Successions of FIAs（foliation inflection/intersection axes preserved within porphyroblasts） provide a relative time scale for deformation and metamorphism.In-situ dating of monazite grains preserved as inclusions wi...Successions of FIAs（foliation inflection/intersection axes preserved within porphyroblasts） provide a relative time scale for deformation and metamorphism.In-situ dating of monazite grains preserved as inclusions within garnet and staurolite porphyroblasts within the foliations defining each FIA from such successions provides a rigorous approach to grouping ages that formed over extended periods of deformation and metamorphism.Matching age and FIA progressions confirms the suitability of this approach plus provides access to lengthy histories that cannot otherwise be determined.Tectonism in the Big Thompson region of the Colorado Rocky Mountains,USA began about a SW-NE trending axis defined by FIA set 1 at around 1761±13 Ma.Subsequent periods of tectonism occurred around 1712±25 and 1672±21 Ma about W-E and NW-SE trending FIAs 2 and 3, respectively.Tectonism in the Balcooma Metamorphic Group NW of Greenvale in NE Queensland, Australia began around 470 Ma with the growth of garnet porphyroblasts about a W-E trending axis defined by FIA set 1.No monazite grains were preserved as inclusions in this mineral phase but they were in subsequently grown staurolite.Tectonism then occurred around 443.2±3.8,424±4 and 408.9±8.9 Ma about NNW-SSE,SSW-NNE and W-E trending FIAs 2,3 and 4,respectively.This test of a FIA based approach to monazite dating in tectonic regimes in different parts of the world and with dramatically different ages suggests it can be used in all orogens containing porphyroblasts preserving inclusion trails.展开更多
Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al...Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al2 SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P-T-t-D path that swaps from clockwise to anticlockwise in the tectono-metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation.展开更多
FIAs have been used extensively for more than a decade to unravel deformation and metamorphic puzzles. Orogenic processes developing early during the history or orogenesis challenge scientists because compositional la...FIAs have been used extensively for more than a decade to unravel deformation and metamorphic puzzles. Orogenic processes developing early during the history or orogenesis challenge scientists because compositional layering in rocks always reactivates where multiple deformations have occurred, leaving little evidence of the history of foliation development preserved in the matrix. The foothills of the Rocky Mountains in Colorado, USA contain a succession of four FIA sets （trends） that would not have been distinguishable if porphyroblasts had not grown during the multiple deformation events that affected these rocks or if they had rotated as these events took place. They reveal that both the partitioning of deformation and the location of isograds changed significantly as the deformation proceeded.展开更多
Although porphyroblast microstructures play an important role in structural and metamorphic studies, there are still controversies in the interpretation. The focus is how porphyroblasts grow during deformation and met...Although porphyroblast microstructures play an important role in structural and metamorphic studies, there are still controversies in the interpretation. The focus is how porphyroblasts grow during deformation and metamorphism. In this paper, we introduce a new approach, the Synchrotron Radiation X-Ray Fluorescence, to a hemi-quantitative interpretation of the growth mode of porphyroblasts. The analysis was done at the Beijing Synchrotron Radiation Facility. The specimens were sampled from metapelite of the Baoyintu Group, northern Urad Middle Banner, Inner Mongolia. The new method is successful for determining the microscopic distribution of trace elements in porphybroblasts. The results support the theory of deformation partition, which has been brought forth by Bell and his colleagues, and demonstrate the existence of porphyroblast growth phases and the growth mode of porphyroblasts by hemi-quantitative mineral chemical analysis. The porphyroblast grows stage by stage in the manner of the distribution of a roseleaf and is controlled by deformation. We call the growth stage of porphyroblast a growth phase.展开更多
FIAS tool has been used extensively by for more than a decade to unravel the deformational puzzle.Orogenic processes have always challenged scientists,as rocks usually reactivate during the repeated cycles of deformat...FIAS tool has been used extensively by for more than a decade to unravel the deformational puzzle.Orogenic processes have always challenged scientists,as rocks usually reactivate during the repeated cycles of deformation and consequently the evidences in the matrix are misleading.This paper presents results obtained fiom Rockies in Colorado USA.A succession of four FIAS as observed in porphyroblasts that could not have been preserved if they had rotated during the展开更多
1 A Method of Determining Early Deformation and Metamorphism History in Orogenic Belts Porphyroblast inclusion trails from orogenic belts represent early-formed foliations composed of oriented metamorphic minerals pre...1 A Method of Determining Early Deformation and Metamorphism History in Orogenic Belts Porphyroblast inclusion trails from orogenic belts represent early-formed foliations composed of oriented metamorphic minerals preserved in rocks in the processes of porphyroblast growth (i.e. progressive and retrogressive metamorphism). Since they were studied in the 1920s, such inclusion trails have been recognized as products of syntectonic rotation due to progressive ductile deformation, which may be used as a known展开更多
文摘Successions of FIAs（foliation inflection/intersection axes preserved within porphyroblasts） provide a relative time scale for deformation and metamorphism.In-situ dating of monazite grains preserved as inclusions within garnet and staurolite porphyroblasts within the foliations defining each FIA from such successions provides a rigorous approach to grouping ages that formed over extended periods of deformation and metamorphism.Matching age and FIA progressions confirms the suitability of this approach plus provides access to lengthy histories that cannot otherwise be determined.Tectonism in the Big Thompson region of the Colorado Rocky Mountains,USA began about a SW-NE trending axis defined by FIA set 1 at around 1761±13 Ma.Subsequent periods of tectonism occurred around 1712±25 and 1672±21 Ma about W-E and NW-SE trending FIAs 2 and 3, respectively.Tectonism in the Balcooma Metamorphic Group NW of Greenvale in NE Queensland, Australia began around 470 Ma with the growth of garnet porphyroblasts about a W-E trending axis defined by FIA set 1.No monazite grains were preserved as inclusions in this mineral phase but they were in subsequently grown staurolite.Tectonism then occurred around 443.2±3.8,424±4 and 408.9±8.9 Ma about NNW-SSE,SSW-NNE and W-E trending FIAs 2,3 and 4,respectively.This test of a FIA based approach to monazite dating in tectonic regimes in different parts of the world and with dramatically different ages suggests it can be used in all orogens containing porphyroblasts preserving inclusion trails.
文摘Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al2 SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P-T-t-D path that swaps from clockwise to anticlockwise in the tectono-metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation.
文摘FIAs have been used extensively for more than a decade to unravel deformation and metamorphic puzzles. Orogenic processes developing early during the history or orogenesis challenge scientists because compositional layering in rocks always reactivates where multiple deformations have occurred, leaving little evidence of the history of foliation development preserved in the matrix. The foothills of the Rocky Mountains in Colorado, USA contain a succession of four FIA sets （trends） that would not have been distinguishable if porphyroblasts had not grown during the multiple deformation events that affected these rocks or if they had rotated as these events took place. They reveal that both the partitioning of deformation and the location of isograds changed significantly as the deformation proceeded.
基金supported by the National Natural Science Foundation of China(grant 40102020).
文摘Although porphyroblast microstructures play an important role in structural and metamorphic studies, there are still controversies in the interpretation. The focus is how porphyroblasts grow during deformation and metamorphism. In this paper, we introduce a new approach, the Synchrotron Radiation X-Ray Fluorescence, to a hemi-quantitative interpretation of the growth mode of porphyroblasts. The analysis was done at the Beijing Synchrotron Radiation Facility. The specimens were sampled from metapelite of the Baoyintu Group, northern Urad Middle Banner, Inner Mongolia. The new method is successful for determining the microscopic distribution of trace elements in porphybroblasts. The results support the theory of deformation partition, which has been brought forth by Bell and his colleagues, and demonstrate the existence of porphyroblast growth phases and the growth mode of porphyroblasts by hemi-quantitative mineral chemical analysis. The porphyroblast grows stage by stage in the manner of the distribution of a roseleaf and is controlled by deformation. We call the growth stage of porphyroblast a growth phase.
文摘FIAS tool has been used extensively by for more than a decade to unravel the deformational puzzle.Orogenic processes have always challenged scientists,as rocks usually reactivate during the repeated cycles of deformation and consequently the evidences in the matrix are misleading.This paper presents results obtained fiom Rockies in Colorado USA.A succession of four FIAS as observed in porphyroblasts that could not have been preserved if they had rotated during the
基金Project supported by the National Natural Science Foundation of China.
文摘1 A Method of Determining Early Deformation and Metamorphism History in Orogenic Belts Porphyroblast inclusion trails from orogenic belts represent early-formed foliations composed of oriented metamorphic minerals preserved in rocks in the processes of porphyroblast growth (i.e. progressive and retrogressive metamorphism). Since they were studied in the 1920s, such inclusion trails have been recognized as products of syntectonic rotation due to progressive ductile deformation, which may be used as a known
