Geology,geochemistry and petrogenesis of late Precambrian granitoids in the Central Hijaz Region of the Arabian Shield

Late Precambrian granitoid rocks occurring within a 44,000 km² area of the western Arabian Shield are subdivided on the basis of geology and petrology into older (820 to 715 Ma) and younger (686 to 517 Ma) assemblages. The older assemblage contains major complexes which can be assigned to either one of a granodioritic or trondhjemitic petrologic association. The earliest granitoid rocks are trondhjemitic tonalites (trondhjemite association), depleted in Ba, Ce, F, La, Li, Nb, Rb, Y and Zr compared to granitoids of the slightly younger granodiorite association, which are related to a calcic, calc-alkaline suite of rocks ranging in composition from gabbro through monzogranite. The plutonic rocks of the older assemblage were probably emplaced in the cores of contemporary island arcs.The younger plutonic assemblage is dominated by three, geochemically distinct, coeval granitic associations: the alkali granite, alkali-feldspar granite and monzogranite associations. The alkali granite association is composed of perthite granites (alkali granites and genetically related alkali-feldspar granites). Rocks of this association are marginally peralkaline or metaluminous and are characterized by low contents of Ba, Co, Li, Rb, Sc and Sr, and high contents of Be, Cu, F, REE, Nb, Sn, Y, Zn and Zr. The alkali-feldspar granite association is mainly composed of alkali-feldspar granites and syenogranites. Rocks of this association are marginally peraluminous or metaluminous and contain low Ba, Sr, and high F, Rb, Sn, Th and U. The monzogranite association consists mainly of monzogranites and granodiorites. Rocks of this association are peraluminous or marginally metaluminous and have the highest contents of Ba, Cu, Co, Li, Sc, Sr, Ta, and V, and the lowest contents of REE, Nb, Rb, Sn, Th, U, Y, Zn and Zr of the three granitic associations.These voluminous granitic magmas, together with the felsic component of a coeval sequence of bimodal volcanic rocks, are partial melts of the earlier island arc terrain produce during a prolonged fusion event. Subsolvus, highca granites of the monzogranite association have I-type features and represent partial melts of previously unfused crust, while low-Ca perthite granites of the alkali granite and alkali-feldspar granite associations have A-type features and represent partial melts of previously fused crust.This type of petrogenetic model can account for much of the petrologic diversity of the Pan-African granitic terrain of the Arabian Shield.     

千里山花岗岩体地质地球化学及与成矿关系

千里山花岗岩由似斑状黑云母花岗岩、等粒黑云母花岗岩和花岗斑岩组成。前两期岩体分别与两期钨多金属矿化有关，后一期与铅锌银成矿密切相联。两套花岗岩虽然均来自地壳，但取于不同源地。该岩体既为富Ｆ、Ｌｉ，Ｒｂ，Ｂｅ，Ｇａ的ＢＥＬＩＦ花岗岩，又是富Ｕ，Ｔｈ的高热花岗岩。     

Trace element constraints on pegmatite genesis: Tin Mountain pegmatite,Black Hills,South Dakota

The Tin Mountain pegmatite is a small, zoned granitic body that is extremely enriched in Rb and Li, but has moderate concentrations of Sr and Ba. These trace elements are modelled using granitic distribution coefficients in order to test the potentials of partial melting of metasedimentary rocks and fractionation of a less-evolved granitic melt to have produced the parental liquid to the Tin Mountain pegmatite. Batch melting of any reasonable metasedimentary source rock would likely have yielded melts that were either insufficiently enriched in Rb and Li to be the parental liquid, or that had Sr and Ba concentrations that were much higher than those estimated for the parental liquid. The modelling of simple fractional crystallization and equilibrium crystallization of a granitic melt within the compositional range of the spatially associated Harney Peak Granite gives calculated melt compositions with either lower Sr and Ba concentrations or inadequate Rb and Li enrichments, to be the parent liquid of the pegmatite. At least two variants from simple crystal-liquid fractionation models can, however, successfully account for the derivation of the parent liquid: 1) generation of a Rb-, Li-, Ba- and Sr-rich granitic melt (outside of the compositional range of the sampled portions of the Harney Peak Granite complex) by low degrees of partial melting of metasedimentary rocks found in the Black Hills, followed by moderate extents of fractional or equilibrium crystallization, 2) derivation from Harney Peak granite via a complex, multi-stage crystal-liquid fractionation process, such as progressive equilibrium crystallization.     

Metallogeny and Mineralization Potential of the Bazman Granitoids,SE Iran

The Mesozoic Bazman granitoids are located in Sistan and Baluchestan province, southeastern Iran. Geology of the study area consists of Carboniferous shale, sandstone, and limestone and Permian siltstone, shale, sandstone, limestone, and dolomite that were intruded by the Bazman granitoids. These granitoids include various phases of granite, granodiorite, quartz‐monzodiorite, monzodiorite, diorite, and gabbro. They are metaluminous to slightly peraluminous, reduced, calc‐alkaline and I‐type, and display geochemical characteristics of continental margin (ensialic) granitoids. In this paper, field, petrography, and geochemical data were used to discriminate the Bazman granitoids either as productive or barren granitoids. Although there are a few skarn‐related mineral occurrences adjacent to the Bazman granitoids, most exposed intrusions are not hydrothermally altered and mineralized. Rb/Sr, Zr/Hf, and K/Rb ratios indicate that the granitic magmas that formed most of the Bazman granitoids indicate that they are moderately evolved and have generally not undergone post‐magmatic hydrothermal activity. The Sm/Eu and Rb/Ba ratios and the concentrations of Rb, Ba, and Sr within the aforementioned granitoids show that the rocks are similar to the averages of granitoids devoid of Li, Be, U, Sn, W, and Ta deposits. The I‐type arc characteristics and other geochemical features of the Bazman granitoids show that they are not typical of parental magmas to Sn, W, Mo, and Zn mineralization, but are mainly fertile for Cu and Fe (Au) skarn‐related granitoids.     

河南栾川南部地区与Mo—W矿床有关的燕山期花岗岩特征

河南栾川南部分布着一系列与钼钨矿化有关的燕山期花岗岩小岩体。根据这些岩体的含矿性、地质及地球化学特征可将其分为三类。第一类岩体往往与大型一超大型Ｍｏ－Ｗ矿床有关，岩体顶部有纹层状石英层，石英辉钼矿脉发育。岩石中ＳｉＯ２、Ｋ２Ｏ、Ｒｂ含量高，Ｋ２Ｏ／Ｎａ２Ｏ、Ｒｂ／Ｓｒ比值高，Ａｌ２Ｏ３、ＦｅＯ、ＣａＯ、Ｎａ２Ｏ、Ｓｒ含量低。第二类岩体往往与中小型Ｍｏ－Ｗ矿床有关，岩体中含辉钼矿石英脉发育较差，岩石中ＳｉＯ２、Ｋ２Ｏ含量中等，Ｋ２Ｏ／Ｎａ２Ｏ比值中等。第三类岩体不含Ｍｏ－Ｗ矿，岩体中各种脉体不发育，岩石中ＳｉＯ２、Ｋ２Ｏ、Ｒｂ含量低，Ｋ２Ｏ／Ｎａ２Ｏ、Ｒｂ／Ｓｒ比值相对较低，Ａｌ２Ｏ３、Ｎａ２Ｏ、Ｓｒ含量相对较高。研究还表明小岩体的分异演化程度与小岩体的合矿性有密切的内在联系。     

黄土高原南部全新世黄土-古土壤 序列若干元素分布特征及意义*

选择黄土高原南部的XJN,XMC和JYC全新世剖面为研究对象。通过对地层中Ca,Ba,Rb和Sr元素分布的研究,发现Ba/Sr和Rb/Sr比值在不同地层中含量差异十分明显,并与成土作用强度显著正相关,可作为良好的气候替代指标;表生环境中Rb和Ba较稳定,Sr和Ca元素十分活跃,易于迁移,其中Ca的迁移能力高于Sr元素;从XJN→XMC→JYC剖面,Rb和Ba元素含量增加,而Sr和Ca元素含量降低,这与区域环境差异有关;全新世中期暖湿的亚热带气候主要出现关中盆地地区,六盘山以西则是暖温带气候。     

华南地区中生代Cu (Mo) W Sn矿床成矿作用与洋岭/转换断层俯冲

华南地区是我国重要的金属矿产资源产地,除了发育大量的钨锡钼铋和稀土等金属矿产外,还有铜金矿床分布。本文通过对华南地区29个典型CuMoWSn矿床的时空分布及其与之有关的花岗质岩体的侵位年龄分析,探讨了与不同成矿类型有关的花岗质岩石的地球化学特征。本文认为华南地区10个典型的与Cu有关的矿床主要发生在180~170Ma、160~150Ma以及105~90Ma三个时期,而10个钨矿床主要集中于170~130Ma;4个WSn矿床集中于170~130Ma和120~110Ma;而5个Sn矿床则发育于170~150Ma、130~110Ma以及100~90Ma三个时期。Cu矿床主要与同熔型花岗岩有关,而Mo、WSn既与同熔型花岗岩有关,又与改造型花岗岩有关。在岩石地球化学上,与Cu(Mo)WSn成矿作用有关的花岗质岩石也表现出不同的地球化学特点,如,从Cu(Mo)矿床到WSn矿床SiO2含量有逐渐增大、氧化性逐渐降低、还原性逐渐增加以及分异演化程度有逐渐增高的趋势。与Cu(Mo)Au矿床有关的花岗质岩石具有较低的SiO2（60.3%~68.1%）,氧化性较高（Fe2O3/FeO=0.31~1.81）,分异演化程度较低（Rb/Sr=0.05~3.3）的特点;与Cu(Pb)(Zn)矿床有关的花岗质岩石具有相对较高的SiO2（73.3%~75.2%）,氧化性稍高（Fe2O3/FeO=0.68~1.74）,分异程度稍低（Rb/Sr=10.8~57.8）的特点;而与Mo矿床有关的花岗质岩石具有较宽的SiO2（67.3%~76.2%）变化范围,氧化性稍低（Fe2O3/FeO=0.68~1.74）,分异演化程度稍低（Rb/Sr=0.6~9.29）;与W矿有关的花岗质岩石的SiO2含量为69.9%~80.1%,还原性稍低（Fe2O3/FeO=0.19~0.76）,分异演化程度稍高（Rb/Sr=21.9~61.7）;与WSn矿床有关的SiO2为74.8%~78.7%,还原性较低（Fe2O3/FeO=0.08~0.59）,分异程度较高（Rb/Sr=10.8~139）;与Sn矿床有关的花岗质岩石的SiO2为64.8%~76.9%,还原性高（Fe2O3/FeO=0.01~0.58）,分异演化程度高（Rb/Sr=1~530）。在结合华南地区花岗岩类岩石的分布特征以及盆岭构造的特点,本文提出华南地区CuMoWSn矿床的成矿作用是不同时期大洋板块或者洋岭多阶段俯冲结果的新成因模型,即早侏罗世休眠的FarallonIzanagi洋岭俯冲导致早—中侏罗世Cu成矿作用;中—晚侏罗世活动的FarallonIzanagi洋岭和转换断层俯冲是中晚侏罗世Cu(Mo)(W)成矿作用以及多阶段WSn成矿作用的触发动力,而白垩纪Izanagi大洋板块俯冲则是白垩纪斑岩型CuWSn成矿作用的诱因。该模型的提出较好地解释了华南中生代大规模岩石圈拆沉—减薄—伸展的机制及其大规模成矿作用的动力。     

华北板块北缘东段中三叠世构造演化——来自辽宁法库地区侵入岩的证据

本文对华北板块北缘东段辽宁北部法库地区中三叠世风歧堡岩体和靠陵沟岩体进行了岩相学、锆石U-Pb年代学、地球化学及Lu-Hf同位素研究。LA-ICP-MS锆石U-Pb测年结果显示,风歧堡岩体和靠陵沟岩体加权平均年龄分别为（241±1） Ma和（243±1） Ma,侵位时代为中三叠世。风歧堡岩体的Ba和Sr质量分数分别为（290.00×10^-6~484.00×10^-6）和（129.00×10^-6~338.00×10^-6）,Sr/Y值为13.27~28.17,Sr/Yb值为117.50~250.28;靠陵沟岩体具有较高的Ba质量分数（899.00×10^-6~1 300.00×10^-6）和Sr质量分数（772.00×10^-6~997.00×10^-6）,以及较高的Sr/Y值（67.47~78.21）和Sr/Yb值（661.81~781.32）,Y、Rb和Yb质量分数较低,分别为11.00×10^-6~14.70×10^-6、55.80×10^-6~78.40×10^-6、1.17×10^-6~1.39×10^-6,地球化学特征上具有高Ba-Sr花岗岩的特征。此外,凤歧堡岩体样品富集大离子亲石元素Rb和K,亏损高场强元素Nb、P、Ti和大离子亲石元素Ba;靠陵沟岩体样品富集大离子亲石元素Ba、K、Sr,亏损高场强元素Nb、P、Ti。凤歧堡和靠陵沟岩体样品Nb/Ta值（4.18~10.26）和Zr/Hf值（30.39~38.76）与地壳平均值相近,Ni、Co和Cr质量分数较低;岩石地球化学特征表明法库地区中三叠世花岗质岩浆源岩为壳源岩石。中三叠世—晚三叠世早期,华北板块北缘东段处于造山地壳加厚阶段。研究区中三叠世花岗岩的ε_Hf（t）值均为正值,亏损地幔二阶段模式年龄（T_DM2）为949~555 Ma,结合岩石地球化学特征,中三叠世花岗质岩浆源岩为造山地壳加厚过程中新元古代新生下地壳部分熔融的产物。     

和龙百里坪银、多金属矿化集中区白垩纪岩浆岩地球化学特征与成矿

百里坪银、多金属矿化集中区白垩纪岩浆岩主要有花岗质与闪长质两个岩石系列。前者为富钾质钙碱性岩石,后者为富钠质碱钙性岩石,二者具有不同的变异曲线特征;花岗质岩石Co/N i值平均为2.644,闪长质岩石平均为0.498;花岗质岩石R b/S r值平均为0.223,闪长质岩石平均为0.020;在R b、S r、B a演化趋势上,花岗质岩石趋向富集R b,闪长质岩石趋向富集S r、B a,二者明显不同;两个岩系代表性岩石在稀土含量、稀土比值以及稀土模式上都不相同。两者的成矿专属性为:花岗质岩石对A g、Cu、P b、Zn矿化有利,闪长质岩石对A g、A u矿化有利。     

The geochemistry of Precambrian granulite facies rocks from the Lewisian complex of Tiree,Inner Hebrides,Scotland

The metamorphism and geochemistry of the major components of a small area of granulite facies rock are described and discussed, and a chemical model for the evolution of anomalous trace element distributions in such materials is suggested. The local complex was subjected to medium to high pressure granulite facies metamorphism between 2,900 and 2,600 m.y. All the analysed granulite facies rocks from Tiree; acid to intermediate gneisses, basic metamorphic rocks, and granitic rocks, have anomalous chemistries, being depleted in K, Rb, Nb, Y and Th, and have high K/Rb, Ba/Rb and Ca/Y ratios, and very low K/Ba and Rb/Sr ratios relative to normal portions of the upper continental crust. The gneisses seem to have been enriched in Ba and Sr.The chemical features of the rocks are considered to reflect their stable mineral assemblages in the granulite facies, and to be representative of deep-level crustal materials. The geochemical peculiarities of the complex may have been largely controlled by an upward intergranular diffusion, or “degassing” caused by high-grade metamorphism. It is suggested that such diffusion may have been active at the crust/upper mantle interface, some diffused material of mantle origin accounting for certain chemical oddities typical of Lewisian and some other Precambrian granulite facies rocks.     

Metasomatism of a depleted granulite facies terrain in the Arunta Block,central Australia

Geochemical investigations in the Utralanama Block, an intermediate pressure granulite facies terrain in the Arunta Block, central Australia, has revealed several anomalous features, not consistent with the depletion of granitophile components generally considered to accompany granulite facies metamorphism. However, other geochemical features are indicative of depletion. The mean K₂O for the Utralanama Block is exceptionally low relative to most other granulite facies terrains, but Rb contents are comparatively high. Consequently, the mean K/Rb ratio is relatively low for granulite facies terrains as is the mean Ba/Rb ratio, whilst mean K/Sr and Rb/Sr ratios are much higher than usual for such terrains. Only the K/Ba ratio shows equivalent values to depleted terrains elsewhere.Comparison of these ratios for the three main compositional groups of rocks in the Utralanama Block reveals that for mafic rocks all the above ratios are characteristic of extreme depletion, whereas, for all but the K/Ba ratio, mean ratios for the pelitic rocks, and to a lesser extent for the quartzofeldspathic rocks approach normal crustal values or values for metasomatic rocks. The abnormally high Rb/Sr ratios of these rocks compared to average crustal rocks suggest, however, that metasomatism is the cause of the anomalous geochemical features of the Utralanama Block, and this is supported by field and microstructural evidence. Thus, Rb/Sr ratios appear to be useful indicators of metasomatism where no gross mineralogical or microstructural evidence for metasomatism is obvious, and under such conditions the K/Ba ratio may be more reliable than the K/Rb ratio for indicating prior depletion of the terrain.     

Fractionnement des éléments en trace Li,Rb, Ba,Sr dans les séries andésitiques et shoshonitiques du Pérou. Comparaison avec d'autres zones orogéniques

In the calc-alkaline rocks of Peru, the rubidium content and the K/Ba, Rb/Sr ratios increase, while the strontium content and the K/Rb, Ba/Rb ratios decrease according to the distance of the trench. It is suggested that theses variations are related to a fractionation of plagioclase and contamination with differential migration of mobile elements. A comparative study between andesites of various localities shows in Peru an enrichment in Rb, Sr and Ba and a disparition of the Rb-Ba correlation; this last observation looks characteristic of continental margin andesites. The shoshonitic rocks differ from the andesites by a high content of Sr and Ba. The genetic relationships between these two kinds of rocks are discussed. It appears that the shoshonites are originated from a different magmatic source.     

K,Rb, Sr,Ba, U and Th geochemistry of the Lapland Granulites (Fennoscandia). LILE fractionation controlling factors

The LILE geochemical patterns of the three main lithological units (graywacke-shale metasedimentary sequence, tholeiitic metaigneous rocks and migmatitic rocks) of the Lapland Granulite belt are described. K, Ba, Sr and Th concentrations in metasediments are nearly similar to average continental crust, whereas Rb and U are unevenly impoverished. In particular graphitic metashales and calcsilicate rocks are not significantly depleted in uranium. Tholeiitic metaigneous rocks comprises metavolcanics which present K/Rb ratios similar to metasediments, and metaplutonics with LILE abundances close to those of the low-K-tholeiites. Migmatites show wide range in LILE content. Metatexites and diatexites have higher K, Rb, Th and U concentrations and similar K/Rb ratios with respect to equivalent unmobilized rocks. Potassic pegmatoïds are strongly enriched K, Rb, Ba and Th but moderately in Sr and U. Plagioclasic pegmatoids and ferromagnesian restites are rich in Sr and poor in other LIL elements.A comparative review of the LILE geochemistry between Lapland granulites and equivalent lithological units taken from non metamorphosed to high grade terrains suggest that fractionation processes are not systematic but controlled by original lithology and mineralogy, mineral — fluid equilibria during progressive (or retrogressive) metamorphism and mineral-melt-fluid equilibria during anatexis. Moreover, statistical analysis on K-Rb distribution patterns in these various rock types shows that there is no metamorphic trend characteristic of granulite facies terrains as previously suggested.Large Ion Lithophile Elements     

挥发份对高硅岩浆演化趋势的制约:以东南沿海白垩纪晚期花岗岩类岩石为例SCIEI北大核心CSCD

东南沿海分布大面积的白垩纪晚期侵入岩。这些岩石可分为两期:其中115~100Ma以钙碱性系列岩石为主,岩石组合为辉长岩-闪长岩-花岗闪长岩-二长花岗岩-碱性长石花岗岩;而100~86Ma的岩石为碱性系列,岩石组合为石英二长斑岩-正长斑岩-碱性长石花岗岩。115~100Ma的辉长岩以角闪辉长岩为主,具有极高的CaO、MgO和Al_(2)O_(3)含量,具有极低的SiO_(2)(42.9%~53.8%)、全碱(K_(2)O+Na_(2)O:0.86%~5.28%)、Ba、Nb、Th、Rb和Zr含量,也具有极低的FeO^(T)/MgO、La/Yb和Zr/Hf比值,较高的Eu/Eu^(*)、Sr/Y比值和Sr含量,为基性-超基性堆晶岩。与辉长岩同期的闪长岩和细粒暗色包体具有较高的SiO_(2)(50.34%~63.68%),较低的CaO、P_(2)O_(5)、MgO、Al_(2)O_(3)含量,相对低的Eu/Eu^(*)和Sr/Y比值,变化较大的La/Yb和Zr/Hf比值,代表了从基性岩浆储库中抽取的富硅熔体。115~100Ma的花岗闪长岩和二长花岗岩类岩石为准铝质岩石,SiO_(2)含量变化较大(61.7%~75.3%),具有较低的FeO^(T)/MgO、Ga/Al比值和Nb、Zr及Nb+Zr+Ce+Y元素含量,显示出典型I型花岗岩的特征。这些花岗岩具有相对高的La/Yb、Eu/Eu^(*)和Zr/Hf比值和高的Sr、Ba和Zr含量。结合岩相学特征,这些花岗岩为堆晶花岗岩。而115~100Ma的碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),低的Eu/Eu^(*)、La/Yb、Zr/Hf和Sr/Y比值,具有低的Ba、Sr和Zr含量和高的Rb、Nb、Y和Th含量和Rb/Sr比值,表明这些花岗岩是由富硅岩浆储库中抽离的高硅熔体侵入地壳形成。100~86Ma期间形成的二长斑岩和正长斑岩具有极高的全碱含量,可以达到8%~12%,其SiO_(2)主要集中在60%~70%,具有极高的Zr、Sr和Ba含量和Eu/Eu^(*)、La/Yb和Sr/Y比值,显示出堆晶花岗岩的特征。而100~86Ma期间形成的大部分碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),并显示出A型花岗岩的特征,具有高的Rb/Sr比值和高的Rb、Y和Th和低的Ba、Sr含量和低的Zr/Hf、La/Yb、Eu/Eu^(*)和Sr/Y比值,表明它们是由富硅岩浆储库抽离的高硅熔体侵入浅部地壳形成。东南沿海高硅花岗岩的形成和穿地壳岩浆系统密切相关,高硅花岗岩是由浅部地壳内晶体-熔体分异产生的熔体侵入地壳所形成,而高硅花岗岩的地球化学特征与岩浆储库的水及挥发份含量密切相关。115~100Ma期间,从富水的岩浆储库抽离的熔体形成具有低高场强元素含量和低Rb/Sr比值的高硅花岗岩,这一过程与古太平洋板块俯冲有关;100~86Ma期间,从富挥发份的岩浆储库抽离的熔体形成碱性特征、富含高场强元素和具有高的Rb/Sr比值的高硅花岗岩,这一过程和古太平洋板块回撤软流圈上涌有关。     

Fertility of Rare-Metal Peraluminous Granites and Formation Conditions of Tungsten Deposits

The tungsten distribution in rocks of the Kukulbei Complex in eastern Transbaikal region results in a high potential of rare-metal peraluminous granites (RPG) for W mineralization and displays a different behavior of W in Li–F and “standard” RPG. These subtypes differ in the behavior of W in melt, spatial localization of mineralization, and the timing of wolframite crystallization relative to the age of the parental granitic rocks. The significant of W concentration is assumed to be due to fractionation of the Li–F melt; however, wolframite mineralization in Li–F enriched granite is not typical in nature. The results of experiments and our calculations of W solubility in granitic melt show that wolframite hardly ever crystallizes directly from melt; it likely migrates in the fluid phase and is then removes from the magma chamber to the host rocks, where secondary concentration takes place in exocontact greisens and quartz–cassiterite–wolframite veins. At the same time, the isotopic age of accessory wolframite (139.5 ± 2.1 Ma) within the Orlovka massif of Li–F granite is close to the formation age of the massif (140.6 ± 2.9 Ma). A different W behavior is recorded in the RPG subtype with a low lithium and fluorine concentration, exemplified by the Spokoininsky massif. There is no significant W gain in the melt. All varieties of wolframite mineralization in the Spokoininsky massif are derived from greisens, veins, and pegmatoids yielding the same crystallization ages (139.5 ± 1.1 Ma), which are 0.9–1.8 Ma later (taking into account the mean-square weighted deviation) than the Spokoininsky granite formation (144.5 ± 1.4 Ma). Perhaps this period corresponds to the time of transition from the magmatic stage to hydrothermal alteration. Comparison of the isotope characteristics (Rb–Sr and Sm–Nd isotope systems) of rocks and the associated ore minerals (wolframite, cassiterite) from all examined deposits shows a depletion in ε_Nd values for ore minerals relative to the rock and the opposite behavior for the intial Sr isotope ratios. This may indicate the specific nature of ore matter, where the effect of the juvenile component is definitely expressed. Our geochronological results show that tantalum and tungsten mineralization took place within a narrow age interval, almost synchronously with the crystallization of associated granites. The coeval development of peraluminous magmatism enriched in lithophile rare elements and volatiles with ore complexes located in different structural settings and separated by a considerable distance from each other (up to 500 km) suggests a regional and deep-seated magma source. Rifting and increased thermal flux from the mantle, manifestations of which have been recorded during this period in the territory, may be a deep-seated process.     

A post-collisional magmatic plumbing system: Mesozoic granitoid plutons from the Dabieshan high-pressure and ultrahigh-pressure metamorphic zone, east-central China

Three groups of Mesozoic shoshonitic or high-K calc-alkaline intrusive rocks are identified in Dabieshan high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic zone, east-central China and they are related to: (I) slab breakoff; (II) magmatic underplating; and (III) doming. Group-I, the slab breakoff-type, consists of late Triassic (210 Ma) mafic monzodiorites. It has moderate to high Sr, and low Rb and Ba abundances, and moderate light rare earth element (LREE)/heavy rare earth element (HREE) and K/Rb ratios. Group-II, the underplating-type, consists mainly of middle Jurassic–early Cretaceous (160–120 Ma) hornblende quartz monzonitic, biotite monzogranitic, and syenogranitic plutons, characterized by relatively high LREE/HREE and K/Rb ratios, and by a large range in concentration of Sr and Ba, coupled with much smaller range in Rb. Group-III, the doming-type, is represented by Cretaceous (125–95 Ma) granitic stocks and granitic porphyry. Compared with group-II, it has high Rb, Y and HREE abundances, low Sr and Ba abundances and low LREE/HREE and K/Rb ratios. All groups have similar Nd and Sr isotopic compositions. Among the three groups, post-collisional granitoid magmatism (group-II) with ages of 160 to 120 Ma, post-dating the HP and UHP metamorphism at 245 to 220 Ma, is the most abundant in the Dabieshan area. The post-collisional granitoid plutons were initially emplaced at different levels ranging from mid-crust to near-surface. This study shows that the whole-rock chemistry of the granitoids vary systematically with crystallization pressures. For example, K₂O, normative Or, Rb and Zr show the strongest increase with decreasing pressure, whereas Ba, Nb, Nd, Yb, MnO, and normative An decrease upward in the Dabie Block. It is suggested that ascent of differentiated, buoyant liquids, combined with fractionation paired with assimilation (AFC), is responsible for the vertical variation. Geological, geochemical and petrological data indicate that group-I could have been generated by partial melting of enriched subcontinental lithosphere mantle due to slab breakoff. Group-II rocks could have been produced mainly from crustal assimilation/melting and fractional crystallization of mantle-derived magmas, whereas group-III magma could have derived from anatexis of the Dabie complex and was highly evolved in a hot doming setting. The late Triassic-early Jurassic slab breakoff may be responsible for the exhumation of UHP rocks through the mantle. The voluminous granitic emplacement together with an episode of rapid denudation suggests that magmatic underplating and inflation could have played a role in the Middle Jurassic–Early Cretaceous rapid exhumation of Dabieshan.     

钨的地球化学性质与华南地区钨矿成因

在地球演化早期的强还原条件下,钨表现为中等亲铁元素,因此地球中 90%的钨进入地核。在地幔和地壳的演化过程中,钨是极度不相容亲石元素,从而导致钨元素在地壳中的丰度约是地幔丰度的250倍。钨在岩浆熔体中主要以钨酸的形式迁移,在成矿热液中主要以氟、硼化合物或其络合物的形式运移。钨的矿化需要其在部分熔融、岩浆演化和晚期热液等各阶段逐渐富集。中国是世界上钨矿产资源最丰富的国家,约占世界总储量的60%以上,其中绝大多数矿床产在华南地区,与华南大规模的中生代岩浆活动具有密切的时空联系。微量元素特征(高Rb/Sr和K/Rb比值,低Nb/Ta和Zr/Hf比值)显示它们往往经历了强烈的岩浆分异,这可能与这些花岗岩通常具有高挥发分含量(如F)有关。岩浆中高的F含量对钨的富集和矿化十分重要,它可以降低熔体固相线、粘度和密度,有利于提高岩浆的结晶分异程度,因而使得高度不相容的钨元素在岩浆演化过程和后期热液阶段的富集与矿化。富挥发分岩浆的形成可能与俯冲板块后撤,软流圈物质上涌导致的多硅白云母等富F矿物的高温分解有关。研究表明,华南南岭地区侏罗纪的钨矿化花岗岩主要形成于太平洋板块的俯冲后撤,而华南南部晚白垩世钨成矿作用与新特提斯洋的俯冲后撤有关。     

Distribution and petrogenetic behaviour of trace elements in granitic pegmatite quartz from South Norway

The present study documents that the trace-element distribution in granitic quartz is highly sensitive to CAFC processes in granitic melts. Igneous quartz efficiently records both the origin and the evolution of the granitic pegmatites. Aluminium, P, Li, Ti, Ge and Na in that order of abundance, comprises >95% of the trace elements. Most samples feature >1 ppm of any of these elements. The remnant 5% includes K, Fe, Be, B, Ba and Sr whereas the other elements are present at concentrations lower than the detection limit. Potassium, Fe, Be and Ti are relatively compatible hence obtain the highest concentrations in early formed quartz. Phosphorous, Ge, Li and Al are relatively incompatible and generally obtain the highest concentrations in quartz that formed at lower temperatures from more evolved granitic melts. The Ge/Ti, the Ge/Be, the P/Ge and the P/Be ratios of quartz are strongly sensitive to the origin and evolution of the granitic melts and similarly the Rb/Sr and the Rb/K ratios of K-feldspars may be utilised in petrogenetic interpretations. However, the quartz trace element ratios are better at distinguishing similarities and differences in the origin and evolution of granitic melts. After evaluating the different trace element ratios, the Ge/Ti ratio appears to be most robust during subsolidus processes in the igneous systems, hence probably should be the preferred ratio for analysing and understanding petrogenetic processes in granitic igneous rocks.Editorial responsibility: J. Hoefs     

苏鲁地体南缘超高压变质带朐山二云花岗片麻岩的地球化学特征及其构造意义

二云花岗片麻岩是组成苏鲁地体南缘超高压变质带朐山杂岩体的重要岩石类型,虽然经历了超高压变质作用,但仍保留了花岗岩的岩石学特征。常量元素和微量元素分析结果表明该片麻岩具有高w(K₂O)、低w(CaO)、高w(TFeO)/w(MgO)比值、铝饱和指数偏高的A型花岗岩的特征,岩石类型为高钾碱性过铝质A型花岗岩。稀土元素中轻稀土富集、分馏程度高、Eu强烈亏损,微量元素中Ba、P、Ti、Sc具有明显的负异常,w(Sr)/ w(Y)、w(La)/ w(Yb)和w(Rb)/ w(Sr)、w(Rb)/ w(Ba)较高,尤其是w(TiO₂)＜0.2％和w(Y)/ w(Nb)＞1.2的特征,以及在w(Rb)-w(Yb+Ta）和w(Rb)-w(Y+Nb）判别图解上样品投点位于板内环境区等,表明该片麻岩的原岩形成于板内与裂谷有关的非造山环境。锆石SHRIMP U-Pb测年结果揭示其侵位时代为新元古代中晚期((722±32）Ma）,与杂岩体中早期侵位的二长花岗片麻岩及杂岩体上覆地层中的变质火山岩同为Rodinia大陆裂解、扬子地块陆内裂谷形成过程中伴随的岩浆活动的产物。     

湘东邓阜仙花岗岩成因及对成矿的制约:锆石/锡石U-Pb年代学、锆石Hf-O同位素及全岩地球化学特征

南岭地区晚三叠世成矿规模较小且零散,而晚侏罗世成矿规模巨大,以往的研究较少关注两期花岗岩之间的成因联系及与成矿的关系。湘东邓阜仙花岗岩体位于南岭地区中段,是具有晚三叠世、晚侏罗世两期岩浆活动的复式岩体,并发育有钨矿床。本文对区内花岗岩及蚀变岩型矿体进行了锆石/锡石U-Pb定年、锆石Hf-O同位素与全岩主微量分析,以期揭示两期花岗岩的地球化学特征、成因联系和与成矿的关系。锆石SIMS U-Pb定年结果表明,区内花岗岩的成岩年龄分别为~228Ma和~153Ma。湘东钨矿的锡石U-Pb定年结果为154.4±2.1Ma,表明钨锡矿化形成于晚侏罗世。两期花岗岩均具有高硅、高钾、弱过铝质至强过铝质的特征,结合锆石的Hf-O同位素组成,指示它们具有相似的成因,均起源于中-古元古代基底地壳物质的部分熔融,晚三叠世花岗岩混入了更多的成熟地壳物质,区域的富矿地层对于湘东钨矿形成的直接影响不大。邓阜仙晚侏罗世花岗岩更高的Fe含量和Rb/Sr、Rb/Ba比值,更显著的Eu、Ce负异常,指示其经历了更高程度的分异演化,两期成岩过程中的差异可能与区域上的晚侏罗世发生的太平洋俯冲作用相关。