Imbricate structure of Luobusa ophiolite, southern Tibet

Abstract

sequence has a fault contact with the Triassic flysch-type sedimentary rocks. The northern and the southern boundaries dip gently to the south. Mesoscopic structures were observed on outcrop surfaces which are nearly perpendicular to the foliation and nearly parallel to the lineation. Microscopic observations were made on polished slabs and thin sections of oriented samples taken from the shear zones near to the top and bottom boundaries of the Luobusa ophiolite. The slabs and thin sections were made on the section perpendicular to the foliation and parallel to the mineral lineation. A serpentine melange zone, which lies along the northern margin of ophiolite sequence occupies the structural bottom of Luobusa ophiolite. The serpentine melange zone contains lenses of gabbroic rocks, pillow lavas and Cretaceous marine sedimentary rocks. These rocks occur as blocks in a partly serpentinized ultramafic matrix. Individual lithologies are irregularly distributed and the serpentinite matrix is intensively deformed. In the outcrops and oriented samples sets of subparallel shear and minor shear zones occur in the serpentinite. The shear are oblique to foliation in serpentinite and are regarded as C'-type shear bands (Figure 1). Consistent top-to-the-north displacements are observed at three localities in the serpentine melange zone.