scholarly journals Lower-crustal earthquakes in southern Tibet are linked to eclogitization of dry metastable granulite

2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Feng Shi ◽  
Yanbin Wang ◽  
Tony Yu ◽  
Lupei Zhu ◽  
Junfeng Zhang ◽  
...  
Keyword(s):  
Southern Tibet ◽  
Crustal Earthquakes ◽  
Lower Crustal

Lower crustal earthquake facilitated by overpressurized frictional melts

2020 ◽  
Author(s):  
Xin Zhong ◽  
Arianne Petley-Ragan ◽  
Sarah Incel ◽  
Marcin Dabrowski ◽  
Niels Andersen ◽  
...  
Keyword(s):  
Wall Rock ◽  
Rapid Quenching ◽  
Elastic Model ◽  
Shear Rigidity ◽  
Geological Time ◽  
Differential Stress ◽  
Crustal Earthquakes ◽  
Fluid Pressurization ◽  
Frictional Melting ◽  
Lower Crustal

<p>Earthquakes are among the most catastrophic geological events that last only several to tens of seconds. During earthquakes, many processes may occur including rupturing, frictional sliding, pore fluid pressurization and occasionally frictional melting. However, little direct records of these fast processes remain preserved through geological time. During rapid shearing, frictional melt may form that lubricates the rocks and facilitates further sliding. The frictional melt layer may quench quickly within seconds to minutes depending on its thickness. After quenching, the product pseudotachylyte preserves valuable information about the conditions when the frictional melt was generated. Here, we study pseudotachylyte from Holsnøy Island in the Bergen Arcs of Western Norway, an exhumed portion of the lower continental crust. The investigated pseudotachylyte vein is ca. 1-2 cm thick and free of injection veins along the 2 m visible length of the fault. The pseudotachylyte matrix is made up of fine-grained omphacite (Jd<sub>38</sub>), sodic plagioclase (Ab<sub>83</sub>) and kyanite with minor rutile and sulphides. Many dendritic garnets are found within the pseudotachylyte showing gradual grain size reduction towards the wall rock. This suggests that the garnets crystallized during rapid quenching. The stability of epidote, kyanite and quartz in the wall rock plagioclase, and omphacite and albitic plagioclase together with quartz in the pseudotachylyte matrix constrains the ambient P ca. 1.5-1.7 GPa and T ca. 650-750°C. Using Raman elastic barometry, the constrained pressure condition from quartz inclusions in the dendritic garnets in the pseudotachylyte is > 2 GPa. Based on an elastic model (Eshelby’s solution), it is not possible to maintain 0.5 GPa overpressure within a thin melt layer by thermal pressurization or melting expansion. A potential explanation is that GPa level differential stress was present in the wall rocks and the melt pressure approached the normal stress when shear rigidity vanished during frictional melting. Our study illustrates how overpressure can be created within frictional melt veins under conditions of high differential stress, and offers a mechanism that facilitates co-seismic weakening during lower crustal earthquakes.  </p>

scholarly journals Dynamic earthquake rupture in the lower crust

2019 ◽  
Vol 5 (7) ◽  
pp. eaaw0913 ◽  
Author(s):  
Arianne Petley-Ragan ◽  
Yehuda Ben-Zion ◽  
Håkon Austrheim ◽  
Benoit Ildefonse ◽  
François Renard ◽  
...  
Keyword(s):  
Lower Crust ◽  
Failure Process ◽  
Wall Rock ◽  
Ductile Deformation ◽  
Earthquake Rupture ◽  
Seismic Slip ◽  
Crustal Earthquakes ◽  
Sequence Of Events ◽  
Deformation Processes ◽  
Lower Crustal

Earthquakes in the continental crust commonly occur in the upper 15 to 20 km. Recent studies demonstrate that earthquakes also occur in the lower crust of collision zones and play a key role in metamorphic processes that modify its physical properties. However, details of the failure process and sequence of events that lead to seismic slip in the lower crust remain uncertain. Here, we present observations of a fault zone from the Bergen Arcs, western Norway, which constrain the deformation processes of lower crustal earthquakes. We show that seismic slip and associated melting are preceded by fracturing, asymmetric fragmentation, and comminution of the wall rock caused by a dynamically propagating rupture. The succession of deformation processes reported here emphasize brittle failure mechanisms in a portion of the crust that until recently was assumed to be characterized by ductile deformation.

Eocene thickening without extra heat in a collisional orogenic belt: A record from Eocene metamorphism in mafic dike swarms within the Tethyan Himalaya, southern Tibet

2021 ◽  
Author(s):  
Yuhua Wang ◽  
Lingsen Zeng ◽  
Li-E Gao ◽  
Zhenyu Chen ◽  
Sanzhong Li
Keyword(s):  
Large Scale ◽  
High Mountain ◽  
Southern Tibet ◽  
Crustal Rocks ◽  
Flow Estimation ◽  
Environmental Consequences ◽  
Slab Breakoff ◽  
Orogenic Belts ◽  
Lower Crustal ◽  
Tethyan Himalaya

Knowledge of the nature of the earliest metamorphism experienced by collisional orogenic belts is essential for reconstruction of tectonic processes that build high mountain chains and their environmental consequences. Understanding the metamorphic nature of Eohimalayan-phase orogeny of the Himalayan orogen, one of the typical examples of orogenic belts worldwide, could provide some important constraints to test different tectonic models (shallow continental subduction vs. slab breakoff) for the early phases of the development of large-scale orogenic belts. As exhumed middle- to lower-crustal rocks in the Kangmar gneiss dome, the garnet amphibolites with a protolith age of 176.4 ± 3.6 Ma experienced a phase of metamorphism at 47.2 ± 1.8 Ma with an increase in pressure as well as temperature from 3−5 kbar and 550−600 °C to over ∼11 kbar and 650 °C. This suggests that the middle- to lower-crustal rocks experienced heating at least by ∼50 °C while they underwent compression and thickening. Heat-flow estimation further demonstrates that the self-produced heat was high enough to achieve the observed pressure-temperature conditions recorded by the garnet amphibolite. Therefore, an additional heat supply is not required during early Eocene metamorphism. A breakoff of the leading part of the subducting Indian continental slab, if it occurred, should be younger than ca. 47 Ma.

scholarly journals Lower-crustal earthquakes in the West Kunlun range

2011 ◽  
Vol 38 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Guo-Chin Dino Huang ◽  
Steven W. Roecker ◽  
Vadim Levin
Keyword(s):  
The West ◽  
Crustal Earthquakes ◽  
West Kunlun ◽  
Lower Crustal

scholarly journals Pseudotachylyte as field evidence for lower crustal earthquakes during the intracontinental Petermann Orogeny (Musgrave Block, Central Australia)

2017 ◽  
Author(s):  
Friedrich Hawemann ◽  
Neil Mancktelow ◽  
Sebastian Wex ◽  
Alfredo Camacho ◽  
Giorgio Pennacchioni
Keyword(s):  
Crustal Earthquakes ◽  
Field Evidence ◽  
Central Australia ◽  
Lower Crustal

The Mechanism and Dynamics of N-S trends normal faults in Tibetan Plateau: Insight From Thermochronology, Magnetotellurics, Magmatism and GPS Measurements

2020 ◽  
Author(s):  
Han-Ao Li ◽  
in-Gen Dai ◽  
Le-Tian Zhang ◽  
Ya-Lin Li ◽  
Guang-Hao Ha ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Lower Crust ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Gps Measurements ◽  
Southern Tibet ◽  
Magnetotelluric Data ◽  
Deep Process ◽  
Lower Crustal Flow ◽  
Lower Crustal

<p>The N-S trends normal faults are widespread through the whole Tibetan Plateau. It records key information for the growth and uplift of the Tibetan Plateau. Numerous models are provided to explain the causes of rifting in the Tibetan Plateau based on the low-temperature thermochronology<sup>1</sup>. With the developments of the geophysical and magmatic geochemistry methods and its applications on the Tibetan Plateau, we could gain more profound understanding on the sphere structure of the Tibetan Plateau. This would give us more clues on how the deep process affect the formation and evolution of the shallow normal faults. However, few researchers pay attention on this and the relationship between the surface evolution and deep process of these faults. In order to solve these puzzles, we collected the published thermochronology data, magnetotelluric data, faults-related ultrapotassic, potassic and the adakitic rocks ages and present-day GPS measurements. We find that the distribution of the N-S trends normal faults are closely related to the weak zones in the middle to lower crust (15-50 km) revealed by the magmatism and magnetotelluric data<sup>2</sup>. Besides, the present-day GPS data show that the E-W extension rates match well with the eastward movements speeds interior Tibetan Plateau<sup>3</sup>. Combined with the thermochronology data (25-4 Ma), we concluded that 1.The weak zone in the middle to lower crust influence the developments and evolution of the N-S trends normal faults. 2. The material eastward flow enhance the N-S normal faults developments. 3. The timing of the middle to lower crustal flow may begin in the Miocene.</p><p><strong>Key words:</strong> N-S trends normal faults; Thermochronology; Magnetotellurics; Magmatism; GPS Measurements; middle to lower crustal flow</p><p><strong>References:</strong></p><p><sup>1</sup>Lee, J., Hager, C., Wallis, S.R., Stockli, D.F., Whitehouse, M.J., Aoya, M. and Wang, Y., 2011. Middle to Late Miocene Extremely Rapid Exhumation and Thermal Reequilibration in the Kung Co Rift, Southern Tibet. Tectonics, 30(2).</p><p><sup>2</sup>Pang, Y., Zhang, H., Gerya, T.V., Liao, J., Cheng, H. and Shi, Y., 2018. The Mechanism and Dynamics of N-S Rifting in Southern Tibet: Insight from 3-D Thermomechanical Modeling. Journal of Geophysical Research: Solid Earth.</p><p><sup>3</sup>Zhang, P.-Z., Shen, Z., Wang, M., Gan, W., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z., Sun, J., Wu, J., Hanrong, S. and Xinzhao, Y., 2004. Continuous Deformation of the Tibetan Plateau from Global Positioning System Data. Geology, 32(9).</p><p><strong>Acknowledgements:</strong></p><p>We thank Shi-Ying Xu, Xu Han, Bo-Rong Liu for collecting data. Special thanks are given to Dr. Guang-Hao Ha and Professors Jin-Gen Dai, Le-Tian Zhang，Ya-Lin Li and Cheng-Shan Wang for many critical and constructive comments.</p>

Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift

2009 ◽  
Vol 72 (1) ◽  
pp. 55-62 ◽  
Author(s):  
Heidi Soosalu ◽  
Janet Key ◽  
Robert S. White ◽  
Clare Knox ◽  
Páll Einarsson ◽  
...  
Keyword(s):  
The North ◽  
Crustal Earthquakes ◽  
Askja Volcano ◽  
Lower Crustal

scholarly journals Lower crustal earthquakes near the Ethiopian rift induced by magmatic processes

2009 ◽  
Vol 10 (6) ◽  
pp. n/a-n/a ◽  
Author(s):  
Derek Keir ◽  
Ian D. Bastow ◽  
Kathryn A. Whaler ◽  
Eve Daly ◽  
David G. Cornwell ◽  
...  
Keyword(s):  
Ethiopian Rift ◽  
Crustal Earthquakes ◽  
Magmatic Processes ◽  
Lower Crustal

scholarly journals Lower crustal earthquake associated with highly pressurized frictional melts

2021 ◽  
Author(s):  
Xin Zhong ◽  
Arianne J. Petley-Ragan ◽  
Sarah H. M. Incel ◽  
Marcin Dabrowski ◽  
Niels H. Andersen ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Maximum Principal Stress ◽  
Elastic Model ◽  
Differential Stress ◽  
Fault Surface ◽  
Seismic Fault ◽  
Crustal Earthquakes ◽  
Lower Crustal

AbstractEarthquakes at lower crustal depths are common during continental collision. However, the coseismic weakening mechanisms required to propagate an earthquake at high pressures are poorly understood. Transient high-pressure fluids or melts have been proposed as a viable mechanism, but verifying this requires direct in situ measurement of fluid or melt overpressure along fault planes that have hosted dynamic ruptures. Here, we report direct measurement of highly overpressurized frictional melts along a seismic fault surface. Using Raman spectroscopy, we identified high-pressure quartz inclusions sealed in dendritic garnets that grew from frictional melts formed by lower crustal earthquakes in the Bergen Arcs, Western Norway. Melt pressure was estimated to be 1.8–2.3 GPa on the basis of an elastic model for the quartz-in-garnet system. This is ~0.5 GPa higher than the pressure recorded by the surrounding pseudotachylyte matrix and wall rocks. The recorded melt pressure could not arise solely from the volume expansion of melting, and we propose that it was generated when melt pressure approached the maximum principal stress in a system subject to high differential stress. The associated palaeostress field demonstrates that a strong lower crust accommodated up to 1 GPa differential stress during the compressive stage of the Caledonian orogeny.

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