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A ubiquitous low‐velocity layer at the base of the mantle transition zone
Author(s) -
Shen Xuzhang,
Yuan Xiaohui,
Li Xueqing
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2013gl058918
Subject(s) - geology , classification of discontinuities , discontinuity (linguistics) , transition zone , mantle (geology) , coesite , stishovite , seismology , stratification (seeds) , subduction , crust , geophysics , oceanic crust , mantle wedge , petrology , quartz , tectonics , paleontology , eclogite , seed dormancy , mathematical analysis , germination , mathematics , botany , dormancy , biology
Global stacks of receiver functions clearly exhibit the upper mantle stratification. Besides the most prominent seismic discontinuities, such as the Moho and the 410 and 660 km discontinuities, a negative discontinuity is detected at a depth of ~600 km, indicating a low‐velocity layer at the base of the mantle transition zone. The slant‐slack technique helps to identify the primary conversions from the multiple reverberations. Presence of the negative 600 km discontinuity underneath both continent and ocean island stations, where the crustal thickness significantly differs, also precludes the possible cause of crustal reverberations. We conclude that the negative 600 km discontinuity could be a global feature, possibly resulted from accumulation of ancient subducted oceanic crust. The X‐discontinuity at ~300 km depth is also observed in our global stacks, which can be explained by the coesite‐stishovite phase transformation.