Flow of Devonian anatectic crust in the accretionary Altai Orogenic Belt, central Asia: Insights into horizontal and vertical magma transfer

2021 ◽  
Author(s):  
Sheng Wang ◽  
Yingde Jiang ◽  
Roberto Weinberg ◽  
Karel Schulmann ◽  
Jian Zhang ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Crustal Thickening ◽  
Drainage Network ◽  
Vertical Flow ◽  
Granite Emplacement ◽  
Deep Crust ◽  
Gradual Evolution ◽  
Mass Redistribution ◽  
Granite Complex ◽  
Crustal Differentiation

Flow of partially molten crust is a key contributor to mass and heat redistribution within orogenic systems, however, this process has not yet been fully understood in accretionary orogens. This issue is addressed in a Devonian migmatite-granite complex from the Chinese Altai through structural, petrological, and geochronological investigations presented in this study. The migmatite-granite complex records a gradual evolution from metatexite, diatexite to granite and preserves a record of two main Devonian phases of deformation designated D1 and D2. The D1 phase was subdivided into an early crustal thickening episode (D1B) and a later extensional episode (D1M) followed by D2 upright folding. The D1M episode is associated with anatexis in the deep crust. Vertical shortening, associated with D1M, gave rise to the segregation of melt and formation of a sub-horizontal layering of stromatic metatexite. This fabric was reworked by the D2 deformation associated with the migration of anatectic magma in the cores of F2 antiforms. Geochronological investigations combined with petro-structural analysis reveal that: (1) D1M partial melting started probably at 420−410 Ma and formed sub-horizontal stromatic metatexites at ∼30 km depth; (2) The anatectic magma accumulated and migrated when a drainage network developed, as attested by the pervasive formation of massive diatexite migmatites, at 410−400 Ma; (3) Soon after, massive flow of the partially molten crust from orogenic lower to orogenic upper crustal levels, assisted by the interplay between D2 upright folding and magma diapirism, led to migmatite-granite emplacement in the cores of regional F2 antiforms that lasted until at least 390 Ma; (4) a terminal stage was manifested by the emplacement of 370−360 Ma granite dykes into the surrounding metamorphic envelope. We propose that Devonian anatexis assisted by deformation governed first the horizontal and then the vertical flow of partially molten orogenic lower crust, which drove crustal flow, mass redistribution, and crustal differentiation in the accretionary system of the Chinese Altai.

scholarly journals Orogenic plateau margin and the coexistence of HP and HT metamorphic rocks

2020 ◽  
Author(s):  
Christian Teyssier ◽  
Donna L Whitney ◽  
Patrice F Rey ◽  
Françoise Roger
Keyword(s):  
Strike Slip ◽  
Crustal Thickening ◽  
Metamorphic Rocks ◽  
Gravitational Potential Energy ◽  
Slip Systems ◽  
Massif Central ◽  
Deep Crust ◽  
Hp Metamorphism ◽  
Orogenic Plateau ◽  
Shallow Crust

<p>Mature orogenic plateaux grow in response to the lateral redistribution of plateau material, driven by gravitational potential energy, from the thick plateau crust toward the thinner foreland crust. Folding and thrusting in the shallow crust as well as flow of weak deep crust toward the foreland result in plateau growth. The balance between plateau growth processes, including gravitational collapse of the orogenic crust, and the resistance to plateau propagation controls the position of plateau margins. Toward the end of orogenic plateau development, plateau margins are the loci of steep topographic gradients, where erosional processes can be aggressive. The margins also represent the transition between thick crust and thin/weak lithosphere beneath the plateau, and thinner crust and strong/thick lithosphere below the foreland.</p><p>The juxtaposition of thick and thin lithosphere favors strain localization along plateau margins, where thick lithosphere may partially subduct, or where strike-slip systems, such as the Altyn Tagh region of northern Tibet, develop. In either case, it is likely that the deep, flowing, partially molten crust will sample and entrain high-P (HP) metamorphic rocks such as granulite and eclogite. In the case of lithospheric strike-slip systems, crustal thickening in transpressional domains may lead to HP metamorphism, and crustal thinning in transtensional domains may lead to rapid exhumation of the deep crust, particularly where pull-apart structures in the shallow-crust allow the upward flow and emplacement of migmatite domes. For example, the Montagne Noire dome (French Massif Central) formed at the southern margin of the Variscan orogen in the late Carboniferous (315-295 Ma). This dome is filled with Variscan migmatite containing eclogite fragments that were sampled near Moho depths and entrained in the flowing partially molten crust; eclogitization and early crystallization of melt were coeval. In this example, the redistribution of mass and heat across the plateau margin, including the exhumation of near-Moho rocks, stabilized the crust and marked the end of orogeny.</p>

scholarly journals Mesozoic Crustal Thickening of the Longmenshan Belt (NE Tibet, China) by Imbrication of Basement Slices: Insights From Structural Analysis, Petrofabric and Magnetic Fabric Studies, and Gravity Modeling

Tectonics ◽  
2017 ◽  
Vol 36 (12) ◽  
pp. 3110-3134 ◽  
Author(s):  
Zhenhua Xue ◽  
Guillaume Martelet ◽  
Wei Lin ◽  
Michel Faure ◽  
Yan Chen ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Magnetic Fabric ◽  
Crustal Thickening ◽  
Gravity Modeling

scholarly journals On the Relation of Net Balance, Ice Flow, and Surface Lowering of Lewis Glacier, Mount Kenya, East Africa, 1982–86

1987 ◽  
Vol 33 (115) ◽  
pp. 315-318 ◽  
Author(s):  
Stefan Hastenrath
Keyword(s):  
Vertical Flow ◽  
Glacier Surface ◽  
Ice Flow ◽  
Ice Surface ◽  
Mass Redistribution ◽  
Observation Program ◽  
Glacier Ice ◽  
Long Term Observation

AbstractThe second 4 year phase of a long-term observation program on Lewis Glacier, Mount Kenya, was completed in March 1986. As for the 1978–82 interval, net-balance results at a stake network and repeated mapping of the ice-surface topography allowed assessment of the mass economy by both “glaciological” and “geodetic” methods.The general findings from the 1978–82 observations are confirmed: the vertical flow component is directed downward in the upper glacier, and upward in the lower glacier; surface lowering and negative net balance increase down-glacier; ice flow mitigates surface lowering by the negative net balance in the lower glacier, but enhances it in the upper glacier. However, the major difference between the 1982–86 and 1978–82 periods is the progressive slow-down of ice flow. This entails a reduction of mass redistribution, in consequence of which the surface lowering becomes increasingly dependent on thein-situnet balance. It is expected that this circumstance will simplify any inference on future glacier behavior.

Emplacement, rapid burial, and exhumation of 90-Ma plutons in southeastern Alaska

2004 ◽  
Vol 41 (1) ◽  
pp. 87-102 ◽  
Author(s):  
Glen R Himmelberg ◽  
Peter J Haeussler ◽  
David A Brew
Keyword(s):  
Structural Analysis ◽  
Country Rock ◽  
Crustal Thickening ◽  
Thermal Decay ◽  
Pluton Emplacement ◽  
The North ◽  
Regional Deformation ◽  
Mineral Assemblages ◽  
Accreted Terranes ◽  
Gravina Belt

In southeastern Alaska, granodiorite–tonalite plutons of the Admiralty–Revillagigedo belt intruded the Jurassic–Cretaceous Gravina belt along the eastern side of the Alexander terrane around 90 Ma. These plutons postdate some deformation related to a major contractional event between the previously amalgamated Wrangellia and Alexander terranes and the previously accreted terranes of the North American margin. We studied the aureole mineral assemblages of these plutons near Petersburg, Alaska, determined pressure and temperature of equilibration, and examined structures that developed within and adjacent to these plutons. Parallelism of magmatic and submagmatic fabrics with fabrics in the country rock indicates synchroneity of pluton emplacement with regional deformation and suggests that magma transport to higher crustal levels was assisted by regional deformation. Replacement of andalusite by kyanite or sillimanite indicates crustal thickening soon after pluton emplacement. Regional structural analysis indicates the crustal thickening was accomplished by thrust burial. Thermobarometric analyses indicate the aureoles reached near-peak temperatures of 525 to 635 °C at pressures of 570 to 630 MPa. Consideration of the rate of thermal decay of the aureoles suggests that burial was rapid and occurred at rates around 5 to 8 mm/year. Structural observations indicate there was contractional deformation before, during, and after emplacement of the 90-Ma plutons. Initial exhumation of the Admiralty–Revillagigedo belt in the Petersburg area may have occurred along a thrust west of the pluton belt within the Gravina belt.

Structural history and granite emplacement in the Rottenstone Domain during closure of the Trans-Hudson Orogen, Davin Lake, northern Saskatchewan

2009 ◽  
Vol 46 (4) ◽  
pp. 287-306 ◽  
Author(s):  
Nicholas G. Culshaw ◽  
D. Barrie Clarke
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Northwestern Part ◽  
Granite Emplacement ◽  
Oblique Convergence ◽  
Structural History ◽  
Northern Saskatchewan ◽  
Thrust Sheets ◽  
Granitoid Rocks

The Rottenstone Domain at Davin Lake northern Saskatchewan, exhibits structural and granite-emplacement evidence for crustal thickening, and possible Himalayan-style extrusion, overprinted by transpressional strain increasing toward the contact with the Wathaman Batholith. Three discrete Rottenstone subdomains parallel the regional strike of the Trans-Hudson Orogen: (i) the southeast Rottenstone subdomain (SERSD) with gently northwest-dipping migmatitic straight gneiss (S1) and white granitoid rocks with pinch-and-swell structures parallel to the straight gneissosity; (ii) the central Rottenstone subdomain (CRSD), which partly preserves the same NW-dipping fabric (S1) but is overprinted at its margins by tight upright F2 folds and includes a stockwork of pink monzogranitic aplites and pegmatites; and (iii) the northwest Rottenstone subdomain (NWRSD) in which the F2 folds are generally tighter and penetrative and its network of narrow white granitoid rocks is deformed and transposed by the F2 folds; but in the northwestern part, a wide, syn-D2 complex of schlieric white tonalitic and diatexite sheets strikes parallel the orogen. The SERSD D1 straight zone may be a remnant of Himalayan-type extrusion zone although it could be the lowest member of a stack of ductile thrust sheets. The CRSD stockwork may represent fluid-assisted magma injection into extensional fractures above the postulated extrusion zone. The increasing transpressional strain northwestward expressed primarily by the F2 folds in CRSD and NWRSD defines the Davin Lake shear zone, into which the NWRSD granitoid dyke complex represents syntectonic magma injection. Both the postulated extrusion and transpression are related to oblique convergence of the Archean Sask craton with the Archean Rae–Hearne craton.

scholarly journals Thrusting, exhumation, and basin fill on the western margin of the South China block during the India-Asia collision

2020 ◽  
Vol 133 (1-2) ◽  
pp. 74-90 ◽  
Author(s):  
Kai Cao ◽  
Philippe Hervé Leloup ◽  
Guocan Wang ◽  
Wei Liu ◽  
Gweltaz Mahéo ◽  
...  
Keyword(s):  
Structural Analysis ◽  
South China ◽  
Hanging Wall ◽  
Crustal Thickening ◽  
South China Block ◽  
Thrust Belt ◽  
Western Margin ◽  
Crustal Shortening ◽  
Fold And Thrust Belt ◽  
Early Cenozoic

Abstract The pattern and timing of deformation in southeast Tibet resulting from the early stages of the India-Asia collision are crucial factors to understand the growth of the Tibetan Plateau, but they remain poorly constrained. Detailed field mapping, structural analysis, and geochronological and thermochronological data along a 120 km section of the Ludian-Zhonghejiang fold-and-thrust belt bounding the Jianchuan basin in western Yunnan, China, document the early Cenozoic tectonic evolution of the conjunction between the Lanping-Simao and South China blocks. The study area is cut by two major southwest-dipping brittle faults, named the Ludian-Zhonghejiang fault and the Tongdian fault from east to west. Numerous kinematic indicators and the juxtaposition of Triassic metasedimentary rocks on top of Paleocene strata indicate thrusting along the Ludian-Zhonghejiang fault. Similarly, structural analysis shows that the Tongdian fault is a reverse fault. Between these structures, fault-bounded Permian–Triassic and Paleocene rocks are strongly deformed by nearly vertical and upright southwest-vergent folds with axes that trend nearly parallel to the traces of the main faults. Zircon and apatite (U-Th)/He and apatite fission-track data from a Triassic pluton with zircon U-Pb ages of 237–225 Ma in the hanging wall of the Ludian-Zhonghejiang fault, assisted by inverse modeling, reveal two episodes of accelerated cooling during 125–110 Ma and 50–39 Ma. The Cretaceous cooling event was probably related to crustal thickening during the collision between the Lhasa and Qiangtang terranes. The accelerated exhumation during 50–39 Ma is interpreted to record the life span of the fold-and-thrust belt. This timing is corroborated by the intrusive relationship of Eocene magmas of ca. 36–35 Ma zircon U-Pb age into the fold-and-thrust belt. Early Cenozoic activity of the deformation system controlled deposition of alluvial-fan and braided-river sediments in the Jianchuan basin, as evidenced by eastward and northeastward paleoflows and terrestrial clasts derived from the hanging wall of the Ludian-Zhonghejiang thrust. Since 39 Ma, decreasing cooling rates likely reflect cessation of activity on the fold-and-thrust belt. Early Cenozoic compressive deformation on the western margin of the South China block together with geological records of contraction in central, northern, and eastern Tibet document Eocene upper-crustal shortening located in the Himalaya, Qiangtang terrane, and northern plateau margins together with contractional basin development in the intervening Lhasa, Songpan-Garze, and Kunlun terranes, coeval with or shortly after the onset of the India-Asia collision. This suggests that moderate crustal shortening affected a large part of Tibet in a spaced way, contrary to models of homogeneous crustal thickening soon after the collision, and prior to the main crustal thickening, propagating progressively from south to north. This complex deformation pattern illustrates the complexity of Asian crustal rheology, which contrasts with assumptions in existing geodynamic models.

scholarly journals On the Relation of Net Balance, Ice Flow, and Surface Lowering of Lewis Glacier, Mount Kenya, East Africa, 1982–86

1987 ◽  
Vol 33 (115) ◽  
pp. 315-318 ◽  
Author(s):  
Stefan Hastenrath
Keyword(s):  
Vertical Flow ◽  
Glacier Surface ◽  
Ice Flow ◽  
Ice Surface ◽  
Mass Redistribution ◽  
Observation Program ◽  
Glacier Ice ◽  
Long Term Observation

AbstractThe second 4 year phase of a long-term observation program on Lewis Glacier, Mount Kenya, was completed in March 1986. As for the 1978–82 interval, net-balance results at a stake network and repeated mapping of the ice-surface topography allowed assessment of the mass economy by both “glaciological” and “geodetic” methods.The general findings from the 1978–82 observations are confirmed: the vertical flow component is directed downward in the upper glacier, and upward in the lower glacier; surface lowering and negative net balance increase down-glacier; ice flow mitigates surface lowering by the negative net balance in the lower glacier, but enhances it in the upper glacier. However, the major difference between the 1982–86 and 1978–82 periods is the progressive slow-down of ice flow. This entails a reduction of mass redistribution, in consequence of which the surface lowering becomes increasingly dependent on the in-situ net balance. It is expected that this circumstance will simplify any inference on future glacier behavior.

scholarly journals Partial Melting and Crustal Deformation during the Early Paleozoic Wuyi–Yunkai Orogeny: Insights from Zircon U-Pb Geochronology and Structural Analysis of the Fuhuling Migmatites in the Yunkai Region, South China

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 621
Author(s):  
Zhang ◽  
Liu ◽  
Yakymchuk ◽  
Sa ◽  
Zeng ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Partial Melting ◽  
South China ◽  
Structural Characteristics ◽  
Early Paleozoic ◽  
Deep Crust ◽  
Crucial Information ◽  
The Absolute ◽  
Lower Temperature

：Migmatites record crucial information about the rheology and tectonothermal evolutionof the deep crust during orogenesis. In the Wuyi–Yunkai orogen in South China, migmatites at Fuhuling record Early Paleozoic high temperatures and associated partial melting. However, the absolute timing and implications for the rheology of the deep crust during orogenesis are poorly constrained. In this contribution, we used spatial analysis of migmatitic leucosomes, structural analysis, and U-Pb geochronology of zircon to elucidate the absolute timing of crustal partial melting, the degree of partial melting, and the role of partial melting on the rheology of the crust during the Wuyi–Yunkai orogeny. Partial melting of the Fuhuling migmatites occurred at c. 440 Ma during Early Paleozoic Wuyi–Yunkai orogenesis. Subsequent lower temperature metamorphism associated with Indosinian movement that caused minor zircon recrystallization was temporally associated with the crystallization of nearby biotite monzogranites, but it did not influence the morphology of the Fuhuling migmatites. The migmatites preserve a morphological transition from metatexite to diatexite with an increasing proportion of leucosome. This transition preserves different structural characteristics that represent the response of the solid framework and melt network to variable melt fractions during partial melting. The large proportion of in situ or in source leucosome in the Fuhuling migmatites suggests that it was a melt-rich crustal horizon during orogenesis, and that a substantial proportion of anatectic melt was retained in the deep crust. The rheological transition documented in the Fuhuling migmatites was caused by changes in the melt fraction, and it is an analogue for the rheological transition characteristics of melt-rich crustal horizons in the Yunkai region during Early Paleozoic Wuyi–Yunkai orogenesis and subsequent orogenic collapse.

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