Analysis and Interpretation of Shear Zones in Kaladgi Basin Exposed at and Around Sirasangi, Belgaum District, Karnataka, India

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

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

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). For the Trend Frequency Trend Frequency Trend Frequency structural point of view, it is necessary to know the shear N8⁰E 06 N35⁰E 05 N65⁰E 02 patterns in the field, hence the area has been bifurcated into three major parts which are western part, central part and the N15⁰E 02 N40⁰E 10 N70⁰E 05 eastern part of the study area. Shear directions obtained in these three parts are shown in figure 4.3, 4.4 and 4.5 in the N20⁰E 01 N50⁰E 07 N75⁰E 03 form of circular stereonet type of projections. Data of the same are plotted in the rosette diagram in figure 3.1 A and 3.1 B N25⁰E 02 N55⁰E 08 N80⁰E 01 according their trend. The shear planes in the study area have N30⁰E 05 N60⁰E 04 N85⁰E 01 variation in the directions, as in few areas they intersect. Rocks exposed in such areas are highly ruptured and are considered as ‗shatter zones‘. In case of areas where two different directions intersect, formation of rhombic pattern of joints has resulted (Plate 4.5) which has been mentioned in section 3.3.1. In the overall area no doubt the rocks are deformed due to shearing the shear sense in the area are maximum oriented in two direction as observed from the data in table 3.1 A and B and rosette diagrams from Fig 3.1 A and B. With respect to the intensity of the shear sense in the NE- SW trending shear, maximum of N40⁰E – S40⁰W is observed and N55⁰W – S55⁰E in NW-SE trending shear. Overall the shear sense fall between NE-SW and NW-SE direction. Comparative study of shear sense, sector wise (Fig 3.3) indicate that the rocks have been sheared differently. Fig 3.2 represents the different intensity of the shear sense which Fig 4: Interpretation of frequency of the shears trending have been observed in the field of three different sectors. In NW-SE using rosette diagram. overall area the general shear sense is almost lies in NE-SW direction and almost equivalent amount of shearing is seen in the NW-SE direction, as discussed in the section 3.3.2. It has been clearly observed that the trend of these shear lies Table 2: Shears trending in general NW-SE direction between N-S to N85⁰E with respect to the NE-SW trending shear and N-S to N90⁰W in the NW-SE trending shear. Thus, the detailed study of the frequency of shear sector wise will Trend Frequency Trend Frequency Trend Frequency be discussed in the upcoming paragraphs. N5⁰W 02 N35⁰W 05 N65⁰W 02

N15⁰W 02 N40⁰W 09 N70⁰W 03 N20⁰W 04 N50⁰W 05 N75⁰W 03

N25⁰W 02 N55⁰W 10 N80⁰W 01

N30⁰W 06 N60⁰W 04 N85⁰W 01

Fig 3: Interpretation of frequency of the shears trending NE -SW using rosette diagram.

Plate 1.1 : (A): Field photo of quartzarenites that have developed fracture cleavage along joint planes, this due to closely placed shears. The distance between the shear planes is less than 5mm. The trend of the cleavage planes is N45⁰E – S45⁰W (Note the hammer is kept parallel to the cleavage planes). Location: 3km towards west of Mullur ghat. Direction of view: N45⁰E; (B): Field photograph showing a fan like structure (lineations) formed by shearing of the rock. Note the lineation planes are multidirectional and indicate intense rupturing of the area. Location: 3 Km west of Mullur, Ramalingeshwar Temple. Direction of view: N60⁰W.

Fig 5: Frequency of shear sense represented in the form of rose tte diagram developed in three sectors of study area

In the western part of the study area more than 20 shear angle but in few areas shear sense intersect perpendicular to sense where identified and are represented, frequency of all each other. In the eastern part of the study area, shear sense the shear sense isn‘t the same. Among these shears sense behaves a little differently as they bisect with a small acute the prominent ones are N30⁰E, N45⁰E and N90⁰W are most angle or closely spaced acute angle between them. The most frequent direction (identical value of the frequency is 03). frequent shear directions in the eastern part N30⁰W, N45⁰W, However, the shear sense trending NE-SW are more frequent E-W, N25⁰E and N45⁰E. The shear sense in whole study area than NW-SE direction. Yet few directions like N10⁰E, N20⁰E behave differently from sector to sector, from the study of and N25⁰E are very less frequent as it is observed in one or these shear sense the preponderant shear direction can be two places in the western part of the study area. Similar derived for all the three different sectors. In order to appreciate procedure was followed for studying the shear sense in the these aspects, different preponderant directions of shears central part of the study area. Identified shear sense trend in have been set out in the Table 3.2. NE-SW and also in NW-SE direction, frequency of NW-SE trending shears is more comparative to the western part of the Table 3: Preponderant Direction of Shearing study area. Prominent trend of the shears are N-S, N40⁰E, N45⁰E, N50⁰E, N70⁰E, N15⁰W and N50⁰W. In this sector three Sl. Sector/Area Direction of No. of Strike of the intersection point of the shears are observed forming a No. shearing Direction rocks rhombic or a rectangular pattern in the quartzarenites (plate 1. Western N45⁰E-S45⁰W Two NNE-SSW N45⁰W-S45⁰E 4.5). Considering the shear pattern and intensity it can be 2. Central N45⁰E-S45⁰W Three N45⁰E-S45⁰W inferred that the rocks in the central part have comparatively E-W E-W higher deformation rate (plate 4.10,4.11 and 4.12). In the N-S western part of the study area the dip direction as well as the 3. Eastern N45⁰E-S45⁰W One NNW-SSE dip angle has changed leading to the deformation of the rocks. N-S The shear sense of this area trends N45⁰E, N55⁰E, N85⁰E, N25⁰W and E-W. In the western part of the study area From the data of Table 3.2 it can be observed that the western equivalent amount of high rate deformation similar to the part has two, central part has three and eastern pat has one central part. In the overall area under investigation the preponderant shear direction, these have been presented in shear patterns differ as it is traversed from western part to the Fig 3.4 to for the clear understanding with respect to the study eastern part. Western part shows comparatively less area. The shear sense varies between N-S, E-W, N45⁰E - deformation with respect to the central and the eastern part. S45⁰W and N45⁰W - S45⁰E. These variation in the shear Dip and strike of the area from the eastern part has remained sense indicate the varying deformative forces. This aspect will constant till the end of the central part but slight variation is be elaborated while dealing with different deformation seen in the western part of the study area. There is complete structures encountered in the area under investigation. change in the attitude of bed in the north-western part, strike almost trending E-W in the eastern and central part has changed to N-S in the north-western part (near Kolchi ), this may be due to the processes of rotation of the block and will be discussed in detail in the later stages of this chapter. Sector-wise deposition of shear sense in the form of stereograms. In the previous section i.e., 3.2.2.1 detailed account of shear patterns their frequency and preferred direction of the shear that have been recognized in the study area. Regardless of frequency it is very important to indicate the shear sense with respect to their geographical locations for much clear understanding of the behavior of the shear sense. Thus, several shear directions which were noted in the field are represented in the form of stereograms with their respective spots of observation in fig 3.3. In the western sector, the shear sense in the rocks indicate that these have been sheared in two directions only. These two directional shears in some places represent that the angle made between them is acute angle. Out of all the shear sense in the western part, four are more frequent, which are N5⁰W, N30⁰E, N45⁰E and N95⁰W. Considering these shear sense it can be inferred that the preponderant shear direction of the area lies in NE-SW and SW-SE directions (Fig 3.4). In the central part of the study area the shear sense here has been struck with three directional in few areas mainly near Mullur Ghat and Kallur region as these two areas have been highly deformed. The most frequent shear directions in the central part are N15⁰W, N20⁰E, N85⁰E, N55⁰W. In Plate 4.13, two shear planes intersect almost perpendicular as one running at 0⁰ (towards north) and another at 274⁰ (towards west). But majority of the shear planes intersect at an acute

Fig 6: Representation of shear sense in the form of stereograms developed in three sectors of

the study area

Fig 7: Preponderant shear sense developed in three sectors of the study area

4. CONCLUSION Shear zone contain valuable information with which many major structural and tectonic structures can be interpreted. Thus, by understanding the attitude, shear sense, it can be inferred that the rocks exposed in this area are highly deformed. Both brittle and ductile shear zones are observed, but the intensity of the brittle shear zone is more comparative to the ductile ones. As the rocks have been actively sheared, the formation of rhombic patterns is seen in the field. However, the intensity of the shear is isn‘t the same in all the area. The central and the eastern part of the study area are intensely deformed, this can be described by clearly observing the shear pattern plotted in the maps provided. With respect to the attitude of the shear and beds, they change as it is moved from western to eastern part indicating the structural deformation. Overall the upliftment of the Kaladgi Basin is the necessary cause for deformation of these rocks as the magnitude of the deformative forces are not constant throughout the study area.

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