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Duggen, S., K.A. Hoernle, F. Hauff, A. Kluegel, M

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Duggen, S., K.A. Hoernle, F. Hauff, A. Kluegel, M Downloaded from geology.gsapubs.org on March 1, 2010 Flow of Canary mantle plume material through a subcontinental lithospheric corridor beneath Africa to the Mediterranean S. Duggen1,2*, K.A. Hoernle1, F. Hauff1, A. Klügel3, M. Bouabdellah4, M.F. Thirlwall2 1IFM-GEOMAR, Leibniz Institute of Marine Sciences, Research Division Dynamics of the Ocean Floor, Wischhofstrasse 1-3, 24148 Kiel, Germany 2Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 OEX, UK 3Universität Bremen, Fachbereich 5, Geowissenschaften, Postfach 33 04 40, 28334 Bremen, Germany 4Department of Geology, Faculty of Sciences, B.P. 524, 60000 Oujda, Morocco ABSTRACT the passive continental margin near the Canary We present geochemical data of lavas from northwest Africa, allowing us for the fi rst time Islands to at least the Middle Atlas (Fig. 1). to carry out large-scale “mapping” of sublithospheric mantle fl ow beneath the northwest Afri- The geodynamic evolution of the western- can plate. Our study indicates that Canary mantle plume material traveled laterally along a most Mediterranean is complex, but Miocene subcontinental lithospheric corridor (i.e., at depths that are usually occupied by continental subduction rollback of old Tethys oceanic litho- lithospheric mantle) more than 1500 km to the western Mediterranean, marking its route sphere, causing progressive delamination (peel- over the last 15 m.y. through a trail of intraplate volcanism. A three-dimensional geodynamic ing off) of subcontinental lithospheric mantle reconstruction, integrating results from geophysical studies, illustrates that long-distance ca. 8–10 Ma (continental-edge delamination), lateral fl ow of mantle material into and through a subcontinental lithospheric corridor can affected both the lithospheric thickness and be caused by a combination of (1) defl ection of upwelling plume material along the base of mantle fl ow beneath northern Morocco (Duggen the lithosphere, (2) delamination of subcontinental mantle lithosphere beneath northwest et al., 2003, 2005; Gutscher et al., 2002). Africa, and (3) subduction suction related to the rollback of the subducting oceanic plate in The geochemical composition of lavas the western Mediterranean. Although the fl ow of plume material beneath oceanic lithosphere from the northwest African plate can provide to mid-ocean ridges or along the base of continental rifts has been previously shown, this study important information about their sources and demonstrates that plume material can also fl ow large lateral distances through subcontinental processes in the upper mantle. We present new corridors from suboceanic to nonrifting subcontinental settings, generating continental intra- major and trace element and Sr-Nd-Pb-isotopic plate volcanism without the need for a plume to be located directly beneath the continent. data from mafi c Middle Atlas lavas (Tables DR1 and DR2 and details about analytical methods INTRODUCTION In northwest Africa, mafi c Neogene intraplate are found in the GSA Data Repository1) and The oceanic and continental parts of the volcanism is found in the Atlas system and along integrate these with published geochemical northwest African plate host areas with Neo- the Mediterranean coast (volcanic fi elds Siroua, and geophysical results from other (volcanic) gene igneous activity (Lustrino and Wilson , Saghro, Middle Atlas, Guilliz, Gourougou , and areas on the northwest African plate. This study 2007), linked to different geodynamic Oujda-Oranie; Fig. 1A) (Lustrino and Wilson, allows the northwest African upper mantle com- processes . In the eastern Atlantic Ocean, 2007). The Atlas Mountains extend from the position to be mapped for the fi rst time and pro- Canary Islands volcanism is associated with passive Atlantic-African continental margin vides new constraints for mantle fl ow and the well-resolved low P- and S-wave seismic adjacent to the Canary Islands to the Mediter- origin of continental intraplate volcanism. tomographic velocity anomalies, extending to ranean coast and represent an inverted, failed the core-mantle boundary (see Montelli et al., rift system, formed during the opening of the RESULTS AND DISCUSSION 2006, including their summary of other seis- central Atlantic in the early Mesozoic. Over Composition of the Upper Mantle Beneath mic tomographic models). The Canary Islands the past 45 m.y., the former rift was deformed the Northwest African Plate and seamounts to the northeast have intraplate due to compression during the collision of the Mafi c lavas with intraplate geochemical sig- geochemical compositions and form a volcanic African and European plates (Gomez et al., natures on the northwest African plate are inter- chain with a northeast to southwest age pro- 2000). Removal (delamination) of subcontinental preted to be derived from sublithospheric mantle gression over the last 70 m.y. (Fig. 1A) (Geld- mantle lithosphere is proposed to result from the sources by low-degree partial melting (Duggen macher et al., 2005; Hoernle and Schmincke, collision of these major plates and to be respon- et al., 2005; El Azzouzi et al., 1999; Geldmacher 1993; Hoernle et al., 1991; Lundstrom et al., sible for intermediate-depth earthquakes and et al., 2005; Hoernle and Schmincke, 1993; 2003). The age progression can be explained volcanism in the Atlas system (Ramdani, 1998). Hoernle et al., 1991, 1995; Lundstrom et al., by movement of the lithosphere above a deeper Elevated topography, high heat fl ow, and 2003; Lustrino and Wilson, 2007). Mafi c igne- upwelling using the same Euler pole and angu- gravity and geoid anomalies point to the exis- ous rocks from the Middle Atlas have trace ele- lar plate velocity as other volcanic chains in the tence of an abnormally shallow lithosphere- ment patterns similar to those from the Canary Atlantic Ocean. Although other models have asthenosphere boundary beneath the western Islands (Fig. 2) and show a similar range of ele- been proposed to explain the Canary Islands part of the Atlas system (60–80 km, compared vated Dy/Yb and Zr/Hf ratios and high FeO but volcanism (e.g., see summaries in Anguita to 130–160 km for normal northwest Afri- relatively low SiO2. For the Middle Atlas and the and Hernan, 2000, and Lustrino and Wilson, can lithospheric thickness), as illustrated on Canary Islands, respectively, Dy/Yb = 2.8–3.4 2007), the plume hypothesis can best explain six lithospheric profi les across northwest Africa the geophysical, geochemical, and geological (Urchulutegui et al., 2006; Missenard et al., 1GSA Data Repository item 2009071, Tables DR1 constraints (Geldmacher et al., 2005; Hoernle 2006; Teixell et al., 2005) (Fig. 1). The region of (major and trace element data) and DR2 (Sr-Nd-Pb- and Schmincke, 1993; Hoernle et al., 1991; abnormally thin lithosphere forms a northeast- isotope data), and details about analytical methods, is available online at www.geosociety.org/pubs/ft2009. Lundstrom et al., 2003). striking subcontinental lithospheric corridor htm, or on request from [email protected] or beneath northwest Africa that is ~80–120 km Documents Secretary, GSA, P.O. Box 9140, Boulder, *E-mail: [email protected]. high and ~200–300 km wide and extends from CO 80301, USA. © 2009 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, March March 2009; 2009 v. 37; no. 3; p. 283–286; doi: 10.1130/G25426A.1; 3 fi gures; Data Repository item 2009071. 283 Downloaded from geology.gsapubs.org on March 1, 2010 A 5° W 0.705 NW African lithosphere 10° W W. Mediterranean 35° N A Gourougou Oujda-Oranie 15° W Guilliz Canary hotspot track 250 km 30° N 68 Ma 55 Ma Atlas Middle system Atlas F 47 Ma E 0.704 30 Ma >17 Ma Saghro Agadir Siroua Gou- D Sr Canary Islands Lanzarote C W. Mediterranean >15 Ma B rougou Oujda-Oranie 4 Ma 12 Ma A 86 n subcont. Gourougou NW Africa tion) Mid 11 Ma 15 Ma 25 Ma r (projec F 1 Ma lithospheric corrido Atlasdle Guilliz Guilliz HIMU E Sr/ Middle D 87 C Sag 0.703 Atlas 100 km B S hro Current Changing A iroua oceanic lithosph B Su Atlantic Canary plume center lithospheric thickness Islands 50 km 400 km bducted slab MORB 150150 km km 0.702 dor . corri 18 19 20 21 hosph ont. lit 206 204 an subc NW Afric Pb/ Pb HIMU ere of 15.7 NW B African lithos- Oujda-Oranie Canary Delaminated Slab rollback and phere Atlas subcontinental continental-edge delamination Pb Gou- mantle plume Middle lithosphere causing subduction suction 204 rougou 15.6 Atlas (70–0 Ma) (since 45–25 Ma) (since ca. 10–8 Ma) Pb/ Guilliz Figure 1. Map of the northwest African plate (A) and fl ow of Canary mantle plume material 207 Atlantic Canary MORB Islands under northwest Africa through a subcontinental lithospheric corridor in a three-dimensional model (B). A: The orange area displays the Canary hotspot track on the oceanic side of the northwest African plate with ages of the oldest lavas from each island (red areas) or sea- 15.5 NHRL mount (gray circles), indicating a southwest-directed age progression and the location of 18 19 20 21 206Pb/204Pb the current plume center beneath the western Canary Islands (Geldmacher et al., 2005). Also 15 shown are the Atlas Mountains (gray fi eld), location of the northwest African subcontinen- NW African lithosphere C tal lithospheric corridor in green, inferred from profi les (A–F) based on geophysical data Lower Shoshonites (Urchulutegui et al., 2006; Missenard et al., 2006; Teixell et al., 2005), and northwest African 10 crust Neogene continental intraplate volcanic fi elds. B: The three-dimensional model illustrates how Canary mantle plume material fl ows along the base of the oceanic lithosphere that Gourougou thins to the east (Neumann et al., 1995) and into the subcontinental lithospheric corridor be- 7/4 Pb 5 Δ neath the Atlas system, reaching the western Mediterranean.
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