Lithospheric heterogeneity in the Kyrgyz Tien Shan imaged by magnetotelluric studies

Bielinski, Robert A.; Park, Stephen K.; Рыбин, А. В.; Batalev, V. Yu.; Shen, Jun; Sears, Clayton

doi:10.1029/2003gl017455

Cited by 55 publications

(32 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Lateral and vertical variations in electrical conductivity by up to 2 orders of magnitude were nevertheless mapped in the Slave and Kaapvaal cratonic lithosphere (Jones et al, 2001;Evans et al, 2011). Large lateral variations in electrical conductivity have also been observed beneath plate-scale shear zones with ages ranging from Archean to Cenozoic, such as the Great Slave and Snowbird tectonic zones in Canada (Jones et al, 2002;Eaton et al, 2004), the Pernambuco shear zone in northeast Brazil (Santos et al, 2014), the North Pyrenean fault (Pous et al, 2004), and the Tien Shan fault in the Himalaya (Bielinski et al, 2003). Electrical conductivity signatures of shear zones in the lithospheric mantle vary.…”

Section: Accepted Manuscriptmentioning

confidence: 95%

Heterogeneity and anisotropy in the lithospheric mantle

2015

View full text Add to dashboard Cite

International audienceThe lithospheric mantle is intrinsically heterogeneous and anisotropic. These two properties govern the repartition of deformation, controlling intraplate strain localization and development of new plate boundaries. Geophysical and geological observations provide clues on the types, ranges, and characteristic length scales of heterogeneity and anisotropy in the lithospheric mantle. Seismic tomography points to variations in geothermal gradient and hence in rheological behavior at scales of hundreds of km. Seismic anisotropy data substantiate anisotropic physical properties consistent at scales of tens to hundreds of km. Receiver functions imply lateral and vertical heterogeneity at scales < 10 km, which might record gradients in composition or anisotropy. Observations on naturally deformed peridotites establish that compositional heterogeneity and Crystal Preferred Orientations (CPOs) are ubiquitous from the mm to the km scales. These data allow discussing the processes that produce/destroy heterogeneity and anisotropy and constraining the time scales over which they are active. This analysis highlights: (i) the role of deformation and reactive percolation of melts and fluids in producing compositional and structural heterogeneity and the feedbacks between these processes, (ii) the weak mechanical effect of mineralogical variations, and (iii) the low volumes of fine-grained microstructures and difficulty to preserve them. In contrast, olivine CPO and the resulting anisotropy of mechanical and thermal properties are only modified by deformation. Based on this analysis, we propose that strain localization at the plate scale is, at first order, controlled by large-scale variations in thermal structure and in CPO-induced anisotropy. In cold parts of the lithospheric mantle , grain size reduction may contribute to strain localization, but the low volume of fine-grained domains limits this effect

show abstract

Section: Accepted Manuscriptmentioning

confidence: 95%

Heterogeneity and anisotropy in the lithospheric mantle

2015

View full text Add to dashboard Cite

show abstract

“…An important question to be understood is what factors control this spatial distribution of deformation. Bielinski et al (2003) describe a combined broadband and long-period MT profile that crosses from the Tarim Basin to the Kazakh Platform. The crust in the Tien Shan is 70-80 km thick on the northern and southern margins, yet thins to 50 km in the centre.…”

Section: Tien Shanmentioning

confidence: 99%

Magnetotelluric Studies of Active Continent–Continent Collisions

Unsworth

2009

Surv Geophys

103

View full text Add to dashboard Cite

Continent-continent collisions are an important tectonic process and have played a fundamental role in the evolution of the modern continents. A combination of geological and geophysical data has provided new constraints on the structure and temporal evolution of these orogens. Magnetotelluric (MT) studies have been an important part of these studies since they can constrain the fluid content and thermal structure which are key parameters for defining the rheology of the crust and upper mantle. MT studies of the Himalaya have defined the geometry of active faults associated with continued plateau growth. Orogen scale MT studies have shown that both the India-Asia collision (Tibetan Plateau and Himalaya) and the Arabia-Eurasia collision (Eastern Anatolia) have developed a low resistivity mid-crustal layer with upper surface at 10-20 km that is likely due to a combination of partial melt and associated aqueous fluids. The properties of this layer are consistent with a strength contrast that permits crustal flow over geological timescales. The upper mantle from the Moho to at least 100 km beneath both Northern Tibet and the Anatolian Plateau is characterized by low resistivity values (10-30 Xm) indicating the presence of shallow asthenosphere. Future integrated seismic and MT studies of collision zones are needed fully to explore the 3D structures associated with deformation and further constrain geodynamic models.

show abstract

“…The collision caused propagation of crustal shortenings and underthrusting into the interior of the Eurasian continent, resulting in further crustal thickening and intracontinental mountain building in the region with higher temperatures on the Moho discontinuity and weaker lithospheric strength [ Neil and Houseman , 1997]. The lithosphere structure beneath Tien Shan was investigated recently in the MT study along the north‐south profile in the region [ Bielinski et al , 2003]. …”

Section: Geological Setting and Host Lavasmentioning

confidence: 99%

“…The higher conductivity of igneous‐olivine‐bearing samples relative to methamorphic‐olivine‐bearing rocks has been noted by Constable et al [1992]. The results of MT SI along a 76°E profile, 450 km long, across Tien Shan are shown in Figure 10b [ Bielinski et al , 2003]. The isotherms indicated in in Figure 10b have been calculated as follows.…”

Section: Electrical Conductivity Measurementsmentioning

confidence: 99%

State of lithosphere beneath Tien Shan from petrology and electrical conductivity of xenoliths

Bagdassarov¹,

Batalev²,

Egorova³

2011

J. Geophys. Res.

View full text Add to dashboard Cite

[1] The shortening of Tien Shan and the evolution of its lithosphere have been evaluated from P-T geothermobarometry of xenoliths and from comparison of their electrical conductivity with conductivities obtained from the inversion of magnetotelluric (MT) data. Spinel lherzolite and granulite xenoliths found in basaltic outcrop Ortosuu represent upper mantle and crust beneath southern Tien Shan. The spinel lherzolite xenoliths correspond to the lithospheric mantle close to the crust-mantle boundary. The studied mantle xenoliths record two types of the upper mantle processes: a low-degree partial melting (about 7-10%) and a cryptic metasomatism. The granulite xenoliths are fragments of the lower crust captured from differing depths. The temperature and pressure estimates of the garnet granulite xenoliths indicate that they were derived from near the crust-mantle boundary. P-T equilibration conditions of mafic granulites and spinel lherzolites infer that the paleogeotherm corresponded to the heat flux 80-85 mW m −2 about 70-66 Myr ago. The present-day heat flux in the region is about 55-60 mW m −2 . The position of the Moho discontinuity 70-66 Myr ago was at a depth of 30-35 km, and the present depth of the Moho boundary is 55-60 km. The observed seismic P wave velocities above and below the present-day Moho boundary are 7.3 and 7.9 km s −1 , respectively. Elastic P velocities measured on xenoliths samples in laboratory and extrapolated to PT conditions of the Moho discontinuity (1.8 GPa and ∼750°C) are 6.8 km s −1 for the mafic granulite and 8.0 km s −1 for the spinel lherzolite. The electrical conductivity of xenoliths has been measured at 0.8-1.0 GPa and in the range between 500°C and 850°C for mafic granulites and at 1.0-1.5 GPa and from 500°C to 1050°C for spinel lherzolites. The contrast in conductivities between mafic granulite and spinel lherzolite samples under P-T conditions corresponding to the geotherm with the heat flux ∼60 mW m −2 agrees well with the contrast of MT electrical conductivity below and above the present-day Moho boundary at a depth of 55-60 km. Thus, the thickening of the Tien Shan lithosphere is about 25 ± 5 km. Before the shortening of Tien Shan about 20-30 Myr ago the lithosphere was rather hot, with a temperature of 500°C at a 15 km depth and of 850°C at the Moho boundary. In comparison to Tien Shan, the lithosphere beneath the neighboring Tarim Basin was rather cold, 350°C at the depth of 15 km and 500°C at the Moho boundary. These temperature differences were the main factors that caused the mechanical weakening of the Tien Shan crust and upper mantle. The modern strain rates of the Tien Shan shortening are 10 −14 × 3 to 10 −15 s . In the past the lithosphere strength beneath Tien Shan was ∼10 12 N m −1 , which was more than 1000 times weaker in comparison with the lithospheric strength of Tarim Basin at the beginning of the continental compression in the region.Citation: Bagdassarov, N., V. Batalev, and V. Egorova (2011), State of lithosphere beneath Tien Shan from petrology and e...

show abstract

Lithospheric heterogeneity in the Kyrgyz Tien Shan imaged by magnetotelluric studies

Cited by 55 publications

References 15 publications

Heterogeneity and anisotropy in the lithospheric mantle

Heterogeneity and anisotropy in the lithospheric mantle

Magnetotelluric Studies of Active Continent–Continent Collisions

State of lithosphere beneath Tien Shan from petrology and electrical conductivity of xenoliths

Contact Info

Product

Resources

About