Spelling suggestions: "subject:"phenocrysts"" "subject:"phenocsrysts""
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Geochemical distribution of selected elements in basalts and their constituent phasesGoodman, Roger J. January 1970 (has links)
No description available.
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The melt inclusions in quartz phenocrysts of the quartz-feldspar porphyry, Harvey Station, New Brunswick /Payette, Christine. January 1985 (has links)
No description available.
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The melt inclusions in quartz phenocrysts of the quartz-feldspar porphyry, Harvey Station, New Brunswick /Payette, Christine. January 1985 (has links)
No description available.
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Petrology of Inclusion-Rich Lavas at Minna Bluff, McMurdo Sound, Antarctica: Implications for Magma Origin, Differentiation, and Eruption DynamicsScanlan, Mary K. 19 September 2008 (has links)
No description available.
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Geochronology and geochemistry of the Postberg ignimbrites, Saldanha, Western Cape, South AfricaMisrole, Matthew January 2020 (has links)
>Magister Scientiae - MSc / The Saldania Belt in southern Africa, a product of the Pan-African Saldanian Orogeny, forms part of a system of Neoproterozoic mobile belts that border and weld older cratons on the African continent. It is a low-grade orogenic belt situated along the southwestern margin of the Kalahari Craton and is composed of several inliers of greenschist facies metasedimentary and metavolcanic rocks (Malmesbury Group), unroofed in megaanticlinal hinges of the Permo-Triassic Cape Fold Belt. The Malmesbury Group rocks were syn- and post-tectonically intruded in a pervasive transpressive regime between 555 Ma and 515 Ma by Neoproterozoic to early Cambrian S-, I- and A-type granites, monzodiorites, gabbros and quartz syenites, which collectively constitute the rocks of the Cape Granite Suite (CGS). Along the south-western coastline of South Africa, the Saldanha Bay Volcanic Complex (which forms part of the CGS) is divided into two eruption centres both of which have been identified as “intra-caldera pyroclastic ignimbrites”. The Postberg eruption centre is situated to the south of the Saldanha Bay entrance and the Saldanha eruption centre is situated to the north of the entrance. Both eruption centres display distinct geochemical signatures, the most apparent being the greater TiO2 concentrations (> 0.25 wt. %) of the Saldanha centre ignimbrites when compared to its Postberg centre counterparts. The Postberg eruption centre consists of S-type rhyolitic ignimbrites which are subdivided into the two geochemically distinct Plankiesbaai and Tsaarsbank Ignimbrites. Small amounts of the Jacobs Bay and Saldanha Ignimbrites (less felsic tephra from the Saldanha eruption centre) are also present in the Postberg eruption centre. A robust geochemical analysis of both the Plankiesbaai and Tsaarsbank magma groups display high SiO2 content (>76 wt. %), a lack of variation in TiO2 and Zr, high Al2O3 and ASI (aluminium saturation index) values (> 1.0 and generally >1.1 which, on average, is higher than the Saldanha eruption centre ignimbrites), low CaO and Na2O, and a highly ferroan character. The Plankiesbaai ignimbrite also display lower #Mg concentration compared to the Tsaarsbank ignimbrite. Typical geochemical trends in the Postberg eruption centre include the lack of variation in Zr content, higher Rb content and lower Sr, Ba, V and Zn concentrations when compared to the tephra of the Saldanha eruption centre found in the Postberg area.
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Geochemical Study Of The Mamainse Point Rhyolites, Algoma District, OntarioJackson, Michael R. 04 1900 (has links)
<p> A series of shallow intrusive and extrusive silicic
volcanic rocks near Mamainse Point, Ontario, were sampled and
analyzed for major and trace elements. The rocks are mainly
fine grained, silicified rhyolites grading to dacites
containing phenocrysts of quartz and feldspar.
The analyses performed (XRF, AAS) indicate that many
of these rocks have been altered from the normal igneous
spectrum of rocks to potassic keratophyres. An enrichment
in potash from potash metasomatism has accompanied low
grade, burial metamorphism to produce a secondary mineral
assemblage including chlorite, carbonate, and sericite.
Local intense alteration of some rocks involved the depletion
of mobile alkalis and addition of water and co2 to form
calcite and kaolin.
The overall field and chemical evidence suggest a
single magmatic source for these rocks. </p> / Thesis / Bachelor of Arts (BA)
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A trace element study of plagioclase and clinopyroxene phenocrysts in historical lavas from Mt. Etna, Sicily, by laser ablation ICP-MSRusso, Christopher J. 20 July 2001 (has links)
Graduation date: 2002
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Source and magmatic evolution of the Neapolitan volcanoes through time (Southern Italy)Iovine, Raffaella Silvia 09 February 2018 (has links)
No description available.
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Breccia of Frog Lakes : reconstructing Triassic volcanism and subduction initiation in the east-central Sierra Nevada, CaliforniaRoberts, Sarah Elizabeth 12 March 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / The Antler and Sonoma orogenies occurred along the southwest-trending passive Pacific margin of North America during the Paleozoic concluding with the accretion of the McCloud Arc. A southeast-trending sinistral transform fault truncated the continental margin in the Permian, becoming a locus for initiation of an east-dipping subduction zone creating the Sierran magmatic arc. Constrained in age between two early Triassic tuff layers, the volcanic clasts in the breccia of Frog Lakes represent one of the earliest records of mafic magmatism in the eastern Sierra Nevada. Tholeiitic rock clasts found in the breccia of Frog Lakes in the Saddlebag Lake pendant in the east central Sierra Nevada range in composition from 48% to 63% SiO2. Boninites produced by early volcanism of subduction initiation by spontaneous nucleation at the Izu-Bonin-Mariana arc are more depleted in trace element concentrations than the clasts while andesites from the northern volcanic zone of the Andes produced on crust 50 km thick have similar levels of enrichment and provide a better geochemical modern analogue. Textural analysis of the breccia of Frog Lakes suggest a subaqueous environment of deposition from a mature magmatic arc built on continental crust > 50 km thick during the Triassic. The monzodiorites of Saddlebag and Odell Lakes are temporal intrusive equivalents of the breccia of Frog Lakes and zircon geochemistry indicates a magmatic arc petrogenesis.
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