Clay Minerals: Paleogeographic and Diagenetic Aspects

Abstract

of the Academy of Sciences of the USSR, Vladivostok X-ray DiffractionWe obtained X-ray diffraction patterns of oriented specimens using a DRON-1,5 X-ray diffractometer with CUKQ, emission and a Ni-filter. Slit openings of 0.5, 1,1, and 0.5 mm were used.Each sample was dried in the air, treated with ethylene glycol, and heated at 500 to 550°C for 1 to 2 hours. Clay fractions were treated with 10 per cent HC1 at 90 to 100°C for 1 hour for identification of kaolinite and dioctahedral and trioctahedral minerals. Expanding vermiculite was determined by Mg-ethylene glycol tests. Some samples were K-saturated to test the nature of expanding minerals after Weaver's method (Weaver, 1958). The ratio of 17-Å reflection shoulders (i.e., the Z-coefficient) was calculated. Electron Diffraction Analysis and Electron MicroscopyWe obtained electron diffraction patterns using an electronograph EG-100M with accelerating voltage 100 kv. These patterns were used for determining illite polytypes, the degree of structural ordering of montmorillonite, and the ^-parameter (accuracy ± 0.01 Å). Electron microdiffraction made it possible to recognize acicular crystals and amorphous phases.

Record of forearc devolatilization in low‐T, high‐P/T metasedimentary suites: Significance for models of convergent margin chemical cycling

“…Sedimentary clay mineral composition is more difficult to determine, as the clays are both finer‐grained and more reactive than the other clasts. However, clay‐mineral analysis of other accretionary wedge and trench sediments suggests that these rocks probably contained a variety of sedimentary clay minerals such as chlorite, illite, smectite, kaolinite and montmorilinite, and some mixed‐layer clays [i.e., Karnosov et al , 1977; Karpoff , 1992; Underwood and Deng , 1997] (ODP‐Leg 185). Clay minerals have variable, but high, water contents; ideal kaolinite (Al 2 Si 2 O 5 (OH) 4 ) contains 14 wt.% H 2 O and most illites contain ∼10 wt.% H 2 O (for comparison, white‐micas, stabilized at higher grades by the breakdown of clays, contain ∼5 wt.% H 2 O).…”

“…Sedimentary clay mineral composition is more difficult to determine, as the clays are both finer-grained and more reactive than the other clasts. However, clay-mineral analysis of other accretionary wedge and trench sediments suggests that these rocks probably contained a variety of sedimentary clay minerals such as chlorite, illite, smectite, kaolinite and montmorilinite, and some mixed-layer clays [i.e., Karnosov et al, 1977;Karpoff, 1992;Underwood and Deng, 1997] [25] As these sediments progressed downward in the subduction zone, they underwent mineralogical changes that must have resulted in significant chemical redistribution, at least at the local scale. Even the lowest-grade rocks of the Coastal Belt differ from likely sedimentary protoliths in several important ways.…”

Mineralogy of Sediments from the Middle America Trench (Guatemala Transect)

“…In the late Miocene, Site 495 approached the terrigenous hemipelagic sedimentation area; at this time hemipelagic mud began to accumulate over the pelagic section. A marked increase in terrigenous and volcaniclastic supply with corresponding development of hemipelagic sedimentation was noted in the late Miocene in many other regions around the Pacific (Kurnosov et al, 1980).…”

Methods

“…Previous expeditions that used these standard mixtures sampled sediments from the Nankai Trough accretionary complex. The dominant minerals are broadly similar between the southern (e.g., Steurer and Underwood, 2003;Guo and Underwood, 2012) and northern (Mann and Müller, 1980;Kurnosov et al, 1980) sections of the Japan margin. Therefore, the mineral types and weight percent ranges within the standards developed for the Nankai Trough sediments encompass those from offshore the Shimokita Peninsula.…”