty of felsic and mafic dikes in the rim mainly formed during this period. The granitic rocks of the Dayheen Ring Complex mainly formed during the transitional stage of post-collison to within-plate extension after the collision between East and West Gondwana continents, and part of them formed during the early stage of the within-plate extension. U, Th, Zr, Nb, and rare earth element mineralization mainly formed during the early stage of the last period, having a close relationship with the intrusion of white peralkaline biotite-aegirine-riebeckite granite.

ASTER Analysis for Locating REE-Bearing Granites in Arid Regions:Example from the Arabian Shield

The world’s increasing demand for rare earth elements(REEs)highlights the potential for using new multispectral remote sensing techniques to define new exploration targets in arid regions,such as the Kingdom of Saudi Arabia(KSA),Egypt,and regions of central and western China.Although REEs cannot be detected by satellite multispectral instruments,REEs-bearing alkaline granites can be identified on ASTER imagery.Herein,we develop a new ASTER band ratio scheme to delineate mineralization-related features of the Ghurayyah REE-bearing peralkaline granite in the northwestern KSA.The Ghurayyah peralkaline stock is located at the intersection of a NW striking segment of the Najd-fault system,and an E-W striking fault.It is surrounded to the north and west by metavolcanics,from east by the Jabal Dabbagh alkali granite,and from the south by monzogranite.The mineralogical composition of granitic rocks resulted in spectral variation and causes absorption features at different wavelengths in the shortwave infrared(SWIR).The newly developed band ratios were constructed from(b6+b8)/(b6–b8)in red;(b6+b8)/b4 in green,and(b7–b9)/(b7+b9)in blue,enabling the discrimination between the Ghurayyah REE-bearing peralkaline granite,Jabal Dabbagh alkali granite,monzogranite,and metavolcanics.Future work will be carried out to perform higher-resolution drone-based hyperspectral imaging for new high-resolution mapping and evaluate the existing REE deposits,emphasizing field spectral measurements to identify the spectral reflectance of REEs mineralized zones and the absorption features of monazite,columbite-tantalite,and aeschynite-(Y),coupled with rock sampling for petrographical,spectral,and geochemical analyses.These methods have great potential for locating REEs-bearing peralkaline granites in the Arabian shield and elsewhere,such as arid portions of central and western China and adjacent regions.

Late Neoproterozoic adakitic magmatism of the eastern Arabian Nubian Shield

Late Neoproterozoic adakitic magmatism within the Eastern Arabian Nubian Shield has been dated at633.2±9.0 Ma(2σ).These magnas intrude the forearc Ad Dawadimi Basin,which is composed of metapelitic schists and greywacke along with ophiolitic melanges of boninitic affinity which underwent inversion and deformation by^620 Ma.This adakitic magmatism,while intruding parts of the Ad Dawadimi Basin,predates this deformation,but is possibly coincident with basin closure.As adakitic magmatism requires melting of an amphibolite or eclogitic source,empirical and experimental constraints require anomalously hot supra-subduction zone mantle.Considering that this magmatism immediately predates basin inversion,these magmas possibly pinpoint the timing of the slab breaking,marking the terminal stages of arc magmatism,terrane accretion and the influx of hot oceanic asthenospheric mantle.This influx of hot asthenospheric mantle may also be responsible for postcolltsional A-type magmatism.

Transpressive Structures in the Ghadir Shear Belt, Eastern Desert, Egypt: Evidence for Partitioning of Oblique Convergence in the Arabian-Nubian Shield during Gondwana Agglutination

Transpressional deformation has played an important role in the late Neoproterozoic evolution of the ArabianNubian Shield including the Central Eastern Desert of Egypt.The Ghadir Shear Belt is a 35 km-long,NW-oriented brittleductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic.Within this shear belt,strain is highly partitioned into shortening,oblique,extensional and strike-slip structures at multiple scales.Moreover,strain partitioning is heterogeneous along-strike giving rise to three distinct structural domains.In the East Ghadir and Ambaut shear belts,the strain is pure-shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple-shear dominated.These domains are comparable to splay-dominated and thrust-dominated strike-slip shear zones.The kinematic transition along the Ghadir shear belt is consistent with separate strike-slip and thrustsense shear zones.The earlier fabric(S1),is locally recognized in low strain areas and SW-ward thrusts.S2 is associated with a shallowly plunging stretching lineation(L2),and defines^NW-SE major upright macroscopic folds in the East Ghadir shear belt.F2 folds are superimposed by^NNW–SSE tight-minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation.F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt.The sub-parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation in fold zones.Dextral ENEstriking shear zones were subsequently active at ca.595 Ma,coeval with sinistral shearing along NW-to NNW-striking shear zones.The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt.Oblique convergence may have been provoked by the buckling of the Hafafit gneiss-cored domes and relative rotations between its segments.Upright folds,fold with vertical axes and sinistral strike-slip shear zones developed in response to strain partitioning.The West Ghadir Shear Zone contains thrusts and strikeslip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian-Nubian Shield during agglutination of East and West Gondwana.

Tonian–Ediacaran Tectonometamorphic History of the Sa'al Complex,Sinai(Egypt):Implications for the Tectonostratigraphic Framework of the Northern Arabian–Nubian Shield

The Sa'al Metamorphic Complex(SMC;southern Sinai)encompasses the oldest arc rocks in the Arabian–Nubian Shield,comprising two non-consanguineous metavolcanic successions(the Agramiya Group and the Post-Ra'ayan Formation)separated by the metasediments of the Ra'ayan Formation.It experienced three distinct deformational events(D_(1)–D_(3))and two low-medium grade regional metamorphic events(M_1–M_(2)).The Agramiya Group and the Ra'ayan Formation experienced all tectonometamorphic events(D_1–D_(3)and M_(1)–M_(2)),whereas the Post-Ra'ayan volcanic rocks were only affected by the D_(3)and M_(2)events.D_(1)is an extensional event and is connected to the late Rodinia break-up(~Tonian;900–870 Ma).The M_(1)metamorphism variably affected the older Agramiya Group,the rhyolitic tuffs experiencing lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks undergoing amphibolite facies metamorphism.The Ra'ayan Formation metasediments experienced upper greenschist to amphibolite facies metamorphism.The upper greenschist facies M_(2)affected the youngest Post-Ra'ayan volcanic rocks and other stratigraphic successions.The compressive D_(2)and D_(3)events were coeval with the accretion of dismembered terranes in the assembly of Gondwana.D_(2)can be linked to the Tonian–Cryogenian arc-arc assembly(~880–760 Ma;in Elat and Sinai),whereas D_(3)and the accompanying M_(2)is constrained to 622–600 Ma(Ediacaran).

阿拉伯地盾地质构造演化与关键地质矿产问题浅析

阿拉伯地盾位于阿拉伯板块的西南部,与红海西岸的努比亚地盾共同组成努比亚−阿拉伯地盾,是新元古代东、西冈瓦纳大陆汇聚过程中形成的泛非造山带的重要组成部分。在“沙特阿拉伯地盾精细地质填图”技术标编制过程中,笔者综合分析了该区的地质调查和研究成果,总结了阿拉伯地盾8个次级地体、主要蛇绿岩构造混杂岩带及新元古代沉积盆地的地质特征,并将阿拉伯地盾的地质演化细分为4个构造演化阶段。其中,在新元古代洋−陆转化过程中阿拉伯地盾形成了一系列重要的矿产资源。在此基础上,系统梳理了区内地层、构造、岩浆作用及与成矿相关的地质问题,提出了未来精细地质填图过程中的工作建议。

非洲东北部阿拉伯-努比亚地盾(ANS)构造演化与金成矿作用

阿拉伯-努比亚地盾(Arabian Nubian Shield,简称ANS)是900~550Ma期间冈瓦纳超大陆汇聚过程中形成的增生造山带,这一造山过程也被称为是泛非造山运动。它记录了一个长期的造山演化历史,经历了从大洋俯冲、岛弧形成及弧后的岩浆作用到大陆板块碰撞地体的拼合,再到新生地壳的逃逸构造、走滑剪切、张性断裂一系列的构造演化过程。这个演化可以分为四个阶段:(1)洋盆形成阶段(870~800 Ma);(2)洋壳俯冲阶段(800~670 Ma);(3)造山阶段(750~550 Ma);(4)后造山阶段(550 Ma~三叠纪),其中后三个阶段都有金的富集成矿作用。洋壳俯冲阶段的金矿化主要赋存在Algoma型含铁建造层(BIF)、凝灰质变质碎屑岩,以及火山成因的块状硫化物矿床内。造山阶段的主要金矿化类型为含金石英-碳酸盐脉状金矿化、与斑岩铜矿化有关的金矿化,以及与辉长岩类岩体有关的含金石英脉状矿化。与后造山阶段有关的金矿化以少量浸染状、网脉状并伴有Sn-W-Ta-Nb矿化的石英脉为特征。目前在ANS中发现了大量金矿床或矿点,它们具有各种不同的成因类型。根据构造背景及赋矿围岩,ANS原生金矿化可以划分为三类:(1)与火山沉积序列有关的金矿化,包括VMS型、浅成热液型;(2)空间分布上与碳酸盐化蛇绿岩带相关的金矿化;(3)与后造山或造山晚期闪长岩-花岗岩岩体或次火山岩有关的金矿化。

基于小波分析和金属因子的双频激电综合解释(英文)

在矿产勘查中,人们常应用电阻率和极化率参数来解释激电异常。当地质体和激电异常较为复杂时,利用这些参数就难以对异常源的性质进行合理解释,还可能推断出错误结论。采用小波处理法和金属因子法综合解释阿迪布拉达矿区复杂地质体的激电异常,选择db5小波基对激电数据进行二尺度分解与重构,较好地压制了绿片岩相区域变质和岩浆侵入的噪音干扰,且其能量较集中,边界问题不明显。在此基础上利用金属因子法有效提取了激电矿致异常。

Field, Mega- and Microscopic Description of the Volcaniclastic Red Beds and the Associated Scoriaceous Basalt of Wadi Al Roaian, Ablah Area, Assir Terrain

The study area is located in the entrance of Wadi Girshah in Ablah area, Assir terrain, southwestern Saudi Arabia. The present study aims to shed light on the field, mega- and microscopic description of the volcaniclastic red beds and the associated scoriaceous basalts of Wadi Al Roaian. It is based mainly up on the field works augmented by petrographic description. The present study revealed that, the succession of the upper part of Girshah Formation comprises three main horizons: 1) lower unit of epidotized and silicified basaltic and andesitic tuffs;2) middle unit of volcaniclastic red beds-scoriaceous basalts of successive cycles (each of these cycles begins by reddish tuffaceous mudstone and sandstone and is terminated by the calcite-bearing scoriaceous basalt). This unit indicated the deposition in lacustrine environments and the red iron oxyhydroxides minerals were formed either by the direct hematitization of the deposited tuffs or by the diagenetic hematitization of the green clays formed instead of the precursor tuffaceous materials;3) upper scoriaceous basalt unit composed from hematitized and calcitized basalt. The unit was formed by basic volcanic eruptions in subaerial condition which was predominated by the formation of calcium carbonate lakes associated with the progressive and subsequent calcitization of the Ca-plagioclase minerals of the basalt and the associated glassy tuffaceous material. The scoriaceous basalts of Wadi Al Roaian area represent subaerial basic volcanic eruption in continental situation and are associated with subsequent events of mineral alteration and formation of secondary minerals i.e. calcite, hematite and goethite.

沙特阿拉伯金矿地质特征及找矿潜力

沙特阿拉伯作为“一带一路”沿线重要节点国家,与我国在矿产资源开发领域具有深入合作。沙特阿拉伯境内有资料记载的金矿点(床)近1000个,开展过钻探勘查的有51个,都分布于阿拉伯地盾区,与新元古代克拉通的形成关系密切。通过搜集大量资料,本文重点研究描述了MAHD ADH DHAHAB金矿床和AL AMAR金矿床的成矿地质特征,并在此基础上对全国35个工作程度较高的地区(5个金矿床和30个远景勘查区)成矿特征进行了总结,认为绝大多数金矿化都是与粗粒侵入岩、岩床或岩墙、火山沉积岩中的石英脉以及火山沉积岩中的层状矿化相关的原生矿化,次生矿化主要发育在一些富含硫化物的氧化带及砂矿中,具有与苏丹、厄立特里亚相似的矿床产出特征,开发潜力巨大。

Serpentinized Peridotites at the North Part of the Wadi Allaqi District(Egypt): Implications for the Tectono-Magmatic Evolution of Fore-arc Crust

The Neoproterozoic Allaqi-Heiani suture （800-700 Ma） in the south Eastern Desert of Egypt is the northernmost linear ophiolitic belt that defines an arc-arc suture in the Arabian- Nubian shield （ANS）. The Neoproterozoic serpentinized peridotites represent a distinct lithology of dismembered ophiolites along the Allaqi-Heiani suture zone. The alteration of peridotites varies, some contain relicts of primary minerals （Cr-spinel and olivine） and others are extremely altered, especially along thrusts and shear zones, with development of talc, talc-carbonate and quartz-carbonate. The fresh cores of the chromian spinels are rimmed by ferritchromite and Cr- magnetite. The fresh chromian spinels have high Cr# （0.62 to 0.79）, while Mg# shows wider variation （0.35-0.59）. High Cr# in the relict chromian spinels and Fo content in the primary olivines indicate that they are residual peridotites after extensive partial melting. The studied ophiolitic upper mantle peridotites are highly depleted and most probably underwent high degrees of partial melting at a supra-subduction zone setting. They can be produced by up to -20%-22% dynamic melting of a primitive mantle source. The mineralogical and geochemical features of the studied rocks reflect that the mantle peridotites of the north part of the Wadi Allaqi district are similar to the fore-arc peridotites of a supra-subduction zone.

Geochemical Constraints of the Ediacaran Volcano-Sedimentary Succession of the Sa'al Metamorphic Complex at Wadi Zaghra, South Sinai, Egypt

The volcano-sedimentary succession around Wadi Zaghra in Sinai, at the northernmost segment of the Arabian Nubian Shield, comprises volcanic rocks interbedded with rather immature sediments. The succession is dominated by intermediate to silicic volcanics of medium-to high-K calc-alkaline affinity. It is divided into two units, the lower unit includes intermediate rocks and dacites interbedded with graywackes, semi-pelites and pelites and topped by polymict conglomerates. This unit is subjected to folding and regional metamorphism(up to garnet zone) and is intruded by quartz diorite-granodiorite inducing, locally, low-pressure contact thermal metamorphism. The unmetamorphosed upper unit encompasses acid volcanics intercalated with litharenite, sublitharenite and minor arenite. The rhyolites of this unit pertain to the highly fractionated granites and are characterized by an agpaitic index(NK/A) ranging from 0.87 to 0.96. They may reflect either extensive interaction of subduction-related magmas with the continental crust or a change in the tectonic regime. The present lithological and geochemical characteristics of the studied sediments together with available zircon ages indicate rather distal provenance of their detritus. This detritus comprises fluvial-alluvial sediments accumulated in the intermontane basins, which are half-grabens or tilted fault blocks. The tectonic setting of the depositional basins is active continental margin and continental island arcs. Geochemical patterns of the Zaghra volcano-sedimentary succession indicate their correlation with the Dokhan Volcanics-Hammamat Clastics sequence of the Eastern Desert of Egypt. Also, the Zaghra volcanics display geochemical similarities with those exposed in Sinai, at the Rutig, Ferani and Iqna Shar'a areas. The Zaghra succession is dated as Ediacaran but is not related either to the ensimatic island arc assemblage or to the rift-related assemblage formed during the early stages of the break-up of Rodinia as previously thought.

Petrogenesis of granitic rocks of the Jabal Sabir area,South Taiz City,Yemen Republic

The Tertiary granitic intrusive body(～21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening.This intrusive body occupies the southern sector of Taiz City.It is triangular in shape,affected by two major faults,one of which is in parallel to the Gulf of Aden,and the other is in parallel to the eastern margin of the Red Sea coast.The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.The granitic body of Jabal Sabir belongs to the alkaline or peralkaline suite of A-type granites.It is enriched in the REE.The tight bundle plot of its REE pattern reflects neither tectonism nor metamorphism.This granite body is characterized by high alkali(8.7%-10.13%),high-field strength elements(HFSE),but low Sr and Ba and high Zn contents.The abundance of xenoliths from the neighboring country rocks and prophyritic texture of the Jabal Sabir granite body indicate shallow depths of intrusion.The major and trace elements data revealed a fractional crystallization origin,probably with small amounts of crustal contamination.It is interpreted that the Jabal Sabir intrusion represents an anorogenic granite pertaining to the A-type,formed in a within-plate environment under an extensional tectonic setting pertaining to rift-related granites.

Using Coarse Grain Geological Study to Predict the Origin of Sediments SW-Iraq

This research deals with coarse grain sediments obtained from sieving of quaternary depression and valley fill sediments from desert and desert boarder’s regions southwest Najaf city-Iraq. Physical, chemical and mineralogical analyses of these sediments were done to reveal the sedimentary origin of these sediments. The results indicated that parent rocks of these sediments were not from the Arabian shield where they were transported for short distances from sedimentary rocks cover that is located at the outskirts of the Arabian shield.