Hyperobliquity of Changlang Block of eastern Arunachal Pradesh, India and the role of Mishmi Block, India and Hukawng Block, Myanmar in its development
Authors: Zaman Farha , Goswami Uttam , Bezbaruah Devojit 
Published: March 2020

&lt;p&gt;Plate tectonic history of northeast Indian subcontinent can be viewed as a window to the&lt;br&gt;evolution of Southeast Asia. One such important tectonic feature is the northern most part of&lt;br&gt;Indo-Burmese Ranges where this research work has been carried out. Here we propose an&lt;br&gt;evolutionary model that shows northward moving &amp;#8216;horse-tail&amp;#8217; feature of the Hukawng Block&lt;br&gt;from the Burma basin, pushed this region towards the rigid Mishmi Block and Upper Assam&lt;br&gt;shelf, that caused the hyperoblique pattern of the ranges. It is the juxtaposition of the three&lt;br&gt;continental blocks: India-Asia-Burma, where there are tectonic and geomorphic influences in&lt;br&gt;the Block from both the Himalayan and Indo-Burmese orogeny. Stress distribution among&lt;br&gt;north-easterly moving Indian plate and comparatively stiff Eurasian and Burma plates, within&lt;br&gt;the India specific reference frame, is resulting in further changes. The study area mainly falls&lt;br&gt;under Changlang district of Arunachal Pradesh, India; and the regional study has been done in&lt;br&gt;the quadrangle from 26&amp;#176; to 28&amp;#176;N in latitudes and 95&amp;#176; to 97&amp;#176;E in longitudes. Morphotectonic&lt;br&gt;study, lineament analysis, fault system characterisation, focal plane mechanism along with&lt;br&gt;dynamic topography, seismic tomography and gravity anomaly have been incorporated in the&lt;br&gt;field evidences. Morphotectonic study for Noa-Dihing River basin has resulted in a value of&lt;br&gt;56.59 for Asymmetric Factor, which shows similar asymmetry result like in the Chi (&amp;#967;)&lt;br&gt;analysis. This SW-ward tilted basin is moderately asymmetrical with Transverse Topographic&lt;br&gt;Symmetric Factor value of 0.42. This indicates that the major river basin along with other subbasins&lt;br&gt;are under the influence of active oblique rotational component. The regional lineaments&lt;br&gt;are showing mean orientations of N11&amp;#176;E-S11&amp;#176;W, N70&amp;#176;W-S70&amp;#176;E and EW whereas some local&lt;br&gt;trends of minor lineaments, in some places have mean orientations of N40&amp;#176;W-S40&amp;#176;E, N82&amp;#176;WS82&amp;#176;&lt;br&gt;E and N42&amp;#176;E-S42&amp;#176;W. In Mishmi block the major regional trends are N35&amp;#176;W-S35&amp;#176;E and&lt;br&gt;N40&amp;#176;E-S40&amp;#176;W comprising of probable cross-faults. In Hukawng Block, the lineament&lt;br&gt;orientation changes from N50&amp;#176;W-S50&amp;#176;E in the west to N30&amp;#176;W-S30&amp;#176;E, N-S and N15&amp;#176;E-S15&amp;#176;W&lt;br&gt;in the central valley region (north of Jade mines) and then to N50&amp;#176;E-S50&amp;#176;W in the eastern side.&lt;br&gt;Major fault systems are mostly thrust, with some showing very low angle slip component,&lt;br&gt;along with some oblique slip faults (e.g. Noa-Dihing River). The dynamic topography and&lt;br&gt;seismic tomographic studies indicate presence of a high seismic velocity zone beneath Mishmi&lt;br&gt;block indicating the crystalline rock materials. The block is still actively exhuming. Moreover,&lt;br&gt;Changlang and Hukawng blocks have undergone uplift and then phases of subsidence during&lt;br&gt;the last 20Ma. This indicates that the Low Velocity materials that are present underneath were&lt;br&gt;subjected to some crustal deformations. This tectonic process has also resulted in gravity&lt;br&gt;anomalies. The role of massive and rigid Mishmi block, comprising older crystalline rocks and,&lt;br&gt;later forming Burma basins formed the oblique rotation of the Changlang block which is&lt;br&gt;observed from all stated methods. Hukawng Block, which is controlled by the motion of&lt;br&gt;Sagaing Fault, have influenced the Changlang Block by its varied strike-slip stress components.&lt;br&gt;Moreover, Indo-Burmese Ranges also has an influence on this block and vice-versa.&lt;/p&gt;