Journal ArticleDOI
The continental lithospheric mantle: characteristics and significance as a mantle reservoir.
D.G. Pearson,Geoff Nowell +1 more
TLDR
Observations lead us to question the requirement for CLM participation in the source of oceanic magmas and to promote consideration of a mantle that is chemically heterogeneous on all scales.Abstract:
The continental lithospheric mantle (CLM) is a small-volumed (ca. 2.5% of the total mantle), chemically distinct mantle reservoir that has been suggested to play a role in the source of continental and oceanic magmatism. It is our most easily identifiable reservoir for preserving chemical heterogeneity in the mantle. Petrological and geophysical constraints indicate that the maximum depth of the CLM is ca. 250 km. There is a clear secular variation of CLM composition, such that CLM formed in the last 2 Gyr is less depleted and therefore less dynamically stable than ancient CLM formed in the Archean. We present new trace-element data for kimberlite-hosted lithospheric peridotites and metasomites. These data, combined with other data for spinel peridotites from non-cratonic regions, show that neither hydrous nor anhydrous lithospheric mantle xenoliths make suitable sources for continental or oceanic basalts. Addition of a hydrous phase, either amphibole or phlogopite, to depleted peridotite results in positive Nb and Ti anomalies that are the opposite of those predicted for some flood-basalt sources on the basis of their trace-element abundances. Overall, the Sr and Nd isotopic composition of cratonic and non-cratonic CLM is close to bulk Earth, with cratonic CLM showing small numbers of extreme compositions. Thus, while the CLM is certainly ancient in many locations, its average composition is not significantly 'enriched' over primitive upper mantle, in terms of either radiogenic isotopes or trace elements. These characteristics, plus a change in lithospheric chemistry with depth, indicate that the elemental and isotopic composition of lithospheric mantle likely to be re-incorporated into convecting mantle via delamination/thermal erosion processes is probably not very distinct from that of the convecting mantle. These observations lead us to question the requirement for CLM participation in the source of oceanic magmas and to promote consideration of a mantle that is chemically heterogeneous on all scales. Hf and Nd isotope compositions identify a distinctive source component in deeply derived alkaline volcanics associated with continents. This component cannot be constrained to the CLM but may originate from a deeper reservoir of ancient, subducted oceanic crust stored in the mantle.read more
Citations
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Book ChapterDOI
Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds
TL;DR: A review of the geochemistry of mantle xenoliths can be found in this article, where the authors review the geochemical properties of mantle nodules and find that they are dominantly alkaline in nature.
Journal ArticleDOI
Integration of geology, geophysics and geochemistry: A key to understanding the North China Craton
TL;DR: In this paper, the authors studied the North China Craton (NCC) at the end of the Pre-Cambrian and revealed decoupling brought about by repeated orogenic events over the history of NCC.
Journal ArticleDOI
Physical, chemical, and chronological characteristics of continental mantle
TL;DR: The sub-crustal mantle as discussed by the authors consists of a thick section of material left behind after extensive partial melt extraction, possibly from the wedge of mantle overlying a subducting oceanic plate.
Journal ArticleDOI
Building and Destroying Continental Mantle
TL;DR: In this paper, the authors show that continents are underlain by highly melt-depleted peridotites, which result in a chemically distinct boundary layer that is intrinsically buoyant and strong (owing to dehydration).
Journal ArticleDOI
Geochemistry of South African On- and Off-craton, Group I and Group II Kimberlites: Petrogenesis and Source Region Evolution
Megan Becker,Anton P. le Roex +1 more
TL;DR: In this paper, the authors used bulk-rock geochemical compositions of hypabyssal kimberlites, emplaced through the Archaean Kaapvaal craton and Proterozoic Namaqua-Natal belt, to estimate close-to-primary magma compositions of Group I kimbers.
References
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Journal ArticleDOI
The composition of the Earth
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Journal ArticleDOI
The Volume and Composition of Melt Generated by Extension of the Lithosphere
Dan McKenzie,Mike J. Bickle +1 more
Journal ArticleDOI
The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system
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Journal ArticleDOI
Mantle dynamics, uplift of the Tibetan Plateau, and the Indian Monsoon
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Journal ArticleDOI
Relationships between Lu–Hf and Sm–Nd isotopic systems in the global sedimentary system
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