Pb−Sr−Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira Massif, Western Alps, Italy-II: what is the age of the ultrahigh-pressure metamorphism?

1991 ◽  
Vol 108 (1-2) ◽  
pp. 22-33 ◽  
Author(s):  
G. R. Tilton ◽  
W. Schreyer ◽  
H. -P. Schertl
Keyword(s):  
Western Alps ◽  
Ultrahigh Pressure ◽  
Crustal Rocks ◽  
Ultrahigh Pressure Metamorphism

Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

2021 ◽  
Author(s):  
Lorenzo G. Candioti ◽  
Joshua D. Vaughan-Hammon ◽  
Thibault Duretz ◽  
Stefan M. Schmalholz
Keyword(s):  
Numerical Models ◽  
A Priori ◽  
Western Alps ◽  
Ultrahigh Pressure ◽  
Plate Motion ◽  
Crustal Rock ◽  
Plate Boundaries ◽  
Crustal Rocks ◽  
Natural Data ◽  
The Alps

<p>Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.</p><p> </p><p>Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called mélanges. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.</p><p> </p><p>Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.</p><p> </p><p>The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.</p>

scholarly journals Ultrahigh-pressure metamorphism of crustal rocks from the Rhodope metamorphic province: evidence from coesite, diamond and majoritic garnet in eclogites and metapelites

2001 ◽  
Vol 34 (3) ◽  
pp. 931
Author(s):  
E. MPOSKOS ◽  
D. KOSTOPOULOS
Keyword(s):  
Ultrahigh Pressure ◽  
Majoritic Garnet ◽  
Crustal Rocks ◽  
Laser Raman ◽  
The North ◽  
Ultrahigh Pressure Metamorphism ◽  
The Individual ◽  
Indicator Minerals ◽  
First Time

The Rhodope Metamorphic Province represents an area of continental collision between the Balkan domain to the north and the Pangaeon domain to the south. Today, exposed astride the suture zone are Palaeozoic and Mesozoic protoliths of both continental and oceanic provenance that underwent Alpine deformation and metamorphism in a subduction zone setting. From petrostructural studies the picture that emerged is one of a central, structurally lower, marble-dominated terrain (i.e. a metamorphic core complex), and a surrounding, structurally higher, gneiss-dominated terrain. Here, for the first time, we report the presence of ultrahigh-pressure metamorphic indicator minerals such as coesite, diamond and Si-Ti-Na-P-rich (i.e. majoritic) garnet in amphibolitized eclogites and garnet-biotitekyanite gneisses from localities scattered throughout the structurally higher terrain. These findings, corroborated by optical microscopy, electron microprobe analyses and in situ laser Raman microspectroscopy, suggest that the protoliths of these rocks were dragged down to mantle depths exceeding 200 km. The individual pressure-temperature paths published before for various subunits of the structurally higher terrain should henceforth be regarded as peculiarities of the exhumation path followed by the subunits.

35 Ma old ultrahigh-pressure metamorphism and evidence for very rapid exhumation in the Dora Maira Massif, Western Alps

Lithos ◽  
1997 ◽  
Vol 41 (1-3) ◽  
pp. 5-24 ◽  
Author(s):  
D. Gebauer ◽  
H.-P. Schertl ◽  
M. Brix ◽  
W. Schreyer
Keyword(s):  
Western Alps ◽  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism

A New Occurrence of Ultrahigh-Pressure Metamorphism, Central Macedonia, Northern Greece: Evidence from Graphitized Diamonds?

2000 ◽  
Vol 42 (6) ◽  
pp. 545-554 ◽  
Author(s):  
Dimitris K. Kostopoulos ◽  
Nikos M. Ioannidis ◽  
Spyros A. Sklavounos
Keyword(s):  
Ultrahigh Pressure ◽  
Northern Greece ◽  
Ultrahigh Pressure Metamorphism

scholarly journals OH defects in coesite and stishovite during ultrahigh-pressure metamorphism of continental crust

2018 ◽  
Vol 46 (1) ◽  
pp. 77-89 ◽  
Author(s):  
C. Frigo ◽  
R. Stalder ◽  
T. Ludwig
Keyword(s):  
Continental Crust ◽  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism ◽  
Oh Defects

Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China

2003 ◽  
Vol 21 (6) ◽  
pp. 539-550 ◽  
Author(s):  
R. Y. Zhang ◽  
J. G. Liou ◽  
J. S. Yang ◽  
K. Ye
Keyword(s):  
Eastern China ◽  
Garnet Peridotite ◽  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism ◽  
Sulu Terrane

Ar/Ar geochronology of ultrahigh-pressure metamorphism in central China

Tectonics ◽  
1995 ◽  
Vol 14 (4) ◽  
pp. 994-1006 ◽  
Author(s):  
Bradley R. Hacker ◽  
Qingchen Wang
Keyword(s):  
Central China ◽  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism ◽  
Ar Geochronology

Evolution of geodynamics since the Archean: Significant change at the dawn of the Phanerozoic

Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 488-492 ◽  
Author(s):  
M. Brown ◽  
C.L. Kirkland ◽  
T.E. Johnson
Keyword(s):  
Ultrahigh Pressure ◽  
Secular Change ◽  
Metamorphic Rocks ◽  
Data Sets ◽  
Ultrahigh Pressure Metamorphism ◽  
Slab Breakoff ◽  
Wide Range ◽  
O Isotope ◽  
Global Data Sets ◽  
Global Data

Abstract A time-series analysis of thermobaric ratios (temperature/pressure [T/P]) for Paleoarchean to Cenozoic metamorphic rocks identified significant shifts in mean T/P that may be related to secular change in the geodynamics on Earth. Thermobaric ratios showed significant (>95% confidence) change points at 1910, 902, 540, and 515 Ma, recording drops in mean T/P, and at 1830, 604, and 525 Ma, recording rises in mean T/P. Highest mean T/P occurred during the Mesoproterozoic, and lowest mean T/P occurred from the Cambrian to the Oligocene. Correlated changes were seen between T/P and global data sets of time-constrained hafnium (Hf) and oxygen (O) isotope compositions in zircon. The range of correlated variation in T/P, Hf, and O was larger during the formation of Rodinia than Columbia. Large changes and a wide range for these variables continued through the Phanerozoic, during which a statistically significant 83 m.y. frequency of T/P excursions recorded the high tempo of orogenic activity associated with the separation, migration, and accretion of continental terranes during the formation of Pangea. Since the early Tonian, the decreasing mean T/P of metamorphism, widespread appearance of blueschist and ultrahigh-pressure metamorphism, and wide fluctuations in Hf and O isotope compositions document a change to the modern plate-tectonic regime, characterized by widespread continental subduction and deeper slab breakoff than in the Proterozoic.

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