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Origin of the Diorite

The following field and petrographic evidences indicate the formation of the diorite rocks by magmatic origin.

Field evidences:

(1) According to the regional geological setting, diorites are found as the marginal facies of Kanzachaung Batholith in the study area (IGCP, 1978).

(2) The diorite is closely associated with granitic rock.

(3) The common intergrowth texture of the diorite seems to suggest the simultaneous crystallization of intergrown minerals from a magma (A.F.Buddington, 1959).

Petrographic evidences:

(1) Perthitic texture, noted in some diorites, suggests that it is formed as a result of exsolution process during the deuteric stage.

(2) Inclusions of plagioclase within hornblende provide the poikilitic texture which may develop during normal crystallization of magma, or may result from post-magmatic alteration. (Williams, Turner, Gilbert, 1965)

(3) The texture of these rocks shows that the paragenesis of the constituent minerals normally follow the reaction series.

Field evidences are not available precisely to indicate the origin of the diorite .But, petrographic criteria mentioned above undoubtedly suggest that these rocks are magmatic in origin.

Origin of the Leucogranite

The following field and petrographic criteria are the indicatives of the formation of the granitic rocks by magmatic intrusion rather than formation in place by a granitization process.

Field evidences:

(1) Leucogranite is associated with diorite, andesite, rhyolite and dacite.

(2) Absence of relic bedding and ghost structures in the granitic bodies suggests that this rock is not formed by the process of granitization,

(3) Xenoliths of preexisting rocks such as the diorites are found in the leucogranite.

(4) Intrusion of aplite dykes and quartz veins which probably connected to the magma source, and belong to the latest phase of magmatic activity occur commonly in the major joint sets of the leucogranite.

Petrographic evidences:

(1) Micrographic texture is developed in leucogranite.

(2) The development of myrmekitic texture indicates that this rock is formed at the later phase of crystallization from magma.

(3) Exsolution texture, like string perthite, is common in leucogranite.

(4) Hydrothermal alteration products which are developed at the late stage in the rocks of magmatic origin are occurred.

Origin of the Dacite

Magmatic origin of the dacite is indicated by the following facts.

Field evidences:

(1) Dacites are found associated with older volcanic rocks such as andesite and rhyolite as well as plutonic rocks of diorite and leucogranite.

(2) Dacite occurs as sub conical dome-like hill which is likely to be broken up locally by the self-infliction process.

(3) Development of flow structure and occurrence of agglomerate and stratified tuff indicate the volcanic eruption.

(4) Xenoliths of andesite are observed within the dacite.

Petrographic evidences:

(1) Porphyritic texture is well developed.

(2) Groundmass is hypocrystalline and often holocrystalline.

(3) Microstructures of perthite and anti perthite are present.

(4) Corroded structure in quartz crystals are produced by the magmatic corrosion

(5) Kaolinization and sericitization are developed by the hydrothermal alterationprocesses at the late stage of magmatic origin.

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