DOCSLIB.ORG

Título Aquí (Times New Roman 16, Negrita, Centrado)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Título Aquí (Times New Roman 16, Negrita, Centrado) XII Congreso Geológico Chileno Santiago, 22-26 Noviembre, 2009 S7_032 Petrologic Constraints on Magma Ascent Rates in the Arc and Back-Arc Near the Magallanes Fault Zone, Austral Chile Stern, C.R.1, Skewes, M.A.1 (1) Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0399, USA: [email protected] General The Magallanes Fault Zone (MFZ) forms the plate boundary between the South American and Scotia plates (Fig. 1). This dominantly strike-slip continental fault generates a complex system of structural responses, including rotation and rifting over a broad area [1-3]. Volcanoes located within the extended area of this fault system include Mt. Burney stratovolcano and Cook Island dome complex, the two southernmost volcanoes in the Austral Volcanic Zone of the Andean arc [4], and the Pali-Aike field of back-arc basalts, the southernmost field of the Patagonian plateau lavas [5,6]. Here we review petrologic constraints on relative differences in magma ascent rates between these two different tectonic environments, both in the area of the MFZ, compared to volcanoes in similar environments further to the north, outside the area of influence of the MFZ. Pali-Aike back-arc basalts The alkali olivine basalt of the Pali-Aike volcanic field formed between 3.8 Ma to <10,000 Ka [6] in the northern part of the area of structural complexity generated by the MFZ [2,3]. These basalts erupted from cones and fissures aligned in northwest-southeast, east-west, and southeast-northwest directions, subparallel to the alignment of both the MGZ and normal faults associated with rotation and rifting generated by this fault system. Their chemical compositions are similar to some oceanic island basalts (OIB) consistent with derivation by low degrees of melting of mantle asthenosphere, either due to subduction-induced thermal and mechanical perturbation [5,7], or uprise through a slab-window formed due to subduction of the Chile Rise [6]. A number of lines of evidence indicate that the Pali-Aike basalts ascended from their mantle source, at >80 km, to the surface at rates of 1 to >6 m/sec [8,9], similar to the velocities estimated for the emplacement of kimberlite magmas and more rapidly than 1 XII Congreso Geológico Chileno Santiago, 22-26 Noviembre, 2009 olivine basalts in other fields of the Patagonian plateau lavas located north of the area of the MFZ. This evidence includes, first, the presence in these basalts of garnet-peridotite xenolith derived from up to 60-80 km depth [5,10,11]. Garnet-peridotite xenoliths are not found elsewhere in Patagonia plateau lavas. Some of these xenoliths are as large as >40 cm in diameter, which implies rapid turbulent rise of the Pali-Aike magmas, because the density of the peridotite xenoliths (~3.3 gm/cm) is greater than that of basaltic magma (~3.0 gm/cm), and they could not be carried by these magmas to the surface without turbulent motion. Second, petrologic features of the xenoliths, including the lack of evidence for decompression melting along mineral grain boundaries, and the persistence of amphibole, suggest that these peridotites, which equilibrated in the mantle at temperatures between 720 to 1180°C, did not have time to be significantly heated as they were transported to the surface by the basaltic magmas that erupted at temperatures estimated between 1200 to 1290°C [6]. Finally, determination of dehydration profiles in olivine crystals from these xenoliths, when compared with experimentally determined diffusion coefficients for dehydration of olivine, imply ascent rates from 70 km of 6 ± 3 m/sec [9], bringing the xenoliths to the surface in between only 2 to <7 hours. Mt. Burney and Cook Island adakitic andesite arc volcanoes The Mt. Burney stratovolcano and the Cook Island dome complex, both active in the Holocene, are the southernmost volcanic centers in the Andean arc (Fig. 1). The Cook Island dome complex occurs on the Scotia plate, along the Beagle Canal south of the Magallanes Fault, in an area below which the slow subduction of the Antarctic plate is highly oblique. Mt. Burney occurs north of the MFZ, above arc-parallel strike-slip faults associated with thias system, in a region of less oblique subduction. Both volcanoes have erupted adakitic andesites formed by melting of subducted oceanic lithosphere, followed by relatively limited interaction with the overlying mantle wedge and continental crust compared to the other four AVZ volcanoes located north, out of the area of the MFZ [4]. The four more northern volcanoes in the AVZ contain strongly corroded, partially oxidized and recrystallized amphibole phenocrysts, suggesting extensive water loss in the upper crust, and groundmass glass with variable composition possibly produced by magma mixing. Both Mt. Burney and Cook Island adakites contain high Mg# and high Cr/(Cr +Al) clinopyroxenes (Fig. 2), typically in the cores of lower Mg# magmatic clinopyroxenes [4]. These high Mg# clinopyroxene cores are interpreted as mantle- derived xenocrysts. Mt. Burney adakites also contain rare high Mg# olivine xenocrysts. The geochemical evidence for the relatively limited interaction of the parental slab- derived adakite melts erupted from Cook Island and Mt. Burney volcanoes, as well the presence of possible mantle-derived clinopyroxene xenocyrsts in their volcanic products, suggest that Cook Island and Mt Burney adakites rose more rapidly to the surface from their subcrustal source regions than andesites and dacites erupted from the other four AVZ volcanoes located to the north of the MFZ. 2 XII Congreso Geológico Chileno Santiago, 22-26 Noviembre, 2009 Discussion and Conclusions Pali-Aike alkali olivine basaltic magma apparently ascended to the surface both from deeper and also more rapidly than other basalts of the Patagonian plateau lavas, as indicated by the larger size of their garnet-peridotite xenoliths, derived from greater depths in the lithosphere than xenoliths that occur in other Patagonian plateau lava fields. Cook Island and Mt. Burney adakitic andesites also apparently rose to the surface more rapidly than adakitic magmas erupted from more northern volcanoes in the AVZ, based on both the geochemical evidence for their more limited interaction with the mantle and crust, and the presence of mantle-derived clinopyroxene xenocrysts in the adakites erupted by these two volcanoes. Thus, it appears that the complex continental fault system generated by the MFZ has provided structural pathways for relatively rapid ascent of magmas in both the arc and back-arc compared to these same environments further to the north outside the influence of this fault system. The data also indicate that although the Mt. Burney and Cook Island adakitic andesites did not ascend as rapidly as the back- arc basalts, these arc magmas did not undergo MASH processes of mixing, assimilation, storage and homogenization as they rose from their source region to the surface. Figure 1. Map of the six volcanoes in the Andean Austral Volcanic Zone, the southernmost units of the Patagonian plateau lavas including the Pali-Aike field, and the major plate boundaries in southernmost South America. 3 XII Congreso Geológico Chileno Santiago, 22-26 Noviembre, 2009 References [1] Polonia, A., Brancolini, G., Torelli, L., Vera, E. (1999) Structural variability at the active continental margin off southernmost Chile. Journal of Geodynamics, vol. 27, 289- 307. [2] Diraison, M., Cobbold, P.R., Gapais, D., Rossello, E.A. (1997) Magellan Strait: Part of a Neogene rift system. Geology, vol. 25, 703-706. [3] Diraison, M., Cobbold, P.R., Gapais, D., Rossello, E.A., Le Corre, C. (2000) Crustal thickening, wrenching and rifting in the foothills of the southernmost Andes. Tectonophysics, vol. 316, 91-116. [4] Stern, C.R., Kilian, R. (1996) Role of the subducted slab, mantle wedge and continental crust in the generation of adakites from the Andean Austral Volcanic Zone. Contributions to Mineralogy and Petrology, vol. 123, 263-281. [5] Skewes, M.A., Stern, C.R. (1979) Petrology and geochemistry of alkali basalts and ultramafic inclusions from the Pali-Aike volcanic fields in southern Chile and the origin of the Patagonian plateau lavas. Journal of Volcanology and Geothermal Research, vol. 6, 3-25. [6] D'Orazio, M., Agostini, S., Mazzarini, F., Innocenti, F., Manetti, P., Haller, M.J., Lahsen, A. (2000) The Pali Aike volcanic field, Patagonia: slab-window magmatism near the tip of South America. Tectonophysics, vol. 321, p. 407–427. [7] Stern, C.R., Frey, F.A., Futa, K., Zartman, R.E., Peng, Z., Kyser, T.K. (1990) Trace element and Sr, Nd, Pb and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau Lavas of southernmost South America. Contributions to Mineralogy and Petrology, vol. 104, 294-308. [8] Selverstone, J., Stern, C.R. (1983) Petrochemistry and recrystallization history of granulite xenoliths from the Pali-Aike volcanic field, Chile. American Mineralogist, vol. 68, 1102-1112. [9] Demouchy, S., Jacobson, S.D., Gaillard, F., Stern, C.R. (2006) Rapid magma ascent recorded by water diffusion profiles in mantle olivine. Geology, vol. 34, 429-432. [10] Stern, C.R., Kilian, R., Olker, B., Hauri, E.H., Kyser, T.K. (1999) Evidence from mantle xenoliths for relatively thin (<100 km) continental lithosphere below the Phanerozoic crust of southernmost South America. Lithos, vol. 48, 217-235. 4.
Load more

Recommended publications
  • Uplift, Rupture, and Rollback of the Farallon Slab Reflected in Volcanic
    PUBLICATIONS Journal of Geophysical Research: Solid Earth RESEARCH ARTICLE Uplift, rupture, and rollback of the Farallon slab reflected 10.1002/2017JB014517 in volcanic perturbations along the Yellowstone Key Points: adakite hot spot track • Volcanic perturbations in the Cascadia back-arc region are derived from uplift Victor E. Camp1 , Martin E. Ross2, Robert A. Duncan3, and David L. Kimbrough1 and dismemberment of the Farallon slab from ~30 to 20 Ma 1Department of Geological Sciences, San Diego State University, San Diego, California, USA, 2Department of Earth and • Slab uplift and concurrent melting 3 above the Yellowstone plume Environmental Sciences, Northeastern University, Boston, Massachusetts, USA, College of Earth, Ocean, and Atmospheric promoted high-K calc-alkaline Sciences, Oregon State University, Corvallis, Oregon, USA volcanism and adakite generation • Creation of a seismic hole beneath eastern Oregon resulted from thermal Abstract Field, geochemical, and geochronological data show that the southern segment of the ancestral erosion and slab rupture, followed by Cascades arc advanced into the Oregon back-arc region from 30 to 20 Ma. We attribute this event to thermal a period of slab rollback uplift of the Farallon slab by the Yellowstone mantle plume, with heat diffusion, decompression, and the release of volatiles promoting high-K calc-alkaline volcanism throughout the back-arc region. The greatest Supporting Information: • Supporting Information S1 degree of heating is expressed at the surface by a broad ENE-trending zone of adakites and related rocks • Data Set S1 generated by melting of oceanic crust from the Farallon slab. A hiatus in eruptive activity began at ca. • Data Set S2 22–20 Ma but ended abruptly at 16.7 Ma with renewed volcanism from slab rupture occurring in two separate • Data Set S3 regions.
    [Show full text]
  • Mantle Peridotite Xenoliths
    Earth and Planetary Science Letters 260 (2007) 37–55 www.elsevier.com/locate/epsl Mantle peridotite xenoliths in andesite lava at El Peñon, central Mexican Volcanic Belt: Isotopic and trace element evidence for melting and metasomatism in the mantle wedge beneath an active arc ⁎ Samuel B. Mukasa a, , Dawnika L. Blatter b, Alexandre V. Andronikov a a Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA b Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA Received 6 July 2006; received in revised form 3 May 2007; accepted 7 May 2007 Available online 13 May 2007 Editor: R.W. Carlson Abstract Peridotites in the mantle wedge and components added to them from the subducting slab are thought to be the source of most arc magmas. However, direct sampling of these materials, which provides a glimpse into the upper mantle beneath an active margin, is exceedingly rare. In the few arc localities where found, peridotite xenoliths are usually brought to the surface by basaltic magmas. Remarkably, the hornblende-bearing ultramafic xenoliths and clinopyroxene megaxenocrysts from El Peñon in the central Mexican Volcanic Belt were brought to the surface by a Quaternary high-Mg siliceous andesite, a rock type usually considered too evolved to be a direct product of mantle melting. The xenoliths and megaxenocrysts from El Peñon represent lithospheric mantle affected by significant subduction of oceanic lithosphere since as early as the Permian. Trace element and radiogenic isotope data we report here on these materials suggest a history of depletion by melt extraction, metasomatism involving a fluid phase, and finally, limited reaction between the ultramafic materials and the host andesite, probably during transport.
    [Show full text]
  • Depleted Spinel Harzburgite Xenoliths in Tertiary Dykes from East Greenland: Restites from High Degree Melting
    Earth and Planetary Science Letters 154Ž. 1998 221±235 Depleted spinel harzburgite xenoliths in Tertiary dykes from East Greenland: Restites from high degree melting Stefan Bernstein a,), Peter B. Kelemen b,1, C. Kent Brooks a,c,2 a Danish Lithosphere Centre, éster Voldgade 10, DK-1350 Copenhagen K, Denmark b Woods Hole Oceanographic Institution, Woods Hole, City, MA 02543, USA c Geological Institute, UniÕersity of Copenhagen, éster Voldgade 10, DK-1350 Copenhagen K, Denmark Received 28 April 1997; revised 19 September 1997; accepted 4 October 1997 Abstract A new collection of mantle xenoliths in Tertiary dykes from the Wiedemann Fjord area in Southeast Greenland shows that this part of the central Greenland craton is underlain by highly depleted peridotites. The samples are mostly spinel harzburgites with highly forsteritic olivinesŽ. Fo87± 94 , average Fo 92.7 . This, together with unusually high modal olivine contentsŽ. 70±)95% , places the Wiedemann harzburgites in a unique compositional field. Relative to depleted Kaapvaal harzburgites with comparable Fo in olivine, the Wiedemann samples have considerably lower bulk SiO2 Ž average 42.6 wt% versus 44±49 wt%. Spinel compositions are similar to those in other sub-cratonic harzburgites. Pyroxene equilibrium temperatures average 8508C, which is above an Archaean cratonic geotherm at an inferred pressure of 1±2 GPa, but low enough so that it is unlikely that the xenoliths represent residual peridotites created during Tertiary magmatism. Among mantle samples, the Wiedemann harzburgites are, in terms of their bulk composition, most similar to harzburgites from the ophiolites of Papua New GuineaŽ. PNG and New Caledonia Ž.
    [Show full text]
  • Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona
    Mantle Origin and Flow Sorting of Megacryst-Xenolith Inclusions in Mafic Dikes of Black Canyon, Arizona U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1541 AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current- year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" are no longer available. Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry. Order U.S. Geological Survey publications by mail or over the counter from the offices given below. BY MAIL OVER THE COUNTER Books Books and Maps Professional Papers, Bulletins, Water-Supply Papers, Tech­ Books and maps of the U.S. Geological Survey are available niques of Water-Resources Investigations, Circulars, publications over the counter at the following U.S. Geological Survey offices, of general interest (such as leaflets, pamphlets, booklets), single all of which are authorized agents of the Superintendent of Docu­ copies of Earthquakes & Volcanoes, Preliminary Determination of ments. Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out of print at the Superin­ • ANCHORAGE, Alaska—4230 University Dr., Rm.
    [Show full text]
  • Experimental Constraints on Adakitic Metasomatism of Mantle Wedge Peridotites Below Patagonia
    O EOL GIC G A D D A E D C E I H C I L E O S F u n 2 d 6 la serena octubre 2015 ada en 19 Experimental constraints on adakitic metasomatism of mantle wedge peridotites below Patagonia Alexandre Corgne * and Manuel Schilling D. Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile *Contact email: [email protected] Abstract. We performed a series of high-pressure (1.5 and Quaternary alkali lavas in the back-arc region (e.g. GPa) and high-temperature (1000-1300 ºC) experiments to Stern and Kilian, 1996; Gorring et al., 1997). The back-arc investigate the geochemical imprints of adakitic lavas are hosts of frequent mantle xenoliths, the study of metasomatism on mantle wedge peridotite. Reaction which has contributed to a better understanding of the couples were prepared using a powdered adakite from petrological and geochemical variability of the sub- Cerro Pampa (Argentina) placed next to a fragment of continental lithospheric mantle (e.g. Stern et al., 1990, spinel lherzolite from Pali Aike (Chile). Preliminary results 1999; Gorring and Kay, 2000; Laurora et al., 2001; show that the main changes in phase relations are Bertotto, 2002; Kilian and Stern, 2002; Bjerg et al., 2005, incongruent dissolution of olivine and associated 2009; Schilling et al., 2005; Rivalenti et al., 2004; Ntaflos precipitacion of secondary orthopyroxene, incongruent dissolution of primary spinel and formation of secondary et al., 2007; Wang et al., 2008; Dantas et al. 2009). spinel, as well as precipitation of secondary clinopyroxene and in some instances zoned plagioclase.
    [Show full text]
  • Geology of the Saline County Xenolith and Surrounding Area
    A.G.E.S. Brochure Series 005 State of Arkansas Arkansas Geological Survey Bekki White, State Geologist Geology of the Saline County Xenolith and surrounding area By J. Michael Howard Illustrations and photos by Angela Chandler _______________________________________________________ _______________________________________________________ Xenolith – “ a foreign inclusion in an igneous rock.” Glossary of Geology American Geological Institute 1987 (from the Greek words Xenos, meaning guest or stranger, and Lithos, meaning stone.) _______________________________________________________ _______________________________________________________ Introduction Located in Saline County, Arkansas, at the south edge of the community of Bauxite, this natural outcrop of nepheline syenite contains several geologically interesting features, including a xenolith. Sloping west, the outcrop encompasses about one-quarter acre near the center of section 21, Township 2 South, Range 14 West. In early 1990, the Aluminum Company of America (ALCOA) donated the outcrop along with approximately five surrounding acres of land to the Arkansas Geological Commission so that the site can be preserved for educational purposes. Outcrop of nepheline syenite at xenolith locality. History of the site The outcrop and its geologic features were first described by J. Francis Williams in 1891 in The Igneous Rocks of Arkansas, Arkansas Geological Survey Annual Report for 1890, Volume II. Williams discussed the outcrop and xenolith in some detail and included a sketch of the xenolith (see title page). However, for many years the outcrop location remained unknown to most scientists. In the late 2 1960’s employees in the mining division of ALCOA, suspecting that the site was on their property, began a concerted search. Soon afterward the outcrop was rediscovered and was visited by a staff member of the Arkansas Geological Commission, who in turn told Dr.
    [Show full text]
  • Potassic “Adakite” Magmas and Where They Come From: a Mystery Solved? John Clemens Kingston University (London) Long Xiao China University of Geosciences (Wuhan)
    1 Potassic “adakite” magmas and where they come from: a mystery solved? John Clemens Kingston University (London) Long Xiao China University of Geosciences (Wuhan) 2 3 4 . Adakites are volcanic and intrusive igneous rocks with 55 to 65 wt% SiO2, Al2O3 > 15 wt%, K2O/Na2O typically < 0.6, high La/Yb and Sr/Y ratios and strong depletion in Yb, Y, and HFSE. The name is from Adak island in the Alaskan Aleutians (Aleut “adak” = father). They are typically found in island and continental arc settings. Some believe then to be equivalents of Archæan TTG rocks – hence their importance. Their geochemical and isotopic characteristics suggest an origin by partial melting of mafic crust at pressures high enough to stabilise garnet and eliminate plagioclase. 5 . Adakites that occur in arcs have been interpreted as melts of the down-going slab. Thermal models suggest that slab melting should be restricted to young, hot subduction zones. Atherton and Petford (1993) suggested melting of young lower crustal rocks, in the upper plate, as an alternative to slab melting. There is some direct geological evidence for this alternative in some areas. 6 . Late Mesozoic granitoids in eastern China occur over wide areas, and lack either temporal or spatial association with subduction. Apart from their SiO2 contents, some have all the other geochemical attributes of typical subduction-related adakites, including a lack of Eu anomalies in their REE spectra, except that their K2O/Na2O > 0.95. This is possibly an erroneous attribution as “adakitic”. However this occurrence casts doubt on the assumption of a subduction-related origin for all adakitic magmas.
    [Show full text]
  • Petrogenesis of Cretaceous Adakite-Like Intrusions of the Gangdese Plutonic Belt, Southern Tibet: Implications for Mid-Ocean Ridge Subduction and Crustal Growth
    Lithos 190–191 (2014) 240–263 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Petrogenesis of Cretaceous adakite-like intrusions of the Gangdese Plutonic Belt, southern Tibet: Implications for mid-ocean ridge subduction and crustal growth Yuan-chuan Zheng a,b,⁎, Zeng-qian Hou b, Ying-li Gong c, Wei Liang a,Qing-ZhongSunb,SongZhanga, Qiang Fu a, Ke-Xian Huang a, Qiu-Yun Li a,WeiLia a School of Earth Sciences and Resources, China University of Geosciences, Beijing 100082, PR China b Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China c Laboratory of Department of Thermal Engineering, Tsinghua University, Beijing 100084, PR China article info abstract Article history: We have conducted a whole-rock geochemical, U–Pb zircon geochronological, and in situ zircon Hf–Oisotopic Received 15 August 2013 compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre Accepted 16 December 2013 dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz–diorite). U– Available online 24 December 2013 Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two- Keywords: – – Geochemistry mica granite were emplaced at ca. 96 Ma and 80 76 Ma, respectively, and that the Nuri quartz diorite was fi U–Pb zircon ages emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and ma c enclaves in the Langxian area, Zircon Hf–Oisotopes felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite- 18 Adakite-like rocks like rocks.
    [Show full text]
  • Can Slab Melting Be Caused by Flat Subduction? Geology
    See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/234073692 Can slab melting be caused by flat subduction? Geology Article in Geology · June 2000 DOI: 10.1130/0091-7613(2000)28<535:CSMBCB>2.0.CO;2 CITATIONS READS 428 1,167 4 authors, including: M.-A. Gutscher René C Maury Université de Bretagne Occidentale Université de Bretagne Occidentale 164 PUBLICATIONS 5,573 CITATIONS 356 PUBLICATIONS 11,783 CITATIONS SEE PROFILE SEE PROFILE Erwan Bourdon CFG Services 38 PUBLICATIONS 1,092 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: ACTIVEMARGINS View project Eastern Indonesian Geodynamic Evolution View project All content following this page was uploaded by M.-A. Gutscher on 20 May 2014. The user has requested enhancement of the downloaded file. Can slab melting be caused by flat subduction? Marc-André Gutscher* Laboratoire GTS, UMR 5573, Université Montpellier II, F-34095 Montpellier, France René Maury IUEM/Université Bretagne Occidentale, Place Nicolas Copernic, F-29280 Plouzané, France Jean-Philippe Eissen IRD Centre de Bretagne, B.P. 70, F-29280 Plouzané, France Erwan Bourdon ABSTRACT tion of adakitic magmas for these cases, related to Slab melting has been suggested as a likely source of adakitic arc magmas (i.e., andesitic an unusual subduction geometry known as flat and dacitic magmas strongly depleted in Y and heavy rare earth elements). Existing numerical subduction (Fig. 3) (Sacks, 1983; Pennington, and petrologic models, however, restrict partial melting to very young (<5 Ma) oceanic crust 1984; Cahill and Isacks, 1992; Abbott et al., (typically at 60–80 km depth).
    [Show full text]
  • Title of Thesis
    Additions and Modifications to the Igneous Rock Classification Scheme Senior Thesis Submitted in partial fulfillment of the requirements for the Bachelor of Science Degree in Geological Sciences At The Ohio State University By Matthew R. H. Dugan The Ohio State University 2010 Approved by Anne E. Carey, Advisor School of Earth Sciences T ABLE OF C ONTENTS Abstract………………………………………………………………………....3 Acknowledgements……………………………………………………….…….4 Introduction……………………………………………………………………..5 Discussion……………….………………………………………………………5 Application……………….……………………………………………………..10 References Cited….……….……………………………………………………18 2 Abstract Igneous rocks as they are currently defined are in a sloppy state. Vague wording is throughout the whole of the definition, and there is not even any clear consensus on what it should be defined as. In this paper, I redefine igneous rocks in such a way as to remove a great deal of imprecision, and I go through some of the logical implications of the refined definition. I do not seek to change the intent of the definition, and I do not believe that I have. The most interesting implication of this change is that water, as it occurs on Earth, is an igneous rock, and I construct a basic classification scheme for it. 3 Acknowledgements I wish to thank Dr. Anne Carey for her intense support of the writing of this thesis, her wonderful edits and her dedication to keeping me on this. I also wish to acknowledge my lab group, also lead by Dr. Steve Goldsmith, for their wonderful feedback and encouragement. Dr. Fritz Graf, Professor and chair of the Department of Greek and Latin, was a great asset to me and he deserves recognition for his help in coining neologisms.
    [Show full text]
  • Miocene to Late Quaternary Patagonian Basalts (46–478S): Geochronometric and Geochemical Evidence for Slab Tearing Due to Active Spreading Ridge Subduction
    Journal of Volcanology and Geothermal Research 149 (2006) 346–370 www.elsevier.com/locate/jvolgeores Miocene to Late Quaternary Patagonian basalts (46–478S): Geochronometric and geochemical evidence for slab tearing due to active spreading ridge subduction Christe`le Guivel a,*, Diego Morata b, Ewan Pelleter c,d, Felipe Espinoza b, Rene´ C. Maury c, Yves Lagabrielle e, Mireille Polve´ f,g, Herve´ Bellon c, Joseph Cotten c, Mathieu Benoit c, Manuel Sua´rez h, Rita de la Cruz h a UMR 6112 bPlane´tologie et Ge´odynamiqueQ, Universite´ de Nantes, 2 rue de la Houssinie`re, 44322 Nantes, France b Departamento de Geologı´a. Fac. Cs. Fı´sicas y Matema´ticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile c UMR 6538 bDomaines oce´aniquesQ, UBO-IUEM, place Nicolas-Copernic, 29280 Plouzane´, France d CRPG-CNRS UPR A2300, BP 20, 54501 Vandoeuvre-les-Nancy, France e UMR 5573, Dynamique de la Lithosphe`re, Place E. Bataillon, case 60, 34095, Montpellier Cedex 5, France f LMTG-OMP, 14 Avenue E. Belin, 31400 Toulouse, France g IRD-Departamento de Geologia de la Universidad de Chile, Chile h Servicio Nacional de Geologı´a y Minerı´a, Avda. Santa Marı´a 0104, Santiago, Chile Received 18 May 2005; received in revised form 29 August 2005; accepted 14 September 2005 Abstract Miocene to Quaternary large basaltic plateaus occur in the back-arc domain of the Andean chain in Patagonia. They are thought to result from the ascent of subslab asthenospheric magmas through slab windows generated from subducted segments of the South Chile Ridge (SCR). We have investigated three volcanic centres from the Lago General Carrera–Buenos Aires area (46–478S) located above the inferred position of the slab window corresponding to a segment subducted 6 Ma ago.
    [Show full text]
  • Andean Flat-Slab Subduction Through Time
    Andean flat-slab subduction through time VICTOR A. RAMOS & ANDRE´ S FOLGUERA* Laboratorio de Tecto´nica Andina, Universidad de Buenos Aires – CONICET *Corresponding author (e-mail: [email protected]) Abstract: The analysis of magmatic distribution, basin formation, tectonic evolution and structural styles of different segments of the Andes shows that most of the Andes have experienced a stage of flat subduction. Evidence is presented here for a wide range of regions throughout the Andes, including the three present flat-slab segments (Pampean, Peruvian, Bucaramanga), three incipient flat-slab segments (‘Carnegie’, Guan˜acos, ‘Tehuantepec’), three older and no longer active Cenozoic flat-slab segments (Altiplano, Puna, Payenia), and an inferred Palaeozoic flat- slab segment (Early Permian ‘San Rafael’). Based on the present characteristics of the Pampean flat slab, combined with the Peruvian and Bucaramanga segments, a pattern of geological processes can be attributed to slab shallowing and steepening. This pattern permits recognition of other older Cenozoic subhorizontal subduction zones throughout the Andes. Based on crustal thickness, two different settings of slab steepening are proposed. Slab steepening under thick crust leads to dela- mination, basaltic underplating, lower crustal melting, extension and widespread rhyolitic volcan- ism, as seen in the caldera formation and huge ignimbritic fields of the Altiplano and Puna segments. On the other hand, when steepening affects thin crust, extension and extensive within-plate basaltic flows reach the surface, forming large volcanic provinces, such as Payenia in the southern Andes. This last case has very limited crustal melt along the axial part of the Andean roots, which shows incipient delamination.
    [Show full text]