The Origin of HIMU in the SW Pacific: Evidence from Intraplate Volcanism in Southern New Zealand and Subantarctic Islands

This paper presents field, geochemical and isotopic (Sr, Nd,Pb) results on basalts from the Antipodes, Campbell and ChathamIslands, New Zealand. New ⁴⁰Ar/³⁹Ar age determinations alongwith previous K–Ar dates reveal three major episodes ofvolcanic activity on Chatham Island (85–82, 41–35,5 Ma). Chatham and Antipodes samples comprise basanite, alkaliand transitional basalts that have HIMU-like isotopic (²⁰⁶Pb/²⁰⁴Pb>20·3–20·8, ⁸⁷Sr/⁸⁶Sr <0·7033,¹⁴³Nd/¹⁴⁴Nd >0·5128) and trace element affinities(Ce/Pb 28–36, Nb/U 34–66, Ba/Nb 4–7). Thegeochemistry of transitional to Q-normative samples from CampbellIsland is explained by interaction with continental crust. Thevolcanism is part of a long-lived (100 Myr), low-volume, diffusealkaline magmatic province that includes deposits on the Northand South Islands of New Zealand as well as portions of WestAntarctica and SE Australia. All of these continental areaswere juxtaposed on the eastern margin of Gondwanaland at >83Ma. A ubiquitous feature of mafic alkaline rocks from this regionis their depletion in K and Pb relative to other highly incompatibleelements when normalized to primitive mantle values. The inversionof trace element data indicates enriched mantle sources thatcontain variable proportions of hydrous minerals. We proposethat the mantle sources represent continental lithosphere thathost amphibole/phlogopite-rich veins formed by plume- and/orsubduction-related metasomatism between 500 and 100 Ma. Thestrong HIMU signature (²⁰⁶Pb/²⁰⁴Pb >20·5) is consideredto be an in-grown feature generated by partial dehydration andloss of hydrophile elements (Pb, Rb, K) relative to more magmaphileelements (Th, U, Sr) during short-term storage at the base ofthe lithosphere. KEY WORDS: continental alkaline basalts; lithospheric mantle, mantle metasomatism; New Zealand; OIB, HIMU; Sr, Nd and Pb isotopes; West Antarctica     

XRF AND INAA DETERMINATIONS OF MAJOR AND TRACE ELEMENTS IN GEOLOGICAL SURVEY OF JAPAN IGNEOUS AND SEDIMENTARY ROCK STANDARDS

Major and trace element analyses have been obtained by wavelength dispersive X-ray fluorescence for the Geological Survey of Japan Igneous rock series and selected samples from the Sedimentary rock series reference samples. Additional trace element data for the Igneous rock series were obtained by instrumental neutron activation analysis. Samples were analyzed multiple times for 10 major elements (with loss-on-ignition) and the following trace elements; As, Ba, Ce, Co, Cr, Cs, Cu, Eu, Ga, Hf, La, Lu, Nb, Nd, Ni, Pb, Rb, Sb, Sc, Sm, Sr, Ta, Tb, Th, U, V, W, Y, Yb, Zn and Zr.     

Mineralogy and Geochemistry of a Basanite to Phonolite Sequence at Hut Point Peninsula, Antarctica, based on Core from Dry Valley Drilling Project Drillholes 1, 2 and 3

The Dry Valley Drilling Project (DVDP) cored three holes (DVDP1, 2 and 3) at Hut Point Peninsula (HPP) on Ross Island, Antarctica.DVDP 1 reached 201 m and penetrated 40 stratigraphic units,mainly basanite and Ne-hawaiite lava flows and associated pyroclasticrocks. DVDP 2 and 3 are nearly identical. DVDP 3 reached 381m and penetrated 15 stratigraphic units. The lower unit is a214 m thick basanite hyaloclastite, this is overlain by flowsand pyroclastic rocks of basanite, Ne-hawaiite, and then alternatingNe-mugearite and Ne-benmoreite flows. Phonolite stratigraphicallyoverlies the drill site. Primary olivine (Fo₈₈-Fo₇₄) is confined to the basanites, althoughxenocrysts occur in other rock types. Calcium-rich clinopyroxeneis ubiquitous but shows little variation in terms of Ca, Mg,Fe²⁺. Kaersutite is common in all lavas except the basanitesand shows very little compositional variation. It is believedto have crystallized at temperatures below 1100 °C and atpressures between 1·5 and 10 kb. Rhönite, a titanosilicateis a common groundmass phase in some basanite lavas. Oxide mineralsshow a wide range of compositions; spinel and chromian spineloccur as inclusions in olivine in the basanites. Titano-magnetiteoccurs in most samples examined. Labradorite is the predominantfeldspar in the basanite, with andesine and oligoclase importantin all other rock types. DVDP and HPP samples show a well-defined sequence of basanite-Ne-hawaiite-Ne-mugearite-Ne-benmoreite-phonolite,termed the DVDP lava lineage. Differentiation of the lineagehas been modeled using major element least squares mass balancemodels. Over 75 per cent of the evolution from basanite to phonoliteoccurs in the initial step from basanite to Ne-hawaiite, whichrepresents a 43 per cent residual. The phonolite is only a 25per cent residual from a basanite parent; thus even though Ne-mugeariteand Ne-benmoreite are common, they represent only minor stepsin the differentiation sequence. The mass balance models indicatethat olivine, clinopyroxene, kaersutite, opaque oxides and feldsparare the dominant fractionated phases. Trace element (includingrare earth element) contents calculated using the Rayleigh equationconfirm all models. ^* Present address: Department of Geoscience, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801.     

REGIONALISM IN THE MIDDLE EAST AND THE CASE OF TURKEY

ABSTRACT. Turkey is a republic that borders on, regularly interacts with, and actively seeks to define itself as a part of neighboring regions. As such, it provides a significant example of how Middle East nation‐states are not only affected by globalization but also deeply involved in contributing to the related processes of regionalization and regional (re)definition. Far from a unique phenomenon, regionalism involving Turkey is flexible and multifaceted, profoundly dynamic, and inextricably linked to virtually all aspects of the nation's foreign and domestic affairs. Regionalism in Turkey demonstrates clearly how processes of globalization are not simply economic but also directly implicated in contemporary shifts in national identity and even in the very nature of the nation‐state itself. This study surveys and analyzes the constructs and dynamics of regionalism that are shaping the Turkish nation and state, contributing to varieties of transnationalism, and reconstituting the scales at which Turkey is located, both in the Middle East and elsewhere in the world.     

The Origins of Glass and Amphibole in Spined--Wehrlite Xenoliths from Foster Crater, McMurdo Volcanic Group, Antarctica

Vesicular interstitial glass in four kaersutite-bearing spinel–wehrlitexenoliths from Foster Crater, Antarctica has reacted with hostolivine (Fo_75–79) and clinopyroxene (Ca₄₇ Mg₄₅ Fe₈) andcontains a microphenocryst assemblage of spinel, olivine, andclinopyroxene together with later rhonite and plagioclase. Electronmicroprobe analyses of the glasses have low SiO₂ (46–49wt. per cent) and MgO (2.2–3.7) contents and high contentsof alkalis, TiO₂ (3.4–4.8), Al₂O₃ (18.1–20.6) andP₂O₅ (1.1–1.3). Olivine microphenocryst cores in glassare magnesian (up to Fo₈₈) and must have precipitated from moreprimitive liquids; rim compositions are Fe-rich (Fo₇₅) and inequilibrium with glass. Continuous core to rim zonation in theolivine microphenocrysts indicate that glass compositions havefractionated due to crystallization of the enclosed mineralassemblage. Mass balance addition calculations, using the compositionsand proportions of the crystals in glass, produce melt compositionsappropriate to primary alkali basaltic magmas. Glasses showlight rare earth element (REE) enrichment relative to chondrites(Ce/YbN = 10.5) and, together with Ba, Rb, Cr, Hf, Ta, and Thare similar to many of the basanites from the Erebus VolcanicProvince. Textural relationships of the kaersutite are complex owing tothe instability of kaersutite in the presence of melt. However,in the association with glass we observe textural evidence suchas olivine and clinopyroxene microphenocrysts, identical tothe liquidus phases of the glasses, enclosed by kaersutite crystals.We believe that relationships such as this link the crystallizationof kaersutite to mafic melt which infiltrated and reacted withthe host wehrlite. Thus, the melt did not form in situ withinthe xenolith but originated elsewhere in the upper mantle.     

Petrologic Evolution of Anorthoclase Phonolite Lavas at Mount Erebus, Ross Island, Antarctica

Mount Erebus, Ross Island, Antarctica, is an active, intraplate,alkaline volcano. The strongly undersaturated sodic lavas rangefrom basanite to anorthoclase phonolite, and are termed theErebus lineage (EL). The lavas are porphyritic with olivine(Fo₈₈–51), clinopyroxene (Wo₄₅–53En₃₆–41Fs₈–30),opaque oxides (Usp₃₁–76), feldspar (An₇₂–11), andapatite. Rare earth element (REE) contents increase only slightlywith increasing differentiation compared with other incompatibleelements. The light REE are enriched (La_N/Yb_N= 14–20)and there are no significant Eu anomalies. ⁸⁷Sr/⁸⁶Sr is uniformand low ({small tilde} 0.7030) throughout the EL, suggestingderivation of the basanites from a depleted asthenospheric mantlesource, and lack of significant crustal contamination duringfractionation of the basanite. Regular geochemical trends indicatethat the EL evolved from the basanites by fractional crystallization.Major element mass balance calculations and trace element modelsshow that fractionation of 16% olivine, 52% clinopyroxene, 14%Fe-Ti oxides, 11% feldspar, 3% nepheline, and 3% apatite froma basanite parent leaves 23.5% anorthoclase phonolite. Minor volumes of less undersaturated, more iron-rich benmoreite,phonolite, and trachyte are termed the enriched iron series(EFS). The trachytes have ⁸⁷Sr/⁸⁶Sr of 0.704, higher than otherEFS and EL rocks, and they probably evolved by a combined assimilation-fractionalcrystallization process. The large volume of phonolite at Mt. Erebus requires significantbasanite production. This occurs by low degrees of partial meltingin a mantle plume (here termed the Erebus plume) rising at arate of about 6 cm/yr.     

Analysis of NBS Coal Standard Reference Materials 1632a and 1635 by Instrumental Neutron Activation Analysis

NBS SRM 1635 and NBS SRM 1632a were analyzed for trace and minor element contents by instrumental neutron activation analysis. The results of these analyses show excellent agreement with NBS certified values and/or literature values.