Multiple Foliations Defined by Different Sillimanite Crystal Habits, Partial Melting and the Late Metamorphic Development of the Cannington Ag-Pb-Zn Deposit, Northeast Australia     

Hyeong Soo Kim  Tim H. Bell   《Gondwana Research》2005,8(4):493-509

A succession of foliations defined by different sillimanite-bearing structural fabrics suggests that the macroscopic, isoclinal synform that dominates the geometry of the Cannington Ag-Pb-Zn deposit, northwest Queensland, Australia formed during D₂. The five foliations in this succession, S₁ to S₅, are defined by aligned sillimanite with habits ranging from individual crystals in S₁ through S₄ to clusters of fibrolite in S₅ in both the matrix and as inclusion trails within garnet and gahnite (Zn-rich spinel) porphyroblasts. S₁, S₃ and S₅ formed as sub-horizontal foliations, whereas S_1a, S₂ and S₄ formed sub-vertically. Foliation intersection/inflexion axes (FIAs) within garnet and gahnite porphyroblasts preserve a succession of trends that shifts from W-E to N-S. This succession indicates that this region experienced N-S followed by W-E bulk crustal shortening. N-S shortening occurred during D₁and D_1a, and W-E shortening occurred from D₂ to D₅. Prismatic and rhombic sillimanite produced during D₁-D₄ accompanied prograde metamorphism to ca. 634 62°C and 4.8 1.3 kbar. The coexistence of fibrous, prismatic and rhombic sillimanite resulted from post peak metamorphic reactivation of the early foliations during D₅. The synformal D₂ fold was intensified during D₄ by W-E bulk shortening. Local partial melting occurred after D₁ in the appropriate bulk rock compositions, based on calculation of P-T pseudosections in the chemical systems KFMASH, KFMASHTO, NCKFMASH and MnNCKFMASH. Zn mineralization related to gahnite growth occurred during D₃ through D₄, and was redistributed by partial melting into structural and rheological sites during D₄ and D₅shearing.  相似文献   

Survival Conditions of Folding in Different Depth During Orogenesis-Deformation in Texas Creek and Chester Dome,USA   总被引：1，自引：0，他引：1  

CAO Hui  XU Cuiping 《《地质学报》英文版》2014,88(1):103-112

A succession of 5 FIA trends（foliation intersection or inflection axes in porphyroblasts） preserved in high temperature-low pressure regime PreCambrian rocks in the Texas Creek, Arkansas River region reflected by the fold axial plane traces and schistosity data in this region. Similar fold axial plane trace data measured in Palaeozoic rocks in Chester Dome, Vermont, which is high temperature to medium pressure regime, only preserve the effects of the youngest FIAs of the all 5 FIA sets that obtained in this region. The other three FIA sets have no equivalent fold axial planes. This difference from shallow to deeper orogenic regimes reflects decreasing competency at greater pressure with collapse and unfolding of earlier formed folds. The greater overlying load of rocks has tended to flatten all but the very largest early-formed structures, preserving only those folds that were more recently developed.  相似文献   

SYN-AND POST-THICKENING EXTENSIONS IN THE YULONG—HABA MOUNTAIN RANGE IN SOUTHWEST CHINA     

Zhang J.S.  Han Z.J. 《地学前缘》2000,(Z1)

SYN-AND POST-THICKENING EXTENSIONS IN THE YULONG—HABA MOUNTAIN RANGE IN SOUTHWEST CHINA  相似文献