Hornblende Granodiorite Research Articles

Arc related dioritic–granodioritic magmatism from southeastern Peninsular Malaysia and its tectonic implication

In Peninsular Malaysia, Late Cretaceous (95-76 Ma) plutons are found within the Eastern Belt. Their compositions are diverse, ranging from biotite granite, hornblende granodiorite, diorite, and gabbro. The Aur Pluton is the easternmost body and is exposed in the Johore Archipelago, southeast of Peninsular Malaysia. The rock types vary from diorite, quartz monzodiorite and granodiorite. Ar-Ar stepheating age of the diorite and zircon U/Pb age of the granodiorite yielded ages of 77.9 ± 2 Ma and 79 ± 0.7 Ma, respectively. The overall major and trace element trends are consistent with two magmatic pulses, i.e., diorite-quartz monzodiorite and granodiorite. The diorite-quartz monzodiorites are characterized by high Fe2O3 (6.7–8.3 wt.%), CaO (5.5–7.6 wt.%), MgO (2.9–4.1 wt.%) and high but variable Sr concentrations (570–1300 ppm). The granodiorites have significantly higher total alkali content (8.49–8.91%), with high K2O concentrations (3.8–4.6%) and low Fe2O3 (4.7–6.5%), CaO (2.7–3.9%) and MgO (1.4–2.0%) concentrations. Low Nb/U and distinct Pb anomalies suggest that both rock types are likely derived from the crust. Furthermore, elevated LREE and trace element contents for the granodiorites, e.g., FTh (10–20 ppm), Pb (10–30 ppm), and U (2–5 ppm), also indicate that upper crustal components are involved in the magma generation. The dioritic rocks are chemically classified as calc-alkaline volcanic arc (VAG) rocks, but they also have field relationships and mineralogies typically associated with an active continental margin (ACM).

Continental crust growth induced by slab breakoff in collisional orogens: Evidence from the Eocene Gangdese granitoids and their mafic enclaves, South Tibet

Collisional orogens are traditionally regarded as main regions related to crustal reworking with limited or without crust growth. However, our study on the granitoids and their mafic enclaves of the Ringqênzê plutonic complex, a representative syn-collisional intrusive complex of Gangdese batholith, shows huge mantle contributions and considerable continental crust growth. Zircon U-Pb dating yields Eocene ages of 50.2 ± 0.5 Ma, 46.4 ± 0.5 Ma, 50.6 ± 0.6 Ma and 50.4 ± 0.5 Ma for the quartz diorite, hornblende granodiorite, host pyroxene-bearing granodiorite and its dioritic enclave, respectively. Reverse zoning of plagioclase (spike zone), pyroxene and plagioclase relicts in both of the dioritic enclaves and the granitoids, as well as the mixing trends on plots of major and trace elements, indicate a petrogenesis of magmatic mixing. The relatively low SiO2 (53.43–56.23 wt%) contents, high Mg# values (48–56) and mineral compositions further suggest that precursor magmas of the enclaves are mantle-derived. The dioritic enclaves and granitoids have indistinguishable (87Sr/86Sr)i ratios (0.70460–0.70480) but slightly different εNd(t) values (+1.8 to +3.0 for the dioritic enclaves and +0.2 to +0.6 for the granitoids). The (87Sr/86Sr)i ratios and εNd(t) values plot on the mixing line defined by depleted mantle (DM) and lower crust xenolith from the Southern Lhasa subterrane and further simulation reveals a contribution of >55% from mantle. In the zircon εHf(t) versus δ18O diagram, the dioritic enclaves (εHf(t) = +3.7–+8.5, δ18O = 4.56–7.00‰) and the granitoids (εHf(t) = +1.2–+8.5, δ18O = 5.59–7.21‰) plot around the mixing line defined by zircons from granulite xenolith and a relatively depleted zircon from the dioritic enclaves. Meanwhile, the simple binary mixing calculation based on Hf-O isotopes suggests that the mantle contributions are not <30% (55–65% in average) to the magma of these granitoids. In addition, the synthesized data show the majority of the syn-collisional Gangdese granitoids were also generated by magma mixing processes with similar large quantity of mantle contributions to the Ringqênzê granitoids. Therefore, the extensive and significant mantle contributions in the magma of the collision-related Gangdese granitoids demonstrate considerable continental crust growth during the syn-collisional period. Furthermore, our data combined with previously published data suggest that the ca. 50 Ma samples have highest Ti-in-zircon temperatures (up to 900 °C) and high pyroxene crystallizing temperatures (>1000 °C), whereas other samples show lower Ti-in-zircon temperatures mostly below 750 °C. Because the Gangdese granitoids with unusual high temperatures had been produced dominantly at a very short time (~50 Ma) and the high temperature was related to underplating of mantle materials, we suggest that a slab breakoff was most likely responsible for the formation of the high-temperature magmas and the continental crust growth at the syn-collisional period in collisional orogens.

Evidence of a Late Jurassic Ridge Subduction Event: Geochemistry and Age of the Quartz Mountain Stock, Manastash Inlier, Central Cascades, Washington

AbstractPrevious studies of rocks in California and Oregon suggest that a Late Jurassic ridge subduction event occurred. The geology of the Manastash inlier in Washington State supports this Late Jurassic ridge subduction. The biotite hornblende granodiorite and biotite hornblende tonalite of the Quartz Mountain stock and its cupolas are located in the Manastash inlier, central Cascades, Washington. This stock and its cupolas intrude the low-PT metamorphosed Lookout Mountain Formation turbidites—which are interpreted to have formed in a forearc depositional setting—and the suprasubduction zone Hereford Meadow amphibolite. A new single-crystal sensitive high-resolution ion microprobe–reverse geometry U-Pb age from stock zircons has an age of 157.4 ± 1.2 Ma (2σ). This new age corroborates the published age from the stock and is interpreted to be the crystallization age of the stock. New whole-rock major- and trace-element geochemistry suggests that the granitoids from this stock were generated by shallow ma...

Syn‐collision Biotite Hornblende Granodiorite from the Zedong Area, Tibet: Zircon U–Pb Isotope Chronology, Petro‐geochemistry, and Geodynamic Significance

AbstractCu–Au mineralization is rare in the Jurassic–Early Tertiary batholiths related to the India–Asia collision. Geochemical analysis and U–Pb isotope chronology was carried out on Shuangbujiere biotite hornblende granodiorite from the Zedong area. Zircon grains of the biotite hornblende granodiorite show oscillatory growth zonation and have high Th/U ratios of 1.08–2.39, indicating a magmatic origin for the zircons. Geochrological test yielded a LA‐ICP‐MS U‐Pb age of 51.5±1.0 Ma, suggesting that the emplacement age of the biotite hornblende granodiorite is Early Eocene. The Shuangbujiere biotite hornblende granodiorites have geochemical features characteristic of adakite and are associated with a calc–alkaline metaluminous I‐type granite enriched in Sr, high in Mg# (49.6–54.9) and Sr/Y, and depleted in Y and Yb. These results indicate that this intrusion formation may have been associated with crustal thickening caused by the early collision of the Indian and Eurasian Plates. As the process of crustal thickening continued, the heating of the underplated basaltic magma caused the thickened lower crust amphibolite to dehydrate the melt and form a high‐K calc–alkaline adakitic melt at about 848°C. Meanwhile, magma mixing of the underplated basaltic melt and high‐K calc–alkaline adakitic melt formed a high‐Mg# adakite representative of the sys‐collisional tectonic setting.

Structural and metallogenic map of late Variscan Arbus Pluton (SW Sardinia, Italy)

ABSTRACTThis paper presents the geological, structural and metallogenic map of the Arbus Pluton, a late Variscan composite intrusion belonging to the Corsica-Sardinia Batholith. The pluton is surrounded and crosscut by a wide variety of vein ore deposits. The Arbus Pluton was emplaced at shallow crustal levels at the end of the Variscan Orogeny, along an E–W trending shear zone located in the low-grade external nappe pile of the Sardinian basement. The architecture of the pluton is roughly concentric with a core of cordierite-bearing leucogranites and an outer shell composed of pyroxene-bearing and hornblende granodiorites. New U/Pb dating on zircons of granodiorite yields an emplacement age of 303.7 ± 1.1 which improves previous Rb/Sr and Ar/Ar dating. The map has been compiled on the basis of new geological/structural surveys and petrographical studies coupled with in situ gamma ray spectrometry. All the data-sets have been processed using a geographical information system.

Geochemistry and geochronology of granitoids in the Kibi-Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana

In Ghana the West African Craton is represented by Birimian and Tarkwaian rocks with extensive granitoid bodies. Granitoids from Asamankese area of the Kibi-Winneba volcanic belt, southern Ghana were analysed for major and trace element contents and found to be characterised by highly-fractionated REE, enrichments, in LILE, and depletion in Nb, Ta and Sr. The LILE enrichment relative to strong Nb–Ta depression, indicates that these granitoids were emplaced in an active margin. Based on field relations, geochemical composition and geochronological data, the granitoids from the Kibi-Asamankese area can be divided into three types, namely; the Eburnean biotite granodiorite (2133–2127Ma) and hornblende granodiorite (2147Ma), and the Pre-Eburnean gneissic biotite granite (2193Ma). The geochemical data of the studied rocks plot in the tholeiitic field, whereas on the A/CNK–A/NK diagram, they generally fall within the metaluminous field, with A/CNK values between 0.69 and 0.88. U–Pb dating of zircons in the granitoids yielded ages ranging from 2193 to 2127Ma, which are among the oldest ages obtained from the granitoid plutons in Ghana. Such high-precision geochronological data indicate that magmatism occurred over a time-span of about 70Ma. This provides further evidence that the period 2.1–2.2Ga was one of the important stages of Birimian magmatism that led to the generation of the granitoids. From the above-mentioned ages, it is possible to link the geological activities to crustal processes and establish the cyclic geotectonic evolution in the West African Craton over time as part of an arc-back-arc basin system.

Anatomy of the Cretaceous Hobenzan pluton, SW Japan: Internal structure of a small zoned pluton, and its genesis

Abstract Field, petrographic, geochemical, and K–Ar and U–Pb age data were used to elucidate the internal structure of the Cretaceous Hobenzan pluton, SW Japan, and the processes which generated that structure. The pluton is elongated E–W with dimensions of about 6.5 × 2.0 km (13 km2), and was emplaced at ~ 95 Ma as a pluton in accretionary complexes. The pluton contains an early tonalite, but most of the body consists of later granitoids that show a continuous differentiation series from biotite–hornblende granodiorite (GD) to hornblende–biotite granite (HBG) and biotite granite (BG). The contacts between the GD and HBG are gradational. The pluton provides an exceptional cross-sectional view of a simple cooling magma body. The GD shows no vertical variations in modal and chemical compositions, whereas the HBG displays differentiation from the lowermost exposure to the top of the pluton. Initial Sr isotope ratios (SrI) in the HBG increase from the lower part to the top of the pluton. The granitoids show continuous compositional variations from 65 to 79 wt.% SiO2 (anhydrous basis), and magmatic differentiation was dominantly controlled by crystal fractionation of hornblende and plagioclase. Field, elemental and Sr–Nd isotope data are consistent with limited operation of assimilation with pelitic rocks and fractional crystallization (AFC), in which assimilation increased with higher degrees of differentiation. The Hobenzan pluton retains a history of granitoid magma evolution in a subvolcanic magma reservoir. The GD formed as a rigid sponge, and melt fraction increases inwards from the walls, forming the HBG mush by fractional crystallization, coupled with small degrees of assimilation of adjacent schists. A more evolved and enriched low-density melt segregated from the mushy cumulate of the HBG by incomplete crystal–melt separation, and moved upwards with the assistance of gas-driven filter pressing, as indicated by the presence of miarolitic cavities, thus forming the BG at the roof of the pluton.

New zircon U–Pb ages for erratic emplacement of 2213–2130 Ma Paleoproterozoic calc-alkaline I-type granitoid rocks in the Lawra Volcanic Belt of Northwestern Ghana, West Africa

Paleoproterozoic Birimian granitoid rocks from the Lawra volcanic belt of northwestern Ghana have been analyzed for their major, trace, REE concentrations and their zircon U–Pb age. Based on the mineral assemblages, the calc-alkaline, metaluminous to weakly peraluminous I-type granitoids were classified as: (1) gneissic biotite granite, (2) hornblende granodiorite, (3) biotite granite, (4) two-mica granite and (5) pyroxene hornblende gneiss. The high LaN/YbN (∼4–146) values of the granitoids, characterized by enriched LREE pattern and flat to depleted HREE pattern ((Dy/Yb)N=0.95–3.47), is typical of rocks derived from an evolved magma or partial melting of the depleted mantle. Similarly, the slightly negative Sr- and Eu-anomalies indicate varying degrees of plagioclase fractionation. Their high but varying SiO2 contents (58.1–76.1wt.%), K2O/Na2O ratios (0.17–1.2) and (FeO+Fe2O3)/MgO ratios (0.98–4.02), and low Ce and Ti suggest that they are volcanic arc granites (VAG). The granitoids have zircon U–Pb ages between 2130.8±9.5Ma and 2213±76Ma, and preclude the contamination of the juvenile Birimian crust by notable amounts of reworked Archaean crustal material. However, these ages spanning ∼81Ma were recorded by all the rock types in the study area, with no distinct age difference among them. Accordingly, the area could be described as an undifferentiated terrain that experienced erratic emplacement of pulses of granitic magma during the period. Furthermore, the oldest ages of 2211Ma and 2213Ma recorded in this study suggest that the emplacement of Birimian granitoids in Ghana may have commenced much earlier than previously reported in the literature. The results demonstrate the juvenile character of the granitoid rocks. We therefore infer that the Birimian granitoids of the Lawra volcanic belt formed from large-scale crustal growth process with large amounts of juvenile crust formed from the depleted mantle in an island arc environment.

Origin and evolution of granitoids associated with the Kadiri greenstone belt, eastern Dharwar craton: A history of orogenic to anorogenic magmatism

Different tectonic models have been proposed to explain the Neoarchaean evolution of the eastern Dharwar craton (EDC). Here we present whole-rock elemental and Nd isotopic compositions coupled with zircon U–Pb age and trace elemental data on granitoids associated with the Neoarchaean Kadiri greenstone belt, EDC to track the tectonic evolutionary history of the terrain. Earlier works on volcanic rocks of the Kadiri belt (tholeiitic oceanic plateau basalt, high Mg# andesite and potassic adakite) envisaged continental margin arc–oceanic plateau collision. In this work the oldest recognized granitoid is a 2.56Ga syntectonic, sanukitoid-like hornblende granodiorite enriched in large-ion lithophile as well as ferromagnesian elements. It was probably derived from a metasomatized mantle wedge above a subduction zone. This is followed by syntectonic emplacement of 2.54Ga transitional TTGs and potassic adakitic volcanic rocks. Intrusion of 2.51–2.52Ga crustally derived granites (mostly K-rich; ɛNd=+0.9 to −3.7) marks the end of orogenesis in the area. A convergent orogenic setting characterized by assembly of diverse terranes, repeated slab-break-off and crustal reworking is proposed to interpret the association of various granitoids and volcanic rocks. Finally, intrusion of crustally derived, highly silicic, K-rich A-type granite (ɛNd=−0.6 to −4.8) and mantle-derived syenite occurred in a post-subduction, non-compressive environment during Palaeoproterozoic. Lithospheric delamination and attendant mantle melting and crustal reworking are suggested as possible mechanism for generation of these rocks. The negative ɛNd values and Mesoarchaean Nd depleted mantle model ages of some Neoarchaean to Palaeoproterozoic Kadiri granitoids attest to the presence of older crust in the eastern part of the EDC. The final cratonization of the EDC (2.52–2.50Ga) occurred later than in most of the other cratons.

Geology and Magmatic-Hydrothermal Evolution of the Giant Pebble Porphyry Copper-Gold-Molybdenum Deposit, Southwest Alaska

The Pebble deposit is located ∼320 km southwest of Anchorage, Alaska. It is one of the largest porphyry deposits known with a total resource of 10.78 billion tons (Bt). It comprises the East and West zones, which are approximately equal in size, with slightly lower grade mineralization in the center of the deposit where the peripheries of the two zones merge. The West zone was discovered by Cominco America in 1989 and the East zone was discovered by Northern Dynasty Minerals in 2005. The oldest rock in the Pebble district is the Jurassic-Cretaceous Kahiltna flysch unit, which contains basinal turbidites, interbedded basalt flows, and associated gabbro intrusions. These rocks were intruded between 99 and 96 Ma by coeval granodiorite and diorite sills, followed shortly thereafter by alkalic monzonite intrusions and related breccias. Subalkalic hornblende granodiorite porphyry plutons of the Kaskanak batholith were emplaced at ∼90 Ma. Similar, smaller granodiorite plutons were emplaced around the margins of the batholith and are related to Cu-Au-Mo mineralization. Re-Os dates on molybdenite are between 89.7 and 90.4 Ma. A Late Cretaceous volcanic and sedimentary ”cover sequence” completely conceals the East zone, whereas the West zone is overlain only by glacial sediments and is exposed in one small outcrop. Eocene volcanic rocks and subvolcanic intrusions occur east and southeast of the Pebble deposit and unconsolidated glacial sediments are widespread. The East and West zones represent two coeval hydrothermal centers within a single system. The West zone extends from surface to ∼500-m depth and is centered on four small granodiorite plutons emplaced into flysch, diorite, and granodiorite sills, and alkalic intrusions and breccias. The much higher grade East zone extends to at least 1,700-m depth and is hosted by a larger granodiorite pluton and adjacent granodiorite sills and flysch. The granodiorite plutons merge with depth. On the east side of the deposit, high-grade mineralization has been dropped 600 to 900 m into the NE-trending East graben, where the deposit remains undelineated to the east and to depth. Variations in hypogene grade and metal ratios reflect multiple stages of metal introduction and redistribution. Hornfels related to the Kaskanak batholith formed prior to hydrothermal activity at Pebble and is most intensely developed in flysch. Disseminated and vein-hosted Cu-Au-Mo mineralization, dominated by chalcopyrite and locally accompanied by bornite, formed with potassic alteration in the shallow part of the East zone and with approximately coeval sodic-potassic alteration in the West zone and at depth in the East zone. Illite ± kaolinite alteration overprinted potassic and sodic-potassic alteration throughout the deposit and variably redistributed copper and gold. High-grade copper-gold mineralization is related to advanced argillic alteration controlled by a synhydrothermal brittle-ductile fault zone which overprinted potassic, sodic-potassic, and illite ± kaolinite alteration in the East zone. Advanced argillic alteration comprises a core of pyrophyllite alteration associated with chalcopyrite, bounded to the west by an upward-flaring zone of sericite alteration which contains hypogene bornite, digenite, covellite, and trace enargite and tennantite. Late quartz veins introduced additional molybdenum in several parts of the deposit. Grade-destructive quartz-sericite-pyrite alteration forms a halo to the entire deposit and yields outward to propylitic alteration. A quartz-illite-pyrite cap is preserved in the weakly mineralized center of the deposit. Mineralization at Pebble is predominately hypogene. A thin, incompletely developed zone of supergene mineralization occurs in the West zone and is overlain by a thin leached capping. There is no evidence for paleosupergene mineralization or leaching below the cover sequence in the East zone. Molybdenite contains high concentrations of rhenium throughout the deposit. Elevated palladium concentrations are associated with pyrophyllite alteration in the East zone. The Pebble deposit occurs in one of a number of large, deep-seated magnetic anomalies which are located at the intersection of crustal-scale structures both parallel and at high angles to a mid-Cretaceous magmatic arc. This setting is similar to fertile porphyry environments in northern Chile and suggests that southwestern Alaska is highly prospective for porphyry exploration. The large size and high hypogene grades of the Pebble deposit may reflect a combination of multiple stages of metal introduction with vertically restricted, lateral fluid flow induced by hornfels aquitards in flysch.

Dados de campo e petrográficos de granitoides dos tipos I e A de 1,90 a 1,88 Ga da região central do Cráton amazônico, NE do Estado do Amazonas, Brasil

The SW Presidente Figueiredo district, which is located in the northeastern Amazonas State of the central Amazonian Craton, Brazil, consists of 1890 to 1898 Ma I-type granitoids (Terra Preta Granite, Água Branca Suite), A-type hornblende-bearing syenogranites (Canoas Syenogranite, Mapuera Suite), felsic to intermediate volcanic rocks (Iricoumé Group), and 1883 to 1889 Ma rapakivi granites (São Gabriel Granite, Mapuera Suite) and related rocks (quartz-gabbro-anorthosite and diorite), in addition to Castanhal quartz-monzonite, mylonites, and hornfels. The quartz-diorite facies of Terra Preta Granite were formed by mingling processes between a synplutonic quartz-gabbro dike and a hornblende granodiorite. Partially assimilated globules of Canoas hornblende-bearing syenogranite and their clear contacts with Terra Preta hornblende granodiorite suggest that Canoas Syenogranite is slightly younger than Terra Preta Granite. Canoas Syenogranite xenoliths inside São Gabriel Granite show that the granite is younger than the Canoas Syenogranite. New geologic and petrographic evidence improve the petrological understanding of these rocks and suggest that, in addition to fractional crystallization, assimilation and magma mingling played a role, at least at the local scale, in the evolution and compositional variation of the plutons. Such evidence is found in Terra Preta Granite mingled quartz-diorite, felsic material associated with the Canoas Syenogranite and in the intermediate microgranular enclaves, which exhibit primary biotite in hornblende-bearing rocks, plagioclase dissolution, corrosion of feldspars rims, alkali feldspar mantles, second apatite generation, and high xenocrystal contents in intermediate enclaves formed from the fragmentation of mafic intrusions. Petrographic analyses show that a deformational event recorded in the western part of the study area (with progressive deformation from E to W) is dated between the 1.90 Ga postcollisional magmatism and the intrusions of the São Gabriel Granite and related mafic/intermediate rocks (intra-plate). However, it is extremely necessary to obtain absolute ages for this metamorphic event.

The Fazenda Gavião granodiorite and associated potassic plutons as evidence for Palaeoproterozoic arc-continent collision in the Rio Itapicuru greenstone belt, Brazil

Abstract Several granitic plutons have intruded the Palaeoproterozoic Rio Itapicuru greenstone belt, Sao Francisco craton, Brazil, in the time interval 2163-2080 Ma, but their tectonic significance is poorly understood. The Fazenda Gaviao granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with Archaean migmatite-gneiss basement. The pluton is mostly composed of hornblende granodiorite, occasionally crosscut by syn-plutonic mafic dykes. The FGG is metaluminous, medium- to high-K calc-alkaline with relatively constant silica abundances (SiO2 ∼ 63–66 wt%), high Sr (900–800 ppm) and high Ba (1000–1500 ppm). The associated mafic dykes are ultrapotassic, with high abundances of Ba, Sr, MgO, Ni, Cr, and light rare earth elements, suggesting derivation from partial melts of an enriched mantle source. The FGG originated probably by fractional crystallization from a primitive K-rich mafic magma that interacted with crustal melts. Its zircon U–Pb SHRIMP age of 2106 ± 6 Ma indicates that the FGG is younger than the early (2163-2127 Ma) tonalite-trondhjemite-granodiorite (TTG) and calc-alkaline arc plutons of the greenstone belt, and is closely related in time and space with potassic to ultrapotassic plutons (ca. 2110-2105 Ma). The negative eNd(t) of FGG and coeval K-rich plutons of the Rio Itapicuru greenstone belt contrasts markedly with the positive eNd(t) of the older arc plutons, indicating a major change of isotope signatures in granites of the Rio Itapicuru greenstone belt with time. This isotope shift may be related to magma contamination with older continental material and/or derivation of the parental potassic magma from enriched lithospheric mantle sources. We suggest that the K-rich plutons were emplaced during or shortly after Palaeoproterozoic arc-continent collision.

زمین شناسی، آلتراسیون، کانی سازی و ژئوشیمی محدوده جنوب ارغش (نیشابور)

The Arghash area is located 45 km to southwest of Neyshabour. The subvolcanic rocks in the area consist of biotite hornblende quartz monzodiorite porphyry, hornblende biotite quartz monzodiorite porphyry, hornblende monzonite porphyry, biotite hornblende monzonite porphyry, monzodiorite porphyry and biotite quartz monzodiorite porphyry units. The volcanic rocks consist of hornblende biotite dacite, biotite hornblende dacite, and andesite and pillow lava. The plutonic rocks consist of hornblende monzodiorite, hornblende monzonite, quartz monzonite, hornblende quartz monzodiorite, biotite granodiorite, hornblende granodiorite, biotite hornblende granodiorite, biotite quartz diorite and pyroxene dolerite units. Five types of alteration including propylitic, carbonate, argillic, silicification and sericitic were recognized. Those are subdivided into twelve sub-zones based on the mineral abundances and intensity of alteration. Primary pyrite, 3-4%, is found mainly as disseminated. Secondary mineralization includes limonite, hematite and jarosite. Twenty rock chip and 8 stream sediment samples were collected for geochemical exploration. The samples were analysed for Cu, Zn, Pb, Ag and Sb using Atomic Absorbtion Spectrophotometric (AAS) method. In stream sediment samples, Cu abundance is 34-58 ppm, Zn 45-422 ppm, Pb 28-42 ppm and Ag 2-12 ppm; whereas in rock chip samples, Cu abundance is 8-1137 ppm, Zn 13-411 ppm, Pb 15-97 ppm and Ag 3-32 ppm.

Carboniferous high-potassium I-type granitoid magmatism in the Eastern Pontides: The Gümüşhane pluton (NE Turkey)

The Gümüşhane pluton, a high-K calc-alkaline I-type granodiorite/granite complex, forms an important component of the pre-Liassic basement of the Eastern Pontides (NE Turkey). In its eastern part, the pluton shows a compositional zonation ranging from biotite–hornblende granodiorite in the NW through biotite–hornblende granite to leucogranite/granophyre in the SE. Numerous mafic microgranular enclaves (up to ∼ 40 cm in diameter) suggest the former presence of globules of mafic melt during crystallization. Emplacement of the pluton occurred during the latest Early Carboniferous, as shown by the 320 ± 4 Ma 40Ar– 39Ar biotite/hornblende and 324 ± 6 Ma LA-ICP-MS U–Pb zircon ages. In Harker diagrams, samples of the different rock types exhibit well-defined data trends. With increasing SiO 2, the abundances of TiO 2, Al 2O 3, Fe 2O 3 tot, MnO, MgO, CaO, P 2O 5 and Sc decrease, but those of K 2O and Rb increase. However, the variations of Sr, Ba, (La/Yb) cn, Sr/Y and ∑ REEs vs. SiO 2 form distinctive groupings, which cannot be explained by a simple fractional crystallization. Chondrite-normalized (cn) REE patterns of granodiorite/granite samples show concave-upward shapes with (La/Yb) cn ranging from 5.2 to 12.4 and Eu/Eu* from 0.84 to 0.47, while there is almost no fractionation of the middle REE relative to the heavy REE. In primitive mantle-normalized element concentration diagrams, all rocks display marked negative anomalies in Ba, Nb/Ta, Sr, P and Ti, but positive anomalies in K and Pb. These geochemical features imply a fractionating mineral assemblage of clinopyroxene, amphibole and plagioclase without significant involvement of garnet. The granophyres are, on the other hand, characterized by higher K 2O/Na 2O and Rb/Sr ratios, lower (La/Yb) cn ratios (1.3 to 4.8) and more pronounced negative anomalies in Ba, Nb/Ta, Sr, Eu, P and Ti. Initial ε Nd values range from − 3.78 to − 5.30 and Nd model ages from 1.38 to 163 Ga. The magmas of the granite/granodiorite portion were probably generated by partial melting of high-potassic amphibolitic rocks, and those of the granophyres by a relatively felsic micaceous crustal source. The Gümüşhane pluton was emplaced at the wake of the low-pressure–high-temperature metamorphism, and is regarded as a late phase of Hercynian orogeny in the Eastern Pontides.

The Cluanie granodiorite, NW Highlands of Scotland: a late Caledonian pluton of trondhjemitic affinity

Synopsis The Cluanie Pluton is a late Caledonian granitoid emplaced into the Glenfinnan Division of the Moine Supergroup in the NW Scottish Highlands. A field investigation of the pluton and its internal facies is presented along with new major- and trace-element whole-rock XRF analyses, and geobarometric and geothermometric studies. Cluanie is predominantly composed of hornblende granodiorite characterized by varying concentrations of distinctive alkali feldspar megacrysts, with minor amounts of biotite granodiorite and rare mingled porphyritic microgranodiorite. The alkali feldspar megacrysts appear to be magmatic in origin. Rare spectacular pegmatitic concentrations most likely represent physical accumulation of the megacrysts. The pluton is geochemically a high Na/K trondhjemite, the only such pluton known among the Newer Granites of Scotland. On the basis of geochemical evidence and a comparison with partial melting experiments, we propose that the magmas were derived by fluid-rich melting of an amphibolitic source leading to relatively low temperature magmas which were significantly contaminated by Moine metasediments. The pluton was emplaced in the mid crust at about 4.3 kbar during an episode of dextral shear on the Glen Glass Fault related to regional strike-slip faulting on the Great Glen Fault system at c . 425 Ma.

Isotopic and geochemical evidence for differentiation and crustal contamination from granitoids of the Berens river subprovince, Superior province, Canada

Nd isotope and geochemical data are presented for biotite tonalite, hornblende tonalite, hornblende granodiorite, biotite granite and peraluminous granite from the Archean Berens River subprovince of the Superior province in northwestern Ontario, Canada. The older tonalitic suites were synchronous with greenstone belt volcanism and were followed by granodioritic and granitic intrusions. The suites vary from 57 to 74% SiO 2, are light rare-earth element (REE) enriched, with variable Eu and Nb anomalies and heavy REE depletion among the tonalites. The Nd isotope compositions for the granitoids vary from depleted values of ɛ Nd = +1.5 (tonalites) to enriched values of −1.5 (peraluminous granite). The range of isotopic composition supports a model where the granitoids were emplaced into, contaminated by, and locally melted an older pre-existing Archean crust (ca. 3.0 Ga). The Nd isotope compositions of the granites and the tonalites decrease towards the north (increased crustal contamination) away from the greenstone belts that form the southern margin. This implies a thickening of the crust towards the north and is consistent with an Andean-style convergent margin in which oceanic crust subducted northwards beneath an older Archean crustal plate. Crustal contamination increased heavy REE contents in the tonalites and decreased the Sr/Y ratios for all granitoids. Failure to account for this crustal contamination can lead to errors in estimating the degree of partial melting based on the Sr/Y ratio. Compositional differences between the biotite tonalites and hornblende tonalites likely reflect different degrees of partial melting of a garnet-bearing amphibolite source.

Petrogenesis of the Puerto Edén Igneous and Metamorphic Complex, Magallanes, Chile: Late Jurassic syn-deformational anatexis of metapelites and granitoid magma genesis

A suite of schists, gneisses, migmatites, and biotite granitoids from the Puerto Edén Igneous and Metamorphic Complex (PEIMC) and biotite–hornblende granitoids of the South Patagonian batholith (southern Chile) has been studied. For that purpose, the chemistry of minerals and the bulk rock composition of major and trace elements including Rb–Sr and Sm–Nd isotopes were determined. Mineralogical observations and geothermobarometric calculations indicate high-temperature and low-pressure conditions (ca. 600–700 °C and 3 to 4.5 kbar) for an event of metamorphism and partial melting of metapelites in Late Jurassic times (previously determined by SHRIMP U–Pb zircon ages). Structures in schists, gneisses, migmatites and mylonites indicate non-coaxial deformation flow during and after peak metamorphic and anatectic conditions. Andalusite schists and sillimanite gneisses yield initial 87Sr/ 86Sr ratios of up to 0.7134 and εNd 150 values as low as − 7.6. Contemporaneous biotite granitoids and a coarse-grained orthogneiss have initial 87Sr/ 86Sr ratios between 0.7073 and 0.7089, and εNd 150 values in the range − 7.6 to − 4.4. This indicates that metamorphic rocks do not represent the natural isotopic variation in the migmatite source. Thus, a heterogeneous source with a least radiogenic component was involved in the production of the biotite granitoids. The PEIMC is considered as a segment of an evolving kilometre-sized and deep crustal shear zone in which partial melts were generated and segregated into a large reservoir of magmas forming composite plutons in Late Jurassic times. A biotite–hornblende granodiorite and a muscovite–garnet leucogranite show initial 87Sr/ 86Sr ratios of 0.7048 and 0.7061, and εNd 100 values of − 2.6 and − 1.8, respectively, and are thus probably related to Early Cretaceous magmas not involved in the anatexis of the metasedimentary rocks.

Development of igneous layering during growth of pluton: The Tarçouate Laccolith (Morocco)

We discuss the significance of igneous layering with respect to pluton growth processes. The case study is the Tarçouate Laccolith (Morocco), whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves, contrasting with peripheral, non-layered biotite granodiorites with low amount of enclaves. Rhythmic layering, with modal grading, cross-stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves. Its steep dips ≥ 45° result from tilting that occurred above solidus conditions, as indicated by sub-vertical and synmagmatic granite, aplite and monzodiorite dykes cutting across the layering. The systematic association of igneous layering with mafic enclaves in calc-alkaline plutons suggests that layering originates from recurrent injection of mafic magma. Viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the Tarçouate Laccolith. Intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection, formation of mafic enclaves and development of igneous layering through protracted crystallization.

Telescoping of three distinct magmatic suites in an orogenic setting: Generation of Hercynian igneous rocks of the Albera Massif (Eastern Pyrenees)

The petrogenesis of the Hercynian magmatic rocks of the Albera Massif (eastern Pyrenees) is investigated in this work, in order to establish spatial and temporal relationships between deformation episodes, high temperature–low pressure metamorphism and igneous activity, by using fieldwork together with petrological and geochemical methods. Hercynian magmatic rocks comprise (i) calc-alkaline granitoids of La Jonquera composed mainly by biotite, and biotite–hornblende granodiorites; (ii) the leucogranitic pluton of El Castellar; (iii) small mafic complexes composed mainly by amphibole-bearing gabbros and diorites, and (iv) stocks of anatectic leucogranites. Hercynian deformation structures can be classified in two phases, D1 and D2, both reflecting progressive deformation (first compressional, then transpressional) closely linked to the development of regional metamorphism. Spatial relationships between igneous and metamorphic rocks suggest that the emplacement of magmatic bodies was a syn-D2 event, and was concomitant with the metamorphic climax of the country rocks. The compositional and textural variation of the rocks of the mafic complexes is interpreted to reflect fractional crystallization of hydrous mafic magma with a composition similar to that of calc-alkaline basalts, documenting the involvement of basaltic magmas during the generation of Hercynian crustal granitoids. The anatectic leucogranites crystallized from peraluminous magmas produced by partial melting of metasediments and orthogneisses similar to those found in the local migmatite zone. The similar Sr and Nd isotope signatures of the El Castellar leucogranitic pluton, some anatectic leucogranites, and the orthogneissess supports the hypothesis that these leucogranites were generated by partial melting of the orthogneisses. Based on field, petrographic, geochemical and isotopic lines of evidence, La Jonquera granodiorite can be clearly distinguished from the gabbros, and from the anatectic and El Castellar leucogranites. The high CaO content of the granodiorites precludes an origin by partial melting of local metamorphic rocks, and it is suggested that the calc-alkaline granitoids (La Jonquera) were produced by fractional crystallization of a granodioritic magma generated by partial melting of metatonalites in the lower crust. Although the magmatic rocks were emplaced contemporaneously (at about 280 My based on Rb–Sr whole-rock data), they reflect the occurrence of three genetically distinct igneous suites: one granodioritic, one leucogranitic and one mafic. The metamorphic and igneous evolution documented in the Albera Massif bears strong similarities with those described in the neighbouring Hercynian domains from the Pyrenees. The Hercynian regional HT–LP metamorphism and magmatism in the Pyrenees are two processes linked to the same deep-seated thermal anomaly that was generated in a transpressive context.

Geology of the plutonic basement rocks of Stewart Island, New Zealand

Exposures of basement rocks on Stewart Island provide a c. 70 km long by 50 km wide map of part of the Median Batholith that spans the margin of the Western Province. Because of their distance from the present plate boundary, these rocks are relatively unaffected by Cenozoic tectonism, allowing examination of unmodified Carboniferous‐Cretaceous relationships within the Median Batholith. Thirty individual plutons (>c. 20 km2) have been mapped along with numerous relatively small intrusions (<c. 5 km2). The large plutons form 85–90% of the Median Batholith on Stewart Island while the many smaller intrusions comprise 10–15%, mostly in the north. Lithologies include: biotite ± minor hornblende granodiorite, granite and leucogranite with accessory titanite ‐ magmatic epidote and allanite (c. 50%); biotite ± muscovite ± garnet granite with S‐type affinities (c. 10%); alkaline quartz monzonite, granite, and alkali feldspar granite with rare aegirine and blue‐green amphibole (c. 3%); quartz monzodiorite and diorite with hornblende > biotite (c. 23%); gabbro and anorthosite (c. 12%) and ultramafic rocks (c. 2%). U‐Pb zircon and monazite dating indicates that c. 12% of these plutonic rocks were emplaced during the Carboniferous between 345 and 290 Ma, c. 20% in the Early‐Middle Jurassic at c. 170–165 Ma, c. 30% in the latest Jurassic to earliest Cretaceous between 152 and 128 Ma, and c. 38% in the Early Cretaceous between 128 and 100 Ma. The distribution of Pegasus Group schists and peraluminous granitoid rocks indicates that the northern limit of extensive early Paleozoic Western Province basement is located either within the Gutter Shear Zone or at the Escarpment Fault, 10–15 km south of the Freshwater Fault System previously thought to mark this boundary. Carboniferous and Middle Jurassic magmatism extended plutonic basement northwards as far as the Freshwater Fault System, while further magmatism during the latest Jurassic and earliest Cretaceous produced the basement north of the Freshwater Fault System. The focus of Early Cretaceous plutonism then returned southwards into the Western Province, although the older basement in this area was only involved in the genesis of subordinate peraluminous plutonism at this time and not the more extensive metaluminous rocks. The Escarpment Fault disrupted this c. 40 km wide section across the margin of the Western Province at c. 110–100 Ma.