Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan

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1 American Journal of Earth and Environmental Sciences 2018; 1(2): Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan Mehrab Khan 1, Muhammad Jahangir Khan 1, *, Muhammad Ishaq Kakar 2, Khalid Mehmud 3 1 Department of Earth & Environmental Sciences, Bahria University (Karachi Campus), Karachi, Pakistan 2 Center of Excellence in Mineralogy, University of Balochistan, Quetta, Pakistan 3 Department of Earth Sciences,University of Sargodha, Sargodha, Pakistan address * Corresponding author Citation Mehrab Khan, Muhammad Jahangir Khan, Muhammad Ishaq Kakar, Khalid Mehmud. Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan. American Journal of Earth and Environmental Sciences. Vol. 1, No. 3, 2018, pp Received: February 11, 2018; Accepted: March 7, 2018; Published: May 18, 2018 Abstract: The ophiolite is exposed near Nal village (Khuzdar district) of Balochistan, Pakistan which represents the northern part of Bela ophiolite. The Nal ophiolites are scattered outcrops and erected in an elongated N-S trend which is relatively thin (in E-W direction) as compared to Bela ophiolites. In this study, these ophiolitic outcrops were mapped on the detailed scale, such a detailed plan of geological units of understudy area was not available before. The Nal ophiolite along with Bela ophiolite is emplaced on the Indian continental margin sediments in Paleocene. The Nal ophiolite consists of serpentinized harzburgite, serpentinized dunite, gabbro, norite, troctolite, diorite and pillow lavas and dikes. A large number of doleritic dikes and clinopyroxenite dikes are intruded in the mantle section of understudy area. In the second part of this study we have discussed the petrography of primary minerals which are composed of the rock units of Nal ophiolite. These rocks exhibit a variety of textures, commonly, porphyritic, glomeroporphyritic, amygdaloidal, ophitic to sub-ophitic, mylonitic, and porphyroclastic. Keywords: Nal Ophiolite, Peridotite, Pillow Lava, Doleritic Dike, Mantle Section 1. Introduction The study of Nal ophiolites (Balochistan, Pakistan) reveals several secrets of plate kinematics and paleogeography of Indian and Afghan block. Neo-Tethys oceanic crust development is engendered by geotectonic evolution which is helpful to study the Earth s Mantle section in western margin of Indian plate. Locally, the study of Peridotite (ultramafic rocks) and Nal ophiolite is important for geological understanding and mapping of ophiolites in Balochistan. This geological study will also be beneficial for hunting ore deposits in ophiolites and to determine certain petrogenetic processes in Baluchistan. The Nal ophiolites were first reported by [5] named the said rocks as porali intrusions. The Nal ophiolite scattered and outcrop in an elongated N-S trend which is relatively thin (in E-W direction) as compared to Bela ophiolites (Figure 1). No detail work of these rocks has been done so far, nevertheless, many geologists ([1], [2], [3], [12]) worked on the southern part of Bela ophiolite The Bela ophiolite is underlain by Thar formation and overlain by the Nal Limestone. The contact between ophiolitic rocks and the Nal limestone in unconformable. The Hinglaj group traditionally overlies the Nal Limestone and Kech conglomerate unconformably overlies the Hinglaj group (Figure 2). The geological contributions of [3] proposed that the Bela ophiolite consists of two units, the upper and lower units. The upper unit represents the slice of overriding plate while the lower unit signifies the piece of subducting plate (under thrusting) which was adjacent to the Indian plate. The upper unit is well exposed between Khuzdar-Nal and Sunaro village (Figure 1). While the lower unit mainly covers the area between Sunaro village and Uthal town. The upper unit comprises metamorphic sole rocks, peridotites, Gabbro, sheeted dikes and pillow lavas. The complete sequence of Bela ophilite is exposed between Ornach cross - Sunaro village Khanozai village (Figure 3) However, a large and dismembered pieces of upper unit is also exposed in Nal,

2 116 Mehrab Khan et al.: Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan Wad, Darakolo, and Harargangi (Figure 1). Here the lower unite is visible between Sunaro village and Uthal town (Figure 1) which is mainly composed of pillow lavas and sheet flows covered by sedimentary rocks (radiolarian cherts, shales and calciturbidite) [3]. The lower unit is intruded or capped by microgabbro intrusions, sills and alkaline volcanic rocks related to Reunion hot spot. These Reunion related rocks cover as much as 30% of the lower unit [3]. Figure 1. An overview of the Nal oceanic lithosphere assemblages.

3 American Journal of Earth and Environmental Sciences 2018; 1(3): The study area lies in the Survey of Pakistan topo-sheet No. 35 1/1 and 35 ½ and is bounded by 66 7 E to E longitudes and N to N latitudes. This study presents first time the field mapping, petrography and modal analysis of Nal ophiolite. Figure 2 illustrates the detailed field map of Nal ophiolite. Figure 2. Detailed Geological map of rock units of Nal Ophiolite. The Longitudes (along x axis) and Latitudes (along y axis) are in Degree Decimal system.

4 118 Mehrab Khan et al.: Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan Figure 3. (a) A geologic map for the upper unit of Bela ophiolite (modified after [3]). (b) Landsat ETM+ image distinguishes the upper unit of Bela ophiolite with lithological boundaries (modified after [3]). 2. The Tectonic Settings The tectonic model suggested by [3] and [6] reveals that before the emplacement of Bela ophiolite, the intraoceanic subduction initiated in Neo-Tethys sea at the western side of Indian plate at 70 Ma (late Cretaceous). Because of this subduction the Neo- Tethys Sea started to close and Bela ophiolite was emplaced on the Indian continental margin in Paleocene ([3] and [11]). After emplacement of ophiolite over the continental sediments the sea was still present and shallow marine Nal Limestone (Eocene) and Hinglaj (Oligocene) formations were deposited on Bela ophiolite. Continued subduction closed the Neo-Tethys Sea located on the western side of Indian plate and finally Indian plate and Afghan micro continent collided in late Oligocene. The overlying sediments of Bela ophiolite evidence that the NeoTethys Sea located on the western side of Indian plate closed late (Oligocene) as compared to the collision in the north between Indian and Eurasian plates. The Indian plate at its western side collides with Afghan block in Oligocene while in the north the collision occurred in Eocene (50Ma) ([10] and [9]). Because of this collision between Indian plate and Afghan Block the Indian continental margin sediments got highly deformed, folded and thrusted and formed Sulaiman Kirther range. This zone of folds and thrusts is km wide, with a strike length of about 1,250 km. It extends southward from Waziristan, through Loralai-Bugti area, around the Quetta syntaxes, down south to Karachi [8]. The collision ceased and converted into Transform fault movement. The Chaman Transform fault generated at (2520Ma) ([4]). So, the western boundary of Indian plate shows an excellent geological laboratory in which the subduction, followed by a collision and then followed by Transform fault movement can be well studied. The major tectonic elements

American Journal of Earth and Environmental Sciences 2018; 1(3): 115-123 119 are annotated in Table 1. Table 1. The major tectonic subdivision of western Indian plate from West to East. 3.

5 American Journal of Earth and Environmental Sciences 2018; 1(3): are annotated in Table 1. Table 1. The major tectonic subdivision of western Indian plate from West to East. 3. Methodology The present study emphasized on extensive field work of Nal ophiolite for the collection of spatially distributed field sample (nearly 100 samples) of various rock units. The results in this paper provide substantial information about the geology of Peridotite (ultramafic rocks) exposed in Nal area. Thin sections of the selected field sample were prepared for petrographical anlysis. The polarizing microscope was used to distinguish the mineral composition of the understudy rock units and modal analysis helped in determining the percentage of minerals in rocks. 4. Results and Discussion The results are based on field work, mineralogical and textural learning along with the study of dikes and veins in the mantle section The petrographical results communicate that the rocks of the peridotite (ultramapfic rocks) can be divided into five groups known as serpentinized harzburgite, serpentinized dunite, gabbro, norite, troctolite, diorite and pillow lavas and dikes. The findings are sum-up in the following. A) Ultramafic Rocks (Peridodites) Peridotites consist of Harzburgite and Dunite which are usually serpentinized, that covers about 75% of the studied area. Serpentinized Harzburgite Harzburgite is mainly composed of olivine and orthopyroxene where as other constituents include clinopyroxenes, chromite, magnetite, ilmenite, serpentinite and calcite. Following types of alteration are found in the harzburgite. a) The olivine is altered into serpentinite b) The orthopyroxene is altered into basalt c) The clinopyroxenes are slightly altered into actinolite and green hornblende. Serpentinized Dunite The dunites are found at the top level of harzburgite and are rooted into the harzburgite. The contact between dunite and harzburgite is gradational. They are mainly composed of more than 90% olivine and spinels (1-2%) from which about 30% of olivine is altered to serpentine. Serpentinite In hand specimens, serpentinites are light green, dark green or brown in color and are extremely fine grained. They show numerous slickensides in the field and give a soapy feeling of touch. They are mainly composed of antigorite but in some thin sections chrysotile is also found. Unaltered remnants of olivine and pyroxene and Opaque minerals are also present in minor amounts. These rocks have been derived by the alteration of olivine and pyroxene being parent rocks as is indicated by the unaltered grains present in the cores surrounded by serpentine. B) Mafic Rocks The mafic rocks in the study area are Gabbro, Norite, and Troctolite. Gabbro The gabbros are coarse to medium grained rocks composed essentially of plagioclase and clinopyroxenes (augite). Clinopyroxenes is the most characteristic ferromagnesian mineral of these rocks. Inclusions of the opaque minerals are present in clinopyroxenes and altered into tremolite as well as hornblende. Orthopyroxne is also present but forms not more 2% of the rocks. Biotite, Zoisite and Apatite are also found in a very less amount and the opaque iron oxide which is magnetite, found less than one percent. The alteration in these rocks is slight to moderate, but in some cases it is intense. The alteration products are sericite, hornblende, tremolite and chlorite. Plagioclase is altered to finely grained sericite and the pyroxene phenocrysts show alteration to tremolite as well as chlorite. Hornblende is an alteration product of pyroxene whereas Biotite shows slight alteration to chlorite. Norite These rocks are coarse grained, consisting mainly of calcic plagiolclase and orthopyroxene. In the studied area these rocks found in the form of Layers. Their weathered color is brownish black to black and a fresh surface is mottled white and black to grey black and some are greenish black. The mineralogical composition in these rocks is, Plagioclase (28%), orthopyroxene (31%), clinopyroxenes (10%) Hornblende (9%). The plagioclase found in these rocks is labradorite to bytownite in composition. These rocks show moderate to intense alteration. Orthopyroxene and clinopyroxene show alteration to hornblende. Reaction rims are present around the pyroxene, which are composed of hornblende. The grains of clinopyroxenes show alteration to chlorite and tremolite. Troctolite These are essentially composed of olivine and plagioclase. Olivine is the major constituent of these rocks. Smidgens of olivine are surrounded by very fine-grained chlorite and serpentine. In some rocks olivine is completely altered to serpentine. Chlorite is very fine-grained fibrous and alteration product of biotite. Picotite and magnetite are present in very small amounts, not even exceeding one percent. These rocks show moderate to intense alteration. The alteration products are serpentine, chlorite and sericite. Amygdaloidal Pillow Lavas Pillow lavas form the upper most unit of the ophiolite.

6 120 Mehrab Khan et al.: Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan They are amygdaloidal in texture and amygdules are filled by zeolites and calcite. The pillows are beautifully zoned and have radial fractures. Pillow lavas of Nal area are up to meter across. Basalts are composed of plagioclase (Labradorite to anorthite) and pyroxene. Opaque minerals are present in fewer amounts and in some cases olivine is also present. The amygdaloidal basalts are present in the north of Nal and Karku village. (Figure 2). C) Intermediate Rocks Diorite In hand specimen these rocks are medium to course grained. The weathered surface is black grey, the fresh surface is dark grey. These rocks are mainly composed of andesine with anorthite of 46-48%, hornblende 25-30%, secondary chlorite, 17-20% present, pyroxene 2-3%, quartz 1-2%, and the rest accessories are apatite, epidote, sphene, and opaque minerals. Diorite show intense to moderate alteration. The alteration products are sericite, chlorite, and hornblende. Sericite is the alteration product of plagioclase whereas Hornblende has been altered from pyroxene. D) Felsic Rocks Granite Intrusion Granite rocks are exposed north of Karku village (Figure 2). It is coarse to medium and mainly composed of quartz, alkali feldspar (orthoclase), plagioclase, biotite as major constituents whereas muscovite, clinopyroxenes (augite), zircon, apatite are found as accessory minerals. About 1% iron oxide is also found in the granite. Apatite occurs in a very less amount and zircon is associated with biotite and also occurs in association with quartz. Opaque iron oxide includes magnetite and ilmenite and does not exceed more than 1% by volume. E) Dikes and Veins Five groups of dikes and veins have been distinguished in the Nal ophiolite. These are Pyroxenite dikes, Anorthosite lenses, magnesite veins, chromite deposits and doleritic dikes. Clinopyroxenite Dikes The Clinopyroxenites are found in the form of dikes. Their thickness varies from 10cm-30m. These are found in the harzburgite as well as in the dunite. They mainly consist of diopside (81-91%) with minor orthopyroxene (2-4%). The altered minerals are 2-5% and opaque 4%. Some samples contain a small amount of plagioclase. Anorthosite Lenses The Anorthosites are found in the form of lenses. Their thickness varies from 1-2 meter. These are found in harzburgite. In hand specimen the rock is phaneritic in texture. The weathered surface is light grey to brownish and fresh surface is greenish white. They are mainly composed of plagioclase (Bytownite to Anorthite) while the other constituents are augite and hornblende. Calcite is present as secondary mineral here. Magnesite Veins On certain locations magnesite veins run through the peridotites. The magnesite occurs mostly as cryptocrystalline, massive form, whereas some of them show well developed acicular transparent crystals which magnesite forms lenses and veins. Chromite Deposits. Podiform chromites are found in dunite and are a few cm to m thick and extend several kilometers in lengths. The veins are often discontinued due to the displacement of faults. They are concordant and discordant with the host rock. Two types of chromite deposits are more common: nodular and massive. The chromite deposits are being mined on large scale. Doleritic Dikes A large number of dikes are intruded in the mantle section. They give chilled margins. Younger calcite veins occur cross cutting the doleritic dikes which vary in thickness from 30cm-10meters. These rocks are mainly composed of plagiolclase and clinopyroxenes (augite) with the opaque minerals present as an accessory. In some cases, quartz is present up to 2% by volume. There are a few quartz dolerites consist of 67% plagioclase, 9% clinopyroxenes, 8% quartz as essential minerals while the hornblende dolerites contain plagioclase, hornblende and clinopyroxenes as their vital minerals. Plagioclase and pyroxene are also highly altered products. Table 2. Modal Analysis of Field Samples (SERPENTINITES). Sr. Sample No. No. OL OPX CPS Srp Cal OP 1. K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M K-M

7 American Journal of Earth and Environmental Sciences 2018; 1(3): Table 3. Modal Analysis of Field Samples (PYROXENITES). Sr. No. Sample No. OPX CPX Srp Hbl P1 Chl op 1. K-M K-M K-M K-M K-M Table 4. Modal Analysis of Field Samples (HARZBURGITES). Sr. No. Sample No. 01 Opx Cpx Srp Op 1. K-M K-M Table 5. Modal Analysis of Field Samples (ANORTHOSITES). Sr. No. Sample No. Pl Cpx Hbl Cal Op 1. K-M K-M Table 6. Modal Analysis of Field Samples (GABBROS). Sr. No. Sample No. Pl Or Cpx Opx Bl Hbl Chl Tre Ep Op 1. K-M K-M K-M K-M K-M Table 7. Modal Analysis of Field Samples (NORITES). Sr. No. Sample No. Pl Cpx Opx Srp Hbl Chl Tre 1. K-M K-M Table 8. Modal Analysis of Field Samples (TROCTOLITES). Sr. No. Sample No. P1 01 Srp Bt Chl Cal Op 1. K-M K-M Table 9. Modal Analysis of Field Samples (DIORITES). Sr. No. Sample No. Pl Cpx Opx Srp Hbl Chl Ep Op 1. K-M K-M K-M K-M K-M K-M Table 10. Modal Analysis of Field Samples (BASALT). Sr. No. Sample No. Pl Cpx Opx Nat Qtz Chl Cal Op 1. K-M K-M K-M K-M K-M Table 11. Modal Analysis of Field Samples (GRANITES). Sr. No. Sample No. Pl Or Bt Ms Qtz Op 1. K-M K-M

8 122 Mehrab Khan et al.: Geology and Tectonic Setting of Nal Ophiolite, District Khuzdar, Balochistan, Pakistan Table 12. Modal Analysis of Field Samples (DOLERITES). Sr. No. Sample No. Pl Cpx Opx Chl Qtz Bt Ep Cal Op Spn 1. K-M K-M K-M K-M K-M Table 13. Modal Analysis of Field Samples (QUARTZ DOLERITES). S. No. Sample No. Pl Cpx Opx Hbl Chl Qtz Bt Cal Op 1. K-M K-M K-M K-M Table 14. Modal Analysis of Field Samples (HORNBLENDE DOLERITES). SR. No. Sample No. Pl Hbl Cpx Qtz Op 1. K-M K-M K-M K-M Conclusion Nal ophiolite is found in the northern part of Bela ophiolite. The Nal ophiolite comprises serpentinized harzburgite, serpentinized dunite, clinopyroxenite dikes, gabbro, norite, troctoctolite, diorite and pillow lavas. A large number of doleritic dikes are intruded in the mantle section. Nal ophiolite is harzburgitic in composition so it is harzburgite type ophiolite. The Nal ophiolite along the Bela ophiolite emplaced in Paleocene on Indian continental margin sediments. Acknowledgements The authors acknowledge the efforts of field volunteers and students for collecting the field samples and mapping of rock units. Nomenclature Sr Symbol Mineral 1. Ol Olivine 2. Opx Orthopyroxene 3. Cpx Clinopyroxene 4. Srp Serpentine 5. Hbl Hornblende 6. Pl Plagioclase 7. Qtz Quartz 8. Chl Chlorite 9. Cal Calcium 10. Ep Epidote 11. Tre Termolite 12. Bt Biotite 13. Or Orthoclase Sr Symbol Mineral 14. Ms Muscovite 15 Nate Natrolite 16 Op Opaque Minerals References [1] Ahmed, Z., (1991). A supra-subduction origin of the Bela ophiolite indicated by acidic rocks, Khuzdar District, Pakistan. Acta, Miner, Pakistan 5, pp [2] Ahsan, S. N., Akhtar, T. and Ali, Khan, Z., (1988). Petrology of the Bela-Khuzdar ophiolites, Baluchistan, Pakistan. Geological Survey of Pakistan Inf. Rel., 307, pp. 24. [3] Gnos, E; Khan, M; Mahmood, K; Khan, A. S; Shafique N. A; and Villa. I. M (1998). Bela oceanic lithosphere assemblage and its reation to the Reunion hotspot. Terra Nova 10, pp [4] Hadi S., Khan S. D., Owen L. A., Khan S. A., Hedrick K. A., Caffee M. W., (2013). Slip rate of Chaman fault; Implication for transient strain accumulation and strain partitioning along the western indian plate margin. Tectonophysics 608, pp [5] Hunting Survey Corporation (HSC), (1960). Reconnaissance geology of part of West Pakistan: a report published for Government of Pakistan by the Government of Canada, Toronto, pp [6] Khan, M (1999). Petrological and structural studies of the ophiolites of the Baran Lak area, Bela- Khuzdar, District, Baluchistan, Pakistan. Ph.D. Thesis (unpublished) University of Balochistan, Quetta, Pakistan, pp [7] Khan, M; Gnos, E; Khan, A. S; and Mahmood, K (1998). Genetically two different types of basaltic rocks from Bela ophiolite Balochistan, Pakistan. Acta. Mineralogica Pakistani ca, 9, pp

9 American Journal of Earth and Environmental Sciences 2018; 1(3): [8] Kazmi, A. H; and Jan, M. Q (1997). Geology and tectonics of Pakistan. pp [9] Patriat, P; & Achache, J (1984). India-Eurasia collision chronology and its implication for crustal shortening and driving mechanisms of plates. Nature, 311, pp [10] Powell, C, Mc A (1979). A speculative tectonic history of Pakistan and surroundings: Some constraints from the Indian Ocean. In: Farah, A; & DeJong, K. A: (eds.) Geodynamics of Pakistan. Geol. Surv. Pak; Quetta, pp [11] Zaigham, N. A, and Malik, K. A (1992). Upward continuity filtering of the Uthal gravity data. Acta Miner. Pakistan; 6, pp [12] Zaigham, N. A (1991). Bela Ophiolite and associated mineralization in the southern part of Axial- belt of Pakistan Unpublished doctoral dissertation, University of Karachi Pakistan, pp. 370.

Geology and Petrography of Peridotites (Mantle Section) from Bela Ophiolite, Balochistan, Pakistan

Geology and Petrography of Peridotites (Mantle Section) from Bela Ophiolite, Balochistan, Pakistan Mehrab Khan, Muhammad Jahangir Khan Department of Earth & Environmental Sciences Bahria University Karachi