Introduction with review of the definition, distribution and geotectonic significance of ultrahigh pressure metamorphism

2015 ◽  
pp. 3-9 ◽  
Author(s):  
Dennis A. Carswell ◽  
Roberto Compagnoni
Keyword(s):  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism

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.

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.

Fluids in coesite-bearing rocks of the Tso Morari Complex, NW Himalaya: evidence for entrapment during peak metamorphism and subsequent uplift

2009 ◽  
Vol 146 (6) ◽  
pp. 876-889 ◽  
Author(s):  
BARUN K. MUKHERJEE ◽  
HIMANSHU K. SACHAN
Keyword(s):  
High Salinity ◽  
Granulite Facies ◽  
Ultrahigh Pressure ◽  
Nw Himalaya ◽  
Rock Interaction ◽  
Low Salinity ◽  
Ultrahigh Pressure Metamorphism ◽  
Indian Lithosphere ◽  
External Sources ◽  
Tso Morari

AbstractFluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phases present during ultrahigh-pressure metamorphism. The subduction-related coesite-bearing eclogites of the Tso Morari Complex, Himalaya, contain five major types of fluids identified by microthermometry and Raman spectroscopy. These are: (1) high-salinity brine, (2) N2, (3) CH4, (4) CO2and (5) low-salinity aqueous fluids. These fluids were trapped during both deep subduction and exhumation processes. The coesite-bearing rocks are inferred to have been buried to a depth of >120 km, where they experienced ultrahigh-pressure metamorphism. The fluid–rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica–carbonate assemblages in eclogite. High salinity brine, N2and CH4inclusions are remnants of prograde and peak metamorphic fluids, whereas CO2and low-salinity aqueous fluids appear to have been trapped late, during uplift. The high-salinity brine was possibly derived from subducted ancient metasedimentary rocks, whereas the N2and CH4fluids were likely generated through chemical breakdown of NH3-bearing K minerals and graphite. Alternatively, CH4might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks. High density CO2is associated with matrix minerals formed during granulite-facies overprinting of the ultrahigh-pressure eclogite. During retrogression to amphibolite-facies conditions, low-salinity fluids were introduced from external sources, probably the enclosing gneisses. This source enhances salinity differences as compared to primary saline inclusions. The subducting Indian lithosphere produced brines prior to achieving maximal depths of >120 km, where fluids were instead dominated by gaseous phases. Subsequently, the Indian lithosphere released CO2-rich fluids during fast exhumation and was then infiltrated by the low-salinity aqueous fluids near the surface through external sources. Elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions.

Introduction to geodynamics for high- and ultrahigh-pressure metamorphism

Island Arc ◽  
1998 ◽  
Vol 7 (1-2) ◽  
pp. 1-5 ◽  
Author(s):  
J. G. Liou ◽  
S. M aruyama ◽  
B. C ong
Keyword(s):  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism
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