• ABHISHEK LAKHOTE

      Articles written in Journal of Earth System Science

    • Evaluating the seismic hazard in the Kachchh Region, western India using the river gradient length anomaly technique

      RAJ SUNIL KANDREGULA GIRISH CH KOTHYARI GAURAV CHAUHAN VASU PANCHOLI SWAMY K V ABHISHEK LAKHOTE SNEHA MISHRA THAKKAR M G

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      In the present study, we assess seismic hazard potential and surface deformation pattern along and across the strike of major active faults in the intra-plate Kachchh Rift Basin (KRB). Towards this, we adopted river Gradient Length Anomaly (GLA) technique, which detects recent tectonic deformation along a river profile on local and regional scales. The major deviations along the river profile can be correlated with exogenic (erosion/sedimentation/anthropogenic) and endogenic (active tectonic movement) processes. We analysed 130 river profiles for GL anomalies, over an area of ${\sim}$26,700 km$^{2}$ in the KRB to identify possible locations that have undergone active tectonic deformation associated with the fault movement. The acquired results show that the higher magnitude negative GL anomalies (uplift) are observed proximal to the fault zones. Our estimates reveal that, around 13% of the study area falls under high tectonically active zone, around 27% of the area falls under moderately active zone, while 60% of the area shows very low or negligible tectonic activity. The estimated results of the GL anomalies are compared with the existing double-difference tomograms, to understand the role of subsurface fault dynamics on the GL anomalies. Furthermore, the results of GLA are correlated with the existing results of the peak ground acceleration (PGA) values of the basin, in order to obtain the precise information regarding surface deformation and site-specific ground acceleration for accurate assessment of seismic hazard.

    • Nepheline syenite and related rocks at Meruda Takkar hill, northern Kachchh: Neoproterozoic Malani basement or Mesozoic alkaline magmatism?

      M G THAKKAR GAURAV CHAUHAN YASH SHAH CHIRAG JANI BHAVYATA CHAVADA ABHISHEK LAKHOTE SURAJ BHOSALE C P MISTRY

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      An extremely small but significant exposure of possibly Precambrian or Pre-Deccan Mesozoic plutonic rocks spanning 200 $\times$ 90 m in size with 15 m elevation, remotely located amidst vast salt flats of the Great Rann of Kachchh received attention when it was first reported by Biswas in 1968; however, systematic petrological and petrographical studies remained undone. Therefore, in the present study, we addressed complete geological accounts to establish its possible origin. Our detailed geological study indicates that the complex is made up of nepheline and aegirine bearing alkali feldspar syenite with numerous fine-to-medium grained felsic dykes. It lays two viewpoints: (1) it has affinity with Trans Aravalli Belt anorogenic felsic magmatism, i.e., Precambrian and (2) it is genetically related to the pre-Deccan Mesozoic plutonic intrusives like Nir Wandh in Pachham Island and Mundwara and Sarnu–Dandali complexes in Rajasthan. The nearest felsic magmatic suite is an exposure of gray and pink granites of Nagar Parkar of Neoproterozoic age. Presence of undersaturated minerals and xenoliths of diorites within syenite parent body may suggest partial melting of lower crust probably during Rodinia supercontinent rifting. However, presence of alkali-rich minerals, alkali feldspars, kaersutite, aegirine, apatite and rutile needles and the complex being part of the Kachchh rift basin suggests its genetic resemblance with Pre-Deccan Mesozoic plutonic events. The radiometric age will confirm the age of this plutonic massif.

      $\bf{Highlights}$

      Based on the field geological and petrographical studies of Meruda Takkar syenitic complex, two viewpoints have been raised:

      $\bullet$ The alkali feldspar syenite complex of Meruda has close affinity with the anorogenic felsic igneous suites contemporaneous with Malani Igneous Suite and slightly younger than post-Delhi Erinpura granites, i.e., Neoproterozoic intraplate magmatism chronologically equivalent to the splitting of Rodinia supercontinent,

      $\bullet$ The alkali feldspar syenites of Meruda Takkar have genetic and mineralogical resemblance with the pre-Deccan trap Mesozoic plutonic activities allied to what is prevailing at alkaline complexes of Mundwara and Sarnu–Dandali and in the northern Island belt alkaline intrusives of Nir Wandh, Kuran, Kaladungar and Sadhara sills and dykes.

      Radiometric age determination and geochemical analysis of the Meruda syenite are needed to establish its age and origin.

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