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.

scholarly journals Nisyros Volcanic Island: A Geosite through a Tailored GIS Story

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 132
Author(s):  
Varvara Antoniou ◽  
Paraskevi Nomikou ◽  
Dimitrios Panousis ◽  
Effrosyni Zafeirakopoulou
Keyword(s):  
Spatial Data ◽  
Hot Springs ◽  
Volcanic Rocks ◽  
Data Communication ◽  
Aegean Sea ◽  
Volcanic Island ◽  
Eastern Aegean ◽  
Strongly Connected ◽  
Historical Heritage ◽  
Available Information

The volcanic island of Nisyros (Greece) is here presented as it presents unique characteristics being a Quaternary volcano in the eastern Aegean Sea, composed of volcanic rocks, and featuring a central caldera that is surrounded by volcanic domes and thick lavas. Its history is strongly connected to the volcano impressing the visitors with steaming hydrothermal craters, intensive smell of sulfur and fumarolic gases, and hot springs. Due to its morphology and geographical position, its cultural and historical heritage has been unchanged in time, bequeath to the island plenty of churches, monasteries with hagiographic frescoes, castles, caves, and spas. To present the geodiversity, the cultural environment, and the biodiversity of this geosite, a relatively new geographic approach was used, ESRI Story Maps. Being web-based applications, they are widespread as an interactive responsive tool used for spatial data communication and dissemination, by combining thematic 2D and 3D webmaps, narrative text, and multimedia content. Such applications can be an ideal way for presenting the available information of places characterized as geosites or protected areas worldwide, providing quick access to the available information to a broader, non-technical audience, developing the interest, and possibly motivating the public to learn more or visit them.

Petrogenesis of the Upper Cretaceous volcanism in the Kefken region, Western Pontides, NW Turkey

2021 ◽  
Author(s):  
Turgut Duzman ◽  
Ezgi Sağlam ◽  
Aral I. Okay
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Partial Melting ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Early Eocene ◽  
Heavy Rare Earth ◽  
Heavy Rare Earth Elements ◽  
Cretaceous Volcanism ◽  
Oceanic Slab

<p>The Upper Cretaceous volcanic and volcaniclastic rocks crop out along the Black Sea coastline in Turkey. They are part of a magmatic arc that formed as a result of northward subduction of the Tethys ocean beneath the southern margin of Laurasia. The lower part of the Upper Cretaceous volcanism in the Kefken region, 100 km northeast of Istanbul, is represented by basaltic andesites, andesites, agglomerates and tuffs, which have yielded Late Cretaceous (Campanian, ca. 83 Ma) U-Pb zircon ages. The volcanic and volcanoclastic rocks are stratigraphically overlain by shallow to deep marine limestones, which range in age from Late Campanian to Early Eocene.  Geochemically, basaltic andesites and andesites display negative anomalies in Nb, Ta and Ti, enrichment in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). Light rare earth elements (LREE) show slightly enrichment relative to heavy rare earth elements (La<sub>cn</sub>/Yb<sub>cn</sub> =2.51-3.63) and there are slight negative Eu anomalies (Eu/Eu* = 0.71-0.95) in basaltic andesite and andesite samples. The geochemical data indicate that Campanian volcanic rocks were derived from the partial melting of the mantle wedge induced by hydrous fluids released by dehydration of the subducted oceanic slab.</p><p>There is also a horizon of volcanic rocks, about 230 m thick, within the Late Campanian-Early Eocene limestone sequence.  This volcanic horizon, which consists of pillow basalts, porphyritic basalts,  andesites and dacites, is of Maastrichtian age based on paleontological data from the intra-pillow sediments and U-Pb zircon ages from the andesites and dacites (72-68 Ma).  The Maastrichtian andesites and dacites are geochemically distinct from the Campanian volcanic rocks. They show distinct adakite-like geochemical signatures with high ratios of Sr/Y (>85.5), high La<sub>cn</sub>/Yb<sub>cn </sub>(16.4-23.7) ratios, low content of Y (7.4-8.6 ppm) and low content of heavy rare-earth elements (HREE). The adakitic rocks most probably formed as a result of partial melting of the subducting oceanic slab under garnet and amphibole stable conditions.</p><p>The Upper Cretaceous arc sequence in the Kefken region shows a change from typical subduction-related magmas to adakitic ones, accompanied by decrease in the volcanism.</p><p> </p><p> </p>

Geochemistry and tectonic environment of the Şarkışla area volcanic rocks in central Anatolia, Turkey

1987 ◽  
Vol 51 (362) ◽  
pp. 553-559 ◽  
Author(s):  
E. Gökten ◽  
P. A. Floyd
Keyword(s):  
Upper Cretaceous ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Central Anatolia ◽  
Magmatic Arc ◽  
Early Tertiary ◽  
Tectonic Environment ◽  
Geochemical Study ◽  
Lithological Composition ◽  
Back Arc

AbstractThe volcanic rocks of the Şarkışla area in northeastern central Anatolia are associated with volcaniclastics, turbiditic limestones and pelagic-hemipelagic shales of Upper Cretaceous-Palaeocene age. A preliminary geochemical study was undertaken to constrain local tectonic models, and due to the variable altered nature of the volcanics, determine the lithological composition and magma type. Chemically the volcanics are an andesite-dominated suite of calc-alkali lavas, probably developed adjacent to an active continental margin in a local (ensialic back-arc?) basinal area. The volcanic activity was probably related to a postulated magmatic arc just south of the area during the early Tertiary.

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.

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