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Sequence and Age of Emplacement

The igneous rocks of the study area are developed in the Early Cretaceous to Eocene interval Two plutonism and three volcanisms has been occurred. Based mainly on the field relationship and radiometric dating by DGSE (1976) and by 1GCP (1978) the sequence of emplacement in the present area are recognized as follows:

(1) In the study area the igneous activity began with the eruption of andesite.

(2) The eruption of the andesite was followed by the extrusion of rhyolite and rhyolitic tuff at that time.

(3) After the volcanism, diorite pluton associated with Kanzachaung Batholith emplaced as the first stage of plutonism.

(4) The leucogranite intruded the older units as a later phase intrusion of the large granitic pluton.

(5) The major emplacement of igneous rock within the study area was ended up by building of dacite cone and local eruption of its pyroclastics (6) After the major plutonism and volcanism, it was followed by the minor intrusions of aplite and tonalite dykes and quartz veins.

The various igneous rock types might have been emplaced as successive phases within a certain limit of geological time span.

According to field relationship, the andesite of the study area are older than the Kanzachaung Batholith of 93.8 + 3.4 Ma and 97.8 ±3.6 Ma (DGSE, 1976). Besides, this than the Shwedaung Formation which is correlated with the Ngapyaw daw unit is youngerung Formation of Late Triassic age in the Katha-Tigyaing area (Myint Thein et al 1983). Therefore, the age of the andesite is possibly Early Cretaceous.

After the eruption of the andesite, the extrusion of rhyolite and rhyolitic tuff followed as differentiated portion of the and desitic magma. Therefore, the rhyolite is early cretaceous in age.

The smaller pluton of diorite is interpreted as a marginal facies of the larger granodiorite intrusion (Kanzachaung Batholith). Due to the radiometric dating the diorite intruded in Late Cretaceous age. (DGSE, 1976)

According to radiometric dating the secondary hydrothermal muscovite of the leucogranite (defined as altered quartz-diorite) yields an age of 52.9 2.5 Ma (Early Eocene) by DGSE (1976). Therefore, the age of leucogranite is possibly Late Cretaceous.

Dacite and its pyroclastics extruded contemporaneously with the deposition of Ketpanda sediments during Eocene time. The estimated age is supported by K-Ar dating of andesite sill intruded in these sediments at Middle Eocene, 50.1 2.5 Ma (DGSE, 1976). The possible age of the dacite is Eocene.

The age of the various types of dykes and veins cannot be determined certainly However, the age of dykes is possibly Post Cretaceous. According to the IGCP Report (1978), the age of tonalite dyke occurred in the leucogranite is given as Lower Oligocene.

Therefore, it may be concluded that the age of igneous rocks exposed in the study area may be regarded as Early Cretaceous to possibly Oligocene.

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