Metamorphic constraints on the tectonic evolution of the High Himalaya in Nepal: the art of the possible

2019 ◽  
Vol 483 (1) ◽  
pp. 325-375 ◽  
Author(s):  
David J. Waters
Keyword(s):  
Tectonic Evolution ◽  
Hanging Wall ◽  
Lower Boundary ◽  
Personal View ◽  
Micro Scale ◽  
Lower Division ◽  
Ductile Flow ◽  
Peak Metamorphism ◽  
Multidisciplinary Studies ◽  
Metamorphic Gradient

AbstractThis review presents an objective account of metamorphic, microstructural and geochronological studies in the Greater Himalayan Sequence (GHS) and adjacent units in Nepal in the light of recent research. The importance of integrated, multidisciplinary studies is highlighted. A personal view is presented of strategies for determining pressure–temperature evolution, and of petrological processes at the micro scale, particularly in relation to departures from equilibrium and the behaviour of partially-melted rock systems. Evidence has accumulated for the existence within the GHS of a High Himalayan Discontinuity, marked by differences in timing of peak metamorphism in the hanging wall and footwall, and changes in P–T gradients and paths. Whether or not this is a single continuous horizon, it forms at each location the lower boundary to a migmatitic zone capable of ductile flow, and separates the GHS into an upper division in which channel flow may have operated in the interval 25–18 Ma, and a lower division characterized by an inverted metamorphic gradient, and by metamorphic ages that decrease downsection and are best explained by sequential accretion of footwall slices between 20 and 6 Ma. An overall model for extrusion of the GHS is still not resolved.

scholarly journals The Timing of Metamorphism, Magmatism, and Cooling in the Zanskar, Garhwal, and Nepal Himalaya

1995 ◽  
Vol 11 ◽  
Author(s):  
M. P. Searle
Keyword(s):  
Hanging Wall ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Eastern Himalaya ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Main Central Thrust ◽  
Southern Tibet ◽  
Peak Metamorphism ◽  
Exhumation Rates

Following India-Asia collision, which is estimated at ca. 54-50 Ma in the Ladakh-southern Tibet area, crustal thickening and timing of peak metamorphism may have been diachronous both along the Himalaya (pre-40 Ma north Pakistan; pre-31 Ma Zanskar; pre-20 Ma east Kashmir, west Garhwal; 11-4 Ma Nanga Parbat) and cross the strike of the High Himalaya, propagating S (in Zanskar SW) with time. Thrusting along the base of the High Himalayan slab (Main Central Thrust active 21-19 Ma) was synchronous with N-S (in Zanskar NE-SW) extension along the top of the slab (South Tibet Detachment Zone). Kyanite and sillimanite gneisses in the footwall formed at pressure of 8-10 kbars and depths of burial of 28-35 km, 30- 21 Ma ago, whereas anchimetamorphic sediments along the hanging wall have never been buried below ca. 5-6 km. Peak temperatures may have reached 750 on the prograde part of the P-T path. Thermobarometers can be used to constrain depths of burial assuming a continental geothermal gradient of 28-30 °C/km and a lithostatic gradient of around 3.5-3.7 km/kbar (or 0.285 kbars/km). Timing of peak metamorphism cannot yet be constrained accurately. However, we can infer cooling histories derived from thermochronometers using radiogenic isotopic systems, and thereby exhumation rates. This paper reviews all the reliable geochronological data and infers cooling histories for the Himalayan zone in Zanskar, Garhwal, and Nepal. Exhumation rates have been far greater in the High Himalayan Zone (1.4-2.1 mm/year) and southern Karakoram (1.2-1.6 mm/year) than along the zone of collision (Indus suture) or along the north Indian plate margin. The High Himalayan leucogranites span 26-14 Ma in the central Himalaya, and anatexis occurred at 21-19 Ma in Zanskar, approximately 30 Ma after the collision. The cooling histories show that significant crustal thickening, widespread metamorphism, erosion and exhumation (and therefore, possibly significant topographic elevation) occurred during the early Miocene along the central and eastern Himalaya, before the strengthening of the Indian monsoon at ca. 8 Ma, before the major change in climate and vegetation, and before the onset of E-W extension on the Tibetan plateau. Exhumation, therefore, was primarily controlled by active thrusts and normal faults, not by external factors such as climate change.

P–T conditions of Grenville-age eclogite facies metamorphism and amphibolite facies retrogression of the Glenelg–Attadale Inlier, NW Scotland

2005 ◽  
Vol 142 (5) ◽  
pp. 605-615 ◽  
Author(s):  
C. D. STOREY ◽  
T. S. BREWER ◽  
S. TEMPERLEY
Keyword(s):  
Tectonic Evolution ◽  
Amphibolite Facies ◽  
Geodynamic Evolution ◽  
Broad Agreement ◽  
Grenville Orogeny ◽  
Basement Rocks ◽  
Facies Metamorphism ◽  
Uplift Rates ◽  
Peak Metamorphism ◽  
Eclogite Facies

Peak and retrograde P–T conditions of Grenville-age eclogites from the Glenelg–Attadale Inlier of the northwest Highlands of Scotland are presented. Peak conditions are estimated as c. 20 kbar and 750–780°C, in broad agreement with previous work. The eclogites subsequently followed a steep decompression path to c. 13 kbar and 650–700°C during amphibolite facies retrogression. Peak eclogite facies metamorphism occurred > 1080 Ma and retrogression at c. 995 Ma, suggesting fairly sluggish uplift rates of < 0.3 km/Ma and cooling rates of < 1.25°C/Ma, when compared with other parts of the Grenville orogeny and/or modern orogens. However, current poor constraints on the timing of peak metamorphism mean that these rates cannot be used to interpret the geodynamic evolution of this part of the orogen. The P–T–t data, together with petrology and the field relationships between the basement rocks of the Glenelg–Attadale Inlier and the overlying Moine Supergroup, mean that it is difficult to support the currently held view that an unconformable relationship exists between the two. It is suggested that more data are required in order to re-interpret the Neoproterozic tectonic evolution of the northwest Highlands of Scotland.

scholarly journals Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway 

2021 ◽  
Author(s):  
Stephan Höpfl ◽  
Jiří Konopásek ◽  
Holger Stünitz ◽  
Steffen G. Bergh
Keyword(s):  
The Arctic ◽  
Low Grade ◽  
Prograde Metamorphism ◽  
Northern Norway ◽  
Metamorphic History ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
History Of ◽  
Peak Metamorphism ◽  
Metamorphic Gradient

&lt;p&gt;Deciphering the structural and metamorphic history of the Balsfjord Series in the Upper Allochthon of the Scandinavian Caledonides in northern Norway&lt;/p&gt;&lt;p&gt;H&amp;#246;pfl Stephan&lt;sup&gt;1&lt;/sup&gt;, Konop&amp;#225;sek Ji&amp;#345;&amp;#237;&lt;sup&gt;1&lt;/sup&gt;, St&amp;#252;nitz Holger&lt;sup&gt;1,2&lt;/sup&gt; Bergh G., Steffen&lt;sup&gt;1&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;UiT Norges arktiske universitet, Institutt for geovitenskap, [email protected]&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt;Department of Geosciences, UiT The Arctic University of Norway, Troms&amp;#248; 9037, Norway&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&lt;/sup&gt;Institut des Sciences de la Terre (ISTO), Universit&amp;#233; d&amp;#8217;Orleans, Orleans 45100, France&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;The Balsfjord Series is located in the central part of Troms&amp;#8211;Finnmark County, northern Norway, and is part of the upper allochthon of the Scandinavian Caledonides. It consists of an Ordovician&amp;#8211;Silurian metsedimentary sequence lying on top of the mostly gabbroic Lyngen Magmatic Complex (LMC). The unit exhibits an inverted metamorphic gradient, where the metamorphic conditions increase from the base to the top, from very low grade in the southeast to medium grade in the west and northwest. The Balsfjord Series is sandwiched between two high-grade units, the Nakkedal + Troms&amp;#248; Nappe Complex in the hanging wall and the Nordmannvik Nappe as the top part of the Reisa Nappe Complex (RNC) in the footwall. The Nakkedal + Troms&amp;#248; Nappe Complex features metamorphic peak ages of ca. 455&amp;#8211;450 Ma and the Nordmannvik Nappe of ca. 430 Ma. The peak metamorphism of the Balsfjord Series has never been dated and the role of the inverted metamorphic gradient is not yet understood. One of the main motivations in this project is to resolve the Caledonian deformation history in the Balsfjord Series, ideally leading to a regional tectonic model explaining the tectonostratigraphic and metamorphic relationships between the abovementioned units.&lt;/p&gt;&lt;p&gt;The Balsfjord Series features two main discernible folding phases. The earlier phase displays tight to isoclinal folds with flat lying axial surfaces parallel to the penetrative foliation. Observed fold axes are parallel with the stretching lineation. These folds are best preserved in the northwestern, upper part of the unit and are syn-metamorphic in certain areas, as they fold original bedding (transposed foliation). A later folding phase is represented by mainly open folds with inclined to steep axial surfaces. Their fold axes are gently plunging with a predominant NE&amp;#8211;SW orientation. We interpret these two folding events to be genetically related but slightly diachronous. The earlier folding phase with flat lying axial surfaces was likely generated during nappe thrusting and peak metamorphism of the Balsfjord Series. The subsequent open folding with inclined to steep axial surfaces is explained as a result of continued shearing and shortening of the weaker metapelitic Balsfjord Series against the more rigid gabbroic part of the LMC during the late stages of the Caledonian nappe thrusting.&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;Observed thrust kinematics and penetrative retrogression at the bottom of the Nakkedal + Troms&amp;#248; Nappe Complex suggest that its final exhumation took place during prograde metamorphism of the underlying Balsfjord Series. The ongoing dating of the prograde metamorphism in the Balsfjord series will provide important information about a possible continuity between the timing of peak metamorphism in the Nakkedal + Troms&amp;#248; Nappe Complex, the Balsfjord series and the underlying RNC.&lt;/p&gt;

scholarly journals The Curinga–Girifalco Line in the framework of the tectonic evolution of the remnant Alpine chain in Calabria (southern Italy)

2020 ◽  
Vol 109 (7) ◽  
pp. 2583-2598
Author(s):  
Vincenzo Festa ◽  
Marianna Cicala ◽  
Fabrizio Tursi
Keyword(s):  
Tectonic Evolution ◽  
Southern Italy ◽  
Hanging Wall ◽  
Shear Zones ◽  
Late Eocene ◽  
Kinematic Data ◽  
South Eastern ◽  
The North ◽  
Subduction System ◽  
North Western

Abstract In the peri-Mediterranean metamorphic belts, the tectonic evolution of the Calabria–Peloritani terrane during the dominant compressive tectonics of the Eocene represents one of the most problematic points in palinspastic restorations. A matter of particular debate is its shortening, which could have occurred during the Alpine or the Apennine subduction. In this regard, a crucial joint is provided by the kinematics of one of the most relevant shear zones such as the Curinga–Girifalco Line, cropping out in central Calabria. This shear zone juxtaposed a nearly complete Hercynian crustal section (i.e. the Sila and Serre Unit) onto the remnants of the Castagna Unit. The data in the available literature on ductile kinematics from the south-eastern branch of the Curinga–Girifalco Line indicate a downward movement of the hanging wall. In the present paper we show new, ductile kinematic data and petrographic evidence from outcrops in the north-western and south-eastern branches of the Curinga–Girifalco Line. Our results highlight the coherent kinematics of the Eocene shortening during the Alpine subduction system, followed by (late Eocene?)Oligocene to early Miocene, dominantly ductile extensional reworking, relating to the Apennines subduction system.

The role of the flexural rotation/rolling hinge model in the tectonic evolution of the Alaşehir graben, western Turkey

2002 ◽  
Vol 139 (1) ◽  
pp. 15-26 ◽  
Author(s):  
GÜROL SEYİTOĞLU ◽  
OKAN TEKELİ ◽  
İBRAHİM ÇEMEN ◽  
ŞEVKET ŞEN ◽  
VEYSEL IŞIK
Keyword(s):  
Tectonic Evolution ◽  
Middle Miocene ◽  
Hanging Wall ◽  
Fault System ◽  
Sequential Process ◽  
Western Turkey ◽  
Extensional Structure ◽  
Hinge Model ◽  
Sedimentary Unit

The Alaşehir graben is a well-defined prominent extensional structure in western Turkey, generally trending E–W and containing four sedimentary units. At the beginning of graben formation during Early–Middle Miocene times, the first fault system was active and responsible for the accumulation of the first and second sedimentary units. In Pliocene times, a second fault system developed in the hanging wall of the first system and a third sedimentary unit was deposited. The recently active third fault system separates older graben fill and a fourth sedimentary unit. Activity on each fault system caused the rotation and uplift of previous systems, similar to the ‘flexural rotation/rolling hinge’ model, but our field observations indicate that the rotated first fault system is also active, allowing exhumation of larger amounts of rock units. This paper documents that graben formation in western Turkey is a sequential process. Its different periods are represented by three fault systems and associated sedimentation. Consequently, recent claims using age data from only the second and/or third sedimentary units to determine the timing of graben formation are misleading.

40Ar/39Ar thermochronometric constraints on the tectonic evolution of the Clachnacudainn complex, southeastern British Columbia

1999 ◽  
Vol 36 (12) ◽  
pp. 1989-2006 ◽  
Author(s):  
Maurice Colpron ◽  
Raymond A Price ◽  
Douglas A Archibald
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Tectonic Evolution ◽  
Thermal Evolution ◽  
Hanging Wall ◽  
Closure Temperature ◽  
Widespread Distribution ◽  
Early Tertiary ◽  
Intrusive Rocks ◽  
Structural Levels

40Ar/39Ar thermochronometry from the Clachnacudainn complex indicates that the thermal evolution of the complex was controlled primarily by the intrusion of granitoid plutons in mid- and Late Cretaceous times. Hornblendes from the eastern part of the complex cooled below their Ar closure temperature (ca. 500°C) shortly after intrusion of the mid-Cretaceous plutons; those from the western part of the complex have latest Cretaceous cooling dates, indicating cooling of these hornblendes after intrusion of the leucogranite plutons at ca. 71 Ma. Micas from the southern Clachnacudainn complex exhibit a pattern of progressive cooling toward lower structural levels, where Late Cretaceous and younger intrusions occur. The occurrence of Late Cretaceous - Paleocene mica cooling dates in both the hanging wall and footwall of the Standfast Creek fault refutes the hypothesis that there has been significant Tertiary extensional exhumation of the Clachnacudainn complex along the Standfast Creek fault. Furthermore, the widespread distribution of Late Cretaceous - Paleocene mica cooling ages suggests that an important volume of Late Cretaceous - early Tertiary intrusive rocks must be present in the subsurface beneath the Clachnacudainn complex.

scholarly journals 3D density modelling of Gemeric granites of the Western Carpathians

2017 ◽  
Vol 68 (3) ◽  
pp. 177-192 ◽  
Author(s):  
Ján Šefara ◽  
Miroslav Bielik ◽  
Jozef Vozár ◽  
Martin Katona ◽  
Viktória Szalaiová ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Lower Boundary ◽  
Western Carpathians ◽  
Mountain Range ◽  
The South ◽  
Geophysical Research ◽  
The North ◽  
Basement Rocks ◽  
Tectonic Contact ◽  
Upper Boundary

Abstract The position of the Gemeric Superunit within the Western Carpathians is unique due to the occurrence of the Lower Palaeozoic basement rocks together with the autochthonous Upper Palaeozoic cover. The Gemeric granites play one of the most important roles in the framework of the tectonic evolution of this mountain range. They can be observed in several small intrusions outcropping in the western and south-eastern parts of the Gemeric Superunit. Moreover, these granites are particularly interesting in terms of their mineralogy, petrology and ages. The comprehensive geological and geophysical research of the Gemeric granites can help us to better understand structures and tectonic evolution of the Western Carpathians. Therefore, a new and original 3D density model of the Gemeric granites was created by using the interactive geophysical program IGMAS. The results show clearly that the Gemeric granites represent the most significant upper crustal anomalous low-density body in the structure of the Gemeric Superunit. Their average thickness varies in the range of 5–8 km. The upper boundary of the Gemeric granites is much more rugged in comparison with the lower boundary. There are areas, where the granite body outcrops and/or is very close to the surface and places in which its upper boundary is deeper (on average 1 km in the north and 4–5 km in the south). While the depth of the lower boundary varies from 5–7 km in the north to 9–10 km in the south. The northern boundary of the Gemeric granites along the tectonic contact with the Rakovec and Klátov Groups (North Gemeric Units) was interpreted as very steep (almost vertical). The results of the 3D modelling show that the whole structure of the Gemeric Unit, not only the Gemeric granite itself, has an Alpine north-vergent nappe structure. Also, the model suggests that the Silicicum–Turnaicum and Meliaticum nappe units have been overthrusted onto the Golčatov Group.

Metamorphosed boninitic basalts, arc tholeiites, and cryptic volcanic stratigraphy from the Elzevir Terrane of the Grenville Province, Calumet mine, Quebec

1992 ◽  
Vol 29 (1) ◽  
pp. 26-34 ◽  
Author(s):  
Patrick J. Williams
Keyword(s):  
Alkaline Earth ◽  
Hanging Wall ◽  
Minor Element ◽  
The Other ◽  
Grenville Province ◽  
Volcanic Stratigraphy ◽  
Element Chemistry ◽  
Discrete Interval ◽  
Peak Metamorphism ◽  
Primary Structures

Amphibolites (hornblende–plagioclase rocks with Tpeak metamorphism = 650–700 °C) are abundant near the old Calumet Zn–Pb–Ag mine and Au prospect 90 km northwest of Ottawa. They lack primary structures and their original petrochemical character is obscured by metamorphism and profound alteration manifested by a variety of phlogopite–biotite-, garnet-, cummingtonite-, gahnite-, clinopyroxene-, carbonate scapolite-, and calcite-bearing assemblages. This alteration has modified the SiO2, alkali, and most alkaline earth distributions. Trace and minor element chemistry demonstrates that the amphibolites are metaigneous and bimodal, with two suites, one derived from differentiated arc tholeiites and the other from relatively undifferentiated rocks having transitional arc basalt – boninite chemistry. The complex rock package enclosing mineralization includes metatholeiites, whereas the boninitic metabasalts occur in a discrete interval in the structural hanging wall of the mineralization. Although these rocks represent a new geochemical assemblage in the Allochthonous Monocyclic Belt (Central Metasedimentary Belt), their implied geotectonic setting is comparable to those previously inferred for several other areas, including that near Montauban, Quebec, where there are very similar styles of mineralization.

Mineralogy, textural characteristics and mineral chemistry of remobilised sulphides and sulphosalts in the Rävliden Norra VMS deposit, Skellefte district, northern Sweden

2020 ◽  
Author(s):  
Jonathan Rincon ◽  
Simon Johansson ◽  
Nils Jansson ◽  
Helen Thomas ◽  
Majka Christiane Kaiser ◽  
...  
Keyword(s):  
Boundary Migration ◽  
Hanging Wall ◽  
Volcanic Rocks ◽  
Mineral Chemistry ◽  
Massive Sulphide ◽  
Ductile Deformation ◽  
Sulphide Mineralization ◽  
Micro Scale ◽  
Metasedimentary Rocks ◽  
Skellefte District

&lt;p&gt;Remobilisation of sulphides in metamorphosed volcanic-hosted massive sulphide deposits has been investigated in many VMS districts with regards to scale, mineral assemblages, texture and relative competence of minerals under certain p-t conditions (Gilligan &amp; Marshall, 1987; Marshall &amp; Gilligan, 1987). Examples of syn-tectonic remobilisation can be found at the R&amp;#228;vliden Norra (RVN) volcanic-hosted massive sulphide in the Skellefte district. At R&amp;#228;vliden, polymetallic sulphide mineralization occurs at the transition from meta-volcanic rocks of the Skellefte group rocks to the overlying Vargfors group, comprising volcaniclastic metasedimentary rocks and graphitic shales. This contribution details features of mesoscale (0.1-50 cm) remobilisation of sulphides, such as sulphide-rich veins, tension gashes, ball-ore, massive sulphides with cataclastic texture, and micro-scale features such as infilling of pressure shadows, displaying evidences of brittle and ductile deformation. Sulphide-rich veins containing sphalerite, galena, and a relative high content of Ag-sulphosalts (e.g. freibergite, pyrargyrite, pyrostilpnite) are hosted in the hanging wall (HW) of the RVN mineralization. Brittle deformation is shown in accessory quartz and calcite as bulging recrystallization, grain boundary migration and deformation lamellae or twinning. Ductile expressions include ball-ore (i.e. &amp;#8220;durchbewegung&amp;#8221;) textures, typically made up of two components, one composed of clasts of graphite shale or tremolite-, actinolite-, talc-altered meta-volcanic rocks and the other comprising a matrix of massive sulphide mineralization. In the massive sulphide matrix of sphalerite, chalcopyrite or pyrrhotite, micro-scale tension gashes and/or pressure shadows occur around clasts infilled by pyrrhotite, chalcopyrite, galena, freibergite, boulangerite, or gudmundite. A similar mineralogy is observed in ore lenses in the ore zone, comprising sphalerite, galena and Ag-Sb-As sulphosalts, hosted structurally above chalcopyrite + pyrrhotite stringer zones in the footwall (FW). Sulphosalts and galena present a high silver content relative to other VMS deposits in the district. This is evidenced by SEM and EMPA analysis in both HW and FW ore lenses. Argentopyrite, sternbergite and stephanite are also locally present in the HW as minor silver species hosted in veins. Inclusions of freibergite in galena contain Ag with average values of 18.4 wt. % in the HW (n=5), 18 wt. % in the massive sphalerite and ball-ore (n= 15), and 20.2 wt. % in the chalcopyrite + pyrrhotite stringer zone (n= 5). Similarly, Pb is 0.2 wt. %, 0.3 wt. %, and 0.4 wt. %, respectively. For sphalerite, Fe is on average 8.0 wt. % (n=3), 7.4 wt. % (n = 11), and 8.3 wt. % (n=3), respectively. Our preliminary results suggest that mineralization in the HW is remobilized from the main ore and textural relationships support a hypothesis that remobilisation involved a relative silver-enrichment in paragenetically later assemblages. At least two stages of deformation in the deposit can be recognized. In the first stage, sphalerite- and chalcopyrite-rich mineralization was deformed along with tremolite and talc to form a S1 foliation. The second stage involved folding of S1, and remobilisation of galena, chalcopyrite and Ag-Sb-As sulphosalts as veins or breccia infill in the HW or filling tension gaps or ball-ore, in the FW. These are often parallel to S2 crenulation or axial planes.&lt;/p&gt;

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