scholarly journals Geotermobarometria y Quimica Mineral del Pluton Sienito "Pajeú" Serra Talhada, Pernambuco, NE de Brasil

1998 ◽  
Vol 25 (1) ◽  
pp. 61
Author(s):  
CRISTINA NANCY REYES
Keyword(s):  
Alkali Feldspar ◽  
Mineral Chemistry ◽  
Northeastern Brazil ◽  
Calc Alkaline ◽  
Calcic Plagioclase ◽  
Perfect Agreement ◽  
Fine Grained ◽  
Microgranular Enclaves ◽  
High Alkali ◽  
Opaque Minerals

The Pajeu Syenitic Complex, Serra Talhada, Pernambuco province, northeastern Brazil is tectonically emplaced within the framework of Neoproterozoic (Brasiliano). In the present work were studied whole rock and specific mineral chemical data (85’24” – 816’31” S and 3819’8” – 3836’2” W). Two distinct petrographic facies have been identified. The predominant porphyritic syenite facies is characterized by perthite microcline megacrysts (up to 8 cm long) and fine grained syenite; both facies have distributed melanocratic microgranular enclaves of syenitic composition. The mineral assemblage comprising alkali feldspar, plagioclase, quartz, biotite, hornblende and accessory amounts of zircon, opaque minerals, epidote, allanite, sphene etc. the geochemical signatures define overlapping calc-alkaline and shoshonitic affinities and metaluminous to peraluminous nature. The complex is characterized by silica enrichment (62.2% - 72.4%), moderate alumina (14% - 16.6%) and high alkali abundance (8.6% - 9.1%). The enclaves have low silica (54.2% - 56.4%) and corresponding enrichment in mafic phases. High alkali abundance, preponderance of K2O over Na2O and TiO2 variation between 0.22% to 0.57% are in agreement with shoshonitic affinities. Mineral chemistry of amphiboles enables their classification as edenite – magnesian hornblende. The micas are mainly magnesian biotite. Plagioclase is usually oligoclase (An20) and K-feldspar is orthoclase. The geochemical signatures of biotite and amphibole are in perfect agreement with the other shoshonitic rocks of northeastern of Brazil. Temperatures estimateds for calcic plagioclase and amphibole pairs indicate a temperature range of 646-671C for porphyritic syenite and 629-650C for enclaves. Geobarometric estimates, using Al in amphiboles indicate equation pressure of 1,48 Kbar to 2,26 Kbar for porphyritic syenite and 1,01 Kbar for enclaves. Other pressure estimates yielding 2,25 Kbar to 2,91 Kbar and 1,76 Kbar respectively, though at variance with the earlier estimates correspond with epizonal emplacement of the pluton.

scholarly journals Epizonal I- and A-type granites and associated ash-flow tuffs, Fogo Island, northeast Newfoundland

1995 ◽  
Vol 32 (11) ◽  
pp. 1835-1844 ◽  
Author(s):  
Hamish A. Sandeman ◽  
John Malpas
Keyword(s):  
Alkali Feldspar ◽  
Granitic Rocks ◽  
Calc Alkaline ◽  
Fine Grained ◽  
Sedimentary Sequences ◽  
Intrusive Rocks ◽  
High Silica ◽  
Composite Nature ◽  
End Members ◽  
Devonian Age

Magmatic activity of Silurian–Devonian age is widespread in the Appalachian–Caledonian Orogen. A marked characteristic of this magmatism is the composite nature of the igneous suites, which range from peridotite to granodiorite in single plutonic bodies. The origin of these suites is still enigmatic, and the assumption that all are the same not proven. Such a suite of intrusive rocks, ranging in composition from minor peridotite to granodiorite, intrudes an openly folded sequence of Silurian volcanogenic sandstones and ash-flow tuffs on Fogo Island, northeast Newfoundland. Two units, the Rogers Cove and Hare Bay microgranites, consist of fine-grained hastingsite granites with spherulitic and flow-banded textures, and exhibit drusy cavities and microfractures that contain the mineral assemblage hastingsitic hornblende + plagioclase + magnetite + zircon. These rocks are characterized by elevated high field strength element contents (e.g., Zr = 74–672 and Y = 21–103 ppm), very high FeO*/MgO ratios (FeO*/MgO = 2.4–93.5), and 10 000 Ga/Al ratios of 1.67–10.52, indicating an A-type granitoid affinity. A third and the most voluminous granitic unit, the Shoal Bay granite, is an alkali-feldspar-phyric, medium-grained, equigranular biotite–hastingsite granite with hastingsite and annitic biotite interstitial to euhedral plagioclase, anhedral quartz, and perthite crystals. The Shoal Bay granite exhibits mineral parageneses similar to the microgranites, but chemical characteristics more typical of calc-alkaline, I-type granitoids. Volcanic–sedimentary sequences spatially associated with the granitic rocks include dense, welded, high-silica, hastingsite-bearing ash-flow tuffs with compositions that suggest they represent erupted equivalents of fractionated end members of the Shoal Bay granite. The rocks making up the Fogo Island batholith have been directly equated with the bimodal, calc-alkaline Mount Peyton batholith of northeast Newfoundland, but the specialized A-type nature of the Fogo granites suggests differing source conditions for the two suites.

scholarly journals Petrogenesis of the synplutonic high-magnesian porphyritic dykes from the mafic-granitoid plutons of the East-European Craton, Voronezh crystalline massif

2019 ◽  
Vol 64 (4) ◽  
pp. 356-371
Author(s):  
R. A. Terentiev
Keyword(s):  
Trace Elements ◽  
Magma Chamber ◽  
Earth Element ◽  
Parent Magma ◽  
Chrome Spinel ◽  
Calc Alkaline ◽  
East European ◽  
Fine Grained ◽  
Mineral Inclusions ◽  
Metasomatized Mantle

This paper documents the data on high-Mg porphyrite dykes (PDs) from the mafic to felsic (~2.09 Ma) plutons of Elan complex (EC). The low-thickness (first centimeters) synplutonic dykes are characterized by sharp straight contacts without visible chilling zones, in contrast to the larger (up to 119 m) dykes that have gradual transitions. The dykes are fresh, porphyritic (bronzite, Al-enstatite, labradorite) and has fine-grained mainly quartzo-feldspathic (+biotite, sulfides, accessories, ±hypersthene) matrix. Based on geochemistry data the PDs are intermediate rocks (SiO2 = 58.9–60.3 wt. %) and plot into calc-alkaline series with high magnesian of whole rock (Mg# ~0.7) and felsic (68.9–70.2 wt. %) matrix (Mg# ~0.5). The PDs show differentiated rare-earth element patterns with negligible Eu anomalies. The bronzite phenocrysts varying sizes are characterized by block zoning and contain irregular inclusions of olivine (Mg# ~0.85), clinopyroxene (Mg# ~0.88), phlogopite (Mg# up to 0.94), labradorite, chrome spinel, graphite and sulfides. The Al-enstatite phenocrysts are practically sterile with respect to trace elements and mineral inclusions. The geochemical features as well as diffusion zones, reaction rims, and resorbed faces of the phenocrysts such as orthopyroxene and plagioclase indicate processes of recrystallization and/or partial dissolution of nonequilibrium crystals in the melt and indicate intratelluric nature of the dyke phenocrysts that cores are inherited from the EC derivatives/cumulate. The mineral thermometry estimates are: (1) the parent magma starting temperatures of 1200–1400 °С and (2) the EC crystallization temperatures 1080–1155 °С, (3) the PD emplacement temperatures 910–1070 °С. The petrogenetic model supposes the generation of EC high-temperature magmas similar to boninites from an upper metasomatized mantle. The melt is contaminated with continental crust lithologies. It implies the half-way evolved magma chamber in the crust. The PD melt, as a result of ending of the half-way magma chamber evolution, was emplaced into the still unheated EC plutons.

scholarly journals MINERAL CHEMISTRY AND GEOCHEMISTRY OF HYPERSTHENE-BEARING DIORITE FROM ERUSU AKOKO, SOUTHWESTERN NIGERIA

2020 ◽  
Vol 4 (1) ◽  
pp. 13-18
Author(s):  
E. J. Oziegbe ◽  
V. O. Olarewaju ◽  
O. O. Ocan
Keyword(s):  
Chemical Composition ◽  
Chemical Properties ◽  
Mineral Chemistry ◽  
Accessory Mineral ◽  
Southwestern Nigeria ◽  
Hydrous Minerals ◽  
Icp Ms ◽  
Composition Of Minerals ◽  
Textural Relationship ◽  
Opaque Minerals

Samples of mafic intrusive rock were analyzed for their mineralogical and chemical properties. The textural relationship was studied using the petrographic microscope, elemental composition of minerals was determined using the Electron Microprobe and the whole rock chemical analysis was done using the XRF and ICP-MS. The following minerals were observed in order of abundance; pyroxene, amphibole, plagioclase, biotite, opaque minerals, quartz and chlorite, with apatite and zircon occurring as accessory mineral. Two types of pyroxenes were observed; orthopyroxene (hypersthene) and clinopyroxene. Texturally, amphiboles have inclusions of plagioclase and pyroxene. The plagioclase has undergone sericitization. The chemical composition of the pyroxene is En51.95Fs44.53Wo3.52, biotite has Fe/(Fe+Mg):0.42, Mg/(Fe+Mg):0.59, and plagioclase is Ab63.5An34.55Or1.95. Whole rock chemistry shows a chemical composition; SiO2: 45.15 %, Al2O3: 14.04 %, Fe2O3: 16.01 %, MgO: 5.65 %, CaO: 7.58 % and TiO2: 3.59 %. There is an enrichment of LREE and a depletion of HREE. Based on the minerals, mineral chemistry and the geochemistry of the studied rock, the rock is mafic and hydrous minerals formed by hydration recrystallization of pyroxene. The rock has extensively retrogressed but has not been affected by any form of deformation.

scholarly journals Age and origin of the Cannon Point syenite, Essex County, New York: southernmost expression of Monteregian Hills magmatism?

2017 ◽  
Vol 54 (4) ◽  
pp. 379-392
Author(s):  
David G. Bailey ◽  
Marian Lupulescu ◽  
Jeffrey Chiarenzelli ◽  
Jonathan P. Traylor
Keyword(s):  
New York ◽  
New York State ◽  
Alkali Feldspar ◽  
Crustal Material ◽  
Lake Champlain ◽  
Essex County ◽  
York State ◽  
Fine Grained ◽  
The North ◽  
Basement Faults

Two syenite sills intrude the local Paleozoic strata of eastern New York State and are exposed along the western shore of Lake Champlain. The sills are fine-grained, alkali feldspar syenites and quartz syenites, with phenocrysts of sanidine and albite. The two sills are compositionally distinct, with crossing rare earth element profiles and different incompatible element ratios, which eliminates the possibility of a simple petrogenetic relationship. Zircon extracted from the upper sill yields a U–Pb age of 131.1 ± 1.7 Ma, making the sills the youngest known igneous rocks in New York State. This age is similar to that of the earliest intrusions in the Monteregian Hills of Quebec, >100 km to the north. Sr and Nd radiogenic isotope ratios are also similar to those observed in some of the syenitic rocks of the eastern Monteregian Hills. The Cannon Point syenites have compositions typical of A-type, within-plate granitoids. They exhibit unusually high Ta and Nb concentrations, resulting in distinct trace element signatures that are similar to those of the silicic rocks of the Valles Caldera, a large, rift-related magmatic system. We suggest that the Cannon Point syenites were melts derived primarily by anatexis of old, primitive, lower crustal material in response to Mesozoic rifting and to the intrusion of mantle-derived magmas. The sills indicate that the effects of continental rifting were spatially and temporally extensive, resulting in the reactivation of basement faults in the Lake Champlain Valley hundreds of kilometers west of the active rift boundary, and crustal melting >50 Ma after the initiation of rifting.

Norito e charnoenderbitos da borda do maciço intrusivo de Venda Nova, Espírito Santo

2002 ◽  
Vol 25 ◽  
pp. 99-124
Author(s):  
Julio Cezar Mendes ◽  
Cristina Maria Wiedemann ◽  
Ian McReath
Keyword(s):  
Calc Alkaline ◽  
Espírito Santo ◽  
Fine Grained ◽  
Massive Structure ◽  
Incompatible Elements ◽  
Residual Phase ◽  
Depleted Mantle ◽  
Espirito Santo ◽  
Porphyritic Texture ◽  
Narrow Ring

An irregular and narrow ring of charnoenderbites and norite envelopes gabbros and syenomonzonites in the Venda Nova inversely zoned pluton, Espírito Santo. The former have an almost massive structure, with foliation only locally well marked. The norite is a fine-grained cumulatic rock with granular hypidiomorphic to intergranular texture. The medium-grained charnoenderbites comprise enderbites, Opx-quartzdiorites and Opx-granodiorites. They are leucocratic to mesocratic with granular hypidiomorphic to porphyritic texture. Ortho and clinopyroxene are present in the both lithotypes. Subsolidus textures occur in the norite and charnoenderbites. The whole rock chemistry separates two different sequences: a basic one, with tholeiitic affinities, correspond to the noritic cumulate, and an intermediary one, medium-K calc-alkaline, comprising the charnoenderbites. They show clearly different chemical signature when compared to the alkalic affinity rocks of the inner domain of the pluton. Both the sequences have similar geochemical characteristics: they are metaluminous, Ca, Fe and Al enriched, and have low to moderate incompatible elements contents. Normal to depleted mantle protolith is inferred for both sequences, and garnet probably was a residual phase during the mantle partial melting.

Mineral chemistry and geothermobarometry of the Balıkesir Volcanites (NW Anatolia, Turkey) 

2021 ◽  
Author(s):  
Alp Ünal ◽  
Şafak Altunkaynak
Keyword(s):  
Mineral Composition ◽  
Magma Chamber ◽  
Magma Mixing ◽  
Textural Properties ◽  
Mineral Chemistry ◽  
Oscillatory Zoning ◽  
Magma Chamber Processes ◽  
Crystallization Conditions ◽  
Compositional Variations ◽  
Opaque Minerals

<p>Balıkesir Volcanites (BV) are included into the Balıkesir Volcanic Province and contain various products of Oligo-Miocene volcanic activity in NW Anatolia. BV are formed from trachyandesite, andesite and dacite lavas with associated pyroclastic rocks. In this study, we report the petrographical investigations, mineral chemistry results and geothermobarometry calculations of the Balıkesir Volcanites in order to deduce the magma chamber processes and crystallization conditions. Andesites present a mineral composition of plagioclase (An35–50) + amphibole (edenitic hornblende) +biotite ± quartz and opaque minerals. The major phenocryst phases in dacite lavas are plagioclase (An39–53), quartz, amphibole (magnesio-hornblende), biotite, sanidine and opaque minerals. The mineral composition of the trachyandesites, on the other hand, is represented by plagioclase (An38–57) + amphibole (pargasitic hornblende) + biotite + clinopyroxene (endiopside- augite) ± sanidine ± quartz ± opaque minerals. Balıkesir Volcanites present distinct textural properties such as rounded plagioclase phenocrysts with reaction rims, oscillatory zoning, honeycomb and sieve textures in plagioclase, reverse mantled biotite and hornblende crystals. The plagioclase- amphibole geothermobarometry calculations of Balıkesir volcanites indicate that, andesite and dacite lavas present similar crystallization temperature and pressures conditions of 798- 813°C and 1,98- 2.17 kbar. Oppositely, trachyandesites were crystallized under 857°C and 3,72 kbar temperature and pressure conditions. These results show that the andesite and dacite lavas were originated from the same magma chamber with the depth of 7km whereas trachyandesites were evolved in a deeper magma chamber with 13 km depth. Combined mineral chemistry, petrography and geothermobarometry studies indicate that the open system processes such as magma mixing/mingling and/or assimilation fractional crystallization (AFC) were responsible for the textural and compositional variations of the Balıkesir Volcanites.</p>

Fluids composition in the mantle beneath the Eastern Transylvanian Basin inferred from mineral chemistry and noble gases in fluid inclusions of ultramafic xenoliths

2021 ◽  
Author(s):  
Andrea Luca Rizzo ◽  
Barbara Faccini ◽  
Costanza Bonadiman ◽  
Theodoros Ntaflos ◽  
Ioan Seghedi ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Noble Gases ◽  
Mineral Chemistry ◽  
Mantle Xenoliths ◽  
Alkaline Magmatism ◽  
Volcanic Area ◽  
Crustal Material ◽  
Calc Alkaline ◽  
Depleted Mantle ◽  
Magmatic Gases

<p>The investigation of noble gases (He, Ne, Ar) and CO<sub>2</sub> in fluid inclusions (FI) of mantle-derived rocks from the Sub Continental Lithospheric Mantle (SCLM) is crucial for constraining its geochemical features and evolution as well as the volatiles cycle, and for better evaluating the information arising from the study and monitoring of volcanic and geothermal gases. Eastern Transylvanian Basin in Romania is one of the places in Central-Eastern Europe where mantle xenoliths are brought to the surface by alkaline magmatism, offering the opportunity for applying the above-mentioned approach. Moreover, this locality is one of the few places on Earth where alkaline eruptions occurred contemporaneously with calc-alkaline activity, thus being a promising area for the investigation of subduction influence on the magma sources and volatiles composition.</p><p>In this work, we studied petrography, mineral chemistry and noble gases in FI of mantle xenoliths found in Perşani Mts. alkaline volcanic products. Our findings reveal that the local mantle recorded two main events. The first was a pervasive, complete re-fertilization of a previously depleted mantle by a calc-alkaline subduction-related melt, causing the formation of very fertile, amphibole-bearing lithotypes. Fluids involved in this process and trapped in olivine, opx and cpx, show <sup>4</sup>He/<sup>40</sup>Ar* ratios up to 1.2 and among the most radiogenic <sup>3</sup>He/<sup>4</sup>He values of the European mantle (5.8 ± 0.2 Ra), reflecting the recycling of crustal material in the local lithosphere. The second event is related to a later interaction with an alkaline metasomatic agent similar to the host basalts, that caused slight LREE enrichment in pyroxenes and crystallization of disseminated amphiboles, with FI showing <sup>4</sup>He/<sup>40</sup>Ar* and <sup>3</sup>He/<sup>4</sup>He values up to 2.5 and 6.6 Ra, respectively, more typical of magmatic fluids.</p><p>Although volcanic activity in the Perşani Mts. is now extinct, strong CO<sub>2</sub> degassing (8.7 × 10<sup>3</sup> t/y) in the neighbouring Ciomadul volcanic area may indicate that magma is still present at depth (Kis et al., 2017; Laumonier et al., 2019). The gas manifestations present from Ciomadul area are the closest to the outcrops containing mantle xenoliths for comparison of the noble gas composition in FI. <sup>3</sup>He/<sup>4</sup>He values from Stinky Cave (Puturosul), Doboşeni and Balvanyos are up to 3.2, 4.4 and 4.5 Ra, respectively, indicating the presence of a cooling magma (Vaselli et al., 2002 and references therein). In the same area and more recently, Kis et al. (2019) measured <sup>3</sup>He/<sup>4</sup>He ratios up to 3.1 Ra, arguing that these values indicate a mantle lithosphere strongly contaminated by subduction-related fluids and post-metasomatic ingrowth of radiogenic <sup>4</sup>He. Our findings consider more likely that magmatic gases from Ciomadul volcano are not representative of the local mantle but are being released from a cooling and aging magma that resides within the crust. Alternatively, crustal fluids contaminate magmatic gases while they are rising to the surface.</p><p> </p><p>Kis et al. (2017). Journal of Volcanology and Geothermal Research 341, 119–130.</p><p>Kis et al. (2019) Geochem. Geophys. Geosyst. 20, 3019-3043.</p><p>Laumonier et al. (2019) Earth and Planetary Science Letters, 521, 79-90.</p><p>Vaselli et al. (2002) Chemical Geology 182, 637–654.</p>

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.

Brittle–ductile fabrics and P–T conditions of deformation in the East Pernambuco shear zone (Borborema Province, NE Brazil)

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-109
Author(s):  
Paulo Castellan ◽  
Gustavo Viegas ◽  
Frederico M. Faleiros
Keyword(s):  
Shear Zone ◽  
Microstructural Analysis ◽  
Mineral Chemistry ◽  
Prism Slip ◽  
Content Type ◽  
Fine Grained ◽  
Brittle Ductile Transition ◽  
Epma Analysis ◽  
Borborema Province ◽  
Supplementary Material

Fabrics of the East Pernambuco shear zone (EPSZ) were studied via microstructural analysis, mineral chemistry and isochemical phase diagram modelling to constrain the pressure and temperature conditions of deformation during shearing. Granitic mylonites show fractured feldspar porphyroclasts embedded in a fine-grained, recrystallized quartzo-feldspathic matrix. These mylonites grade laterally into banded ultramylonites characterized by stretched feldspar clasts alternated with recrystallized quartz bands. Fractures in these ultramylonites are filled by phyllosilicates. The mineral chemistry of the feldspars points to systematic changes between porphyroclasts, grains within fractures and fine-grained mixtures. Quartz crystallographic fabrics in the mylonites suggest activation of prism slip, while the ultramylonites show the activation of both rhomb and basal slip systems. Thermodynamic modelling suggests that the mylonites were formed at 4.75 ± 0.25 kbar and 526 ± 9°C, while the ultramylonites yield conditions of 5.9 ± 1 kbar and 437 ± 17°C. These observations suggest that the EPSZ records a heterogeneous path of strain accommodation, marked by decreasing temperature from its western sector to its eastern termination. The differences in metamorphic conditions are consistent with a transitional, brittle–ductile strain regime. Such characteristics indicate that the EPSZ is a Neoproterozoic shear belt nucleated and heterogeneously exhumed at the brittle–ductile transition, possibly in an intracontinental setting.Supplementary Material: EPMA analysis of feldspars in Caruaru and Gravatá domains and T-X(O2) pseudosections are available at https://doi.org/10.6084/m9.figshare.c.5125957

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