scholarly journals Mechanisms for the formation of spiraled inclusion trails in garnet porphyroblasts from the Precambrian core of the Laramie Mountains, southeastern Wyoming

2013 ◽  
Author(s):  
Mark A. Sutcliffe
Keyword(s):  
Garnet Porphyroblasts ◽  
Laramie Mountains ◽  
Inclusion Trails

scholarly journals Microstructure characteristics of the ganet-bearing schist from Nam Co formation, Son La area, Song Ma suture zone, Northwestern Vietnam

2021 ◽  
Vol 62 (1) ◽  
pp. 64-72
Author(s):  
Hau Vinh Bui ◽  
Hai Thanh Tran ◽  
Thanh Xuan Ngo ◽  
Chi Kim Thi Ngo ◽  
Keyword(s):  
Mineral Assemblage ◽  
Suture Zone ◽  
Nam Co ◽  
Garnet Porphyroblasts ◽  
Microstructure Characteristics ◽  
Inclusion Trails ◽  
Compositional Zonation

The garnet-bearing schists of the Nam Co formation have an identical mineral assemblage consisting of garnet, chlorte, albite, quartz and muscovite, together with accessory apatite, zircon, monazite, xenotime, and ilmenite. An aggregate of muscovite and chlorite defines the major foliations (Sn). Both albite and garnet occur as a porphyroblast, ranging in size 0.2÷1 mm and 0.5÷1.2 mm, respectively. Albite porphyroblasts commonly have the curved to sigmoidal inclusion trails defined by graphitic materials (Sn-1). Garnet porphyroblasts in the sample is generally characterized by paucity of inclusions and retrograde corona of bitotite and chlorite. Garnet also occurs as an inclusion within albite porphyroblast. Porphyroblastic garnet shows the compositional zonation typified by a bell-shaped spessartine profile balanced by increasing almandine from core to rim. Whereas, inclusion garnet is homogeneous compositions with rich in almandin and poor in spessatin, pyrop and grossula. All the above microstructures suggest two deformation and metamorphic stages (M1 and M2) that were affected to politic rocks of the Nam Co formation, Song Ma suture zone.

scholarly journals The formation mechanism of garnet porphyroblast in quartz schist, Namche Barwa, east Himalaya

2013 ◽  
Vol 46 ◽  
Author(s):  
Zhihui Cai ◽  
Hui Cao
Keyword(s):  
Suture Zone ◽  
Electron Backscattered Diffraction ◽  
Garnet Porphyroblasts ◽  
Shear Sense ◽  
The Matrix ◽  
Yarlung Tsangpo ◽  
Namche Barwa ◽  
Growth Zoning ◽  
Inclusion Trails ◽  
Garnet Porphyroblast

The quartz schist in the Indus-Yarlung Tsangpo suture zone, from Namche Barwa, east Himalaya undergone extensive mylonization with well developed, foliation and lineation; its S-C fabric, "σ" and "δ" type porphyroblasts and asymmetrical folds indicate the northwestward normal slip ductile shear deformation. The electron backscattered diffraction (EBSD) data, lattice preferred orientation (LPO) patterns for quartzes in the matrix foliation (or external foliation, S) and inclusion-trails in the rim of the garnet porphyroblasts (S) both show a top-to-NW (normal) shear sense. While LPO patterns for quartzes of the inclusion-trails in the garnet porphyroblast cores (S) show an opposite shear sense (top-to-SE). The garnet compositional zonation indicates a growth zoning characteristic from energy dispersive spectroscopy (EDS) analysis. By connecting the inclusion-trails in garnet cores, an initial foliation trace with asymmetrical fold shape can be obtained. It suggests that these garnet porphyroblasts with snov, ball structure formed on the asymmetrical folds by the rotation of external shear sense rather than the rotation of garnet porphyroblasts. Gamet porphyroblast with snowball structure proposed that the rocks from the lndus Yarlung Tsangpo suture zone west side of the Namche Barwa syntaxis have undergone southeastward thrusting and later followed by northwestward normal slipping.

Eclogite from central Yukon: a record of subduction at the western margin of ancient North America

1983 ◽  
Vol 20 (9) ◽  
pp. 1389-1408 ◽  
Author(s):  
Philippe Erdmer ◽  
Herwart Helmstaedt
Keyword(s):  
North America ◽  
North American ◽  
Stability Field ◽  
Western Margin ◽  
Thrust Sheets ◽  
The Stability ◽  
Basic Igneous Rock ◽  
Inclusion Trails ◽  
Tectonic Boundary ◽  
Host Rocks

Eclogite occurring in central Yukon, at Faro and near Last Peak, as lenses interleaved with muscovite–quartz blastomylonite has the chemical and field characteristics of group C rocks. From sigmoidal inclusion trails in garnet, from geothermometry and geobarometry, and from mineral parageneses, the eclogite is inferred to have a crustal protolith and to have followed a hysteretic, subduction-cycle P–T trajectory. Transformation of basic igneous rock into schist was followed by eclogite metamorphism during which pressure was at least 1000 MPa and temperature was between 600 and 700 °C. Uplifting involved passage through the stability field of glaucophane; the eclogite and its host rocks were then subjected to greenschist fades metamorphism and deformation, with temperature at approximately 400 °C. The rocks were emplaced as thrust sheets against or onto the western North American cratonal margin. The tectonic boundary ranges from nearly vertical, where it is outlined by a zone of steeply dipping mélange, to nearly horizontal beneath klippen of cataclastic rocks that lie on North American miogeoclinal strata. Together with occurrences of eclogite on strike, in Yukon, near Fairbanks (Alaska), and near Pinchi Lake (British Columbia), eclogite at Faro and near Last Peak implies that the Yukon Cataclastic Complex is a deeply eroded collision mélange that borders over 1000 km of the ancient continental margin.

Reversal of the spiral direction of inclusion-trails in paratectonic porphyroblasts

1978 ◽  
Vol 51 (1-2) ◽  
pp. 83-97 ◽  
Author(s):  
S.K. Ghosh ◽  
H. Ramberg
Keyword(s):  
Inclusion Trails
Sign in / Sign up

Export Citation Format

Share Document