Mafic and felsic magmatism in the Wadi Kalalat area, South Eastern Desert, Egypt: mineralogy, geochemistry and geodynamic evolution during the Neoproterozoic in the Nubian Shield

In the south Eastern Desert of Egypt,two contrasting types of magmatism(mafic and felsic) are recorded in the Wadi Kalalat area,and form the Gabal El Motaghiarat and Gabal Batuga intrusions,respectively.The two intrusions post-dates ophiolitic and arc associations represented by serpentinite and metagabbro-diorite,respectively.The mafic intrusion has a basal ultramafic member represented by fresh peridotite,which is followed upward by olivine gabbro and anorthositic or leucogabbro.This mafic intrusion pertains to the Alaskan-type mafic-ultramafic intrusions in the Arabian-Nubian Shield(ANS)being of tholeiitic nature and emplaced in a typical arc setting.On the other hand,the Gabal Batuga intrusion comprises three varieties of fresh A-type granites of high K-calc alkaline nature,which is peraluminous and garnetbearing in parts.A narrow thermal aureole in the olivine gabbro of the mafic intrusion was developed due to the intrusion of the Batuga granites.This results in the development of a hornfelsic melagabbro variety in which the composition changed from tholeiitic to a calc-alkaline composition due to the addition of S_(i)O_(2),Al_(2)O_(3),alkalis,lithosphile elements(LILEs) such as Rb(70 ppm) and Y(28 ppm) from the felsic intrusion.Outside the thermal aureole,Rb amounts 2-8 ppm and Y lies in the range <2-6ppm.It is believed that the Gabal Batuga felsic intrusion started to emplace during the waning stage of an arc system,with transition from the pre-collisional(i.e.,arc setting) to post-collisional and within plate settings.Magma from which the Gabal Batuga granites were fractionated is high-K calc-alkaline giving rise to a typical post-collisional A-type granite(A_(2)-subtype) indicating an origin from an underplating crustal source.Accordingly,it is stressed here that the younger granites in the ANS are not exclusively post-collisional and within-plate but most likely they started to develop before closure of the arc system.The possible source(s) of mafic magmas that resulted in the formation of the two intrusions are discussed.Mineralogical and geochemical data of the post-intrusion dykes(mafic and felsic) suggest typical active continental rift/within-plate settings.

Preparation of Thermal Insulation Ceramics Using Felsic Tailings as Main Raw Material and Soda-ash Dregs as Flux

Low-cost thermal insulation porous ceramics with uniform pore diameter and low bulk density were prepared with soda-ash dregs and felsic tailings.We investigated the effect of temperature,foaming agent,fluxing agent,Al_(2)O_(3)and CaO content on the pore structure and crystal phase of porous ceramics.The effect of Ca^(2+)in soda-ash dregs on the preparation of quartz-feldspar based porous ceramics was studied.The results showed that the contribution of Ca^(2+)to the preparation of porous ceramics in this system was mainly to accelerate the Si-O bond fracture and reduce the sintering temperature at the initial stage of sintering,which destroyed the needle-like feldspar in the high temperature melt and reduced the melt viscosity,thus reduced the foaming resistance and promoted the porous products with uniform pore size distribution.The Ca^(2+)content on the high side can participate in the formation of crystals in sintering.The generated needle-like diopside and augite,which have small length-diameter ratio,will negligibly change in the viscosity of melt at high temperatures,and their inhibition effect on pores is not as good as that of feldspar with large length-diameter ratio,resulting in the merger and collapse of pores.But the increase of diopside and augite can improve the compressive strength of porous products to some extent.Porous ceramic products containing needle-like feldspar phase can be prepared by using two kinds of solid waste,which can improve the compressive strength of the products and reduce the raw material cost and energy consumption while comprehensively utilizing the double solid waste.The optimal product has a bulk density of 0.45 g/cm^(3),a compressive strength of 3.17 MPa,and a thermal conductivity of 0.11 W/(m·K).

Petrological Implication of the Albite Rims in the Felsic Gneisses of the Fuping Complex

The albite rim is present in most felsic gneisses of the Fuping Complex. The presence of the rim indicates the coexistence of plagioclase and K-feldspar in the rock. The rim is formed immediately after the myrmekite, and both textures were derived from the alteration of K-feldspar. The difference is that that there is no quartz present in the rim, and the rim is nearly albite and the anorthite content of the rim plagioclase is substantially lower than that of the myrmekite plagioclase. Formed at 400- 500~C the albite rim was derived from the K-feldspar composition adjustment in the late or post- magmatism stage. As the temperature decreased, the equilibrium between K-feldspar and plagioclase could be maintained, and reactions between the minerals occurred. The leucocratic veins in the complex show distinguished magma or migmatitic characteristics. The rim might form in the late magma or deuteric stage. The formation of the rim implies obvious granitic magmaor melt-injection activity. Typical metamorphic rocks cannot produce the rims. Anatexis after medium-high grade metamorphism might be subordinate. If present, the anatexis is water-present, but the rim texture cannot be taken as the symbol of anatexis.

Geochemistry of the Eocene Felsic Porphyric Rocks and High-Mg Potassic Rocks along JARSZ:Implication for the Tectonic Evolution in Eastern Tibet

Eocene felsic porphyric rocks and the high-Mg potassic volcanic rocks（HMPR） occur along the Jinshajiang-Ailao Shan-Red River shear zone（JARSZ） in eastern Tibet.Compared with the HMPR,which are generally believed to be sourced from an enriched mantle,the felsic porphyric rocks show similar K_2O contents,enrichment in LREE and LILE,particularly radiogenic isotope（e.g.Sr and Nd） features much similar to the former,implying generation of the felsic porphyric rocks most likely related to the HMPR,although they both have clearly different major and trace element compositions. The close relationship in spatial-temporal distribution and similar Sr-Nd characteristics between the felsic porphyric rocks and HMPR in eastern Tibet indicate that both of them were possibly formed by a similar tectonic process（event）.Combining the basic dikes in southern and eastern Tibet,we suggest that the break-off of north-dipping Neo-Tethyan slab in southern Tibet during 50-40 Ma,triggered formation of high-Mg potassic magma.This led to developing felsic porphyric magma production by partial melting of underplating HMPR in the lower crust,or fractionation crystallization of the high-Mg potassic magmas.The break-off of slab in the Eocene may also have contributed to the abundant ore-forming material related to earlier subduction events,resulting in formation of the porphyric deposits along JARSZ in eastern Tibet.

LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207^ pb/206^Pb age in the range of （2 49±54 ） -- （2 500±180） Ma. The magmatic genesis-derived detrltal zircon domain gives a 207^pb/ 206^Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206^ pb/ 238^U age of （2 790 ± 150） Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a diesordia with an upper intercept age of （2 044. 7 ± 29.3 ） Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. -2.8 Ga magmatlsm and -2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at （2.04±0.03） Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT （ultrahigh temperature） metamorphosed slab.

Age of the Marwar Supergroup,NW India:A note on the U–Pb geochronology of Jodhpur Group felsic volcanics

The Marwar Supergroup(NW Peninsular India)is thought to be of Ediacaran-Cambrian age,based on previous paleontological and geochronological studies.However,direct constraints on the onset of sedimentation within the Marwar basin are still scarce.In this study,we report U–Pb zircon,LA-ICP-MS,and SIMS ages from the Chhoti Khatu felsic volcanic rocks,interlayered with the Jodhpur Group sandstones(Lower Marwar Supergroup).The cathodoluminescence images of the zircons indicate complex morphologies,and core-rim textures coupled with the wide range of ages indicate that they are likely inherited or in the case of thin poorly indurated ash-beds,detrital in origin.The age spectra of 68 zircon analyses from our sampling display a dominant 800–900 Ma age peak corresponding to the age of basement"Erinpura granite"rocks in the region.The youngest inherited zircon from a felsic ash layer yielded a U–Pb age of651 Ma±18 Ma that,together with previous studies and paleontological evidence,indicates a postCryogenian age for the initiation of Marwar sedimentation following a~125 Ma hiatus between the end of Malani magmatism and Marwar deposition.

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya,Northeast India

The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics （47%--56% w（SiO2））, with subordinate felsic volcanics （67%--75% w（SiO2））. The felsic volcanics are dacitic to rhyolitic in composition and are typically en- riched in LREE （La/SmN = 3.09--3.90） with high REE contents （256--588 ppm）, moderately fraction- ated REE patterns （CeN/YbN = 6.54--9.52） and pronounced negative Eu anomalies （Eu/Eu＊ = 0.55-- 0.72）. Wide variations in Rb/Zr, K/Rb and La/Sm ratios suggest that they were derived from magmas which were randomly contaminated with crustal material. Chemical characteristics and petrogenetic modelling indicate that the dacites were generated by ~ 15% partial melting of a mafic source leaving a residue with 55% plagioclase, 14% orthoclase, 18% clinopyroxene, 5% orthopyroxene, 8% hornblende. The silica-rich rhyodacites and rhyolites were derived from a dacite magma source by a higher degree （〉45%） fractional crystallization of an assemblage consisting of 70% plagioclase, 12% clinopyroxene, 7% amphibole and 11% magnetite. The associated LREE-LILE enrichment and pronounced negative anomalies for HFSE （Nb, E and Ti） exhibited by these felsic volcanics are characteristic of continental rift volcanism, implying that they were emplaced during lithospheric extension.

Crust-derived felsic magmatism in the Emeishan large igneous Province:New evidence from zircon U-Pb-Hf-O isotope from the Yangtze Block,China

Numerous intrusive bodies of mafic–ultramafic to felsic compositions are exposed in association with volcanic rocks in the Late Permian Emeishan large igneous province(ELIP),southwestern China.Most of the granitic rocks in the ELIP were derived by differentiation of basaltic magmas with a mantle connection,and crustal magmas have rarely been studied.Here we investigate a suite of mafic dykes and Ⅰ-type granites that yield zircon U-Pb emplacement ages of 259.9±1.2 Ma and 259.3±1.3 Ma,respectively.The εHf(t)values of zircon from the DZ mafic dyke are–0.3 to 9.4,and their corresponding TDM1 values are in the range of 919–523 Ma.The εHf(t)values of zircon from the DSC Ⅰ-type granite are between–1 and 3,with TDM1 values showing a range of 938–782 Ma.We also present zircon O isotope data on crust-derived felsic intrusions from the ELIP for the first time.The δ18O values of zircon from the DSC Ⅰ-type granite ranges from 4.87‰to 7.5‰.The field,petrologic,geochemical and isotopic data from our study lead to the following salient findings.(i)The geochronological study of mafic and felsic intrusive rocks in the ELIP shows that the ages of mafic and felsic magmatism are similar.(ii)The DZ mafic dyke and high-Ti basalts have the same source,i.e.,the Emeishan mantle plume.The mafic dyke formed from magmas sourced at the transitional depth between from garnet-lherzolite and spinel-lherzolite,with low degree partial melting(<10%).(iii)The Hf-O isotope data suggest that the DSC Ⅰ-type granite was formed by partial melting of Neoproterozoic juvenile crust and was contaminated by minor volumes of chemically weathered ancient crustal material.(iv)The heat source leading to the formation of the crust-derived felsic rocks in of the ELIP is considered to be mafic–ultramafic magmas generated by a mantle plume,which partially melted the overlying crust,generating the felsic magma.

Geochemistry and Zircon U-Pb Dates of Felsic-Intermediate Members of the Late Cretaceous Yüksekova Arc Basin: Constraints on the Evolution of the Bitlis–Zagros Branch of Neotethys(Elazig, E Turkey)

During the Late Cretaceous in the Eastern Mediterranean, the northern branch of the southern Neotethys was closed by multiple northward subductions. Of these, the most northerly located subduction created the Baskil continental arc at around 82–84 Ma. The more southerly and intra-oceanic subduction, on the other hand, produced an arc-basin system,the Yüksekova Complex, as early as the late Cenomanian–early Turonian. The abundant and relatively well-studied basaltic rocks of this complex were intruded by dykes, sills and small stocks of felsic–intermediate rocks, not previously studied in detail. The intrusives collected from five different localities in the Elazig region of eastern Turkey are all subalkaline, with low Nb/Y values. Most of them have been chemically classified as rhyodacites/dacites, whereas a small number appear to be andesites. In normal mid-ocean-ridge basalt(N-MORB)-normalised plots, the intrusives are characterised by relative enrichments in Th and La over Nb, Zr, Hf, Ti and high field strength elements(HREEs), indicating their derivation from a subduction-modified source. While their relatively high, positive εN d(i) values(+6.4 and +7.2) might suggest a depleted mantle source for their ultimate origin, somewhat radiogenic Pb values indicate a sedimentary contribution to the source of the rocks. The overall geochemical characteristics indicate their generation in an oceanic arc setting. The zircon U-Pb Laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) data obtained from five felsic-intermediate rock samples yielded intrusion dates of 80–88 Ma. This suggests that the Elazig oceanic arc-related intrusives are slightly younger than those of the Yüksekova arc-basin system, but coeval with the Baskil continental arc. However, the felsic–intermediate intrusives show different geochemical characteristics(oceanic arc-type, with a lack of crustal contamination)to those of the Baskil continental arc. This indicates that these two igneous systems are unrelated and likely developed in different tectonic settings. This, in turn, supports a geodynamic model in which the northern strand of the southern Neotethys was consumed by multiple northward subductions.

Petrological Investigations and Zircon U-Pb Dating of High Pressure Felsic Granulites from the Yushugou Complex, South Tianshan, China

As a window of insight into the lower crust, high pressure granulite has received much attention since last decade. Yushugou high pressure granulite-peridotite Complex was located in the northeast margin of Southern Tianshan, NW China. Previous ideas agreed that the peridotite unit in Yushugou, combined with the ultramafic rocks in Tonghuashan and Liuhuangshan, represent an ophiolite belt. However, the metamorphic evolution and tectonic mechanism of the Yushugou high pressure （HP） granulite remain controversial. Petrological investigations and phase equilibrium modelling for two representative fclsic granulitc samples suggest two stages metamorphism of the rocks in Yushugou Complex. Granulite facies metamorphism （Stage I） with P-T conditions of 9.8-10.4 kbar at 895-920℃ was recorded by the porphyroblastic garnet core; HP granulite facies metamorphism （Stage II） shows P-T conditions of 13.2-13.5 kbar at 845-860℃, based on the increasing grossular and decreasing pyrope contents of garnet rims. The Yushugou HP felsic granulites have recorded an anti- clockwise P-T path, characterized by the temperature decreasing and pressure increasing simultaneously. The LA-ICP-MS isotopic investigations on zircons from the felsic granulite show that the protolith ages of the granlulites are -430 Ma, with two age groups of-390 Ma and 340-350 Ma from the metamorphic rims of zircon, indicating the Stage I and II metamorphic events, respectively. A tectonic model was proposed to interpret the processes. The investigated felsic granulite was derived from deep rooted hanging wall, with Stage I granulite facies metamorphism of -390 Ma, which may he related to the Devonian arc magmatic intrusion; Stage II HP granulite facies metamorphism （340-350 Ma） may due to the involvement of being captured into the subducting slab and experienced the high pressure metamorphism.

Tuff beds in Kurnool subbasin,southern India and implications for felsic volcanism in Proterozoic intracratonic basins

A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave base, have rheomorphie features indicative of viscoplastic flow, and geochem- ical signatures of rhyolitic to rhyodacitic unwelded to welded tufts, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag- matic reactions. The widespread and repeated occurrences of felsic tufts in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.

Seismic wave velocity of Archaeozoic felsic rocks from North China and its existing location in the crust

This paper contains two contents. The first is seismic velocity of felsic crystalline rocks of North China at room temperature and high pressures and at both high temperatures and pressures. The second is heating acoustic emission of felsic rocks at atmosphere pressure and the temperature of the quartz (-( transition. The results of these experiments show that velocities of the felsic crystalline rocks are obviously lower than that of the basic rocks and no visible relationship with metamorphic phase. The velocity curves of rocks containing quartz display peaks of the (-( phase reaction, which are different from other rocks in configuration. When the heating temperature is up to the phase transition temperature of quartz at the atmosphere pressure, felsic hypometamorphic rocks and magma granite produce acoustic emission. While the other kind of the granite generated by metasomatism does not produce acoustic emission. These results have the following implications. It explains the crustal constitution of the North China craton in combination with other geoscientific data, and clarifies the existing space of ( quartz and ( quartz. It also indicates that the (-( quartz transition and dehydration melting of amphibole and biotite in the lower crustal rocks of the Cenozoic tectonic subsidence area are likely associated with faulting (tensional fault) and seismic activities.

The possible source of uranium mineralization in felsic volcanic rocks,Eastern Desert,Egypt of the Arabian-Nubian Shield:Constraints from whole-rock geochemistry and spectrometric prospection

The present work deals with the detailed geology,mineralogy,geochemistry,and spectrometric prospection of the felsic volcanic rocks at the Eastern Desert,Egypt of the Arabian-Nubian Shield.Felsic volcanic rocks are an essential source for rare earth elements(REEs)and uranium occurrences in this area.They are compositionally uniform with tholeiitic to calc-alkaline affinities,peraluminous and belong to the series of rhyolite with high-K melt.They exhibit more enrichment in high field strength elements(HFSE,e.g.Zr,Ta,Nd,Th,and U)and large-ion lithophile elements(LILE,e.g.Pb and Rb)compared to the country rocks of the studied area,with REE ranging from 188.20 to 442.70 ppm and strong depletion in Ti,Sr,P with deep negative Eu oddities.The felsic volcanic rocks were mostly generated from the partial melting of quartz-amphibolite facies accreted during the Neoproterozoic.Positive oddities of Zr-U-Th for the felsic volcanic rocks determine the involvement of crustal materials.Felsic volcanic rocks are found in A-type suites of magma and represent highly fractionated rocks derived from rhyolitic magma,with insignificant interaction with continental crust in the low-pressure environment and during fractional crystallization.Felsic volcanic rocks have higher values of radioactivity in which eU range from 0.5 to 121 ppm and eTh from 1.0 to 415.10 ppm.The high values of eU and eTh can be ascribed to the mineralization of uranium and the presence of accessory minerals of radiogenic nature such as uranophane,uranothorite,zircon,and monazite.Uranophane is considered as the mineral with most enriched uranium contents in the studied felsic volcanic rocks in which(UO2=87.30 wt%).Also,they are enriched with REE-bearing accessory minerals comprising allanite,titanite,and apatite.The geological investigations of the felsic volcanic rocks in the studied areas are inappropriate to clear the feasible economic potentialities of rare earth elements and U occurrences;itemized and invaluable explorational work is as yet needed.Whilst,the environmental impact of mineralization,owing to U and Th and their radiogenic daughter products,is observed and must be elaborated minutely.

Geochemistry and Tectonic Settings of Felsic Dykes in the Neoproterozoic Nagar Parkar Igneous Complex, SE Sindh, Pakistan

The Nagar Parkar complex consists of Neoproterozoic igneous and metamorphic rocks dissected by episodic mafic and felsic dykes.The latter can be classified broadly into porphyritic felsic dykes and aplitic felsic dykes(minor)

Multiple Episodes of Zircon Growth during Anatectic Metamorphism of Metasedimentary Rocks in Collisional Orogens:Constraints from Felsic Granulites in the Bohemian Massif

Zircon is a key accessary mineral for metamorphic geochronology and geochemical tracing,but it has been a challenge to interpret its complex chemical zoning and age record acquired during multiple episodes of anatectic metamorphism in collisional orogens.This is illustrated by a combined study of petrography,phase equilibrium modeling and metamorphic P-T-t determination for granulites from the Bohemian Massif in the Variscan Orogen.These rocks record multiple episodes of zircon growth during anatectic metamorphism.They started from the compressional heating for prograde metamorphism to high-pressure(HP)to ultrahigh-pressure(UHP)eclogite facies with low degrees of partial melting.Afterwards,they underwent a decompressional stage from UHP eclogite facies to HP granulite facies for dehydration melting.These were followed by a further decompressional stage either to kyanite granulite facies or to sillimanite granulite facies at ultrahigh-temperature(UHT)conditions.Episodes of zircon growth are linked to specific metamorphic conditions for peritectic reactions on the basis of zoning patterns,trace element signatures,index mineral inclusions in dated domains and textural relationships to coexisting minerals.The results indicate that relict zircon domains are preserved even at UHT granulite facies conditions.A few zircon domains in the kyanite granulite grew during the prograde to peak UHP metamorphism,possibly corresponding to consumption of biotite and plagioclase but growth of garnet.During the decompressional exhumation to the HP granulite-facies,relict or prograde zircon domains were mostly dissolved into anatectic melts produced by muscovite breakdown.Most zircon grains grew during this transition to the HP granulite-facies in the kyanite granulite and are chemically related to continuous growth of garnet,whereas abundant zircon grains grew subsequently at the UHT granulite facies in the sillimanite granulite and are chemically related to garnet breakdown reactions.Another peak of zircon growth occurred at the final crystallization of anatectic melts in the sillimanite granulite rather than in the kyanite granulite,and these zircon grains mostly show oscillatory zoning,low HREE+Y contents and significantly negative Eu anomalies.In terms of the inference for protolith nature,it appears that zircon in metasedimentary rocks can grow at a short timescale in different stages of anatectic metamorphism,and its dissolution and growth are mainly dictated by anatectic conditions and extent,the property of peritectic reactions,and the stability of Ti-rich minerals.

从长英质侵入体揭示火山喷发过程与岩浆通道系统

汇聚板块边缘的大型长英质火山喷发是地球上最具破坏性的自然灾害之一。然而,与这些火山相关的岩浆通道系统的结构及其对火山活动的控制方式迄今仍知之甚少。基于在青藏高原北部东昆仑造山带三叠纪火山岩与侵入体关系的观察以及全球岩浆通道系统的研究进展,本文提出要将火山机构与侵入体结合起来开展研究,通过重建岩浆通道系统来揭示侵入体(古岩浆储库)与火山活动的潜在联系。本文指出,地球上只有少部分侵入岩与火山活动存在密切关系,这些侵入岩可能是抽取火山喷发物质后留下的岩浆储库残余物质。有些岩浆储库不仅为火山喷发提供物质,还在提供火山喷发动力、控制火山喷发方式在溢流式与爆炸式之间的转换以及影响火山机构定位等方面发挥着关键作用。富挥发分的流体大量溢出地表会减少大型伟晶岩型和斑岩型矿床的形成机会,特别是在爆炸式的长英质火山喷发过程中。本文将岩浆通道系统划分为5个区域,即部分熔融区、岩浆聚集区、岩浆迁移区、岩浆侵位区和火山喷口区,这些区域构成了一个复杂的纵向递进、横向连接的岩浆网络系统,是构造环境(构造阶段)、地壳状态和岩浆动力学属性的耦合产物。为了深入理解长英质岩浆通道系统结构和动力学演化及其对火山活动机制的控制,本文建议要将火山机构、侵入体和围岩系统作为岩浆通道系统的组成部分,开展构造地质学、岩石学、矿物学、岩浆动力学、地球化学、地球物理学等多学科的综合研究,以精细解剖典型岩浆通道系统的组成和结构,重建其岩浆动力学过程。

琼东南盆地二叠纪-三叠纪长英质岩浆作用:对南海北部陆缘构造属性与演化过程的启示

琼东南盆地发育二叠纪-三叠纪岩浆岩类,为研究南海北部陆缘古构造属性与大地构造演化过程提供了岩石探针。本文以基底长英质岩浆岩为研究对象,开展岩石学、锆石U-Pb年代学、岩石地球化学和锆石Lu-Hf同位素研究,探讨琼东南盆地二叠纪-三叠纪岩浆岩的时空分布、岩石成因及动力学背景。LA-ICP-MS锆石U-Pb年代学表明,琼东南盆地发育二叠纪-早三叠世、中三叠世和晚三叠世三期长英质岩浆作用(271~217Ma),且岩浆活动具有自南向北迁移的趋势。岩石地球化学分析揭示,二叠纪-早三叠世长英质岩具有较低的FeO/MgO和10000×Ga/Al比值,且强烈亏损Zr、Hf、Nb、Ta等元素,属于典型的陆缘弧I型花岗岩类;中三叠世和晚三叠世岩浆岩均具有较高的SiO_(2)、Mg^(#)、10000×Ga/Al和FeO/MgO比值,大多属于A型花岗岩类。同时,二叠纪-早三叠世长英质岩具有较低的Hf同位素组成(ε_(Hf)(t)=-7.61~-0.65),而中-晚三叠世长英质岩则大多具有较高的Hf同位素组成。岩石成因分析揭示,二叠纪-早三叠世I型花岗岩类起源于古老陆壳的部分熔融,而中三叠世和晚三叠世A型花岗岩类则部分起源于古老长英质地壳熔融,部分则起源于新生地壳熔融,并伴随有壳幔相互作用。综合分析表明,二叠纪-三叠纪期间南海北部陆缘主要受控于古特提斯造山作用控制,且先后经历了二叠纪至早三叠世的古特提斯洋壳俯冲、中三叠世印支板块与华南板块碰撞以及晚三叠世碰撞后伸展等动力学过程。

胶-辽-吉造山带辽河群含钴层位里尔峪组变火成岩成因机制及其对复杂构造演化过程的制约

辽河群里尔峪组变基性岩与变长英质粒状岩石记录了胶-辽-吉古元古代造山带复杂演化过程的重要信息。该组不仅是辽东钴富集成矿的关键层位,也是深入探讨胶-辽-吉造山带古元古代起始构造背景及其演化过程的关键研究对象。本文通过野外地质调查、岩相学、全岩地球化学、锆石年代学以及Lu-Hf同位素的综合研究,对里尔峪组中变基性岩与变长英质粒状岩石的原岩属性、成因机制、年代格架及构造背景进行了深入研究,结合胶-辽-吉带古元古代的构造演化过程及其与Co元素的初始来源的内在成因关系进行了初步讨论。里尔峪组变基性岩岩石主要由斜长角闪岩与变角闪石岩组成,变长英质粒状岩石包括浅粒岩和变粒岩。野外观察发现大量变基性岩侵入到变长英质粒状岩石中。锆石U-Pb定年结果表明,变基性岩的原岩形成时代为2160~2130Ma,变长英质粒状岩石原岩的形成时代为2200~2160Ma,两者共同经历了1950~1850Ma古元古代变质事件的改造。根据地球化学特征,变基性岩可分为三种类型:第一类斜长角闪岩属于拉斑玄武岩系列,轻微富集LREE,类似E-MORB特征,Nb、Ta、Ti、Zr和Hf轻微亏损,暗示有限的流体交代和地壳混染,变质锆石ε_(Hf)(t)值为-2.3~5.9,t DM1集中在2200~2100Ma,表明其原岩来源于亏损的软流圈地幔,指示古元古代新生地壳生长事件;第二类斜长角闪岩属于钙碱性系列,具有右倾的稀土元素配分曲线,Nb、Ta和Ti元素明显亏损,Zr、Hf正异常,表明其原始岩浆在离开源区后可能经历了地壳混染;第三类变角闪石岩属于超基性岩,REE总量相对偏高,LREE相对富集,Nb、Ta、Ti、Zr和Hf明显亏损,显示出有限的地壳混染和大量流体交代,岩浆锆石ε_(Hf)(t)值为-2.3~6.7,t DM1集中在2500~2200Ma;变质锆石ε_(Hf)(t)值为-5.9~-0.4,t DM1集中在2500~2300Ma,其原岩应来源于富集的岩石圈地幔。在变长英质粒状岩石中,变粒岩的SiO 2含量低于浅粒岩的,二者原岩均属于钙碱性系列并具有相似地球化学属性,暗示原岩来源于相同的岩浆源区。变长英质岩LREE富集而HREE相对亏损;Zr、Hf正异常,而Nb、Ta和Ti元素明显亏损,与弧源陆壳岩石特征相似;岩浆锆石的ε_(Hf)(t)值集中在-2~4,变质锆石ε_(Hf)(t)值则集中在-7~-1,两者t DM2集中在2900~2600Ma之间,表明其原岩为大陆下地壳太古宙TTG的部分熔融的产物。变长英质粒状岩石与变基性岩均指示其原岩形成于弧后盆地的构造环境,并经历了弧后盆地持续张裂至碰撞造山的演变过程,该过程可以划分为三个阶段:(1)2200~2160Ma期间,狼林陆块与北澳大利亚克拉通之间的大洋板块由西南向东北俯冲,随着俯冲的大洋岩石圈板块后撤,岩石圈开始伸展导致弧后盆地初始张裂;这一伸展作用导致软流圈地幔上涌,加热上覆太古宙大陆地壳;而由于持续的加热,大陆地壳开始部分熔融,形成了大量酸性火山岩(里尔峪组)及酸性侵入岩(条痕状花岗岩)。(2)2160~2130Ma期间,随着俯冲的大洋岩石圈板块后撤,导致上覆岩石圈进一步伸展减薄,弧后盆地继续拉张,软流圈地幔进一步上涌,减压熔融形成2160~2130Ma的基性岩浆;与此同时,软流圈上涌加热上覆岩石圈地幔,部分熔融形成少量富集型基性岩浆。(3)1950~1850Ma期间,狼林陆块与龙岗陆块发生陆-陆碰撞造山作用,并发生区域内角闪岩相-麻粒岩相变质作用;更为重要的是,里尔峪组钴的来源可能与基性岩浆作用密切相关,火山喷发过程中沿裂隙的流体从基性岩中萃取了Co元素,进而在里尔峪组沉淀形成富钴层位,并经历了古元古代变质-变形事件的改造。

陆相断陷咸化湖盆细粒沉积岩特征及沉积环境——以泌阳凹陷核桃园组H3Ⅲ亚段为例

泌阳凹陷作为国内典型的陆相断陷咸化湖盆,在古近系核桃园组三段广泛发育细粒沉积岩。文中利用长井段连续取心资料以及薄片观察、二维XRF扫描、XRD分析、扫描电镜以及地球化学测试等手段,以矿物组分、沉积构造和粒度作为主要依据,把泌阳凹陷H3Ⅲ亚段细粒沉积岩划分为9种岩相类型,其中纹层状混合质页岩、纹层状长英质页岩是发育类型最多的细粒沉积岩;通过Mg/Ca、Al含量、Ti含量、(Fe+Al)/(Ca+Mg)、P/Ti、Sr/Ba和V/(V+Ni)等地球化学指标的垂向变化及岩相组合来分析沉积环境的演化特征。泌阳凹陷H3Ⅲ亚段沉积环境是半深湖—深湖环境,水体盐度为半咸水—咸水,陆源输入总体较强,气候变化相对较大,从下到上经历了干旱、干湿交替、湿润以及干旱的气候变化。岩相的垂向变化受气候、陆源输入、水深、水体盐度的影响,气候、陆源输入、水深决定了长英质矿物和黏土矿物的含量,而碳酸盐矿物的含量主要受到水体盐度和气候的影响。

Study and implication of the high-pressure felsic granulite in the Qinling complex of East Qinling

There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃ and 1.3 -1.6GPa and has experienced two stages of retrograde metamorphism at 600- 650 ℃, 0.8-1.0GPa and 500-600℃, 0.3-0.6GPa, forming two retrograde metamorphic assemblages of margarite + plagiodase (PlI)+quartz and sillimanite + biotite + plagioclase(PlII) + microdine+quartz, respectively. They construct a two-stage clockwise P-T path which shows down-pressure cooling in both early and late stage.