Ultrahigh-pressure metamorphism in western Tianshan, China: Part I. Evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites

2002 ◽  
Vol 87 (7) ◽  
pp. 853-860 ◽  
Author(s):  
Lifei Zhang ◽  
David J. Ellis ◽  
Wenbo Jiang
Keyword(s):  
Ultrahigh Pressure ◽  
Ultrahigh Pressure Metamorphism ◽  
Western Tianshan

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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