Volcaniclastic Deposits and Volcanic Activity of Inde Hill, Budalin Township, Sagaing Region
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University Journal of Creativity and Innovative Research 2020 Vol-01 Issue-01 Volcaniclastic Deposits and Volcanic Activity of Inde Hill, Budalin Township, Sagaing Region Aung Zaw Oo Shwebo University [email protected] Abstract Table 1. Stratigraphic succession of the study area The study area is located in the Monywa District of Rock Unit Age the Sagaing Region. It covers approximately 120 sq. km. Alluvium Geotectonically, the study area is mainly composed of Younger Tephra-lithic sedimentary and volcanic rocks of Tertiary age. The tuff, coarse ash and Pliocene to Holocene sedimentary rocks are Irrawaddy Formation and Lapilli tephra Khabo Formation of sandstone, siltstone and mudstone. Inde Basalt Volcanic rocks are olivine basalt (Inde hill). Basaltic Upper Miocene to Irrawaddy Formation tuff and volcaniclastic rocks are dominant in the area. Pliocene The regional trend of the volcanic rocks is generally Khabo Sandstone Middle Miocene about NE-SW direction. Tephra deposits were founded at Inde hill. These pyroclastic deposits can reflected the The study area is mainly composed of sedimentary type of volcanic eruption of the study area. The and volcanic rocks of Tertiary age. The sedimentary volcanic activities can be divided as least five major rocks are sandstone, siltstone and mudstone. Volcanic events. Each major event has been found minor rocks are olivine basalt and microcrystalline augite episodes. The type of volcanism is strombolian type at basalt. The igneous rock units are spastically exposure Inde Hill. In accordance with the field relationship, the over the sedimentary rock unit. The good exposures are volcanic eruption of the study area occurred during found in car-road and stream section. Inde hill, eastern Pliocene to Holocene time. part of research area, yield good exposure of volcanic and pyroclastic rocks for systematic study. Moreover, 1. Introduction volcanic rocks are better exposure than the sedimentary rocks which are exposed along the stream section and The study area laid between N-22º 23ʹ 15ʺ to 22º 27ʹ on the locally uplifted ridges. The regional trend of the 15ʺ and E- 95º 32ʹ 24ʺ to 95º 12ʹ 30ʺ in one inch to one volcanic rocks is generally about NE-SW direction. mine scale topographic maps 84 N/3. The study area falls in the Monywa District of the Sagaing Region. Location map is shown in Fig. (1). It covers approximately 120 sq km. It is readily accessible throughout the year by car or motorcycle. Geotectonically, the study area lies in the Chindwin Basin which located in the western part of Central Cenozoic Belt. The study area is mostly a flat plain expect where the volcanic crater, volcanic hills and sedimentary ridges are present. Western and Eastern part of the study area is occupied by igneous rock units Figure 1. Location map of the research area and the rest is comprised by the sedimentary rock units. The main objective of this study is to known the type and nature of volcanic eruption. The detailed geological map of the area is shown in Fig. (2). The major rock sequence of the study area is shown in table (1) based on the stratigraphic position. Figure 2. Geological map of the research area 302 University Journal of Creativity and Innovative Research 2020 Vol-01 Issue-01 vi. presence of basalt layering and 2. Method of Research lamination in tuff vii. individual bed typically shows normal Universal Traverse Marketer (UTM) map sheep grading of constituent particles. No.2295-03 used as the base map for this research. Pyroclastic rocks of Inde hill are air fall deposit Detail measurement of features of volcanic and with basaltic composition. They are transported volcaniclastic (pyroclastic) rocks as well as through the air and fall back to the surface as air fall or sedimentary rocks were made by using the measuring fall out deposits. These pyroclastic beds are indicated tape with Brunton compass and location of the feature that the style of volcanic eruption of Inde hill is and rock samples taken by GPS. Detailed studies were strombolian type. made the vertical section measurement of volcanic and Section measurements of pyroclastic rocks were pyroclastic rocks. This is done to known the nature of done at the north, northeastern and southern parts of these rocks and estimated the intensity and type of Inde hill to know the nature of volcanic eruption of the volcanic eruption of ancient volcanoes. In the volcanic study area as shown in Fig. (3). This volcanic sequence crater, random sampling was made along the radial can be subdivided into five units according to bombs traverse lines. Grain size percentages of these rocks are and blocks present, grain size and colour differences. analysis to classify the volcaniclastic rocks. 3. Igneous Activity 3.1. Igneous Magnification Inde hill has distance forms of igneous magnifestion such as volcanic craters, lava flows and tuff deposits. The lava flow had been capped on the ash fall and tephra deposits. This volcanic hill may be monogenetic basaltic volcano (tuff ring type) (in Reading, 1996) because pyroclastic deposits are relatively rising above the surrounded region. The eastern part of the crater was hill but slope down toward the west of the crater. So, the volcanic crater of Inde hill was curve shape. Figure 3. Section measurements of pyroclastic rocks 3.2 Sequence of Volcanic Eruption of Inde hill 3.2.1. Unit A The study area lies in Central Volcanic Arc which is onshore volcanic arc. It constitutes the back-bone of the This unit exposed at road cut section, NE of Inde Central Cenozoic Belt. The volcanic of this arc are post Village. It consists of two layers of light to dark grey; Paleocene to Recent in age (Ali Akbar Khan, 2010). In lapilli tephra and coarse ash tuff are interbedded that the study area, basaltic and pyroclastic rocks are are overlying by a thin ash bed. In each layer of lapilli dominant. Tuff, coarse ash bed and lapilli tephra are tephra have been normal grading. Coarse ash beds are main constituent in pyroclastic rock which are air fall good sorting. It is about 1 m in thickness. The upper deposits in nature. thin ash layer contains ash grains with a few lapilli The characteristic features of pyroclastic air fall grains. deposits in the study area are as follows; i. well bedded nature 3.2.2. Unit B ii. bedding planes are nearly horizontal This unit is composed by five layers of pale grey to iii. bedding thickness decrease away from dark grey, well sorted lapilli tephra and ash fall beds the site of eruption are interbedded. The upper most part of this unit cap iv. individual bed show good to moderate by the thin-bedded coarse ash layer. Near the volcano, sorting this unit typically is 3 m thick and comprises many thin v. blocks and bombs were deposited ash beds. The upper part of this unit intercalated by relatively close to the site of eruption coarse pumice and lapilli grains. This unit directly 303 University Journal of Creativity and Innovative Research 2020 Vol-01 Issue-01 overlies the upper part of the unit A. Unit B is Layer C2 consists of lapilli and ash fall beds which conspicuous in north and northeast flank of the Inde are alternated. At the base of layer C2 is lapilli tephra hill. Contact between unit B and unit C shown in Fig. which is moderately sorted. Volcanic blocks are present (4). in this bed and light grey to grey in color and about 60 Layer B1 consists of several thin beds of yellowish cm in thick. Ash fall beds are present above the lapilli grey to brownish grey pumiceous lapilli at the base of tephra. In some part of ash fall beds have been the unit B. Most pumice in this layer is more compact intercalated with thin lapilli layers. Ash fall beds are than that of other layer. The layer B1 is indefinable good sorting and buff color. The upper part of layer C2 chiefly as the basal coarse pumiceous layer of the unit decreased both bedding thickness and grain size. B. Layer C3 is comprised by lapilli tephra and ash fall Layer B2 consists of dark grey colored pumice and beds which are interbedded. Bedding thickness is bombs as a single layer about 80 cm in thickness. The decreased from base to top in this layer. At the base of lapilli grains of this layer are loose and poor to this layer is a lapilli tephra which is coarse-grained and moderate sorting. Volcanic bombs are present in the thicker than the other beds in this layer. Lapilli tephra upper part of this layer. This layer is relatively highly are light grey to dark grey in color while ash fall beds weathered and brecciated than the other layer. are light grey to buff color. The middle part of this Layer B3 is comprised by thinly bedded coarse ash layer is ash fall beds. In some part of this beds have layers which are yellowish to light grey in color. been intercalated by thin lapilli bed (about 2 cm). The Individual bed is about 1 to 3 cm thick. This layer upper part of this layer is ash fall beds and lapilli tephra consists of rock fragments and small pumice grains. are interbedded which are thinly bedded, well sorted Layer B4 is a single layer which is light grey to grey and fine-grained than the lower part. in color, moderately sorted in grain size lapilli tephra. Layer C4 is mainly composed by ash fall bed but This layer is denser than the layer B2. Small amount of lapilli tephra are intercalated between them.