Rock Magnetic and Paleomagnetic investigations of Sylhet traps, Shillong Plateau, NE India

Results of rock magnetism (RM) and Anisotropy of Magnetic susceptibility (AMS) study apart from Paleomagnetism have been established from the basalts of Sylhet Traps, Shillong plateau, India. The stable RM properties indicate that magnetite and minor titanomagnetite are the main remanence carrier minerals present and also elucidate the cooling history of the lava flow and its emplacement dynamics. First time an attempt has been made through Anisotropy of Magnetic susceptibility (AMS) studies to elucidate the lava flow directions and possible fissure location for the existence of ST (Sylhet Traps) exposures which shows the scattering of stereonets plotted. The combined RM and AMS studies revealed that due to the higher viscosity and slower velocity of the lava flow the scattering in stereoplots is observed, from this we suggested that the ST marks the tale of the lava emplacement activity. Paleomagnetism results gives mean declination = 255° and mean inclination = −57° (α95 =3.44°; k =16.74) and the paleopole position of -26.79°N, 330.75°E (dp=3.6 and dm=5) with a paleolatitude of 37.6°S during 117 Ma. The combination of all these studies have revealed that the emplacement of ST marks the end of  Rajmahal-Bengal-Sylhet Traps volcanic province. Also concluded that ST is the later event than its contemporary Rajmahal Traps placed around 400 Km west of ST in the state of Jharkhand.

 

Figure Caption: A representative hysteresis loop (left) and Susceptibility Vs. Temperature (k-T) curve (right) which shows the presence of fine-grained, low coercive magnetic mineral with the Curie point analogous with the Magnetite.

Figure Caption: A typical Equal-area projection demonstrates the distribution of the principal susceptibility axes in the analyzed ST basalt sample. The stereonet showing the presence of triaxial shape anisotropy in the sample.

Figure Caption: The red square indicates the paleolatitude of India obtained from the Sylhet trap basalts which is 37.6° S.

 

Citation:

Kapawar MR, Venkateshwarlu M, 2019. Rock Magnetic and Paleomagnetic investigations of Sylhet traps, Shillong Plateau, NE India, Journal of Geodynamics, https: //doi. org/ 10.1016/j.jog.2019.05.003, published online on 6th May, 2019.