A study on the b0 parameter and crystallinity index of K-white micas from low-grade metapelites in Deokpyeong and Miwon areas, central Ogcheon metamorphic belt, Korea

2000 ◽  
Vol 4 (3) ◽  
pp. 201-209 ◽  
Author(s):  
Hyeoncheol Kim ◽  
Moonsup Cho ◽  
Jung Ho Ahn
Keyword(s):  
Crystallinity Index ◽  
Low Grade ◽  
Metamorphic Belt ◽  
Ogcheon Metamorphic Belt

Metamorphic K-Feldspar in Low-grade Metasediments from the Ogcheon Metamorphic Belt in South Korea

2002 ◽  
Vol 5 (4) ◽  
pp. 849-855 ◽  
Author(s):  
Sung Won Kim ◽  
Tetsumaru Itaya ◽  
Hironobu Hyodo ◽  
Takaaki Matsuda
Keyword(s):  
South Korea ◽  
Low Grade ◽  
Metamorphic Belt ◽  
Ogcheon Metamorphic Belt

Establishing the Origin of Elevated Uranium Concentrations in Groundwater near the Central Ogcheon Metamorphic Belt, Korea

2013 ◽  
Vol 42 (1) ◽  
pp. 118-128 ◽  
Author(s):  
S. H. Moon ◽  
J. Hwang ◽  
J. Y. Lee ◽  
S. P. Hyun ◽  
B. K. Bae ◽  
...  
Keyword(s):  
Metamorphic Belt ◽  
Ogcheon Metamorphic Belt

Low-grade metamorphic belt in Jamaica and its tectonic implications

1976 ◽  
Vol 87 (9) ◽  
pp. 1283 ◽  
Author(s):  
G. DRAPER ◽  
R. R. HARDING ◽  
W. T. HORSFIELD ◽  
A. W. KEMP ◽  
A. E. TRESHAM
Keyword(s):  
Low Grade ◽  
Metamorphic Belt ◽  
Tectonic Implications

scholarly journals Nucleation and Initial Growth of Garnet in Low-Grade Metamorphic Rocks of the Sanbagawa Metamorphic Belt, Kanto Mountains, Japan

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 292 ◽  
Author(s):  
Mutsuko Inui ◽  
Yumenosuke Wakai ◽  
Hiirou Sakuragi
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
Crystal Size ◽  
Crystal Size Distribution ◽  
Garnet Growth ◽  
Low Grade ◽  
Initial Growth ◽  
Metamorphic Belt ◽  
The Core ◽  
Log Normal

The beginning of the recrystallization of minerals within a subducting oceanic plate provides a valuable record of dehydration within the subduction zone. Pelitic schists of the Nagatoro area, Kanto Mountains, Japan, record the initial stages of garnet growth. Consequently, these rocks were studied to analyze garnet nucleation and growth during metamorphism of the Sanbagawa metamorphic belt, one of the world’s most comprehensively studied subduction complexes. The garnet grains are small, euhedral, and occur only within micaceous lamellae that define the schistosity. Crystal size distribution analyses revealed most of the garnet grains follow the log-normal size distribution, indicating that they formed in the same event. A few exceptionally large garnet grains exist that do not seem to follow the log-normal distribution. The latter garnet grains contain a rounded fragmental area with a different chemical composition inside the core. It is possible that detrital fragments of garnet contribute to the irregular crystal size distribution of garnet in the studied area. Many of the smaller (log-normal) garnet grains have relatively large, homogeneous Mn-rich cores. The lack of chemical zoning within the garnet cores suggests that they grew under constant pressure and temperature in response to overstepping of the garnet-in reaction. The chemical composition changes very sharply at the boundary between the core and the surrounding mantle. The size of the Mn-rich core is different from sample to sample, suggesting that the nucleation was controlled by the local chemical condition of each sample.

scholarly journals Transmission electron microscopy study of very low-grade metamorphic evolution in Neoproterozoic pelites of the Puncoviscana formation (Cordillera Oriental, NW Argentina)

Clay Minerals ◽  
2003 ◽  
Vol 38 (4) ◽  
pp. 459-481 ◽  
Author(s):  
M. Do Campo ◽  
F. Nieto
Keyword(s):  
Electron Microscopy ◽  
High Pressure ◽  
Long Range ◽  
Regional Metamorphism ◽  
Analytical Electron Microscopy ◽  
Crystallinity Index ◽  
Microscopy Study ◽  
Electron Microscopy Study ◽  
Low Grade ◽  
Wide Range

AbstractThe Puncoviscana Formation, largely cropping out in NW Argentina, is mainly composed of a pelite-greywacke turbidite sequence affected by incipient regional metamorphism and polyphase deformation. Metapelites, composed mainly of quartz, albite, dioctahedral mica and chlorite, were sampled in the Lules-Puncoviscana and Choromoro belts. Lattice-fringe images, selected area electron diffraction and analytical electron microscopy analyses, coupled with previous data from white mica crystallinity index, indicate a state of reaction progress for Puncoviscana slates consistent with medium anchizone- to epizone-grade metamorphism. The 2Mpolytype prevails in dioctahedral micas, coexisting in a few cases with the 1Mdpolytype as a consequence of lack of equilibrium. The 2Mpolytype coexists with 3Tin two slates and long-range four-layer and ten-layer stacking sequences were identified in another sample. Samples with 3Tand long-range stacking sequences presentbvalues characteristic of intermediate–high pressure metamorphism and ordered chlorites (1L, 2L, 3Land 7L) prevail.Based on the Si contents of dioctahedral micas and considering peak temperatures of ∼350 –400ºC, pressures from 5 kbar and 5 –7 kbar were derived for metapelites from the Lules- Puncoviscana and Choromoro belts, respectively. These values agree with facies series derived from thebvalues. Micas with a wide range of phengitic substitution, as evidenced by Fe + Mg and Si contents, coexist. These variations could not arise from the disturbing effect of detrital white K-mica because TEM evidence indicates that they are absent or represent <10% of the mica population. Thus, compositional variations suggest that dioctahedral micas of individual slates crystallized at different pressure conditions in response to theP-Tpath of the metamorphism. Moreover, in several biotite-free slates the illite crystallinity (IC) values lead to an underestimation of the metamorphic grade attained in these rocks.The coexistence of IC corresponding to anchizone and the occurrence of biotite in some slates and felsic metavolcanic rocks intercalated in the Puncoviscana metasediments are interpreted to be the result of a metamorphic path including a relatively high-pressure/ low-temperature (HP/LT) event, followed by a lower-pressure overprint possibly at higher temperatures than the HP/LTevent. Small micas formed during the high-pressure stage would prevail in the <2 mm fraction, producing anchizone IC.

Sign in / Sign up

Export Citation Format

Share Document