Slab-mantle interactions I: Formation of the source regions of intraplate basalts
2
Citation
0
Reference
10
Related Paper
Keywords:
Peridotite
Massif
Mantle plume
Radiogenic nuclide
To ascertain factors controlling melt production along a typical distal, ‘hotspot-interacting’ mid-ocean ridge, we investigated the extent and distribution of both plume-related and plume-unrelated basalt from the central Indian ridge (CIR) between 15°S and 20°S. Comprehensive geochemical data of fresh-quenched volcanic glasses and basalts were used. Variation of Sr, Nd, and Pb isotopic compositions and Nb/Zr, Ba/Nb, and Ba/La content were interpreted by mixing of three melt end members: the Indian depleted MORB mantle derived melt; radiogenic and enriched melt derived from source mantle for Rodrigues Ridge and the intermediate series of Mauritius Island (RE2, radiogenic enriched component 2); and radiogenic but depleted melt derived from source mantle for Gasitao Ridge (RD, radiogenic depleted component). On the basis of quantitative mantle melting and melt mixing model, results show that sources for RE2 and RD are geochemically distinct from those of the Réunion plume (RE1, radiogenic enriched melt component 1). Moreover, the geochemical variation of MORB of 15°S to 20°S is unrelated to contamination of the upper mantle by the Réunion plume. These results suggest strongly that plume-unrelated heterogeneity is widespread throughout the upper mantle. The chemical characteristics of RE2 are remarkably pronounced in basalt from the central portion of ridge segment 16 around 18°S, suggesting substantial magma production. The influence of RE2 decreases along with decreasing magma production to the north, and is only slightly identifiable in basalt from the northern part of segment 18. Although the influence of RE2 decreases somewhat to the south, basalts with extreme RE2 signature were produced in the center of segment 15 around 19°S, where magma production is high. In contrast to RE2, the geochemical signature of RD in basalt is geographically limited to two localities: the south end of segment 18 and the center of segment 15. However, these observations reveal that both RE2 and RD contribute strongly to magma production on segment 15. Results show that melting of ancient recycled plate materials with a low melting point regulates voluminous magma production along the CIR.
Radiogenic nuclide
Hotspot (geology)
Mantle plume
Cite
Citations (17)
Peridotite
Solidus
Coesite
Pyroxene
Cite
Citations (79)
The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1968)
On the basis of Fe2+-Mg partition between coehisting garnet and clinopyroxene of eclogites in the Higasi-akaisi peridotite mass, both from the Gongen valley and from the main adit of the Akaisi mine, it is suggested that the crystallization temperatnre of the eclogites in this peridotite mass corresponds to that of lower amphibolite fades. The temperature thus estimated appears to be higher than that of surrounding metabasites, and eclogites enclosed therein. The chemical compositions of six pairs of gamet-clinopyroxene assemblage, including the new analyses of three pairs, are described in Table 1.
Peridotite
Cite
Citations (2)
Peridotite
Forsterite
Coesite
Cite
Citations (2)
Massif
Radiogenic nuclide
Heat flow
Radiometric dating
Cite
Citations (14)
Peridotite
Cite
Citations (0)
Peridotite
Cite
Citations (0)
Experimentally at 7 GPa phase relations in two sections of the system garnet peridotite–eclogite– carbonatite are studied in connection with the problem of physico-chemical conditions of differentiation of the upper mantle ultrabasic-basic magmas and formation of continuous series of peridotite–eclogite rocks as well as the syngenesis of diamond and primary inclusions of peridotitic and eclogitic parageneses. Diagrams of equilibrium and fractional crystallization of the boundary silicate multicomponent system peridotite–eclogite are constructed. As a result, a new effect of “peridotite–eclogite tunnel” is established. The tunnel provides formation of the continuous series of peridotite–eclogite rocks of the Earth’s upper mantle. Also, diagrams of equilibrium and fractional crystallization for the polythermal section peridotite30carbonatite70–eclogite35carbonatite65 are constructed. As a result, a combined action of the effects of peridotite–eclogite tunnel and carbonatization of peridotitic magnesian phases is recognized. The effects provide consecutive formation of the phases of peridotitic and eclogitic parageneses in the natural processes of diamond origin.
Peridotite
Ultramafic rock
Fractional crystallization (geology)
Cite
Citations (1)
Previous reports on Nové Dvory garnet peridotites indicated that they lacked primary spinel, and prograde metamorphism evidence was uncommon. This study revealed the presence of Al– and Cr–rich spinels, clinopyroxenes with a lower content of Na and Fe than what has been previously reported, and chemical heterogeneity in garnet in Nové Dvory garnet peridotites. Cr–poor (0.06–0.12 a.p.f.u.) and Cr–rich (0.10–0.27 a.p.f.u.) garnet populations were identified, and they had contrasting coronas around garnet. The garnet peridotite samples were classified into three types on the basis of the chemical composition of garnet and constituent minerals: type A that includes Cr–rich spinel and Cr–rich garnet; type B that includes Cr–poor garnet and no spinel; and type C that includes both Al– and Cr–rich spinel and both Cr–rich and Cr–poor garnet. The finding of spinel relics {Cr# = [100 Cr/(Cr + Al)] ~ 60–70} in garnet from type A peridotite suggests that the Nové Dvory peridotite body may have been located at relatively shallow depths prior to the ultrahigh–pressure metamorphic stage of >4 GPa. Suitable geothermobarometers were used to establish the P–T history of the rocks. The core compositions of clinopyroxene inclusions in garnet and host garnet yielded 978–1002 °C, 4.87–5.12 GPa (type B) and 1034 °C, 4.93 GPa (type C); stage I. Garnet porphyroblasts in type A peridotite lack clinopyroxene inclusions. The core compositions of garnet and pyroxenes yielded 1005–1072 °C, 4.42–4.46 GPa (type A); stage II. The innermost garnet rims and cores of matrix pyroxenes surrounding garnet yielded 1222–1325 °C, 5.03–5.67 GPa (type B) and 1189–1267 °C, 5.59–6.97 GPa (type C); stage II. Thus, Nové Dvory peridotite has experienced an increase in the P–T conditions, and its chemical heterogeneity (especially in the Cr content of garnet) in type C peridotites may have been created by the mechanical mixing of different rock types (i.e., Cr–rich and Cr–poor types) during the compression and/or decompression stage(s).
Massif
Peridotite
Cite
Citations (4)