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Автор: Grafiati

Опубліковано: 6 вересня 2023

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Tharimena, Saikiran, Catherine A. Rychert, and Nicholas Harmon. "Seismic imaging of a mid-lithospheric discontinuity beneath Ontong Java Plateau." Earth and Planetary Science Letters 450 (September 2016): 62–70. http://dx.doi.org/10.1016/j.epsl.2016.06.026.

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Goev, A. G. "Deep velocity structure of the eastern margin of the Sarmatian protocraton based on the «Aleksandrovka» seismic station data from the receiver function technique." Moscow University Bulletin. Series 4. Geology, no. 6 (February 6, 2023): 88–94. http://dx.doi.org/10.33623/0579-9406-2022-6-88-94.

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A velocity section was obtained to a depth of about 250 km on the eastern margin of the Sarmatia protocraton (East-European Craton) based on P receiver functions (PRF). Seismograms of the new broadband station «Aleksandrovka» were used as initial data. The section reveals the main seismic boundaries, and also shows the presence of mid-lithospheric discontinuity in the upper mantle (MLD).

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Kind, R., X. Yuan, J. Mechie, and F. Sodoudi. "Structure of the upper mantle in the north-western and central United States from USArray S-receiver functions." Solid Earth Discussions 7, no. 1 (March 6, 2015): 1025–57. http://dx.doi.org/10.5194/sed-7-1025-2015.

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Abstract. We used more than 40 000 S-receiver functions recorded by the USArray project to study the structure of the upper mantle between the Moho and the 410 km discontinuity from the Phanerozoic western United States to the cratonic central US. We obtained clear observations of downward velocity reductions in the uppermost mantle which are commonly interpreted as the lithosphere-asthenosphere boundary (LAB) in the western US and as the mid-lithospheric discontinuity (MLD) in the cratonic US. We observe the western LAB reaching partly to the mid-continental rift system underneath the cratonic crust. The MLD is surprisingly plunging steeply towards the west from the Rocky Mountains Front to about 200 km depth near the Sevier Thrust Belt. There is a significant break in the lithosphere at the Sevier Thrust Belt. We also observe a velocity reduction about 30 km above the 410 km discontinuity in the same region where in the western US the LAB is observed, but not in the cratonic US.

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Kind, R., X. Yuan, J. Mechie, and F. Sodoudi. "Structure of the upper mantle in the north-western and central United States from USArray S-receiver functions." Solid Earth 6, no. 3 (July 31, 2015): 957–70. http://dx.doi.org/10.5194/se-6-957-2015.

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Abstract. We used more than 40 000 S-receiver functions recorded by the USArray project to study the structure of the upper mantle between the Moho and the 410 km discontinuity from the Phanerozoic western United States to the cratonic central US. In the western United States we observed the lithosphere–asthenosphere boundary (LAB), and in the cratonic United States we observed both the mid-lithospheric discontinuity (MLD) and the LAB of the craton. In the northern and southern United States the western LAB almost reaches the mid-continental rift system. In between these two regions the cratonic MLD is surprisingly plunging towards the west from the Rocky Mountain Front to about 200 km depth near the Sevier thrust belt. We interpret these complex structures of the seismic discontinuities in the mantle lithosphere as an indication of interfingering of the colliding Farallon and Laurentia plates. Unfiltered S-receiver function data reveal that the LAB and MLD are not single discontinuities but consist of many small-scale laminated discontinuities, which only appear as single discontinuities after longer period filtering. We also observe the Lehmann discontinuity below the LAB and a velocity reduction about 30 km above the 410 km discontinuity.

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Zhang, Yaoyang, Ling Chen, Yinshuang Ai, and Mingming Jiang. "Lithospheric structure beneath the central and western North China Craton and adjacent regions from S-receiver function imaging." Geophysical Journal International 219, no. 1 (July 25, 2019): 619–32. http://dx.doi.org/10.1093/gji/ggz322.

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Summary To elucidate the nature and extent of the lithospheric modification in the central and western North China Craton (NCC) and adjacent regions, we used the wave equation–based migration technique of S-receiver function on teleseismic data collected from 314 broadband stations in this region to image the lithospheric structure. Incorporating data from previous lithospheric structure studies, we obtained unprecedented high-resolution depth maps of the lithosphere–asthenosphere boundary (LAB) and mid-lithospheric discontinuity (MLD) in the NCC. Our results show more detailed variations of the lithospheric thickness in the central and western NCC and adjacent regions, which ranges from 100 to >170 km, in marked contrast to the thinned lithosphere (60–100 km) in the eastern NCC. Despite its generally thick lithosphere (>130 km), the Ordos Block shows a concordant N–S difference from the surface to deep lithosphere with a boundary at the latitude of 37–38°N. The central NCC is laterally heterogeneous in the lithospheric structure, and the thick lithosphere (∼160 km) in the south is interpreted as a remnant cratonic mantle root. The central Qinling Orogenic Belt preserves a thick lithosphere (∼150 km), which may block the asthenospheric flow driven by extrusion of the Tibetan Plateau to the west of the NCC. Moreover, a negative MLD is widely identified at the depth of 80–110 km within the thick lithosphere, which corroborates the global existence of the MLD in continental regions. The consistence in the depth of the MLD and the shallow LAB in the eastern NCC supports the conjecture that the MLD may have played an important role in the lithospheric modification of the eastern NCC.

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Smart, Katie A., Sebastian Tappe, Alan B. Woodland, Chris Harris, Loretta Corcoran, and Antonio Simonetti. "Metasomatized eclogite xenoliths from the central Kaapvaal craton as probes of a seismic mid-lithospheric discontinuity." Chemical Geology 578 (September 2021): 120286. http://dx.doi.org/10.1016/j.chemgeo.2021.120286.

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Shi, Ya-Nan, Fenglin Niu, Zhong-Hai Li, and Pengpeng Huangfu. "Craton destruction links to the interaction between subduction and mid-lithospheric discontinuity: Implications for the eastern North China Craton." Gondwana Research 83 (July 2020): 49–62. http://dx.doi.org/10.1016/j.gr.2020.01.016.

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Liu, Lin, Simon L. Klemperer, and Alexander R. Blanchette. "Western Gondwana imaged by S receiver-functions (SRF): New results on Moho, MLD (mid-lithospheric discontinuity) and LAB (lithosphere-asthenosphere boundary)." Gondwana Research 96 (August 2021): 206–18. http://dx.doi.org/10.1016/j.gr.2021.04.009.

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Saha, Sriparna, Rajdeep Dasgupta, and Kyusei Tsuno. "High Pressure Phase Relations of a Depleted Peridotite Fluxed by CO2 -H2 O-Bearing Siliceous Melts and the Origin of Mid-Lithospheric Discontinuity." Geochemistry, Geophysics, Geosystems 19, no. 3 (March 2018): 595–620. http://dx.doi.org/10.1002/2017gc007233.

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Peng, Ye, and Mainak Mookherjee. "Thermoelasticity of tremolite amphibole: Geophysical implications." American Mineralogist 105, no. 6 (June 1, 2020): 904–16. http://dx.doi.org/10.2138/am-2020-7189.

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Abstract We investigated the structure, equation of state, thermodynamics, and elastic properties of tremolite amphibole [Ca2Mg5Si8O22(OH)2] up to 10 GPa and 2000 K, using first principles simulations based on density functional perturbation theory. We found that at 300 K, the pressure-volume results can be adequately described by a third-order Birch-Murnaghan equation of state with bulk moduli K0 of 78.5 and 66.3 GPa based on local density approximation (LDA) and generalized gradient approximation (GGA), respectively. We also derived its coefficients of the elastic tensor based on LDA and GGA and found that the LDA result is in good agreement with the experimental results. At 300 K, the shear modulus G0 is 58.0 GPa based on LDA. The pressure derivative of the bulk modulus K′ is 5.9, while that of the shear modulus G′ is 1.3. The second Grüneisen parameter, or δT = [–1/(αKT)](∂KT/∂T)P, is 3.3 based on LDA. We found that at ambient conditions, tremolite is elastically anisotropic with the compressional wave velocity anisotropy AVP being 34.6% and the shear wave velocity anisotropy AVS being 27.5%. At higher pressure corresponding to the thermodynamic stability of tremolite, i.e., ~3 GPa, the AVP reduces to 29.5%, whereas AVS increases to 30.8%. To evaluate whether the presence of hydrous phases such as amphibole and phlogopite could account for the observed shear wave velocity (VS) anomaly at the mid-lithospheric discontinuity (MLD), we used the thermoelasticities of tremolite (as a proxy for other amphiboles), phlogopite, and major mantle minerals to construct synthetic velocity profiles. We noted that at depths corresponding to the mid-lithosphere, the presence of 25 vol% amphibole and 1 vol% phlogopite could account for a VS reduction of 2.3%. Thus based on our thermoelasticity results on tremolite amphibole, it seems that mantle metasomatism could partly explain the MLD.

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Kumar, P., X. Yuan, R. Kind, and J. Mechie. "The lithosphere-asthenosphere boundary observed with USArray receiver functions." Solid Earth Discussions 4, no. 1 (January 6, 2012): 1–31. http://dx.doi.org/10.5194/sed-4-1-2012.

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Abstract. The dense deployment of seismic stations so far in the western half of the United States within the USArray project provides the opportunity to study in greater detail the structure of the lithosphere-asthenosphere system. We use the S receiver function technique for this purpose which has higher resolution than surface wave tomography, is sensitive to seismic discontinuities and has no problems with multiples like P receiver functions. Only two major discontinuities are observed in the entire area down to about 300 km depth. These are the crust-mantle boundary (Moho) and a negative boundary which we correlate with the lithosphere-asthenosphere boundary (LAB) since a low velocity zone is the classical definition of the seismic observation of the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a depth of 70–80 km in large parts of westernmost North America. East of the Rocky Mountains its depth is generally between 90 and 110 km. Regions with LAB depths down to about 140 km occur in a stretch from northern Texas over the Colorado Plateau to the Columbia Basalts. These observations agree well with tomography results in the westernmost USA and at the east coast. However, in the central cratonic part of the USA the tomography LAB is near 200 km depth. At this depth no discontinuity is seen in the S receiver functions. The negative signal near 100 km depth in the central part of the USA is interpreted by Yuan and Romanowicz (2010) or Lekic and Romanowicz (2011) as a recently discovered mid lithospheric discontinuity (MLD). A solution for the discrepancy between receiver function imaging and surface wave tomography is not yet obvious and requires more high resolution studies at other cratons before a general solution may be found. Our results agree well with petrophysical models of increased water content in the asthenosphere, which predict a sharp and shallow LAB also in continents (Mierdel et al., 2007).

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Kumar, P., X. Yuan, R. Kind, and J. Mechie. "The lithosphere-asthenosphere boundary observed with USArray receiver functions." Solid Earth 3, no. 1 (May 24, 2012): 149–59. http://dx.doi.org/10.5194/se-3-149-2012.

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Abstract. The dense deployment of seismic stations so far in the western half of the United States within the USArray project provides the opportunity to study in greater detail the structure of the lithosphere-asthenosphere system. We use the S receiver function technique for this purpose, which has higher resolution than surface wave tomography, is sensitive to seismic discontinuities, and is free from multiples, unlike P receiver functions. Only two major discontinuities are observed in the entire area down to about 300 km depth. These are the crust-mantle boundary (Moho) and a negative boundary, which we correlate with the lithosphere-asthenosphere boundary (LAB), since a low velocity zone is the classical definition of the seismic observation of the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a depth of 70–80 km in large parts of westernmost North America. East of the Rocky Mountains, its depth is generally between 90 and 110 km. Regions with LAB depths down to about 140 km occur in a stretch from northern Texas, over the Colorado Plateau to the Columbia basalts. These observations agree well with tomography results in the westernmost USA and on the east coast. However, in the central cratonic part of the USA, the tomography LAB is near 200 km depth. At this depth no discontinuity is seen in the S receiver functions. The negative signal near 100 km depth in the central part of the USA is interpreted by Yuan and Romanowicz (2010) and Lekic and Romanowicz (2011) as a recently discovered mid-lithospheric discontinuity (MLD). A solution for the discrepancy between receiver function imaging and surface wave tomography is not yet obvious and requires more high resolution studies at other cratons before a general solution may be found. Our results agree well with petrophysical models of increased water content in the asthenosphere, which predict a sharp and shallow LAB also in continents (Mierdel et al., 2007).

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Yang, Haibin, Irina M. Artemieva, and Hans Thybo. "The Mid‐Lithospheric Discontinuity caused by channel flow in proto‐cratonic mantle." Journal of Geophysical Research: Solid Earth, March 21, 2023. http://dx.doi.org/10.1029/2022jb026202.

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Shi, Ya‐Nan, Zhong‐Hai Li, Ling Chen, and Jason P. Morgan. "Connection between a subcontinental plume and the mid‐lithospheric discontinuity leads to fast and intense craton lithospheric thinning." Tectonics, September 6, 2021. http://dx.doi.org/10.1029/2021tc006711.

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Goldhagen, Gillian B., Heather A. Ford, and Maureen D. Long. "Evidence for a lithospheric step and pervasive lithospheric thinning beneath southern New England, northeastern USA." Geology, June 21, 2022. http://dx.doi.org/10.1130/g50133.1.

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In this study, we use data from the SEISConn seismic experiment to calculate Sp receiver functions in order to characterize the geometry of upper-mantle structure beneath southern New England (northeastern United States). We image robust negative-velocity-gradient discontinuities beneath southern New England that we interpret as corresponding to the lithosphere-asthenosphere boundary (LAB) and identify a well-defined step of 15 km in LAB depth at a longitude of 73°W, which we interpret to be the boundary between Laurentian and Appalachian lithosphere, although the offset may be larger if the putative LAB phase is reinterpreted to be a mid-lithospheric discontinuity. We infer that the lithosphere throughout the region is substantially thinner than elsewhere in the continental interior, consistent with regional tomographic studies and previously published Sp receiver function results. The presence of thinned lithosphere suggests that the low-velocity Northern Appalachian Anomaly (NAA) in the upper mantle may extend as far south as coastal Connecticut. The presence of regionally thinned lithosphere and a step in lithospheric thickness suggests that inherited structure may be preserved in present-day lithosphere, even in the presence of more recent dynamic processes associated with the NAA.

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Saxena, Arushi, and Charles Adam Langston. "Detecting lithospheric discontinuities beneath the Mississippi Embayment using S wave receiver functions." Geophysical Journal International, September 9, 2021. http://dx.doi.org/10.1093/gji/ggab367.

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Abstract Identifying upper-mantle discontinuities in the Central and Eastern US is crucial for verifying models of lithospheric thinning and a low-velocity anomaly structure beneath the Mississippi Embayment. In this study, S-wave receiver functions (SRFs) were used to detect lithospheric boundaries in the embayment region. The viability of SRFs in detecting seismic boundaries was tested before computing them using the earthquake data. A careful analysis using a stochastic noise and coda model on the synthetics revealed that a negative velocity contrast could be detected with certainty at low to moderate noise levels after stacking. A total of 31518 SRFs from 688 earthquakes recorded at 174 seismic stations including the Northern Embayment Lithospheric Experiment, EarthScope Transportable Array and other permanent networks were used in this study. Common depth point stacks of the SRFs in 1○ × 1○ bins indicated a continuous and broad S-to-p converted phase (Sp) arrival corresponding to a negative velocity contrast at depths between 50 and 100 km. The observed negative Sp phase is interpreted as a mid-lithospheric discontinuity (MLD), and several possible origins of the velocity drop corresponding to the MLD are explored. After quantitative analysis, a combination of temperature, water content, and melt content variations are attributed to explain the observed MLD in this study. The observations and interpretations in this study support the previous claims of a MLD in the Central and Eastern US and provide a possible mechanism for its origin.

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Qi, Rui, Jie Liao, Xiaohui Liu, and Rui Gao. "Numerical Investigation on the Dynamic Evolution of Intra-Crustal Continental Delamination." Frontiers in Earth Science 10 (March 9, 2022). http://dx.doi.org/10.3389/feart.2022.829300.

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Delamination often occurs in continental regions, through which process the lithospheric mantle detaches from the continental crust and sinks into the underlying asthenospheric mantle. Various modes of continental delamination are proposed, including the typical mode of delamination along the Moho and the newly proposed delamination along the mid-lithospheric discontinuity. Geological and geophysical observations reveal the possibility of an alternative mode of delamination, i.e., intra-crustal continental delamination, which is rarely studied. Using the 2D thermo-mechanical coupled geodynamical models, we systemically study the dynamic evolution of the intra-crustal continental delamination. Model results suggest that the intra-crustal continental delamination develops along the base of the upper crust, promoted by the intra-crustal decoupling, i.e., the mechanical strength decoupling between the upper and lower crust. The three physical parameters, i.e., the upper crustal thickness, the lower crustal rheology, and the initial Moho temperature all affect intra-crustal strength decoupling, and thus influence continental delamination. Combining with geological and geophysical observations, we speculate that intra-crustal continental delamination taking place along the upper and lower crustal interface is a possible way of continental destruction.

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"Models of mantle convection: one or several layers." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 328, no. 1599 (July 4, 1989): 417–24. http://dx.doi.org/10.1098/rsta.1989.0045.

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Numerical model calculations are used to determine if convection in the Earth’s mantle could be organized in two or more layers with only limited mass exchange in between. The seismic discontinuity at 670 km depth and the top of the D"-layer at the bottom of the mantle are considered as candidates for internal boundaries. If the 670 km discontinuity is caused by an isochemical phase transition, it has to have a Clapeyron slope of dp/dT ⩽ — 6 MPa k -1 to prevent convection currents from crossing; this value is improbably low. If the discontinuity represents a chemical boundary, the intrinsic density difference has to exceed 3 % to prevent subducted lithospheric slabs from penetrating deeply into the lower mantle; also the condition is possibly hard to meet. The least improbable mechanism for a mid-mantle barrier for convection currents would be a combination of endothermic phase transition and chemical change. The boundary between upper and lower mantle would show considerable topography, and a limited material exchange is to be expected at any rate. The possibility of a downward segregation of former oceanic crust, transformed to dense eclogite, is studied in a further model series. It requires a region of low viscosity, as the Delayer probably is, and is faciliated by the decrease of the thermal expansion coefficient with pressure. About 20% of subducted oceanic crust could accumulate at the core-mantle boundary. The dense material would concentrate underneath rising therm al plumes, and some of it is entrained into the plumes, possibly affecting their geochemical signature.

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Kind, Rainer, Walter D. Mooney, and Xiaohui Yuan. "New insights into the structural elements of the upper mantle beneath the contiguous United States from S-to-P converted seismic waves." Geophysical Journal International, April 25, 2020. http://dx.doi.org/10.1093/gji/ggaa203.

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Summary The S-receiver function (SRF) technique is an effective tool to study seismic discontinuities in the upper mantle such as the mid-lithospheric discontinuity (MLD) and the lithosphere-asthenosphere boundary (LAB). This technique uses deconvolution and aligns traces along the maximum of the deconvolved SV signal. Both of these steps lead to acausal signals, which may cause interference with real signals from below the Moho. Here we go back to the origin of the S-receiver function method and process S-to-P converted waves using S-onset times as the reference time and waveform summation without any filter like deconvolution or bandpass. We apply this ‘causal’ SRF (C-SRF) method to data of the USArray and obtain partially different results in comparison with previous studies using the traditional acausal SRF method. The new method does not confirm the existence of an MLD beneath large regions of the cratonic US. The shallow LAB in the western US is, however, confirmed with the new method. The elimination of the MLD signal below much of the cratonic US reveals lower amplitude but highly significant phases that previously had been overwhelmed by the apparent MLD signals. Along the northern part of the area with data coverage we see relics of Archean or younger north-west directed low-angle subduction below the entire Superior Craton. In the cratonic part of the US we see indications of the cratonic LAB near 200 km depth. In the Gulf Coast of the southern US we image relics of southeast directed shallow subduction, likely of mid-Paleozoic age.

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Shaikh, Azhar M., Sebastian Tappe, Yannick Bussweiler, Suresh C. Patel, Subramanian Ravi, Robert Bolhar, and Fanus Viljoen. "Clinopyroxene and Garnet Mantle Cargo in Kimberlites as Probes of Dharwar Craton Architecture and Geotherms, with Implications for Post-1·1 Ga Lithosphere Thinning Events Beneath Southern India." Journal of Petrology, August 26, 2020. http://dx.doi.org/10.1093/petrology/egaa087.

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Abstract The Wajrakarur Kimberlite Field (WKF) on the Eastern Dharwar Craton in southern India hosts several occurrences of Mesoproterozoic kimberlites, lamproites and ultramafic lamprophyres, for which mantle-derived xenoliths are rare and only poorly preserved. The general paucity of mantle cargo has hampered the investigation of the nature and evolution of the continental lithospheric mantle (CLM) beneath cratonic southern India. We present a comprehensive study of the major and trace element compositions of clinopyroxene and garnet xenocrysts recovered from heavy mineral concentrates for three c.1·1 Ga old WKF kimberlite pipes (P7, P9, P10), with the goal to improve our understanding of the cratonic mantle architecture and its evolution beneath southern India. The pressure-temperature conditions recorded by peridotitic clinopyroxene xenocrysts, estimated using single-pyroxene thermobarometry, suggest a relatively moderate cratonic mantle geotherm of 40 mW/m2 at 1·1 Ga. Reconstruction of the vertical distribution of clinopyroxene and garnet xenocrysts, combined with some rare mantle xenoliths data, reveals a compositionally layered CLM structure. Two main lithological horizons are identified and denoted as layer A (∼80–145 km depth) and layer B (∼160–190 km depth). Layer A is dominated by depleted lherzolite with subordinate amounts of pyroxenite, whereas layer B comprises mainly refertilised and Ti-metasomatized peridotite. Harzburgite occurs as a minor lithology in both layers. Eclogite stringers occur within the lower portion of layer A and at the bottom of layer B near the lithosphere–asthenosphere boundary at 1·1 Ga. Refertilisation of layer B is marked by garnet compositions with enrichment in Ca, Ti, Fe, Zr and LREE, although Y is depleted compared to garnet in layer A. Garnet trace element systematics such as Zr/Hf and Ti/Eu indicate that both kimberlitic and carbonatitic melts have interacted with and compositionally overprinted layer B. Progressive changes in the REE systematics of garnet grains with depth record an upward percolation of a continuously evolving metasomatic agent. The intervening zone between layers A and B at ∼145–160 km depth is characterized by a general paucity of garnet. This ‘garnet-paucity’ zone and an overlying type II clinopyroxene-bearing zone (∼115–145 km) appear to be rich in hydrous mineral assemblages of the MARID- or PIC kind. The composite horizon between ∼115–160 km depth may represent the product of intensive melt/rock interaction by which former garnet was largely reacted out and new metasomatic phases such as type II clinopyroxene and phlogopite plus amphibole were introduced. By analogy with better-studied cratons, this ‘metasomatic horizon’ may be a petrological manifestation of a former mid-lithospheric discontinuity at 1·1 Ga. Importantly, the depth interval of the present-day lithosphere–asthenosphere boundary beneath Peninsular India as detected in seismic surveys coincides with this heavily overprinted metasomatic horizon, which suggests that post-1·1 Ga delamination of cratonic mantle lithosphere progressed all the way to mid-lithospheric depth. This finding implies that strongly overprinted metasomatic layers, such as the ‘garnet-paucity’ zone beneath the Dharwar craton, present structural zones of weakness that aid lithosphere detachment and foundering in response to plate tectonic stresses.

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