10:00 〜 10:15
[SIT10-05] Where was the Permian Emeishan mantle plume in southwestern China?
★招待講演
キーワード：mantle Plume, Emeishan LIP, Permian
During the past two decades, extensive geological and geophysical studies have been conducted on the Permian Emeishan flood basalt province in southwestern China, which is interpreted as a large igneous province (LIP). Most previous studies proposed that the Emeishan LIP was sourced from a mantle plume, based on the following lines of evidence: (1) 1-km of domal uplift prior to large-scale basalt eruptions; (2) the spatial distribution of low-Ti and high-Ti basalts from the inner zone to the outer zone of the LIP; (3) the presence of picrite in basalt layers and elevated MgO contents, which suggest high temperatures; (4) rapid eruptions of basalt over a short period of less than 1 Myr; and (5) fluctuations in paleo-temperatures and the occurrence of a mass extinction event.
However, recent structural, petrological, sedimentological, and geochemical evidence, together with precise zircon U–Pb dating, does not support previous interpretations of a mantle plume beneath the Emeishan LIP. Recent data show that the apparent 1 km of domal uplift is an artifact of modeling multi-stage deformation. Furthermore, there is no distinct spatial pattern in Ti-enrichment, only with respect to lower (low-Ti) and upper (high-Ti) profile features. Additionally, the initial response of the lithosphere to mantle upwelling would have been a rift system. Rather than picrite lava, there are mafic–ultramafic intrusions and cumulative olivine phenocrysts with corrosion structures, which cannot be used as evidence of a high-temperature primitive magma. Precise U–Pb age data show that the basalts erupted over a period of 10–15 Myr, but large-scale eruptions occurred rapidly within a period of ca. 5 Myr. However, the record of paleobiological evolution shows that the mass extinction event did not coincide with the large-scale eruptions during the 5 m.y. interval.
The available evidence does not support the hypothesis of a mantle plume beneath the Permian Emeishan flood basalt province. As the Emeishan LIP formed during the assembly of the Pangea supercontinent, the large-scale upwelling of volcanic magma may be explained by horizontal flow of the asthenosphere and northward motion of the Yangtze plate.
However, recent structural, petrological, sedimentological, and geochemical evidence, together with precise zircon U–Pb dating, does not support previous interpretations of a mantle plume beneath the Emeishan LIP. Recent data show that the apparent 1 km of domal uplift is an artifact of modeling multi-stage deformation. Furthermore, there is no distinct spatial pattern in Ti-enrichment, only with respect to lower (low-Ti) and upper (high-Ti) profile features. Additionally, the initial response of the lithosphere to mantle upwelling would have been a rift system. Rather than picrite lava, there are mafic–ultramafic intrusions and cumulative olivine phenocrysts with corrosion structures, which cannot be used as evidence of a high-temperature primitive magma. Precise U–Pb age data show that the basalts erupted over a period of 10–15 Myr, but large-scale eruptions occurred rapidly within a period of ca. 5 Myr. However, the record of paleobiological evolution shows that the mass extinction event did not coincide with the large-scale eruptions during the 5 m.y. interval.
The available evidence does not support the hypothesis of a mantle plume beneath the Permian Emeishan flood basalt province. As the Emeishan LIP formed during the assembly of the Pangea supercontinent, the large-scale upwelling of volcanic magma may be explained by horizontal flow of the asthenosphere and northward motion of the Yangtze plate.