The origin of the Canary Island Seamount Province - New ages of old seamounts

The Canary Island Seamount Province forms a scattered hotspot track on the Atlantic ocean floor ,1300 km long and,350 km wide, perpendicular to lithospheric fractures, and parallel to theNWAfrican continental margin. New 40Ar/39Ar datings show that seamount ages vary from 133 Ma to 0.2 Ma in the central archipelago, and from 142 Ma to 91 Ma in the southwest. Combining 40Ar/39Ar ages with plate tectonic reconstructions, I find that the temporal and spatial distribution of seamounts is irreconcilable with a deep fixed mantle plume origin, or derivation from passive mantle upwelling beneath a mid-ocean ridge. I conclude that shallow mantle upwelling beneath the Atlantic Ocean basin off the NW African continental lithosphere flanks produced recurrent melting anomalies and seamounts from the Late Jurassic to Recent, nominating the Canary Island Seamount Province as oldest hotspot track in the Atlantic Ocean, and most long-lived preserved on earth

40Ar/39Ar ages of Pliocene-Pleistocene fallout tephra layers and volcaniclastic deposits in the sedimentary aprons of Gran Canaria and Tenerife (Sites 953, 954, and 956)

Six fallout tephra layers and 16 heterolithologic volcaniclastic deposits drilled at Holes 953A, 954A, 954B, and 956A, during Leg 157 in the sedimentary aprons of Gran Canaria and Tenerife, have been dated by single crystal laser 40Ar/39Ar analysis. The fallout tephra markers range in age from 0.273 ± 0.006 Ma to 2.74 ± 0.01 Ma. Maximum sedimentation ages determined for the volcaniclastic deposits range from 0.24 ± 0.01 Ma to 2.24 ± 0.02 Ma, closely matching the nannofossil and paleomagnetic chronostratigraphies of the cores. Both tephra and volcaniclastic layers represent material from Pliocene–Pleistocene explosive eruptions of the Cañadas Caldera (Tenerife), mixed with Miocene volcanic debris only in the holes drilled north of Gran Canaria (954A and 954B). Two fallout layers (0.61 ± 0.02 Ma and 1.83 ± 0.02 Ma) and five volcaniclastic deposits reflect explosive eruptions, which took place during postulated dormant stages of the Cañadas edifice

Northwestern Central American Volcanic Arc: Increased contribution of enriched lithosphere to lavas along the volcanic front from Nicaragua to Guatemala and behind the volcanic front

The Central American Volcanic Arc (CAVA) has been subject of intensive research over the past decades, leading to a large variety of different models for the origin of CAVA lavas with various source components. Based on a comprehensive new geochemical data set (i.e. major and trace elements and Sr-Nd-Pb-Hf-O isotope ratios) of mafic volcanic front (VF), behind the volcanic front (BVF) and back-arc (BA) lava and tephra samples from NW CAVA (Nicaragua to Guatemala), we present a new model for the NW Central American Volcanic Arc volcanism. Additional potential source component sample data from subducting Cocos Plate sediments, igneous oceanic crust and Guatemalan granitic and metamorphic continental basement further contributes to our new model. We find systematically increasing Pb isotope ratios and decreasing Nd and Hf isotope ratios along the arc from NW Nicaragua to Guatemala. BVF lavas generally have more radiogenic Pb and less radiogenic Nd and Hf isotopic compositions than related VF lavas, similar to what is observed for trace element ratios going northwards along the VF. Combined isotope and trace element data indicate the presence of three endmembers for the volcanism in NW Central America: (1) NW Nicaraguan VF samples with very high Ba/(La, Th) and U/Th, low La/Yb, relatively radiogenic Sr, Nd and Hf but unradiogenic Pb, (2) NW Guatemalan VF and Guatemalan and Honduran BVF samples with low Ba/(La, Th) and U/Th, high La/Yb, radiogenic Sr and Pb but unradiogenic Nd and Hf, and elevated d18O, and (3) Honduran and Nicaraguan BVF samples with low Ba/(La, Th) and U/Th, high La/Yb, unradiogenic Sr but radiogenic Nd, Hf and Pb. We interpret the NW Nicaragua VF endmember to be dominated by a largely serpentinite-derived fluid flux from the subducting slab, possibly with small amounts (<1 wt. %) of sediment melts, to a depleted N-MORB type of mantle wedge, resulting in large degrees of melting of primarily peridotitic material. Based on combined Hf and Nd and Hf and Pb isotope systematics, the isotopically enriched Guatemala VF and BVF endmember cannot be explained by the addition of subducted pelagic sediments to the source. Instead this endmember could be derived from pyroxenitic cumulates in the lithospheric mantle (and possibly lower crust) that were derived from parental magmas for plutonic rocks in NW Central America, which were melted during the Quaternary subduction-related volcanism. The isotopically depleted Honduras and Caribbean BA endmember could be derived from melting of young, recycled, oceanic crust in the asthenosphere upwelling in the back-arc, based on the OIB-like major and trace element but relatively depleted isotopic compositions of these samples. Mixing between these three endmember types of magmas can explain the observed systematic geochemical variations along and across the NW Central American Arc

Chronostratigraphy of Gran Canaria

A chronostratigraphy of Miocene/Pliocene volcanism on Gran Canaria (Canary Islands) has been established by single- crystal 40Ar/39Ar laser dating of feldspar crystals from 58 samples of welded ignimbrites, lava flows, fallout tephra layers, and intrusive rocks. All subaerially exposed volcanic and intrusive rocks of Gran Canaria were emplaced within the last 14.5 Ma, comprising three major magmatic/volcanic cycles. The subaerial Miocene evolution started with the rapid formation (<0.5 Ma) of the exposed, mildly alkalic shield basalts. The basaltic shield phase ended between 14.04 ± 0.10 Ma and 13.95 ± 0.02 Ma and was followed by a 0.6-m.y. magmatism of trachytic to rhyolitic composition (Mogán Group). Single-crystal 40Ar/39Ar laser dating shows that the ash flows erupted at intervals of 0.03 − 0.04 m.y., with peak eruption rates as much as 2000 km3/m.y. during the initial stages of silicic magma production (Lower Mogán Formation). High-precision ages have been determined for major, widespread lithostratigraphic markers of the Mogán Group, such as ignimbrite P1 (13.95 ± 0.02 Ma), ignimbrite X (13.71 ± 0.02 Ma), ignimbrite D (13.44 ± 0.01 Ma), and ignimbrite E (13.37 ± 0.03 Ma). After the rhyolitic stage, >500 km3 of silica-undersaturated nepheline trachyphonolitic ash flows, lava flows, and fallout tephra, as well as rare basanite and nephelinite dikes and lavas were erupted between 13.29 Ma and 13.04 Ma (Montaña Horno Formation) and 12.43 Ma and 9.85 Ma (Fataga Group). This stage was accompanied and followed by intrusive syenites and a large cone sheet swarm in the central caldera complex, lasting until at least 8.28 Ma. Following a major, nearly nonvolcanic hiatus lasting ~4.7 m.y. (Las Palmas Formation), eruptions resumed with the local emplacement of small volumes of nephelinites, basanites, and tholeiites at ~5 to 4.5 Ma, with peak activity and eruptions of highly evolved phonolite magma between 4.15and 3.78 Ma (Roque Nublo Group)

Quartär-geologisch-tephrostratigraphische Neuaufnahme und Interpretation des Pleistozänprofils Kärlich

Die quartäre Sedimentfolge der Kärlicher Tongrube ist ein Schlüsselprofil für das Pleistozän Mitteleuropas: (a) Rhein- und Mosel-Terrassenablagerungen belegen die junge tektonische Hebung des paläozoischen Rheinischen Schildes, (b) Löß- und Paläobodenschichten spiegeln spätquartäre Klimaschwankungen wider, (c) Artefakt-Horizonte dokumentieren eine ausgedehnte frühmenschliche Geschichte des Mittelrheinraums, und (d) zahlreiche eingeschaltete Tephralagen — abgelagert während explosiver Vulkaneruptionen im Osteifel-Vulkanfeld — bilden ideale chronostratigraphische Leithorizonte. Die chemische und mineralogische Zusammensetzung zweier phonolithischer Bims-Fallablagerungen, die bisher als „Wehrer Bimse" bezeichnet wurden, unterscheidet sich drastisch von schlotnahen Tephraablagerungen am Wehr-Vulkan selber. Darüber hinaus zeigen (40)Ar/(39)Ar-Laseranalysen von Feldspat-Kristallen, daß die beiden Tephraablagerungen, mit Eruptionsaltern von 452.000 ± 8.000 Jahren vor Heute (KAE-DT2) und < 618.000 ± 13.000 Jahren v. h. (KAE-DTl), bis zu doppelt so alt sind, wie bislang angenommen. Schlotnahe, strombolianisch-phreatomagmatische, mafische Tephraschichten (KAE-BT4; lokale Bezeichnung: „Brockentuff"), die einem interglazialen Paläobodenhorizont im Hangenden der jüngeren Bimsablagerung eingeschaltet sind (lokale Bezeichnung: „Kärlicher Interglazial"), stammen von einem heute erodierten, kleinen Eruptionszentrum NW der Tongrube. (40)Ar/(39)Ar-Datierungen von Phlogopit-Ein-sprenglingen nach dem Stufenheizungs- und Laserverfahren ergeben für KAE-BT4 ein Eruptionsalter von 396.000 ± 20.000 Jahren v. h. Unsere Untersuchung zeigt, daß das Kärlicher Profil vor allem terrestrische Pleistozänablagerungen enthält, die zur Zeit der marinen Sauerstoffisotopenstadien 11 bis 19 abgelagert wurden. Jüngere Schichten sind nur unvollständig im Hangenden von KAE-BT4 erhalten. Das „Kärlicher Interglazial locus typicus" repräsentiert eine ca. 400.000 Jahre alte interglaziale Klimaphase und wird hier mit dem marinen Sauerstoffisotopenstadium 11 korreliert. Frühmenschliche Artefakte, die in Schichten unmittelbar im Hangenden der Tephra KAE-BT4 auftreten, könnten demnach ebenfalls bis zu ca. 400.000 Jahre alt sein

Evidence for Miocene subduction beneath the Alboran Sea (Western Mediterranean) from 40Ar/39Ar age dating and the geochemistry of volcanic rocks from holes 977A and 978A

Volcanic pebbles in gravels from Sites 977 and 978 in the Alboran Sea (western Mediterranean) were dated (using the 40Ar/ 39Ar single-crystal laser technique) and analyzed for their major- and trace-element compositions (determined by X-ray fluorescence and inductively coupled plasma-mass spectrometry). The samples range from basalts to rhyolites, and belong to the tholeiitic, calc-alkaline, and shoshonitic series. Single-crystal and step-heating laser 40Ar/39Ar analyses of plagioclase, sanidine, biotite, and amphibole phenocrysts from basaltic to rhyolitic samples indicate that eruptions occurred between 6.1 and 12.1 Ma. The age data conform to the stratigraphy and agree with microfossil ages, when available. The major-element and compatible trace-element data of samples with H2O < 4 wt% show systematic variations, consistent with fractionation of the observed phenocryst phases (plagioclase, olivine, clinopyroxene, magnetite, hornblende, quartz, and biotite). The incompatible-element patterns formed by normalizing to primitive mantle for all samples show spiked patterns with peaks generally at mobile elements and troughs at immobile elements, in particular Nb and Ta. The calc-alkaline affinities and the incompatible-element systematics are characteristic of subduction zone volcanism, which indicates that subduction occurred beneath the eastern Alboran from 6 to at least 12 Ma. We propose that the change in chemistry from calc-alkaline and potassic to sodic compositions between 5– 6 Ma reflects detachment of the subducting slab. Uplift of the Strait of Gibraltar, associated with this detachment, could have caused the Messinian Salinity Crises

The Christmas Island Seamount Province, Indian Ocean: Origin of Intraplate Volcanism by Shallow Recycling of Continental Lithosphere?

The east-west-trending Christmas Island Seamount Province (CHRISP, 1800x600 km) in the northeastern Indian Ocean is elongated orthogonal to present-day plate motion, posing the question if a mantle plume formed this volcanic belt. Here we report the first age (Ar/Ar) and geochemical (Sr- Nd-Hf-Pb DS isotopic data) from the CHRISP seamount chain. A crude E-W age decrease from the Argo Basin (136 Ma), to the Eastern Wharton Basin (115-94 Ma) to the Vening-Meinesz seamounts (96-64 Ma) to the Cocos-Keeling seamounts (56-47 Ma) suggests spatial migration of melting. Christmas Island, however, yields much younger ages (44-4 Ma), inconsistent with an age progression. The isotopic compositions (e.g. 206Pb/204Pb = 17.3-19.3; 207Pb/204Pb = 15.49- 15.67; 143Nd/144Nd = 0.51220-0.51295; 176Hf/177Hf = 0.28246- 0.28319) range from enriched MORB (or “C”) to very enriched mantle (EM1) type compositions more typical of continental than oceanic volcanism. Lamproitic and kimberlitic rocks from western Australia, India and other continental areas, derived from metasomatized subcontinental lithospheric mantle, could serve as the EM1 type endmembers. The morphology, ages and chemical composition of the CHRISP, combined with plate tectonic reconstructions, cannot be easily explained within the framework of the mantle plume hypotheses. We therefore propose that the seamounts are derived through the recycling of continental lithosphere (mantle ± lower crust) delaminated during the breakup of Gondwana and brought to the surface at the former spreading centers separating Argoland (western Burma), Greater India and Australia

The 40Ar/39Ar age dating of the Madeira Archipelago and hotspot track (eastern North Atlantic)

The 40Ar/39Ar ages for 35 volcanic rocks and 14C ages for two charcoal samples from the Madeira Archipelago and Ampère Seamount (eastern North Atlantic) are presented. The volcanic evolution of Madeira can be divided into a voluminous shield stage (>4.6–0.7 Ma) and a subsequent low-volume posterosional stage (70 Myr old hotspot which formed Porto Santo Island (11.1–14.3 Ma), Seine, Ampère (31 Ma), Corral Patch and Ormond (65–67 Ma [Féraud et al., 1982, 1986]) Seamounts, and the Serra de Monchique (70–72 Ma [McIntyre and Berger, 1982]) complex in southern Portugal. Age and spatial relationships result in a calculated absolute African plate motion above the hotspot of 1.2 cm/yr around a rotation pole located at 43°36′N/ 24°33′W

New 40Ar/39Ar age and geochemical data from seamounts in the Canary and Madeira volcanic provinces: support for the mantle plume hypothesis

The role of mantleplumes in the formation of intraplate volcanic islands and seamount chains is being increasingly questioned. Particular examples are the abundant and somewhat irregularly distributed island and seamount volcanoes off the coast of northwest Africa. New40Ar / 39Ar ages and Sr–Nd–Pb isotope geochemistry of volcanic rocks from seamounts northeast of the Madeira Islands (Seine and Unicorn) and northeast of the Canary Islands (Dacia and Anika), however, provide support for the plumehypothesis. The oldest ages of shield stage volcanism from Canary and Madeiravolcanic provinces confirm progressions of increasing age to the northeast. Average volcanicage progression of ∼1.2 cm/a is consistent with rotation of the African plate at an angular velocity of ∼0.20° ± 0.05 /Ma around a common Euler pole at approximately 56° N, 45° W computed for the period of 0–35 Ma. A Euler pole at 35° N, 45° W is calculated for the time interval of 35–64 Ma. The isotope geochemistry further confirms that the Madeira and Canary provinces are derived from different sources, consistent with distinct plumes having formed each volcanic group. Conventional hotspot models, however, cannot easily explain the up to 40 m.y. long volcanic history at single volcanic centers, long gaps in volcanic activity, and the irregular distribution of islands and seamounts in the Canary province. A possible explanation could involve interaction of the Canarymantleplume with small-scale upper mantle processes such as edge-driven convection. Juxtaposition of plume and non-plume volcanism could also account for observed inconsistencies of the classical hotspot concept in other volcanic areas