DOCSLIB.ORG

Osmium Isotope Constraints on Lower Crustal Recycling and Pluton Preservation at Lassen Volcanic Center, CA

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Osmium Isotope Constraints on Lower Crustal Recycling and Pluton Preservation at Lassen Volcanic Center, CA Earth and Planetary Science Letters 199 (2002) 269^285 www.elsevier.com/locate/epsl Osmium isotope constraints on lower crustal recycling and pluton preservation at Lassen Volcanic Center, CA Garret L. Hart a;Ã, Clark M. Johnson a, Steven B. Shirey b, Michael A. Clynne c a Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USA b Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015, USA c U.S. Geological Survey, 345 Middle¢eld Road MS910, Menlo Park, CA 94025, USA Received 12 July 2001; received in revised form 22 February 2002; accepted 28 February 2002 Abstract Osmium isotope compositions of intermediate- to silicic-composition calc-alkaline volcanic rocks from the Lassen volcanic region of the Cascade arc are significantly more radiogenic (QOs = +23 to +224) than typical mantle. These evolved arc rocks in the Lassen region have unradiogenic Sr, Nd, and Pb isotope compositions which overlap with those of contemporaneous mafic lavas. Crystal fractionation of mafic- to intermediate-composition magmas produces Re/Os ratios that are high enough to evolve to very radiogenic Os isotope compositions in only a few million years, providing a potential fingerprint for detecting the involvement of such young, relatively mafic crust in magmatic systems. However, the Sr, Nd, and Pb isotope compositions will remain constant over such short time intervals due to relatively low parent/daughter enrichment during magmatic evolution. The radiogenic Os isotope compositions in typically evolved Lassen rocks are interpreted to reflect significant interaction with lower crustal material that has radiogenic Os isotope compositions. Beneath this section of the Cascade arc, large amounts of such high-QOs lower crust may have formed and been isolated from MASH zone mixing and homogenization processes during the Pliocene or Late Miocene. The results from this study indicate that Os isotopes may provide a unique glimpse into lower crustal processes, such as recycling, in primitive orogenic arcs. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: osmium; rhenium; felsic composition; subduction zones; crust 1. Introduction orogenic arcs is generally thought to be one of the primary means by which the continental Magmatic and tectonic accretion of juvenile mass has grown [1^3]. The fact that juvenile arcs are more ma¢c than estimates for bulk continen- tal crust [4,5] suggests that such arcs represent the starting point for magmatic addition and intra- * Corresponding author. Tel.: +1-608-262-8960; crustal di¡erentiation which eventually produce Fax: +1-608-262-0693. E-mail addresses: [email protected] (G.L. Hart), the compositionally evolved cratons that accreted [email protected] (C.M. Johnson), [email protected] to continental cores and may even have produced (S.B. Shirey), [email protected] (M.A. Clynne). the cores themselves. Oxygen, Sr, Nd, and Pb 0012-821X / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S0012-821X(02)00564-2 EPSL 6191 21-5-02 270 G.L. Hart et al. / Earth and Planetary Science Letters 199 (2002) 269^285 isotopes have been used to identify the many sources involved in the production of orogenic rocks where the isotopic contrast between mantle and crust is large [6^11]. However, in young oro- genic arcs where the O, Sr, Nd, and Pb isotope contrast between mantle and crust is small, it is di⁄cult to study processes of assimilation, melt- ing, mixing, and compositional strati¢cation in the arc crustal column. Alternatively, the Os isotope system, when combined with other isotopic and elemental evi- dence, has great potential for tracing intra-crustal processes in orogenic crustal sections because of the stark Os isotope contrast that can exist be- tween mantle and crustal components. Osmium isotope contrasts between components develop because of the extreme parent/daughter fractiona- tions (Re/Os) produced during crystallization of ma¢c magmas [12^15]. These extreme parent/ daughter ratios may allow signi¢cant radiogenic Os to be generated in primitive ma¢c crust in only a few million years. The goal of this work is to Fig. 1. Generalized map (modi¢ed from [17,18]) of the Cas- assess intra-crustal processes by evaluating poten- cade Range showing the distribution of the major Cascade tial sources of radiogenic Os in intermediate- to volcanoes (triangles) including Lassen Peak, located in Las- silicic-composition lavas from the Lassen region sen Volcanic National Park in northern California. Shading denotes major areas of Cenozoic igneous rock. LVC rests on of the southern Cascade arc and by focusing on Pliocene^Quaternary volcanic units which overlie Sierran^ the role of the lower crust. This study focuses on Klamath plutonic^metamorphic basement units. silicic rocks because of their potential for crustal interaction and because of a general lack of silicic Os isotope data. Osmium isotope analyses of pass (250^200 ka), Eagle Peak (75^0 ka), and primitive basalts [16] provide a useful baseline Twin Lakes (300^0 ka) sequences. Estimated vol- with which to discuss the evolved rocks in this umes of erupted magma at LVC include V80 study. km3 of largely stage I and II andesites of Brokeo¡ Volcano and V50 km3 of stage III andesites and dacites. LVC is surrounded and/or underlain by 2. Lassen Volcanic Center (LVC) ¢ve clearly identi¢ed Pleistocene and Pliocene vol- canic centers including the Maidu Volcanic Cen- 2.1. Geologic summary ter (V2^0.8 Ma) (unpublished data, M.A. Clynne). LVC lies at the southern end of the active Cas- cade arc (Fig. 1) and is built on older volcanic 2.2. Previous geochemical studies centers and regional lavas that erupted from mono- genetic volcanoes [19]. The calc-alkaline volcan- Strontium and Nd isotope compositions of the ism at LVC includes three stages, where stage I LVC silicic lavas match trends observed in other (600^470 ka) and stage II (470^400 ka) represent Cascade volcanoes (Fig. 2). The isotopic compo- the cone-building sequences of Brokeo¡ Volcano, sitions of Cascade rocks in general and Lassen and stage III represents the most evolved volcanic rocks in particular are among the most mantle- episode, and includes the Loomis (400 ka), Bum- like of continental arcs, overlapping those of EPSL 6191 21-5-02 G.L. Hart et al. / Earth and Planetary Science Letters 199 (2002) 269^285 271 This pattern is interpreted to re£ect the decreasing in£uence of slab-derived material toward the arc axis, such that little slab in£uence is thought to be present in the predominantly low-[Sr/P]N basaltic mantle input of the current arc axis [27]. In addi- tion, the mantle wedge is interpreted to become progressively depleted (i.e. more ‘MORB-like’ with lower K2O contents) from east to west as a result of arc melt extraction [30]. The range in chemical, and Sr, Nd, and Pb isotope composi- tions of primitive ma¢c lavas in the Lassen region are therefore thought to re£ect mixing between mantle source and slab components rather than crustal contamination [27,31]. Osmium isotope compositions of primitive ba- Fig. 2. Sr^Nd isotope variations for Quaternary Cascade vol- salts (MgO v 8 wt%) from the Lassen region are canic rocks, Juan de Fuca^Gorda MORB, and Marianas interpreted by Borg et al. [16] to re£ect mixing and Tonga arcs. The isotopic compositions of the Cascade between a slab-dominated source (high-QOs and rocks are among the most sub-arc mantle-like of any conti- high-[Sr/P] ) and a mantle-dominated source nental arc and overlap those of the Marianas and Tonga N Q Q 187 arcs (dashed line; data from [20^22]), and nearly overlap the (low- Os and low-[Sr/P]N)(Os =(( Os/ 188 187 188 Sr isotope compositions of Juan de Fuca and Gorda Ridge Osmeasured)/ ( Os/ Osmantle)31)U100), consis- mid-ocean ridge basalts (JDF-G MORB; [23,24]). Data for tent with earlier interpretations based on Sr iso- Cascade volcanoes from [25,26]. Volcanic rocks from the tope compositions. The QOs values of the high-QOs Lassen region span the average range of analyzed Cascade (and high-[Sr/P] ) basalts are much higher than volcanic rocks, and extend to slightly higher 87Sr/86Sr ratios. N The range in Sr^Nd isotope compositions for the Cascade those previously estimated for sub-arc mantle rocks is primarily interpreted to re£ect mixing between slab- based on analyses of xenoliths from a backarc dominated (slab box) and mantle-dominated (non-slab box) setting [32], but are within the range of those mea- components rather than crustal interaction [27]. sured for other arc lavas [33]. The high-QOs basalts also contain the lowest whole-rock Os contents, primitive oceanic arcs such as the Marianas and suggesting that if these basalts re£ect a slab-dom- Tonga arcs (references cited in Fig. 2). Based on inated source, such a source may also have low detailed study of the most primitive Lassen lavas Os contents. As noted by Borg et al. [16], it seems available, Borg et al. [27] call for a heterogeneous unlikely that the high-QOs basalts, which have low mantle source that has both mid-ocean ridge ba- Os contents, re£ect extensive crystallization be- salt (MORB) and ocean island basalt (OIB) a⁄n- cause all Lassen region basalts have similar Re ities, coupled with material derived from the slab, contents. An alternative to the slab-material inter- as major components in the regional ma¢c lavas pretation is that the high-QOs basaltic lavas in the in the Lassen region. Borg et al.
Load more

Recommended publications
  • Ancient Helium and Tungsten Isotopic Signatures Preserved in Mantle Domains Least Modified by Crustal Recycling
    Ancient helium and tungsten isotopic signatures preserved in mantle domains least modified by crustal recycling Matthew G. Jacksona,1, Janne Blichert-Toftb,2, Saemundur A. Halldórssonc,2, Andrea Mundl-Petermeierd, Michael Bizimise, Mark D. Kurzf, Allison A. Pricea, Sunna Harðardóttirc, Lori N. Willhitea,g, Kresten Breddamh, Thorsten W. Beckeri,j, and Rebecca A. Fischerk aDepartment of Earth Science, University of California, Santa Barbara, CA 93106-9630; bLaboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon, CNRS, and Université de Lyon, 69007 Lyon, France; cNordVulk, Institute of Earth Sciences, University of Iceland, 102 Reykjavík, Iceland; dDepartment of Lithospheric Research, University of Vienna, 1090 Vienna, Austria; eSchool of the Earth, Ocean and Environment, University of South Carolina, Columbia, SC 29208; fDepartment of Marine Chemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; gDepartment of Geology, University of Maryland, College Park, MD 20742; hRadiation Protection, Danish Health Authority, 2300 Copenhagen, Denmark; iInstitute for Geophysics, The Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78713; jDepartment of Geological Sciences, The Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78713; and kDepartment of Earth & Planetary Sciences, Harvard University, Cambridge, MA 02138 Edited by Albrecht W. Hofmann, Max Planck Institute for Chemistry, Mainz, Germany, and approved October 22, 2020 (received for review May 14, 2020) Rare high-3He/4He signatures in ocean island basalts (OIB) erupted Sr-Nd-Pb isotopic space, these four geochemical endmembers can at volcanic hotspots derive from deep-seated domains preserved in be used to define the apices of a tetrahedron (8) (Fig.
    [Show full text]
  • Mantle Plumes
    Geol. 655 Isotope Geochemistry Lecture 21 Spring 2007 ISOTOPIC EVOLUTION OF THE MANTLE IV THE ORIGIN OF MANTLE PLUMES AND THE COMMON COMPONENT IN PLUMES Determining how the various geochemical reservoirs of the mantle have evolved is among the most vexing problems in geochemistry. The principal observation to be explained is that mantle plumes in- variably have less depleted isotopic signatures than MORB, and the isotopic compositions of some in- dicate net enrichment in incompatible elements. As we saw in the previous lecture, mantle plumes were initially thought to consist of primitive mantle (e.g., Schilling, 1973). As we found, mixing be- tween primitive and depleted mantle can explain the Sr and Nd isotopic compositions of some plumes, but virtually none of the Pb isotope data can be explained this way, nor are the trace element composi- tions of OIB consistent with plumes being composed of primitive mantle. Indeed, although ‘primitive mantle’ has proved to be a useful hypothetical concept, no mantle-derived basalts or xenoliths have appropriate compositions to be ‘primitive mantle’ or derived from it. It is possible that no part of the mantle retains its original, primitive, composition (on the other hand, to have survived, primitive man- tle must not participate in volcanism and other such processes, so the absence of evidence for a primi- tive mantle reservoir is not evidence of its absence). Hofmann and White (1982) suggested mantle plumes obtain their unique geochemical signature through deep recycling of oceanic crust (Figure 21.1). Partial melting at mid-ocean ridges creates oce- anic crust that is less depleted in incompatible elements than the depleted upper mantle.
    [Show full text]
  • Diamonds Deliver the Dirt Dinosaurs Usually Found in Younger Sediments
    NEWS AND VIEWS RESUME------ - - complexes such as [Mlll(bipy-h] rather may be regarded as 'expanded' ele­ Early bird than [M0 (bipyh). The niceties of this ments, in which the effective size of the How a routine re-examination of a ambiguity are of direct relevance, as the alkali metal atom has been increased - modest fossil reptile turned into a complex cation [Ru(bipyh)2+ plays a instead of finding the electron in one of search for the closest relatives of birds vital role in many chemical photoconver­ the valence orbitals of the metal ion it is is recounted by A. R. Milner and S. E. sion systems. The critical excited state found slightly out in the orbitals of the Evans in Palaeontology (34, 503-513; [Ru(bipy)3] 2+* is best described10 as directly bonded ligands. D 1991). Fragmentary material of charge-separated [Ru III(bipy h(bipy-) ]2 + •. Lisboasaurus estesi from Guimarota in Portugal, about 160 million years old, The new compound described by Lehn Edwin C. Constable is in the Cambridge originally described as from a lizard. and co-workers. provides a structural Centre for Molecular Recognition, University was model for this photoexcited state as well Chemical Laboratory, University of Cam­ Further study by R. Estes revealed the as challenging our preconceptions about bridge, Lensfield Road, Cambridge CB2 presence of socketed teeth, more the ionic state. These new compounds 1EW, UK. characteristic of archosaurs (crocodiles, MANTLE GEOCHEMISTRY ________________ dinosaurs and birds). Milner and Evans now show that Lisboasaurus most closely resembles the troodontids, a group of advanced, birdlike theropod Diamonds deliver the dirt dinosaurs usually found in younger sediments.
    [Show full text]
  • The Role of Crustal Recycling During the Assembly of the Supercontinent
    The role of crustal recycling during the assembly of the supercontinent NUNA: Geochemical and isotopic constraints from felsic magmatism in the Makkovik Province, Labrador. Alana M. Hinchey Geological Survey, Department of Natural Resources, Government of Newfoundland and Labrador, *(e-mail: [email protected]) Summary The Makkovik Province of Labrador documents the early stages of the Great Proterozoic Accretionary Orogen recording part of the amalgamation of the supercontinent NUNA. During this supercontinent amalgamation, most continental crustal growth occurred in a relatively short period of time between 1900 and 1800 Ma. Insight into the assembly of NUNA is preserved in the felsic rocks from the Aillik Domain of the Makkovik Province. Major and trace element lithogeochemical signatures indicate compositions typical of “A-type‟ rhyolites and granites. Extended trace and rare earth element patterns are typical of the compositions of melts derived by partial melting of sialic crust, with strongly negative Nb and Ti anomalies; typical of crustal derived melts related either to the subduction processes or to crustal contamination processes. The trace element ratios, such as high La/Yb(PM) and Zr/Y ratios, are indicative of a low degree of partial melting at high temperatures (~850 - 900 oC) where garnet and amphibole were stable in the residue. The felsic volcanic rocks and synvolcanic intrusions have εNd(T) values that range from -0.86 to -4.62, with T(DM) model ages that range from 2160 Ma to 2775 Ma, suggesting derivation by partial melting sialic crust of predominantly Late Archean to Paleoproterozoic age. The neodymium crustal index (NCI) indicates a crustal neodymium contribution ranging from 31% to 61%, with an average of 46%, suggesting an equal amount of recycling of crust relative to the addition of juvenile crust during the derivation of the felsic rocks.
    [Show full text]
  • There Were No Large Volumes of Felsic Continental Crust in the Early Earth GEOSPHERE; V
    Research Paper THEMED ISSUE: Subduction Top to Bottom 2 GEOSPHERE There were no large volumes of felsic continental crust in the early Earth GEOSPHERE; v. 13, no. 2 Hugh Rollinson Geoscience, University of Derby, Kedleston Road, Derby DE22 1GB, UK doi:10.1130/GES01437.1 7 figures ABSTRACT Dhuime et al., 2012; Roberts and Spencer, 2015). In the model of Dhuime et al. (2012), the authors calculate that as much as 65% of the present-day volume CORRESPONDENCE: [email protected] New model growth curves for the continental crust based upon Hf iso- of the continental crust had formed by 3.0 Ga. Thus these findings reopen the topes in zircon suggest that large volumes of felsic continental crust were debate initiated by Armstrong (1968, 1991) about the early creation and subse- CITATION: Rollinson, H., 2017, There were no large present in the Hadean and early Archean. These models sit uncomfortably quent destruction of the continental crust. volumes of felsic continental crust in the early Earth: Geosphere, v. 13, no. 2, p. 235–246, doi:10.1130 with estimates of the volume of ancient crust preserved today and imply that The significance of these studies is far reaching because frequently the for- /GES01437.1. the large volumes of crust that were created early in Earth history are now mation of felsic continental crust is linked to the processes of plate tectonics. lost. However, this paper argues that there is no evidence from modern man- So for example Harrison et al. (2005) proposed that because of the large vol- Recieved 30 September 2016 tle geochemistry that very large volumes of early continental crust have been umes of Hadean continental crust that were required by their model, subduc- Revison received 21 November 2016 recycled into the mantle.
    [Show full text]
  • Tectonics and Crustal Evolution
    Tectonics and crustal evolution Chris J. Hawkesworth, Department of Earth Sciences, University peaks and troughs of ages. Much of it has focused discussion on of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, the extent to which the generation and evolution of Earth’s crust is UK; and Department of Earth Sciences, University of St. Andrews, driven by deep-seated processes, such as mantle plumes, or is North Street, St. Andrews KY16 9AL, UK, c.j.hawkesworth@bristol primarily in response to plate tectonic processes that dominate at .ac.uk; Peter A. Cawood, Department of Earth Sciences, University relatively shallow levels. of St. Andrews, North Street, St. Andrews KY16 9AL, UK; and Bruno The cyclical nature of the geological record has been recog- Dhuime, Department of Earth Sciences, University of Bristol, Wills nized since James Hutton noted in the eighteenth century that Memorial Building, Queens Road, Bristol BS8 1RJ, UK even the oldest rocks are made up of “materials furnished from the ruins of former continents” (Hutton, 1785). The history of ABSTRACT the continental crust, at least since the end of the Archean, is marked by geological cycles that on different scales include those The continental crust is the archive of Earth’s history. Its rock shaped by individual mountain building events, and by the units record events that are heterogeneous in time with distinctive cyclic development and dispersal of supercontinents in response peaks and troughs of ages for igneous crystallization, metamor- to plate tectonics (Nance et al., 2014, and references therein). phism, continental margins, and mineralization. This temporal Successive cycles may have different features, reflecting in part distribution is argued largely to reflect the different preservation the cooling of the earth and the changing nature of the litho- potential of rocks generated in different tectonic settings, rather sphere.
    [Show full text]
  • Subducting Carbon Terry Plank1* & Craig E
    REVIEW https://doi.org/10.1038/s41586-019-1643-z Subducting carbon Terry Plank1* & Craig E. Manning2 A hidden carbon cycle exists inside Earth. Every year, megatons of carbon disappear into subduction zones, affecting atmospheric carbon dioxide and oxygen over Earth’s history. Here we discuss the processes that move carbon towards subduction zones and transform it into fluids, magmas, volcanic gases and diamonds. The carbon dioxide emitted from arc volcanoes is largely recycled from subducted microfossils, organic remains and carbonate precipitates. The type of carbon input and the efficiency with which carbon is remobilized in the subduction zone vary greatly around the globe, with every convergent margin providing a natural laboratory for tracing subducting carbon. n addition to its familiar cycling between the ter- however, and currently six volcanoes are esti- restrial biosphere and atmosphere, carbon moves mated to control the global budget of direct emis- I from microfossils on the seafloor to erupting vol- sions (Nyiragongo, Popocateptl, Etna, Ambrym, canoes and deep diamonds, in a cycle driven by plate Bagana and Aoba; together contributing more tectonics. Subduction links surface biological pro- than 5 Mt C yr−1)11. The largest volcanic emis- cesses with the deep Earth, creating a planet suffused with the signature sions, however, may be emanating diffusely from calderas and faults10. of life. The fate and flux of carbon vary from trench to trench, as every Although current anthropogenic fluxes (about 9,500 Mt C yr−1)12 dwarf subducting slab delivers to the mantle a singular mix of organic and inor- volcanic ones, the long-term fluxes of carbon to the atmosphere have ganic carbon that heats and pressurizes at a particular rate determined by been dominated by volcanic sources over most of Earth’s history.
    [Show full text]
  • The Persistent Mantle Plume Myth D
    This article was downloaded by: [217.44.161.233] On: 09 October 2013, At: 03:09 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/taje20 The persistent mantle plume myth D. L. ANDERSON a a Seismological Laboratory , California Institute of Technology , Pasadena , CA , 91125 , USA Published online: 26 Sep 2013. To cite this article: D. L. ANDERSON , Australian Journal of Earth Sciences (2013): The persistent mantle plume myth, Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, DOI: 10.1080/08120099.2013.835283 To link to this article: http://dx.doi.org/10.1080/08120099.2013.835283 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
    [Show full text]
  • Mantle Convection in Terrestrial Planets
    MANTLE CONVECTION IN TERRESTRIAL PLANETS Elvira Mulyukova & David Bercovici Department of Geology & Geophysics Yale University New Haven, Connecticut 06520-8109, USA E-mail: [email protected] May 15, 2019 Summary surfaces do not participate in convective circu- lation, they deform in response to the underly- All the rocky planets in our Solar System, in- ing mantle currents, forming geological features cluding the Earth, initially formed much hot- such as coronae, volcanic lava flows and wrin- ter than their surroundings and have since been kle ridges. Moreover, the exchange of mate- cooling to space for billions of years. The result- rial between the interior and surface, for exam- ing heat released from planetary interiors pow- ple through melting and volcanism, is a conse- ers convective flow in the mantle. The man- quence of mantle circulation, and continuously tle is often the most voluminous and/or stiffest modifies the composition of the mantle and the part of a planet, and therefore acts as the bottle- overlying crust. Mantle convection governs the neck for heat transport, thus dictating the rate at geological activity and the thermal and chemical which a planet cools. Mantle flow drives geo- evolution of terrestrial planets, and understand- logical activity that modifies planetary surfaces ing the physical processes of convection helps through processes such as volcanism, orogene- us reconstruct histories of planets over billions sis, and rifting. On Earth, the major convective of years after their formation. currents in the mantle are identified as hot up- wellings like mantle plumes, cold sinking slabs and the motion of tectonic plates at the surface.
    [Show full text]
  • Crust Recycling in the Sources of Two Parallel Volcanic Chains in Shandong, North China
    Earth and Planetary Science Letters 302 (2011) 359–368 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Crust recycling in the sources of two parallel volcanic chains in Shandong, North China Gang Zeng a, Li-Hui Chen a,⁎, Albrecht W. Hofmann b,c, Shao-Yong Jiang a, Xi-Sheng Xu a a State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China b Max-Planck-Institut für Chemie, Postfach 3060, D-55020 Mainz, Germany c Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY 10964, USA article info abstract Article history: Recycled crustal components have been documented for many sources of hotspot-related ocean island basalts, Received 23 June 2010 buttheyhavebeendifficult to identify in continental basalts, because in continental settings, hotspots are often Received in revised form 7 December 2010 obscured and recycled crustal sources are difficult to distinguish from crustal contamination. We show major, Accepted 8 December 2010 trace element and Sr–Nd–Hf isotopic compositions for two parallel chains of Cenozoic volcanoes from Shandong Available online 8 January 2011 Province, North China, which are free of crustal contamination and show clear evidence for recycling of mafic Editor: R.W. Carlson lower crust. Sr, Nd, and Hf isotopes in the two volcanic chains form separate binary mixing arrays, which converge on the composition of Dashan, an isolated, nephelinitic volcano with the most depleted isotopic signature. The Keywords: two chains have lower CaO values and significantly diverging isotope enrichment trends from this common alkaline basalts endmember.
    [Show full text]
  • Production and Recycling of Oceanic Crust in the Early Earth
    Chapter 6 Production and recycling of oceanic crust in the early Earth Abstract Because of the strongly different conditions in the mantle of the early Earth regarding temperature and viscosity, present-day geodynamics cannot simply be extrapolated back to the early history of the Earth. We use numerical thermochemical convection mod- els including partial melting and a simple mechanism for melt segregation and oceanic crust production to investigate an alternative suite of dynamics which may have been in operation in the early Earth. Our modelling results show three processes that may have played an important role in the production and recycling of oceanic crust: (1) Small scale (x · 100km) convection involving the lower crust and shallow upper mantle. Partial melt- ing and thus crustal production takes place in the upwelling limb and delamination of the eclogitic lower crust in the downwelling limb. (2) Large scale resurfacing events in which (nearly) the complete crust sinks into the (eventually lower) mantle, thereby form- ing a stable reservoir enriched in incompatible elements in the deep mantle. New crust is simultaneously formed at the surface from segregating melt. (3) Intrusion of lower mantle diapirs with a high excess temperature (about 250 K) into the upper mantle, caus- ing massive melting and crustal growth. This allows for plumes in the Archean upper mantle with a much higher excess temperature than previously expected from theoretical considerations. 6.1 Introduction As no oceanic crust on Earth is older than about 200 million years, we have no direct evidence on the nature of oceanic crust in the early Earth.
    [Show full text]
  • Continental Recycling: the Oxygen Isotope Point of View L
    Continental recycling: The oxygen isotope point of view L. Simon, Christophe Lécuyer To cite this version: L. Simon, Christophe Lécuyer. Continental recycling: The oxygen isotope point of view. Geo- chemistry, Geophysics, Geosystems, AGU and the Geochemical Society, 2005, 6 (8), pp.1-10. 10.1029/2005GC000958. hal-00184120 HAL Id: hal-00184120 https://hal.archives-ouvertes.fr/hal-00184120 Submitted on 13 Feb 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Article Geochemistry 3 Volume 6, Number 8 Geophysics 18 August 2005 Q08004, doi:10.1029/2005GC000958 GeosystemsG G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society Continental recycling: The oxygen isotope point of view L. Simon ‘‘Pale´oenvironnements and Pale´obiosphe`re,’’ UMR CNRS 5125, Campus de la Doua, Universite´ Claude Bernard Lyon 1, F-69622 Villeurbanne, France Now at Institut fu¨r Geologie und Mineralogie, Universita¨t Erlangen-Nu¨rnberg, Schlossgarten 5, D-91054 Erlangen, Germany ([email protected]) C. Le´cuyer ‘‘Pale´oenvironnements and Pale´obiosphe`re,’’ UMR CNRS 5125, Campus de la Doua, Universite´ Claude Bernard Lyon 1, F-69622 Villeurbanne, France Also at Institut Universitaire de France, 103 Boulevard Saint Michel, F-75005 Paris, France 18 [1] Mass balance calculations based on a data compilation lead us to estimate a d O value of 8.9 ± 0.7% for the continental crust.
    [Show full text]