Mineral chemistry of perpotassic lavas of the Vulsinian district, the Roman Province, Italy

1982 ◽  
Vol 46 (340) ◽  
pp. 379-386 ◽  
Author(s):  
Paul M. Holm
Keyword(s):  
Magma Mixing ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Mineral Chemistry ◽  
Low Pressure ◽  
Major Elements ◽  
Crystal Fractionation ◽  
High Concentrations ◽  
Roman Province ◽  
Pressure Crystallization

SynopsisThe Vulsinian district is the largest and northernmost of the Roman Provinces. There is very little modern mineralogical data on the Italian Pliocene to Recent perpotassic alkaline volcanic rocks and this account deals with the compositions of the phenocrysts in the Vulsinian lavas.The lavas comprise two suites: a leueite-bearing undersaturated series of leucitites, leueite tephrites, leucite phonolites, and trachytes; and a subordinate hy-normative series of mainly trachytes and latites. All lavas are porphyritic with mostly 1–15 vol. % phenoerysts. No cumulates were found. Major elements, and Cr and Ni were determined in the phenocrysts by microprobe analysis and more than 20 trace elements were determined on mineral separates by PIXE.The undersaturated suite. Ubiquitous clinopyroxene phenoerysts belong to the Di-Hedss series and range from Di97 to Di46. Important amounts of Fe3+ are always present. In the mafic rocks the diopside is chromian, but Ti is low. AI mainly substitutes in the Z positions in all lavas. Only minor Na enrichment occurs with increasing total Fe (0–7 mole % acmite) and thus Ca ferri-Tschermak's component is important. In many of the maric lavas diopside mantles green cores of salite, which has a composition very like the salite of felsic lavas. Leucites contain 5–22 mole % orthoelase in solid solution, but show no systematic variation. Plagioclase, mostly An93-An72, occurs in the felsie lavas, and alkali feldspar only in some phonolites. They both have exceptionally high concentrations of Sr and Ba, with a maximum of 1.3 wt. % SrO and 5.6 wt. % BaO in hyalophanes. Olivine, Fo92-Fo66, occurs in some leucititic lavas in mostly accessory amounts. Phlognpite, magnetite and nepheline are accessory phases of the felsic lavas. Apatite only occur as micro-phenocrysts of the fclsic lavas. Haüyne in trace amounts is found in a few phonolites. Pargasitic amphibole microphenocrysts are found in one lava.In most marie members diopside ±leuctie ±olivine were liquidus phases. This study does not confirm that these rocks are related by crystal fractionation. In more felsie lavas clinopyroxene (salite-ferrosalite) and leucite are joined by: plagioclase, magnetite ±phlogopite, and Ba-rich alkali feldspar ±haüyne. The felsic rocks are thought to be related by crystal fractionation.Salitic green cores of phenocrystic pyroxene, mantled by diopside in rocks which also carry normally-zoned diopside, are relicts which provide evidence of either a relatively high PH2O, prior to the crystallization of diopside or magma mixing in the earlier life of these lavas. Pyroxene chemistry points towards low-pressure crystallization (2 kbar), generally in a dry environment.The hy-normative suite. All lavas have phenocrysts of augite, sanidine, plagioclase, magnetite, biotite, and olivine. The pyroxene is less calcic and has less alumina, but is otherwise rather similar to the salites of the undersaturated suite. Compared to the undersaturated suite, feldspars do not have high Sr and Ba, magnetite has higher TiO2 and olivine crystallized from even the felsic lavas. The pyroxenes show the signs of low-pressure crystallization.

The Tertiary Kærven Syenite Complex, Kangerdlugssuaq, East Greenland: Mineral Chemistry and Geochemistry

1988 ◽  
Vol 52 (367) ◽  
pp. 435-450 ◽  
Author(s):  
Paul Martin Holm ◽  
Niels-Ole Prægel
Keyword(s):  
Magma Mixing ◽  
Crustal Contamination ◽  
Outer Part ◽  
Alkali Feldspar ◽  
Mineral Chemistry ◽  
Crystal Fractionation ◽  
Maximum Pressure ◽  
General Sequence ◽  
East Greenland ◽  
Rock Suite

AbstractThe Kærven syenite complex, which reflects the hitherto earliest recorded stages in the Tertiary of East Greenland, outcrops in the middle reaches of the Kangerdlugssuaq Fjord as a peripheral intrusion to the Kangerdlugssuaq intrusion. The rocks of the Kærven complex range from syenite through alkali feldspar quartz-syenite to alkali feldspar granite. The general sequence of crystallization of the Kærven magmas was: alkali feldspar ± olivine(Fa96−99) ± plagioclase(An41−11), clinopyroxene (augite, ferrosalite, ferrohedenbergite), quartz and amphibole. Whole-rock major and trace-element data show coherent geochemical trends which suggest comagmatism. The data reveal that the Kærven rocks are distinct from the rocks from the adjacent Kangerdlugssuaq intrusion (e.g. higher TiO2, FeOT in low-SiO2 samples, lower Na2O, approx. constant Zr/Nb). The mineral chemistry supports this conclusion, as the Kærven samples typically have calcic amphiboles and clinopyroxenes with a very limited Na-enrichment in contrast to the sodic trends of the Kangerdlugssuaq intrusion. Normative feldspar compositions plot near to the Ab-Or cotectic in the Q-Ab-Or system and a maximum pressure of crystallization of 3–5 kbar with moderate to low PH2O is indicated.Trace elements preferently incorporated in plagioclase and alkali feldspar, i.e. Sr, Ba and Rb, show systematics which are not compatible with an evolution of the rock suite by crystal fractionation of these phases, though possibly alkali feldspar may be partially accumulated in a few very evolved rocks. Numerical calculations do not suggest a magmatic evolution by fractional crystallization of the observed phases. The variation of Sr, Ba and Rb as well as of the incompatible elements Nb, Zr and Th support a derivation of the rock suite mainly by mixing two components, a syenitic and a granitic end-member. It is concluded that magma mixing was the most significant process in the formation of the Kærven rock suite accompanied by some crystal fractionation. Evidence for crustal contamination is detected in a few samples from the outer part of the intrusion but has not affected the main suite of rocks.

scholarly journals Mineral Chemistry Studies and Evidences For Magma Mixing of Bala Zard Basic- Intermediate Volcanic Rocks, Lut Block, Iran

2015 ◽  
Vol 10 (Special-Issue1) ◽  
pp. 1194-1205 ◽  
Author(s):  
Omid Namin ◽  
Afshin Ardalan ◽  
Mohammad Razavi ◽  
Arash Gourabjeripour ◽  
Abdollah Yazdi
Keyword(s):  
Magma Mixing ◽  
Volcanic Rocks ◽  
Mineral Chemistry ◽  
Lut Block

Distribution of gallium between phenocrysts and melt in peralkaline salic volcanic rocks, Kenya Rift Valley

2010 ◽  
Vol 74 (2) ◽  
pp. 351-363 ◽  
Author(s):  
R. Macdonald ◽  
N. W. Rogers ◽  
B. Bagiński ◽  
P. Dzierżanowski
Keyword(s):  
Rift Valley ◽  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Volcanic Complex ◽  
Kenya Rift ◽  
Inductively Coupled ◽  
Plasma Mass Spectrometry ◽  
Kenya Rift Valley

AbstractGallium abundances, determined by laser ablation-inductively coupled plasma-mass spectrometry, are presented for phenocrysts and glassy matrices from a metaluminous trachyte and five peralkaline rhyolites from the Greater Olkaria Volcanic Complex, Kenya Rift Valley. Abundances in the glasses range from 28.9 to 33.3 ppm, comparable with peralkaline rhyolites elsewhere. Phenocryst Ga abundances (in ppm) are: sanidine 31.5–45.3; fayalite 0.02–0.22; hedenbergite 3.3–6.3; amphibole 12; biotite 72; ilmenite 0.56–0.72; titanomagnetite 32; chevkinite-(Ce) 364. The mafic phases and chevkinite-(Ce) are enriched in Ga relative to Al, whereas Ga/Al ratios in sanidine are smaller than in coexisting glass. Apparent partition coefficients range from <0.01 in fayalite to 12 in chevkinite-(Ce). Coefficients for hedenbergite, ilmenite and titanomagnetite decrease as melts become peralkaline. The sharp increase in Ga/Al in the more fractionated members of alkaline magmatic suites probably results from alkali feldspar-dominated fractionation. Case studies are presented to show that the Ga/Al ratio may be a sensitive indicator of such petrogenetic processes as magma mixing, interaction of melts with F-rich volatile phases, mineral accumulation and volatile-induced crustal anatexis.

scholarly journals PETROGRAPHY AND MINERAL CHEMISTRY OF OLIGOCENE SHOSHONITIC DACITES FROM THE CENTRAL BOSNIA

2020 ◽  
Vol 1 (22) ◽  
Author(s):  
Zehra Salkić ◽  
Boško Lugović ◽  
Elvir Babajić
Keyword(s):  
Pannonian Basin ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Mafic Magma ◽  
Mineral Chemistry ◽  
Southeastern Part ◽  
Vardar Zone ◽  
High K ◽  
Insight Into ◽  
Zoned Plagioclase

Postorogenic volcanic rocks of different Tertiary ages are very common in the Sava-Vardar Zone of the Dinarides and in the southeastern part of adjoing Pannonian Basin. South of the Sava-Vardar Zone, in central Bosnia, Tertiary volcanic rocks occur within ophiolite sequences and genetically related sedimentary formations of the Dinaride Ophiolite Zone. Central Bosnia volcanic rocks are mostly dacites, and highly subordinately andesites as the members of the high-K calc-alkaline series.It appears from the mineralogical and petrographic characteristics obtained some insight into the processes that occurred during the genesis of the rocks. The presence of primary igneous minerals: clinopyroxene, orthopyroxene, hornblende and biotite from ferromagnesian minerals, and plagioclase, sanidine and quartz, indicates that the fractional crystallization played a significant role in the genesis of the rocks. Reaction edge on many rounded quartz phenocrysts indicates the possibility of magma mixing with the formation of Tertiary volcanic rocks of the central Bosnia. On magma mixing different temperature and chemical composition also indicates the existence of zoned plagioclase and amphibole phenocrysts.Complex compositional and zoning patterns of biotite and plagioclase phenocrysts and disequilibrium microstructures of plagioclase and quartz phenocrysts suggest interaction of fractionating, mantle derived melts with continental crust during a shalow level pre-eruptive stage and mixing with small amount of devolatilized phlogopite-phyric mafic magma before eruption.

C-type magmas: igneous charnockites and their extrusive equivalents

1992 ◽  
Vol 83 (1-2) ◽  
pp. 155-164 ◽  
Author(s):  
Jonathan A. Kilpatrick ◽  
David J. Ellis
Keyword(s):  
Partial Melting ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Magma Type ◽  
Mineral Assemblages ◽  
Melting Event ◽  
Distinctive Type ◽  
High Concentrations ◽  
Very High ◽  
Inverted Pigeonite

ABSTRACTIgneous charnockites are characterised by distinctively high abundances of K2O, TiO2, P2O5 and LIL elements and low CaO at a given SiO2 level compared to metamorphic charnockites, and I-, S- and A-type granites. They form a distinctive type of intrusive igneous rocks, the Charnockite Magma Type (CMT or C-type), which generally lack hornblende and consist of pyroxene, alkali feldspar, plagioclase, quartz, biotite, apatite, ilmenite and titanomagnetite. Although this mineral assemblage superficially resembles that of metamorphic charnockites, magmatic charnockites are characterised by inverted pigeonite, exceptionally calcic alkali feldspar, potassic plagioclase, and coexisting opaque oxides, all with crystallisation temperatures of 950-1050°C. Apatite is a ubiquitous phase which, together with the very high concentrations of Zr and TiO2 over a wide silica range, is consistent with the derivation of the Charnockite Magma Type by very high temperature partial melting and fractionation.The credibility of intrusive charnockites as a magmatic type has historically foundered because of their apparent restriction to granulite belts and the absence of any reported extrusive equivalents. We report examples of volcanic rocks, of various ages, with the same distinctive major and trace element compositions, mineral assemblages and high temperatures of crystallisation as intrusive chamockites.The Charnockite Magma Type is considered to be derived by melting of a hornblende-free or poor, LILE-enriched fertile granulite source which had not been geochemically depleted by a previous partial melting event but which was dehydrated in an earlier metamorphism. Whereas H2O-saturated melting produces migmatites or "failed" granites, and vapour-absent melting of an amphibolite can produce I-type granites, according to this model the vapour-absent melting of a hornblende-free or hornblende-poor granulite at even higher temperatures produces charnockites.

Mineralogical Evidence of Pre-caldera Magma Petrogenesis in the Jemez Mountains Volcanic Field, New Mexico, USA

2020 ◽  
Vol 61 (7) ◽  
Author(s):  
Jie Wu ◽  
Michael C Rowe ◽  
Shane J Cronin ◽  
John A Wolff
Keyword(s):  
Low Temperature ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Mineral Chemistry ◽  
Volcanic Field ◽  
Magmatic System ◽  
Upward Migration ◽  
Jemez Mountains ◽  
Almost All ◽  
Shallow Crust

Abstract The Jemez Mountains volcanic field (JMVF) is the site of the two voluminous, caldera-forming members of the Bandelier Tuff, erupted at 1·60 and 1·25 Ma, following a long and continuous pre-caldera volcanic history (∼10 Myr) in this region. Previous investigations utilizing whole-rock geochemistry identified complex magmatic processes in the two major pulses of pre-caldera magmatism including assimilation–fractional crystallization (AFC) and magma mixing. Here we extend the petrological investigation of the pre-caldera volcanic rocks into the micro-realm and use mineral chemistry and textural information to refine magma evolution models. The results show an increasing diversity of mineral populations as the volcanic field evolved. A range of plagioclase textures (e.g. sieved cores and rims) indicate disequilibrium conditions in almost all pre-caldera magmas ranging from andesite to rhyolite, reflecting plagioclase dissolution and regrowth. Coarsely sieved or dissolved plagioclase cores are explained by resorption via water-undersaturated decompression during upward migration from a deep melting, assimilation, storage and homogenization (MASH) zone. Plagioclase crystals with sieved rims are almost ubiquitous in dacite-dominated magmatism (La Grulla Plateau andesite and dacite erupted at ∼8–7 Ma, as well as Tschicoma Formation andesite, dacite and rhyolite at ∼5–2 Ma), reflecting heating induced by magma mixing. These plagioclase crystals often have An-poor cores that are chemically distinct from their An-rich rims. The existence of different plagioclase populations is consistent with two distinct amphibole groups that co-crystallized with plagioclase: a low-Al, low-temperature, high-fO2 group, and a high-Al, high-temperature, low-fO2 group. Calculation of melt Sr, Ba, La, and Ce concentrations from plagioclase core and rim compositions suggests that these chemical variations are largely produced by magma mixing. Multiple mafic endmembers were identified that may be connected by AFC processes in the MASH zone in the middle to lower crust. The silicic component in an early andesite-dominated magmatic system (Paliza Canyon andesite, dacite and rhyolite, 10–7 Ma) is represented by contemporaneous early rhyolite (Canovas Canyon Rhyolite). A silicic mush zone in the shallow crust is inferred as both the silicic endmember involved in the dacite-dominant magmatic systems and source of the late low-temperature rhyolite (Bearhead Rhyolite, 7–6 Ma). Recharging of the silicic mush by mafic melts can explain observed diversity in both mineral disequilibrium textures and compositions in the dacitic magmas. Overall, the pre-caldera JMVF magmatic system evolved towards cooler and more oxidized conditions with time, indicating gradual thermal maturation of local crust, building up to a transcrustal magmatic system, which culminated in ‘super-scale’ silicic volcanism. Such conditioning of crust with heat and mass by early magmatism might be common in other long-lived volcanic fields.

Hydrochemistry and carbonate sediment characterisation of Bacalar Lagoon, Mexican Caribbean

2019 ◽  
Vol 70 (3) ◽  
pp. 382 ◽  
Author(s):  
Nidia I. Tobón Velázquez ◽  
Mario Rebolledo Vieyra ◽  
Adina Paytan ◽  
Kyle H. Broach ◽  
Laura M. Hernández Terrones
Keyword(s):  
Trace Elements ◽  
Water Column ◽  
Saturation Index ◽  
Major Elements ◽  
Anthropogenic Sources ◽  
Pollution Indices ◽  
Mexican Caribbean ◽  
High Concentrations ◽  
Geochemical Analyses ◽  
Changes Over Time

The aim of the study is to determine the distribution of trace and major elements in the water and in the sediments of the south part of the Bacalar Lagoon and to identify the sources of the trace elements and their changes over time. The western part of the lagoon water column is characterised by high concentrations of Ca2+, HCO3– and Sr2+, derived from groundwater input. In contrast, the eastern part of the lagoon is characterised by high concentrations of Mg2+, Na+ and Cl–. The lagoon is not affected by present-day seawater intrusion. Water column and sediment geochemical analyses performed in Bacalar Lagoon show clear spatial distribution of different parameters. The saturation index of the water column indicates three main groups: (1) a zone oversaturated with regard to aragonite, calcite and dolomite; (2) an undersaturated area where all three minerals are dissolving; and (3) an area with calcite equilibrium and undersaturation with regard to the other minerals. Herein we present the first measurements of trace element (Ba2+, Mn2+, K+, Ni2+, Zn2+) concentrations in carbonates obtained from sediments in Bacalar Lagoon. In order to evaluate whether the trace elements are derived from natural or anthropogenic sources, four pollution indices were calculated. The results confirmed that Bacalar Lagoon sediments are not contaminated with Ni2+, K+, Mn2+ and Ba2+, and that the Zn2+ seems to have a predominantly anthropogenic origin.

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
Keyword(s):  
Subduction Zone ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Alkaline Basalt ◽  
Complex Process ◽  
Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

scholarly journals Peran Kontaminasi Kerak pada Diferensiasi Magma Pembentuk Batuan Vulkanik Sungai Ampalas, Mamuju, Sulawesi Barat

EKSPLORIUM ◽  
2020 ◽  
Vol 41 (2) ◽  
pp. 73
Author(s):  
Windi Anarta Draniswari ◽  
Sekar Indah Tri Kusuma ◽  
Tyto Baskara Adimedha ◽  
I Gde Sukadana
Keyword(s):  
Magma Mixing ◽  
Volcanic Rocks ◽  
Geochemical Characteristics ◽  
X Ray ◽  
Radioactive Mineral ◽  
Alkaline Feldspar ◽  
High Alkalinity ◽  
Preliminary Study ◽  
Xrf Analyses

ABSTRAK Anomali radiometri telah ditemukan di area Sungai Amplas pada bongkah batuan vulkanik. Nilai yang terukur dari spektrometer gama adalah 787 ppm eU dan 223 ppm eTh. Penemuan ini menarik untuk pengembangan eksplorasi. Studi lebih lanjut diperlukan untuk mengetahui karekteristik batuan pembawa mineral radioaktif dari sampel in-situ. Penelitian ini bertujuan untuk mengetahui karakteristik petrologi dan geokimia batuan vulkanik Ampalas sebagai studi awal untuk mengetahui proses akumulasi mineral radioaktif pada batuan vulkanik Ampalas. Metodologi yang digunakan meliputi pengamatan lapangan, pengambilan sampel batuan, analisis petrografi dan X-Ray Fluorescence (XRF). Batuan vulkanik ampalas tersusun atas ponolit, foidit, dan foid-syenit. Tekstur batuannya terdiri dari porfiritik, aliran, rim piroksen, zoning, pseudo-leusit, korosi, inklusi mafik, dan sieve. Karakteristik geokimia menunjukkan alkalinitas tinggi dan indikasi pengayaan mineral radioaktif yang tersebar dalam batuan. Proses magmatis yang berperan dalam pembentukan batuan vulkanik adalah fraksionasi kristal (fraksionasi leusit dan alkali felspar), asimilasi kerak kontinen, dan pencampuran magma. Interaksi antara magma dan kerak menyebabkan diferensiasi magma berkelanjutan yang menghasilkan akumulasi uranium dan torium lebih tinggi.ABSTRACT Anomalous radiometry has been found in Ampalas River Area on volcanic rock boulder. The values measured from gamma spectrometer are 787 ppm eU and 223 ppm eTh. This discovery is promising for exploration development. Further study need to figure the radioactive mineral bearing rock characteristic from in-situ samples. The research aim is to determine the petrology and geochemical characteristics of Ampalas volcanic rocks as preliminary study to find radioactive mineral accumulation process of Ampalas volcanic rocks. The methodologies are field observation, rock sampling, petrography, and X-Ray fluorescence (XRF) analyses. The Ampalas volcanic rocks consist of phonolite, phoidite, and phoid syenite. Their textures are porphyritic, flow, pyroxene rim, zoning, pseudo-leucite, corrosion, mafic inclusions, and sieve. The geochemical characteristics show high alkalinity and radioactive mineral enrichment disseminating on rock. The magmatic processes which play a significant role in radioactive mineral-bearing rocks formation are crystal fractionations (leucite and alkaline feldspar fractionations), continental crust assimilation, and magma mixing. Long interaction between magma and crust creates advanced magma differentiation causing higher uranium and thorium accumulation.  

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