SUMMARY Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ≈5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL-1A global set of relative plate angular velocities is estimated. HS3-NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL-1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically ±20 to ±40 km Myr −1 and ranges up to ±145 km Myr −1 . The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2-NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2-NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3NUVEL1A angular velocity, while all fourteen of the HS3-NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2-NUVEL1 angular velocity. The HS2-NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3-NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 ± 0.10 deg Myr −1 ) than the average (0.70 deg Myr −1 ) since the 47-Myr-old bend in the Hawaiian‐Emperor chain.

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Young tracks of hotspots and current plate velocities

Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of 

American Geophysical Union for personal use, not for redistribution. The definitive version was published 

in Geochemistry Geophysics Geosystems 6 (2005): Q05007, doi:10.1029/2004GC000824.

/pdf/fozo-himu-and-the-rest-of-the-mantle-zoo-108g309c2l.pdf

FOZO, HIMU, and the rest of the mantle zoo

Recycled oceanic crust, with or without sediment, is often invoked as a source component of continental and oceanic alkaline magmas to account for their trace-element and isotopic characteristics Alternatively, these features have been attributed to sources containing veined, metasomatized lithosphere In melting experiments on natural amphibole-rich veins at 15 gigapascals, we found that partial melts of metasomatic veins can reproduce key major- and trace-element features of oceanic and continental alkaline magmas Moreover, experiments with hornblendite plus lherzolite showed that reaction of melts of amphibole-rich veins with surrounding lherzolite can explain observed compositional trends from nephelinites to alkali olivine basalts We conclude that melting of metasomatized lithosphere is a viable alternative to models of alkaline basalt formation by melting of recycled oceanic crust with or without sediment

http://science.sciencemag.org/content/sci/320/5878/916.full.pdf

Metasomatized lithosphere and the origin of alkaline lavas.

We document compositions of minerals and melts from 3 GPa partial melting experiments on two carbonate-bearing natural lherzolite bulk compositions (PERC: MixKLB-1þ2 5 wt% CO2; PERC3: MixKLB-1þ1wt% CO2) and discuss the compositions of partial melts in relation to the genesis of alkalic to highly alkalic ocean island basalts (OIB). Near-solidus (PERC: 1075^11058C; PERC3: 10508C) carbonatitic partial melts with 510 wt% SiO2 and 40 wt% CO2 evolve continuously to carbonated silicate melts with 425 wt% SiO2 and525 wt%CO2 between 1325 and 13508C in the presence of residual olivine, orthopyroxene, clinopyroxene, and garnet. The first appearance of CO2-bearing silicate melt at 3 GPa is 1508C cooler than the solidus of CO2-free peridotite.The compositions of carbonated silicate partial melts between 1350 and 16008C vary in the range of 28^46 wt% SiO2, 1 6^0 5 wt% TiO2, 12^10 wt% FeO , and 19^29 wt% MgO for PERC, and 42^48 wt% SiO2, 1 9^0 5 wt%TiO2, 10 5^8 4 wt% FeO , and 15^26 wt%MgOforPERC3.TheCaO/Al2O3weight ratio ofsilicate melts ranges from 2 7 to 1 1 for PERC and from 1 7 to 1 0 for PERC3.The SiO2 contents of carbonated silicate melts in equilibrium with residual peridotite diminish significantly with increasing dissolved CO2 in the melt, whereas the CaO contents increase markedly. Equilibrium constants for Fe ^Mg exchange between carbonated silicate liquid and olivine span a range similar to those for CO2-free liquids at 3 GPa, but diminish slightly with increasing dissolved CO2 in the melt.The carbonated silicate partial melts of PERC3 at520% melting and partial melts of PERC at 15^33% melting have SiO2 andAl2O3 contents, and CaO/Al2O3 values, similar to those of melilititic to basanitic alkali OIB, but compared with the natural lavas they are more enriched in CaOand they lack the strong enrichments inTiO2 characteristic of highly alkalic OIB. If a primitive mantle source is assumed, theTiO2 contentsofalkalicOIB, combinedwith bulkperidotite/melt partition coefficients ofTiO2 determined in this study and in volatile-free studiesofperidotite partialmelting, canbe used to estimate that melilitites, nephelinites, and basanites from oceanic islands are produced from 0^6% partial melting.The SiO2 and CaOcontents of such small-degree partial melts of peridotite with small amounts of total CO2 can be estimated from the SiO2^CO2 and CaO^CO2 correlationsobserved inourhigher-degreepartialmeltingexperiments.These suggest that many compositional features of highly alkalic OIBmay be produced by 1^5% partial melting of a fertile peridotite source with 0 1^0 25 wt% CO2. Owing to very deep solidi of carbonated mantle lithologies, generationofcarbonated silicatemelts inOIBsource regions probably happens by reaction between peridotite and/or eclogite and migrating carbonatitic melts produced atgreaterdepths.

/pdf/partial-melting-experiments-of-peridotite-co2-at-3-gpa-and-4d4ajjl4rx.pdf

Partial Melting Experiments of Peridotite + CO2 at 3 GPa and Genesis of Alkalic Ocean Island Basalts

[1] Recycling of oceanic crust together with different types of marine sediments has become somewhat of a paradigm for explaining the chemical and isotopic composition of ocean island basalts. New high-precision trace element data on samples from St. Helena, Gough, and Tristan da Cunha, in addition to recent data from the literature, show that the trace element and isotope systematics in enriched mantle (EM) basalts are more complex than previously thought. EM basalts have some common characteristics (e.g., high Rb/La, Ba/La, Th/U, and Rb/Sr and low Nb/La and U/Pb) that distinguish them from HIMU basalts (high μ = 238U/204Pb). The isotopically distinct EM-1 and EM-2 basalts, however, cannot be clearly distinguished on the basis of incompatible trace element ratios. Ultimately, each suite of EM basalts carries its own specific trace element signature that must reflect different source compositions. In contrast, HIMU basalts show remarkably uniform trace element ratios, with a characteristic depletion in incompatible trace elements (Rb, Ba, Th, U, and Pb) and enrichment in Nb and Ta relative to EM basalts. Compositional similarities between HIMU and EM basalts (e.g., Nb/U, La/Sm, La/Th, Sr/Nd, Ba/K, and Rb/K) suggest that their sources share a common precursor, most likely recycled oceanic lithosphere. The compositional differences between HIMU and EM basalts, on the other hand, can only be explained if the EM sources contain an additional heterogeneous component. Parent-daughter ratios in subducted marine sediments have a unimodal distribution. Recycling of sediments alone can therefore not account for the isotopic bimodality of EM basalts. The upper and lower continental crust have similarly variable trace elements ratios but are systematically distinct in their Rb/Sr, U/Pb, Th/Pb, and Th/U ratios. Thus the upper and lower continental crust evolve along two distinct isotopic evolution paths but retain their complex trace element characteristics, similar to what is observed in EM basalts. We therefore propose that recycling of oceanic lithosphere together with variable proportions of lower and upper continental crust, which are introduced into the mantle together with the oceanic lithosphere via subduction erosion and/or subduction of marine sediments, respectively, provides a plausible explanation for the trace element and isotope systematics in ocean island basalts.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005GC001005

Trace element composition of mantle end‐members: Implications for recycling of oceanic and upper and lower continental crust

Contrasting old and young volcanism in Rurutu Island, Austral chain

Trace element behavior in the alkali basalt-comenditic trachyte series from Mururoa Atoll, French Polynesia

The scale and geometry of chemical and isotopic heterogeneities in the source of plumes have important scientific implications on the nature, composition and origin of plumes and on the dynamics of mantle mixing over time. Here, we address these issues through the study of Marquesas Islands, one of the Archipelagoes in Polynesia. We present new Sr, Nd, Pb, Hf isotopes as well as trace element data on lavas from several Marquesas Islands and demonstrate that this archipelago consists of two adjacent and distinct rows of islands with significantly different isotopic compositions. For the entire 5.5 Ma construction period, the northern islands, hereafter called the Ua Huka group, has had systematically higher 87Sr/86Sr and lower 206Pb/204Pb ratios than the southern Fatu Hiva group at any given 143Nd/144Nd value. The shape and curvature of mixing arrays preclude the ambient depleted MORB mantle as one of the mixing end-members. We believe therefore that the entire isotopic heterogeneity originates in the plume itself. We suggest that the two Marquesas isotopic stripes originate from partial melting of two adjacent filaments contained in small plumes or "plumelets" that came from a large dome structure located deep in the mantle under Polynesia. Low-degree partial melting under Marquesas and other "weak" Polynesian hot spot chains (Pitcairn-Gambier, Austral-Cook, Society) sample small areas of the dome and preserve source heterogeneities. In contrast, more productive hot spots build up large islands such as Big Island in Hawaii or Reunion Island, and the higher degrees of melting blur the isotopic variability of the plume source.

https://hal-insu.archives-ouvertes.fr/insu-00720199/document

The size of plume heterogeneities constrained by Marquesas isotopic stripes

Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia): geochemical dependence on the age of the lithosphere

On the basis of the first systematic mapping of Ua Pou, long known for its exceptionally abundant phonolites, we estimate that these rocks cover 65% of the surface of the island whereas mafic lavas cover 27% and intermediate ones 8%. The silica-undersaturated suite was erupted in a restricted time span (2 9–2 35Myr), following the emplacement of tholeiites derived from a young HIMU-type source at c. 4Ma. Primitive basanites, derived from a heterogeneous mantle source with a dominant EM II HIMU signature, represent likely parental magmas. The series is characterized by a Daly gap defined by a lack of phonotephrites. We consider that the most likely model for the origin of evolved lavas is partial melting at depth of primitive basanites, leaving an amphibole-rich residuum and producing tephriphonolitic magmas. These tephriphonolitic magmas may have evolved by closed-system fractional crystallization towards Group A phonolites. Three other groups of phonolites could have been derived from tephriphonolitic magmas by open-system fractional crystallization processes, characterized respectively by seawater contamination (Group B), assimilation of nepheline syenite-type materials (Group C) and extreme fractionation coupled with assimilation of the underlying oceanic crust (Group D). The prominence of evolved lavas is a consequence of their origin from partial melting of mafic precursors followed by crustal contamination.

Origin of Exceptionally Abundant Phonolites on Ua Pou Island (Marquesas, French Polynesia): Partial Melting of Basanites Followed by Crustal Contamination

Gérard Guille

Papers

Contrasting old and young volcanism in Rurutu Island, Austral chain

Trace element behavior in the alkali basalt-comenditic trachyte series from Mururoa Atoll, French Polynesia

The size of plume heterogeneities constrained by Marquesas isotopic stripes

Basalts from Mururoa, Fangataufa and Gambier islands (French Polynesia): geochemical dependence on the age of the lithosphere

Origin of Exceptionally Abundant Phonolites on Ua Pou Island (Marquesas, French Polynesia): Partial Melting of Basanites Followed by Crustal Contamination