Lithological mapping of Bela ophiolite with remote-sensing data

Abstract

Bela ophiolite (BO), the largest ophiolite in Pakistan, is important to our understanding of the western margin of the Indian plate, particularly the collisional history of Indian and Eurasian plates. However, it is located in a remote location and has not been extensively studied. For example, no detailed geological map for this area exists. In this article, remote-sensing data were processed by different techniques that were selected based on reflectance spectroscopy data and compared with a local geological map for the upper unit of BO. False-colour images (Landsat Enhanced Thematic Mapper plus (ETM+) bands 7, 4, 2 in the red, green, blue (RGB)), colour-ratio composite images of Landsat ETM+ data (5/7, 5/1, 5/4 in the RGB), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data (4/5, 6/7, 3/4 in the RGB) and mafic index images are used to discriminate different lithologies. Our results are consistent with published local geological maps. Based on these images and field data, we created a detailed geological map of BO. Two types of basalts are differentiated, and an ultramafic body around 66° 15′ E, 26° 39′ N is recognized for the first time in the lower unit of BO. Integrating all the available data, we suggest that BO formed in two episodes; the upper unit is a classic ophiolite sequence and is younger than the lower unit. First, it was obducted onto the lower unit, and then the two units obducted as one onto the Indian continental edge.