Partially melted, mica-bearing crust in Central Tibet

Hacker, Bradley R.; Ritzwoller, M. H.; Xie, Jing

doi:10.1002/2014tc003545

Cited by 118 publications

(98 citation statements)

References 100 publications

(146 reference statements)

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“…Various explanations have been put forward as to the cause of the mid-crustal low velocity zone including the presence of partial melt (Caldwell et al 2009;Hacker et al 2014;Jiang et al 2014), aqueous fluids (Caldwell et al 2009), anisotropy from the alignment of micas in the crust (Yang et al 2012;Hacker et al 2014) or some combination of these mechanisms (Agius & Lebedev 2014). These explanations imply that the mid-crust is mechanically weak (Klemperer 2006), providing support for the idea that deformation in Tibet occurs due to crustal flow (e.g.…”

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 92%

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

“…Caldwell et al 2009;Hacker et al 2014;Jiang et al 2014) . Velocities less than 3.4 km s −1 , such as those observed throughout the Tibetan Plateau would be in agreement with the presence of melt from rocks of composition and temperatures that are plausible for Tibet (Hacker et al 2014). Further, this explanation also agrees with magnetotelluric studies in southeast Tibet (Unsworth et al 2004) and in the Pamirs (Sass et al 2014) that observe a conductive layer in the mid-crust, which would be consistent with the presence of melt and/or fluids.…”

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

“…Chung et al 2005) across the Tibetan Plateau. Hacker et al (2014) suggest that this could be explained by either earlier melting events already depleting the crust, meaning that only small amounts of melt are produced by present heating, or by the melts that are produced not reaching the surface because they are highly viscous or are produced in small batches that freeze without erupting.…”

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

“…• C, (Hacker et al 2000(Hacker et al , 2014. Agius & Lebedev (2014) argue that temperatures of ∼ 800…”

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

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Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Gilligan

2018

Geophysical Journal International

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S U M M A R YThe processes involved in continental collisions remain contested, yet knowledge of these processes is crucial to improving our understanding of how some of the most dramatic features on the Earth have formed. As the largest and highest orogenic plateau on the Earth today, Tibet is an excellent natural laboratory for investigating collisional processes. To understand the development of the Tibetan Plateau, we need to understand the crustal structure beneath both Tibet and the Indian Plate. Building on previous work, we measure new group velocity dispersion curves using data from regional earthquakes (4424 paths) and ambient noise data (5696 paths), and use these to obtain new fundamental mode Rayleigh wave group velocity maps for periods from 5 to 70 s for a region including Tibet, Pakistan and India. The dense path coverage at the shortest periods, due to the inclusion of ambient noise measurements, allows features of up to 100 km scale to be resolved in some areas of the collision zone, providing one of the highest resolution models of the crust and uppermost mantle across this region. We invert the Rayleigh wave group velocity maps for shear wave velocity structure to 120 km depth and construct a 3-D velocity model for the crust and uppermost mantle of the Indo-Eurasian collision zone. We use this 3-D model to map the lateral variations in the crust and in the nature of the crust-mantle transition (Moho) across the Indo-Eurasian collision zone. The Moho occurs at lower shear velocities below northeastern Tibet than it does beneath western and southern Tibet and below India. The east-west difference across Tibet is particularly apparent in the elevated velocities observed west of 84• E at depths exceeding 90 km. This suggests that Indian lithosphere underlies the whole of the Plateau in the west, but possibly not in the east. At depths of 20-40 km our crustal model shows the existence of a pervasive mid-crustal low velocity layer (∼10% decrease in velocity, V s < 3.4 km s −1 ) throughout all of Tibet, as well as beneath the Pamirs, but not below India. The thickness of this layer, the lowest velocity in the layer and the degree of velocity reduction vary across the region. Combining our Rayleigh wave observations with previously published Love wave dispersion measurements, we find that the low velocity layer has a radial anisotropic signature with V sh > V sv . The characteristics of the low velocity layer are supportive of deformation occurring through ductile flow in the mid-crust.

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Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 92%

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

“…• C, (Hacker et al 2000(Hacker et al , 2014. Agius & Lebedev (2014) argue that temperatures of ∼ 800…”

Section: P O S S I B L E C Au S E O F T H E L O W V E L O C I T Y L Amentioning

confidence: 99%

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Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Gilligan

2018

Geophysical Journal International

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Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

Vozár

Jones

Fullea

et al. 2014

Geochem. Geophys. Geosyst.

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We undertake a petrologically driven approach to jointly model magnetotelluric (MT) and seismic surface wave dispersion (SW) data from central Tibet, constrained by topographic height. The approach derives realistic temperature and pressure distributions within the upper mantle and characterizes mineral assemblages of given bulk chemical compositions as well as water content. This allows us to define a bulk geophysical model of the upper mantle based on laboratory and xenolith data for the most relevant mantle mineral assemblages and to derive corresponding predicted geophysical observables. One-dimensional deep resistivity models were derived for two groups of MT stations. One group, located in the Lhasa Terrane, shows the existence of an electrically conductive upper mantle layer and shallower conductive upper mantle layer for the other group, located in the Qiangtang Terrane. The subsequent one-dimensional integrated petrological-geophysical modeling suggests a lithosphere-asthenosphere boundary (LAB) at a depth of 80-120 km with a dry lithosphere for the Qiangtang Terrane. In contrast, for the Lhasa Terrane the LAB is located at about 180 km but the presence of a small amount of water in the lithospheric mantle (<0.02 wt%) is required to fit the longest period MT responses. Our results suggest two different lithospheric configurations beneath the southern and central Tibetan Plateau. The model for the Lhasa Terrane implies underthrusting of a moderately wet Indian plate. The model for the Qiangtang Terrane shows relatively thick and conductive crust and implies thin and dry Tibetan lithosphere.

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Constraints on the evolution of crustal flow beneath Northern Tibet

Pape

Jones

Unsworth

et al. 2015

Geochem Geophys Geosyst

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Crustal flow is an important tectonic process active in continent‐continent collisions and which may be significant in the development of convergent plate boundaries. In this study, the results from multidimensional electrical conductivity modeling have been combined with laboratory studies of the rheology of partially molten rocks to characterize the rheological behavior of the middle‐to‐lower crust of both the Songpan‐Ganzi and Kunlun terranes in the northern Tibetan Plateau. Two different methods are adopted to develop constraints on melt fraction, temperature, and crustal flow velocity in the study area. The estimates of these parameters are then used to evaluate whether crustal flow can occur on the northern margin of the Tibetan plateau. In the Songpan‐Ganzi crust, all conditions are satisfied for topography‐driven channel flow to be dominant, with partial melt not being required for flow at temperature above 1000°C. Further north, the Kunlun fault defines the southern boundary of a transition zone between the Tibetan plateau and the Qaidam basin. Constrained by the estimated melt fractions, it is shown that channel injection across the fault requires temperatures close to 900°C. The composition of igneous rocks found at the surface confirm those conditions are met for the southern Kunlun ranges. To the north, the Qaidam basin is characterized by colder crust that may reflect an earlier stage in the channel injection process. In the study area, at least 10% of the eastward directed Tibetan crustal flow could be deflected northward across the Kunlun Fault and injected into the transition zone defining the northern margin of the Tibetan plateau.

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Partially melted, mica-bearing crust in Central Tibet

Cited by 118 publications

References 100 publications

Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Integrated geophysical-petrological modeling of lithosphere-asthenosphere boundary in central Tibet using electromagnetic and seismic data

Constraints on the evolution of crustal flow beneath Northern Tibet

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