Geochemistry and Petrogenesis of Kunduru Betta Calc-Alkaline Ring Complex in the Dharwar Craton,Southern India

The Kunduru Betta Ring Complex (KRC), at the southern margin of Dharwar craton, South India, comprises metaluminous sub-solvus syenites and quartz monzonite with a concentric disposition younging towards the center. An outer mafic syenite (of lamprophyric affinity) is followed by porphyritic monzonite, quartz monzodiorite and finally a quartz monzonitic stock at the centre.SiO₂, Al₂O₃ and Na₂O increase from the primitive lamprophyric mafic syenite to the quartz monzonite through the intermediate members, while CaO, MgO, Fe₂O₃^T, TiO₂, P₂O₅ and MnO show an opposite trend suggesting fractionation of hornblende, clinopyroxene, biotite, apatite, sphene, and iron oxide minerals. Rb, Th and U increase with a complementary decrease in Sc, V, Cr, Co, Cu, Sr and Ba from the outer mafic syenite to the inner quartz monzonite. Y, Zr and Hf decrease from lamprophyric mafic syenite to quartz monzodiorite and the trend is reversed in the final quartz monzonite phase. However, the suite is characterised by a compositional gap between quartz monzodiorite and quartz monzonite. Total REE gradually decrease from the mafic syenite to quartz monzonite and the REE distribution patterns show LREE-enriched and HREE-depleted parallel distributions with negligible Eu anomalies.The geochemical data suggest that the rock types were formed as products of progressive differentiation by crystal fractionation of calc-alkaline lamprophyric parent magma which was derived by partial melting of metasomatically enriched mantle in the Kabini lineament. Although the quartz monzonites conform to the trend of differentiated Kunduru Betta suite, the compositional gap between them and the quartz monzodiorite precludes their origin by simple differentiation. It is suggested that convective liquid fractionation might have resulted in the discrete body of quartz monzonite.     

Isotopic Geochronology of the Late Paleozoic Kanggur Gold Deposit of East Tianshan Mountains, Xinjiang, NW China

Abstract: The Kanggur gold deposit lies in East Tianshan mountains, eastern section of Central Asia orogenic belt. The gold mineralization occurs on the northern margin of the Aqishan‐Yamansu Paleozoic island arc in the Tarim Plate. It was hosted mainly in Middle‐Lower Carboniferous calc‐alkaline volcanic rocks, and controlled by the distributions of syn‐tectonic intrusions and ductile shear zones. In order to determine ore‐forming age of the Kanggur deposit, samples were collected from ores, wall rocks, altered rocks and intrusions. The dating methods include Rb‐Sr isochron and Sm‐Nd isochron, and secondly ⁴⁰Ar/³⁹Ar age spectrum, U‐Pb and Pb‐Pb methods. Based on the mineral assemblage and crosscutting relationship of ore veins, five mineralization stages are identified. This result is confirmed by isotope geochronologic data. The first stage featuring formation of pyrite‐bearing phyllic rock, is mineralogically represented by pyrite, sericite and quartz with poor native gold. The Rb‐Sr isochron age of this stage is 2905 Ma. The second stage represents the main ore‐forming stage and is characterized by native gold–quartz–pyrite–magnetite–chlorite assemblage. Magnetite and pyrite of this stage are dated by Sm‐Nd isochron at 290.47.2 Ma and fluid inclusion in quartz is dated by Rb‐Sr isochron at 282.35 Ma. The third mineralization stage features native gold–quartz–pyrite vein. In the fourth stage, Au‐bearing polymetallic sulfide‐quartz veins formed. Fluid inclusions in quartz are dated by Rb‐Sr isochron method at 25821 Ma. The fifth stage is composed of sulfide‐free quartz–carbonate veins with Rb‐Sr age of 2547 Ma. The first and second stages are related to ductile‐brittle deformation of shear zones, and are named dynamo‐metamorphic hydrothermal period. The third to fifth stages related to intrusive processes of tonalite and brittle fracturing of the shear zones, are called magmato‐hydrothermal mineralization period. The Rb‐Sr isochron age of 2905 Ma of the altered andesite in the Kanggur mine area may reflect timing of regional ductile shear zone. The Rb‐Sr isochron age of 28216 Ma of the quartz‐syenite porphyry and the zircon U‐Pb age of 2757 Ma of tonalite in the north of Kanggur gold mine area are consistent with the age of gold mineralization (290‐254 Ma). This correspondence indicates that the tonalite and subvolcanic rocks may have been related to gold mineralization. The Rb–Sr, Sm‐Nd and U‐Pb ages and regional geology support the hypothesis that the Kanggur gold deposit was formed during collisional orogenesis process in Late Variscan.     

Experimental and geochemical evidence for derivation of the El Capitan Granite,California, by partial melting of hydrous gabbroic lower crust

Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850°C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635–661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486–1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening.     

河北东坪金矿区水泉沟岩体的地球化学特征

水泉沟岩体主要由二长岩构成。主要矿物是碱性长石和斜长石,它们的含量高达80%以上。石英不多见,暗色矿物含量少。副矿物主要是磁铁矿、石榴石、榍石和锆石。交代结构发育,蚀变现象普遍。主要化学组分和微量元素含量及δ¹⁸O值变化范围大。该二长岩体是由老片麻岩经热液碱交代作用而成。     

Geology,geochemistry and petrogenesis of post-collisional adakitic intrusions and related dikes in the Khoynarood area,NW Iran

The Khoynarood area is located in the northwest of Iran, lying at the northwestern end of the Urumieh–Dokhtar volcano-plutonic belt and being part of the Qaradagh–South Armenia domain. The main intrusive rocks outcropped in the area have compositions ranging from monzonite–quartz monzonite, through granodiorite, to diorite–hornblende diorite, accompanied by several dikes of diorite–quartz diorite and hornblende diorite compositions, which were geochemically studied in order to provide further data and evidence for the geodynamic setting of the region. The SiO₂, Al₂O₃ and MgO contents of these rocks are about 58.32–68.12%, 14.13–18.65% and 0.68–4.27%, respectively. They are characterized by the K₂O/Na₂O ratio of 0.26–0.58, Fe₂O₃ + MnO + MgO + TiO₂ content about 4.27–13.13%, low Y (8–17 ppm) and HREE (e.g., 1–2 ppm Yb) and high Sr contents (750–1330 ppm), as well as high ratios of Ba/La (13.51–50.96), (La/Yb)_N (7–22), Sr/Y (57.56–166.25), Rb/La (1.13–2.96) and La/Yb (10–33.63), which may testify to the adakitic nature of these intrusions. Their chemical composition corresponds to high-silica adakites, displaying enrichments of LREEs and LILEs and preferential depletion of HFSEs, (e.g., Ti, Ta and Nb). The REE differentiation pattern and the low HREE and Y contents might be resulted from the presence of garnet and amphibole in the solid residue of the source rock, while the high Sr content and the negative anomalies of Ti, Ta and Nb may indicate the absence of plagioclase and presence of Fe and Ti oxides in it. As a general scenario, it may be concluded that the adakitic rocks in the Khoynarood were most likely resulted from detachment of the subducting Neo-Tethyan eclogitic slab after subduction cessation between Arabian and Central Iranian plates during the upper Cretaceous–early Cenozoic and partial melting of the detached slab, followed by interactions with metasomatized mantle wedge peridotite and contamination with continental crust.     

Petrogenesis and geodynamic evolution of the Kajan Neogene subvolcanic rocks,Nain, Central Iran

Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO₂ (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO₂, P₂O₅, MnO, Al₂O₃ and Fe₂O₃ define linear trends with negative slopes against SiO₂, whilst Na₂O and K₂O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO₂, whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (La_N/Yb_N = 4.5–6.4) with moderate HREE fractionation (Sm_N/Yb_N = 1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the ⁸⁷Sr/⁸⁶Sr initial ratios vary from 0.704432 to 0.705989, and the ¹⁴³Nd/¹⁴⁴Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks.     

Geochemistry and evolution of the Wolf River Batholith,a late Precambrian Rapakivi Massif in North Wisconsin,U.S.A.

The Wolf River Batholith is an anorogenic rapakivi massif in central and northeastern Wisconsin with an age of 1.5 Ga. The Batholith has alkaline affinities and consists of biotite granite and biotite-hornblende adamellite with minor occurrences of quartz syenite and older monzonite and anorthosite. The batholith is part of a major Late Precambrian (1.4–1.5 Ga) magmatic event of continental proportions, represented by separate intrusions extending from Labrador to southern California (Silver et al., 1977).The major and trace element composition (Li, Rb, Sr, Ba, and REE) of 40 samples from the anorthosite, monzonite, and rapakivi granite and adamellite plutons precludes a comagmatic (although not cogenetic) model between all three rock units. However, the monzonite may be related to the anorthosite alone by fractional crystallization of plagioclase, orthopyroxene, clinopyroxene, and apatite. Alternatively, the monzonite may be a separate parent melt or a hybrid associated with the granite and adamellite plutons. The high REE content of the monzonite precludes it from being related to the rapakivi granite and adamellite plutons as a source material, a residuum, or a cumulate.A major portion of the Batholith is an undifferentiated intrusive sequence ranging from older rapakivi granite to younger adamellite. The compositions of these plutons suggest a crustal fusion origin at intermediate to lower levels of the crust (25–36 km). The trace element data are consistent with partial fusion of tonalitic to granodioritic source material.During crystallization and emplacement into the upper crust (less than 4 km), 55–70% fractionation of two feldspars, biotite and hornblende from one of the granite plutons produced a small volume of differentiated granitic melt high in Si, Fe/Mg, Rb, Li, and REE (except Eu), and low in Ca, Mg, Al, Ca/Na, Sr, Ba, and K/Rb and with a large negative Eu anomaly. Presumed associated cumulate material ranges from silica-poor quartz monzonite and quartz syenite.The chemical and mineralogical similarity between the Wolf River Batholith and younger magmatic analogs associated in continental break-up (Nigerian younger granites, White Mountain magma series, and the peralkaline volcanics of the Red Sea Region) are suggestive but not conclusive of an extensional tectonic setting. A preliminary tectonic model suggests that the 1.4–1.5 Ga event is in response to thermal doming in an extensional regime leading to continental separation in the western Cordillera (pre-Belt) and extensive crustal fusion with no rifting or separation across the North American Craton.     

Geochemical and isotopic characteristics of the Cretaceous Orikabe Plutonic Complex,Kitakami Mountains,Japan: magmatic evolution in a zoned pluton and significance of a subduction-related mafic parental magma

The Orikabe Plutonic Complex, northeast Japan, is a zoned pluton and one of the Cretaceous intrusions in the Circum-Pacific area. In the Main body, K-rich calc-alkaline rocks composed of marginal gabbro and a large amount of monzodiorite–quartz monzonite–monzogranite are intruded successively by innermost calc-alkaline rocks of granodiorite. The gabbro and monzodiorite–monzogranite have a continuous chemical variation, while the granodiorite has lower concentrations of K, Rb, Y, Zr, Nb and F at the same SiO₂ content. The gabbro and monzodiorite–quartz monzonite have a Rb-Sr whole-rock age of 119±12 Ma with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.70392±0.00007. The initial ⁸⁷Sr/⁸⁶Sr ratio of the innermost granodiorite is estimated to be about 0.7042. The ¹⁸O values of fresh rocks range from +6.7 to +8.3, indicating a positive correlation with SiO₂ contents. The K-rich calc-alkaline rocks were derived through fractional crystallization from a mafic parental magma with a slightly high ¹⁸O value, implying a major contribution of a sub-arc mantle at a continental margin. Trace element modeling indicates that the source could have been a fertile lherzolite enriched in LILE and depleted in HFSE. The innermost granodiorite was the differentiation product of a distinct parental magma, suggesting the involvement of a small amount of crustal component in the source and partial melting under a more hydrous condition.Editorial responsibility: J. Hoefs     

Alkaline orogenic plutonism in the Karakorum batholith: the Upper Cretaceous Koz Sar complex (Karambar valley,N. Pakistan)

Abstract

The Karakorum is located north of the India/Kohistan-Ladakh/Eurasia sutures. Along the Karambar valley, its axial batholith comprises four plutonic complexes. (1) The largest one represents the westerly continuation of the huge mid-Cretaceous calc-alkaline Hunza plutonic unit. This unit here displays a remarkable reverse zoning that would result from a differentiation at depth followed by multipulse intrusions. (2) A stock of subalkaline (i.e. intermediate between alkaline and calc-alkaline) granitoids (Warghut porphyritic granite). (3) A composite group of fine-grained granitoids. (4) The so-called Koz Sar alkaline complex (KSAC), a unique example of this composition of plutonism so far reported in the batholith. In addition, leucogranite dykes and rare alkaline mafic ones occur.

The KSAC is a heterogeneous and more or less deformed body, ca. 5 km wide and possibly 20 km long, comprising two coeval groups of rocks. (1) Medium- to coarse-grained rocks are the most representative members of the complex. They consist of metaluminous to slightly peralkaline monzonite, quartz monzonite, granite and leucogranite, with iron-rich mafic silicates and Fe-Ti oxide. These subsolvus granitoids define a strongly ferriferous alkaline series. Five monzonite and quartz monzonite samples yield an isochron Rb-Sr age of 88 ± 4 Ma (⁸⁷Sr/⁸⁶Sr_i = 0.70440 ± 7; MSWD = 1.7). (2) Fine-grained rocks (monzogabbro to quartz syenite) are compositionally comparable to the dark-coloured members of the preceding group.

The KSAC was emplaced into a post-collisional environment resulting from the accretion, maybe at least since Aptian times, of the Kohistan island arc to the Karakorum. Its alkaline character testifies to the development of extensional tectonics, a process compatible with an oblique collision and/or with the decrease, at the time of collision, of the convergence velocity between the two colliding terrenes. Available data suggest that this alkaline complex (1) is late-orogenic, (2) is genetically-related to the nearby subalkaline granitoids and originates from the same mantle-source with a small crustal contribution, and (3) represents the ultimate member of the mid-Cretaceous subduction-related plutonism emplaced into the Karakorum continental margin.     

Geochemical constraints on the petrogenesis of the Paleozoic granitoids of the Sierra de San Luis,Sierras Pampeanas,Argentina

The Paleozoic granitoids of the Sierra de San Luis comprise the Ordovician tonalite suite (OTS; metaluminous to mildly peraluminous calcic tonalite–granodiorites) and granodiorite–granite suite (OGGS; peraluminous calcic to calc-alkaline granodiorite–monzogranites), as well as the Devonian granite suite (DGS; peraluminous alkali-calcic monzogranites) and monzonite–granite suite (DMGS; metaluminous alkali-calcic quartz monzonite–monzogranite ± granodiorite, mildly peraluminous alkalicalcic monzogranites). The OTS has relatively high K₂O, CaO, and Yb_N and low Cr, Ni, Ba, Sr, Rb/Sr, Sr/Y, and (La/Yb)_N, as well as negative Eu/Eu¹, high ⁸⁷Sr/⁸⁶Sr (0.70850–0.71114), and unradiogenic ε_Nd(470Ma) (−5.3 to −6.0), which preclude an origin of variably fractionated mantle melts and favour a mafic lower crustal source. The OGGS consists of two granitoids: (1) high-temperature characterized by low Al₂O₃/TiO₂, Rb/Sr, and (La/Yb)_N, a smooth negative Eu/Eu¹, and relatively high CaO and (2) low-temperature with high Al₂O₃/TiO₂ and Rb/Sr, low CaO, (La/Yb)_N, and Sr/Y, and negative Eu/Eu¹. Melting of metagreywackes at pressures below 10 kbar with a variable supply of water could account for the chemistry of the high-T OGGS, whereas dehydration melting of biotite-bearing metasedimentary sources at low pressures is proposed for the low temperature OGGS. Melting of crustal sources relates to a contemporaneous mafic magmatism.Devonian magmatism is characterized by high Ba, Sr, K₂O, Na₂O, Sr/Y, and (La/Yb)_N. Sources for the DGS include metasedimentary or metatonalitic protoliths. Biotite dehydration melting triggered by the addition of heat, supplied by mantle-derived magmas, is proposed. High Ba, Sr, LREE, MgO, Cr, Ni, Zr, and V of the monzonites suggest an enriched lithospheric mantle source. Low Yb and Y and high Sr and (La/Yb)_N indicate a garnet-rich residual assemblage (P ⩾ 10 kbar). Melts for the peraluminous rocks may have derived from a metasedimentary or metaigneous source at lower pressures in a process dominated by biotite consumption and plagioclase in the residue.The Ordovician granitoids are synkinematic with compressive deformation related to the early stages of Famatinian convergence. The Devonian magmatism is synkinematic with a system of shear zones that were active during the Achalian cycle.     

Origin and geochemistry of Pan-African granitoid rocks in the Gabal Um Shomer area,Southwestern Sinai,Egypt

Geological, petrological and geochemical studies indicated that there are two distinct types of granitoid rocks: older quartz diorites to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a meta-aluminous chemistry and a calc-alkaline character, with high MgO, Fe2O3, TiO2, CaO, P2O5, Sr and low SiO2, K2O, and Rb. Their major and trace elements data, together with low 87Sr/ 86Sr ratios (0.7029±0.0008) are indicative of I-type affinities. The second-...     

Minor-element and Sr-isotope geochemistry of tertiary stocks,Colorado mineral belt

Rocks of the northeast portion of the Colorado mineral belt form two petrographically, chemically and geographically distinct rock suites: (1) a silica oversaturated granodiorite suite; and (2) a silica saturated, high alkali monzonite suite. Rocks of the granodiorite suite generally have Sr contents less than 1000 ppm, subparallel REE patterns and initial ⁸⁷Sr/ ⁸⁶Sr ratios greater than 0.707. Rocks of the monzonite suite are restricted to the northeast part of the mineral belt, where few rocks of the granodiorite suite occur, and generally have Sr contents greater than 1000 ppm, highly variable REE patterns and ⁸⁷Sr/⁸⁶Sr initial ratios less than 0.706.Despite forming simple, smooth trends on major element variation diagrams, trace element data for rocks of the granodiorite suite indicate that they were not derived from a single magma. These rocks were derived from magmas having similar REE patterns, but variable Rb and Sr contents, and Rb/Sr ratios. The preferred explanation for these rocks is that they were derived by partial melting of a mixed source, which yielded pyroxene granulite or pyroxenite residues.The monzonite suite is chemically and petrographically more complex than the granodiorite suite. It is subdivided here into alkalic and mafic monzonites, and quartz syenites, based on the textural relations of their ferromagnesian phases and quartz. The geochemistry of these three rock types require derivation from separate and chemically distinct magma types. The preferred explanation for the alkalic monzonites is derivation from a heterogeneous mafic source, leaving a residue dominated by garnet and clinopyroxene. Early crystallization of sphene from these magmas was responsible for the severe depletion of the REE observed in the residual magmas. The lower Sr content and higher Rb/Sr ratios of the mafic monzonites requires a plagioclase-bearing source.The Sr-isotope systematics of the majority of these rocks are interpreted to be largely primary, and not the result of crustal contamination. The positive correlation of Rb/Sr and ⁸⁷Sr/⁸⁶Sr ratios for the least fractionated samples indicate that the sources from which parent magmas of both the granodiorite and monzonite suites were derived are Precambrian in age.     

Geochemical exploration of a Precambrian Batholith, source of a Cu-W mineralization of the tourmaline breccia in Southern Finland

The Hämeenkyrö batholith is a round-shaped plutonic body of an areal size of 147 km². It is composed of calc-alkaline to alkaline rocks that intruded previously metamorphosed Svecofennian volcanogenic and sedimentary schists 1860 Ma ago. The Cu-W bearing tourmaline breccia of the Ylörvi deposit occurs in metavolcanic rocks close to the eastern contact of the batholith.The average sampling density in the batholith was 1 sample per km², and 175 samples were analyzed for Cu, Au, Ag, Ni, Pb, Co, Zn, S by AAS for SiO₂, TiO₂, Al₂O₃, FeO, MnO, MgO, CaO, Na₂O, K₂O, As, Sn and P by X-ray fluorescence. Mo and W were determined colorimetrically. Barth mesonorms were calculated for each sample and the rock type was determined according to Streckeisen's classification. Element distributions are displayed on contour maps.The rock types of the batholith exhibit an asymmetric concentric arrangement, the order from the center towards the margin being alkali-feldspar granite, syenogranite, monzogranite, quartz monzonite, quartz syenite, alkali-feldspar, quartz syenite, syenite and alkali-feldspar syenite. Anomalously high Cu, As, Sn, S, K₂O and Na₂O contents have been found at the eastern margin of the batholith in a N—S-trending zone, which is characterized by hydrothermal alteration phenomena, propylitization, tourmalinization and scapolitization. Three anomalous areas have been defined within this zone, one of them is associated with the Ylöjärvi deposit and the other two are regarded as exploration targets.     

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.     

Geochemistry and Genesis of the Late Jurassic Granitoids at Northern Great Hinggan Range: Implications for Exploration

<正>The Longgouhe and Ershiyizhan intrusions of the Late Jurassic,located in the Upper Heilongjiang Basin of the northern Great Hinggan Range,are closely related to porphyry Cu-Au mineralizations.In lithology the intrusions are quartz diorite,quartz monzodiorite and granodiorite of high-K calc-alkaline series,with minor aspects of shoshonite series.Their SiO_2 and Al_2O_3 contents range from 61.37%to 66.59%and 15.35%to 17.06%,respectively.The MgO content ranges from 2.02%to 3.47%,with Mg~# indices of 44-59.The(La/Yb)_N and Eu/Eu~* values range from 16.85 to 81.73 and 0.68 to 0.93,respectively,showing strong differentiation rare earth element(REE) patterns similar to those of adakites.The rocks are enriched in Ba,Sr and light REE(LREE),obviously depleted in Nb and Ta,slightly depleted in Rb and Ti,and poor in Yb and Y,with Yb and Y contents of 0.31-1.32 ppm and 4.32-12.07 ppm,respectively.As indicated by Sr/Y ratios of 67.74-220.60,the rocks are characterized by low-Y and high-Sr contents,which characterize the adakites in the world.Holistically, geochemical tracers suggest that the interested intrusions are adakitic rocks.Given that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic,respectively,the interested intrusions should be formed by partial melting of delaminated crust,which had been thickened during collisional orogeny between the Siberian and Mongolian-Sinokorean continents.     

Geology,geochronology and geochemistry of granitic intrusions and the related ores at the Hongshan Cu-polymetallic deposit: Insights into the Late Cretaceous post-collisional porphyry-related mineralization systems in the southern Yidun arc,SW China

The Hongshan Cu-polymetallic deposit is located in the southern Yidun arc in southwestern China, where both subduction-related (Late Triassic) and post-collisional (Late Cretaceous) porphyry–skarn–epithermal mineralization systems have been previously recognized. In this study, two distinct magmatic events, represented by diorite porphyry and quartz monzonite porphyry, have been revealed in the Hongshan deposit, with zircon SHRIMP U–Pb ages of 214 ± 2 Ma and 73.4 ± 0.7 Ma, respectively. The 73 Ma age is comparable to the Re–Os ages of 77 to 80 Ma of ore minerals from the Hongshan deposit, indicating that the mineralization is related to the Late Cretaceous quartz monzonite porphyries rather than Late Triassic diorite porphyries. The Late Triassic diorite porphyries belong to the high-K calc-alkaline series and show arc magmatic geochemical characteristics such as enrichment in Rb, Ba, Th and U and depletion in HFSEs, indicating that they were formed during the westward subduction of the Garzê–Litang Ocean. In contrast, the Late Cretaceous quartz monzonite porphyries show shoshonitic I-type geochemical characteristics, with high SiO₂, K₂O, LILE, low HREE, Y and Yb contents, and high LREE/HREE and La/Yb ratios. These geochemical characteristics, together with the Sr–Nd–Pb isotopic compositions (average (⁸⁷Sr/⁸⁶Sr)_i = 0.7085; ε_Nd(t) = − 6.0; ²⁰⁶Pb/²⁰⁴Pb = 19.064, ²⁰⁷Pb/²⁰⁴Pb = 15.738, ²⁰⁸Pb/²⁰⁴Pb = 39.733) suggest that the quartz monzonite porphyries originated from the partial melting of the ancient lower crust in response to underplating of mafic magma from subduction metasomatized mantle lithosphere, possibly triggered by regional extension in the post-collisional tectonic stage. The S isotopic compositions (δ³⁴S_V-CDT = 3.81‰ to 5.80‰) and Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.014 to 18.809, ²⁰⁷Pb/²⁰⁴Pb = 15.550 to 15.785, and ²⁰⁸Pb/²⁰⁴Pb = 38.057 to 39.468) of ore sulfides indicate that the sulfur and metals were derived from mixed mantle and crustal sources. It is proposed that although the Late Triassic magmatic event is not directly related to mineralization, it contributed to the Late Cretaceous mineralization system through the storage of large amounts of sulfur and metals as well as water in the cumulate zone in the mantle lithosphere through subduction metasomatism. Re-melting of the mantle lithosphere including the hydrous cumulate zone and ancient lower crust during the post-collisional stage produced fertile magmas, which ascended to shallow depths to form quartz monzonite porphyries. Hydrothermal fluids released from the intrusions resulted in porphyry-type Mo–Cu ores in and near the intrusions, skarn-type Cu–Mo ores in the country rocks above the intrusions, and hydrothermal Pb–Zn ores in the periphery.     

Strontium and oxygen isotopic variations in Mesozoic and Tertiary plutons of central Idaho

Regional variations in initial ⁸⁷Sr/⁸⁶Sr ratios (r _i) of Mesozoic plutons in central Idaho locate the edge of Precambrian continental crust at the boundary between the late Paleozoic-Mesozoic accreted terranes and Precambrian sialic crust in western Idaho. The r _i values increase abruptly but continuously from less than 0.704 in the accreted terranes to greater than 0.708 across a narrow, 5 to 15 km zone, characterized by elongate, lens-shaped, highly deformed plutons and schistose metasedimentary and metavolcanic units. The chemical and petrologic character of the plutons changes concomitantly from ocean-arc-type, diorite-tonalite-trondhjemite units to a weakly peraluminous, calcic to calcalkalic tonalite-granodiorite-granite suite (the Idaho batholith). Plutons in both suites yield Late Cretaceous ages, but Permian through Early Cretaceous bodies are confined to the accreted terranes and early Tertiary intrusions are restricted to areas underlain by Precambrian crust. The two major terranes were juxtaposed between 75 and 130 m.y. ago, probably between 80 and 95 m.y. Oxygen and strontium isotopic ratios and Rb and Sr concentrations of the plutonic rocks document a significant upper-crustal contribution to the magmas that intrude Precambrian crust. Magmas intruding the arc terranes were derived from the upper mantle/subducted oceanic lithosphere and may have been modified by anatexis of earlier island-arc volcanic and sedimentary units. Plutons near the edge of Precambrian sialic crust represent simple mixtures of the Precambrian wall-rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r _i of 0.7035. Rb/Sr varies linearly with r _i, producing “pseudoisochrons” with apparent “ages” close to the age of the wall rocks. Measured δ ¹⁸O values of the wall rocks are less than those required for the assimilated end-member by Sr-O covariation in the plutons, however, indicating that wall-rock δ ¹⁸O was reduced significantly by exchange with circulating fluids. Metasedimentary rocks of the Belt Supergroup are similarly affected near the batholith, documenting a systematic depletion in ¹⁸O as much as 50 km from the margin of the batholith. Plutons of the Bitterroot lobe of the Idaho batholith are remote from the accreted terranes and represent mixtures of Precambrian wall-rocks with melts dominated by continental lower crust (r _i>0.708) rather than mantle. “Pseudoisochrons” resulting from these data are actually mixing lines that yield apparent “ages” less than the true age of the wall rocks and meaningless “r_i”. Assimilation/ fractional-crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region.     

Geochemistry of the Adamello massif (northern Italy)

The Tertiary Adamello massif, outcropping over an area of more than 550 km² in the southern Alps (northern Italy) is composed mainly of granitoid rocks (granodiorite, tonalite, quartz diorite) with minor amounts of diorite and gabbro. The major and trace element composition of these rocks is comparable to calc-alkaline volcanic rocks of continental margins. The granitoid rocks display spatial and temporal variations in their composition, particularly in Na, P, Sr, La, Nb and Y contents and ⁸⁷Sr/⁸⁶Sr ratios. The variations were probably produced by concurrent contamination/wall-rock assimilation and fractional crystallization of high-alumina basaltic magma.     

东昆仑祁漫塔格阿确墩地区侵入岩U-Pb年代学、地球化学及其地质意义

祁漫塔格地区岩浆岩的成岩时代和形成环境的确定能对东昆仑造山带加里东期构造演化时限加以约束.对祁漫塔格西北部阿确墩地区石英闪长岩和二长花岗岩进行了年代学和岩石地球化学研究,结果显示,石英闪长岩属准铝质-弱过铝质钙碱性系列岩石;轻重稀土分馏明显,具中等-轻微铕负异常（δEu=0.79~0.90）;相对富集Rb、K、Hf、Zr、Tb、Nd等元素,不同程度地亏损Ba、P、Ti、Nd、Ta、Y;具有I型花岗岩类特征.二长花岗岩属弱过铝质钙碱性系列岩石;轻重稀土分异程度极大,具明显铕负异常（δEu=0.42~0.45）;富集大离子亲石元素（如Rb、K、La、Ce、Nd、Tb等）,亏损高场强元素（P、Ti、Nd、Ta）和Ba、Sr、U等元素;为高分异I型花岗岩.Nd/Th、Nb/Ta、Mg#值等指标显示石英闪长岩为壳源特征且受到幔源岩浆的影响,推测是幔源岩浆底侵地壳物质发生部分熔融形成的;二长花岗岩则是壳源的,可能与幔源岩浆底侵诱发的上地壳物质部分熔融有关,且经历了强烈的结晶分离作用.石英闪长岩和二长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为448.8±3.9 Ma和405.2±3.6 Ma,代表其形成时代.石英闪长岩总体显示出与俯冲消减作用有关的岛弧岩浆岩地球化学特征;二长花岗岩在构造环境图解中显示为碰撞背景,但微量元素与同碰撞花岗岩典型特征不符,综合分析认为形成于后碰撞构造背景下.结合区域构造演化,推测东昆仑祁漫塔格地区在晚奥陶世持续处于俯冲消减环境中,早泥盆世之前进入后碰撞造山阶段.      

云南大坪金矿床赋矿闪长岩锆石SHRIMP U-Pb定年及其地质意义

云南大坪金矿床是哀牢山金矿带中最重要的金矿之一,主要赋存在受到强烈剪切和水-岩反应的闪长岩中,是典型的喜马拉雅期造山型金矿。本文对大坪金矿床赋矿闪长岩中锆石进行了SHRIMP U-Pb定年,得出闪长岩围岩的年龄为773±12Ma,为晚元古代,显示该岩体为华南地区晋宁-澄江期大规模基性到酸性岩浆活动的产物,是Rodinia 超大陆形成、裂解后冈瓦纳大陆形成过程的响应,而不是前人普遍认为的加里东期岩体。该岩体侵入年龄与大坪金矿脉石英流体包裹体⁴⁰Ar-³⁹Ar 年龄测定给出的高温坪年龄(765.5±7.0Ma)基本一致,显示大坪金矿床具有多期成矿的特征,其主体形成于喜马拉雅期碰撞造山运动,但早在晋宁造山运动中就有金的初步富集。在闪长岩中还发现了年龄为33.7±1.1Ma的锆石,其时代与大坪金矿床含金石英脉中热液绢云母的⁴⁰Ar-³⁹Ar定年结果(33.76Ma)基本一致,显示它们很可能为该区强烈的韧性剪切和局部岩浆部分熔融作用的产物。