1 edition of Global isotopic signatures of oceanic island basalts found in the catalog.
Global isotopic signatures of oceanic island basalts
Lynn A. Oschmann
by Available from the National Technical Information Service in Springfield, Va
Written in English
|The Physical Object|
|Number of Pages||263|
rocks from continental and oceanic settings, spanning from 3 billion years ago to the present day, together with O and C isotopic ratios for 37 samples. Calcium-, Mg-, and Fe-rich carbonatites have isotopically lighter Ca than mantle- derived rocks such as basalts and fall within the range of isotopically light Ca from ancient marine carbonates. So far we have concentrated on the crustal and depleted mantle reservoirs. We now turn to the isotope systematics of ocean island basalts (OIB). Unlike MORB, the OIB have considerable isotopic variability. Interpretations of this variability require an identification of the sources of OIB.
Lead, oxygen, and osmium isotopic ratios measured on Hawaiian basalts can be matched with the isotopic ratios inferred for recycled ancient oceanic crust. High-precision hafnium isotopic data for lavas from several Hawaiian volcanoes identify old pelagic sediments in their source. These observations support the recycling hypothesis, whereby the mantle source of ocean island basalts includes. Oceanic basalts are the most abundant rock type found at the earth's surface, and as such they have been the subject of considerable research, particularly since the concept of .
A key observation is that oceanic island basalts carrying primordial noble gas signatures have trace element and isotopic (e.g., Nd, 87 Sr, Hf) compositions far more depleted than expected. Systematic measurements of Sr-Nd-Pb isotopic compositions in Oceanic Island Basalts (OIB) for 30 years have shown the complex nature of mantle sources.
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Sr, Nd and Pb isotopic analyses of samples representing 30 islands or island groups, 3 seamounts or seamount chains, 2 oceanic ridges and 1 oceanic plateau (for a total of 36 geographic features) are compiled to form a comprehensive oceanic island basalt (OIB) data set.
Global isotopic signatures of oceanic island basalts / by Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), Includes bibliographical references (p. M.D. Ballmer, G.
Ito, in Treatise on Geophysics (Second Edition), Tracing mantle heterogeneity by isotopic signatures of OIB. The geochemical signatures of ocean island basalts (OIBs) may provide key constraints on the composition of mantle reservoirs.
Highlighting the differences between OIB and MORB, we have focused on 87 Sr/ 86 Sr, Pb/ Pb, and 3 He/ 4 He (Table 1). The He isotopic signatures released from the sparse fluid inclusions vary from to R/Ra (Figs. 1 and 2).
This range is larger than the variation found in plume-related by: 5. It is generally presumed that the highly variable radiogenic isotopic composition of ocean island basalt (OIB) is inherited from chemically heterogeneous deep mantle sources (Zindler and Hart,Hofmann, ; White,White, ).
Trace-element ratios (e.g. Ce/Pb, Nb/U) and radiogenic isotopes (Sr, Nd, Pb and Hf) are commonly used to constrain the source heterogeneity of Cited by: 1.
Introduction  One of the fundamental advances in modern geochemistry of the solid Earth is the recognition of compositional heterogeneities in the Earth's mantle through studies of oceanic basalts.
Ocean island basalts (OIB) are particularly variable in composition such that several isotopically distinct mantle source end‐members (e.g., “DM”, “EM1”, “EM2”, “HUMU. Ocean island basalts (generally referred to as OIBs) are a type of basalt erupted within the oceans, mainly in intraplate settings.
Thus, OIB volcanism contrasts with the other principal types of volcanism in the ocean basins that occur along plate boundaries: mid-ocean ridge basalt (MORB) volcanism, where basalt is erupted at divergent plate boundaries, and subduction zone (or arc) volcanism.
Isotopic variations in oceanic igneous rocks provide important constraints on models of oceanic mantle structure. Of particular interest is the global negative correlation between 87Sr/86Sr and.
The isotopic signatures of some oceanic islands have been interpreted as being derived from crustal material mixed into the mantle sources of these islands . Specifically, the EMII signature of high S'Sr/S6Sr and high Pb/ao4Pb ratios has been attributed to the recycling of sediments in the mantle [9,10].
Based on Pb isotopic data, Jackson et al. () concluded that West Greenland rocks, as well as stratigraphically equivalent high 3 He/ 4 He Baffin Island basalts (e.g., Starkey et al., ), were derived from a little degassed mantle source reservoir that formed between and Ga.
Based primarily on Nd isotopic compositions, they. Ocean island basalt (OIB) is a volcanic rock, usually basaltic in composition, erupted in oceans away from tectonic plate gh ocean island basaltic magma is mainly erupted as basalt lava, the basaltic magma is sometimes modified by igneous differentiation to produce a range of other volcanic rock types, for example, rhyolite in Iceland, and phonolite and trachyte at the.
Abstract. Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), Includes bibliographical references (p.
).Sr, Nd and Pb isotopic analyses of samples representing 30 islands or island groups, 3 seamounts or seamount chains, 2 oceanic ridges and 1 oceanic plateau [for a.
Seismic tomography and distinctive geochemical signatures of Ocean Island Basalts (OIBs) and Mid-Ocean Ridge Basalts (MORBs) provide compelling evidence for recycling of lithospheric components into the convecting mantle, and subsequent incorporation of this material into upwelling mantle plumes (Hofmann, ; van der Hilst et al., ).
of Rhode Island, Narragansett, Rhode Island, USA, 7Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia Abstract Ocean island basalts (OIB) with extremely radiogenic Pb-isotopic signatures are melts of a mantle component called HIMU (high m,highU/Pb).
Until now, deeply dredged submarine HIMU glasses have. To investigate the effect of partial melting on Ca isotopic fractionation and the mechanism for Ca isotopic heterogeneity in the mantle, we report high‐precision Ca isotopic compositions of the normal Mid‐Ocean Ridge Basalts (N‐MORB) from the southern Juan de Fuca Ridge.
δ 44/40 Ca of these N‐MORB samples display a small variation. Recycling of oceanic crust and sediment is a common mechanism to account for the presence of chemical heterogeneities observed in oceanic island basalts (OIBs).
Because of the sizeable fractionation of lithium isotopes in low‐temperature environments, lithium serves as a tracer for recycled material in OIB sources. Based on an evaluation of major and trace element data for ocean island basalts (OIB), we demonstrate that oceanic lithosphere thickness variation, which we refer to as the lid effect, exerts the primary control on OIB geochemistry on a global scale.
The lid effect caps the final depth (pressure) of melting or melt equilibration. The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is. Although all mantle plume (ocean island) basalts seem to contain more water than mid-ocean-ridge basalts, we demonstrate that basalts associated.
Although many ocean island basalts (OIBs) are argued to contain a recycled component9, their uranium isotopic compositions do not differ from those of the bulk Earth. These values are typical of ocean island basalts and may reflect a part of the spectrum of Os isotopic compositions of the Kerguelen plume.
The remaining xenoliths from Lac Superieur are grouped at Os/ Os ≈ ± 7, within the range of compositions estimated for the modern oceanic lithosphere from abyssal peridotites (19, 24). Approximately two thirds of the Earth are covered by large ocean basins submerged under, on average, a m deep layer of water.
The oceanic crust is dominated by basalts, gabbros and exposed mantle rocks and has a limited age of approximately 0– Ma due to constant recycling (e.g., Müller et al.
).This contrasts with the elevated continents that comprise a diverse rock .The Pb isotopic compositions of basalts from the island of Hawaii are distinct for each of the five volcanoes, and within each volcano, Pb's of tholeiites and alkali basalts are similar.