Consequences of plume-lithosphere interactions

Abstract

Splitting or thinning of lithosphere above a mantle plume can result in voluminous melt generation, leading to the formation of large igneous provinces, or LIPs. Examples of LIPs include continental flood basalt provinces and oceanic plateaus. Basaltic samples from the Ontong Java Plateau, Nauru Basin and Manihiki Plateau, which are among the largest of the LIPs, have isotopic compositions within the range of ocean island basalts. The majority of continental basalts, however, record a trace element and isotopic contribution from the lithosphere through which they have erupted. We are thus unable to reconcile the available compositional data with models which derive the isotopic and large-ion lithophile element-enriched character of continental flood basalts solely from sub-lithospheric mantle plume sources. A combination of mantle sources is indicated, with the thermal energy being supplied by voluminous melts from a plume, and the lithospheric components in continental flood basalts being inherited by contamination of plume-derived melts by low melting point hydrous and carbonated fractions in the lithosphere. Successive injection of plume-derived melts serves to heat the lithosphere, reducing its viscosity and making it susceptible to rupture if allowed by regional plate forces. Furthermore, the lithosphere, including the mechanical boundary layer, may be thinned by thermal stripping from below, allowing the plume mantle to ascend and decompress further. Such a system has the potential for positive feedback leading to rapid melt generation. While we do not exclude recent models of LIP formation which require the sudden impact of a new mantle plume, we favour a model whereby the thermal anomaly builds gradually, incubating beneath a steady-state lithospheric cap.

Paleozoic tectonics of the southern Chinese Tianshan: Insights from structural, chronological and geochemical studies of the Heiyingshan ophiolitic mélange (NW China)

“…At Wuwamen (Fig. 1B), the source of N-MORB-like tholeiitic basalts was interpreted to have been metasomatized by slab-derived fluids (Dong et al 2005), and their high primitive-mantle-normalized Th/Nb ratios (1.4-5.9) suggest significant crustal contamination (Saunders et al, 1992). At the Kulehu and Serikeya localities (Fig.…”

Geochemistry, zircon U–Pb ages and Lu–Hf isotopes of early Paleozoic plutons in the northwestern Chinese Tianshan: Petrogenesis and geological implications

“…8), suggesting an origin from a depleted mantle source. These mafic rocks exhibit negative Ta, Nb, Ti anomalies, which are distinct from those of depleted asthenosphere-derived magmas (N-MORB) and oceanic island basalts (OIB) since such basic rocks generally have very low primitive mantle-normalized (Th/Nb) PM ratios of b1 (Saunders et al, 1992;Su et al, 2012). However, the early Paleozoic mafic rocks in this study have much higher (Th/Nb) PM ratios (0.74-7.16), suggesting a magma source different from N-MORB.…”

The Early Permian Tarim Large Igneous Province: Main characteristics and a plume incubation model

“…One attributes the formation of LIPs to the arrival of a plume head at the base of the lithosphere, and subsequent decompression melting of a deflated plume head with a diameter reaching up to 2000 km (Campbell and Griffiths, 1990;Richards et al, 1989). The other proposes that a plume head grows more slowly (incubates) especially underneath thick continental lithosphere (N 120 km) which inhibits melting of mantle plumes Saunders et al, 1992). However, melting of a mantle plume in this scenario is possible when the overlying lithosphere is thinned and removed by conductive heating, melt injection and extension (White and McKenzie, 1989).…”