Estimating Influence of Crystallizing Latent Heat on Cooling-Crystallizing Process of a Granitic Melt and Its Geological Implications

Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period （AtL） of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows：△tL=QL×△tcol/（TM-TC）×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature （TM） to its crystallization temperature （Tc）, QL latent heat of the granite melt. The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith.

Copper partitioning between granitic silicate melt and coexisting aqueous fluid at 850°C and 100 MPa

Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 ℃, 100 MPa and oxygen fugacity （fO2） buffered at approaching Ni-NiO （NNO）. Partition coefficients of Cu （Dcu = Cfluid/Cmelt） were varied with different alumina/alkali mole ratios [Al2O3/（Na2O ＋ K2O）, abbreviated as Al/ Alk], Na/K mole ratios, and SiO2 mole contents. The DCu increased from 1.28 ± 0.01 to 22.18 ±0.22 with the increase of Al/Alk mole ratios （ranging from 0.64 to 1.20） and Na/K mole ratios （ranging from 0.58 to 2.56）. The experimental results also showed that Dcu was positively correlated with the HCl concentration of the starting fluid. The Dcu was independent of the SiO2 mole content in the range of SiO2 content considered. No Dcu value was less than 1 in our experiments at 850 ℃ and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatichydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than the melt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl^- fluid.

An experimental determination of W,Nb,and Ta partition coefficients between P-rich peraluminous granitic melt and coexisting aqueous fluid

The partition coefficients of W,Nb,and Ta between the P-rich peraluminous granitic melt and the coexisting aqueous fluid were determined at 800-850 °C and 0.5-1.5 kbar.The experimental results showed that the partition coefficients D_w,D_(Nb) and D_(Ta)(D_i^(v/m) = C_i^V/C_i^m,where C_i^V and C_i^m denote the concentrations of an element,i,in the aqueous fluid and the melt,respectively) were less than 0.1.All partition coefficients were affected by pressure,but there was no evidence for the complexation of P2O5 with these elements in the granitic melt or aqueous fluid,except for with W in the fluid.The results showed that W,Nb,and Ta tended to partition into the granitic melt and,in the late period of crystallization of P-rich magma,they formed independent minerals.

LIQUID SEPARATION OF TUNGSTEN-TIN-BEARING GRANITIC MELT AT 85℃ AND 150 MPa

ＬＩＱＵＩＤＳＥＰＡＲＡＴＩＯＮＯＦＴＵＮＧＳＴＥＮ－ＴＩＮ－ＢＥＡＲＩＮＧＧＲＡＮＩＴＩＣＭＥＬＴＡＴ８５℃ＡＮＤ１５０ＭＰａＣｈｅｎＺｉｌｏｎｇ；ＰｅｎｇＳｈｅｎｇｌｉｎ（ＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｌｏｇｙ，ＣｅｎｔｒａｌＳｏｕｔｈＵｎｉｖｅ...

Interdiffusion of Na, K, and Ca Between Granitic Melts and NaCl Liquid

This study is aimed at determining the diffusion coeffcient of net-work modifiers（mainly Na, K, and Ca） in a two-phase melt-NaCl system, in which the melts are granitic andthe system is NaCl-rich in composition. The diffusion coefficients of Na, K, and Ca were measured at the temperatures of 750 -1400℃, pressures of 0. 001×108 - 2×108 Pa, and initialH2O contents of O wt% - 6. 9 wt% in the granitic melts. The diffusion coefficients of Fe andMg were difficuIt to resolve. In all experiments a NaCl melt was present as well. In the absence of H2O, the diffusion of net-work modifiers folows an Arrhanious equation at 1 ×105 Pa:lgDCa= - 3. 88 - 5140/ T, lgDK = - 3. 79 - 4040/ T, and lgDNa=- 4.99 - 3350/ T,where D is in cm2/s and T is in K. The diffusion coefficients of Ca, Na, K, and Fe increasenon-linearly with increasing H2O cOntent in the melt. The presence of about 2 wt% H2O inthe melt will lead to a dramatical increase in diffusivity, but higher H2O content has only a minor effect. This change is probably the result of a change in the melt structure when H2O ispresent. The diffusion coefficients measured in this study are significantly different from thosein previous woks. This may be understood in terms of the "transient two-liquid equilibrium"theory. Element interdiffusion dapends not only on its concentration, but also on its activity coefficient gradient, which is reflected by the distribution coefficient, of the two contactingmelts.

Phase Equilibria in the Granite-H_2O-HF System and Effect of Fluorine on Granitic Melt Structure

Experiments carried out in the system granites-H2O-HF at 0. 1 GPa show that the crystal-liquid equllibrium temperature of quartz rises and that of alkali-feldspar goes down with increasing F content. The calculated results of quartz and alkali feldspar crystal-liquid equilibri-um show that the activity of SiO2 in melt increases and the activities of NaAlSi3O8 (Ab) and KAlSi3O8(Or) decrease, with a greater decreasing extent for than . These systematic changes are believed to be caused by F complexing with Al, Na, K, but not Si in the melt,and are consistent with F decomposing AlO2 tetrahedra and more preferentially forming com-plexes with Na than K. The comarison between effects of F and H2O on phase equilibrium suggests that the maximum difference affecting melt structure between F and OH is F complex-ing without Si and OH complexing with Si in granitic melt.

Geochemical characterization of Granitoids in Katchuan Irruan area: further evidence for peraluminous and shoshonitic compositions and post-collisional setting of granitic rocks in the Precambrian Basement Complex of Nigeria

Petrographic studies on Granitoids from Katchuan Irruan and adjoining areas,southeastern Nigeria,has shown that they are garnetiferous biotite granite,aplitic granite,porphyritic hornblende biotite granite,porphyritic muscovite biotite granite,weakly foliated leucogranodiorite and simple pegmatite.They are closely associated with the Precambrian Basement Complex rocks which they intruded.Modal analysis shows that the rocks consist of quartz(10%-25%),oligoclase(10%-30%),K-feldspar(15%-35%),biotite(3%-25%),with occasional garnet,hornblende,muscovite,and accessory chlorite,haematite and magnetite.Geochemical data indicates that the rocks are generally shoshonitic,alkali-calcic to calcic,ferroan and peraluminous.They are enriched in large ion lithophile elements as well as high field strength elements(Hf,Ta,Yb,Sm,Zr and Y).Their trace elements and REE patterns are similar,indicating that they are co-genetic.They are characterized by high fractionation factor(La/Yb)N(3.04-228.44)and pronounced negative Eu anomalies(Eu/Eu*)(0.23-0.71).Their overall geochemical features indicate that they were most likely derived from partial melting of crustal materials in an orogenic(post-collisional)tectonic setting.They are therefore related to the Pan-African granites,otherwise known as the Older Granites which were emplaced during the Pan African orogenic event.

Geochronology,Petrogenesis and Tectonic Setting of the Late Jurassic I-type Granites in the North Qinling Orogenic Belt,Central China

The North Qinling Orogenic Belt(NQOB)is a composite orogenic belt in central China.It started evolving during the Meso-Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic.The Meso-Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt,with the tectonic evolution of the middle part of the belt being particularly controversial.The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB.The main lithology of Dayu and Kuyu granites is biotite monzogranite,and the zircon U-Pb dating yielded intrusive ages of 151.3±3.4 Ma and 147.7±1.5 Ma,respectively.The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic.The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO_(2)(64.50-68.88 wt%)and high Al_(2)O_(3)(15.12-16.24 wt%)and Na_(2)O(3.55-3.80 wt%)contents.They are also enriched in light rare earth elements,large ion lithophile elements(e.g.,Ba,K,La,Pb and Sr),and depleted in high field strength elements(HFSEs)(e.g.,Ta,Nb,P and Ti).Additionally,the granites have weakly negative-slightly positive Eu anomalies(δEu=0.91-1.19).Zircon Lu-Hf isotopic analysis showedε_(Hf)(t)=-6.1--3.8,and the two-stage model age is T_(2DM(crust))=1.5-1.6 Ga.The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites.They formed by partial melting of the thickened ancient lower crust,accompanied by the addition of minor mantle-derived materials.During magma ascent,they experienced fractional crystallization,with residual garnet and amphibole for a certain proportion in the magma source region.Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression-extension transition regime.It may have been a response to multiple tectonic mechanisms,such as the late Mesozoic intra-continental southward subduction of the North China Craton and the remote effect of the Paleo-Pacific Plate subduction.

Genesis of Rare Element Mineralized Granites in Southern China:Evidence from Melt and Fluid Inclusions

Rare element mineralized granites of me Yanshan period in Southern China are characterized by high contents of SiO2,Na2o,K2O,and F and are enriched in Nb,Ta,REE,W,Sn,Be and Li .Opinions differed over whether they are of metasomatk or magmatic origin .In this paper ,we present results of a study on melt and fluid inclusions in topaz-albite feldspar granite from Limo Nb-Ta-W-Sn granite and 414 Ta-Li albhe granite .Our data, which come from 15 mineralized granites, provide strong support magmatic origin .Mett inclusions are recognized in both topaz and quartz, and are associated with primary gas-rich incluaons.Crystallites of a Nb (Ta) -bearing mineral and cassiterite are also commonly present as inclusions in the topaz .Multiphase (mett+fluid) inclusions are observed in some quartz from granites and granite-related pegmatite .Mett inclusions start to mett at a temperature of approximately 540 ℃ in topaz and 650 ℃ in quartz .Final homogenization temperature is 700-900 ℃ in quartz ,700-800℃ in topaz and 440-550 ℃ for primary gas-rich inclusions coexisting with mett inclusions in topaz .The fluid inclusion data show that there was a continuous evobtion of the fluid from Nb-Ta granites and pegmatites to W-Sh hydrothermal vein. The coexistence of mett .vapour-rich fluid inclusions, and rare element crystaffites in topaz and quartz indicates that these minerals crystallized from a vapour-saturated mett enriched in Na.K,F and rare elements (Li,Be,Nb,Ta) .The evidence from fluid inclusion study shows that the possible genesis of the rare dement mineralization inLi-F granites of Yanshan period in Southern China results from magmatic differentiation .

Petrogenesis,Geodynamics and Radioactivity of the Granitic Rocks of the Nugrus Weakness Zone,South Eastern Desert,Egypt

The studied granitic bodies belong to the south Eastern Desert of Egypt.They extend in a NNW–SSE trend along the same strike of the Nugrus weakness zone by which they are structurally controlled.These rocks are composed of biotite and biotite-muscovite monzogranites to syenogranites.Geochemically,a higher abundance of Ba and Rb in biotite granites with a relatively low abundance in biotite-muscovite granites as well as the diversity of Th,U,Nb,Ta,Zr,and REE reflects their origin from different sources and geodynamic settings.The biotite granites are predominantly metaluminous to low peraluminous whereas the biotite-muscovite granites have a peraluminous nature.Potassium enrichment at the expense of calcium in these rocks reflects a derivation from crustal sources by partial melting in the presence of a volatile system.Radiometric investigation showed high abundances of U(up to 38 ppm)and Th(up to 26 ppm)in biotite-muscovite granites relative to biotite granites(up to 5 ppm U and 18 ppm Th).Radioactive anomalies furthermore have been recorded in parts of biotite-muscovite granites that were affected by the faults(up to 116 ppm eU and 97 ppm eTh).Consequently,biotite-muscovite granites form a potentially fertile source for uranium mineralization.

Experimental Studies on Partial Melting of Massive Samples of Granite

As a basis of modern petrology,the equilibrium relations describing the melting of granite were established mainly on melting experiments of Powder samples.Such experiments,however,have serious limitations in providing information about the variations in compositional and fabric features of the minerals and in the composition and distribution of the melt.Our experiments using massive samples indicate that melt occure mainly at the quartz-plagioclase and quartz-potash feldspar boundaries and the composition of the melt is dependent on local characteristics in the melting system,showing no correlation with the bulk composition of the rock samples.At lower temperatures(740-760℃,0.2GPa),the melt plots at or near the eutectic point in Q-Ab-Or-An-H2O diagram,indicating equilibrium melting.At higher temperatures(790-800℃，0.2GPa)the melt becomes lower in SiO2 and higher in Na2O,deviating makedly from the eutectic line but without disappearance of any mineral phase,suggesting a non-equilibrium process.It is obvious that the phase-equilibrium relations in natural massive granites may be greatly different from those deduced from powder experiments.

喜马拉雅造山带聂拉木地区渐新世深熔作用的厘定

喜马拉雅新生代淡色花岗岩记录了地壳深熔作用和花岗岩侵位的地球化学和构造物理效应。与形成于增厚地壳条件下和伸展背景下的始新世和中新世花岗岩相比,渐新世花岗岩分布比较局限,且源区和形成机制还存在着较大的争议。位于喜马拉雅造山带中部的聂拉木地区,可见32.1Ma的含电气石黑云母的花岗岩、29.8Ma的含黑云母的花岗岩、26.6Ma的含电气石黑云母的伟晶花岗岩侵入到高喜马拉雅岩系上部。这三组渐新世花岗岩具有以下特征:(1)较高的SiO_(2)、Al_(2)O_(3)、K_(2)O和Na_(2)O,A/CNK>1.0;(2)Ba、Nb、Ta、Sr和Ti的负异常;(3)略微富集轻稀土,亏损中稀土和重稀土,高度变化的Eu异常和微弱的负Nd异常;(4)均一的初始Sr-Nd同位素比值,^(87)Sr/^(86)Sr(t)=0.7463~0.7471,ε_(Nd)(t)=-15.0~-14.6。此外,含电气石黑云母的花岗岩和含电气石黑云母的伟晶花岗岩具有较高的Sr和Ba,较低的Rb/Sr比值,其Rb/Sr比值与Ba和Sr含量都无相关性,表明其为富B流体参与高喜马拉雅变沉积岩含水部分熔融作用的产物。而含黑云母的花岗岩具有较低的Sr和Ba,较高的Rb/Sr比值,且其Rb/Sr比值与Ba和Sr含量显示明显的负相关关系,表明其为变沉积岩发生脱水熔融作用的产物。综合喜马拉雅造山带已有的研究成果,得出以下认识:渐新世花岗岩的源区从下地壳基性物质转变为中地壳变泥质岩,展示了源区向上迁移的过程,并经历了一期重要的岩浆热液交代作用;渐新世深熔作用记录了造山带从缩短增厚向伸展垮塌转换阶段深部地壳的响应,从而促使了高喜马拉雅岩系的折返。

含氟流体助熔华南基底片麻岩的实验研究:对稀土成矿花岗岩成因的制约

为了明确含氟流体对花岗岩源区岩浆过程中稀土元素地球化学行为的影响,本文采用华南代表性的高稀土片麻岩和低稀土片麻岩作为初始物质,与~4%的流体(纯水、1.5 mol/L HF、1.0 mol/L NaF)在0.8 GPa、1000℃的条件下开展了流体助熔的部分熔融实验。实验结果表明,所有片麻岩的熔融程度达到40%以上,残余矿物组合主要为斜长石+石英+斜方辉石±单斜辉石+钛铁矿+磷灰石±黑云母。部分熔融产生的熔体的成分主要为花岗闪长质‒花岗质,总体具有高氟(0.11%~0.27%)、高水(0.38%~1.86%)和A2型花岗岩的特征;其中,高稀土片麻岩部分熔融形成的熔体为钾玄质和准铝质,而低稀土片麻岩熔融形成的熔体偏高钾钙碱性和强过铝质。在微量元素蛛网图上,两者均表现为富集K、Rb、Th、Ce、Sm、Y、Yb等元素,亏损Ba、Nb、Ta、Zr、Hf、Ti等元素;稀土元素配分曲线则表现为右倾、负Eu异常的特征。相对于原岩,含氟流体助熔会强化熔体中Si、K、Na、Rb、Sr、Ba、Th、U、LREE和F的富集,并增加熔体的La_(N)/Yb_(N)值。同时,实验也证实片麻岩部分熔融形成的熔体的稀土元素含量主要受原岩控制,高稀土片麻岩更易于熔出稀土元素初始富集的熔体;相对于原岩,各类流体助熔均会造成稀土元素在熔体中不同程度的富集,其中,含HF流体助熔最高可富集稀土46%~49%(近1.5倍富集)。我们因此认为在华南LREE型和HREE型成矿花岗岩形成过程中,含F流体发挥重要的作用。此外,本文也提出了一种新的A2型花岗岩形成机制,即含F流体助熔地壳基底岩石,这很好地解释了华南晚中生代大规模分布的与稀土、稀有金属及氟成矿相关的陆内A2型花岗岩的形成。

胶东金矿成矿物质来源:来自与金成矿有关地质单元金含量的约束

胶东是世界第三大金矿集区,金矿找矿和成矿理论研究不断取得新突破,但对矿床成因和成矿物质来源的认识尚存在较大分歧。为了科学合理地解释金矿床相对于各类围岩高达万倍的Au富集,通过系统采集胶东地区未遭受矿化蚀变的晚中生代花岗岩和早前寒武纪变质岩样品,对其进行了Au元素含量测试。结果表明:97件花岗岩Au含量平均值为0.31×10^(-9),其中玲珑型、郭家岭型和伟德山型花岗岩的Au含量平均值分别为0.25×10^(-9)、0.28×10^(-9)和0.35×10^(-9),397件早前寒武纪变质岩的Au含量平均值为1.05×10^(-9),总体与地壳中Au元素丰度和华北板块中Au含量平均值接近或偏低,但早前寒武纪变质岩中Au含量是晚中生代花岗岩中的3.39倍。结合前人研究结果认为,胶东地区不存在Au异常富集的源区或矿源岩(层),巨量金的成矿物质源自古老变质基底在晚中生代的部分熔融,在下地壳基底变质岩部分熔融形成花岗质岩浆的过程中,在超高温环境中约70%以上的金以类似“熔炼”的方式析出,并产生了贫金花岗岩。成矿前与岩浆活动相关的流体有利于Au元素的迁移和富集;成矿期及其后花岗岩的岩石地球化学成分发生了显著变化,影响了流体的化学平衡,为金的沉淀提供了有利条件。

U and Th Contents and Th/U Ratios of Zircon in Felsic and Mafic Magmatic Rocks:Improved Zircon-Melt Distribution Coefficients

High-precision data on U and Th contents and Th/U ratios of zircon obtained using secondary ion mass spectrometry analysis have been collected from the literature. Zircon in the granitic rocks has median values of 350 ppm U, 140 ppm Th, and Th/U=0.52; the recommended zircon-melt partition coefficients are 81 for Du and 8.2 for DTh. In zircon from mafic and intermediate rocks, the median values are 270 ppm U, 170 ppm Th, and Th/U=0.81, and the recommended zirconmelt partition coefficients are 169 for Du and 59 for DTh. The U and Th contents and Th/U ratios of magmatic zircon are low when zircon crystallizes in equilibrium with the melt. Increasing magma temperature should promote higher Th contents relative to U contents, resulting in higher Th/U ratios for zircon in mafic to intermediate rocks than in granitic rocks. However, when zircon crystallizes in disequilibrium with the melt, U and Th are more easily able to enter the zircon lattice, and their contents and Th/U ratios depend mainly on the degree of disequilibrium. The behavior of U and Th in magmatic zircon can be used as a geochemical indicator to determine the origins and crystallization environments of magmatic zircon.

Biocomposites Based on Thermoplastic Starch and Granite Sand Quarry Waste

Granite stone is a by-product of the rock crushing manufacturing.An industrial waste in powder form that causes health problems and environmental pollution.Fine particles fraction can be used as a partial replacement of sand in concrete manufacture.In this work,an alternative exploitation of this waste fraction is proposed.Granite sand(GS)with particles mean size of ~1μm was employed as thermoplastic starch(TPS)filler at different concentrations.Biocomposites were obtained by melt-mixing and thermo-compression,achieving translucent and easy to handle films.A good GS dispersion within the matrix was evidenced by SEM.Mineral presence induced a shift of starch’s melting point to higher values and a better thermal resistance.TPS UV absorption capacity was increased ~90% by GS addition.An increment in TPS Young’s modulus and maximum tensile stress of 5 and 3 times,respectively was observed by adding 5%w/w GS.

EXPERIMENTAL STUDY ON FUSION OF TIN-BEARING GRANITES IN GUANGXI,SOUTHERN CHINA

Experiments have been carried out for studying the melting characteristics of two representative types of granite complexes relating to tin ore deposits in Guangxi. The curves of the beginning melting of the Longxiangai porphyritic biotite granite (LPBG), the Longxiangai granular biotite granite (LGBG), the margin phase and central phase of the rocks of the Pinyin granite (MPPG and CPPG) are determined by the experiments. The results of the experiments show that the temperature of the beginning melting points of the tin -bearing granite not only depends on the type and features of the rocks, but also varies with the total water vapour pressure (PH2O) and the one of the different granites decrease with the increasing pressure. In different ranges of the pressure,the variance gradient of the beginning melting points sharply varies. When PH2O is less than or equal to 136 MPa, the beginning melting temperatures of LPBG somewhat lower than those of LGBG ;Whe P H2O is larger than 136MPa,The beginning temperatures of LPBG are higher than those of LGBG. The beginning teperatures of CPPG are always higher than those of MPFG at the conditions of PH2O from 75 to 250 MPa.

西藏冈底斯岩基羊八井地区古新世I型含石榴子石花岗岩的成因

高硅花岗岩(SiO_(2)>74%)是许多大型花岗岩岩基的重要组成部分,对理解弧岩浆作用过程中的地壳深熔作用和大陆地壳的演化过程具有重要意义。冈底斯岩基羊八井地区发育一套高硅I型含石榴子石花岗岩,结晶时代为古新世早期(锆石U-Pb年龄为64.9±0.3Ma和64.1±0.3Ma)。该套花岗岩具有以下特征:(1)属于高钾钙碱性系列,具有高SiO_(2)和K 2O,低MgO、MnO、CaO和P 2O 5,海鸥状REE分配模式,强烈的Eu负异常,富集K、Rb、Pb、Th和U,亏损Nb、Ti和P的特征,是高分异I型花岗岩;(2)发育岩浆型石榴子石,端元组分为铁铝榴石和锰铝榴石,富集HREE,亏损LREE,富集关键微量元素Sc、Y和Zn,归因于斜长石强烈的分离结晶作用;(3)熔体结构的改变和锆石的分离结晶导致了较低的Zr和Hf含量以及Zr/Hf比值;(4)锆石Hf同位素和全岩Nd同位素组成显示明显的富集特征(εHf(t)=-17.1~-11.7;εNd(t)=-9.0~-7.6)。结合区域研究成果,这套花岗岩的原始熔体来源于古老岩浆岩基底物质的部分熔融,之后经历了强烈的分离结晶作用,最终形成了I型含石榴子石花岗岩。

Songjianghe biotite monzonitic granite zircon U-Pb geochronology and geochemical significance

The authors studied geochronology and geochemical data of the Songjianghe biotite monzogranite in the southern Zhangguangcai Range in order to determine its formation age,magma source,and tectonic environment. The results indicate that the Songjianghe biotite monzogranite was formed in the Middle Jurassic with an age of 168. 2 ± 2. 0 Ma( MSWD = 0. 93). The monzogranite was characterized by high alkali and low Ca O and Mg O,belonging to high-potassium calc-alkaline,metaluminous I-type granite. The rock is enriched in large ion lithophile elements such as Rb,Ba,and K and strongly depleted high field strength elements such as P,Ti,Nb,and Ta. It is concluded that the Songjianghe biotite monzogranite was derived from partial melting of amphibolite facies metamorphism mafic lower-crust and its formation was controlled by the Pacific Plate subduction.

粤北下庄地区白水寨岩体的成因及其对铀成矿作用的意义

白水寨岩体是下庄花岗岩型铀矿田西北部竹筒尖特富型铀矿床的主要赋矿围岩之一,目前其成因及其与铀成矿作用之间的关系还不清楚,为此,文章对该岩体进行了年代学、全岩和矿物地球化学研究。白水寨岩体侵入于下庄大型岩基内,主要由细粒二云母花岗岩和白云母花岗岩构成,单颗粒锆石SHRIMP定年结果显示,两类花岗岩均形成于印支期,年龄分别为229.4 Ma和231.8 Ma;显示了高硅、富碱(Na_(2)O+K_(2)O)、低FeOt+MgO+TiO_(2)含量,低P_(2)O_(5)含量,Rb、Th和U等相对富集,Ba、Sr、P和Ti相对亏损,ACNK≥1.1,富铝矿物含量高等特征,属于强过铝质S型花岗岩。与下庄花岗岩相比,白水寨岩体的两类花岗岩中均富继承锆石,且具有更高的SiO_(2)、Rb/Sr和更低的(FeOt+MgO+TiO_(2))、Zr/Hf、P_(2)O_(5)和黑云母的Fe^(2+)/(Fe^(2+)+Mg)值,指示该岩体源自华南富还原组分的富长英质变泥质岩经低度部分熔融,而并不是源自富镁铁质变泥质岩的下庄花岗岩的母岩浆经分异演化的产物。此外,与二云母花岗岩相比,白水寨白云母花岗岩具有显著的稀土元素四分组效应,更低的稀土总量、Zr/Hf比值和Eu/Eu^(*)值,表明白云母花岗岩在形成的过程中存在富F的流体与岩浆相互作用。白水寨岩体的两类花岗岩均富铀,可成为区内形成热液型铀矿床的铀源岩,其中的白云母花岗岩更富铀,更有利于成为铀成矿作用的铀源岩。