Journal of Earth Science, 2016 online ISSN 1674-487X Printed in China DOI: 10.1007/s12583-016-0911-x Rehanul H. S, Jan M. Q, Kakar M. Iet al., 2016. Petrogenesis of Middle Triassic volcaniclastic rocks from Balochistan, Pakistan: Implications for the break-up of Gondwanaland. Journal of Earth Science, Printed in China. doi:10.1007/s12583-016-0911-x. http://en.earth-science.net Petrogenesis of Middle Triassic Volcaniclastic Rocks from Ba- lochistan, Pakistan: Implications for the Break-up of Gond- wanaland Rehanul Haq Siddiqui 1 , M. Qasim Jan 2 , M. Ishaq Kakar 3* , Andrew C. Kerr 4 , Abdul Salam Khan 3 , Ehsanullah Kakar 1 1. Balochistan University of Information Technology, Engineering and Management Sciences, Quetta, Pakistan 2. National Centre of Excellence in Geology, University of Peshawar, Pakistan & COMSTECH, Islamabad, Pakistan. 3. Centre of Excellence in Mineralogy, University of Balochistan, Quetta, Pakistan4. School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Cardiff, Wales, CF10 3AT, UK. ABSTRACT: Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undi- vided sedimentary rock unit of the Bagh Complex which is the mélange zone beneath the Muslim Bagh Ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several tex- tural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase (An35-78) leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg # and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10-15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks (including Afghan, Iran, Karakorum and Lhasa) from the northern margin of Gondwana. KEY WORDS: Middle Triassic, Wulgai volcaniclastics; juvenile Ceno-Tethys. 1 INTRODUCTION The Mesozoic sedimentary, igneous and metamorphic mélange beneath the Muslim Bagh Ophiolite is known as the Bagh Complex (Mengal et al., 1994). This Complex trends in an ENE direction and dips 10–70 towards west and northwest. It is divided into five tectonic/biostratigraphic units: (1) undi- vided sedimentary rock unit (Permo-Triassic; Anwar et al., 1993), (2) sedimentary rock unit (Jurassic-Cretaceous; Jones, 1961), (3) basalt-chert unit (Early-Late Cretaceous; Kojima et al., 1994), (4) hyaloclastite-mudstone unit (Late Cretaceous; Sawada et al., 1995), (5) serpentine and mudstone-matrix mélange unit (Late Cretaceous; Mengal, et al., 1993). The Wulgai volcaniclastic rocks occur in the undivided sedimentary rock unit of the Bagh Complex as basaltic volcanic conglome- rate (e.g., Naka et al., 1996; Fig.1). This sedimentary rock unit is exposed in a ~100 km long and up to 7 km wide area (Fig.1). The presence of Middle Triassic (Ladinian) grey radiolarian *Corresponding author: kakarmi.cemuob@gmail.com © Centre of Excellence in Mineralogy, University of Balochis- tan, Quetta, Pakistan Manuscript received October 02, 2015. Manuscript accepted April 13, 2016. chert within the upper and lower horizons of the conglomerates indicate that the rocks from which these volcaniclastic rocks were derived were erupted, eroded and re-deposited as volcanic conglomerates in Middle Triassic. The detailed stratigraphy of these volcaniclastic rocks is shown in Figure 1. The geology, biostratigraphy and tectonics of this complex have already been described by many researchers including Otsuki et al. (1989), Kimura et al. (1993), Kojima et al. (1994), Mengal et al. (1994), Naka et al. (1996) and Kakar et al. (2014). This study reports the geochemistry of Wulgai volcaniclastic rocks that occur in the undivided sedimentary rock unit of the Bagh Complex and will assess their petrogenesis and tectono-magmatic setting in relation to the break-up of Gondwana. 2 GEOLOGICAL SETTING The Wulgai volcaniclastic rocks occur in a 13 meter thick bed of volcanic conglomerate, which is well exposed at the base of Wulgai Nala Section (Fig. 1). In the lower 7 m thick part, sub-angular fragments of limestone with minor amygda- loidal basalt fragments occur in a tuffaceous sandy matrix (Fig. 2). This is overlain by 1.5 m thick interbedded sequence of micritic limestone, shale and grey chert, which contains Middle Triassic radiolarians (Otsuki et al., 1989). This sequence is