TY - JOUR AU - Malvoisin, Benjamin AU - Austrheim, Hakon AU - Hetényi, György AU - Reynes, Julien AU - Hermann, Jorg AU - Baumgartner, Lukas P. AU - Podladchikov, Yury Y. TI - Sustainable densification of the deep crust JF - GEOLOGY J2 - GEOLOGY VL - 48 PY - 2020 IS - 7 SP - 673 EP - 677 PG - 5 SN - 0091-7613 DO - 10.1130/G47201.1 UR - https://m2.mtmt.hu/api/publication/31433992 ID - 31433992 AB - The densification of the lower crust in collision and subduction zones plays a key role in shaping the Earth by modifying the buoyancy forces acting at convergent boundaries. It takes place through mineralogical reactions, which are kinetically favored by the presence of fluids. Earthquakes may generate faults serving as fluid pathways, but the influence of reactions on the generation of seismicity at depth is still poorly constrained. Here we present new petrological data and numerical models to show that in the presence of fluids, densification reactions can occur very fast, on the order of weeks, and consume fluids injected during an earthquake, which leads to porosity formation and fluid pressure drop by several hundreds of megapascals. This generates a mechanically highly unstable system subject to collapse and further seismic-wave emission during aftershocks. This mechanism creates new pathways for subsequently arriving fluids, and thus provides a route for self-sustained densification of the lower crust. LA - English DB - MTMT ER - TY - JOUR AU - Alvizuri, Celso AU - Hetényi, György TI - Source mechanism of a lower crust earthquake beneath the Himalayas and its possible relation to metamorphism JF - TECTONOPHYSICS J2 - TECTONOPHYSICS VL - 769 PY - 2019 PG - 7 SN - 0040-1951 DO - 10.1016/j.tecto.2019.06.023 UR - https://m2.mtmt.hu/api/publication/31098644 ID - 31098644 AB - The nature of deep-crustal, intermediate and deep-focus earthquakes and their relation to metamorphic reactions is a topic of debate. Here we seek to better understand a possible link between the earthquake process and metamorphism by analyzing the mechanism of ongoing deep-crustal earthquakes. We focus on a region in the Himalayas with observed seismicity at depths expected to experience active eclogite-facies metamorphism and dehydration reactions. There are few permanent seismic stations in the region, therefore we use waveform data from a temporary seismic array deployment. We find two earthquakes with magnitude and station coverage adequate for moment tensor inversion. For a given earthquake we estimate its seismic full moment tensors (and magnitude) together with uncertainties using all available waveforms. For the largest earthquake (Mw 3.7) we obtain a best-fitting moment tensor and uncertainties that show a double-couple with a tensional crack component. In the context of geological records that document similar processes, and of laboratory experiments conducted at spatial scales that are 5-6 orders of magnitude smaller, this mechanism may be related to dehydration-driven stress changes triggering slight crack opening, and ambient stresses favoring slip along a fault. LA - English DB - MTMT ER - TY - JOUR AU - Schmalholz, Stefan M. AU - Duretz, Thibault AU - Hetényi, György AU - Medvedev, Sergei TI - Distribution and magnitude of stress due to lateral variation of gravitational potential energy between Indian lowland and Tibetan plateau JF - GEOPHYSICAL JOURNAL INTERNATIONAL J2 - GEOPHYS J INT VL - 216 PY - 2019 IS - 2 SP - 1313 EP - 1333 PG - 21 SN - 0956-540X DO - 10.1093/gji/ggy463 UR - https://m2.mtmt.hu/api/publication/31098635 ID - 31098635 AB - Magnitudes of differential stress in the lithosphere, especially in the crust, are still disputed. Earthquake-based stress drop estimates indicate median values <10MPa whereas the lateral variation of gravitational potential energy per unit area (GPE) across significant relief indicates stress magnitudes of ca. 100MPa in average across a 100km thick lithosphere between the Indian lowland and the Tibetan plateau. These standard GPE-based stress estimates correspond to membrane stresses because they are associated with a deformation that is uniform with depth. We show here with new analytical results that lateral variations in GPE can also cause bending moments and related bending stresses of several hundreds of MPa. Furthermore, we perform 2-D thermomechanical numerical simulations (1) to evaluate estimates for membrane and bending stresses based on GPE variations, (2) to quantify minimum crustal stress magnitudes that are required to maintain the topographic relief between Indian lowland and Tibetan plateau for ca. 10 Ma and (3) to quantify the corresponding relative contribution of crustal strength to the total lithospheric strength. The numerical model includes viscoelastoplastic deformation, gravity and heat transfer. The model configuration is based on density fields from the CRUST1.0 data set and from a geophysically and petrologically constrained density model based on in situ field campaigns. The numerical results indicate that values of differential stress in the upper crust must be >ca. 180MPa, corresponding to a friction angle of ca. 10 degrees to maintain the topographic relief between lowland and plateau for >10 Ma. The relative contribution of crustal strength to total lithospheric strength varies considerably laterally. In the region between lowland and plateau and inside the plateau the depth-integrated crustal strength is approximately equal to the depth-integrated strength of the mantle lithosphere. Simple analytical formulae predicting the lateral variation of depth-integrated stresses agree with numerically calculated stress fields, which show both the accuracy of the numerical results and the applicability of simple, rheology-independent, analytical predictions to highly variable, rheology-dependent stress fields. Our results indicate that (1) crustal strength can be locally equal to mantle lithosphere strength and that (2) crustal stresses must be at least one order of magnitude larger than median stress drops in order to support the plateau relief over a duration of ca. 10 Ma. LA - English DB - MTMT ER - TY - JOUR AU - Subedi, Shiba AU - Hetényi, György AU - Vergne, Jerome AU - Bollinger, Laurent AU - Lyon-Caen, Helene AU - Farra, Veronique AU - Adhikari, Lok Bijaya AU - Gupta, Ratna Mani TI - Imaging the Moho and the Main Himalayan Thrust in Western Nepal With Receiver Functions JF - GEOPHYSICAL RESEARCH LETTERS J2 - GEOPHYS RES LETT VL - 45 PY - 2018 IS - 24 SP - 13222 EP - 13230 PG - 9 SN - 0094-8276 DO - 10.1029/2018GL080911 UR - https://m2.mtmt.hu/api/publication/30482510 ID - 30482510 AB - The crustal structure of Western Nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations. The Moho geometry is imaged as it deepens from similar to 40-km depth beneath the foothills and the Lesser Himalaya to similar to 58-km depth beneath the Higher Himalayan range. A midcrustal low-velocity zone is detected at similar to 15-km depth along similar to 55-km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the Main Himalayan Thrust. Our new image allows structural comparison of the Moho and of the Main Himalayan Thrust geometry along-strike of the Himalayas and documents long-wavelength lateral variations. The general crustal architecture observed on our images resembles that of Central Nepal; therefore, Western Nepal is also expected to be able to host large (M-W>8) megathrust earthquakes, as the 1505 CE event. LA - English DB - MTMT ER - TY - JOUR AU - Diehl, T AU - Singer, J AU - Hetényi, György AU - Grujic, D AU - Clinton, J AU - Giardini, D AU - Kissling, E TI - Seismotectonics of Bhutan: Evidence for segmentation of the Eastern Himalayas and link to foreland deformation JF - EARTH AND PLANETARY SCIENCE LETTERS J2 - EARTH PLANET SC LETT VL - 471 PY - 2017 SP - 54 EP - 64 PG - 11 SN - 0012-821X DO - 10.1016/j.epsl.2017.04.038 UR - https://m2.mtmt.hu/api/publication/3273926 ID - 3273926 N1 - N1 Funding details: ETH, Eidgenössische Technische Hochschule Zürich N1 Funding details: 200021_143467, SNF, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung N1 Funding text: Comments by Roger Bilham and one anonymous reviewer helped to improve the manuscript and are thankfully acknowledged. We thank S. Schmid, J.-P. Burg, C. Cauzzi, and T. Tormann for helpful discussions. This work and the deployment of the temporary seismic GANSSER network in Bhutan were funded by the Swiss National Science Foundation (SNF), Grant 200021_143467 (G. Hetényi). The GANSSER acronym was chosen to commemorate the famous geologist Augusto Gansser (1910–2012). D. Grujic thanks the ETH Zurich Visiting Professorship Fund for financial support during the preparation of the manuscript at the Institute of Geophysics (ETH Zurich). The instrument pool of the SED and Seismology and Geodynamics (SEG) group at ETH Zurich provided the station hardware. We thank D. Drukpa and his colleagues at the Department of Geology and Mines of the Kingdom of Bhutan for support during the fieldwork. We thankfully acknowledge also the GANSSER fieldwork team. We thank S. Mitra from the Indian Institute of Science Education and Research Kolkata (IISER Kolkata) for providing phase data for selected events of stations in Sikkim and West Bengal. Moment tensor inversions were derived by the SCMTV-software provided by GFZ Potsdam/GEMPA GmbH. Megjegyzés-26723440 Group Author: GANSSER Working Grp Megjegyzés-26766825 Group Author: GANSSER Working Grp Megjegyzés-26766826 Group Author: GANSSER Working Grp Megjegyzés-26767115 Group Author: GANSSER Working Grp Megjegyzés-26876796 Group Author: GANSSER Working Grp Swiss Seismological Service, ETH-Zürich, Zurich, 8092, Switzerland Institute of Geophysics, ETH-Zürich, Zurich, 8092, Switzerland Institute of Earth Sciences, University of Lausanne1015, Switzerland Department of Earth Sciences, Dalhousie University, Halifax, NS B3H 4R2, Canada Cited By :22 Export Date: 13 January 2021 Correspondence Address: Diehl, T.; Swiss Seismological Service, ETH-ZürichSwitzerland; email: tobias.diehl@sed.ethz.ch Funding details: Eidgenössische Technische Hochschule Zürich, ETH Funding details: Indian Institute of Science Education and Research Kolkata, IISER-K Funding details: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, SNF Funding details: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, SNF, 200021_143467 Funding details: Indian Institute of Science Education and Research Kolkata, IISER-K Funding text 1: Comments by Roger Bilham and one anonymous reviewer helped to improve the manuscript and are thankfully acknowledged. We thank S. Schmid, J.-P. Burg, C. Cauzzi, and T. Tormann for helpful discussions. This work and the deployment of the temporary seismic GANSSER network in Bhutan were funded by the Swiss National Science Foundation (SNF), Grant 200021_143467 (G. Het?nyi). The GANSSER acronym was chosen to commemorate the famous geologist Augusto Gansser (1910?2012). D. Grujic thanks the ETH Zurich Visiting Professorship Fund for financial support during the preparation of the manuscript at the Institute of Geophysics (ETH Zurich). The instrument pool of the SED and Seismology and Geodynamics (SEG) group at ETH Zurich provided the station hardware. We thank D. Drukpa and his colleagues at the Department of Geology and Mines of the Kingdom of Bhutan for support during the fieldwork. We thankfully acknowledge also the GANSSER fieldwork team. We thank S. Mitra from the Indian Institute of Science Education and Research Kolkata (IISER Kolkata) for providing phase data for selected events of stations in Sikkim and West Bengal. Moment tensor inversions were derived by the SCMTV-software provided by GFZ Potsdam/GEMPA GmbH. AB - The instrumental record of Bhutan is characterized by a lower seismicity compared to other parts of the Himalayan arc. To understand this low activity and its impact on the seismic hazard, a seismic network was installed in Bhutan for 22 months between 2013 and 2014. Recorded seismicity, earthquake moment tensors and local earthquake tomography reveal along-strike variations in structure and crustal deformation regime. A thickened crust imaged in western Bhutan suggests lateral differences in stresses on the Main Himalayan Thrust (MHT), potentially affecting the interseismic coupling and deformation regime. Sikkim, western Bhutan and its foreland are characterized by strike-slip faulting in the Indian basement. Strain is particularly localized along a NW–SE striking mid-crustal fault zone reaching from Chungthang in northeast Sikkim to Dhubri at the northwestern edge of the Shillong Plateau in the foreland. The dextral Dhubri–Chungthang fault zone (DCF) causes segmentation of the Indian basement and the MHT between eastern Nepal and western Bhutan and connects the deformation front of the Himalaya with the Shillong Plateau by forming the western boundary of the Shillong block. The Kopili fault, the proposed eastern boundary of this block, appears to be a diffuse zone of mid-crustal seismicity in the foreland. In eastern Bhutan we image a seismogenic, flat portion of the MHT, which might be either related to a partially creeping segment or to increased background seismicity originating from the 2009 MW6.1 earthquake. In western-central Bhutan clusters of micro-earthquakes at the front of the High-Himalayas indicate the presence of a mid-crustal ramp and stress buildup on a fully coupled MHT. The area bounded by the DCF in the west and the seismogenic MHT in the east has the potential for M7–8 earthquakes in Bhutan. Similarly, the DCF has the potential to host M7 earthquakes as documented by the 2011 Sikkim and the 1930 Dhubri earthquakes, which were potentially associated with this structure. © 2017 Elsevier B.V. LA - English DB - MTMT ER - TY - JOUR AU - Hetényi, György AU - Cattin, R AU - Berthet, T AU - Le Moigne, N AU - Chophel, J AU - Lechmann, S AU - Hammer, P AU - Drukpa, D AU - Sapkota, SN AU - Gautier, S AU - Thinley, K TI - Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies JF - SCIENTIFIC REPORTS J2 - SCI REP VL - 6 PY - 2016 SN - 2045-2322 DO - 10.1038/srep33866 UR - https://m2.mtmt.hu/api/publication/3163088 ID - 3163088 AB - Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen's segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal &India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes. © The Author(s) 2016. LA - English DB - MTMT ER - TY - JOUR AU - Hetényi, György TI - To conserve or not to conserve (mass in numerical models) JF - TERRA NOVA J2 - TERRA NOVA VL - 26 PY - 2014 IS - 5 SP - 372 EP - 376 PG - 5 SN - 0954-4879 DO - 10.1111/ter.12109 UR - https://m2.mtmt.hu/api/publication/3163091 ID - 3163091 AB - Mass conservation is a fundamental physical law. Yet, computer models aiming to simulate Earth evolution commonly fail to respect it. Indeed, most geodynamic models implement phase transitions of rocks - such as metamorphism (solid-solid phase change) or melting (solid-liquid phase change) - following a simplifying assumption dating back to 1897 which is conserving volume rather than mass. The underlying problem is present at different scales, illustrated here by three examples: metamorphism in the continental crust, phase changes in the mantle transition zone and melt crystallization during columnar jointing. These illustrate that phase changes may become a driving force of a system's deformation and point to important differences with respect to simplified models. Developing and applying mass-conserving approaches in future modelling tools are therefore not an option, but a necessity. © 2014 John Wiley & Sons Ltd. LA - English DB - MTMT ER - TY - JOUR AU - Berthet, T AU - Hetényi, György AU - Cattin, R AU - Sapkota, SN AU - Champollion, C AU - Kandel, T AU - Doerflinger, E AU - Drukpa, D AU - Lechmann, S AU - Bonnin, M TI - Lateral uniformity of India Plate strength over central and eastern Nepal JF - GEOPHYSICAL JOURNAL INTERNATIONAL J2 - GEOPHYS J INT VL - 195 PY - 2013 IS - 3 SP - 1481 EP - 1493 PG - 13 SN - 0956-540X DO - 10.1093/gji/ggt357 UR - https://m2.mtmt.hu/api/publication/3163095 ID - 3163095 AB - The current understanding of the Himalayan lithosphere stems mostly from cross-sections through the range at the longitude of the Kathmandu Basin. In this paper we laterally extend the analyses of structures and rheology along the Nepal Himalayas between the Pokhara valley and the Arun river.We take advantage of available information and a new data set including gravity measurements and a receiver function profile. It appears that the geometry of theMoho inferred from seismological profiles and long-wavelength gravity anomalies does not exhibit major East-West variations within the 350-km-wide study area. Using thermomechanical modelling, we show that the northward deepening of the Moho observed along profiles perpendicular to the main thrust faults can be interpreted simply as the bending of a strong India Plate. This result suggests a gradual mechanical decoupling between the crust and the mantle, leading to a northward decrease of the effective elastic thickness of the Indian lithosphere from ~75 km to ~25 km beneath the Ganga Basin and the Tibetan Plateau, respectively. Our results also confirm(partially) eclogitized lower Indian crust beneath southern Tibet. At shorter wavelengths, the observed gravity profiles exhibit some small lateral variations that can be interpreted in terms of east-west variations of the thickness of subsurface geological structures such as the Ganga Basin and the Tethyan Sedimentary Sequence. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. LA - English DB - MTMT ER - TY - JOUR AU - Hammer, P AU - Berthet, T AU - Hetényi, György AU - Cattin, R AU - Drukpa, D AU - Chophel, J AU - Lechmann, S AU - Moigne, NL AU - Champollion, C AU - Doerflinger, E TI - Flexure of the India plate underneath the Bhutan Himalaya JF - GEOPHYSICAL RESEARCH LETTERS J2 - GEOPHYS RES LETT VL - 40 PY - 2013 IS - 16 SP - 4225 EP - 4230 PG - 6 SN - 0094-8276 DO - 10.1002/grl.50793 UR - https://m2.mtmt.hu/api/publication/3163096 ID - 3163096 AB - We investigate flexural geometry and rheology of the India plate beneath the eastern Himalaya from a new gravity data set acquired in Bhutan. Compared to the well-studied Nepal Himalaya, the obtained Bouguer anomaly profiles across the range show shorter wavelength flexure of the lithosphere with a narrower and shallower foreland basin. This new data set and seismic Moho constraints are interpreted together in terms of lithospheric flexure using a 2-D thermomechanical model. Our results suggest that the strongest layer of the continental lithosphere beneath Bhutan is the upper mantle, as it is beneath Nepal. The observed west-to-east decrease in flexural wavelength is associated with weakening mantle rheology. The simulations show that this decrease can be related to ductile mantle behavior: either hydrated wet dunite or dry and hot olivine rheology. Both models display decoupled lithospheric layers leading to an eastward decrease of flexural rigidity from ∼1024 to ∼5·1022 N m in Nepal and Bhutan, respectively. Key Points Flexure and rheology of the India Plate in the Eastern Himalayas is investigated New gravity dataset constrains comprehensive 2D thermo-mechanical modeling Flexural rigidity decreases both across and along (W to E) the range. © 2013. American Geophysical Union. All Rights Reserved. LA - English DB - MTMT ER - TY - JOUR AU - Hetényi, György AU - Godard, V AU - Cattin, R AU - Connolly, JAD TI - Incorporating metamorphism in geodynamic models: The mass conservation problem JF - GEOPHYSICAL JOURNAL INTERNATIONAL J2 - GEOPHYS J INT VL - 186 PY - 2011 IS - 1 SP - 6 EP - 10 PG - 5 SN - 0956-540X DO - 10.1111/j.1365-246X.2011.05052.x UR - https://m2.mtmt.hu/api/publication/3163103 ID - 3163103 AB - Geodynamic models incorporating metamorphic phase transformations almost invariably assume the validity of the Boussinesq approximation that violates conservation of mass. In such models metamorphic density changes take place without volumetric effects. We assess the impact of the Boussinesq approximation by comparing models of orogeny accompanied by lower crustal eclogitization both with and without the approximation. Our results demonstrate that the approximation may cause errors approaching 100 per cent in characteristic measures of orogenic shape. Mass conservation errors in Boussinesq models amplify with model time. Mass conservative models of metamorphism are therefore essential to understand long-term tectonic evolution and to assess the importance of the different geodynamic processes. © 2011 The Authors. Geophysical Journal International © 2011 RAS. LA - English DB - MTMT ER - TY - JOUR AU - Nabelek, J AU - Hetényi, György AU - Vergne, J AU - Sapkota, S AU - Kafle, B AU - Jiang, M AU - Su, HP AU - Chen, J AU - Huang, BS ED - L., Mitchell / Collaborator ED - D., Sherstad / Collaborator ED - M., Arsenault / Collaborator ED - J., Baur / Collaborator ED - S., Carpenter / Collaborator ED - M., Donnahue / Collaborator ED - D., Myers / Collaborator ED - T.-L., Tseng / Collaborator ED - T., Bardell / Collaborator ED - N., VanHoudnos / Collaborator ED - M., Pandey / Collaborator ED - G., Chitrakar / Collaborator ED - S., Rajaure / Collaborator ED - G., Xue / Collaborator ED - Y., Wang / Collaborator ED - S., Zhou / Collaborator ED - X., Liang / Collaborator ED - G., Ye / Collaborator ED - C.-C., Liu / Collaborator ED - J., Lin / Collaborator ED - C.-L., Wu / Collaborator ED - N., Barstow / Collaborator TI - Underplating in the Himalaya-Tibet Collision Zone Revealed by the Hi-CLIMB Experiment JF - SCIENCE J2 - SCIENCE VL - 325 PY - 2009 IS - 5946 SP - 1371 EP - 1374 PG - 4 SN - 0036-8075 DO - 10.1126/science.1167719 UR - https://m2.mtmt.hu/api/publication/1280307 ID - 1280307 AB - We studied the formation of the Himalayan mountain range and the Tibetan Plateau by investigating their lithospheric structure. Using an 800-kilometer-long, densely spaced seismic array, we have constructed an image of the crust and upper mantle beneath the Himalayas and the southern Tibetan Plateau. The image reveals in a continuous fashion the Main Himalayan thrust fault as it extends from a shallow depth under Nepal to the mid-crust under southern Tibet. Indian crust can be traced to 31 degrees N. The crust/mantle interface beneath Tibet is anisotropic, indicating shearing during its formation. The dipping mantle fabric suggests that the Indian mantle is subducting in a diffuse fashion along several evolving subparallel structures. LA - English DB - MTMT ER - TY - JOUR AU - Hetényi, György AU - Cattin, R AU - Brunet, F AU - Bollinger, L AU - Vergne, J AU - Nabelek, J AU - Diament, M TI - Density distribution of the India plate beneath the Tibetan plateau: Geophysical and petrological constraints on the kinetics of lower-crustal eclogitization JF - EARTH AND PLANETARY SCIENCE LETTERS J2 - EARTH PLANET SC LETT VL - 264 PY - 2007 IS - 1-2 SP - 226 EP - 244 PG - 19 SN - 0012-821X DO - 10.1016/j.epsl.2007.09.036 UR - https://m2.mtmt.hu/api/publication/1166018 ID - 1166018 AB - We combine seismological and Bouguer anomaly data with thermo-kinematic and petrological modelling to constrain the extent and kinetics of the eclogitization process in the Indian lower crust underthrusting Tibet. Based on Airy-type isostasy gravity modelling, we show that the presence of denser material (eclogites) is required beneath the Tibetan Plateau. Using the geometries of main crustal interfaces constrained by seismological experiments along three profiles perpendicular to the Himalayan arc, multilayer density-models suggest that eclogitization of the Indian lower crust is completed where the maximal depth of its descent is reached. In an integrated geophysical and petrological approach, the temperature field of the studied area is determined and realistic pressure-temperature-density grids are calculated assuming different hydration levels for the Indian lower crust. The derived density profiles are used to forward model Bouguer anomalies and to compare them to the observations. It appears that eclogitization of the Indian lower crust is delayed compared to where it is expected to occur from phase equilibria. The results show that neither dry nor fully hydrated (free water in excess) lower-crust models are satisfactory. A hydration level of ca. 1 wt.% H2O, consistent with a lower crust having experienced amphibolitic conditions, is more realistic and yields better results. On this basis, the densification delay of the Indian lower crust can be accounted for by a kinetical hindrance (overstepping) of the consumption of the plagioclase component (garnet and clinopyroxene forming reactions), which does not release water. Densification proceeds relatively rapidly (within 6 My) at higher pressure and temperature (at least 100 degrees C above equilibrium), when dehydration reactions start releasing water. These results emphasize the key role of free water in metamorphic reaction kinetics and, consequently, on geodynamical processes. LA - English DB - MTMT ER -