Rock Magnetic and Petrographic Studies of Nidar Ophiolite Complex, Northern India

ABSTRACT Petrography and rock magnetic characteristics of mafic‐ultramafic rocks from the Nidar Ophiolite Complex (NOC) in northern India's Ladakh Himalaya region are studied in order to understand the magnetic mineralogy and its relation to tectonics. Petrography revealed that peridotites, basalts and gabbros contained a magnetic mineral assemblage of spinel, pyrrhotite and magnetite. The detailed rock magnetic analyses include Isothermal remanent magnetization (IRM) acquisition curves (~300 mT), coercivity spectra (< 60 mT), hysteresis loops data along the SD‐MD mixing line with PSD dominance, and thermomagnetic curves showing a steady decay in magnetization near 580°C. The determined magnetic mineralogy is dominated by magnetite (primary and secondary), Ti‐poor magnetite and pyrrhotite. Both the thermomagnetic and petrographic data show indications of significant alteration, especially the serpentinization of olivine in dunite samples. Density values ( ρ = between 2.61 and 2.98 g/cm 3 ) and high degrees of serpentinization ( S = between 41% and 88%) in the samples indicate that secondary magnetite originated as a byproduct of serpentinization. A superimposition on the initial magnetic properties of the oceanic lithosphere, most likely the Tethyan Himalaya, is suggested by the combination of magnetic mineralogy and varying degrees of serpentinization. This alteration is attributed to large‐scale tectonic deformation in response to the collision of the India‐Eurasia plates. Despite being affected by considerable serpentinization, the persistent magnetic mineralogy and grain size found in NOC rocks, they are suitable for future paleomagnetic and magnetic fabric investigations.