Pétrologie des roches volcaniques de sillon de roches vertes archéennes de Matagami–Chibougamau à l'ouest de Chapais (Abitibi est, Québec), 2. Le groupe hautement potassique d'Opémisca

1986 ◽  
Vol 23 (8) ◽  
pp. 1169-1189 ◽  
Author(s):  
Christian Picard ◽  
Michel Piboule
Keyword(s):  
Fractional Crystallization ◽  
Crustal Contamination ◽  
Major Elements ◽  
Geochemical Data ◽  
Continental Margins ◽  
Garnet Lherzolite ◽  
Calc Alkaline ◽  
Volatile Elements ◽  
High K ◽  
Active Continental Margins

In the western part of the Chapais syncline (Abitibi East, Quebec), the Opemisca Group unconformably overlies the Roy Group at a low angle. It consists of a thick turbidite sequence covered by an interdigitated sequence of lavas and alluvial cone sediments. The subaerial lavas include two sequences evolving from porphyric metabasalts to metatrachyandesites and porphyric metatrachytes (lower sequence) or to K-rich aphanitic meta-andesites (upper sequence). These lavas, with calc-alkaline to shoshonitic affinity, have high K2O, Ba, Sr, and Th contents and show highly enriched LREE spectra.The behaviour of major elements, trace elements, and lanthanides suggests an origin from partial melting of a mantle source consisting of a garnet lherzolite enriched in K, Sr, Rb, Ba, and Th by volatile elements and also by crustal contamination and by fractional crystallization mechanisms. The evolution of the lavas of the lower sequence, progressively deficient in Y, seems to have been controlled by fractional crystallization of a plagioclase, clinopyroxene, and olivine mixture; this was followed for the metatrachyandesites and metatrachytes by high H2O activity of a feldspar, amphibole, titanomagnetite, and apatite mixture. The evolution of lavas enriched in Y in the upper sequence seems to have been controlled by weak H2O activity of the anhydrous plagioclase, clinopyroxene, and olivine assemblage.The petrographic and geochemical data suggest an emplacement similar to that occurring on the active continental margins of the central Andes and implies the existence of a late-stage ensialic arc. [Translated by the journal]

scholarly journals GEOCHEMICAL CHARACTERISTICS OF THE ERENLERDAGI VOLCANICS, KONYA, CENTRAL TURKEY

2017 ◽  
Vol 50 (4) ◽  
pp. 2057
Author(s):  
C. Uyanık ◽  
K. Koçak
Keyword(s):  
Fractional Crystallization ◽  
Magma Mixing ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
High K ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
Central Turkey ◽  
Pyroclastic Fall

Late Miocene to Pliocene volcanism produced lava domes with mafic microgranular enclaves (MMEs), nuée ardentes and pyroclastic fall and flow (ignimbrites) deposits in the WSW and NW of Konya city. All samples are predominantly high K-calc alkaline in composition but calc-alkaline and shoshonitic composition also exist. The felsic volcanics are mainly dacite, andesite, basaltic trachyandesite and rare trachyandesite in compositon. But, the MMEs have basaltic andesite and andesite compositon. SiO2 increases with decreasing TiO2, FeOt, MgO and CaO, suggesting fractional crystallization of mafic minerals. All samples have fractionated chondritenormalised REE pattern (La/YbN: 6.7-18.1), and negative Eu anomaly (Eu/Eu*: 0.67- 0.89), indicating plagioclase fractionation. In primitive mantle-normalized spider diagram, the samples show an enrichment in large ion litophile elements (LILE) such as Cs and Ba, and depletion in high field strength elements (HFSE), e.g. Dy and Y. They show negative Nb, Ta and Ti anomalies, indicating a subduction signature for their genesis. Based on geochemical data, the volcanics are suggested to have been formed by Assimilation-Fractional Crystallization (AFC) and/or magma mixing process. Various geotectonic diagrams imply volcanic arc to post collisional setting for the samples.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

2021 ◽  
pp. 1-22
Author(s):  
Jia-Hao Jing ◽  
Hao Yang ◽  
Wen-Chun Ge ◽  
Yu Dong ◽  
Zheng Ji ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Ne China ◽  
Asthenospheric Mantle ◽  
High K ◽  
Wide Range ◽  
Great Xing’An Range ◽  
Subducting Slab

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

Release of Uranium from Uraninite in Granites Through Alteration: Implications for the Source of Granite-Related Uranium Ores

2021 ◽  
Author(s):  
Long Zhang ◽  
Zhenyu Chen ◽  
Fangyue Wang ◽  
Noel C. White ◽  
Taofa Zhou
Keyword(s):  
Uranium Concentration ◽  
Geochemical Data ◽  
Uranium Deposits ◽  
Bulk Rock ◽  
Calc Alkaline ◽  
Alkaline Granite ◽  
Compositional Evolution ◽  
High K ◽  
Backscattered Electron ◽  
Uranium Sources

Abstract Uraninite is the main contributor to the bulk-rock uranium concentration in many U-rich granites and is the most important uranium source for granite-related uranium deposits. However, detailed textural and compositional evolution of magmatic uraninite in granites during alteration and associated uranium mobilization have not been well documented. In this study, textures and geochemistry of uraninites from the Zhuguangshan batholith (South China) were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The geochemical data indicate that the Longhuashan and Youdong plutons are peraluminous leucogranite, the Changjiang pluton is highly fractionated high-K calc-alkaline granite, and the Jiufeng pluton belongs to a high-K calc-alkaline association. Uraninites from the Longhuashan and Youdong granites have lower concentrations of ThO2 (0.9–4.0 wt %) and rare earth elements (REE)2O3 (0.1–1.0 wt %) than those from the Changjiang and Jiufeng granites (ThO2 = 4.4–7.6 wt %, REE2O3 = 0.7–5.1 wt %). Uraninites observed in the Longhuashan, Youdong, Changjiang, and Jiufeng granites yielded chemical ages of 223 ± 3, 222 ± 2, 157 ± 1, and 161 ± 2 Ma, respectively. The samples (including altered and unaltered) collected from the Longhuashan, Youdong, and Changjiang granites are characterized by highly variable whole-rock U concentrations of 6.9 to 44.7 ppm and Th/U ratios of 0.9 to 7.0, consistent with crystallization of uraninite in these granites being followed by uranium leaching during alteration. Alteration of uraninite, indicated by altered domains developing microcracks and appearing darker in backscattered electron (BSE) images compared to unaltered domains, results in the incorporation of Si and Ca and mobilization of U. In contrast, the least altered samples of the unmineralized Jiufeng granite have low U concentrations (5.3–16.4 ppm) and high ΣREE/U (13.6–49.4) and Th/U ratios (2.1–5.6), which inhibit crystallization of uraninite, as its crystallization occurs when the U concentration is high enough to exceed the substitution capacity of other U-bearing minerals. These results indicate that the Longhuashan, Youdong, and Changjiang granites were favorable uranium sources for the formation of uranium deposits in this area. This study highlights the potential of uraninite alteration and geochemistry to assist in deciphering uranium sources and enrichment processes of granite-related uranium deposits.

scholarly journals Widespread Permian granite magmatism in Lower Austroalpine units: significance for Permian rifting in the Eastern Alps

2020 ◽  
Vol 113 (1) ◽  
Author(s):  
Sihua Yuan ◽  
Franz Neubauer ◽  
Yongjiang Liu ◽  
Johann Genser ◽  
Boran Liu ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Eastern Alps ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Three Samples ◽  
High K ◽  
Icp Ms ◽  
Granite Magmatism ◽  
Austroalpine Unit ◽  
Granite Suite

Abstract The Grobgneis complex, located in the eastern Austroalpine unit of the Eastern Alps, exposes large volumes of pre-Alpine porphyric metagranites, sometimes associated with small gabbroic bodies. To better understand tectonic setting of the metagranites, we carried out detailed geochronological and geochemical investigations on the major part of the porphyric metagranites. LA–ICP–MS zircon U–Pb dating of three metagranites sampled from the Grobgneis complex provides the first reliable evidence for large volumes of Permian plutonism within the pre-Alpine basement of the Lower Austroalpine units. Concordant zircons from three samples yield ages at 272.2 ± 1.2 Ma, 268.6 ± 2.3 Ma and 267.6 ± 2.9 Ma interpreted to date the emplacement of the granite suite. In combination with published ages for other Permian Alpine magmatic bodies, the new U–Pb ages provide evidence of a temporally restricted period of plutonism (“Grobgneis”) in the Raabalpen basement Complex during the Middle Permian. Comparing the investigated basement with that of the West Carpathian basement, we argue that widespread Permian granite magmatism occurred in the Lower Austroalpine units. They belong to the high-K calc-alkaline to shoshonitic S-type series on the base of geochemical data. Zircon Hf isotopic compositions of the Grobgneis metagranites show εHf(t) values of − 4.37 to − 0.6, with TDM2 model ages of 1.31–1.55 Ga, indicating that their protoliths were derived by the recycling of older continental crust. We suggest that the Permian granitic and gabbroic rocks are considered as rifted-related rocks in the Lower Austroalpine units and are contemporaneous with cover sediments.

Sr and O isotope constraints on source and crustal contamination in the high-K calc-alkaline and shoshonitic neogene volcanic rocks of SE Spain

Lithos ◽  
1999 ◽  
Vol 46 (4) ◽  
pp. 773-802 ◽  
Author(s):  
R. Benito ◽  
J. López-Ruiz ◽  
J.M. Cebriá ◽  
J. Hertogen ◽  
M. Doblas ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Calc Alkaline ◽  
Se Spain ◽  
High K ◽  
O Isotope

Geochemistry, zircon geochronology, and isotopic systematics of the Zhanbuzhale granites in the East Kunlun, Qinghai Province, northwestern China: implications for the tectonic setting

2020 ◽  
Vol 57 (2) ◽  
pp. 275-291
Author(s):  
Hao-Ran Li ◽  
Ye Qian ◽  
Feng-Yue Sun ◽  
Liang Li
Keyword(s):  
Tectonic Setting ◽  
Alkali Feldspar ◽  
Northwestern China ◽  
Geochemical Data ◽  
Calc Alkaline ◽  
Qinghai Province ◽  
East Kunlun ◽  
Initial Stage ◽  
High K ◽  
Tethys Ocean

The Zhanbuzhale region, in the Eastern Kunlun Orogen of northwestern China, is characterized by large volumes of Phanerozoic granitoid rocks and is an ideal region for investigating the tectonic evolution of the Paleo-Tethys system. However, the exact timing of the final closure of the Paleo-Tethys Ocean and initial continental collision remains controversial because of a lack of precise geochronological and detailed geochemical data. In this paper, we report new zircon U–Pb ages and mineralogical, petrographic, and geochemical data for samples of Middle Triassic granodiorite and alkali feldspar granite from the Zhanbuzhale region. The zircon U–Pb ages indicate that the granodiorite and alkali feldspar granite formed at 239 and 236 Ma, respectively. The granodiorites are high-K calc-alkaline, metaluminous, high Sr content, high Sr/Y ratios, low Y content, and show adakite-like affinities. The alkali feldspar granites display high SiO2, extremely low MgO, and low Zr+Nb+Ce+Y contents as well as low Fe2O3t/MgO ratios, showing metaluminous to peraluminous and high-K calc-alkaline features. Geochemical and petrological characteristics of the alkali feldspar granites suggest that they are highly fractionated I-type granites. The granodiorites and alkali feldspar granites have zircon εHf(t) values ranging from –2.26 to –0.18, and from –2.17 to +2.18, respectively. Together with regional geological data, we propose that the Triassic (approximately 239–236 Ma) granitoids were generated during the later stages of northward subduction of the Paleo-Tethys oceanic plate, and that the initial stage of collision between the East Kunlun and the Bayan Har–Songpan Ganzi terrane occurred at approximately 236–227 Ma.

Morphology and geochemistry of zircons from late Mesozoic igneous complexes in coastal SE China: implications for petrogenesis

2002 ◽  
Vol 66 (2) ◽  
pp. 235-251 ◽  
Author(s):  
X. Wang ◽  
W. L. Griffin ◽  
S. Y. O’Reilly ◽  
X. M. Zhou ◽  
X. S. Xu ◽  
...  
Keyword(s):  
Growth Stages ◽  
Continental Margins ◽  
Calc Alkaline ◽  
Mafic Rocks ◽  
Late Mesozoic ◽  
Igneous Complexes ◽  
Basaltic Magmas ◽  
Morphological Indices ◽  
Active Continental Margins ◽  
Se China

AbstractThe Pingtan and Tonglu igneous complexes in SE China are typical of the calc-alkaline series developed at active continental margins. These two complexes are dominated by felsic rocks, temporally and spatially associated with minor mafic rocks. Morphological and trace-element studies of zircon populations in rocks from each of these complexes show that the zircon populations may be divided into 3–4 distinct growth stages, characterized by different distributions of morphological indices (Ipr, Ipy and Iel), and different contents of the substituting elements (Hf, U, Th, Y and P). The four growth stages recognized in the zircons are believed to have formed successively in the magma chamber, during the emplacement, and in the early and later stages of magma consolidation, respectively. All four stages are recognized in the plutonic Pingtan complex, whereas the stages 3 and 4 are less developed in the volcanic/subvolcanic Tonglu complex. Based on the chemistry and morphology of the different zircon populations of the Pingtan and Tonglu complexes, it is suggested that basaltic magmas underplating at the boundary between crust and mantle caused partial melting of the mid–lower crust and produced granitoid magmas. Subsequently, mixing between magmas was important.

An early Proterozoic volcanic arc succession in southeastern Wyoming

1984 ◽  
Vol 21 (4) ◽  
pp. 415-427 ◽  
Author(s):  
Kent C. Condie ◽  
Craig A. Shadel
Keyword(s):  
Fractional Crystallization ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Geochemical Data ◽  
Alkaline Basalt ◽  
Calc Alkaline ◽  
Early Proterozoic ◽  
Enriched Mantle ◽  
Sierra Madre ◽  
Felsic Volcanic

The Green Mountain Formation of early Proterozoic age in the Sierra Madre Range of southeastern Wyoming comprises a bimodal mafic and felsic volcanic assemblage. The rocks, which are chiefly breccias, agglomerates, flows, and volcaniclastic sediments, represent both subaerial and submarine eruptions and in part were redeposited in fluvial and nearshore marine environments. Volcanic rocks are clearly calc-alkaline in character and share a large number of geochemical features in common with continental-margin arcs or evolved oceanic-arc systems.The low Mg numbers and Ni contents of the basalts require 30–40% olivine fractional crystallization, and the high contents of the most incompatible elements, high (La/Sm)N ratios, and low Zr/Nb ratios require an undepleted or enriched mantle source. Geochemical data are consistent with an origin for the felsic volcanics and associated Encampment River granodiorite by shallow fractional crystallization of calc-alkaline basalt in a tectonic setting similar to modern arc systems. The near absence of andesites may reflect the retention of andesitic magma in crustal reservoirs during fractional cyrstallization.

Stratigraphy, geochemistry, and petrology of the Upper Cretaceous volcanic arc sequence north of Istanbul, Pontides, NW Turkey

2021 ◽  
Author(s):  
Cemre Ay ◽  
Gürsel Sunal ◽  
Aral I. Okay
Keyword(s):  
Black Sea ◽  
Upper Cretaceous ◽  
High Ratio ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
The Black Sea ◽  
Calc Alkaline ◽  
High K ◽  
Nw Turkey ◽  
Pattern Display

<p>Upper Cretaceous arc-related volcanic and volcanoclastic units overlying the Paleozoic sedimentary rocks of the Istanbul Zone are a key unit related to the opening of the Black Sea as a back-arc basin. They formed as a result of north dipping subduction of the Neo-Tethys Ocean beneath Laurasia. We studied the Upper Cretaceous volcanic units north of Istanbul along several stratigraphic sections, and present new geochemical data from the volcanic rocks in order to understand Cretaceous geodynamic evolution of the İstanbul Zone.</p><p>The Upper Cretaceous  volcanic units north of Istanbul are divided into two formations. At the base there is a fore-arc turbidite succession,the İshaklı Formation, which is made up of volcaniclastic sandstone, shale, marl, tuff, debris flow horizons and epiclastic rocks of Turonian age. The İshaklı Formation is conformably overlain by the volcanoclastics,  tuffs, andesite and basalt lavas and agglomerates- the Riva Formation, which represents the arc/ intra-arc series.</p><p>Geochemically, basalts and basaltic andesites of the Riva Formation are low K calc-alkaline to medium-high K calc-alkaline and with magnesium numbers ranging from 32.6% to 51.5% Primitive mantle normalized spider diagram of trace elements show  enrichment in LILE elements (K, Rb, Sr, Cs, Ba, Th and U) and depletion in HFS elements ( Nb,Ta and Ti) . The high ratio of LILE/ HFS and negative Nb-Ta anomalies indicate that the volcanism evolved in subduction setting. Chondirite-normalized REE pattern display slight negative Eu anomalies and the La/Yb ratios of the samples range between 2,76 and 4,89. Our new geochemical, stratigraphical and the regional geological data suggest that north of Istanbul there was a transition from fore-arc deposition to arc volcanism during the Late Cretaceous opening of the Western Black Sea.  Considering the whole Pontide – Sredna-Gora Upper Cretaceous magmatic arc, it can be stated that calc-alkaline volcanism developed in relation to northward subduction of the Neo-Tethys oceanic lithosphere during the Turonian, and may have passed into high-K calc alkaline and shoshonitic magmatism as a result of the progressive extentional tectonism during the Campanian.</p>

Petrology and geochemistry of volcanic rocks of the Cerro Galan caldera, northwest Argentina

1989 ◽  
Vol 126 (5) ◽  
pp. 515-547 ◽  
Author(s):  
P. W. Francis ◽  
R. S. J. Sparks ◽  
C. J. Hawkesworth ◽  
R. S. Thorpe ◽  
D. M. Pyle ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Source Region ◽  
Crustal Contamination ◽  
Crustal Material ◽  
Magma Chambers ◽  
Northwest Argentina ◽  
Incompatible Elements ◽  
High K ◽  
Uniform Region ◽  
Compositional Zonation

AbstractAt least 2000 km3 of relatively uniform dacitic magma have been erupted from the Cerro Galan caldera complex, northwest Argentina. Between 7 and 4 Ma ago several composite volcanoes predominantly of dacitic lava were constructed, and several large high-K dacitic ignimbrites were erupted. 2.2 Ma ago the > 1000km3 Cerro Galan ignimbrite was erupted. The predominant mineral assemblage in the ignimbrites is plagioclase-biotite-quartz-magnetite-ilmenite; the Cerro Galan ignimbrite also contains sanidine. Fe-Ti oxide minerals in the Cerro Galan ignimbrite imply temperatures of 801–816 °C. Plagioclase phenocrysts in the ignimbrites typically have rather homogeneous cores surrounded by complex, often oscillatory zoned, rims. Core compositions show a marked bimodality, with one population consisting of calcic cores surrounded by normally zoned rims, and a second of sodic cores surrounded by reversely zoned rims. The older ignimbrites do not show systematic compositional zonation, but the Cerro Galan ignimbrite exhibits small variations in major elements (66–69% SiO2) and significant variations in Rb, Sr, Ba, Th and other trace elements, consistent with derivation from a weakly zoned magma chamber, in which limited fractional crystallization occurred. The ignimbrites have 87Sr/86Sr = 0.7108–0.7181; 143Nd/144Nd = 0.51215–0.51225, and δ18O = + 10 to + 12.5, consistent with a significant component of relatively non-radiogenic crust with high Rb/Sr and enriched in incompatible elements. Nd model ages for the source region are about 1.24 Ga. 87Sr/86Sr measurements of separated plagioclases indicate that Anrich cores have slightly lower 87Sr/86Sr than less calcic plagioclases, suggesting a small degree of isotopic heterogeniety in different components within the magmas. Pb isotope data for plagioclase show restricted ranges (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb = 18.87–18.92, 15.65–15.69 and 39.06–39.16 respectively), and suggest derivation from Proterozoic crustal material(> 1.5 Ga).Contemporaneous satellite scoria cones and lavas are high-K basalts, basaltic andesites and andesites with SiO2 = 51–57%; K2O = 2–3% and normative plagioclase compositions of An37–48, and may be derived from a mantle source containing both ‘subduction zone’ and ‘within plate’ components. 87Sr/86Sr ranges from 0.7055 to 0.7094 and 143Nd/144Nd from 0.51250 to 0.51290. Variation diagrams such as MgO: SiO2 show two trends, one indicating closed system fractional crystallization and the other crustal contamination. AFC modelling of the open system rocks indicates a parental mantle-derived mafic magma which is itself enriched in K, Rb, Ba, U, Ta/Sm, Ta/Th and Sr, and has 87Sr/86Sr = 0.705–0.706, while the contaminant need not be more radiogenic than the dacitic ignimbrites.The Cerro Galan dacitic magmas are interpreted in terms of a deep and uniform region of the central Andean continental crust repeatedly melted by emplacement of incompatible-element-enriched, mantle-derived mafic magmas, a proportion of which may also have mixed with the dacite magmas. A component of the crustal material had a Proterozoic age. The magmas derived by crustal melting were also enriched in incompatible elements either by crystal/liquid fractionation processes, or by metasomatism of their source regions just prior to magma generation. Much of the crystallization took place in the source region during the melting process or in mid-crustal magma chambers. The magmas may have re-equilibrated at shallow levels prior to eruption, but only limited compositional zonation developed in high-level magma chambers.

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