The Northeast Kingdom batholith,Vermont: magmatic evolution and geochemical constraints on the origin of Acadian granitic rocks

Five Devonian plutons (West Charleston, Echo Pond, Nulhegan, Derby, and Willoughby) that constitute the Northeast Kingdom batholith in Vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution. The batholith consists of metaluminous quartz gabbro, diorite and quartz monzodiorite, peraluminous granodiorite and granite, and strongly peraluminous leucogranite. Contents of major elements vary systematically with increasingSiO<₂ (48 to 77 wt.%). The batholith has calc-alkaline features, for example a Peacock index of 57, and values for K<₂O/Na₂O (<1), K/Rb (60–350), Zr/Hf (30–50), Nb/Ta (2–22), Hf/Ta (up to 10), and Rb/Zr (<2) in the range of plutonic rocks found in continental magmatic ares. Wide diversity and high values of minor- and trace-element ratios, including Th/Ta (0.5–22), Th/Yb (0–27), Ba/La (0–80), etc., are attributed to intracrustal contributions. Chondrite-normalized REE patterns of metaluminous and relatively mafic intrusives have slightly negative slopes (La/Yb_cn<10) and negative Eu anomalies are small orabsent. The metaluminous to peraluminous inter-mediate plutons are relatively enriched in the light REE (La/Yb_cn>40) and have small negative Eu anomalies. The strongly peraluminous Willoughby leucogranite has unique trace-element abundances and ratios relative to the rest of the batholith, including low contents of Hf, Zr, Sr, and Ba, low values of K/Rb (80–164), Th/Ta (<9), Rb/Cs (7–40), K/Cs (0.1–0.5), Ce/Pb (0.5–4), high values of Rb/Sr (1–18) low to moderate REE contents and light-REE enriched patterns (with small negative Eu anomalies). Flat REE patterns (with large negative Eu anomalies) are found in a small, hydrothermally-altered area characterized by high abundances of Sn (up to 26 ppm), Rb (up to 670 ppm), Li (up to 310 ppm), Ta (up to 13.1 ppm), and U (up to 10 ppm). There is no single mixing trend, fractional crystallization assemblage, or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the Northeast Kingdom batholith. The plutons originated by mixing mantle-derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment. Hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks (<50% by mass), and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals.     

Petrogenesis of the Xihuashan Granite in Southern Jiangxi Province,South China: Constraints from Zircon U-Pb Geochronology,Geochemistry and Nd Isotopes

Mesozoic granitic intrusions are widely distributed in the Nanling region,South China.Yanshanian granites are closely connected with the formation of tungsten deposits.The Xihuashan granite is a typica...     

Mineralogy,geochemistry, and genesis of co-genetic granite-pegmatite-hosted rare metal and rare earth deposits of the Kawadgaon area,Bastar craton,Central India

Co-genetic pegmatites associated with the granite of the Kawadgaon area in the Bastar craton, Central India, contain a wide range of ore minerals of Nb, Ta, Be, Sn, Zr, Ti, and REE, including columbite-tantalite, ixiolite, pseudo-ixiolite, wodginite, tapiolite, microlite, fersmite, euxenite, aeschynite, beryl, cassiterite, monazite, xenotime, zircon, ilmenite, triplite, and magnetite. There is a distinct vertical zonation between the rare metal and tin pegmatites in apical parts of the host granite. Geochemically, these are LCT-S type, beryl-columbite-phosphate pegmatites that have notably high contents of SiO₂ (av. 73.80%), Rb (av. 381 ppm), and Nb (av. 132 ppm). The investigated granites probably were derived from the melting of older crustal rocks, as indicated by a high initial ⁸⁷Sr/⁸⁶Sr isotopic ratio, and the major-element geochemistry of the granites and pegmatites. Plots of mol. CaO/(MgO+FeO^t) vs. mol. Al₂O₃/(MgO+FeO^t) suggest that the source rock was pelitic metasediments. Based on the available data, it is postulated that the derivation of pegmatites from the parent granite occurred shortly after granite emplacement in the late Archaean-early Proterozoic (~2500 Ma). The K/Rb, Ba/Rb, and Rb/Sr ratios of the felsic bodies reveal that a substantial part of the granite formed from evolved melts, and further fractionation produced the co-genetic pegmatites and associated rare metal and rare earth deposits.     

Petrogenesis of peraluminous magmas from the Akum-Bamenda Massif,Pan-African Fold Belt,Cameroon

Peraluminous intrusives of the Akum-Bamenda Massif, Pan-African Belt, Central Cameroon, were synkinematically emplaced in a Pan-African sinistral strike-slip shear zone. The rock sequences consist of medium-grained leucogranites, fine-grained leucogranites, and orthogneisses of biotite granite composition; in aggregate, they cover a range from about 65 to 74 wt.% SiO₂, defining a continuous chemical evolutionary trend and displaying characteristics of the high-K and medium calc-alkaline series. Leucogranites are strongly peraluminous (A/CNK > 1.1) and plot in the field of S-type granites, whereas orthogneisses are metaluminous and plot in the field of I-type granitoids. Major and trace element compositions and the Rb/Sr isotopes of the leucogranites indicate crustal derivation by remelting of a composite metapelite?+?metagreywacke protolith similar to the metasedimentary rocks of the central domain of the Cameroon Pan-African North-Equatorial fold belt.     

藏南错那洞淡色花岗岩成因：来自全岩地球化学和锆石U-Pb年龄的约束

藏南错那洞穹隆位于喜马拉雅造山带东部,淡色花岗岩是其核部组成部分之一。对其中的弱定向二云母花岗岩和含石榴子石二云母花岗岩进行LA-ICP-MS锆石U-Pb定年,显示其结晶年龄分别为(20.6±0.3) Ma和(16.7±0.2) Ma,属于喜马拉雅中新世淡色花岗岩。错那洞含石榴子石二云母花岗岩和弱定向二云母花岗岩均具有富硅(w(SiO2)为71.6%~74.6%)、富铝(w(Al2O3)为14.5%~16.1%)、富钾(w(K2O)为4%~4.7%)及高铝饱和指数(A/CNK=1.16~1.22)的特征,属高钾钙碱性系列的强过铝质花岗岩,并且两类花岗岩都富集Rb、U、K、Pb,相对亏损Nb、Ta、Zr、Ti。但含石榴子石淡色花岗岩具有明显的Eu负异常(Eu/Eu*=0.29~0.46),而弱定向二云母花岗岩Eu的负异常相对较弱(Eu/Eu*=0.58~0.80)。弱定向二云母花岗岩的Rb/Sr值为2.4~3.5,Ba含量为(200~253)×10-6,TiO2含量相对较低,表明错那洞弱定向二云母花岗岩是在无水条件下由变泥质岩中的白云母脱水熔融而形成,并且弱定向二云母花岗岩的产生可能与藏南拆离系(STDS)启动造成的构造减压有关。含石榴子石二云母花岗岩的K/Rb、Zr/Hf、Nb/Ta、Y/Ho值呈现出非球粒陨石异常,稀土四分组效应和异常高的Rb/Sr值(18.6~22.2)表明错那洞含石榴子石二云母花岗岩是经过岩浆高度演化而形成的。高度演化的岩浆有利于W、Sn、Be等稀有金属成矿。错那洞含石榴子石二云母花岗岩与错那洞穹隆的W-Sn-Be矿具有相邻的空间位置,两者之间可能存在一定的成因联系;而错那洞弱定向二云母花岗岩与扎西康Pb-Zn矿床在时间上和空间上都具有一致性,两者之间很可能也存在一定的成因联系。     

Geochemistry and zircon geochronology of the Archean granite suites of the Rio Maria granite-greenstone terrane,Carajás Province,Brazil

The Archean granites exposed in the Mesorchean Rio Maria granite-greenstone terrane (RMGGT), southeastern Amazonian craton can be divided into three groups on the basis of petrographic and geochemical data. (1) Potassic leucogranites (Xinguara and Mata Surrão granites), composed dominantly of biotite monzogranites that have high SiO₂, K₂O, and Rb contents and show fractionated REE patterns with moderate to pronounced negative Eu anomalies. These granites share many features with the low-Ca granite group of the Yilgarn craton and CA2-type of Archean calc-alkaline granites. These granites result from the partial melting of rocks similar to the older TTG of the RMGGT. (2) Leucogranodiorite-granite group (Guarantã suite, Grotão granodiorite, and similar rocks), which is composed of Ba- and Sr-rich rocks which display fractionated REE patterns without significant Eu anomalies and show geochemical affinity with the high-Ca granite group or Transitional TTG of the Yilgarn craton and the CA1-type of Archean calc-alkaline granites. These rocks appear to have been originated from mixing between a Ba- and Sr-enriched granite magma and trondhjemitic liquids or alternatively product of interaction between fluids enriched in K, Sr, and Ba, derived from a metasomatized mantle with older TTG rocks. (3) Amphibole-biotite monzogranites (Rancho de Deus granite) associated with sanukitoid suites. These granites were probably generated by fractional crystallization and differentiation of sanukitoid magmas enriched in Ba and Sr.The emplacement of the granites of the RMGGT occurred during the Mesoarchean (2.87–2.86 Ga). They are approximately coeval with the sanukitoid suites (∼2.87 Ga) and post-dated the main timing of TTG suites formation (2.98–2.92 Ga). The crust of Rio Maria was probably still quite warm at the time when the granite magmas were produced. In these conditions, the underplating in the lower crust of large volumes of sanukitoid magmas may have also contributed with heat inducing the partial melting of crustal protoliths and opening the possibility of complex interactions between different kinds of magmas.     

Late Triassic U-bearing and barren granites in the Miao'ershan batholith,South China: Petrogenetic discrimination and exploration significance

The Miao'ershan uranium ore district is one of the most important granite-hosted uranium producers in South China. There are several Triassic granite plutons in the Miao'ershan batholith, but uranium ore deposits mainly occur within the Douzhashan granitic body. Precise zircon U–Pb dating indicated that these Triassic granite plutons were emplaced during 204 to 215 Ma. The Douzhashan U-bearing granite lies in the central part of the Miao'ershan batholith, and has higher U contents (8.0 to 26.1 ppm, average 17.0 ppm) than the nearby Xiangcaoping granite (5.0 to 9.3 ppm, average 7.0 ppm) and the Yangqiaoling granite (6.4 to 18.3 ppm, average 11.5 ppm) in the south part of the batholith. The Douzhashan granite is composed of medium-grained two-mica granite, whereas the Xiangcaoping and Yangqiaoling granites are composed of porphyritic biotite granite. Both the Xiangcaoping and Douzhashan granites have high A/CNK ratios (> 1.10), high (⁸⁷Sr/⁸⁶Sr)_i ratios (> 0.720) and low ε_Nd(t) values (− 11.3 to − 10.4), suggesting that they belong to strongly peraluminous S-type granites. The Douzhashan granite has low CaO/Na₂O ratios, high Rb/Sr and Rb/Ba ratios, indicating a partial melting origin of clay-rich pelitic rocks. In contrast, the Xiangcaoping granite formed from clay-poor psammite-derived melt. The Yangqiaoling granite shows different geochemical characteristics with the Douzhashan and Xiangcaoping granites, indicating a different magma source. The Yangqiaoling granite has higher ε_Nd(t) of − 9.4 to − 8.3 and variable A/CNK values from 0.98 to 1.19, suggesting a mixture source of meta-sedimentary rocks and meta-igneous rocks. Crystallization fractionation is not the main mechanism for U enrichment in the Douzhashan granite. We suggest that U-rich pelitic rock sources may be the key factor to generate peraluminous U-bearing granites in South China. Searching for those granites which are reduced, strongly peraluminous and were derived from U-rich pelitic rocks, is the most effective way for exploring granite-hosted U deposits.     

Petrology and geochemistry of Jura granite and granite gneiss in the Neelum Valley,Lesser Himalayas (Kashmir,Pakistan)

Late Proterozoic rocks of Tanol Formation in the Lesser Himalayas of Neelum Valley area are largely green schist to amphibolite facies rocks intruded by early Cambrian Jura granite gneiss and Jura granite representing Pan-African orogeny event in the area. These rocks are further intruded by pegmatites of acidic composition, aplites, and dolerite dykes. Based on field observations, texture, and petrographic character, three different categories of granite gneiss (i.e., highly porphyritic, coarse-grained two micas granite gneiss, medium-grained two micas granite gneiss, and leucocratic tourmaline-bearing muscovite granite gneiss), and granites (i.e., highly porphyritic coarse-grained two micas granite, medium-grained two micas granite, and leucocratic tourmaline-bearing coarse-grained muscovite granite) were classified. Thin section studies show that granite gneiss and granite are formed due to fractional crystallization, as revealed by zoning in plagioclase. The Al saturation index indicates that granite gneiss and granite are strongly peraluminous and S-type. Geochemical analysis shows that all granite gneisses are magnesian except one which is ferroan whereas all granites are ferroan except one which is magnesian. The CaO/Na₂O ratio (>0.3) indicates that granitic melt of Jura granite gneiss and granite is pelite-psammite derived peraluminous granitic melt formed due to partial melting of Tanol Formation. The rare earth element (REE) patterns of the Jura granite and Jura granite gneiss indicate that granitic magma of Jura granite and Jura granite gneiss is formed due to partial melting of rocks that are similar in composition to that of upper continental crust.     

The Zr/Hf ratio as a fractionation indicator of rare-metal granites

The Zr-Hf geochemical indicator, i.e., the Zr/Hf ratio (in wt %) in granitic rocks is proposed to be used as the most reliable indicator of the fractionation and ore potential of rare-metal granites. It was empirically determined that the fractional crystallization of granitic magma according to the scheme granodiorite → biotite granite → leucogranite → Li-F granite is associated with a decrease in the Zr/Hf ratio of the granites. The reason for this is the stronger affinity of Hf than Zr to granitic melt. This was confirmed by experiments on Zr and Hf distribution between granitic melt and crystals of Hf-bearing zircon (T = 800°C, P= 1 kbar). The application of the Zr/Hf indicator was tested at three classic territories of rare-metal granites: eastern Transbaikalia, central Kazakhstan, and the Erzgebirge in the Czech Republic and Germany. The reference Kukul’bei complex of rare-metal granites in eastern Transbaikalia (J₃) is characterized by a uniquely high degree of fractionation of the parental granitic melt, with the granites and their vein derivatives forming three intrusive phases. The biotite granites of phase 1 are barren, the leucogranites of phase 2 are accompanied by greisen Sn-W mineral deposits (Spokoininskoe and others), and the final dome-shaped stocks of amazonite Li-F granites of phase 3 host (in their upper parts) Ta deposits of the “apogranite” type: Orlovka, Etyka, and Achikan. The Kukul’bei Complex includes also dikes of ongonites, elvanes, amazonite granites, and miarolitic pegmatites. All granitic rocks of the complex are roughly coeval and have an age of 142±0.6 Ma. The Zr/Hf ratio of the rocks systematically decreases from intrusive phase 1 (40–25) to phases 2 (20–30) and 3 (10–2). Compared to other granite series, the granites of the Kukul’bei Complex are enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but are depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From earlier to later intrusive phases, the rocks become progressively more strongly enriched or depleted in these elements, and their Zr/Hf ratio systematically decreases from 40 to 2. This ratio serves as a reliable indicator of genetic links, degree of fractionation, and rare-metal potential of granites. Greisen Sn, W, Mo, and Be deposits are expected to accompany granites with Zr/Hf < 25, whereas granites related to Ta deposits should have Zr/Hf < 5.     

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。     

Chronology,geochemistry and Sr–Nd isotope studies of Jurassic intrusions in the Diyanqinamu porphyry Mo mine,central Inner Mongolia,China

Available cores of porphyritic granite and aplitic granite from the Diyanqinamu porphyry Mo deposit in the north central Great Xing’an Range presented an opportunity to examine and analyze Mesozoic igneous rocks far from the Paleo-Pacific subduction zone. The Diyanqinamu granites are highly fractionated I-type, distinguished from the M-, A- or S-type granite by: high SiO₂, and Rb; low Zr, Nb, Y, and Ce; low Fe₂O₃^total/MgO and (K₂O + Na₂O)/CaO ratios; low alumina saturation index (<1.1); low initial I_Sr ratios (0.70137–0.70451); positive εNd(t) values (2.37–3.77); and negative correlation between P₂O₅ and SiO₂. The aplitic granites were generated by fractional crystallization of the porphyritic granite, as evidenced by: spatial proximity; consistent zircon U–Pb ages (156 Ma) within error; correlations between other oxides and SiO₂ in Haker diagrams; low Ba, Sr, Nb, P, Ti, Eu; linear relationship in both (La/Yb)_N vs. La and Sr vs. Ba diagrams; and, decreasing LREE and ∑REE with increasing SiO₂. The Diyanqinamu granites have young depleted-mantle two-stage model ages (avg. T_DM2 = 660 Ma) similar to those of most Mesozoic voluminous felsic magmas in northeastern China, and were likely sourced from pre-existent crustal components both “old” and juvenile that had been juxtaposed during the tectonic evolution of the Paleo-Asian Ocean. These granites project in the transitional field from syn-collision to post-collision tectonic settings on tectonic discrimination diagrams, implying emplacement in an extensional environment. Extensional volcanism and basin formation in the Great Xing’an Range region in Late Jurassic is coeval with the Diyanqinamu granites, demonstrating that post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean was the main driving force for Late Jurassic magmatism in this region.     

Origin and evolution of topaz-bearing granites from the Nanling Range, South China: a geochemical and Sr–Nd–Hf isotopic study

Summary The F-rich Hongshan pluton in the eastern Nanling Range, southern China, is a topaz-bearing albite leucogranite. It is distinctive from other topaz-bearing felsic rocks in South China with respect to age, size, geochemical evolution and topaz mode and morphology. The Hongshan granites are highly peraluminous and characterized by high K₂O/Na₂O, Si, Rb, Cs, Nb, Ta and F, and low Ca, Ba, Sr, Zr, Hf, P, K/Rb, Zr/Hf and Eu/Eu^*. The granites show significant trace-element variations with magma evolution, with increasing Rb, Cs, Nb, Ta, Sn, W and decreasing Sr, Ba, Zr, Hf, Y, REE, Pb, Th, K/Rb, Zr/Hf, Th/U and Eu/Eu^*. These changes dominantly reflect fractional crystallization of plagioclase, biotite and accessory minerals such as zircon and monazite. The granites also exhibit a decrease in ɛNd(t = 225 Ma) from −7.9 to −11.7 with magma evolution. Modeling shows that the Nd isotopic variation could result from assimilation of the Taoxi Group wall rocks during fractional crystallization. The Hongshan pluton also shows spatial geochemical variations; the most evolved parts are located in the southeastern part of the pluton, which would be the most likely target area for rare-metal mineralization commonly associated with other topaz-bearing granites. Zircon grains from two rock types in the Hongshan body were analyzed in situ for U–Pb ages and Hf isotopic values. The concordant zircon grains mostly range from 218 to 230 Ma with an average of 224.6 ± 2.3 Ma (Indosinian). Some zircons with different internal structures and Hf isotope compositions, as well as monazite fragments, yield U–Pb ages of ca. 280 to 240 Ma, suggesting older thermal events in the studied area. The ɛHf(t) of these older zircons is strongly negative (−12.3), implying a crustal source with a Paleoproterozoic model age, similar to that for the Proterozoic Zhoutan Group. The main (∼225 Ma) zircon population exhibits less negative ɛHf(t) (−3.0 to −7.6) and Mesoproterozoic model ages, suggesting that the original magma of the Hongshan granite was generated from deeper Mesoproterozoic crust.     

Geochronological evidence and tectonic significance of Carboniferous magmatism in the southwest Trabzon area,eastern Pontides,Turkey

The northern and southern zones of the eastern Pontides (northeast Turkey) contain numerous plutons of varying ages and compositions. Geochemical and isotopic results on two Hercynian granitoid bodies located in the northern zone of the eastern Pontides allow a proper reconstruction of their origin for the first time. The intrusive rocks comprise four distinct bodies, two of which we investigated in detail. Based on LA–ICP–MS U–Pb zircon dating, the Derinoba and Kayadibi granites have similar ²⁰⁶Pb/²³⁸U versus ²⁰⁷Pb/²³⁵U Concordia ages of 311.1 ± 2.0 and 317.2 ± 3.5 million years for the former and 303.8 ± 1.5 million years for the latter. Aluminium saturation index values of both granites are between 0.95 and 1.35, indicating dominant peraluminous melt compositions. Both intrusions have high SiO₂ (74–77 wt.%) contents and show high-K calc-alkaline and I- to S-type characteristics. Primitive mantle-normalized element diagrams display enrichment in K, Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti. Chondrite-normalized rare earth element patterns are characterized by concave-upward shapes and pronounced negative Eu anomalies with La_cn/Yb_cn?=?4.6–9.7 and Eu_cn/Eu*?=?0.11–0.59 (Derinoba), and La_cn/Yb_cn?=?2.7–5.5 and Eu_cn/Eu*?=?0.31–0.37 (Kayadibi). These features imply crystal-melt fractionation of plagioclase and K-feldspar without significant involvement of garnet. The Derinoba samples have initial ?Nd values between –6.1 and –7.1 with Nd model ages and T _DM between 1.56 and 2.15 thousand million years. The Kayadibi samples show higher initial ?Nd_(I) values, –4.5 to –6.2, with Nd model ages between 1.50 and 1.72 thousand million years. This study demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios were lowered in some samples by hydrothermal interaction or alteration. Isotopic and petrological data suggest that both granites were produced by the partial melting of early Palaeozoic lower crustal rocks, with minor contribution from the mantle. Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.     

阿尔金造山带南缘中―晚奥陶世正长花岗岩的发现及其地质意义

出露于阿尔金造山带帕夏拉依档沟一带的正长花岗岩,LA-ICP-MS锆石U-Pb测年结果显示其形成年龄为455.1±3.6Ma,属中―晚奥陶世。地球化学结果显示,主量元素具有富硅、富铝、富钾,低钛、贫钙、贫镁的特点,为强过铝质花岗岩系列,具高钾钙碱性特征。稀土元素总量较高,轻稀土元素富集、重稀土元素亏损,稀土元素球粒陨石标准化配分曲线有右倾型特征和明显的负Eu异常,与典型壳源花岗岩配分曲线一致。Ba、Sr、Ti等具负异常,Rb、Th、K等大离子亲石元素具正异常,显示S型花岗岩特征。结合原岩判别图解,推断其源区物质主要来源于上地壳变泥质沉积岩类。结合区域资料,认为正长花岗岩形成于挤压体制向拉张体制转换的构造环境,属后碰撞花岗岩类,表明在中―晚奥陶世阿中地块和柴达木地块已由挤压碰撞阶段转为伸展后碰撞阶段。     

Geochemistry of granulite‐facies granitic rocks from Battye Glacier,northern Prince Charles Mountains,East Antarctica

Proterozoic basement outcrops in the vicinity of Battye Glacier, northern Prince Charles Mountains, are dominated by granulites and gneisses derived from felsic (granitoid) intrusive igneous rocks, and by pegmatites. Felsic orthopyroxene granulites, garnet leucogneisses and garnet pegmatites have major and trace element compositions of highly felsic, but not strongly fractionated, granites. The garnet leucogneisses and garnet pegmatites have S‐type characteristics, whereas the felsic granulites are probably I‐type, although their high Zr+Nb+Y+Ce abundances suggest possible A‐type affinities. Intermediate orthopyroxene ± clinopyroxene granulites mostly resemble I‐type quartz diorites, except for a small subgroup of samples (characterised by low Na₂O and K₂O, and high MgO, Ni, Cr and HREE) of uncertain affinities and significance. Element ratios involving LILE (e.g. K/Rb, Rb/Ba, Rb/Sr, K/La, La/Th) closely match those typical of the inferred granitoid protoliths, suggesting that these rocks have experienced relatively little LILE depletion (except possibly for U) during regional metamorphism. It is therefore inferred that metamorphism was probably broadly isochemical. Because the felsic and intermediate granulites and garnet leucogneisses are Sr‐depleted, Y‐undepleted and mostly have negative Eu anomalies they are inferred to be the products of partial melting of felsic crustal sources leaving plagioclase‐bearing residua. Plagioclase fractionation during crystallisation could also account for these characteristics, but K/Rb, Rb/Ba and Rb/Sr ratios in these rocks are not consistent with strong fractionation of feldspar. Garnet pegmatites differ chemically from garnet leucogneisses mainly in their lower Fe, Ti, Nb, Zn, Zr, Th and REE abundances and positive Eu anomalies, related to lower garnet, ilmenite and zircon contents in the garnet pegmatites. A genetic link between these two rock types, probably involving fractionation of these minerals during partial melting or crystallisation, is inferred. Incompatible‐element abundances suggest that generation of the Battye Glacier granitic magmas from felsic crust might have occurred in a mature continental magmatic arc possibly well removed from an active subduction trench or, perhaps, in an intracontinental setting.     

北祁连龙王山晚志留世花岗岩LA-ICP-MS锆石U-Pb测年及其地球化学特征

通过对龙王山灰白色细粒石英闪长岩和灰白色细粒二长花岗岩样品进行LA-ICP-MS锆石U-Pb测年结果属于晚志留世侵入岩。岩石地球化学特征表明,为高钾过铝质-准铝质碱钙性岩;稀土元素Eu具有弱负异常特征;微量元素中Ta、Nb、gr、Sr、Ti、P相对贫化,Rb、Th、Hf、Ba、Sc、K、Ce、Nd、Sm含量相对富集。Rb／Sr平均值为0．30,介于上地幔值与地壳值之间,反映出壳幔源的特点,为s型花岗岩。综合分析该期花岗岩是弧陆碰撞向陆陆碰撞转化阶段构造背景下形成的同碰撞花岗岩。     

Post-orogenic,Carboniferous granite-hosted Sn–W mineralization in the Sierras Pampeanas Orogen,Northwestern Argentina

The Sierras Pampeanas orogen, in northwestern Argentina, hosts significant Sn–W mineralization in a variety of mostly epizonal granite stocks emplaced in variably metamorphosed country rocks. The San Blas, Huaco and El Durazno granite stocks in the Sierra de Velasco, the La Quebrada granite in the Sierra de Mazán, the Cerro Colorado granite in the Cerro Negro, and the Los Mudaderos and Sauce Guacho granite stocks in the Sierra de Ancasti, are largely peraluminous (ASI between 1.05 and 1.38) and represent S-type granites, are strongly fractionated (i.e., high Rb–Sr ratio), have a low oxidation state (low Fe₂O₃/Fe₂O₃ ratio) and are geotectonically linked to syncollisional magmatism. The U–Pb SHRIMP analyses on zircons from the Cerro Colorado and La Quebrada granites, located in the Cerro Negro and Sierra de Mazán, respectively, revealed ages from Lower Ordovician (Tremadocian) to Carboniferous. All granites display elevated LREE values, low HREE values and negative Eu anomalies. With regards to total REE values, two groups of granite stocks can be recognized. The granites with lower REE contents are highly evolved granites and are related to Sn–W mineralization. The mineralized granites display higher values of Sn, W and Rb, and lower values of Sr and Ba compared to barren granites. These trace element characteristics appear to be diagnostic for Sn–W mineralized granite stocks in the western Sierras Pampeanas. The western Sierras Pampeanas contains locally geochemically evolved Carboniferous granites, which are interpreted to be the main control of significant Sn–W mineralization. The Carboniferous age of western Sierras Pampeanas Sn–W mineralization sets it apart from the Triassic age of the Sn–W mineralization in the Eastern Tin belt of Bolivia.     

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.     

Can trace element distributions in migmatites be used as analogues in understanding petrogenesis of anatectic granites

Trace element concentrations in leucosomes of migmatites in the Black Hills, South Dakota, USA, were examined to determine if their compositions are analogous to those of pelite-derived granites. Melanosomes in the migmatites are dominated by biotite, sillimanite, and quartz. Leucosomes have constant Si/Al that corresponds to a peraluminous granite; however, they have variable proportions of (sil+qtz)/alkali feldspar that are attributed to instability of feldspar relative to sillimanite due to high a_HF in partial melts. There are strong positive correlations of Sr, Ba, Rb, and Cs concentrations with the proportion of feldspar in the leucosomes. The average concentrations of Sr and Ba are higher and of Rb and Cs lower in the leucosomes than in pelite-derived leucogranites. A reaction progress method is used to demonstrate that partitioning of these trace elements between melanosomes and leucosomes represent mineral-mineral equilibrium rather than residue-melt equilibrium. This implies that leucosomes in migmatites may crystallize while maintaining equilibrium with melanosomes and the resulting trace element compositions may not be analogous to those of partial melts.     

The Early Proterozoic Primorskii complex of rapakivi granites (western Cisbaikalia): geochemistry,crystallization conditions,and ore potential

The Primorskii complex in western Cisbaikalia, which formed in the Early Proterozoic at the postcollisional stage in the Siberian craton evolution, comprises rapakivi granites, equigranular biotitic and leucocratic granites, and alaskites. It is a K-rich granitoid assemblage with a medium and high alkalinity, whose F, Ba, Pb, REE, Zr, Th, and Zn contents exceed the clarkes. The complex consists of three plutons: Bugul’deika–Anga, Ulan-Khan, and Trekhgolovyi, which formed in two intrusive stages. The evolution of the main-stage composition was marked by an increase in silica content, with a similtaneous increase in agpaite and Fe contents and a decrease in Na₂O/K₂O. The Bugul’deika–Anga and Trekhgolovyi plutons are the most contrasting in composition and crystallization conditions. The former originated from a weakly differentiated water-undersaturated melt, which crystallized at medium depths (P_tot = 3–4 kbar). The crystallization was unaccompanied by considerable accumulation of granitophile elements (the concentration index (CI) of granitophile elements is ~3) in the leucogranites, except the alaskites, which crystallized in the upper part of the magma chamber (CI = 5). The Trekhgolovyi pluton originated from a leucogranitic melt enriched in Cs, Li, Rb, and Sn, which crystallized at a low P_tot (~2 kbar). The average contents of some elements in the leucogranites are higher than their clarkes in Ca-poor granites: by a factor of 4 for Sn, 3.8 for Th, 2.7 for Rb, 2.5 for Cs, and 2 for F (CI ≈ 9). The final-stage granites in the Trekhgolovyi pluton are associated with quartz-muscovitic (±topaz, fluorite) greisens, which contain cassiterite, columbite, ilmenorutile, wolframite, bismuthinite, and other minerals. The data suggest that the Trekhgolovyi pluton has a Sn potential.