Alkali feldspar liquid equilibrium relationships in peralkaline oversaturated systems and volcanic rocks

1975 ◽  
Vol 49 (1) ◽  
pp. 67-81 ◽  
Author(s):  
Jacques Roux ◽  
Jacques Varet
Keyword(s):  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Liquid Equilibrium ◽  
Equilibrium Relationships

scholarly journals Stitch in the ditch: Nutzotin Mountains (Alaska) fluvial strata and a dike record ca. 117–114 Ma accretion of Wrangellia with western North America and initiation of the Totschunda fault

Geosphere ◽  
2019 ◽  
Vol 16 (1) ◽  
pp. 82-110 ◽  
Author(s):  
Jeffrey M. Trop ◽  
Jeffrey A. Benowitz ◽  
Donald Q. Koepp ◽  
David Sunderlin ◽  
Matthew E. Brueseke ◽  
...  
Keyword(s):  
Fault Zone ◽  
Lower Cretaceous ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Upper Jurassic ◽  
Sediment Provenance ◽  
Lake Formation ◽  
Beaver Lake ◽  
Channel Bar ◽  
Marine Basin

Abstract The Nutzotin basin of eastern Alaska consists of Upper Jurassic through Lower Cretaceous siliciclastic sedimentary and volcanic rocks that depositionally overlie the inboard margin of Wrangellia, an accreted oceanic plateau. We present igneous geochronologic data from volcanic rocks and detrital geochronologic and paleontological data from nonmarine sedimentary strata that provide constraints on the timing of deposition and sediment provenance. We also report geochronologic data from a dike injected into the Totschunda fault zone, which provides constraints on the timing of intra–suture zone basinal deformation. The Beaver Lake formation is an important sedimentary succession in the northwestern Cordillera because it provides an exceptionally rare stratigraphic record of the transition from marine to nonmarine depositional conditions along the inboard margin of the Insular terranes during mid-Cretaceous time. Conglomerate, volcanic-lithic sandstone, and carbonaceous mudstone/shale accumulated in fluvial channel-bar complexes and vegetated overbank areas, as evidenced by lithofacies data, the terrestrial nature of recovered kerogen and palynomorph assemblages, and terrestrial macrofossil remains of ferns and conifers. Sediment was eroded mainly from proximal sources of upper Jurassic to lower Cretaceous igneous rocks, given the dominance of detrital zircon and amphibole grains of that age, plus conglomerate with chiefly volcanic and plutonic clasts. Deposition was occurring by ca. 117 Ma and ceased by ca. 98 Ma, judging from palynomorphs, the youngest detrital ages, and ages of crosscutting intrusions and underlying lavas of the Chisana Formation. Following deposition, the basin fill was deformed, partly eroded, and displaced laterally by dextral displacement along the Totschunda fault, which bisects the Nutzotin basin. The Totschunda fault initiated by ca. 114 Ma, as constrained by the injection of an alkali feldspar syenite dike into the Totschunda fault zone. These results support previous interpretations that upper Jurassic to lower Cretaceous strata in the Nutzotin basin accumulated along the inboard margin of Wrangellia in a marine basin that was deformed during mid-Cretaceous time. The shift to terrestrial sedimentation overlapped with crustal-scale intrabasinal deformation of Wrangellia, based on previous studies along the Lost Creek fault and our new data from the Totschunda fault. Together, the geologic evidence for shortening and terrestrial deposition is interpreted to reflect accretion/suturing of the Insular terranes against inboard terranes. Our results also constrain the age of previously reported dinosaur footprints to ca. 117 Ma to ca. 98 Ma, which represent the only dinosaur fossils reported from eastern Alaska.

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.

Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

1989 ◽  
Vol 26 (10) ◽  
pp. 2145-2158 ◽  
Author(s):  
P. K. Sims ◽  
W. R. Van Schmus ◽  
K. J. Schulz ◽  
Z. E. Peterman
Keyword(s):  
Subduction Zone ◽  
Continental Margin ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Suture Zone ◽  
Island Arcs ◽  
Calc Alkaline ◽  
The South ◽  
Early Proterozoic ◽  
Felsic Volcanic

The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine–Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860–1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835 – 1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subduction zone (Niagara fault zone), whereas the younger one developed as island arcs above a north-dipping subduction zone, the Eau Pleine shear zone. The northward subduction followed deformation related to arc–continent collision at the Niagara suture at about 1860 Ma. The southern Marshfield terrane contains remnants of mafic to felsic volcanic rocks about 1860 Ma that were deposited on Archean gneiss basement, foliated tonalite to granite bodies ranging in age from about 1890 to 1870 Ma, and younger undated granite plutons. Following amalgamation of the two arc terranes along the Eau Pleine suture at about 1840 Ma, intraplate magmatism (1835 Ma) produced rhyolite and anorogenic alkali-feldspar granite that straddled the internal suture.

scholarly journals Geochemistry of Volcanic Rocks of Beka, North East of Ngaoundéré (Adamawa Plateau, Cameroon): Petrogenesis and Geodynamic Context

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Pauline Wokwenmendam Nguet ◽  
Benjamin Ntieche ◽  
Joseph Legrand Tchop ◽  
Bouba Christian Mana ◽  
Eddy Ferdinand Mbossi
Keyword(s):  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Parent Magma ◽  
Spinel Lherzolite ◽  
Chemical Analyses ◽  
Volcanic Zone ◽  
North East ◽  
Low Degree ◽  
Petrographic Study ◽  
Basaltic Lavas

Beka area is situated in the Adamaoua Plateau of Cameroon in central Arica. Lavas in this area has not been studied before the present work.The volcanism of Beka is characterized by basalt, trachyte and phonolite domes and flows. The petrographic study shows that basaltic lavas have porphyritic microlitic textures. The felsic lavas indicate trachytic textures.The rocks are composed of olivine, clinopyroxene, plagioclase and irontitanium oxide minerals for the basalts; clinopyroxene, alkali feldspar (including foids), sphene and titanomagnetite for the felsic lavas. Chemical analyses show that basaltic lavas are basanites. Felsic lavas contain modal feldspathoid (nepheline in phonolites). All these lavas belong to the same series, because the felsic lavas are derived from the differentiation of basaltic lavas by fractional crystallization. They show an alkaline nature according to their geochemistry. Trace elements including Rare Earth Elements characteristics show that rocks emplaced in the Winthin Plate volcanic zone. They derived from an evolved parent magma showing a low degree of partial melting and characteristics closer to a modified and evolved primitive spinel lherzolite.

scholarly journals Caracterização Petrográfica e Geoquímica da Parte Leste do Granito Europa, Distrito Mineiro de Pitinga, AM

2007 ◽  
Vol 34 (1) ◽  
pp. 77 ◽  
Author(s):  
MAURÍCIO PRADO ◽  
JOSÉ TADEU MAXIMINO MIRRAS FERRON ◽  
EVANDRO FERNANDES DE LIMA ◽  
ARTUR CEZAR BASTOS NETO ◽  
VITOR PAULO PEREIRA ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Genetic Relationship ◽  
Crystallization Process ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Mineral Deposits ◽  
Geochemical Data ◽  
Principal Mechanism ◽  
Amazonian Region ◽  
Fractional Crystallization Process

The important mineral deposits of the Pitinga Mine, in the Amazonian region are related to A-type granites intruded in the Iricoumé Group. The Europa granite is one of these A-type rocks, intruded in the Iricoumé Group, which is represented by subaerial vulcanoclastic rocks (crystal-rich ignimbrites, thin massive tuffs and siltic tufaceous arenites) and minor hipabissal rhyolites. The volcanic rocks were probably generated in a caldera environment. The Europa granite is an alkali-feldspar peralkaline granite (hipersolvus) without genetic relationship with to the volcanic rocks of the Iricoumé Group, but it could have been generated during the resurgence stages. The petrographic and geochemical data attest that fractional crystallization process was the principal mechanism during the crystallization, which led to the generation of two different granitic facies. The Nb soil anomalies overprinted on the more differentiated facies are related to the astrophillite weathering.

scholarly journals Geological-geomorphological characteristics and petrographical composition of the St. Anastasia Island

2021 ◽  
Vol 8 (1) ◽  
pp. 118-125
Author(s):  
Dimitar Dimitrov ◽  
Banush Banushev
Keyword(s):  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Alkali Feldspar ◽  
Geological Processes ◽  
The Republic ◽  
Historical Heritage

Abstract St. Anastasia Island is one of the symbols of the cultural and historical heritage of the Republic of Bulgaria. This raises the need for the study of risky oceanographic factors, climatic phenomena, risky geological processes as well as detailed petrographical characteristics of the Upper Cretaceous volcanic rocks forming the islands. The results of the petrographical study show that the island was built by Alkali feldspar trachytes. The volcanics from St. Anastasia Island shows a close petrochemical similarity to the volcanics from Alatepenski paleovolcano belonging to the “Peripheral Volcanic Centers” in the region.

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