Mantle transition zone structure along a profile in the SW Pacific: thermal and compositional variations

Thomas, Christine; Billen, M. I.

doi:10.1111/j.1365-246x.2008.03934.x

Cited by 50 publications

(42 citation statements)

References 76 publications

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“…As a consequence, the TZ becomes thicker near subducted slabs and thinner beneath plumes or high-temperature regions due to small-scale mantle convection (Collier et al, 2001;Helffrich, 2000;Lawrence and Shearer, 2006;Vidale and Benz, 1992). However, the presence of other transforming or non-transforming mantle components can change the characteristics of the phase transitions and makes the interpretation of the corresponding seismic discontinuities more difficult (Cao et al, 2011;Deuss et al, 2006;Stixrude, 1997;Tauzin et al, 2008;Thomas and Billen, 2009;Wang et al, 2004;Weidner and Wang, 1998). In particular, in normal to hot upper mantle and in the presence of Al within garnet, the garnet-to-perovskite transition is expected near the bottom of the TZ with a positive Clapeyron slope (Akaogi et al, 2002;Wang et al, 2004;Weidner and Wang, 1998).…”

Section: -Km and 660-km Discontinuitiesmentioning

confidence: 97%

The upper-mantle transition zone beneath the Ibero-Maghrebian region as seen by teleseismic Pds phases

et al. 2015

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Section: -Km and 660-km Discontinuitiesmentioning

confidence: 97%

The upper-mantle transition zone beneath the Ibero-Maghrebian region as seen by teleseismic Pds phases

et al. 2015

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“…They found that it was difficult to produce coherent results when migrating data from many different events and stations and concluded that maps of the 660 km discontinuity topography are most likely not strongly biased by small scale structures. Migration has been more successful using only a few events and seismic array data, in particular showing observations of the elusive 660 km discontinuity in PP precursors (Thomas and Billen 2009). New methods are currently being developed to use the Radon transform to include scattering on a regional scale (see Gu 2009).…”

Section: Fresnel Zones and Migrationmentioning

confidence: 98%

“…More recently PP precursors have also received increased attention (e.g. Weber 2001, 2002;Chambers et al 2005a, b;Deuss et al 2006;Lawrence and Shearer 2006a;Thomas and Billen 2009).…”

mentioning

confidence: 98%

Global Observations of Mantle Discontinuities Using SS and PP Precursors

2009

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SS and PP precursors are currently the only body wave data types that have significant coverage in both oceanic and continental regions to study the existence and characteristics of mantle discontinuities on a global scale. Here, the techniques used by global seismologists to observe SS and PP precursors are reviewed. Seismograms, aligned on SS or PP, are stacked using normal move out (NMO) techniques to obtain common depth point gathers. Bootstrap methods are employed to determine 95% confidence levels of the stacks and robustness of the observations. With these relatively simple techniques, a range of discontinuities has been found in the mantle up to 1,200 km depth. The stacks are dominated by the transition zone discontinuities at 410, 520 and 660 km depth, but additional discontinuities at 220, 300-350, 800-900 and 1,100-1,200 km depth are also seen in certain regions. An overview is given of the most recent observational results with a discussion of their mineral physical interpretation and geodynamical significance. Both seismology and mineral physics agree on the level of complexity at the transition discontinuities: a simple 410, a more complicated 520 and a highly complicated 660-km discontinuity are consistently found in both disciplines.

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“…Despite the common observations of P 660P at short periods (Benz & Vidale 1993;LeStunff et al 1995), longer period P660P signals are rarely seen (Estabrook & Kind 1996;Shearer & Flanagan 1999). Studies that do record a P660P signal detect an intermittent and complicated discontinuity (Deuss et al 2006;Thomas & Billen 2009;Schmerr & Thomas 2011). Observed P 660P signals, on the other hand, indicate that the '660' is sharp and narrow, with a thickness of less than 4 km (Xu et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Reconciling PP and P′P′ precursor observations of a complex 660 km seismic discontinuity

Day

Deuss

2013

Geophysical Journal International

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S U M M A R YHigh frequency precursors to P P almost invariably observe a narrow 660 km discontinuity, whereas PP precursor studies at long periods struggle to detect a reflection from the '660' despite its apparent sharpness to P P . To investigate these contradictory observations we compare PP and P P precursors in the same region. Using short period P P precursors we observe a sharp 660 km discontinuity, which appears to vary in depth substantially. The apparent topography on the '660' is too large to originate solely from thermal variations, regardless of its cause, therefore indicating chemical variations at the base of the mantle transition zone. Long period P P precursors show no '660' as they are sensitive to a larger area and thus average out the apparent topography, in agreement with long period PP precursors. Instead, we see some evidence in both long period data types for a reflection from 720 km depth, which is likely to correspond to a phase change in the garnet system. Key words: Mantle processes; Composition of the mantle; Body waves . I N T RO D U C T I O NThe 660 km seismic discontinuity (the '660') at the base of the mantle transition zone (MTZ) marks the boundary between the upper and lower mantle. The seismic signature of the '660' is attributed to the post-spinel phase transition in olivine, in which ringwoodite transforms into perovskite and periclase (Ita & Stixrude 1992). The nature of the 660 km seismic discontinuity governs the behaviour of the mantle as a whole, with its properties as a chemical and mechanical boundary controlling mantle convection and the fate of subducting slabs (Schubert et al. 2001).Observations of the 660 km seismic discontinuity in precursors to body waves have painted a complex and sometimes even contradictory picture. Despite the common observations of P 660P at short periods (Benz & Vidale 1993;LeStunff et al. 1995), longer period P660P signals are rarely seen (Estabrook & Kind 1996;Shearer & Flanagan 1999). Studies that do record a P660P signal detect an intermittent and complicated discontinuity (Deuss et al. Here, we explore the complex and potentially contradictory observations of the '660' in compressional body waves by directly comparing P P and long period PP precursor observations in the same region under South East Africa. We investigate the topography of the 660 km discontinuity and the frequency dependence of the seismic signals to reconcile the PP and P P observations. DATA A N D M E T H O D SSurface reflected body waves such as PP and P P are preceded by smaller amplitude arrivals, known as precursors. These arrivals have been reflected at discontinuities below the Earth's surface and are therefore sensitive to the impedance change at the discontinuity. P P df (also known as PKIKPPKIKP and hereafter as P P ) is a seismic phase which traverses the entire Earth before reflecting off the Earth's surface, as illustrated in Fig. 1. P P precursors are referred to as P dP , where 'd' denotes the depth of the interface at which they have been reflected. ...

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Mantle transition zone structure along a profile in the SW Pacific: thermal and compositional variations

Cited by 50 publications

References 76 publications

The upper-mantle transition zone beneath the Ibero-Maghrebian region as seen by teleseismic Pds phases

The upper-mantle transition zone beneath the Ibero-Maghrebian region as seen by teleseismic Pds phases

Global Observations of Mantle Discontinuities Using SS and PP Precursors

Reconciling PP and P′P′ precursor observations of a complex 660 km seismic discontinuity

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