Tectonometamorphic evolution of the Atbashi high-Punits (Kyrgyz CAOB, Tien Shan): Implications for the closure of the Turkestan Ocean and continental subduction-exhumation of the South Kazakh continental margin

2018 ◽  
Vol 36 (8) ◽  
pp. 959-985 ◽  
Author(s):  
Chloé Loury ◽  
Yann Rolland ◽  
Stéphane Guillot ◽  
Pierre Lanari ◽  
Clément Ganino ◽  
...  
Keyword(s):  
Continental Margin ◽  
Tien Shan ◽  
The South ◽  
Continental Subduction

On the application of alkenone- and GDGT-based temperature proxies in the south-eastern Brazilian continental margin

2018 ◽  
Vol 126 ◽  
pp. 43-56 ◽  
Author(s):  
Milena Ceccopieri ◽  
Renato S. Carreira ◽  
Angela L.R. Wagener ◽  
Jens H. Hefter ◽  
Gesine Mollenhauer
Keyword(s):  
Continental Margin ◽  
The South ◽  
South Eastern

Anorogenic magmatism and the Grenvillian Orogeny

1989 ◽  
Vol 26 (3) ◽  
pp. 479-489 ◽  
Author(s):  
Brian F. Windley
Keyword(s):  
United States ◽  
South America ◽  
Continental Margin ◽  
South Atlantic ◽  
Island Arc ◽  
The South ◽  
The West ◽  
Continental Block ◽  
Grenvillian Orogeny ◽  
Alkaline Complexes

The Grenvillian Orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500–1300 Ma in the form of rhyolites, epizonal granites, anorthosites, gabbros, alkaline complexes, and basic dykes. An analogue for the mid-Proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the Hoggar, Niger, and Nigeria, which contain anorthosites, gabbros, and peralkaline granites and were generated in a Cambrian to Jurassic rift that farther south led to the formation of the South Atlantic. An analogue for the 1 × 106 km2 area of 1500–1350 Ma rhyolites (and associated epizonal granites) that underlie the mid-continental United States is provided by the 1.7 × 106 km2 area of Jurassic Tobifera rhyolites in Argentina, which were extruded on the stretched continental margin of South America immediately preceding the opening of the South Atlantic. The mid-Proterozoic complexes were intruded close to the continental margin of the Grenvillian ocean and were commonly superimposed by the craton-directed thrusts that characterized the final stages of the Grenvillian Orogeny. The bulk of the Keweenawan rift and associated anorogenic magmatism formed about 1100 Ma at the same time as the Ottawan Orogeny in Ontario, which probably resulted from the collision of the island arc of the Central Metasedimentary Belt attached to the continental block in the east with the continental block to the west. The most appropriate modern equivalent would be the Rhine Graben, which formed at the same time as the main Alpine compression.

Preliminary analysis of the spectral content of P and S waves from local earthquakes in the Garm, Tadjikistan region

1978 ◽  
Vol 68 (4) ◽  
pp. 949-971
Author(s):  
T. G. Rautian ◽  
V. I. Khalturin ◽  
V. G. Martynov ◽  
P. Molnar
Keyword(s):  
Seismic Moment ◽  
Tien Shan ◽  
Wave Spectra ◽  
The South ◽  
Spectral Content ◽  
Preliminary Results ◽  
Local Earthquakes ◽  
Calculated Stress ◽  
Stress Drops ◽  
Lower Frequencies

abstract This paper reports preliminary results of an analysis of the spectral content of seismic waves from over 1,000 local earthquakes in the Garm, Tadjikistan region. Very low values of Q (∼100) were obtained for the Mesozoic and Cenozoic sedimentary rocks of the Peter I Range compared with those in the crystalline rock of the South Tien Shan (Q ≳ 500). For events with the same low frequency spectra, earthquakes in the South Tien Shan are recorded with more energy at higher frequencies than earthquakes in the Peter I Range, at least in part, because of the greater attenuation of the sedimentary rock in the latter region. There is a wide variety of spectra radiated by earthquakes throughout the Garm region, but a marked difference between spectra radiated by earthquakes from these two regions is not apparent. Nevertheless although calculated stress drops of earthquakes appear to vary considerably throughout the region, there appears to be a dependence on the type of rock in which the earthquakes occurred. The variation in calculated stress drops, however, is greater within either region than between the two. For most regions and for most of the range of seismic moments studied the shape of the spectrum is relatively independent of seismic moment. Consequently, calculated stress drops increase with seismic moment, with the functional dependence varying from region to region. For the largest events, the spectrum shifts to lower frequencies with increasing moment and stress drops become essentially independent of moment. Preliminary results suggest that the stress drops are not detectably different for earthquakes with thrust or normal faulting fault-plane solutions. A limited amount of data are consistent with a change in spectral content and stress drop of earthquakes in the vicinity of and before stronger earthquakes but a clear, consistent pattern is not yet evident. Toward high frequencies, S-wave spectra both begin to decrease at lower frequencies and seem to decrease more rapidly than P-wave spectra, in contrast with predictions of published dislocation models of earthquakes.

Ocean Subduction Dynamics in the Alps

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 9-16
Author(s):  
Philippe Agard ◽  
Mark R. Handy
Keyword(s):  
Transition Zone ◽  
Continental Margin ◽  
North Atlantic ◽  
Subduction Zones ◽  
Mantle Transition Zone ◽  
Continental Subduction ◽  
The Alps ◽  
Slow Spreading ◽  
Selective Preservation

The Alps preserve abundant oceanic blueschists and eclogites that exemplify the selective preservation of fragments of relatively short-lived, small, slow-spreading North Atlantic–type ocean basins whose subducting slabs reach down to the Mantle Transition Zone at most. Whereas no subducted fragments were returned during the first half of the subduction history, those exhumed afterwards experienced conditions typical of mature subduction zones worldwide. Sedimentary-dominated units were under-plated intermittently, mostly at ~30–40 km depth. Some mafic–ultramafic-dominated units formed close to the continent were subducted to ~80 km and offscraped from the slab only a few million years before continental subduction. Spatiotemporal contrasts in burial and preservation of the fragments reveal how along-strike segmentation of the continental margin affects ocean subduction dynamics.

The petrochemistry of the Lower Proterozoic metamorphic rocks from the Dabieshan-Lianyungang area, the southeastern margin of the North China Platform

1991 ◽  
Vol 55 (379) ◽  
pp. 263-276 ◽  
Author(s):  
Sang Longkang
Keyword(s):  
Continental Margin ◽  
North China ◽  
Active Continental Margin ◽  
The South ◽  
North China Platform ◽  
The North ◽  
Lower Proterozoic ◽  
Southeastern Margin ◽  
Tectonic Settings ◽  
North China Plate

AbstractBased on geological studies, 141 rock analyses and 5 trace element analyses of metabasites, the present paper deals with the rock association, chemical features, protolith formation and the original tectonic settings upwards through the Lower Proterozoic metamorphic strata in the Dabieshan-Lianyungang area, in the south-east of the North China Platform. The results of the study indicate that the lower and middle parts of the metamorphic strata comprise terrigenous clastics, phosphoritic and aluminous sedimentary formations which formed under stable continental margin conditions. In the middle-upper part a calc-alkaline volcano-sedimentary formation under the active continental margin was developed. The Lower Proterozoic meta-strata of sedimentary-volcanosedimentary origin from bottom upwards suggest that the tectonic evolution of the south-eastern margin of the North China Platform is a process from stabilization to mobilization. This process suggests a northward subduction of the Yangtze Plate under the North China Plate during the later part of the early Proterozoic.

Evolution of the South-Iberian paleomargin: From hyperextension to continental subduction

2020 ◽  
Vol 138 ◽  
pp. 104122 ◽  
Author(s):  
Antonio Pedrera ◽  
Ana Ruiz-Constán ◽  
Jesús García-Senz ◽  
Antonio Azor ◽  
Carlos Marín-Lechado ◽  
...  
Keyword(s):  
The South ◽  
Continental Subduction
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