Garnet-spinel transition in the upper mantle: Review and interpretation
13
Citation
38
Reference
10
Related Paper
Citation Trend
Keywords:
Peridotite
Peridotite
Cite
Citations (0)
The mantle’s compositional structure reflects the thermochemical evolution of Earth. Yet, even the radial average composition of the mantle remains debated. Here, we analyze a global dataset of shear and compressional waves reflecting off the 410- and 660-km discontinuities that is 10 times larger than any previous studies. Our array analysis retrieves globally averaged amplitude-distance trends in SS and PP precursor reflectivity from which we infer relative wavespeed and density contrasts and associated mantle composition. Our results are best matched by a basalt-enriched mantle transition zone, with higher basalt fractions near 660 (~40%) than 410 (~18–31%). These are consistent with mantle-convection/plate-recycling simulations, which predict that basaltic crust accumulates in the mantle transition zone, with basalt fractions peaking near the 660. Basalt segregation in the mantle transition zone also implies that the overall mantle is more silica enriched than the often-assumed pyrolitic mantle reference composition.
Hotspot (geology)
Classification of discontinuities
Cite
Citations (14)
Abstract The recycling of oceanic crust, with distinct isotopic and chemical signature from the pyrolite mantle, plays a critical role in the chemical evolution of the Earth with insights into mantle circulation. However, the role of the mantle transition zone during this recycling remains ambiguous. We here combine the unique resolution reflected body waves (P410P and P660P) retrieved from ambient noise interferometry with mineral physics modeling, to shed new light on transition zone physics. Our joint analysis reveals a generally sharp 660-km discontinuity and the existence of a localized accumulation of oceanic crust at the bottom mantle transition zone just ahead of the stagnant Pacific slab. The basalt accumulation is plausibly derived from the segregation of oceanic crust and depleted mantle of the adjacent stagnant slab. Our findings provide direct evidence of segregated oceanic crust trapped within the mantle transition zone and new insights into imperfect whole mantle circulation.
Hotspot (geology)
Crustal recycling
Core–mantle boundary
Cite
Citations (20)
Core–mantle boundary
Post-perovskite
Crustal recycling
Hotspot (geology)
Cite
Citations (29)
Melting of the Earth's upper mantle beneath midocean ridge spreading centers is likely to be a dynamic, near-fractional process during which pressure (P), temperature (T), and source composition change as melting proceeds (Cooper and Kohlstedt, 1986; Johnson et al., 1990; Kinzler and Grove, 1992a,b; Langmuir et al., 1992). Well constrained melting models are required in order to use the compositions of mid-ocean ridge basalts to infer characteristics of the melting processes that lead to ocean ridge volcanism. These include the pressure range over which melting occurs, the extent to which the melting process approaches fractional melting; the geometry of the melting region, the role played by garnet in the source region, and the extent to which melts react with their surroundings as they migrate to the surface, etc. Current models for the generation of portions of the oceanic crust generally predict initial pressures of melting of 25-30 kbar (Klein and Langmuir, 1987, 1989; Kinzler and Grove, 1992b, Langmuir et al., 1992), however, the experimental data base available upon which to build full major element peridotite melting models has been limited by a lack of data at pressures greater than ~ 15 kbar. This abstract presents new experimental data relevant for melting of spinel lherzolite obtained over the pressure range of 15-25 kbar. A modified version of the method of Kinzler and Grove (1992a) is used to provide a preliminary parameterization of these data, combined with data from the literature.
Peridotite
Cite
Citations (28)
Peridotite
Metasomatism
Chromite
Massif
Cite
Citations (19)
Peridotite
Cite
Citations (13)
The areas of low-velocity middle mantle shift into the transition zone are distinguished according to 3-d P-velocity model of the Fennoscandian shield mantle and its surroundings using Taylor approximation method. Within the Kola-Karelia megablock there are the White Sea and Varanger mantle domains along with the Kostomuksha and Lapland upper mantle domains. Within the Svecofennian megablock there is the Shellefteo domain, and within the Sveconorwegian megablock - subvertical mantle column of altering high and low-velocity P-waves corresponding to superdeep mantle of the Oslo graben. Based on the conducted analysis the following general velocity features of the distinguished domains are defined: the areas of low-velocity middle mantle shift into the transition zone of the upper mantle, stratification of the upper mantle and its transition zone.
Hotspot (geology)
Core–mantle boundary
Cite
Citations (2)
Peridotite
Cite
Citations (0)
Peridotite
Massif
Collision zone
continental collision
Cite
Citations (4)