Deep Earth Structure - Transition Zone and Mantle Discontinuities

Kind, R.; Li, X.

doi:10.1016/b978-0-444-53802-4.00017-8

Cited by 11 publications

(4 citation statements)

References 412 publications

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“…The first is dissociation of (Mg,Fe) 2 SiO 4 ringwoodite into ferropericlase and bridgmanite and is responsible for the 660 km seismic discontinuity. Due to the similarity in Fe-Mg partitioning across the transformation, it should take place over a narrow pressure interval equivalent to <2 km in depth [Ito and Takahashi, 1989;Ito et al, 1990], which is consistent with seismic observations of short-period reflected and converted phases [Kind and Li, 2007]. The second bridgmanite formation mechanism is via garnet breakdown, which occurs over a ~100 km interval at the top of the lower mantle.…”

Section: Mineralogy and Crystal Chemistry Of The Lower Mantlesupporting

confidence: 77%

Chemistry of the Lower Mantle

Frost

Myhill

2016

Deep Earth

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Earth's lower mantle, extending from 660 to 2891 km depth, contains ~70% of the mass of the mantle and is ~50% of the mass of the entire planet [Dziewonski and Anderson, 1981]. Due to its size, the lower mantle has a large potential to bias the composition of the bulk silicate Earth (BSE), which in major element terms is generally assumed to be the same as the upper mantle [Allegre et al., 1995; McDonough and Sun, 1995; O'Neill and Palme, 1998]. Any chemical differences between the upper and lower mantle would have major implications for our understanding of the scale of mantle convection, the origin of the terrestrial heat flux, and aspects such as the volatile content of the interior. Furthermore, many constraints on the processes involved in the accretion and differentiation of Earth would be lost if element concentrations in the upper mantle could not be reliably assumed to reflect the mantle as a whole. Ultimately the best prospect for determining whether the lower mantle has the same major element composition as the upper mantle is to compare seismic reference models for shear and longitudinal wave velocities in the lower mantle with mineral physical estimates for what these velocities should be if the mantle is isochemical [Birch, 1952;

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Section: Mineralogy and Crystal Chemistry Of The Lower Mantlesupporting

confidence: 77%

Chemistry of the Lower Mantle

Frost

Myhill

2016

Deep Earth

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“…Fukao et al . [] substantiated this implication by pointing out the richness of reported seismic discontinuities in the lower half of the Bullen's transition region including Kawakatsu and Niu [] (see also the review by Kind and Li [], Courtier et al . [], Courtier \and Revenaugh [], Andrews and Deuss [], and Cao et al .…”

Section: Introductionmentioning

confidence: 93%

Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity

2013

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[1] A new P wave tomographic model of the mantle was constructed using more than 10 million travel times. The finite-frequency effect of seismic rays was taken into account by calculating banana-donut kernels at 2 Hz for all first arrival time data, and at 0.1 Hz for broadband differential travel time data. Based on this model, a systematic survey for subducted slab images was developed for the circum-Pacific; including the Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America, arcs. This survey revealed a progressive lateral variation of the configuration of slabs along arc(s), which we interpret as an indication for successive stages of slab subduction through the Bullen's transition region with the 660 km discontinuity at the middle. We identified the four distinct stages: I -slab stagnant above the 660 km discontinuity; II -slab penetrating the 660 km discontinuity; III -slab trapped in the uppermost lower mantle (at a depth of 660-1000 km); and IV -slab descending well into the deep lower mantle. The majority of slab images are found to be either at Stage I or III, suggesting that Stages I and III are relatively stable or neutral and II and IV are relatively unstable or transient. There is a remarkable distinction for the deepest hypocentral distribution between slabs at Stage I and slabs at Stages II or III.Citation: Fukao, Y., and M. Obayashi (2013), Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity,

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“…They are parallel to the LABs (K2 and T) above, showing opposite trends toward the Tien Shan. The L phases may represent the Lehmann discontinuity that is the bottom of the asthenosphere [42].…”

Section: Resultsmentioning

confidence: 99%

Stepwise Lithospheric Delamination Leads to Pulsed Cenozoic Uplifts of Central Tien Shan

2022

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The Tien Shan provides an ideal site to study mechanism of intracontinental orogeny due to distant effect of Indo-Asian collision. We investigate lithospheric structures, in particular the lithosphere-asthenosphere boundary (LAB), of Central Tien Shan (CTS) using S wave receiver functions. The results show distinct structures across the orogen. Under the southern CTS, the LAB is shallower than that of the Tarim Basin; a 50 km vertical offset implies that part of the lithosphere has been delaminated. Under the middle CTS, two phases of negative velocity gradient are obtained, which may indicate a new LAB and an ongoing delamination underneath. Under the northern CTS and Kazakh Shield northward, the lithosphere is stable although the LAB inclines southward slightly. The two periods of lithospheric delamination under the southern and middle CTS account well for pulsed uplifts of the Tien Shan at ~11-8 Ma and ~5-0 Ma, respectively.

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Deep Earth Structure - Transition Zone and Mantle Discontinuities

Cited by 11 publications

References 412 publications

Chemistry of the Lower Mantle

Chemistry of the Lower Mantle

Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity

Stepwise Lithospheric Delamination Leads to Pulsed Cenozoic Uplifts of Central Tien Shan

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