Behaviour of rare-earth elements in highly evolved granitic systems: Evidence from Proterozoic molybdenite mineralized aplites and associated granites in northern Sweden

Field relations, mineralogy, major- and trace-element contents (including REE analyses of whole-rock samples and minerals) of three Proterozoic granites and their associated molybdenite mineralized aplites have been studied at Allebuoda, Munka and Kåtaberget in northern Sweden. The granites crystallized from melts that were not saturated with water. The mineralized potassic aplites formed by quenching of residual melts caused by sudden pressure drop, H₂O saturation and vapour escape during tectonic rupturing. Leucogranites with higher Na₂O/K₂O ratios from Allebuoda and Munka crystallized during H₂O-saturated equilibrium conditions in which the exsolved vapour could continuously migrate away. The pressure was probably 3 kbar at Munka, and somewhat lower at Allebuoda.

The granites have REE patterns characterized by LREE enrichments and negative Eu anomalies. In comparison, the potassic aplites and the more sodic leucogranites are depleted in LREE, enriched in HREE and have larger negative Eu anomalies. Allanite and monazite are the most important REE carriers in the granites. These minerals are strongly enriched in LREE, whereas fluorite and xenotime, which are more abundant in the aplites, are most enriched in HREE. Due to the strong control of accessory minerals on the REE balance, REE are of limited use in petrogenetic modelling of highly evolved granitic systems.     

Petrogenetic significance of rare-earth element behavior in the basement rocks of southern Obudu Plateau, Bamenda Massif, southeastern Nigeria

Rock samples representing various igneous and metamorphic rocks of southern Obudu Plateau were analyzed for rare-earth element ( REE ) behavior by ICP-MS. Results of the analyses indicate a range of REE abundances and distinctive patterns from highly fraetionated patterns with negative Eu anomalies in granitic rocks to relatively low abundances and less REE fractionated flat patterns with little Eu anomaly in some paragneisses, schists, enderbites and dolerites to unfractionated patterns with positive Eu anomalies in some paragneisses and charnockites. Over all, there are low to high ∑ REE contents with negative to positive Eu anomalies. The ratios of different parameters, especially La/Yb and Ce/Yb, show behaviors consistent with crustal to mantle derivation. The heterogeneity of REE abundances and REE patterns reflects mantle to crustal petrogenetic variations of different rock suites on the Plateau. The LREE content is higher than the HREE content in the highly differentiated rocks, as evidenced by their La/Yb,Ce/Yb and La/Sm ratios, which are normally higher in residual products than in primary melts. The dominantly intermediate nature of the source rock of the orthogneisses is suggested by the generally low ∑ REE. The granites enriched in LREE and depleted in HREE and some of the charnockites with negative Eu anomalies were probably formed by partial melting and crystallization.     

Evolution of Pan African A- and I-Type Granites from Southeastern Egypt: Inferences from Geology,Geochemistry, and Mineralization

Field study of granitic rocks in the Gebel Abu Brush-Dahis (ABD) area, Southeastern Desert, Egypt, shows that they comprise two granitic groups, namely A- and I-type suites. The A type is distinguished mineralogically by abundant orthoclase and sodic plagioclase, ferrohornblende, monazite, and allanite. In contrast, the I type has more hornblende and biotite, which are more magnesian in composition, and less feldspar. The parental magmas of both suites have many similar geochemical characteristics, although the A type has slightly higher alkalis, Zr, Hf, Zn, and LREE, and lower CaO, MgO, Sr, Ni, and Fe⁺². The geochemical properties characteristic of leucocratic A-type granites-such as high Ga/Al ratios, Nb, Y, HREE, and F contents-are only manifest in the more felsic members of the A-type suite. These features were produced by 70% fractional crystallization of feldspar, hornblende, quartz, and biotite. Geotectonically, the study revealed that the A-and I-type granites are typical of an arc setting, but the more felsic members of the A-type suite plot in a within-plate regime. Geochemically, the granites are subalkaline and peraluminous to metaluminous. The granodiorites/adamellites (I-type suite) have fractionated LREE and slightly fractionated or nearly flat HREE, with small or no Eu anomalies. The alkali-feldspar granites (A-type suite) have flat REE with large Eu anomalies, except for one sample, which shows increasing LREE and decreasing HREE with large Eu anomalies; the quartz-monzonites have fractionated LREE and nearly flat HREE with no Eu anomaly. The flat HREE and/or HREE enrichment is attributed to involvement of garnet and/or zircon in melt generation at the source.

The uranium and thorium contents in the granitic rocks are present in the accessory minerals—particulary in monazite, titanite, zircon, allanite, fluorite, apatite, and opaques. Anomalous high radioactivity in the bostonite (alkaline) dike as well as uranium mineralization are largely confined to contacts and fracture zones. Uranophane is the characteristic uranium mineral in the oxidation zone. An XRD study of the high anomalies in pegmatite and bostonite reveals that the uranium mineralizations produced uranophane (Usilicate), thorianite, soddyite, zippeite, and becquerelite.     

Sources of stream sediments in the granulite terrain of the Walawe Ganga Basin,Sri Lanka,indicated by rare earth element geochemistry

Thirty-eight samples of stream sediments draining high-grade metamorphic rocks in the Walawe Ganga (river) Basin, Sri Lanka, were analysed for their REE contents, together with samples of metamorphic suites from the source region. The metamorphic rocks are enriched in light REE (LREE) compared to heavy REE (HREE) and are characterised by high La/Lu ratios and negative Eu anomalies. The chondrite-normalised patterns for these granulite-grade rocks are similar to that of the average post-Archaean upper crust, but they are slightly enriched with La and Ce. The REE contents of the <63-μm fraction of the stream sediments are similar to the probable source rocks, but the other grain size fractions show more enriched patterns. The <63-μm stream sediments fraction contains lower total REE, more pronouncd negative Eu anomalies, higher Eu_N/Sm_N and lower La _N/Lu_N ratios relative to other fractions. The lower La _N/Lu_N ratio is related to the depletion of heavy minerals in the <63-μm fraction. The 63–125-μm and 125–177-μm grain size fractions of sediments are particularly enriched in LREE (average ΣLREE=2990 μg/g and 3410 μg/g, respectively). The total HREE contents are surprisingly uniform in all size fractions. However, the REE contents in the Walawe Ganga sediments are not comparable with those of the granulite-grade rocks from the source region of the sediments. The enrichment of REE is accounted for by the presence of REE containing accessory mineral phases such as zircon, monazite, apatite and garnet. These minerals are derived from an unknown source, presumably from scattered bodies of granitic pegmatites.     

Formation,evolution of the granitic complex and its contribution to mineralization in Dongqiyishan deposit,Inner Mongolia: Chronological and geochemical evidencesSCIEI北大核心CSCD

内蒙古东七一山钨多金属矿位于北山造山带东段,是一个以钨为主,共伴生锡、钼、铷、铍、铌、钽、铁和萤石的综合型矿床。本次工作对含矿花岗质杂岩开展了岩石学、地球化学、锆石U-Pb及辉钼矿Re-Os年代学研究。富W-Sn-Mo花岗岩岩性为细粒似斑状二长花岗岩、中细粒似斑状二长花岗岩、花岗斑岩,结晶年龄分别为220.6±1.6Ma、220.4±1.3Ma和220.0±1.1Ma。富Rb-Be-Nb-Ta花岗岩岩性为中粗粒钠长石化似斑状二长花岗岩,结晶年龄为219.9±1.9Ma。辉钼矿Re-Os定年获得加权平均年龄为211±1Ma(MSWD=0.83),说明成岩成矿发生在晚三叠世。含矿花岗质杂岩均具有高硅、富碱、贫铁镁钙特征,为高钾钙碱性花岗岩。其中,富W-Sn-Mo花岗岩为准铝质-过铝质花岗岩;而富Rb-Be-Nb-Ta花岗岩为强过铝质花岗岩。杂岩体轻重稀土具一定分馏,呈现显著的负Eu异常,均富集Rb、K、U、Ta,强烈亏损Ba、Nb、Sr、P、Ti、Zr、Hf。与富W-Sn-Mo花岗岩相比,富Rb-Be-Nb-Ta花岗岩具更低的稀土总量,更显著的Eu负异常,并显示微弱的稀土四分组效应,更高的Li、Ta含量,更低的P、Ti、Zr、Hf、W、Mo、Bi含量。时空关系和地球化学特征表明,杂岩体为同一次岩浆活动不同演化阶段的产物,均经历了较高程度的结晶分异和较强的熔体-流体相互作用。相比而言,富Rb-Be-Nb-Ta花岗岩比富W-Sn-Mo花岗岩结晶分异程度更高,熔体-流体作用更强,花岗质岩浆的高程度分离结晶和熔体-流体相互作用是形成该杂岩体并促使成矿的重要控制因素。     

Petrological and geochemical characteristics of Zhaibei granites in Nanling region,Southeast China: Implications for REE mineralization

Mineralization with ion adsorption rare earth elements (REEs) in the weathering profile of granitoid rocks from Nanling region of Southeast China is an important REE resource, especially for heavy REE (HREE) and Y. However, the Jurassic granites in Zhaibei which host the ion adsorption light REE (LREE) ores are rare. It is of peraluminous and high K calc-alkaline composition, which has similar geochemical features of high K₂O + Na₂O and Zr + Nb + Ce + Y contents and Ga/Al ratio to A-type granite. Based on the chemical discrimination criteria of Eby [Geology 20 (1992) 641], the Zhaibei granite belongs to A1-type and has similar source to ocean island basalts. The rock is enriched in LREE and contains abundant REE minerals including LREE-phosphates and halides. Minor LREE was also determined in the feldspar and biotite, which shows negligible and negative Eu anomalies, respectively. This indicates that the Zhaibei granite was generated by extreme differentiation of basaltic parent magmas. In contrast, granites associated with ion adsorption HREE ores contain amounts of HREE minerals, and show similar geochemical characteristics with fractionated felsic granites. Note that most Jurassic granitoids in the Nanling region contain no REE minerals and cannot produce REE mineralization. They belong to unfractionated M-, I- and S-type granites. Therefore, accumulation of REE in the weathering profile is controlled by primary REE mineral compositions in the granitoids. Intense fractional crystallization plays a role on REE enrichment in the Nanling granitoid rocks.     

Hydrothermal Redistribution of Rare—Earth Elements in Pingxiang Dacite,Guangxi

Distribution of the rare-earth elements (REE) in dacite has been studied so as to get a better understanding of the migration behavior of REE during alteration. Both unaltered and altered samples were collected in an unpolluted area of Guangxi Zhuang Autonomous Region, southwest China. The REE concentrations were analyzed by ICP-MS. It is concluded that the REE were enriched during dacite alteration in varying degrees. The chondrite-normalized REE patterns of altered samples approximately maintain the characteristics of unaltered samples. However, if we normalize the REE concentrations of altered samples with unaltered dacite, fractionation of REE will appear. The LREE are more enriched than HREE in all altered samples with the LREE possibly precipitated as carbonate minerals. Both positive and negative Eu anomalies exist. Enrichment, immobility and depletion are noticed for the element Lu. Heavy mineral alteration, difference in stability constant between carbonate LREE and HREE complexes, downward migration of weathering fluid and microenvironment change may be responsible for the fractionation of REE in the altered dacite.     

REE Geochemical Characteristics of Apatite,Sphene and Zircon from Alkaline Rocks

The accessory minerals apatite and sphene are the main carriers of REE in alkaline rocks.Their chondrite-normalized REE patterns decline sharply to the right as those of the host rocks,In the patterns an obvious negative Eu anomaly and a positive Ce anomaly can be seen in apatite and sphene,respectively.Zircon from alkaline rocks is different in REE pattern,I,e,. a nearly symmetric“V“-shaped pattern with a maximum negative Eu anomaly.Compared with the equivalents from granites,apatite,sphene and zircon from alkaline rocks are all characterized by higher (La/Yb)N ratio and less Eu depletion,As to the relative contents of REE in minerals,apatite,sphene and zircon are enriched in LREE,MREE and HREE respectively,depending on their crystallochemical properties.     

新疆巴里坤县大加山一带碱性花岗岩的特征及构造环境探讨

大加山一带的碱性花岗岩按侵入先后可分为碱长花岗岩单元、钠闪石碱性花岗岩单元、霓石钠门石碱性花岗岩单元，由它们构成大加山超单元。这些岩石大都含碱性暗色矿物，从矿物组合看具贫水特征，岩石化学方面显示高硅、高碱、贫铝、镁、钙等特征；微量元素显示钾、铷、钍富集，锶、钡等强烈亏损特点；稀土元素总量较高，轻稀土较重稀土富集，并具有强的负铕异常。就位机制为断裂扩张并具顶蚀型被动定位类型，同源岩浆演化具反序列演化特点。上述特征和区域构造环境分析表明，大加山一带碱性花岗岩为非造山环境下形成的Ａ型花岗岩。     

新疆富蕴县恰库尔特—带碱性花岗岩的基本特征及形成的大地构造背景

恰库尔特一带的碱性花岗岩按侵入顺序和岩性可分为:晶洞(霓石)钾长花岗岩、(霓石)碱长花岗斑岩、霓石花岗岩.这些岩石大都含碱性暗色矿物.发育指示浅成特点的晶洞构造及文象结构,从矿物组合看岩石具贫水特征;岩石化学方面以高硅、高碱或过碱,贫铝、镁、钙为主要特征;岩石通常具有高的∑REE,其中以过碱性的霓石花岗岩为最高;轻稀土较重稀土富集,并具有强的负Eu异常;微量元素地球化学图谱表明,岩石相当于洋脊花岗岩,具有高钾、铷、钍的含量,而钡、钽、铌的富集程度相对较低.以上特征和区域构造分析表明,恰库尔特一带的碱性花岗岩为阿尔泰造山带造山作用结束以后于中晚三叠世的非造山环境下形成的A型花岗岩.     

REE Mineralization of Weathered Crust and Clay Sediment on Granitic Rocks in the Sanyo Belt,SW Japan and the Southern Jiangxi Province,China

Rare earth element (REE) geochemistry and mineralogy have been studied in the weathered crusts derived from the Early Yanshanian (Jurassic) biotite granites of Dabu and Dingnan, as well as in the Indosinian (Permian) muscovite–biotite granite of Aigao in southern Jiangxi province, China, and the weathered crusts and clay sediments on biotite granites in the Sanyo belt, SW Japan, that is, Okayama, Tanakami, and Naegi areas. In all of the weathered crusts, biotite and plagioclase commonly tend to decrease toward the upper part of the profile, whereas kaolinite and residual quartz and K‐feldspar increase. The weathered crusts of the Dingnan granites and some Naegi granites, which are characterized by the enrichment in light REE (LREE) in C horizons, have higher total REE (ΣREE) content than the parent REE‐enriched granites. Weathering of LREE‐bearing apatite and fluorocarbonates in the Dingnan granites and allanite and apatite in some Naegi granites may account for the leaching of LREE at the B horizons. The leached LREE must result in subsequent enrichment of LREE in the C horizons. The enrichment is probably associated with mainly adsorption onto kaolinite and partly formation of possible secondary LREE‐bearing minerals. In Japan it was found that REE mineralization occurs not in the weathered granitic crusts but in reworked clay sediments, especially kaolinite‐rich layers, derived mainly from the weathering materials of REE‐enriched granitic rocks. The clay sediments are more enriched in LREE, which likely adsorbed onto kaolinite. Concentration of heavy REE within almost all the weathered crusts and clay sediments, however, may reflect mainly residual REE‐bearing minerals such as zircon, which originated in the parent granitic rocks. The findings of the present study support the three processes for fractionation of the REE during weathering: (i) selective leaching of rocks containing both stable and unstable REE‐bearing minerals; (ii) adsorption onto clay minerals; and (iii) presence of possible secondary LREE‐bearing minerals.     

湖北麻城市四道河地区面理化含榴花岗岩的成因

野外和室内研究结果表明,四道河地区面理化含榴花岗岩由古生代沉积岩变质而成。在元素地球化学特征上,具有与岩浆成因的碱性花岗岩一致的特点:高硅(SiO2=75.24%～77.23%)、富碱(Na2O+K2O=6.87%～8.84%)、低铝(Al2O3=11.00%～12.78%);富Rb、Ba、Th、U等大离子亲石元素和Pb,贫Nb、Ta、Zr、Hf等高场强元素;稀土元素含量较高(∑REE=101.08～180.1μg/g),轻稀土元素相对富集(LREE/HREE=3.1～6.8),铕有中等负异常(δEu=0.30～0.68);锆石成因类型及定年结果表明,老核(继承锆石)是异地多时代(元古代-古生代),其寄主岩的原岩是沉积岩,时代不会早于古生代。     

Accessory phase controls on the geochemistry of crustal melts and restites produced during water-undersaturated partial melting

The profound geochemical conseqences of accessory phase behaviour during partial melting of highgrade metapelites are demonstrated with reference to two geochemically distinct crustal melts produced by biotite dehydration melting reactions under granulite facies (kbar, 860°CC) conditions. These two leucogneiss suites, from the Brattstrand Bluffs coastline, eastern Antarctica, have similar field relations, transport distances (10–100 s of metres) and major element chemistry. Type 1 leucogneisses have low Zr, Th and LREE, positive Eu anomalies and Zr/Zr^* and LREE_t/LREE_t ^* values less than 1.0 (i.e. less than required to saturate the melt). Mass balance constraints suggest that these melts have been extracted before equilibration with host melanosomes. The dry, peraluminous nature of vapour-undersaturated melts inhibits monazite and zircon solubility and results in concentration of these phases in the residue. Melts are consequently depleted in LREE and HREE. Melanosomes show complementary enrichment in LREE, while HREE patterns are dominated by residual garnet. Type 2 leucogneisses, in contrast, have strongly enriched Zr, Th and LREE abundances, negative Eu anomalies and Zr/Zr^* and LREE_t/LREE_t ^*>1 resulting from accessory phase entrainment. Vapour-absent partial melting under moderate (6–8 kbar) pressure granulite-facies conditions of a pelitic source containing monazite is likely to give disequilibrium melts depleted in LREE and HREE as monazite and garnet are concentrated in the residue. If temperatures are high enough (850–870° C) to permit relatively large degrees of partial melting then the feldspar component of the source will be removed almost completely, giving melts with large positive Eu anomalies. Melts formed under vapour-present conditions are unlikely to show such extreme LREE and HREE depletion or positive Eu anomalies, even at high degrees of partial melting. Disequilibrium melting coupled with source entrainment could fortuitously produce REE and trace element signatures similar to those typical of S-type granites and usually ascribed to equilibrium melting conditions.     

吉林福安堡棒子山花岗岩锆石U-Pb年龄、岩石地球化学特征及其地质意义

棒子山岩体为福安堡钼矿床的赋矿围岩,其岩性主要为似斑状黑云母二长花岗岩、二长花岗岩、黑云母花岗闪长岩和花岗斑岩等。本次测得似斑状黑云母二长花岗岩和花岗斑岩的LA-ICP-MS锆石U-Pb年龄分别为179±2Ma、172±1Ma,形成于中侏罗世,属燕山早期。棒子山花岗岩的SiO2含量为61.89%～71.06%,相对较高;Al2O3含量很高,为14.54%～17.11%;K2O含量为2.28%～4.38%,Na2O含量为3.74%～7.82%,Fe2O3含量为2.34%～5.91%,MgO含量为0.55%～2.37%。微量元素特征显示,棒子山花岗岩富集Rb、K等大离子亲石元素和不相容元素U、Th,强烈亏损Ba、Ta、Nb、P、Ti等元素;稀土元素特征显示轻稀土富集,重稀土亏损,轻重稀土分馏明显,有轻微的Eu负异常。上述结果表明,棒子山花岗岩石为准铝质-弱过铝质高钾钙碱性系列I型花岗岩,其形成可能与太平洋板块的俯冲有关。     

Mineral geochemistry of the Sangan skarn deposit,NE Iran: Implication for the evolution of hydrothermal fluid

The Sangan iron skarn deposit is located in the Sabzevar-Dorouneh Magmatic Belt of northeastern Iran. The skarn contains zoned garnet, clinopyroxene and magnetite. Cores and rims of zoned garnets are generally homogeneous, having a relatively high ΣREE, low ΣLREE/ΣHREE ratios, and positive Eu anomalies. The cores of the zoned clinopyroxenes are exceptionally HREE-rich, with relatively high ΣREE and HREE/LREE ratios, as well as positive Eu anomalies. Clinopyroxene rims are LREE-rich, with relatively low ΣREE contents and HREE/LREE ratios, and do not have Eu anomalies. Magnetite grains are enriched in LREEs in comparison with the HREEs and lack Eu anomalies. Variations of fluid composition and physicochemical conditions rather than YAG-type substitution mechanism are considered to have major control on incorporating trace elements, including REE, into the skarn mineral assemblage. Based on baro-acoustic decrepitation analysis, the calc-silicate and magnetite dominant stages were formed at similar temperatures, around 350–400 °C. In the Sangan skarns, hydrothermal fluids shifted from near-neutral pH, reduced conditions with relatively high ΣREE, low LREE/HREE ratios, and U-rich characteristics towards acidic, oxidized conditions with relatively low ΣREE, high LREE/HREE ratios, and U-poor characteristics.     

大兴安岭北段博克图地区晚石炭世花岗岩的成因:来自锆石U—Pb年龄、地球化学及Lu—Hf同位素证据

大兴安岭北段博克图地区高吉山岩体的岩石类型为碱长花岗岩,LA—ICP—MS锆石U—Pb定年结果表明高吉山岩体形成于晚石炭世(～311 Ma)。地球化学数据显示碱长花岗岩具有高硅,富钾,贫铁、镁的特点,且轻重稀土元素分馏作用明显[(La/Yb)_N=5. 00～14. 19],相对富集大离子亲石元素(Rb、K),亏损高场强元素(Nb、Ta、Ti)及P元素等,具有负铕异常(Eu/Eu~*)=0. 47～0. 72,∑REE为49. 07×10~(-6)～139. 30×10~(-6),LREE/HREE=7. 93～13. 98。锆石Lu—Hf同位素特征显示碱长花岗岩具有正的ε_(Hf)(t)值(+8. 46～+12. 94),和较年轻的Hf二阶段模式年龄(t_(DM2)=501～783 Ma)。结合相关区域地质研究,认为大兴安岭北段晚石炭世高吉山岩体是新元古代从亏损地幔中新增生地壳物质的部分熔融的产物,可能与古亚洲洋的俯冲作用有关。     

Geochronology and geochemistry of Late Carboniferous dykes in the Aqishan-Yamansu belt,eastern Tianshan:Evidence for a post-collisional slab breakoff

With aim of providing constraints on the Late Paleozoic tectonic evolution of the southern Central Asian Orogenic Belt(CAOB),an integrated study was conducted on the geochronological and geochemical data for dioritic,granitic and diabase dykes from the Aqishan-Yamansu belt in the eastern Tianshan,NW China.Zircon U-Pb dating indicates that the dioritic and granitic dykes were both emplaced in the Late Carboniferous(~311 Ma and^315 Ma).The dioritic dykes show adakitic characteristics and have high Na2 O and positiveεHf(t)values(+12 to+17),which suggest an origin from partial melts of a subducted oceanic slab.The granitic dykes have high SiO2 and K2 O contents and are characterized by en riched light rare earth elements(LREE)and slightly flat heavy rare earth elements(HREE),with negative Eu and Nb-Ta-Ti anomalies.These dykes are alkali-calcic and show geochemical features of highly fractionated Itype granites.Their positiveεHf(t)values(+16 to+17)suggest that they were derived from a juvenile accreted oceanic crustal sou rce.The coeval diabase dykes have low SiO2 and K2 O contents but high TiO2,MgO and Mg#(54-59).They are enriched in LREE and show characteristics of enriched mid-ocean ridge basalts(E-MORB).The relatively high Ba/Th,slightly low Th/Ta ratios,and negative Nb-Ta anomalies imply a mantle source metasomatised by slab-derived fluids.Thus,these basic dykes were generated likely by partial melting of the upwelling asthenosphere mantle with a slight influence of slab-derived fluids.Therefore,we suggest that the formation of these Late Carboniferous dykes were triggered by a post-collisional slab breakoff and the Aqishan-Yamansu belt was a continental arc formed by southdipping subduction of the Kangguer oceanic plate.     

Post-orogenic and anorogenic A-type fluorite-bearing granitoids, Eastern Desert, Egypt: Petrogenetic and geotectonic implications

The present study focuses on four A-type fluorite-bearing granitic plutons in the Eastern Desert of Egypt which are classified into post-orogenic subsolvus (Homrit Waggat, 535 Ma; Homer Akarem, 541 Ma and Ineigi, 571 Ma) and anorogenic hypersolvus (Gabal Gharib, 476 Ma) granites. All the granites are Si- and alkali-rich and MgCaTi poor. Whereas both granite types appear relatively homogeneous in terms of most of their major and trace elements, they differ in that the subsolvus granites are depleted in TiO₂, FeO^*, Ba, Sr and Zr and enriched in Rb and Y with respect to the hypersolvus granites. The two granite types, however, can be distinguished more easily by their rare-earth element (REE) patterns. Chondrite-normalized REE patterns of the hypersolvus granite display a gull-wing shape, characterized by a large negative Eu anomaly and moderate-to-high LREE contents. Relative to the hypersolvus granite, subsolvus granite is depleted in LREE and more enriched in HREE contents. The increase of HREE in the subsolvus granite is presumably caused by F complexing during the late stage of its evolution. This is supported by the abundance of fluorite veins cross-cutting the subsolvus granite. The negative Eu anomalies in the subsolvus granite point to the role of feldspars as residual phase in the source, and as a crystallizing phase during magmatic differentiation.Field relations, textural, mineralogical and geochemical data of the post-orogenic subsolvus granite are consistent with its derivation from a parental basic magma through crystal-liquid fractionation of alkali feldspar, plagioclase, amphibole, FeTi oxides, titanite, zircon, monazite and allanite. Crystallization occurred in a water-enriched and rather oxidizing environment, as a result of which the entire suite has a transitional character between that of a post-orogenic and an anorogenic setting. On the other hand, the most credible mechanism for the origin of the anorogenic hypersolvus granite is partial melting of I-type granodiorite-monzogranite source rocks in the study area.     

内蒙古敖汉旗克力代岩体锆石U-Pb年代及地球化学

通过LA-ICP-MS锆石U-Pb测年对内蒙古敖汉旗克力代岩体进行研究。结果表明,岩浆锆石的加权平均年龄为263±1 Ma,表明其结晶年龄为中二叠世。岩石地球化学分析表明,岩体具有高Si(SiO2=69.94%～72.56%),富ALK(Na2O+K2O=8.04%～9.23%),贫Fe(FeOT=1.50%～1.82%)、Mg(MgO=0.65%～0.86%)、Ti(TiO2=0.32%～0.35%)的特点;A/CNK值为0.87～0.93,为准铝质;A/NKC1.1,显示出I型花岗岩特征。固结指数(SI)为6.06～7.36,分异指数(DI)为88.82～91.82,说明岩体经历了较强的分异演化作用。稀土元素总量较低(ΣREE=91.76×10-6～143.16×10-6),轻稀土明显富集,重稀土相对亏损,LREE/HREE值平均为9.14,(La/Yb)N平均值为8.36,δEu平均值为0.58,为Eu亏损型。大离子亲石元素(LILE)Rb、K较富集,强烈亏损高场强元素(HFSE)Nb、Ti、Ta。因此,判定克力代岩体为高钾钙碱性I型花岗岩。结合测年结果和地球化学特征,判定该岩体为晚海西期华北板块和西伯利亚板块碰撞作用形成的同碰撞型花岗岩。     

The use of vein fluorite as probe for paleofluid REE and Sr-Nd isotope geochemistry: The Santa Catarina Fluorite District, Southern Brazil

Fluorite can be used as a probe for the source of Sr and REE, as well as for the Sr and Nd isotope systematics of mineralizing solutions, allowing characterization of the composition, oxidation state and sources of the fluids. The ⁸⁷Sr / ⁸⁶Sr ratios in vein fluorite from the Santa Catarina Fluorite District, southern Brazil, are low (0.720 to 0.745) relative to those of the majority of host granites at the time of mineralization (90 Ma), but are similar to those of less abundant and less evolved Sr- and Ca-rich granites and plagioclases of the heterogeneous Pedras Grandes granite association. Major contributions of Sr from the unradiogenic Parana Basin rocks (⁸⁷Sr / ⁸⁶Sr_{90 Ma} = 0.705 to 0.718) are unlikely, considering the radiogenic character of the lower ⁸⁷Sr / ⁸⁶Sr end-member in fluorite mixing lines. Estimated fluorite fluid partition coefficients (K_d^Sr-Ca = 0.019 and D^Sr ≈ 600) indicate a Sr / Ca ratio in the fluorite-forming solution of 0.012, and Sr contents of 0.05 to 0.25 ppm, which are similar to those of present-day granitic geothermal waters. Initial Nd isotopic compositions of the vein fluorites (0.5120 to 0.512) are similar to those of the Pedras Grandes granites. The ¹⁴³Nd / ¹⁴⁴Nd_{90 Ma} of the evolved granites of the Tabuleiro granite association, their accessory fluorites and the Parana Basin rocks are considerably more radiogenic (0.5120 to 0.5127) and these are thus considered to be unlikely sources of the fluids. The REE patterns of vein fluorites, normalized to upper continental crust, show a range of LREE-depleted patterns, with highly variable positive and negative Eu anomalies. The host Pedras Grandes granites show flat to slightly depleted UCC normalized LREE patterns with strong negative Eu anomalies. Depletion of the LREE in fluorites resulted from the mobility of HREE fluoride complexes during fluid migration. A REE fractionation model based on ionic potential ratios indicates that Eu³⁺ was stable during fluid migration and fluorite precipitation. The coexistence of pyrite and Eu³⁺ in the mineralizing fluids is consistent with low pH and oxygen fugacities near the hematite-magnetite buffer.