2012 Lecture 16 Basalt

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Flavors of basalts! Flavours of basalts! ü"Alkaline! ü"Sub-alkaline! ü" Tholeiitic ! ü" Calc-alkaline! ü"Mid Ocean Ridge basalts (MORBs)! ü"Ocean Island basalts (OIBs)! ü"Arc basalts! Figure 16-3. Data compiled by Terry Plank (Plank and Langmuir, 1988) Earth Planet. Sci. Lett., 90, 349-370. Ocean islands in the Atlantic See mechanisms of magma Differentiation on next lecture… Figure 14.3. After Wilson (1989) Igneous Petrogenesis. Kluwer. MORBs vs. OIBs! ü"Mid-Ocean Ridge vs. Ocean Island ! Mid-Ocean Ridge System! Oceanic Intraplate Volcanism! MORB vs. OIB! ü"Similar major element concentrations! ü"Difference in trace element abundance! increasing incompatibility Figure 10-13b. Spider diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MORB). From Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989). Calc-alkaline (arc) basalts! Crater Lake vs. Skaergaard intrusion! Magma chamber in hot spot-rifting environment Volcanic Arc Calc-alkaline basalts! Addition of Fluid-mobile elements AFM diagram! Basalts Tholeiitic – hot spot Divergent margins Calc-alkaline Subduction zones (arcs) Alkaline basalts – in every tectonic settings Figure 14.3. After Wilson (1989) Igneous Petrogenesis. Kluwer. Questions! ü"Difference between OIBs and MORBs?! ü"Difference between calc-alkaline basalts (arcs) and MORBs?! ü"Alkaline basalts?! Style of mantle melting! ü"CA basalts => Flux melting! ü"High water content and higher O concentration (fO2) from slab dehydration! ü"Early crystallization of oxide phases (low Fe, Ti, Nb, Ta in residual magmas)! ü"OIBs and MORBs => Decompression melting! ü"Melting at shallow depths form depleted mantle (previously melted)! ü"MORB! ü"Melting deeper from a more enriched mantle! ü"OIB! Alkaline basalts?! ü"Low degrees of mantle melting! Ø" Enrichments in melt-loving elements (incompatible elements)! Amount of melting and depth of melting! 1100 1200 1300 1400 1500 (TºC) % melting (and P) solidus determine the 10 Spinel lherzolite 20% composition of 50 (Ol-opx-cpx-sp) 1% the basaltic 20% 20 magma produced 10% Garnet lherzolite 1% (Ol-opx-cpx-gar) 30 P (kbars) P Depth(km) 100 40 Alkaline magmas: Graphite Low degrees of Diamond 50 melting 150 60 Flavors of basalts! OIB = Alkaline magmas or tholeiites From deeper melting of more primitive mantle MORB Island Arc basalts Tholeiites from shallow Calc-alkaline Continental Arc basalts Melting of depleted (rare) Calc-alkaline From fluxed depleted mantle mantle wedge From fluxed depleted mantle wedge Continental hot spots and rifts: Alkaline magmas or tholeiites .

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Chapter 10: Mantle Melting and the Generation of Basaltic Magma 2 Principal Types of Basalt in the Ocean Basins Tholeiitic Basalt and Alkaline Basalt
Chapter 10: Mantle Melting and the Generation of Basaltic Magma 2 principal types of basalt in the ocean basins Tholeiitic Basalt and Alkaline Basalt Table 10.1 Common petrographic differences between tholeiitic and alkaline basalts Tholeiitic Basalt Alkaline Basalt Usually fine-grained, intergranular Usually fairly coarse, intergranular to ophitic Groundmass No olivine Olivine common Clinopyroxene = augite (plus possibly pigeonite) Titaniferous augite (reddish) Orthopyroxene (hypersthene) common, may rim ol. Orthopyroxene absent No alkali feldspar Interstitial alkali feldspar or feldspathoid may occur Interstitial glass and/or quartz common Interstitial glass rare, and quartz absent Olivine rare, unzoned, and may be partially resorbed Olivine common and zoned Phenocrysts or show reaction rims of orthopyroxene Orthopyroxene uncommon Orthopyroxene absent Early plagioclase common Plagioclase less common, and later in sequence Clinopyroxene is pale brown augite Clinopyroxene is titaniferous augite, reddish rims after Hughes (1982) and McBirney (1993). Each is chemically distinct Evolve via FX as separate series along different paths Tholeiites are generated at mid-ocean ridges Also generated at oceanic islands, subduction zones Alkaline basalts generated at ocean islands Also at subduction zones Sources of mantle material Ophiolites Slabs of oceanic crust and upper mantle Thrust at subduction zones onto edge of continent Dredge samples from oceanic crust Nodules and xenoliths in some basalts Kimberlite xenoliths Diamond-bearing pipes blasted up from the mantle carrying numerous xenoliths from depth Lherzolite is probably fertile unaltered mantle Dunite and harzburgite are refractory residuum after basalt has been extracted by partial melting 15 Tholeiitic basalt 10 5 Figure 10-1 Brown and Mussett, A. E. (1993), The Inaccessible Earth: An Integrated View of Its Lherzolite Structure and Composition.
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Sarah Lambart - 2016 Recap Lecture 16: Isotopes 101 • Radioactive (parent) vs. radiogenic (daugher) isotopes • Unstable (radioactive) vs stable isotopes • Uses: for dating (geochronology) and as tracers (source composition) Recap Lecture 16: Isotopes 101 • As tracers: • Ex.: 87Sr/86Sr: DMM < co < cc High Rb/Sr c.c. Crust evolution o.c. 87Sr 86Sr melting event DMM Low Rb/Sr Mantle Primitive Mantle/BSE Depleted mantle evolution € 4.55 b.y. Time -> today Recap Lecture 16: Isotopes 101 • As tracers: • Ex.: 87Sr/86Sr: DMM < co < cc • Isotopes do not fractionate during partial melting and crystallization processes!!! ⇒ 87Sr/86Sr (source) = 87Sr/86Sr (magma) ⇒ if 87Sr/86Sr (magma) ≠ constant ⇒ several source components (subducted oc, subducted sediments, subcontinental lithosphere, ect…) or crustal contamination (AFC) Mid-Ocean Ridges Basalt (MORB) • Facts: • Oceanic floors: 60% of Earth’s surface • Most of the rocks produced at ridges are MORB • Large compositional variability 3) Source composition 2) Melting conditions (Pressure, Temperature) 4) Melt segregation and transport 1) Magma differentiation/crystallization Structure of Mid-Ocean Ridges • Ridges: submarine (most of the time) mountain chains ≈ 3000m Slow-spreading ridge: Fast-spreading ridge: Ex.: Mid-Atltantic ridge : 2cm/yr Ex.: EPR: 10 cm/yr Fig. 13-15 in Winters Structure of Mid-Ocean Ridges • Ridges: submarine (most of the time) mountain chains ≈ 3000m Slow-spreading ridge: Fast-spreading ridge: Ex.: Mid-Atltantic ridge : 2cm/yr Ex.: EPR: 10 cm/yr - Spreading rate: 8-10 cm/yr - Spreading rate: <5 cm/yr - Axial uplift = horst - Axial valley = rift (relief = 300m) - Bigger magma reservoir ⇒ more differentiation - Numerous normal faults: active seismic zone - Small multiple magma reservoirs? The oceanic lithosphere • Maturation d(m) = 2500 + 350 T1/2 (Ma) Fig.
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29. Sulfur Isotope Ratios of Leg 126 Igneous Rocks1
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Proquest Dissertations
OXIDATION AND METASOMATISM OF LITHOSPHERIC MANTLE BENEATH THE SOUTHERN SOUTH AMERICA by Jian Wang, B.Sc, M.Sc. Thesis submitted to the Faculty of Graduate & Postdoctoral Studies in partial fulfillment of the requirements for the Ph.D. degree in the Earth Sciences Ottawa-Carleton Geoscience Centre and University of Ottawa Ottawa, Canada May, 2007 © 2007 Jian Wang Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-49403-5 Our file Notre reference ISBN: 978-0-494-49403-5 NOTICE: AVIS: The author has granted a non L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in et des droits moraux qui protege cette these. this thesis. Neither the thesis Ni la these ni des extraits substantiels de nor substantial extracts from it celle-ci ne doivent etre imprimes ou autrement may be printed or otherwise reproduits sans son autorisation.
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Slab-Tearing Following Ridge-Trench Collision: Evidence from Miocene Volcanism in Baja California, México ⁎ Carlos Pallares A, , René C
Journal of Volcanology and Geothermal Research 161 (2007) 95–117 www.elsevier.com/locate/jvolgeores Slab-tearing following ridge-trench collision: Evidence from Miocene volcanism in Baja California, México ⁎ Carlos Pallares a, , René C. Maury a, Hervé Bellon b, Jean-Yves Royer a, Thierry Calmus c, Alfredo Aguillón-Robles d, Joseph Cotten b, Mathieu Benoit a, François Michaud e, Jacques Bourgois f a UMR 6538, Domaines Océaniques, IUEM, Université de Bretagne Occidentale, Place Nicolas Copernic, F-29280 Plouzané, France b UMR 6538, Domaines Océaniques, IUEM, Université de Bretagne Occidentale, 6, Av. Le Gorgeu, C.S. 93837, F-29238 Brest Cedex 3, France c Estación Regional del Noroeste, Instituto de Geología, UNAM, Hermosillo, Son., C.P. 83000, México d Instituto de Geología, UASLP, Av. Dr. Manuel Nava no. 5, Zona Universitaria, San Luis Potosí, S.L.P., C.P. 78250, México e UMR 6526, Géosciences Azur, Université Pierre et Marie Curie, F-06235 Villefranche sur Mer, France f IRD and CNRS, UMR 6526, Escuela Politecnica Nacional (EPN), Departamento de Geología y Riesgos Naturales (DGRN), Andalucia n/s, P.O. Box 17-01-2759, Quito, Ecuador Received 15 June 2006; received in revised form 3 November 2006; accepted 12 November 2006 Available online 5 January 2007 Abstract Neogene magmatic activity in Central Baja California underwent a major change at ca. 12.5 Ma, when the Pacific–Farallon active oceanic ridge collided with the trench east of Vizcaíno Peninsula. The calc-alkaline magmatism which built the Comondú volcanic arc vanished and was replaced by unusual volcanic associations, which were erupted within six Late Miocene to Quaternary volcanic fields (Jaraguay, San Borja, San Ignacio, Santa Rosalía, Santa Clara, La Purísima), delineating a 600 km array along the Baja California Peninsula.
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Modern Analogues for Miocene to Pleistocene Alkali
Cent. Eur. J. Geosci. • 2(3) • 2010 • 339-361 DOI: 10.2478/v10085-010-0013-8 Central European Journal of Geosciences Modern analogues for Miocene to Pleistocene alkali basaltic phreatomagmatic fields in the Pannonian Basin: “soft-substrate” to “combined” aquifer controlled phreatomagmatism in intraplate volcanic fields Research Article Károly Németh1∗, Shane J. Cronin1, Miguel J. Haller2, Marco Brenna1, Gábor Csillag3 1 Volcanic Risk Solutions CS-INR, Massey University, PO Box 11 222, Palmerston North, New Zealand, 2 Universidad Nacional de la Patagonia San Juan Bosco – Sede Puerto Madryn, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina, 3 Geological Institute of Hungary, Department of Geological Research, Stefánia út 14, Budapest H-1143, Hungary, Received 29 April 2010; accepted 4 June 2010 Abstract: The Pannonian Basin (Central Europe) hosts numerous alkali basaltic volcanic fields in an area similar to 200 000 km2. These volcanic fields were formed in an approximate time span of 8 million years producing small- volume volcanoes typically considered to be monogenetic. Polycyclic monogenetic volcanic complexes are also common in each field however. The original morphology of volcanic landforms, especially phreatomagmatic volcanoes, is commonly modified. by erosion, commonly aided by tectonic uplift. The phreatomagmatic volcanoes eroded to the level of their sub-surface architecture expose crater to conduit filling as well as diatreme facies of pyroclastic rock assemblages. Uncertainties due to the strong erosion influenced by tectonic uplifts, fast and broad climatic changes, vegetation cover variations, and rapidly changing fluvio-lacustrine events in the past 8 million years in the Pannonian Basin have created a need to reconstruct and visualise the paleoenvironment into which the monogenetic volcanoes erupted.
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Implications for Intraplate Seamount Formation
Article Volume 13, Number 1 7 December 2012 Q0AM05, doi:10.1029/2012GC004301 ISSN: 1525-2027 Detailed volcanostratigraphy of an accreted seamount: Implications for intraplate seamount formation Susan R. Schnur College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 CEOAS Administration Building, Corvallis, Oregon 97331, USA ([email protected]) Lisa A. Gilbert Maritime Studies Program of Williams College and Mystic Seaport, 75 Greenmanville Avenue, Mystic, Connecticut 06355, USA ([email protected]) [1] Seamounts are a ubiquitous feature of the seafloor but relatively little is known about their internal struc- ture. A seamount preserved in the Franciscan mélange of California suggests a sequence of formation com- mon to all seamounts. Field mapping, geophysical measurements, and geochemical analyses are combined to interpret three stages of seamount growth consistent with the formation of other intraplate seamounts such as the Hawaiian volcanoes and the island of La Palma. A seamount begins to form as a pile of closely packed pillows with a high density and low porosity. Small pillow mound volcanoes common at mid-ocean ridges are seamounts that do not grow beyond this initial stage of formation. The second stage of seamount formation is marked by the first occurrence of breccia. As the seamount grows and becomes topographically more complex, slope varies and fractured material may begin to accumulate. Magma supply may also become spatially diffuse as the seamount grows and new supply pathways develop through the edifice. The second stage thus exhibits variability in both flow morphologies and geophysical properties. The final cap stage is composed of thin flows of various morphologies.
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Magma Genesis, Degassing, and Mixing in Rifts and Arcs
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Basalt Tectonic Discrimination Using Combined Machine Learning Approach
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