scholarly journals Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

2010 ◽  
Vol 105 (5) ◽  
pp. 233-250 ◽  
Author(s):  
Michio TAGIRI ◽  
Shingo TAKIGUCHI ◽  
Chika ISHIDA ◽  
Takaaki NOGUCHI ◽  
Makoto KIMURA ◽  
...  
Keyword(s):  
Tien Shan ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
T Path

The nature and origin of cratons constrained by their surface geology

2021 ◽  
Author(s):  
A.M. Celal Şengör ◽  
Nalan Lom ◽  
Ali Polat
Keyword(s):  
North China ◽  
Plate Boundary ◽  
Crustal Thickening ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Subsequent Removal ◽  
Total Removal ◽  
Common Misconception ◽  
Resistance To Deformation ◽  
Surface Geology

To the memory of Nicholas John (Nick) Archibald (1951−2014), master of cratonic geology. Cratons, defined by their resistance to deformation, are guardians of crustal and lithospheric material over billion-year time scales. Archean and Proterozoic rocks can be found in many places on earth, but not all of them represent cratonic areas. Some of these old terrains, inappropriately termed “cratons” by some, have been parts of mobile belts and have experienced widespread deformations in response to mantle-plume-generated thermal weakening, uplift and consequent extension and/or various plate boundary deformations well into the Phanerozoic. It is a common misconception that cratons consist only of metamorphosed crystalline rocks at their surface, as shown by the indiscriminate designation of them by many as “shields.” Our compilation shows that this conviction is not completely true. Some recent models argue that craton formation results from crustal thickening caused by shortening and subsequent removal of the upper crust by erosion. This process would expose a high-grade metamorphic crust at the surface, but greenschist-grade metamorphic rocks and even unmetamorphosed supracrustal sedimentary rocks are widespread on some cratonic surfaces today, showing that craton formation does not require total removal of the upper crust. Instead, the granulitization of the roots of arcs may have been responsible for weighing down the collided and thickened pieces and keeping their top surfaces usually near sea level. In this study, we review the nature and origin of cratons on four well-studied examples. The Superior Province (the Canadian Shield), the Barberton Mountain (Kaapvaal province, South Africa), and the Yilgarn province (Western Australia) show the diversity of rocks with different origin and metamorphic degree at their surface. These fairly extensive examples are chosen because they are typical. It would have been impractical to review the entire extant cratonic surfaces on earth today. We chose the inappropriately named North China “Craton” to discuss the requirements to be classified as a craton.

DENSITIES OF METAMORPHIC ROCKS

Geophysics ◽  
1971 ◽  
Vol 36 (4) ◽  
pp. 690-694 ◽  
Author(s):  
Scott B. Smithson
Keyword(s):  
Metamorphic Rock ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Rock Density ◽  
Rock Types ◽  
Crystalline Crust ◽  
The Mean ◽  
Few Data

Although metamorphic rocks comprise a large part of the crystalline crust, relatively few data concerning metamorphic rock densities are available. In this paper, we present rock densities from seven different metamorphic terrains. Mean densities for rock types range from [Formula: see text] for biotite granite gneiss to [Formula: see text] for diopside granofels. Mean rock densities for metamorphic terrains range from 2.70 to [Formula: see text]. Rock density may decrease in the lower part of the upper crust. Most mean rock densities for metamorphic terrains fall between 2.70 and [Formula: see text]; the mean density of [Formula: see text] commonly used for the upper crystalline crust is too low.

Viscous relaxation of mineral Inclusions and its implications for reaction overstepping calculations in metamorphic rocks

2020 ◽  
Author(s):  
Evangelos Moulas ◽  
Xin Zhong ◽  
Lucie Tajcmanova
Keyword(s):  
Independent Method ◽  
Metamorphic Rocks ◽  
Additional Method ◽  
Natural Systems ◽  
Long Period ◽  
Mineral Inclusions ◽  
Large Peak ◽  
Viscous Relaxation ◽  
T Path ◽  
Temperature Time

<p>Over the recent years, Raman elastic barometry has been developed as an additional method <span>to calculate</span> metamorphic conditions in natural systems. A major advantage of Raman elastic barometry is that it does not depend on thermodynamic databases and classic geobarometry methods <span>but</span> relies on mechanical calculations. As a consequence, Raman elastic barometry offers an independent method for estimating the pressure conditions <span>that prevailed at the</span> <span>time of entrapment</span> of mineral<span>s</span> du<span>ring</span> growth of their host<span>s</span>.</p><p>The di<span>fference between</span> the pressure calculated <span>using</span> elastic geobarometry and <span>that calculated by phase</span> equilibria methods has recently <span>been employed to</span> <span>estimate</span> the extent of metamorphic reaction overstepping in natural systems. <span>Quantification of</span> the <span>latter however implicitly assumes that the rheology</span> of the inclusion-host system <span>is perfectly</span> elastic. This assumption may no<span>t</span> hold at high temperatures, where viscous creep of minerals takes place.</p><p>The amount of viscous relaxation of <span>a host-inclusion</span> system is a path<span>-</span>dependent quantity which mostly depends on the temperature-time (T-t) path <span>followed</span>. <span>Here</span>, we present examples of visco-elastic relaxation of mineral inclusions and calculate the apparent reaction overstepping which results by assuming that the mechanical system is purely elastic. <span>Our modelling shows</span> that host-inclusion systems <span>that</span> experienced large peak temperatures for long period<span>s</span> of time will retain inclusion residual pressures that <span>cann</span>ot be simply related to the growth of the<span>ir hosts</span> and should <span>therefore not</span> be used for reaction overstepping calculations.</p>

Modelling the thermal perturbation of the continental crust after intraplating of thick granitoid sheets: a comparison with the crustal sections in Calabria (Italy)

2002 ◽  
Vol 139 (6) ◽  
pp. 699-706 ◽  
Author(s):  
A. CAGGIANELLI ◽  
G. PROSSER
Keyword(s):  
Metamorphic Rocks ◽  
Thermal Gradients ◽  
Upper Crust ◽  
Mantle Lithosphere ◽  
Thermal Perturbation ◽  
Magma Intrusion ◽  
Lithosphere Thinning ◽  
Peak Metamorphism ◽  
Granitoid Emplacement ◽  
Lower Crustal

Thick granitoid sheets represent a considerable percentage of Palaeozoic crustal sections exposed in Calabria. High thermal gradients are recorded in upper and lower crustal regional metamorphic rocks lying at the roof and base of the granitoids. Ages of peak metamorphism and emplacement of granitoids are mostly overlapping, suggesting a connection between magma intrusion and low-pressure metamorphism. To analyse this relationship, thermal perturbation following granitoid emplacement has been modelled. The simulation indicates that, in the upper crust, the thermal perturbation is short-lived. In contrast, in the lower crust temperatures greater than 700°C are maintained for 12 Ma, explaining granulite formation, anatexis and the following nearly isobaric cooling. An even longer perturbation can be achieved introducing the effect of mantle lithosphere thinning into the model.

scholarly journals Disjunctive dislocations of the upper crust of Tien Shan

2019 ◽  
Vol 484 (3) ◽  
pp. 316-319
Author(s):  
V. S. Burtman
Keyword(s):  
Active Faults ◽  
Tien Shan ◽  
Late Paleozoic ◽  
Seismic Events ◽  
Upper Crust ◽  
No Formation ◽  
The Rose

This paper analyzes the rose diagrams of the directions of 439 faults of the Variscian province, 476 faults of the Caledonian province, and 603 presently active faults of Tien Shan. It is shown that more than half of the faults of the Caledonian province of Tien Shan are a result of Late Paleozoic orogenesis, which spanned its entire territory. Our data indicate that seismic events of Tien Shan have resulted in no formation of new disjunctive dislocation in many cases exhibiting displacements along Paleozoic faults.

scholarly journals Correlation of the state of crustal stresses, seismicity and landslide activity (Fergana basin, Tien Shan)

2019 ◽  
Vol 10 (4) ◽  
pp. 995-1009
Author(s):  
Z. A. Kalmet’eva ◽  
B. D. Moldobekov ◽  
U. A. Abdybachaev
Keyword(s):  
Internal Structure ◽  
The State ◽  
Tien Shan ◽  
Stress Axis ◽  
Hazard Mapping ◽  
Upper Crust ◽  
Strong Earthquakes ◽  
Landslide Activity ◽  
Crustal Stresses ◽  
Local Stresses

The impacts of seismicity on the landslide activity in Kyrgyzstan have been in the focus of our study since 2010 [Kalmetyeva et al., 2010]. As the study progressed [Kalmetyeva, Moldobekov, 2012, 2013; Kalmetyeva et al., 2013, 2014], the initial problem statement has been revised as follows: do earthquake influence the occurrence of land‐ slides, and, if so, what is the mechanism of this influence. This paper presents the results of detailed analysis of the distribution of earthquakes and landslides in space and time in correlation with focal mechanisms (azimuth and plunge of the principal compression stress axis) of earthquakes occurred in the Fergana basin and its mountainous frame. These are grounds to conclude that the landslide activity is mainly influenced by the response of the internal structure of the upper crust to local stresses. The mechanism of influence of strong earthquakes on the landslide activity is redistribution of local stresses, which results from partial release of regional stresses due to rupturing in the source zones of strong earthquakes. Using this concept of the landslide activity, a methodology of landslide‐hazard mapping is the goal of our future studies aimed at the following: (1) zoning of the study area with respect to the features of the internal structure of the upper crust, (2) geological, geophysical and seismological studies of the state of stresses in the study area, (3) instrumental monitoring of landslides movements in the zones that differ in the structure of the upper crust, and (4) analysis of preparation and consequences of past strong earthquakes that took place in the study area in comparison with the landslide activity.

scholarly journals Petrology of metamorphic rocks from the Atbashy complex, Southern Tien-Shan, Kyrgyzstan

2018 ◽  
Vol 9 (6) ◽  
pp. 1795-1807 ◽  
Author(s):  
Maksatbek Satybaev ◽  
Lin Ding ◽  
Akira Takasu ◽  
Apas Bakirov ◽  
Kadyrbek Sakiev ◽  
...  
Keyword(s):  
Tien Shan ◽  
Metamorphic Rocks

Disjunctive Dislocations of the Upper Crust of Tien Shan

2019 ◽  
Vol 484 (1) ◽  
pp. 37-39 ◽  
Author(s):  
V. S. Burtman
Keyword(s):  
Tien Shan ◽  
Upper Crust

Contact metamorphism of the Tethyan Sedimentary Sequence, Upper Mustang region, west-central Nepal

2020 ◽  
Vol 157 (11) ◽  
pp. 1917-1932 ◽  
Author(s):  
Iva Lihter ◽  
Kyle P. Larson ◽  
Sudip Shrestha ◽  
John M. Cottle ◽  
Alex D. Brubacher
Keyword(s):  
Regional Metamorphism ◽  
Contact Metamorphism ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Sedimentary Sequence ◽  
The North ◽  
Central Nepal ◽  
West Central ◽  
Metamorphic Temperature ◽  
Local Movement

AbstractThe Upper Mustang region of west-central Nepal contains exposures of metamorphosed Tethyan Sedimentary Sequence rocks that have been interpreted to reflect either contact metamorphism related to the nearby Mugu pluton or regional metamorphism associated with the North Himalayan domes. New monazite geochronology results show that the Mugu leucogranite crystallized at c. 21.3 Ma, while the dominant monazite age peaks from the surrounding garnet ± staurolite ± sillimanite schists range between c. 21.7 and 19.4 Ma, generally decreasing in age away from the pluton. Metamorphic temperature estimates based on Ti-in-biotite and garnet–biotite thermometry are highest in the specimens closest to the pluton (648 ± 24°C and 615 ± 25°C, respectively) and lowest in those furthest away (578 ± 24°C and 563 ± 25°C, respectively), while pressure estimates are all within uncertainty of one another, averaging 5.0 ± 0.5 kbar. These results are interpreted to be consistent with contact metamorphism of the rocks in proximity to the Mugu pluton, which was emplaced at c. 18 ± 2 km depth after local movement across the South Tibetan detachment system had ceased. While this new dataset helps to characterize the metamorphic rocks of the Tethyan Sedimentary Sequence and provides new constraints on the thickness of the upper crust, it also emphasizes the importance of careful integration of metamorphic conditions and inferred processes that may affect interpretation of currently proposed Himalayan models.

Sign in / Sign up

Export Citation Format

Share Document