scholarly journals The contribution of elastic geothermobarometry to the debate on HP vs. UHP metamorphism

2021 ◽  
Author(s):  
Mattia Gilio ◽  
Marco Scambelluri ◽  
Ross J. Angel ◽  
Matteo Alvaro
Keyword(s):  
Uhp Metamorphism

The first evidence of UHP metamorphism in the Polar Urals (Russia)

2017 ◽  
Vol 476 (2) ◽  
pp. 1222-1225 ◽  
Author(s):  
A. Yu. Selyatitskii ◽  
K. V. Kulikova
Keyword(s):  
Uhp Metamorphism ◽  
Polar Urals ◽  
The Polar Urals

Evidence for ultrahigh-pressure metamorphism discovered in the Appalachian orogen

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 947-951
Author(s):  
Joseph P. Gonzalez ◽  
Suzanne L. Baldwin ◽  
Jay B. Thomas ◽  
William O. Nachlas ◽  
Paul G. Fitzgerald
Keyword(s):  
Direct Evidence ◽  
Ultrahigh Pressure ◽  
Garnet Growth ◽  
Uhp Metamorphism ◽  
Ultrahigh Pressure Metamorphism ◽  
Iapetus Ocean ◽  
Taconic Orogeny ◽  
Growth History ◽  
Appalachian Orogen

Abstract The Appalachian orogen has long been enigmatic because, compared to other parts of the Paleozoic orogens that formed following the subduction of the Iapetus Ocean, direct evidence for ultrahigh-pressure (UHP) metamorphism has never been found. We report the first discovery of coesite in the Appalachian orogen in a metapelite from the mid-Ordovician (Taconic orogeny) Tillotson Peak Complex in Vermont (USA). Relict coesite occurs within a bimineralic SiO2 inclusion in garnet. In situ elastic barometry and trace-element thermometry allow reconstruction of the garnet growth history during prograde metamorphism. The data are interpreted to indicate garnet nucleation and crystallization during blueschist- to eclogite-facies subduction zone metamorphism, followed by garnet rim growth at UHP conditions of > 28 kbar and > 530 ° C. Results provide the first direct evidence that rocks of the Appalachian orogen underwent UHP metamorphism to depths of > 75 km and warrant future studies that constrain the extent of UHP metamorphism.

Microdiamond on Åreskutan confirms regional UHP metamorphism in the Seve Nappe Complex of the Scandinavian Caledonides

2017 ◽  
Vol 35 (5) ◽  
pp. 541-564 ◽  
Author(s):  
I. Klonowska ◽  
M. Janák ◽  
J. Majka ◽  
I. Petrík ◽  
N. Froitzheim ◽  
...  
Keyword(s):  
Uhp Metamorphism ◽  
Scandinavian Caledonides ◽  
Nappe Complex ◽  
Seve Nappe Complex

Triassic to Early Jurassic (c . 200 Ma) UHP metamorphism in the Central Rhodopes: evidence from U-Pb-Th dating of monazite in diamond-bearing gneiss from Chepelare (Bulgaria)

2016 ◽  
Vol 34 (3) ◽  
pp. 265-291 ◽  
Author(s):  
I. Petrík ◽  
M. Janák ◽  
N. Froitzheim ◽  
N. Georgiev ◽  
K. Yoshida ◽  
...  
Keyword(s):  
Early Jurassic ◽  
Uhp Metamorphism

Changing exhumation potential of (U)HP eclogite through geological time

2020 ◽  
Author(s):  
Richard Palin
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Global Network ◽  
Ultrahigh Pressure ◽  
Compositional Variation ◽  
Uhp Metamorphism ◽  
Geological Time ◽  
Geological Record ◽  
Mafic Intrusions ◽  
Archean Crust

<p>Ultrahigh-pressure (UHP) metamorphism is defined by achieving P–T conditions sufficient to transform quartz to coesite (~26–28 kbar at ~500–900 °C), which occurs at ~90-100 km depth within the Earth under lithostatic conditions. Thus, the occurrence of UHP metamorphism is often taken as being a diagnostic indicator of subduction having operated in the geological record, and hence plate tectonics. Yet, the oldest such coesite-bearing rocks belong to the Pan-African belt in northern Mali, and formed at 620 Ma, although there exist multiple lines of evidence to show that a global network of subduction had been operative on Earth for billions of years beforehand. Why, then, are these key geodynamic indicators missing from the majority of the rock record? Here, I show how secular cooling of the Earth's mantle since the Mesoarchean (c. 3.2 Ga) has affected the exhumation potential of UHP (and HP) eclogite through time due to time-dependent compositional variation of both oceanic and continental crust. Petrological modeling of density changes during metamorphism of Archean, Proterozoic, and Phanerozoic composite continental terranes shows that more mafic Archean crust reaches a point-of-no-return during transport into the mantle at shallower depths than less MgO-rich modern-day crust, regardless of whether this occurs via subduction of stagnant lid-like vertical 'drip' tectonics. Thus, while Alpine- and Himalayan-type (U)HP orogenic eclogites represented by metamorphosed mafic intrusions into continental crust may readily have formed during the Precambrian, they would have lacked the buoyancy required for exhumation and preservation in the geological record.</p>

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