The Bagh complex is an assemblage of igneous and sedimentary rocks containing many lithologic
units which are bounded by layered parallel thrusts. The volcanic rocks from basalt-chert unit (Bbc) and
hyaloclastite-mudstone unit (Bhm) are comprised of pillowed and bedded basalt, hyaloclastite and
reworked sediments. Petrography and geochemistry of the basalt from Bbc shows that these rocks are
basaltic trachy-andesite, trachy-andesite and foidite with tholeiitic charecter. While those from Bhm are
tephrite-basanite, basalt and picro-basalt having alkaline nature.
N-MORB-normalized diagram of the tholeiitic rocks have flat pattern of HFS-elements. In contrast
enrichment of LIL-elements with the REE having almost flat pattern between 10X and 20X chondritic which
are typical of N-MORB. The enrichment of LIL-elements, especially Th and depletion of Nb relative to other
incompatible elements are depicting the addition of subduction zone component to a depleted mantle source.
The multi element normalised plots of the volcanic rocks from Bhm show a similar pattern to that of OIB.
Theese show a marked enrichment in the LIL-elements, depletion in some of the HFS-elements enrichments
in LREEs and a marked depletion in the HREEs as compared to NMORB.
The geochemical features on tectonic discrimination diagram of tholiiete from Bbc and alkaline rocks
from Bhm suggest supra-subduction zone and oceanic-island arc tectonic settings respectively. These
rocks were possibly erupted during Cretaceous period in the area which extends from the continental
margin of the Indian subcontinent over the Neo-Tethys Ocean floor, and then were obducted with the
Muslim Bagh ophiolite over the Indian subcontinent.
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.
Two different types of mafic dykes are found in the Muslim Bagh Ophiolite: 1) a sheeted dyke complex and 2) a mafic dyke swarm. Relative to the host plutonic section, the sheeted dykes are poorly developed, implying that they formed in an oceanic setting with a low and intermittent supply of magma, probably because of cyclic accumulation of crystals at the base of the magma chamber. Both the sheeted dykes and the dyke swarms have been metamorphosed to greenschist/amphibolite facies conditions. With the exception of the upper level gabbros and sheeted dykes, the dyke swarms crosscut almost the whole ophiolite suite as well as the metamorphic sole rocks, but are truncated structurally at the contact with the underlying mélange and sediments. Hence, the injection of the dyke swarms postdates the formation of both the main Muslim Bagh Ophiolite and the metamorphic sole rocks, but predates the accretion of the mélange and the final emplacement of the ophiolite onto the Indian plate margin. Both the sheeted dykes and dyke swarms are tholeiitic and have a geochemical signature of either island arc tholeiites (IAT) or are transitional between mid-oceanic ridge basalts and IAT. Oceanic rocks with such characteristics, especially their enrichment in large-ion lithophile elements, are generally thought to have formed by processes involving a subduction zone component in the source region by fluids released from the subducting slab. The Muslim Bagh Ophiolite sheeted dykes originated in the late Cretaceous, in a supra-subduction zone tectonic setting related to the subduction of a narrow branch of the Neo-Tethys Ocean, followed by a subduction rollback due to splitting of the nascent arc in the Tethys Ocean. This intra-oceanic subduction led to the formation of a metamorphic sole, followed by the off-axis intrusion of mafic dykes into the ophiolite through a slab window. The Muslim Bagh Ophiolite was accreted to the Bagh Complex and finally obducted onto the Indian Platform.
The crustal section of Bela ophiolite is well exposed between Wad and Sunaro village. It consists of layered gabbro, foliated gabbro, isotropic gabbro, sheeted dikes and volcanics. The crustal section also contains magmatic intrusions which consisting of plagiogranites, wherlites and troctolites. The crustal section of Bela ophiolite is around 5 km in thickness in which 1.5 km of the layered peridodite and gabbros, layered, foliated and isotropic gabbros, 2 km of sheeted dikes and 1-1.5 km of pillow lavas and sheet flows. The sheeted dikes trend N 130° and dip E &W. Thick crustal section evidenced that Bela ophiolite formed from a big magma chamber which also indicate fast spreading ridge environment.
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