STUDY OF VOLCANIC SEDIMENTS BY MICROBEAM-PIXE TECHNIQUE

Single mineral grains in a suite of Cretaceous (85-90 Ma) volcanic sed imentary rocks were analyzed using the microbeam-PIXE technique to und erstand fundamental geological processes responsible for micro-scale v ariation in elemental composition across mineral zones, twinning, clea vage planes, fractures and grain boundaries. Distributions of major an d trace elements show distinct geochemical features indicative of a sp ecific geological setting and a subsequent diagenetic process in these volcanic sediments. Examples of mineral zoning, microstructures of va riable chemistry and post-depositional fluid flow are discussed using the data on feldspar group of minerals.