Lower crustal granulite xenoliths from the Pannonian Basin, Hungary, Part 2: Sr–Nd–Pb–Hf and O isotope evidence for formation of continental lower crust by tectonic emplacement of oceanic crust

2003 ◽  
Vol 144 (6) ◽  
pp. 671-683 ◽  
Author(s):  
Gábor Dobosi ◽  
Pamela D. Kempton ◽  
Hilary Downes ◽  
Antal Embey-Isztin ◽  
Matthew Thirlwall ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Lower Crust ◽  
Pannonian Basin ◽  
Continental Lower Crust ◽  
Isotope Evidence ◽  
O Isotope ◽  
Lower Crustal ◽  
Granulite Xenoliths

scholarly journals The Role of Lower Crustal Rheology in Lithospheric Delamination During Orogeny

2021 ◽  
Vol 9 ◽  
Author(s):  
Lin Chen
Keyword(s):  
Lower Crust ◽  
Numerical Models ◽  
The Tibetan Plateau ◽  
Mantle Lithosphere ◽  
Laboratory Studies ◽  
Surface Uplift ◽  
Continental Lower Crust ◽  
Lower Crustal ◽  
Flow Laws

The continental lower crust is an important composition- and strength-jump layer in the lithosphere. Laboratory studies show its strength varies greatly due to a wide variety of composition. How the lower crust rheology influences the collisional orogeny remains poorly understood. Here I investigate the role of the lower crust rheology in the evolution of an orogen subject to horizontal shortening using 2D numerical models. A range of lower crustal flow laws from laboratory studies are tested to examine their effects on the styles of the accommodation of convergence. Three distinct styles are observed: 1) downwelling and subsequent delamination of orogen lithosphere mantle as a coherent slab; 2) localized thickening of orogen lithosphere; and 3) underthrusting of peripheral strong lithospheres below the orogen. Delamination occurs only if the orogen lower crust rheology is represented by the weak end-member of flow laws. The delamination is followed by partial melting of the lower crust and punctuated surface uplift confined to the orogen central region. For a moderately or extremely strong orogen lower crust, topography highs only develop on both sides of the orogen. In the Tibetan plateau, the crust has been doubly thickened but the underlying mantle lithosphere is highly heterogeneous. I suggest that the subvertical high-velocity mantle structures, as observed in southern and western Tibet, may exemplify localized delamination of the mantle lithosphere due to rheological weakening of the Tibetan lower crust.

scholarly journals Subhorizontal fabric in exhumed continental lower crust and implications for lower crustal flow: Athabasca granulite terrane, western Canadian Shield

Tectonics ◽  
2010 ◽  
Vol 29 (2) ◽  
pp. n/a-n/a ◽  
Author(s):  
Gregory Dumond ◽  
Philippe Goncalves ◽  
Michael L. Williams ◽  
Michael J. Jercinovic
Keyword(s):  
Lower Crust ◽  
Canadian Shield ◽  
Continental Lower Crust ◽  
Lower Crustal Flow ◽  
Lower Crustal

scholarly journals In situ lower crustal accretion by melt sill injection revealed by seismic layering

2021 ◽  
Author(s):  
Peng Guo ◽  
Satish Singh ◽  
Venkata Vaddineni ◽  
Ingo Grevemeyer ◽  
Erdinc Saygin
Keyword(s):  
Oceanic Crust ◽  
Lower Crust ◽  
Velocity Variation ◽  
Main Process ◽  
Upper Crust ◽  
Crustal Accretion ◽  
Slow Spreading ◽  
Lower Crustal ◽  
Lower Oceanic Crust

Abstract Oceanic crust is formed at mid-ocean spreading centres by a combination of magmatic, tectonic and hydrothermal processes. The crust formed by magmatic process consists of an upper crust generally composed of basaltic dikes and lava flows and a lower crust presumed to mainly contain homogeneous gabbro whereas that by tectonic process can be very heterogeneous and may even contain mantle rocks. Although the formation and evolution of the upper crust are well known from geophysical and drilling results, those for the lower crust remain a matter of debate. Using a full waveform inversion method applied to wide-angle seismic data, here we report the presence of layering in the lower oceanic crust formed at the slow spreading Mid-Atlantic Ridge, ~7-12 Ma in age, revealing that the lower crust is formed mainly by in situ cooling and crystallisation of melt sills at different depths by the injection of magma from the mantle. These layers are 400-600 m thick with alternate high and low velocities, with ± 100-200 m/s velocity variation, and cover over a million-year old crust, suggesting that the crustal accretion by melt sill intrusions beneath the ridge axis is a stable process. We also find that the upper crust is ~400 m thinner than that from conventional travel-time analysis. Taken together, these discoveries suggest that the magmatism plays more important roles in the crustal accretion process at slow spreading ridges than previously realised, and that in-situ lower crustal accretion is the main process for the formation of lower oceanic crust.

Lower crustal granulite xenoliths from the Pannonian Basin, Hungary. Part 1: mineral chemistry, thermobarometry and petrology

2003 ◽  
Vol 144 (6) ◽  
pp. 652-670 ◽  
Author(s):  
Antal Embey-Isztin ◽  
Hilary Downes ◽  
Pamela D. Kempton ◽  
Gábor Dobosi ◽  
Matthew Thirlwall
Keyword(s):  
Pannonian Basin ◽  
Mineral Chemistry ◽  
Lower Crustal ◽  
Granulite Xenoliths

Mafic granulites and clinopyroxenite xenoliths from the Transdanubian Volcanic Region (Hungary): implications for the deep structure of the Pannonian Basin

1990 ◽  
Vol 54 (376) ◽  
pp. 463-483 ◽  
Author(s):  
A. Embey-Isztin ◽  
H. G. Scharbert ◽  
H. Dietrich ◽  
H. Poultidis
Keyword(s):  
Upper Mantle ◽  
Pannonian Basin ◽  
Granulite Facies ◽  
Mantle Xenoliths ◽  
Geochemical Data ◽  
Moderate Pressure ◽  
Spinel Lherzolites ◽  
Volcanic Region ◽  
Lower Crustal ◽  
Granulite Xenoliths

AbstractThe Transdanubian Volcanic Region (TVR) is composed mainly of Pliocene alkali basalts, basanites, olivine basalts and olivine tholeiites, as well as rare nephelinites. The partial melting and genesis of alkali basaltic liquids is a consequence of an upwelling of the upper mantle which also caused thinning of the lithosphere and recent sinking of the Pannonian Basin.Four different types of lower crustal and upper-mantle xenoliths are found within the TVR: garnet-free and garnet-bearing granulites, clinopyroxenites and spinel lherzolites. We present mineralogical and geochemical data on granulite facies and clinopyroxenite xenoliths from three localities in the Hungarian part of the TVR (Bondoróhegy, Szentbékálla and Szigliget). It is concluded that, whilst the protoliths of the granulite facies xenoliths were tholeiitic igneous rocks and could be part of an ancient crust, the clinopyroxenite xenoliths represent recent underplating and may have formed from an alkali basaltic liquid similar to the host lava. Planar contact relations between clinopyroxenites and spinel lherzolites as observed in composite xenoliths, as well as high Al-contents in clinopyroxenes, point to a high-pressure genesis in the upper mantle for these rocks. In contrast, geobarometrical estimates yielded only a moderate pressure range characteristic of lower crustal levels for the garnet-free granulite xenoliths (7–9 kbar). Nevertheless, two-pyroxene geothermometry yielded high temperatures of equilibration (>900°C) for these xenoliths, probably caused by advective heat transfer connected with underplating and in agreement with the high present-day geothermal gradient of this region. In the Central Range localities only garnet-free granulite xenoliths occur, whereas at the border of the TVR both garnet-free and garnet-bearing granulite facies nodules are found. It is possible that the incoming of garnet is retarded by higher temperatures in the lower crust below the Central Range.It is also suggested that the difference in seismically measured crustal thickness between the Central Range and adjacent basin areas may be connected with different thermal conditions below these regions and that the seismically defined Moho and the petrological Moho do not necessarily coincide.

Structural evolution in the Moine of northwest Scotland: a Caledonian linked thrust system?

1986 ◽  
Vol 123 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Robert W. H. Butler
Keyword(s):  
Cross Sections ◽  
Lower Crust ◽  
Structural Evolution ◽  
Amphibolite Facies ◽  
Metamorphic Basement ◽  
Thrust System ◽  
Lower Crustal

AbstractA model is proposed whereby the Caledonian metamorphic basement-cover complex of northwest Scotland (the Moine) is considered as a linked thrust system. This system lies between the Moine thrust at its base and the Naver–Sgurr Beag slide at its top. Ductile fold and thrust zones, which developed at mid crustal levels at metamorphic grades from greenschist to amphibolite facies, are interpreted as decoupling from a detachment presently situated at relatively shallow depths. This model is illustrated by two preliminary balanced cross-sections. These imply shortening across the northwest Scottish Caledonides in excess of 130 km and probably over 200 km. When these structures are restored onto a crustal template a considerable quantity of lower crust is found to be required at depth. The most likely location for the lower crustal wedge is beneath the Grampian Highlands.

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