Gilgit field report by zeeshan (uoh )

GEOLOGICAL FIELD REPORT 05/26/2015

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DEPARTMENT OF GEOLOGY

FIELD REPORT Gilgit Baltistan

1. Zeeshan Wahab

2. Munsif Ahmed

3. Zia ur rehman

4. Akhtar Pervaiz

5. Atta ul Munhim


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REGARDS :

1) Zeeshan Wahab

2) Munsif ahmad

3) Zia ur rehman

4) Akhtar parvez

5) Atta ul munhim

Remember us in ur Prayers please.

Email: [email protected]


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Dedication Dedicated to our beloved parents , respected teachers ,

all student of geology and finally our batch fellows.


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Contents Title Page No. Acknowledgements 5

Abstract 6

CHAPTER NO. 1 7-8 Introduction

CHAPTER NO. 2 9-10 Literature review

CHAPTER NO. 3 11-34 Field description

CHAPTER NO. 4 35-38 Geomorphlogy

CHAPTER NO. 5 39-41 Engineering Geology

CHAPTER NO. 6 42-48 Tectonics


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ACKNOWLEDGEMENTS

All praise to Allah Almighty; who taught us with pen and Whose

Wonders we find all around us.

We feel highly privileged to express our deep sense of gratitude to our

teacher Sir Azeem and Sir Usman , Department of Geology , University

of Haripur, for skill guidance , kind , attitude, invaluable suggestions,

positive criticism and especially continual encouragement during the

completion of this field.

We are grateful to Mr. FAWAD , incharge of Department of Geology ,

for arranging this field .

Regards:

Zeeshan Wahab

Munsif ahmad

Zia ur rehman

Akhtar Parvez

Atta ul munhim


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ABSTRACT The study area of Gilgit – Kohistan is the Northern part of the Pakistan, we study area

along the KKH and Indus river geologically that area are very complex and highly

deformed areas having plats colloid zone and triple junction of the world three largest

mountain series.

Geotectonically there are many large and observable tectonics features in the area, main

suture zone, MMT, MKT, Triple junction, Kohistan island arc, syntaxes collision zone

of Indian and Eurasian plates.

Geomorphologically large number of alluvial fans, hot spring, flysh deposit, mollase

deposited, point bar, mid channel bar, meandering stream. Structurally small fold,

faults (rakaposhi) and fracture in rocks.

The project of Dasu dam and Bhasha dam studied along informative lecture with

respect to construction and engineering geology.

Petrology of different igneous (plutonic and volcanic), metamorphic and Meta sedimentary

rocks with their brief mineralogy and petrology.

Mainly there regionally geology having different types of rock complexes of igneous bodies

and also different grade of metamorphic rocks:

1) Mansehra granitic batholiths

2) Meta sedimentary rocks of Indian continent

3) Dubair granitic complex

4) Kohistan batholiths

5) Kohistan island arc rock

6) Besham complex rock

7) Chalt volcanoes

8) Yaseen group sediments and

9) Ortho / Paragnesis rocks

10) Thilichi group

11) Augen gnesis


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CHAPTER 1 Introduction


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Chapter : Introduction

Our six days field tour is conducted from 11_16 may 2015 to Kohistan- Gilgit areas

1ST DAY: We started this special field work on 10:00 am (11 may 2015) from Haripur

University. At first day we work on different location along road side and at 9:30 pm we reached

to Besham continental hotel to spend the night, and then next early morning we continued our tour

from district Shangla towards Chillas.

2nd DAY: On 2ND day we work on 6TH different location along the lecture of Dasu Dam project

geologist. On that day field work done at Besham city, lower and upper Kohistan district along

KKH and the end of the day at11:00 pm we reached to Shangrilla hotel .

3rd DAY: The next day (3rd) of our field start at 9:15am at the hotel with the lecture of Dr

Ihsanullah about Bhasha Diamir dam and then we start field work at 10:00 am at Chillas city

Babusar top and Jaglot area. We studied SEVEN different location rocks petrology and

mineralogy.

4th DAY: The main Day 4TH of field tour , we spend it in Gilgit Hunza area along KKH. We

work on 5 different location along KKH and reached to Hunza at 2:00pm then return from their

and reached to palace hotel at 6:00pm.

5th DAY: The 5TH day of our field spend it in travelling. The location of Diamir bhasha dam

seen there. We came back from gilgit to Besham and at 10:00pm we reached to Besham continental

hotel district shangla

.6th DAY: It was the last day of field trip at 16 of May 2015 we start our field work from

Besham area . We studied different rocks at three different locations on the way we moving toward

Haripur. And finally we reached to Haripur about 3.30 pm evening, and taken the bags and went

to hostel.


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CHAPTER 2

Literature review


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Chapter : Literature review

For the studying igneous and metamorphic rocks this gilgit area is best. Because in this area the

igneous and metamorphic rocks are well exposed on the surface that’swhy we selected this

area and did field work on this area.we were not the first one who studied this area but more

people also did research on this place so I would like to itroduce some of them.

1. M. ASIF KHAN1, ROBERT J. STERN2, ROBERT F. GRIBBLE2 & BRIAN F. WINDLEY3 1Centre

for Excellence in Geology, Peshawar University, Peshawar, Pakistan 2Center for

Lithospheric Studies, University of Texas at Dallas, Box 830688, Richardson, TX 75083-

0688, USA (e-mail: [email protected]) 3Department of Geology, University of

Leicester, Leicester LE1 7RH, UK

Work : Geochemical and isotopic constraints on subduction polarity, magma sources, and

palaeogeography of the Kohistan intra-oceanic arc, northern Pakistan Himalaya

2. R. A. KHAN TAHIRKHELI

Work : Geology of Kohistan and adjoining Eurasian and indo –pakistan continents

,Pakistan

3. A. K. Jain* Central Building Research Institute, Roorkee 247 667, India

CURRENT SCIENCE, VOL. 106, NO. 2, 25 JANUARY 2014 254

*e-mail: [email protected]

Work : When did India–Asia collide and make the Himalaya ?

Keywords: Batholith, collision of plates, intra-oceanic islands arc, lithosphere


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CHAPTER NO 3

Field description


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CHAPTER : Field description

Day 1

Stop 1:

Co-ordinates:

(N=34°31′ 58.3″, E=73° 10′ 57.8″ )

Elevation = 1267m

Locality: Ahal ( Mansehra )

Rock Observed:

Granodiorite

Detail observation:

It is the part of Mansehra granitic batholith, it does not mean that granitic

batholith have only granite but it consit of granodiorite,quartzite etc. On this stop we study

three different lithology’s 1) Granodiorite 2) Granite 3) Black intrusion of biotite . Foliation,

folding and crushed material is observed, it is due to the tectonic activities (like movement

occour ) structures are disturbed and extensive foliation and folding occour . It is also called

oogi shear zone, fault zone , crush zone and fault swamp.

As we know granite is hard rock but if we see crushing, it shows us that force is so high. The

above all these activities is due to the Himalaya orogeny (25-30 Mya), so some worker called it

MCT. MCT (main central thrust ) separate highly metamorphose rock from less deformed rock

(higher Himalayas from lesser Himalayas).

In Pakistan, no evidence found of MCT . In oogi shear zone some geologist called it MCT, but

the oogi shear zone is combined with Batal fault ( in kaghan ) and its age is not same as the MCT

age. There are ten more places which different geologist says that it eas MCT. So conclusion is

that it have controversies in MCT.


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Stop 2 :

Locality : Ahal area

This is the main locality for shear zone ( oogi shear ). Crush material ( granite ) is seen from right

side of road .


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Stop 3:

Co-ordinates :

(N= 34° 37′ 34″ , E= 73° 5′ 50″ )

Elevation= 1497m

Locality: near Chatter plane ( Sharkool )

Rock Observed :

Orthogneisses

Detial Observation :

Before this area slate like lithology seen on raod side which was Tanawal

Quarzite. Then we moved toward north approaching to suture zone. White and dark band

aligned which are gneisses. The garnet rock now converted into gneisses so called it

Orthogenesis . We called it Orthogneisses because of texture we identify it’s parent rock. The

plutonic rock is coarse grain and sedimentary rock are very fine grain .

GRANDIORITE > CONVERT to > GNEISSES

We observed fracture, veins , joints in the formation . Dark colour is because of weathering and

fresh surface is of white color . It is very lose material, break down easily.


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Day 2

Stop 1:

Co-ordinates:

( N=34° 65′ 39.6″, E=72° 52′ 34.96″ )

Elevation = 603m

Locality: near Besham city ( left side of the bridge )

Rock Observed :

Rocks of Besham complex.

Detail Observation:

As we know besham group rocks are very high grade metamorphic rock. All are

pre Cambrian shield rock first and after then metamorphosed . Here we observed Graphite

schists which is black in colour and consist of iron and Quartz veins , also intrusion of granite

(Aplite ) and also observed Paragneisses and meta Conglomerate . All are different Gneisses

( ortho and para ) . In this area rock of gneisses , white band material is not found or too low

because this was mafic rock ( mafic mineral high ) . Metamorphism in this is before from

Himalayas . The recent metamorphism blind the older metamorphism .


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Stop 2:

Co-ordinates:

( N= 34° 57′ 34.3″ , E= 72° 52′ 48.16″ )

Elevation= 758m

Locality: After Besham ( along indus river , 1 or 2 hour away from besham).

Rock Observed:

Paragneisses

Detail observation:

Our main objective on that stop was mapping , so we developed the map of that

area which was attached in chapter ( ) and their we explained it in detail.

We observe metamorphic rock , it was a part of besham complex . From there we collect rock

of Paragneisses , which was quartz enrichment and have mica in it. Greenish colour is quartz

and back is mica’s biotite.

Sedimentary rock > metamorphosed > Paragneisses


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Stop 3:

Co-ordinates:

( N= 35° 02′ 19.6″ , E= 72° 54′ 03.1″ )

Elevation= 717m

Locality: Dubair area

Rock Observed:

Granodiorite

Detail observation:

Because of too much rain, we did not observed clearly this rock ( granodiorite).

As we know grandiorite is a medium to coarse grained intermediate to acid igneous rock with

essential mineral quartz, plagioclase and feldspar.


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Stop 4 :

Co-ordinates:

( N= 35° 2′ 40.5″ , E= 72° 56′ 37.9″ )

Elevation= 936m

Locality: Jijal

Rock Observed:

Igneous rock

Detail observation:

We observed the rock it was green in colour , mineral like pyroxene and

olivine is present we called it ultramafic rock . It may be observed at thin section that either It is

peridotite rock or dunite rock.

This is the area of Jijal complex area . From this area Kohistan Island arc sequence are started.

In this area MMT is present but for this we have search for it . MMT is thrust fault between

Indian plate and Kohistan Island arc . This area is basically ophilitic zone.


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Stop 5:

Co-ordiantes:

( N= 35° 42′ 28.86″ , E= 72° 57′ 28.6″ )

Locality: Chanchal area

Rock observed:

Granulite

Detail Observation:

Basically, Gabbro (mafic rock) metamorphose and granulite developed.

A granulite is a fine to medium rained metamorphic rock. Granulite typically contain amphibole

, quartz , feldspar, and pyroxene with very little or no mica. We observed the brownish mineral

which is garnet , the green colour is weather colour produce due to serpentinization.


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Stop 6:

Locality: Dasu area

Objective :

We stand on the left side of the indus river near dasu hydro project. Our main

objective on that stop was to study about the dam construction, mapping and thing related to

engineering geology .We discussed it on chapter no ( ).

DAY 3

Stop 1:

Locality: Shringrilla hotal ( Chilas).


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Objective:

In this hotal senior geologist IHSNA ULLAH guide us on Dammer Basha Dam project. The

detail was given in chapter no ().

Stop 2:

Co-ordinates:

(N= 35° 25′ 42.7″, E= 74° 6′ 31.2″ )

Elevation: 1064m

Locality: near Chilas area

Objeactive :

The main objective of this stop is study the Geomorphology of the area, here we observed the

effect of ice age, glacier deposits, ancient channel, non-conformity and the Aeolian deposit.

We further explain it in detail in chapter no ( ). The second objective of that was to draw the

sketch of outcrop.

.


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Stop 3:

Co-ordinates :

( N= 35° 24′ 34″ , S= 74° 8′ 48.6″ )

Elevation= 1051m

Locality: Babu sar top , Gilgit Baltistan police check post

Rock Observed:

Gabbroic rock, Dunites, Pegmatite veins, hornbendite.

Detail Observation:

1) Gabbro is dense, greenish or darker colored and contain pyroxene,

plagioclase, and minor amount of amphibole and olivine . In gabrro

black amount of mineral is high , it is mafic in origin .

2) Dunites, all minerals are olivine , small amount of pyroxene( greenish

colour) . Grains are vitrous . In dunite , some time green colour is due to

serpentinization.

3) Pegmatite viens , have black hornblende mineral.

4) Hornblendite rock , In this hornblend mineral amount is high . It is the

part of Chias complex .


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Stop 4:

Co-ordinates:

( N= 35° 28′ 0″ , S= 74° 33′ 6.06″ )

Elevation= 1190m

Locality: Tatta pani

Observation:

We observed here the hot water spring. The theory behind this is nanga parbat , in

which younger granet intruded and due to the presense of hot chambar the water is hot , and

comes out of surface in the form of HOT SPRINGS. Hot spring is also the clur of Fault.

Researcher says that Nanga parbat made on MMT and they have Rikot fault and because of the

movement of the fault , fracture produced ant the water along this becomes hot . So it is called

as Hot spring of Tatta pani.


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Stop 5:

Locality: Thelechi area

Rock Observed:

Schist/Phyllite

Detail Observation:

We observed Phyllite,,, and in some places schist is present . Grains of this

was not seen , because it was fine grain. It was basically sedimentary rock and they

metamorphose and convert to phyllite/schist. It was the part of Jaglot group.

Jaglot group have different type of meta sediment. It have turbiditic sequence like Shist-

Phyllite, Shist-phylite. In Kohistan island arc sediments were deposit in Back arc and after then

because of collision they metamorphosed. In this area igneous intrusion occur i.e Kohistan

batholith intrude. In this stop rock are the Thelitic formation, which is a part of jaglot group.


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Jaglot group include Thelitic formation, Chalt volcanic formation and gilgit formation.

Stop 6:

Co-ordinates:

( N= 35° 39′ 55.8″ , E= 74° 37′ 0.6″ )

Elevation= 1305m

Locality: Jaglot area

Rock Observed:

Gabbro rock and diorite dikes

Detail Observation We observed gabrro and diorite dikes . The dike is a grey to dark grey

intermediate intrusive igneous rock composed of feldspar , biotite , hornblende and pyroxene.


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Stop 7:

Co-ordinates:

( N= 35° 44′ 9.6″, E=74° 37′ 20.6″ )

Elevation= 1371m

Locality: stop at Thriple Junction

Rock Observed:

Aplite

Detail Observation:

We observed fine grain material of granite which was aplite. Intrusion occur in

granitic rock which is younger then Kohistan batholiths . Mafic rock like gabbro intrusion occur.

In this stop three mountains joints together i.e Himalayas , hindukush and karakoram. That’s

why it is called thriple junction. At this stop we observed that Gilgit river meets with Indus river.


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Day 4

Stop 1:

Co-ordinates:

(N= 35° 59′ 27.5″ , E= 74° 19′ 32.9″ )

Locality: Jutal area

Rock Observed:

Diorite

Detail Observation:

We observed diorite rock in which we saw feldspar, biotite, hornblende .

This diorite rock was grey to dark-grey intrusive igneous rock. In some place basic dike and

intermediate dike was observed , 75 million years ago the veins intruded. We observed the

olivine rich rock known as dunite, dunite is as igneous plutonic rock of ultramafic composition.


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Stop2:

Locality: Nomal area

Objective:

The main objective of that stop was to observed the geomorphology of the area, it

have very complex geomorphology which we discussed in chapter ( ) . This area was still in

KIA.There we saw that all gilgit and nearby area are located on Fans as shown in figure.

Stop 3:

Co-ordinates:

( N= 36° 10′ 2.06″ , E=74° 17′ 6.4″ )

Elevation= 1671m

Locality: Jacot Village


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Rock Observed:

Meta- Basaltic rock

Detail Observation:

We observed volcanic rock ( basaltic rock) which was of dark colored, fine

grain igneous rock . It is most commonly form as an intrusive and extrusive , such as lava flow.

We also observed pillow basalt on right side of the road . Pillow basalt developed at the time of

extension in that area because pillow basalt erupts underwater or flows into the sea and form

pillow like structure. We also observed green schist facies, the green color is due to the mineral

chlorite and epidote mineral it is medium pressure and temperature facies. Greenish color

because of very low grade of metamorphism ( like green schist).

Stop 4:

Locality: Chalt valley (Sikandarabad)

Rock Observed:

Meta-sediments rock

Detail Observation:

It is the collision point of Indian and Eurasian plate. Nearly 50 to 55 million

year ago the two continental plates collide at this junction such as the Indian plate and Eurasian

plate. The tremendous amount of pressure created causes Earth crust to buckle producing large

horizontal and vertical displacement and producing these mountains of the Karakorum. The


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Indian plate is still moving towards north into the Eurasian landmass at about five centimeters a

year causing the mountains to raise about seven millimeters annually. The collision is shown in

the figure.

Stop 5:

Co-ordinates:

(N= 36° 4′ 15.76″ , E= 74° 19′ 35.3″ )

Elevation= 1833m

Locality : Near nagar college

Rock Observed:

Phyllite rock ( meta-sediment )

Detail Observation:

Here we observed meta-sediment rocks which was phyllite , and it was the

part of yaseen group , these rocks can break along cleavage . Yaseen group consist of meta-

sediment rocks. When yaseen group end and igneous rock start , researchers mark it MKT.

Flysch sediments metamorphose , it is Quartzite or Marble ???? It can be observe from HCL. It

was the last part of KIA.


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Stop 6:

Locality: Hunza

Objective:

The main objective is to visit hunza city. Due to our bad luck, the whole city was

closed because of Saniha Safoura (death of 45 Ismailia’s peoples in Karachi), so we come back

after spending a short time in Hunza.

Day 5

Stop 1:

Locality: Near Diamer Basha dam

Objeactive:

Our main objeactive ot that stop was to conduct site investigation information of the

dam but due to visiting of Chief Justice of Pakistan to this area , we only spend 7 mints in this

area. We discussed it in detail in chapter ( ).

Day 6

Stop 1:

Co-ordinates:

(N=34° 52′ 11.3″ , E= 72° 55′ 24.5″ )


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Elevation= 617m

Locality: Near Besham

Rock Observed:

Meta-sedimentary rocks with granitic intrusion.

Detail Observation:

This is basically the part of the Besham complex . It was high weathered zone.

Intrusion in some zone occur . Grain size too low . White rock is igneous rock . Weather zone ,

minerals formed because of weather called weather minerals. Brown color is because of iron.

May be this meta-sedmntary rock is Quartzitic rock.

Stop 2:

Co-ordinates:

(N= 34° 50′ 47.6″ , E= 72° 58′ 28.8″ )

Elevation= 717m

Locality: Near Takhot Bridge

Rock Observed:

Graphitic Schist

Detail Observation:


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Parent rock of Graphitic schist is sedimentary. All are meta sedimentary

rocks. Graphitic schist developed , mark Takhot fault. It is the pre-cambrian rock sequences.

Stop 3:

Co-ordinates:

(N= 34° 41′ 7.1″ , E= 72° 59′ 23.4″ )

Elevation= 962m

Locality: Near batagram

Rock Observed:

Orthogneisses

Detail Obsrvation:

In this igneous rock AUGEN structure is developed. It is the part of

Mansehra batholith . In this we observed non foliated minerals. Parently homogenous material

present in igneous.


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CHAPTER NO 4

Geomorphology


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CHAPTER: geomorphology

DAY 3.

Stop 2:

LOCATION : NEAR CHILAS BAZAR

GEOMORPHOLOGICAL FEATURES OBSERVED:

Mostly glacial deposits of Pleistocene age were seen because

there was no sorting seen in field , different sizes of grains (mix-up of material) were observed

due to debris flow .mostly moraines deposits are seen. Some sand ridges also seen which were

formed due to wind (wind deposit).Some sorted grains (LENSES) were also seen which formed

in the result of melting of glaciers and stream flow. Loose material also observed. This is also

called Jalipur sediments.

Stop 4:

LOCATION : TATTA PANI


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Geomorphological observation:

We observed in this area hot spring called tatta pani. The

cause of hotness of this spring is due to deep seeded water and fault and spring were formed

due to Raikot fault. Raikot fault is basically strike slip fault and its also called tranpressional

fault.

OLD CONCEPT ABOUT TATTA PANI:

The old concept is that there were youngest granitic rocks of Nanga Parbat so there could be

the magmatic chamber trough which this water passed and became hot. Nanaga parbat

syntaxes is the part of MMT.

DAY 4

Stop 2:

LOCATION: NOMAL VILLAGE

Geomorphological observation:

We seen in this stop the following geomorphological features:

Point bar :(is a depositional feature made of alluvium that accumulates on the inside

bend of streams and rivers below the slip-off slope)


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Flood plain : It is an area of land that is prone to flooding. People realize it is prone to

flooding because it has flooded in the past due to a river or stream overflowing its

banks)

Alluvial fans: It is a fan- or cone-shaped deposit of sediment crossed and built up

by streams. If a fan is built up by debris flows it is properly called a debris

cone or colluvial fan. These flows come from a single point source at the apex of the

fan, and over time move to occupy many positions on the fan surface. Fans are typically

found where a canyon draining from mountainous terrain emerges out onto a

flatter plain, and especially along fault-bounded mountain fronts)

Bajada fans: A bajada consists of a series of coalescing alluvial fans along a mountain

front. Thesefan-shaped deposits form from the deposition of sediment)

http://en.wikipedia.org/wiki/Fan_(implement)

http://en.wikipedia.org/wiki/Cone

http://en.wikipedia.org/wiki/Deposition_(geology)

http://en.wikipedia.org/wiki/Sediment

http://en.wikipedia.org/wiki/Streams

http://en.wikipedia.org/wiki/Debris_flows

http://en.wikipedia.org/wiki/Debris_cone

http://en.wikipedia.org/wiki/Debris_cone

http://en.wikipedia.org/wiki/Colluvium

http://en.wikipedia.org/wiki/Apex_(geometry)

http://en.wikipedia.org/wiki/Canyon

http://en.wikipedia.org/wiki/Terrain

http://en.wikipedia.org/wiki/Plain

http://en.wikipedia.org/wiki/Fault_(geology)

http://en.wikipedia.org/wiki/Mountain


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CHAPTER No 5

Engineering Geology


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Chapter : Engineering Geology

Diamer-Bhasha Dam

The lecture was delivered by 4 geologist senior geologist, ihsan ullah guide us on diamer bhasha

dam.

Features of diamer –bhasha dam

LOCATION: The Dam will be located on the River Indus in Northern Pakistan, about 315

km upstream of Tarbela Dam, 165 km downstream of the Northern Areas capital of Gilgit and 40

km downstream of Chilas.

DamType Roller Compacted Concrete (RCC)

MAIN DAM Maximum Height: 270 m

DIVERSION SYSTEM 2 No. Diversion tunnels 1 No. Diversion canal Upstream and

Downstream Cofferdams

MAIN SPILLWAY No. of gates 9 Size of gate

RESERVOIR LEVEL 1160 m Gross capacity 7,300,000 acre feet (9.00×109 m3) Live

capacity 6,400,000

POWERHOUSE(S) 2 underground powerhouse Total installed capacity 4500 MW Location

and type Toe of the Dam (one each on the right and left side)

ESTIMATED COST (YEAR 2008) US$12 Billion

Total Installed Capacity: 4,500 MW

In intial investigation stage four adit were developd to know the lithology ,sub surface geology

and to know about fault.

http://en.wikipedia.org/wiki/Megawatt


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DASU HYDROPOWER PROJECT The lecture was delivered by moheen ud din and habeeb shah

Dasu Hydropower Project is a run of river scheme located 7 km upstream of Dasu village on Indus River, 74 km downstream of Diamer Basha Dam and 350 km from Islamabad. The Project is located in District Kohistan of Khyber Pakhtunkhwa Features of dasu dam:

Type of dam Gravity, roller-compacted concrete

Height 242 m (794 ft)

Length 570 m (1,870 ft)

Total capacity 14,100,000,000 m3(11,400,000 acre·ft)

Installed Capacity (MW) 4320

Type of Dam RCC

Dam Height (m) 242

Construction Period (Years) 18 (in four phases

Power house underground

Reservoir length

73km

We find out Rqd value which is 100

http://en.wikipedia.org/wiki/Dam#Types_of_dams

http://en.wikipedia.org/wiki/Roller-compacted_concrete


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Chapter no 6

Tectonics


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CHAPTER : Tectonics

Regional geologic setting

The Indian Plate margin:

The Indian Plate margin The northernmost parts of the Indian continent crop out between the Main

Boundary Thrust (MBT), to the south, and the Indus Suture to the North. Northern metamorphic units

and a southern, fold-and-thrust sedimentary belt constitute the so-called Lower- (or Lesser-) Himalaya

of Pakistan (Chaudhry et al. 1997). Altogether, it is a low-grade assemblage of a 20 km thick, imbricate

thrust pile of Mesozoic sequences originally deposited on the Indian continental crust represented by

mid-Proterozoic and Paleozoic gneisses and sediments. Cambrian stromatolitic dolomites record the

epicontinental marine transgression on 1.5 - 2.2 Ga old remobilised gneisses. Around 500 Ma old

granitoids, which have been deformed into orthogneiss (Le Fort et al., 1980, Anczkiewicz 1998, DiPietro

& Isachsen 2001), record the widespread magmatic event of that time, which is documented on all

Gondwana-derived continental blocks.

Much of the Phanerozoic shelf sequence (shales, sandstones and limestones) is of Gondwana type,

starting in the Middle-Paleozoic. Early-Permian magmatic ages of metabasaltic dikes and granitegneiss

intrusive into older Indian gneiss are evidence of pervasive magmatism during rifting , which is

associated with the break-up of Gondwana. Rifting produced a suite of alkaline intrusions, including

carbonatites .Sedimentary records indicate that the onset of extension tectonics is Early Carboniferous .

Marine shelf sedimentation was re-established in the Late Triassic. The Mesozoic sedimentary history is

that of carbonates deposited during thermal subsidence of a continental margin, on the southern side of

Neo-Tethys. All these rocks were deformed and metamorphosed between 75 and 40 Ma . Subduction of

at least parts of the Indian craton to depths equivalent to 27-32 kbars at ca. 50 Ma is indicated from the

occurrence, in the Kaghan Valley, of coesite-bearing eclogites likely derived from basaltic Permian dykes

. Thermochronologic studies suggest that before 13 Ma most of the Lower Himalaya rocks were located

Figure 2 - Satellite overview of the area crossed by the field trip.

A GEOLOGICAL TRANSECT FROM THE INDIAN PLATE TO THE EAST HINDU KUSH, PAKISTAN

PR01

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Volume n° 1 - from PRO1 to B15

either beneath a paleo-foreland basin or beneath Main Central Thrust (MCT)-related nappes. Molasse

conglomerates siltstones and shales (termed Siwalik or Sub-Himalaya sediments) lap onto the Indian

Shield. In detail the discontinuous series comprises most of the Cenozoic but there was a general lack of

sedimentation during the Late Eocene and almost the entire Oligocene. This unconformity of 15-20 Myr

may refl ect an important change in orogenic processes. One interpretation involves the passage of a fl

exural forebulge migrating southward through India. Late Oligocene to Early Miocene fl uvial formations

record the emergence of the Himalaya Mountains. The Kohistan Island Arc Complex: Outline The


Page | 44

Kohistan terrane in NE Pakistan (Fig. 3) is regarded as a fossil island arc obducted between the collided

Indian and Asian plates (Bard et al. 1980, Tahirkheli et al., 1979). Owing to the admirable quality of

exposures, the Kohistan offers an unrivalled opportunity to investigate the structure of an island arc and

related subduction processes (Bard 1983, Searle et al., 1999, Treloar et al., 1996). In particular,

numerous time markers in the form of intrusive bodies make the Kohistan an exceptional place to study

the signifi cance of magmatic structures in the deep crust of an arc system.(Fig.3)

The Kohistan sequence displays a structurally coherent section of an island arc terrane, comprised of a

30 to 40 km thick section of metamorphosed, plutonic, volcanic and sedimentary rocks. This succession

is interpreted as plutons intrusive into an oceanic crust and overlain by the calc-alkaline lavas and

associated sediments. Accordingly, the interpretation is an intraoceanic arc that developed during the

Cretaceous through a north-dipping subduction in the equatorial area of the Tethys Ocean (Yoshida et

al. 1996). Six main rock assemblages from north to south, i.e. downward sequence, are present. UPPER

CRUST Upper crustal sequences pertain to two geographically distinct domains. - Just south of the

Northern Suture, they consist of interlayered volcanoclastic sediments, volcanites and rather immature

turbidites deposited in a deep-water environment. Sediments (so-called Yasin Group) are shales,

graywackes and volcanoclastic rocks form a probable back-arc basin of Cretaceous age. They grade

upward into fi ne grained shales and tuffs and contain limestones with an Albian-Aptian fauna (Pudsey

et al. 1985). Volcanites (Chalt Volcanites) are calc-alkaline andesites to rhyolites succeeding to andesitic

lavas, tuffs and agglomerates of Early Cretaceous age. Exceptionally well-preserved pillow lavas are

primitive island-arc-type, tholeiitic lavas that possibly represent part of an ophiolite assemblage

obducted during the Kohistan-Asian collision. The size of this oceanic back arc basin (with respect to the

Kohistan) is conjectural. - To the Southwest and within the Kohistan Complex, metasedimentary

sequence of deep marine origin (Dir, Utror and Kalam Groups) yielded Eocene fossils in upper-level

limestones. Depositional models point to rapid subsidence in Paleocene times in an extensional,

restricted basin. Associated volcanic and volcanoclastic series are calc-alkaline basalts, basaltic andesites

and andesites, emphasising an arc environment (Sullivan et al. 1993). PLUTONIC CRUST Kohistan

batholith: is a name that gathers intrusive calc-alkaline granitoids. The fi rst plutonic stage is dated at ca

105 Ma. Stages 2 and 3 are dated between 85 and 26 Ma. Stage 1 and early stage 2 plutons have

isotopic signatures characteristic of a mantle derivation. The isotopic signatures of younger plutons

show evidence of an increasing crust to mantle ratio, with the latest magmas being entirely crustally

derived. This evolution is interpreted as the result of arc thickening and lower arc melting following

suturing to Asia .

Gabbronorites: a massive body of locally layered gabbronorites marks the axis of the arc. It is the more

than 8 km thick and 300 km long Chilas complex thought to be a layered magma chamber intruded into

the arc in Cretaceous times. In detail, it is a stratiform complex of norites, noritic gabbros and a string of

lenses of diverse ultramafi c-mafi c-anorthosite (UMA) association. The UMA represent apices of intra-

arc mantle diapirs that served as porous fl ow conduits to feed the gabbro-norite.

The gabbro-norite cooled and equilibrated at 600-800°C and 6-8 kbar. A Sm-Nd internal isochron yields

an age of c. 70 Ma, consistent with the conventional zircon U-Pb age of 84 Ma (Schaltegger et al. 2002).


Page | 45

Leaders: M. Gaetani, J.P. Burg, A. Zanchi, Q.M. Jan PR01

Figure 3 - Structural sketch map of the Kohistan Island Arc Complex.

A GEOLOGICAL TRANSECT FROM THE INDIAN PLATE TO THE EAST HINDU KUSH, PAKISTAN

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Meta- gabbros to tonalites: (so-called Kamila amphibolites) form a thick pile of imbricated calcalkaline

laccoliths variably sheared in amphibolite facies conditions. Small inliers of metasediments and

metavolcanic rocks screen these laccoliths and rare granites belong to the plutonic association. Few

intrusion ages are available. They span from 99 to 82 Ma, giving evidence for a succession of short-lived

plutonic events; 82 Ma-old rocks are kyanite-bearing pegmatites produced by partial remelting of

deeper lithologies in the arc . ArAr cooling ages on hornblendes cluster around 80 Ma, hence providing

evidence that this part of the Kohistan island arc complex was cooled below c. 500°C in the Late

Cretaceous (Treloar et al., 1989). Shear strain localisation took place continuously from magmatic

emplacement to solid state deformation during cooling of the gabbroic and dioritic plutons, between

100 and 83 Ma (Arbaret et al., 2000). The related shear strain probably represents arc-related


Page | 46

deformation during subduction of the Tethys oceanic lithosphere below the Kohistan Arc Complex.

MANTLE The so-called Jijal-Patan Complex, is composed of more than 3 km thick ultramafi c rocks

overlain by garnet-plagioclase granulites. Garnet- and plagioclase-free peridotites and a few pyroxenites

dominate the lowest section. The Jijal peridotites represent the sub-arc mantle (Burg et al., 1998). The

sharp contact between the ultramafi c rocks and the overlying granulites, with well-preserved igneous

structures, is the intrusive contact of lower crustal, calc-alkaline garnet-gabbros (the granulites) within

mantle rocks (Burg et al., 1998). The contact is also the lower boundary of the arc crust, i.e. the arc-

Moho. In the granulitic gabbro, metamorphic overprint essentially marks isobaric cooling within

granulite facies conditions (starting T > 1150°C at depth > 50 km although early metamorphic pressures

may have increased. The granulitic gabbros have later re-equilibrated at >700°C and 15 + 4 kbar, which

are pressure conditions similar to those calculated from the underlying ultramafi c rocks (Ringuette et

al., 1998). Sm-Nd isochrons at c. 95 Ma date cooling and provide the minimum age of the Jijal ultramafi c

sequence (Anczkiewicz & Vance 2000, Yamamoto & Nakamura 2000). Arc splitting The calc-alkaline

Chilas norites and noritic gabbros were fi rst interpreted as having crystallised in the

sub-arc magma chamber (Bard et al., 1980). Later geochemical analyses suggested that it was generated

by intra-arc rifting and subsequent mantle diapirism (Khan et al., 1993). The latter interpretation is

consistent with the gabbro-norites having intruded volcanic and sedimentary components of the arc.

Petro-structural observation supportively suggests that the ultramafi c-mafi c-anorthosite associations

occurring as a string of lenses over the >300km length of the gabbro-norite represent apices of intra-arc

mantle diapirs that served as porous fl ow conduits to feed the gabbro-norite (Burg et al., 1998).

According to the zircon U/Pb age of gabbronorites, rifting is about 85 Ma old (Schaltegger et al., 2002).

The Chilas suite of mantle diapirs points to splitting of the Kohistan arc, with initial rifting taking place at

the island arc as documented in modern island systems (e.g. Rocas Verdes). The UMA outcrops point to

mantle diapirism as a key mechanism in opening back-arc basins between a volcanic and a remnant arc,

the latter perhaps now seen as rocks screening the Kohistan Batholith. Obduction - metamorphic record

The Kohistan Arc and India were assembled during closure of Tethys, which produced thrusting along

the Indus Suture. Within the Suture, a discontinuous but up to 20 km wide zone of imbricated ophiolites,

greenschists and blueschists is locally referred to as “mélange unit”. It is a dominantly fore-arc related

assemblage obducted onto the Indian plate (Anczkiewicz et al. 1998). In the footwall, the geology of the

northern margin of the Indian plate is remarkably uniform. However, two highpressure metamorphic

events have accompanied the India-Kohistan convergence: blueschist facies metamorphism at ca. 80 Ma

is linked to oceanic subduction, eclogite facies metamorphism at ca. 50 Ma is linked to continental

subduction. PRE-COLLISION EVENTS Blueschists imbricated within the suture between India and the

Kohistan Arc yielded 40Ar-39Ar and Rb-Sr, phengite and Na-amphibole ages at ca. 80 Ma and thus

record a pre-collisional, Early/Late Cretaceous metamorphism during subduction of the Tethys oceanic

lithosphere (Anczkiewicz et al. 2000). Rapid exhumation and cooling of these highpressure metamorphic

rocks probably took place in an accretionary prism system dominated by corner fl ow processes.


PR01 -

Leaders: M. Gaetani, J.P. Burg, A. Zanchi, Q.M. Jan PR01


Page | 47

COLLISION-RELATED EVENTS Collision with India developed Barrovian metamorphism in the Indian

sequences. U-Pb ages of syn-metamorphic granites and Nd-Sm ages of eclogites indicate that at about

50 Ma the northern margin of India was deeply buried and being metamorphosed in high-pressure

conditions (Spencer et al. 1995). Ar/Ar mineral ages of the metamorphosed sequences on the Indian

plate give cooling ages of hornblende at 38 Ma and muscovite cooling ages of 30 Ma (Treloar et al.

1989). The metamorphic and related structural fabrics in these rocks, therefore, record an important

part of the collisions and the fi nal emplacement of the Kohistan Arc against this segment of the Indian

plate. The post-Eocene thrust directions generated complex, refolded thrust patterns, large slab folding

and rapid uplift with associated brittle faulting and seismic activity. No signifi cant movement has taken

place along the Indus Suture since 20 Ma, as indicated by similar fi ssion track ages on both sides of the

Suture (Zeitler 1985). The North-Kohistan Suture Zone The North-Kohistan Suture marks the fault

contact between the Karakoram margin of the Eurasian Plate, to the North, and the Kohistan Paleo-

Island Arc Complex, to the South. The North-Kohistan and Indus Sutures were two branches of the

Neotethys Ocean and, as such, are western continuations of the Tsangpo Suture, in southern Tibet. As

such the North-Kohistan Suture Zone eastward becomes the Shyok Suture, which separates the Ladakh

Arc from the Karakoram. It has been inferred that the North-Kohistan Suture closed in the Late-

Cretaceous on the basis of two arguments. 1) Undeformed subalkaline plutons of Eocene age are found

on both sides of the Suture (Debon et al., 1987, Coward et al., 1987) and 2) pillow lavas next to the

suture were deformed before intrusion of a 75 Ma old, mafi c dyke, (unpublished Ar-Ar age on

hornblende by D. Rex, in (Petterson & Windley 1985) and mean age despite excess Argon in (Treloar et

al., 1989). However, a signifi cant amount of the Karakoram granitoids is 25 Ma old, or younger (Debon

et al., 1986, Parrish & Tirrul 1989). (Brookfi eld & Reynolds 1981) and (Reynolds et al., 1983) suggested

that the eastern continuation of the North-Kohistan Suture, the Shyok Suture in India, did not close

before the Miocene. The age of this closure remains unsettled, probably because suturing involved

multiple events. In Pakistan, early geological information is due to (Desio 1964, Desio & Martina 1972).

The suture zone turns from its SW-NE trend, along the western Kohistan boundary to nearly E-W along

the northern boundary (Fig. 3). The North-Kohistan Suture is described as a mélange containing blocks

of serpentinite derived mostly from harzburgites, greenstones derived from both volcanic and

volcanosedimentary formations and sediments that include limestones, red shales, conglomerates and

quartzites in a turbiditic, slate-dominated matrix (Pudsey et al. 1985a, Pudsey 1986). The “mélange”

separates volcanic and sedimentary rocks of the Kohistan Arc Complex, to the south, from shelf

sediments of the Karakoram to the north. The so-called mélange is a 1-7 km wide imbricate zone in

which slices with well-defi ned lithologies are bounded by a series of anastomosing, brittle faults that

have faulted away the original suture . Sinistral faults with a minor reverse component dominate the

western segment. The reverse component is more important along the E-W segment. North and south

vergent structures are found on both sides and within the suture. The North-Kohistan Suture Zone

displays polyphase deformation. At least three ductile deformation events have been recognised,

represented by (1) the stretching lineations in conglomerates and marbles, (2) curved fold axes in green

schists and (3) crenulation lineations in black schists and slates. Brittle deformation is principally

represented by recent sinistral strike-slip faulting with the reverse component. In the Drosh area, to the

west youngest fi ssion track ages on apatite and zircon from the north of the suture, are 11 Ma and 20

Ma, respectively. They are 13Ma (apatite) and 20Ma (zircon) south of the suture. Similar apatite ages on


Page | 48

both sides of the suture show that the rocks on either side passed the apatite partial annealing zone

together, around 1113Ma; accordingly, no or little vertical differential movement has taken place along

this fault zone since the late Miocene. No high-pressure rocks have been found along the North-

Kohistan suture whose real markers are therefore the serpentinites considered to derive from the

Neotethys oceanic lithosphere (oceanic back-arc basin?). The systematic organisation of the lithologic

slices, which may represent a reactivated accretionary prism, leads to redefi ne the main lithological

units according to their presumed tectonic origin. This classifi cation is tentative and thus must be

considered

A GEOLOGICAL TRANSECT FROM THE INDIAN PLATE TO THE EAST HINDU KUSH, PAKISTAN PR01

9 - PR01


with caution or even suspicion, in particular because of the lack of ages. Neotethys rocks The North-

Neotethys Ocean lithologies are composed of low-grade pelagic to hemipelagic sediments, banded

cherts, pillow lavas, calcschists, black shales, serpentinites and talc-magnesite schists derived mostly

from harzburgites. However, no typical ophiolitic sequence has been recognised. Serpentinites occur

either as massive lenticular and fault-bounded blocks or (mainly) as thin schistose shreds along major

faults. Gabbros have locally intruded serpentinites. The meta-ultramafi c rocks locally occur as talc-

magnesite felsen and schists, indicating circulation of CO2 fl uids within the suture fault system. The

mineral parageneses indicate greenschist facies metamorphism. North Kohistan rocks The northern

margin of the Kohistan Arc comprises greenschist-facies basaltic and andesitic volcanites, volcanodetritic

and shelf-type sediments that overlie turbiditic red shales, sandstones and conglomerates,

and the calc-alkaline mylonitic gabbros and amphibolitic metavolcanodetritics of the Kohistan Batholith.

Pebbles in low-grade red conglomerates are elongated, hence defi ning a stretching lineation with

variable directions. Fossiliferous (rudists, orbitolinoids) reef-limestone sequences occur within green

basaltic to andesitic volcanites (Pudsey et al., 1985b). It is not clear yet, whether this unit, squeezed

within the suture zone, derived from the Karakoram or Kohistan terrane, or both.


Page | 49

NOTE :

Reader must consult with teachers ,with own observation, with

Books , Class lectures , and additional material apart from this report.

Zeeshan Wahab is not Responsible for any MISHAP!!!!!

THANKS

Gilgit field report by zeeshan (uoh )

Education