Petrogenesis of chromites from the Manipur ophiolite belt, NE India: evidence for a supra-subduction zone setting prior to Indo-Myanmar collision.

Pal, Tapan; Bhattacharya, Anindya; Nagendran, G.; Yanthan, N.; Singh, R.; Raghumani, N.

The Manipur ophiolite belt within the Western Ophiolite Belt of the Indo-Myanmar Ranges (IMR), consists of tectonised to massive serpentinised peridotite, dunite pods, chromitite pods/lenses, cumulates, dykes, volcanic rocks and pelagic sediments. Chromitite pods and lenses hosted in peridotitic mantle rocks show magmatic textures, post magmatic brecciation and ferritchromitisation. Electron microprobe analyses show two types of massive chromitite, with one group having high-Cr (Cr# 75-76), medium-Al (AlO 12.2-12.4 wt%) chromites (Sirohi-type) and the other group (Gamnom-type) having a wide range of compositions with generally lower Cr and higher Al (Cr# 65-71, AlO 15.7-19 wt%). Accessory chromites in peridotitic mantle rocks have consistently low Cr (Cr# 38-39) and high Al (AlO 34-35 wt%), whereas chromites in dunite pods have intermediate compositions (Cr# ~60; AlO 20.7-21.2 wt%). The chromite chemistry suggests moderate (20 %) partial melting of the tectonised mantle harzburgite. The estimated AlO, (FeO/MgO) and TiO for the Sirohi-type chromites indicate boninitic parentage, whereas chromite compositions from the Gamnom area suggest mixed boninitic-island arc tholeiitic magmas. The compositions of magmatic chromites suggest that the Manipur ophiolite was formed in a supra-subduction zone (SSZ) setting.

MANIPUR (India); PETROGENESIS; CHROMITE; OPHIOLITES; PERIDOTITE; VOLCANIC ash, tuff, etc.

Mineralogy & Petrology, 2014, Vol 108, Issue 5, p713

0930-0708

Academic Journal

10.1007/s00710-014-0320-z