Faulting feldspar

So far, only normal diffraction (with sharp maxima at the points of reciprocal lattice) has been mentioned. Investigation of background scattering can provide extended information on various kinds of crystal defects (well beyond stacking faults and the like) as has been demonstrated e.g. on metal and feldspar structures. 

APBs are essentially stacking faults and have been observed by TEM in a number of minerals that undergo order-disorder transformations. Examples include omphacite (Carpenter 1979 Champness 1973 Phakey and Ghose 1973), pigeonite (Bailey et al. 1970 Carpenter 1979 Christie et al. 1971 Fujino, Furo, and Momoi 1988), calcic plagioclase feldspars (Christie et al. 1971 Czank et al. 1973 Czank, Schulz, and Laves 1972 Heuer et al. 1972 McLaren 1973 McLaren and Marshall 1974 Muller et al. 1973 Muller, Wenk, and Thomas 1972 Nord, Heuer, and Lally 1974 ... 

The faulted, non-carbonate cemented sandstones which were sampled from Haltenbanken and Tampen Spur, show clear evidence of diagenetic modifications after the deformation had occurred. Feldspar dissolution, illite precipitation and stylolitization are examples of such diagenetic processes. The pre- and post-faulting diagenetic reactions have been demonstrated to be a useful tool for the purpose of dating fault movements relative to basin subsidence (Sverdrup and Bjprlykke, 1992 Saigal et al., 1995). 

The patterns of diagenetic evolution recognized in this study allow discussion of the conditions for optimum porosity preservation and/or enhancement in the Serraria reservoirs. The best reservoirs of the unit occur in the Caioba area of the distal domain, where porosity was enhanced by dissolution of detrital feldspars and dolomite cement during telogenetic influx of meteoric waters. Similar conditions are expected for other structural blocks of the basin affected by post-rift uplift and erosion, or blocks bounded by major fault systems in which the Serraria Formation was relatively close to the... 

Figure 6. Mid infrared spectra of faulted mordenite (sample No. 2) crystals (A) (Na,K,TOA)-Mordenite, (B) (Na.K)-Mordenite, (C) NH -Mordenite and (D) H-Mordenite. This sample contains small amounts of feldspar impurities.

The rocks consist of quartz-feldspar schist and phyllite derived from sedimentary protoliths of the Robertson Bay Group, from the Molar Formation (Sledgers Group), and from metavolcanic rocks of mafic composition. In contrast to the rocks of the Robertson Bay Group, the Millen Schist was multiply deformed (Bradshaw et al. 1982 Jordan et al. 1984 Findlay 1986) presumably during tectonic activity along the boundary fault. 

X-ray diffraction (XRD) analysis reveals that the fault gouge is mainly composed of calcite, quartz, feldspar, and a few clay minerals (Figure 3, Table 2). Clay mineral is dominated by kaolinite. Quartz is about ten times more than that in the host rock. 

The material source of the watershed fault zone is both from host rock and overlying siliceous rocks. The fault zone is an open system with strong chemical weathering, and alkaline condition. Calcium in limestone is leached, the cohesive force of host rock is reduced and formed smectite. It is easy for feldspar transforms to kaolinite under alkaline condition during faulting. Hence, more geochemistry needed to study in the future, to establish qualitative model between chemical compositions and strength of fault rocks. 

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