I= PETROLOGICAL AND STRUCTURAL STUDIES OF THE IGNEOUS ROCKS OF THE BARAN LAK AREA, BELA-KHUZDAR, DISTRICTS, BALOCHISTAN, PAKISTAN
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Title of Thesis
PETROLOGICAL AND STRUCTURAL STUDIES OF THE IGNEOUS ROCKS OF THE BARAN LAK AREA, BELA-KHUZDAR, DISTRICTS, BALOCHISTAN, PAKISTAN

Author(s)
Mehrab Khan
Institute/University/Department Details
University of Balochistan, Quetta, Pakistan/Department of Mineralogy
Session
1998
Subject
Mineralogy
Number of Pages
147
Keywords (Extracted from title, table of contents and abstract of thesis)
igneous rocks, baran lak area, bela ophiolite, neoptethysian, ophiolites, mylonitic zone, sepentinzed harzburgitic mantle, gabbros, dioritic

Abstract
The Bela ophiolite is a piece of the NeopTethysian oceanic lithosphere, obducted on the western Indo-Pakistan continental margin, during the late Maastrichtian to Early Eocene. It has not yet been crushed by continental collision, as the northern ophiolites of Indo-Pakistan plate were involved in continent-continent collision. The Bela ophiolite has preserved the structures imprinting during its formation and emplacement. It is the largest outcrop of oceanic lithosphere in this western belt and forms a 10-60 km wide, N-S oriented, 300 km long belt.

The mantle peritonitis of the Bela ophiolite have recorded two successive plastic deformation events, the first one related to the accretion of the lithosphere (asthenopheric shear flow) and the second one is imprinted during the first step of its emplacement (intra-oceanic thrusting). During the intra oceanic thrusting, the mantle peridotites were plastically deformed in high stress conditions responsible fro making metamorphic sole. This deformation grades upward into the mylonitic zone

Shear sense determinations in the peridotite mylonite in the ophiolite foot wall and imbrication structures in the underlying accretionary wedge indicate emplacement toward ESE.

New Ar39 /Ar40 dating and paleontological studies show that Bela ophiolite consists of two oceanic lithosphere of different age. The upper unit (true ophiolite) formed around 70 Ma and the lower unit (Accretionary wedge-trench sediments) formed Aptian / Albian-Maasttrichtian.

The upper unit shows a classical ophiolite sequence (in ascending order) : a metamorphic sole, sepentinzed harzburgitic mantle sequence, layered peridotite/gabbros, layered/foliated and isotropic gabbros sheeted dikes and <100m an extrusive sequence. The lower unit contains ocean ridge related pillow lavas, covered by a Mn-enriched horizons, a sedimentary sequence (radiolarian cherts, shales and calci turbidites) and covered or intruded by doleritic to micro dioritic/gabbroic Fe-rich tholeiitic intrusions and alkaline rocks generated due to the passage of Indian Continental margin over the reunion hotspot

Post-Nal limestone (Miocene) faulting and folding structures developed during the post-emplacement tectonic activities. These deformations are related to the evolution of the sinistral Ghazaband and Ornach-Nal fault systems, which developed in response to the Himalayan collision. By this process parts of the upper ophiolitic unit were juxtaposed with the lithologies of the acceretionary prism and with post-emplacement “exotic” Nal limestone blocks, creating the impression of a mélange

At the time of obduction, the Indo-Pakistan plate was not its present position, the Bela ophiolites thus traveled to the margin of the Indian continental plat in the Tertiary where the ophiolite reached to its present position.

Download Full Thesis
2552.62 KB
S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
145.79 KB
2 1 Introduction 5
293.61 KB
  1.1 What is an ophiolite 7
  1.2 Significance of ophiolites 7
  1.3 ophiolite in Pakistan 7
  1.4 Previous work 17
  1.5 Relationship with surrounding sedimentary rocks 19
  1.6 Infra-ophiolite 22
  1.7 Overlying sediments 22
3 2 Methodology 24
124.81 KB
  2.1 Methods of kinematic analyses 24
  2.2 Microstructural studies 28
  2.3 Determination of sense of shear 30
  2.4 Study of viscous deformation 32
  2.5 Study of discontinuous deformation 34
  2.6 Statistical treatment of the directional data, in three dimensions 34
4 3 Metamorphic sole of the Bela ophiolite 36
231.22 KB
  3.1 Metamorphic sole of the Bela ophiolite 39
  3.2 Penetrative structures 41
  3.3 Basal peridotites 42
  3.4 Kinematics 44
  3.5 40 Ar/39Ar Dating 46
5 4 Mantle section 49
835.6 KB
  4.1 Peridotites 49
6 5 Gabbroic section 78
368.36 KB
  5.1 Crustal section 78
  5.2 Magmatic intrusions 86
7 6 Sheeted Dikes and volcanics 90
458.7 KB
  6.1 Sheeted dikes complex 90
  6.2 Pillow lavas 96
  6.3 Volcanics and associated sediments 97
  6.4 Re-rich tholeiitic intrusions and alkali basalt rocks in the accretionary wedge 99
  6.5 Geochemi-cal characterization of the Bela opiolite 101
8 7 Paleo-Tectonic reconstruction and emplacement 118
101.86 KB
  7.1 Paleo-tectonic reconstruction and emplacement 118
  7.2 Post emplacement hidtory 126
9 8 Discussion and Conclusion 127
48.81 KB
  8.1 Discussion 118
  8.2 The characteristics of Bela ophiolite 128
  8.3 Conclusions 130
10 9 References 132
148.32 KB