About 70 square miles of the area in Malakand agency, Pakistan, covering outcrops of the Hari chand ultramafic complex and the adjoining rocks, has been mapped and an original geological map, on scale of inches to 1 mile has been prepared.
The area lies in the southern dart of the attack ‚€“ Hazara area of Pakistan folded arc, the latter represents alien geosynclinals belt of tethys and in the north-***, **** a small part of hamaiyan meganticlinorium.
The country rocks are represented by politic schist‚€™s and phyllites, and calcareous chist and marble; these have suffered regional metamorphism up to green ‚€“ facies (biotite grade of Barrovian type) . These met sediments hold two small, elongated outcrops of gabbros; at present sufficiently saussuritized to be designated as metagabbgros.
The hari chand complex consists of four large linearly arranged outcrops of harzburgite, partially or completely surrounded by peridotite; the inturn grades into serpentines rock along the marginal zones of complex. During is present in harzburgite as well as in peridotite, occurring as xenolithic outcrops of variable sizes, which are randomly distributed in the rocks. Moreover, chromitite rock is at places, exposed within the dunite bodies, while chromite mineral is present in all the rock types of te complex in accessory amount. Whole of the complex is sporadically traversed by dykes of proximate.
In addition, there are lenses or xenoliths of redingote present in the serpentines rock. In the vicinity large xenoliths of metagabroic. Field observations have shown that both the country rocks and the complex shared common tectonic phase (s). The country rocks are regionally folded and have nearly east-west strike and high angle dip, layers in the complex are conformable with the bedding in the country rocks and the longer are conformable with the regional folding of the latter. At the contact zone of the complex with envelope rocks and met gabbroic rock, no sign of thermal indurations or recrvstallization is seen, rather the contact zone is highly sheared and bears sign of upward movement of the complex relative to the envelope rocks. At the contact zone the complex is represented by schistose serpentinite. However, no significant shearing within the complex has been noted.
Petrography characteristics of different rock types of the complex and the envelope rocks have been investigated by studying about 400 thin sections of representative specimens. In this study special emphasis has been given to the contact zone between the complex and the envelope rocks. Moreover detailed study of important silicate minerals from the complex and the metagabbro have been made to determine their precise compositions.
Primary minerals in harzburgite and peridotite include dominant olivine and accessory chromite in both the rock types while bronzite (Bushveld type) is present in harzburgite and augite with subordinate bronzite in peridotite. Dunite consists of olivine and accessory chromite, while chromitite have variable amount of chromite and olivine. The pyroxenite rock in harzburgite generally consists of bronzite, however, this rock from marginal zones of harzburgite sometime have significant augite and olivine with bronzite. The pyroxenite in peridotite consists of augite sometime with subordinate olivine and bronzite. The pyroxenite in peridotite consists of augite, sometime with subordinate olivine and bronzite. The serpentinite rock mainly consists of Antigo rite, while other morphological forms of serpentine are also noted. Primary features of the rocks are generally preserved in this rock type excent for the schistose serpentinite which is sheared.
All the ferromagnesian minerals in the complex have high magician content, and wherever they co-exist in individual rock typed, they show somewhat systematic variation relative to each other. On the basis of composition (magnesian content) of the ferromagnesian minerals, the rocks of the complex have been arranged in order of: chromitite, dunite, barzburcite, peridotite and pyroxenite.
The sequence of crystallization of the component minerals of the complex have been noted as: chromite olivine and pyroxene. In chromitite rock oliving and chromite show simultaneous crystallization.
In order to investigate chemical characteristics of the complex, 8 representative specimens of harzburgite, 9 of peridotite, 5 of serpentinite, 5 dunite, 5 of chromitite and 5 of pyroxenite, were analyzed chemically, 2 specimens of metagabbro were also analyses . The compositions of individual Litho logic units of the complex show variation over narrow rames (though they show great diversities due to alteration of the rocks to different degrees). However, no trend of differentiation comparable with that world over has been established, rather different litho logic types of the complex have been four arangeable when plotted against different, indices. The harzburgite and peridotite show overlapping areas, while rest of the rock show an arrangement comparable with that found on the hoses of mineralogical study.
As a result of field and laboratory investigations, it has been concluded that the complex originated by crystallization-differentiation of a gabbroic magma at some depth in the crust followed by intrusion of this accumulate (crvstal mush) in the upper crustal level. Such intrusion was assisted by lubrication action of intergranular fluids in small amount. The residual fell spathic fraction of the partially crystallized gabbroic magma was totally citer dressed and this crystallized at a different level. It is also concluded that the complex is tectonically emplaced in the present environments accompanied by its tilting along the longer axis, during major tectonic episode (s). This tectonic movement of the complex was assisted by its mar***nal serpentinization the dunite and chromitite rocks are believed to be early fractions of the crystalline mass: these were transport to the site of intrusion of the complex in comparatively solid state.
Certain other problems, arresting out of this investigation, such as nature of intergranlar fluids, lack of thermal metamorphic effects on envelope rocks and the nature of sergentinization of the complex have been studied little detail.