Analysis and Interpretation of Shear Zones in Kaladgi Basin Exposed at and Around Sirasangi, Belgaum District, Karnataka, India
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INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 8, ISSUE 12, DECEMBER 2019 ISSN 2277-8616 Analysis And Interpretation Of Shear Zones In Kaladgi Basin Exposed At And Around Sirasangi, Belgaum District, Karnataka, India ANANT G. PUJAR, A. SREENIVASA. Abstract: Deformation in the lithosphere is observed in the rocks that have undergone strain and are represented as shear zone. These s hear zones mark an important in the interpreting faults associated with them. The area under investigation falls in the Kaladgi Basin exposed around Sirasangi of Belgaum district of Karnataka state, India. Rocks exposed here show varying amount of shear zones indicating that the rocks h ave undergone deformation. The present study happens to be the analysis and interpretation of these shear zones using various techniques after obtaining the attitude of the shear zones. The data obtained like attitude are analyzed with respect to their directional frequency which indicate the deformation sense. Plotting these shear sense in the stereogram visualizes the rate of deformation of the area, resulting in obtaining the preponderant direction for the entire study area. Index Terms: Preponderant direction, rosette diagram, shear sense, shear zone, stereogram —————————— —————————— 1. INTRODUCTION shear trending N-S is seen in the central part of the study area Shear zones differ from joints, in being irregular with respect to starting from Mullur, covering Kallur and adjacent areas. Thus, trends, inclination and distance. Usually shear zone occur near indicating that these areas are highly deformed comparative to to fault plane as the bedding planes are disturbed the the western and the eastern part. appearance of crushed layer appears. In the shear zone the shear plane directions are taken which is perpendicular to the plane of displacement as shown in the figure 1.1. Comparing to joints these shear plane has a small gap between them, in view of shatter zone the planes are in one direction and they remain parallel to each other. Such fracture planes are the result of intersection of one or two planes. Many a times such fracture planes give rise to cleavage in the rocks as observed in plate 1.1 AThe direction of the shears started from the Sirsangi showing differential amount of shear direction trending E-W and the other trending N50⁰E - S50⁰W indicating two sense of shear direction. Radiating shears (Plate 1.1 B) are seen in few of the areas which includes Sirsangi, Mullur Fig 1: Diagrammatical representation of shear zone geometry, Ghat, and parts of Kallur. The direction of these shears where remains almost the same and the trends are mentioned below. i. N45⁰W – S45⁰E 1. ‗x‘ is the width of the shear plane ii. N70⁰W – S70⁰E 2. ‗d‘ is the amount of displacement iii. N50⁰E – S50⁰W From the above figure it can be noted that the shear iv. N – S directions are differing from the western part of the study area v. N85⁰E – S85⁰W to the eastern part of the study area. It is observed that the vi. N40⁰E – S40⁰W shear direction in the central part of the study is showing three These shears appear like a fan structure as shown in plate 1.1 different preponderant shear direction varying from almost N-S B, rest of the area have shown two sets of shear planes to E-W. This is due to the intensive rupture in the zone. Some trending N55⁰E – S55⁰W and N10⁰W-S10⁰E but in places like interesting behavior of the shears are observed in the central Mullur-Ramdurg road the shear is trending the direction of the part of the area near north -west of Kallur temple indicating strike of the rocks exposed, this is the indication of rupture three shear direction trending N-S, N45⁰E-S45⁰W and N45⁰W- along the strike of the rock. With respect to the preponderant S45⁰E these details are been documented in plate 3.9A. shear direction the complete study area has been classified Similar shear with multiple direction are observed in the area into three that is western, central and eastern parts as showing 3km west of Mullur gath, Ramalingeshwar temple which also in fig 3.3. Among these N45⁰E – S45⁰W is the prominent one makes the adjacent area of Kallur (plate 3.9B). These shears and is seen throughout the area under investigation. Whereas showing multiple direction indicate that the area has been ———————————————— structurally disturbed in a higher rate. As mentioned in the Anant G. Pujar is currently pursuing Ph.D. in Structural Geology in above paragraph, quartzarenites which are subjected to Department of Studies in Geology, Karnatak University, Dharwad, irregular shearing in different directions are been termed as Karnataka India. PH-07899990348. E-mail: [email protected] ―shatter zone‖ and these shatter zones are seen throughout Sreenivasa. A, Professor is currently working in Department of the area under investigation. The angle between these shear Studies in Geology, Karnatak University, Dharwad, Karnataka India. directions varies from place to place forming irregular to PH-09845176463. E-mail: [email protected] rectangular to rhombic combinations. Ultimately these quartzarenites around the area are brecciated which has been 3708 IJSTR©2019 www.ijstr.org INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 8, ISSUE 12, DECEMBER 2019 ISSN 2277-8616 considered as the one of the important evidences for locating the fault in the area. Detailed account of fault and its recognition in the area will be discussed later in this chapter. Many shear directions have been recorded in the entire study area and have been given in the table 3.1 A and B. These shears trend in different direction in the entire area, most prominent ones are generally northeast-southwest direction between N8⁰E- S8⁰W to N85⁰E- S85⁰W and northwest- southwest direction between N10⁰W- S10⁰W to N85⁰W- S85⁰W, few showing N-S and E-W direction. With respect to the study from table 3.1 A and B, it can be inferred that among many shear directions rendered throughout the study area the frequency is not equally distributed. Among the intensity of the shear on NE-SW and NW-SE, shears trending N40⁰E – S40⁰W in NE-SW direction and N55⁰W – S55⁰E in NW-SE have the highest frequency suggesting the preferred orientation of the shear in the overall study area. Other directions of the shear are as well prominent and can be better appreciated in the form of rosette diagram shown in Fig 3.2 A and B respectively. Few interesting features can be noted by scrutiny of Fig 3.2 A and B, which are described as follows. i. Among the preferred orientation of the shear between N40⁰E – S40⁰W in NE-SW direction and N55⁰W – S55⁰E in NW-SE, the angle subtended is 110⁰. Apparently, the direction of the strike and dip of Fig 2: Location Map of the Study Area the study area lies almost the same to that of the preferred shear direction. But in the eastern part The area under investigation as discussed previously falls of the study area the trend of the rocks including under Kaladgi Basin, stretching from Sirsangi of Belgaum the dip angle has completely changed, this will be district up to Surebhan in E-W direction. Detailed geographical further discussed in detail further in this chapter. study of the area suggest that the area of Belgaum district ii. Generalizing the overall trend of the shear in the area comprises two main lithounits that is, sedimentary rocks revels that shears are most frequented in NW-SE belonging to Kaladgi series and Archaean Gniesses. In the and NE-SW directions which has been elaborated boundary covering the parent rock, only sedimentary rocks of in the rosette diagram. Kaladgi series are encountered comprising Quartzarenites and Basal Conglomerates running in E-W direction, but few 2 LOCATION AND GEOLOGICAL SETTING OF Argillites are seen in variegated colour in the layer below the soil cover. The Conglomerates are seen to be deposited in THE STUDY AREA between the Quartzarenites. Based on the primary The area under investigation constitutes the northern part of sedimentary structures like cross beddings, ripple marks and the Karnataka State and lies in the Belgaum District (Fig 1.1). graded beddings, these sedimentary rocks are observed to be The study area has been mapped by Survey of India and ―right side up‖ position. Morphologically speaking, these represented in the Toposheet No. 48M/5, it covers an sedimentary rocks of Kaladgi series are seen to be exposed at approximate area of 230 sq.km. The cardinal coordinate of the hill tops to form a big or small cliff. Pebbles of Jasper and area under investigation lies between 15°51҆ N latitude and Quartz are seen in the Conglomerate deposits. Based on the 75°15҆ E longitude. The study area is delineated by marking field relations of the exposed rocks in the present, the the western boundary at Sirsangi village, the eastern limit is following order of superposition has been given. marked by Sureban village, the northern boundary is marked by Ramdurg and southern part is marked by Mullur Ghat. SOILS (RECENT) From the investigation led from the geological point of view the Argillites (variegated colour) study area comprises of southcentral part of Kaladgi Basin KALADGIS Grits and Breccia exposed at and around Sirsang, Belgaum district, Karnataka Quartzarenites Conglomerate state. Basic Dykes DHARWARS AND ARCHAEANS Granitic Gniesses The maximum overall area is maximum covered by Quartzarenites. Contact between Kaladgi and Archaean are seen in Mandi and Saundatti, which makes the adjacent area of the Sirsangi 3709 IJSTR©2019 www.ijstr.org INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 8, ISSUE 12, DECEMBER 2019 ISSN 2277-8616 3 AREA WISE DISTRIBUTION OF SHEAR DIRECTION In the previous descriptions, a generalized account about Table 1: Shears trending in general NE-SW direction shear, shear directions and their frequency of occurrence in the field has been discussed with the help of rosette diagrams (Fig 3.1 A and B) and tabulations (Table 3.1 A and B).