Illitic substitution in micas of very low-grade metamorphic clastic rocks

Characterization of coexisting NH4- and K-micas in very low-grade metapelites

Organic-rich Carboniferous shales with associated coal seams, from the Bacia Carbonífera do Douro-Beira (north Portugal), have been studied by TEM as well as by a variety of other methods. NH4 and K micas and berthierine form small subparallel packets of a few layers separated by lowangle boundaries. Oneand two-layer ordered polytypes, with some spot enlargement typical of minor disorder, occur...

Chlorite-mica aggregates: morphology, orientation, development and bearing on cleavage formation in very-low-grade rocks

-Chlor i te-mica aggregates in slates from northern Spain have been investigated in very-thin thin sections. Specimens from various parts of a fold show different morphologies that are dependent on the operating deformation mechanism. From the limb to the hinge rigid-body rotation becomes less important and folding and intragranular kinking are more common. This is associated with an increasing...

Frequency Dependent Elastic and Anelastic Properties of Clastic Rocks

This study focuses on measurements of clastic rocks ranging from 3 Hz up to 500 kHz in the laboratory and their application to well log analysis and a time-lapse study in the North Sea. Measurements of elastic properties over a large frequency spectrum can provide a better understanding of the dispersion and attenuation mechanisms in rocks and help to predict and model these effects. Sandstones...

Groundwater in Sedimentary, Metamorphic and Volcanic Rocks

An albite-anorthite assemblage in low-grade amphibolite facies rocks

Poikiloblastic amphibole schists from an ophiolite series in the vicinity of the Tertiary Bergell granite contain the assemblage albite (An 0)-anorthite (An 95), actinolite-pargasite, together with clinozoisite. TEM illustrates how large andesine crystals with a periodic APB (anti-phase boundaries) structure of e plagioclase change over a few hundred angstroms to pure albite and pure PT anorthi...