BALOCHISTAN: A GEOLOGICAL WONDERLAND

[Zahida Raees Raji]

BALOCHISTAN:  A GEOLOGICAL WONDERLAND                   
Mahmood Siddiqui & Uzma Mahmood 

 

       Balochistan is indeed a piece of geological wonderland on Earth. Very few segments of the globe may have so many geological marvels congregated in a piece of land equal in area to that of Balochistan. We already know from the previous episode that Balochistan is product of merger of a migrant and an indigenous pieces of Earth’s crusts — a wonder by itself. While sliding past each other, the Indo-Pakistan portion of the Indian-Australian plate rubs its shoulder against the Afghan portion of the Eurasian plate thereby making the Ornach-Nal and Chaman fault tracks exceptionally prominent at places on surface and provide textbook quality of example. Other such instance is produced by the San Andres fault in California. These faults are no less a wonder as they separate two tectonic plates lying side-by-side with in Balochistan. It is only province where three major tectonic plates, viz Indo-Pakistani, Afghan portion of Eurasian, and Ormarian plate meet together to produce the triple plate junction within the county. Ormarian plate is a newly discovered triangular piece broken off from the Arabian oceanic plate.

         Balochistan is also the land where a trench-arc system is currently active and the two essential elements of the structure, the trench and the arc both, occur within its territory. The structure develops following subduction of oceanic plate in the trench and the chain of volcanoes evolves of the material produced following melting of the plate in depths. The west trending trench is located in the Arabian Sea and Gulf of Oman and southwest trending volcanic arc has developed in the Chagai Hills and in south eastern Iran. The arc, which is built of a chain of satellite volcanic cones, connects the dormant Pakistani volcano Koh-i-Sultan at its eastern end to the active Koh-i-Taftan and Bazman in Iran in the west. Subduction of the Ormarian plate (previously called northeastern portion of Arabian oceanic plate) under Eurasia is believed to be responsible to develop this active trench-arc system. The system is attributed to produce several potential copper-gold deposits, including that at Saindak and Reko Dick in Chagai district. Along with the subduction, marine sediments accumulated on the Ormarian plate are scraped off and the Makran coast is essentially built of accretionary wedges or prisms of these off-scraped marine sediments.

         Balochistan mountain belt, a remarkable feature of essentially sedimentary rock formations, enters Balochistan near Loralai from north. Here the belt makes a bend like a garland of flowers and running around Quetta, passes through Kalat, Khuzdar, Bela and finally terminates at Indus delta by the Arabian Sea. These mountain ranges house chromite at Muslimbagh and Khuzdar-Bela section of the ophiolite belt and also in the Ras Koh Range. In fact the Balochistan folded mountain belt together with Ras Koh and Chagai regions are storehouse of numerous economic minerals including, copper-silver-gold, iron, barite, marble, sulphur, fluorite, cement raw material and a variety of building-stones and construction material.

         Discovery of a mammal fossils “Baluchitherium“ in Dera Bugti area in last quarter of the last century has further added a piece of geological marvel to the credit Balochistan. This creature was the largest land animal that ever lived on the Earth and was restricted only to Asia. To have a better understanding of the age-wise succession of sedimentary rock formations and their faunal and floral fossil contents, we may now briefly review the Geological Time Scale.    

GEOLOGICAL TIME SCALE
 

Earth’s life span, since its creation to present, is divided into four Eons: “Hadean” (Beneath the earth), “Archean” (Ancient), “Proterozoic” (Early Life) and “Phanerozoic” (Evident Life). The first three i.e., Hadean (4600–3800 Ma), Archean or Azoic (3800–2500 Ma), and Proterozoic (2500–545 Ma) Eons cumulatively lasted for 4055 million years and constituted the Precambrian Era. The fourth Phanerozoic Eon, which is divided into Palaeozoic, Mesozoic and Cenozoic Eras together spanned over the remaining 545 Ma; from Cambrian to Present. Break-up of the range and duration of the Eras is given in the following table:


 

Era                  Range of Era               Duration of Era

Cenozoic           65–0 Ma                                   65 million years

Mesozoic          248–65Ma ago  183 million years

Palaeozoic        545–248 Ma ago           297 million years

Precambrian     4600–545 Ma ago          ~4055 million years

Age of Earth:    4,600 million years or 4.6 billion years
 
 

Eras are further divided into Periods and Epochs. Following table presents a simplified division of Eras.



Paleozoic Era                       Mesozoic Era                    Cenozoic Era
Permian        286–245 Ma                                          Cretaceous   145.6–66.4 Ma Holocene                   10000yrs– 0 yrs

Carboniferous 360–286 Ma                                         Jurassic        208–145.6 Ma Pleistocene                1.6 Ma–10000 yrs

Devonian      408–360Ma  Triassic        245–208 Ma    Pliocene      5.3–1.6 Ma

Silurian        438–408 Ma                                            Miocene     23.7–5.3 Ma

Ordovician   505–438 Ma                                            Oligocene   36.6–23.7Ma

Cambrian     545–505 Ma                                           Eocene       57.8–36.6Ma                                                                                                   Paleocene      66.4–57.8 Ma

 
 
The sweep of time, starting from the Earth’s birth to present, can best be expressed by a spiral pathway as shown in the diagram (Figure 5–1). Geological time line with absolute ages as is determined by decay of radioactive material and the evolution of organisms is shown in the diagram. Each spiral turn of the diagram corresponds approximately to about 1 billion years
 
continue...
 

[Zahida Raees Raji]

Major Event in the Earth’s History
As mentioned earlier, Earth was born about 4,600 Ma ago and formation of the crust began soon after. Oldest known rocks on the Earth are dated 3,960 Ma whereas oldest moon rocks are about 4,550 Ma old.

         Primitive atmosphere started forming and free oxygen began to accumulate in the Archean Eon. Mountain building in eastern North America began in Ordovician and that in Europe (Urals) in Devonian. The super-continent Pangaea began to form in Permian and started to split in Triassic. Upper crust that had evolved on the western edge of Indo-Pakistan subcontinent in post Permian period was later raised to mountain ranges including the Balochistan Mountain Range. Opening of Atlantic Ocean began in Jurassic. Rocky Mountains formed in North America and the submarine volcanism erupted thick pile of Sinjrani volcanics on sea floor in Chagai area in Cretaceous.

         Paleocene Period witnessed beginning of collision of Indo-Pakistan subcontinent with Eurasia and eruption of Deccan Trap in India. Himalayas and Alps began to rise in Eocene and opening of the Red Sea began in Miocene. Worldwide glaciation of the Ice Age epoch occurred in Pleistocene.   



Figure 5–1. Diagram Showing sweep of time starting from Earth’s birth 4,600 million years ago to present (Source: Press & Siever 2002).

 Origin of Major Life Forms on Earth

   Life on the Earth came much later; in Proterozoic Eon, when the Earth was already over 4,000 million years old. Oldest evidence of life appeared around 3000 Ma in Archean when early bacteria and algae came into being. As is indicated by fossil remains, first life was in the form of jellyfish, which appeared about 670 Ma ago (Chernicoff, 1999). This was followed by multi-celled organisms. Earliest organisms with shell appeared in Cambrian and the Cambrian and Ordovician periods are known as “Age of marine invertebrates.” Fish and earliest land plant came in Silurian, and first evergreen forest appeared in Devonian. Silurian and Devonian periods are also known as “Age of Fish.” Earth witnessed luxurious forests and coal-forming swamps in Carboniferous.  First amphibian and reptile appeared in Carboniferous and the Carboniferous to Permian period is known as “Age of Amphibian.”, Luxurious forests, sharks, variety of insects were characteristics of Carboniferous period. Early birds, mammals, reptiles, flying reptiles and flowering plants appeared in “Age of Reptiles” during Triassic, Jurassic and Cretaceous. In Paleocene epoch dinosaurs and many other species were extinct and Paleocene to Holocene (also called Recent) was “Age of Mammals.”  Eocene epoch witnessed birth of horse and camel and giant birds, and grasslands. Whales, apes and monkey-like primates and flowering plants were distinctiveness of Miocene epoch. Earliest hominid and large carnivores were characteristic of Pliocene and Homo erectus appeared in Pleistocene epoch (Chernicoff, 1999). With the beginning of Holocene many large birds became extinct and modern humans spread.

Baluchitherium:

The Beast of Balochistan
         Geological Survey of Pakistan in year 1985 discovered complete fossilized jaw of a prehistoric animal in Chitarwata formation in the Bugti Hills, north of Sui. The animal, accordingly, was named Bugtitherium that was later changed to Baluchitherium. Further work in the area, in collaboration with a French team of National History Museum Paris, unearthed almost complete fossil remains Baluchitherium the largest land mammal that ever lived. The animal belonged to Rhinoceros family but it was without horn and was much too big in size as compared to the closest modern descendants.

         Petrified remains of the animal indicate that the beast measured 8 meters long and 5.5 meters high at the shoulders and weighted over 20 tonnes — more than 2.5 times heavier than African elephants. Having comparatively long neck and pillar-like tall legs the herbivorous creature is believed to consume close to 2 tonnes of feed every day that this the beast acquired from high up twigs and branches of trees. Habitat of Baluchitherium is now dry and barren land but in late Oligocene and early Miocene epochs (20–30 Ma ago), when the animal roamed around, there must be abundant trees to meet the food requirements of the animal.  Bone fossils of this gigantic creature are currently on display in the museum of the Geological Survey of Pakistan, Quetta

Figure 5-2. An artistic sketch of Baluchitherium

continue...

[Zahida Raees Raji]

LOWER CRUST
         Lower crust is invariably composed of metamorphosed igneous and sedimentary rocks world over. Under major part of Indo-Pakistan subcontinent the lower crust is comprised of Indo-Pakistani shield, which is widely exposed in the Indian peninsula.
http://baask.com/articals/sangat/discover_balochistan/image005.jpg

Figure 5-3. Indo-Pakistani shield and the area around.

Source: Powell (1979), Geodynamics of Pakistan

         In Pakistan, however, the shield is not so well exposed but according to Powell (1979) it extends in the north and northeast beneath the Himalayas at least as far as the Indus Ophiolite Belt in Ladakh and in west under younger rock formations up to the Chaman and Ornach-Nal faults in Balochistan (Figure 5-3), Known exposures of the shield rocks in Pakistan occur only in Nagar Parker area in Sindh and Sargodha area in Punjab where the rocks are named Nagar Igneous complex and Rocks of Kirana Group, respectively.


Ornach-Nal and Chaman Transform Faults
Transform faults are the parting line between two side-by-side lying tectonic plates. Ornach-Nal and Chaman transform faults occur between the Indo-Pakistani plate in the east and the Afghan portion of Eurasian plate in the west. Appearing and disappearing

on and off intermittently, the Ornach-Nal-

Chaman fault runs across entire width of Balochistan.

Ornach-Nal fault, an on land expression of Owen Fracture occurring in the Arabian Sea, enters Balochistan at a distance of about 75 km northwest of Karachi (Figure 5–4 A). The fault, after extending for about 160 km in northerly direction, disappears at the surface. Subsurface, however, it is assumed to join the Chaman fault but definite evidence is not available.

Chaman fault is better exposed as compared to the Ornach-Nal fault and is well studied. At places its track, particularly in the Nushki-Chaman section, offer textbook quality of example. According to Lawrence and Yeat (1979), the fault may mark at least part of western transform boundary of the Indo-Pakistani plate.

http://baask.com/articals/sangat/discover_balochistan/image007.jpg

Figure 5–4. Ornach-Nal and Chaman transform faults shown traversing through Balochistan (A) and a well exposed track of Chaman fault (B) in the Nushki-Chaman section. Source:Lawrence and Yeat (1979)


 

Chman fault appears at about 50 km southeast of Kharan Kalat. According to Kazmi (1979), from here it runs in N10oE to N30oE direction for about 600 km in Pakistan and Afghanistan combined. About 25 km northeast of Nushki near Siah Koh the fault crosses into Afghanistan where it runs for about 75 km and re-enters Pakistan near Spin Tezha. Running in the same northeasterly direction the fault passes about 5 km east of Chaman town, again crosses the boarder into Afghanistan and extends for another 150 km in the country. Lawrence and Yeat (1979) studied Chman fault in details. A well exposed section of the fault near Chaman is presented in their map (Figure 5–4 B).

Ormarian Oceanic Plate:

A New Discovery
Till recently, oceanic portion of the Arabian plate alone was considered subducting under the central Iranian continental slivers, and Lut and Afghan plates annexed with Eurasia. A regional swath-bathymetry survey of the Makran accetionary wedge according to (Kukowski et al. 2000) revealed presence of a new “Sonne” fault that crosses the wedge obliquely in northwesterly direction and separates the seismically active eastern part of the Makran subduction zone from the inactive and event-free western part. A new oceanic plate in eastern Makran, south of Pakistani port town Ormara was thus identified and named “Ormara plate.” To sound consistent with other plate names in the region, a slight modification is made and herein it is called “Ormarian” plate.  The plate, according to the Kukowski et al. (2000), was created when a sizeable triangular piece of Arabian plate was torn-off from the eastern end along the new Sonne Fault. Following discovery of the Ormarian plate, the northerly subduction of Arabian oceanic plate is now considered restricted only in the western part of Makran. In eastern part, which is in Pakistan, the Ormarian plate is considered subducting in the northwesterly direction probably along the Sonne Fault.

Triple Plate Junction
Balochistan lies at such a location where at least three tectonic plates are concurrently interacting. These plates are: (i) Eurasian continental plate with annexed Afghan plate (hereafter referred as Euro-Afghan plate) to west of Chaman fault, (ii) Indo-Pakistani continental plate to the east of the Chaman fault, and (iii) Ormarian oceanic plates to the south of Makran subduction trench. The triple plate junction of the Indo-Pakistani, Euro-Afghan, and Ormarian plates, according to Uchpi et al. (2002), occurs at the apex of the Las Bela valley triangle. According to Jacob and Quittmeyer (1979) the triple plate junction occurs on land due south of the location proposed by Uchupi et al. (2002). Arthurton (1979), who seems to be closest to the reality, shows the triple plate junction in his map offshore at about 150 km west-southwest of Karachi.

 

REFERENCES
Chernicoff, S., Geology (2nded ) 1999: Houghton Mifflin Company, Boston New York. U.S.A

Powell, C. McA, 1979: A Speculative Tectonic History of Pakistan and Surroundings: Some Constraints from the Indian Ocean in Geodyanmics of Pakistan: Fahrah and DeJong (eds), Geological Survey of Pakistan, Quetta Pakistan.

Press, F. and Siever, R., 2002: Understanding Earth (3rd ed) W. H. Freeman  and Company, New York. U.S.A.Inc. New York. U. S. A.

Jacob, K. H, and Quitteyer, R., 1979: The Makran Region of Pakistan and Iran: Rrench Arc System with active subduction. Geological Survey of Pakistan, Quetta Pakistan.

Kazmi, A. H., 1979,.Active Fault Systems in Pakistan:  in Geodyanmics of Pakistan: Fahrah and DeJong (eds), Geological Survey of Pakistan, Quetta Pakistan.

Kukowski. N, Schillhorn..T, Fleuh, E.R. and Huhn. Katrin., 2002 ?. Newly identified strike-slip boundary in the northeastern Arabian Sea: GEOMAR …Germany. 

Lawrence and Yeat., 1979. Geological Reconnaissance of the Chman Fault in Pakistan. Geological Survey of Pakistan, Quetta Pakistan.

Uchupi. E.,  Swift. S.A., & Ross. D. A. 2002 ?. Tectonic Geomorphology of the Gulf of Oman Basin: Geological Society , London Special Publication, 195 17-69.

 

 

 

Curtsey to Monthly Sangat Quetta (April 2008)