NEW DISCOVERY OF OLIVINE/ PYROXENE-RICH SANDSTONES IN THE KOLOSH FORMATION, DYANA AREA, NE IRAQ: AN APPROACH TO PROVENANCE AND TECTONICS OF THE SEDIMENTARY BASIN

Abstract

Abnormal concentrations of fresh olivine and pyroxene grains are reported and studied for the first time in the sandstone beds of the Kolosh Formation in the Dyana area, NE Iraq. The petrologic study revealed relatively high concentrations of fresh pyroxene grains (18.26%), olivine (8.3%), igneous rock fragments of various compositions (11.35%), altered (17.4%), argillaceous rock fragments (3.5%), carbonate fragments (2.45%), chert (2.3%), serpentine and chlorite (6.18%), plagioclase cf. anorthite and labradorite (5.15%), alkali feldspar cf. sanidine (1.02%), quartz and cristobalite (2.56%), opaque minerals including chrome-spinel (4.0%), argillaceous matrix (16.53%) and carbonate cement (1.2%). These mineralogical assemblages refer to ultrabasic and basic plutonic igneous sources associated with basic volcanic rocks. The ultrabasic and basic source is suggested to derived from mantle and oceanic crust origin, represented by the ophiolite sequence of Hasan Beg, Rayat, Choman and Galalah areas. These ophiolites were thrusted and emplaced during Late Cretaceous and were associated with volcanic island arc. The thrusted ophiolites were subjected to rapid submarine erosion and deposition and/ or subjected to subaerial erosion. Intense wave action accelerated erosion of beach rocks, removing the light fraction and leaving the heavy minerals insitue. Intense tectonism slumped these sediments into deeper margins by the turbidity currents.