Fast cooling of normal-fault footwalls: Rapid fault slip or thermal relaxation?

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 333-337
Author(s):  
Reinhard Wolff ◽  
Ralf Hetzel ◽  
István Dunkl ◽  
Aneta A. Anczkiewicz ◽  
Hannah Pomella
Keyword(s):  
Thermal Relaxation ◽  
Normal Fault ◽  
Geothermal Gradient ◽  
European Alps ◽  
Normal Faulting ◽  
Heat Advection ◽  
Tauern Window ◽  
The North ◽  
Cooling Pattern ◽  
Mountain Belts

Abstract Rapid rock exhumation in mountain belts is commonly associated with crustal-scale normal faulting during late-orogenic extension. The process of normal faulting advects hot footwall rocks toward Earth’s surface, which shifts isotherms upwards and increases the geothermal gradient. When faulting stops, this process is reversed and isotherms move downwards during thermal relaxation. Owing to these temporal changes of the geothermal gradient, it is not straightforward to derive the history of faulting from mineral cooling ages. Here, we combine thermochronological data with thermokinematic modeling to illustrate the importance of syntectonic heat advection and posttectonic thermal relaxation for a crustal-scale normal fault in the European Alps. The north-south–trending Brenner fault defines the western margin of the Tauern window (Austria) and caused the exhumation of medium-grade metamorphic rocks during Miocene orogen-parallel extension of the Alps. We analyzed samples from a 2-km-thick crustal section, including a 1000-m-long drill core. Zircon and apatite (U-Th)/He ages along this transect increase with elevation from ca. 8 to ca. 10 Ma and from ca. 7 to ca. 9 Ma, respectively, but differ by only ∼1 m.y. in individual samples. Thermokinematic modeling of the ages indicates that the Brenner fault became active at 19 ± 2 Ma and caused 35 ± 10 km of crustal extension, which is consistent with independent geological constraints. The model results further suggest that the fault slipped at a total rate of 4.2 ± 0.9 km/m.y. and became inactive at 8.8 ± 0.4 Ma. Our findings demonstrate that both syntectonic heat advection and posttectonic thermal relaxation are responsible for the cooling pattern observed in the footwall of the Brenner normal fault.

Fast cooling of normal-fault footwalls: rapid fault slip or thermal relaxation?

2020 ◽  
Author(s):  
Reinhard Wolff ◽  
Ralf Hetzel ◽  
István Dunkl ◽  
Aneta A. Anczkiewicz ◽  
Hannah Pomella
Keyword(s):  
Thermal Relaxation ◽  
Normal Fault ◽  
Geothermal Gradient ◽  
Eastern Alps ◽  
Fault Slip ◽  
European Alps ◽  
Normal Faulting ◽  
Heat Advection ◽  
Fast Cooling ◽  
Parallel Extension

<p>Rapid rock exhumation in mountain belts is often associated with crustal-scale normal faulting during late-orogenic extension. The process of normal faulting advects hot footwall rocks towards the Earth's surface, which shifts isotherms upwards and increases the geothermal gradient. When faulting stops, this process is reversed and isotherms move downwards during thermal relaxation. Owing to these temporal changes of the geothermal gradient, it is not straightforward to derive the history of faulting from mineral cooling ages (Braun, 2016). Here, we combine thermochronological data with thermokinematic modeling to illustrate the importance of syntectonic heat advection and posttectonic thermal relaxation for a crustal-scale normal fault in the European Alps. The N–S trending Brenner fault defines the western margin of the Tauern Window and caused the exhumation of medium-grade metamorphic rocks during Miocene orogen-parallel extension of the Alps (Rosenberg & Garcia, 2011; Fügenschuh et al., 2012). We analyzed samples from a 2-km-thick crustal section, including a 1000-m-long drillcore. Zircon and apatite (U-Th)/He ages along this transect increase with elevation from ~8 to ~10 Ma and from ~7 to ~9 Ma, respectively, but differ by only ~1 Myr in individual samples. Thermokinematic modeling of the ages indicates that the Brenner fault became active 19±2 Ma ago and caused 35±10 km of crustal extension, which is consistent with independent geological constraints. The model results further suggest that the fault slipped at a total rate of 4.2±0.9 km/Myr and became inactive 8.8±0.4 Ma ago. Our findings demonstrate that both syntectonic heat advection and posttectonic thermal relaxation are responsible for the cooling pattern observed in the footwall of the Brenner normal fault.</p><p>References</p><p>Braun, J., 2016, Strong imprint of past orogenic events on the thermochronological record: Tectonophysics, v. 683, p. 325–332.</p><p>Fügenschuh, B., Mancktelow, N., Schmid, S., 2012, Comment on Rosenberg and Garcia: Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps: Int. J. Earth Sci., v. 101, p. 1451–1455.</p><p>Rosenberg, C.L., Garcia, S., 2011, Estimating displacement along the Brenner Fault and orogen-parallel extension in the Eastern Alps: Int. J. Earth Sci., v. 100, p. 1129–1145.</p><p>Wolff, R., Hetzel, R., Dunkl, I., Anczkiewicz, A.A., Pomella, H. 2020, Fast cooling of normal-fault footwalls: rapid fault slip or thermal relaxation? Geology, v. 48, doi:10.1130/G46940.1.</p>

scholarly journals New constraints on the exhumation history of the western Tauern Window (European Alps) from thermochronology, thermokinematic modeling, and topographic analysis

2021 ◽  
Author(s):  
Reinhard Wolff ◽  
Ralf Hetzel ◽  
István Dunkl ◽  
Aneta A. Anczkiewicz
Keyword(s):  
Hanging Wall ◽  
Thermal Relaxation ◽  
Slip Rate ◽  
Normal Fault ◽  
European Alps ◽  
Valley Bottom ◽  
Topographic Analysis ◽  
Tauern Window ◽  
History Of ◽  
Exhumation History

AbstractThe Brenner normal fault bounds the Tauern Window to the west and accommodated a significant portion of the orogen-parallel extension in the Eastern Alps. Here, we use zircon (U–Th)/He, apatite fission track, and apatite (U–Th)/He dating, thermokinematic modeling, and a topographic analysis to constrain the exhumation history of the western Tauern Window in the footwall of the Brenner fault. ZHe ages from an E–W profile (parallel to the slip direction of the fault) decrease westwards from ~ 11 to ~ 8 Ma and suggest a fault-slip rate of 3.9 ± 0.9 km/Myr, whereas AFT and AHe ages show no spatial trends. ZHe and AFT ages from an elevation profile indicate apparent exhumation rates of 1.1 ± 0.7 and 1.0 ± 1.3 km/Myr, respectively, whereas the AHe ages are again spatially invariant. Most of the thermochronological ages are well predicted by a thermokinematic model with a normal fault that slips at a rate of 4.2 km/Myr between ~ 19 and ~ 9 Ma and produces 35 ± 10 km of extension. The modeling reveals that the spatially invariant AHe ages are caused by heat advection due to faulting and posttectonic thermal relaxation. The enigmatic increase of K–Ar phengite and biotite ages towards the Brenner fault is caused by heat conduction from the hot footwall to the cooler hanging wall. Topographic profiles across an N–S valley in the fault footwall indicate 1000 ± 300 m of erosion after faulting ceased, which agrees with the results of our thermokinematic model. Valley incision explains why the Brenner fault is located on the western valley shoulder and not at the valley bottom. We conclude that the ability of thermokinematic models to quantify heat transfer by rock advection and conduction is crucial for interpreting cooling ages from extensional fault systems.

Neogene Exhumation History along TRANSALP: Insights from Low Temperature Thermochronology and Thermo-Kinematic Models

2020 ◽  
Author(s):  
Paul R. Eizenhöfer ◽  
Christoph Glotzbach ◽  
Lukas Büttner ◽  
Jonas Kley ◽  
Todd A. Ehlers
Keyword(s):  
Low Temperature ◽  
Kinematic Model ◽  
Eastern Alps ◽  
European Alps ◽  
Eastern European ◽  
Tauern Window ◽  
The North ◽  
Late Neogene ◽  
Kinematic Models ◽  
Exhumation Rates

<p>Many convergent orogens such as the eastern European Alps display an asymmetric doubly-vergent wedge geometry. Loci of deepest exhumation are located above the overriding retro-wedge, whereas increased fault activity occurs in the pro-wedge on the subducting plate. The main drainage divide separates steeper from more gently sloping topography on the two wedges of different critical taper. We performed apatite and zircon (U-Th)/He analyses densely spaced along the TRANSALP geophysical transect in combination with thermo-kinematic models based on cross-section balancing. Our new low temperature thermochronology data and thermo-kinematic model results underline (i) deepest levels of exhumation across the Tauern Window until the Pliocene and (ii) higher Late Neogene exhumation rates south of the Periadriatic Fault relative to the north, while seismic activity is focussed across the Southern Alps. Our proposed mantle-to-surface link positions the retro-wedge north of the Periadriatic Fault subsequent to subduction polarity reversal during continental collision. Present-day drainage divide migration trends and imaged locations of mantle-lithospheric slabs beneath TRANSALP suggest ongoing, slow slab reversal since Adriatic indentation in the Eastern Alps. </p>

scholarly journals Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Paraskevi Nomikou ◽  
Dimitris Evangelidis ◽  
Dimitrios Papanikolaou ◽  
Danai Lampridou ◽  
Dimitris Litsas ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Activity ◽  
Volcanic Rocks ◽  
Active Tectonics ◽  
Normal Fault ◽  
Aegean Sea ◽  
Northern Margin ◽  
The North ◽  
Eastern Aegean ◽  
Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

Timing of fluorite mineralization and exhumation events in the east Central Alborz Mountains, northern Iran: constraints from fluorite (U–Th)/He thermochronometry

2021 ◽  
pp. 1-17
Author(s):  
Behnam Shafiei Bafti ◽  
István Dunkl ◽  
Saeed Madanipour
Keyword(s):  
Thermal Relaxation ◽  
Geothermal Gradient ◽  
Source Rocks ◽  
Lower Amount ◽  
Mining District ◽  
Northern Iran ◽  
East Central ◽  
Central Alborz ◽  
Ore Mineralization ◽  
History Of

Abstract The recently developed fluorite (U–Th)/He thermochronology (FHe) technique was applied to date fluorite mineralization and elucidate the exhumation history of the Mazandaran Fluorspar Mining District (MFMD) located in the east Central Alborz Mountains, Iran. A total of 32 fluorite single-crystal samples from four Middle Triassic carbonate-hosted fluorite deposits were dated. The presented FHe ages range between c. 85 Ma (age of fluorite mineralization) and c. 20 Ma (erosional cooling during the exhumation of the Alborz Mountains). The Late Cretaceous FHe ages (i.e. 84.5 ± 3.6, 78.8 ± 4.4 and 72.3 ± 3.5 Ma) are interpreted as the age of mineralization and confirm an epigenetic origin for ore mineralization in the MFMD, likely a result of prolonged hydrothermal circulation of basinal brines through potential source rocks. Most FHe ages scatter around the Eocene Epoch (55.4 ± 3.9 to 33.1 ± 1.7 Ma), recording an important cooling event after heating by regional magmatism in an extensional tectonic regime. Cooling of the heated fluorites, as a result of thermal relaxation in response to geothermal gradient re-equilibration after the end of magmatism, or exhumation cooling during extensional tectonics characterized by lower amount of erosion are most probably the causes of the recorded Eocene FHe cooling ages. Oligocene–Miocene FHe ages (i.e. 27.6 ± 1.4 to 19.5 ± 1.1 Ma) are related to the accelerated uplift of the whole Alborz Mountains, possibly as a result of the initial collision between the Afro-Arabian and Eurasian plates further to the south.

The 4 December 2015 Mw 7.1 Normal-Faulting Antarctic Plate Earthquake and Its Seismotectonic Implications

2020 ◽  
Vol 110 (3) ◽  
pp. 1090-1100
Author(s):  
Ronia Andrews ◽  
Kusala Rajendran ◽  
N. Purnachandra Rao
Keyword(s):  
Body Wave ◽  
Focal Depth ◽  
Normal Fault ◽  
Normal Faults ◽  
Oceanic Plate ◽  
Normal Faulting ◽  
Transform Faults ◽  
Wave Inversion ◽  
Spreading Ridges ◽  
Southeast Indian Ridge

ABSTRACT Oceanic plate seismicity is generally dominated by normal and strike-slip faulting associated with active spreading ridges and transform faults. Fossil structural fabrics inherited from spreading ridges also host earthquakes. The Indian Oceanic plate, considered quite active seismically, has hosted earthquakes both on its active and fossil fault systems. The 4 December 2015 Mw 7.1 normal-faulting earthquake, located ∼700  km south of the southeast Indian ridge in the southern Indian Ocean, is a rarity due to its location away from the ridge, lack of association with any mapped faults and its focal depth close to the 800°C isotherm. We present results of teleseismic body-wave inversion that suggest that the earthquake occurred on a north-northwest–south-southeast-striking normal fault at a depth of 34 km. The rupture propagated at 2.7  km/s with compact slip over an area of 48×48  km2 around the hypocenter. Our analysis of the background tectonics suggests that our chosen fault plane is in the same direction as the mapped normal faults on the eastern flanks of the Kerguelen plateau. We propose that these buried normal faults, possibly the relics of the ancient rifting might have been reactivated, leading to the 2015 midplate earthquake.

Understanding pre- and syn-orogenic tectonic evolution in western Himalaya through age and petrogenesis of Palaeozoic and Cenozoic granites from upper structural levels of Bhagirathi Valley, NW India

2021 ◽  
pp. 1-27
Author(s):  
Aranya Sen ◽  
Koushik Sen ◽  
Amitava Chatterjee ◽  
Shubham Choudhary ◽  
Alosree Dey
Keyword(s):  
Inductively Coupled Plasma ◽  
Age Distribution ◽  
Normal Fault ◽  
Western Himalaya ◽  
Indian Plate ◽  
Low Grade ◽  
Inductively Coupled ◽  
The North ◽  
Plasma Mass Spectrometry ◽  
Structural Levels

Abstract The Himalaya is characterized by the presence of both pre-Himalayan Palaeozoic and syn-Himalayan Cenozoic granitic bodies, which can help unravel the pre- to syn-collisional geodynamics of this orogen. In the Bhagirathi Valley of Western Himalaya, such granites and the Tethyan Himalayan Sequence (THS) hosting them are bound to the south by the top-to-the-N extensional Jhala Normal Fault (JNF) and low-grade metapelite of the THS to its north. The THS is intruded by a set of leucocratic dykes concordant to the JNF. Zircon U–Pb laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) geochronology of the THS and one leucocratic dyke reveals that the two rocks have a strikingly similar age distribution, with a common and most prominent age peak at ~1000 Ma. To the north of the THS lies Bhaironghati Granite, a Palaeozoic two-mica granite, which shows a crystallization age of 512.28 ± 1.58 Ma. Our geochemical analysis indicates that it is a product of pre-Himalayan Palaeozoic magmatism owing to extensional tectonics in a back-arc or rift setting following the assembly of Gondwana (500–530 Ma). The Cenozoic Gangotri Leucogranite lies to the north of Bhaironghati Granite, and U–Pb dating of zircon from this leucogranite gives a crystallization age of 21.73 ± 0.11 Ma. Our geochemical studies suggest that the Gangotri Leucogranite is a product of muscovite-dehydration melting of the lower crust owing to flexural bending in relation to steepening of the subducted Indian plate. The leucocratic dykes are highly refracted parts of the Gangotri Leucogranite that migrated and emplaced along extensional fault zones related to the JNF and scavenged zircon from the host THS during crystallization.

scholarly journals Seismic-Scale Evidence of Thrust-Perpendicular Normal Faulting in the Western Outer Carpathians, Poland

Minerals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1252
Author(s):  
Jan Barmuta ◽  
Krzysztof Starzec ◽  
Wojciech Schnabel
Keyword(s):  
Large Scale ◽  
Fault Plane ◽  
Normal Fault ◽  
Normal Faulting ◽  
Seismic Profiles ◽  
Horizontal Movement ◽  
Outer Carpathians ◽  
Differential Uplift ◽  
Seismic Scale ◽  
Detachment Surface

Based on the interpretation of 2D seismic profiles integrated with surface geological investigations, a mechanism responsible for the formation of a large scale normal fault zone has been proposed. The fault, here referred to as the Rycerka Fault, has a predominantly normal dip-slip component with the detachment surface located at the base of Carpathian units. The fault developed due to the formation of an anticlinal stack within the Dukla Unit overlain by the Magura Units. Stacking of a relatively narrow duplex led to the growth of a dome-like culmination in the lower unit, i.e., the Dukla Unit, and, as a consequence of differential uplift of the unit above and outside the duplex, the upper unit (the Magura Unit) was subjected to stretching. This process invoked normal faulting along the lateral culmination wall and was facilitated by the regional, syn-thrusting arc–parallel extension. Horizontal movement along the fault plane is a result of tear faulting accommodating a varied rate of advancement of Carpathian units. The time of the fault formation is not well constrained; however, based on superposition criterion, the syn -thrusting origin is anticipated.

scholarly journals Geological Structure Analysis to Determine the Direction of the Main Stress at Western Part of Kolok Mudik, Barangin District, Sawahlunto, West Sumatera

2017 ◽  
Vol 2 (1) ◽  
pp. 46
Author(s):  
Miftahul Jannah ◽  
Adi Suryadi ◽  
Muchtar Zafir ◽  
Randi Saputra ◽  
Ihsanul Hakim ◽  
...  
Keyword(s):  
Structure Analysis ◽  
Normal Fault ◽  
Geological Structure ◽  
Reverse Fault ◽  
Geological Structures ◽  
The North ◽  
Main Stress

On the study area there are three types of structure, those are fault, fold and joint. Types of fault were found  in the study area, reverse fault with the strike/dip is N215oE/75o, normal fault has a fault directions N22oE and N200oE with pitch 35o, and dextral fault with pitch 10o and strike N219oE. Fold and joint structures used to determine the direction of the main stress on the study area. Further, an analysis used stereonet for data folds and joints. So that from the data got three directions of main stress, those are Northeast – Southwest (T1), North – South (T2) and Southeast – Northwest (T3). On the Northeast – Southwest (T1) stress there are four geological structures, anticline fold at ST.3 , syncline folds at ST. 13a, ST. 13b, ST. 13c and ST. 33, chevron fold at ST. 44 and joint at ST. 2. On the North – South (T2) stress there are three geological structures, those are syncline fold at ST. 35, anticline fold at ST. 54 and joints at ST. 41, ST. 46 and ST. 47. On the Southeast – Northwest (T3) stress were also three geological structures, those are chevron fold at ST 42a, overturned fold at ST. 42b, syncline fold at ST. 42c and joints at ST. 5 and ST. 34.

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