CRUSTAL STRUCTURE OF NW HIMALAYA THROUGH GRAVITY AND MAGNETIC DATA ANALYSIS

Abstract

Our regional gravity and magnetic profiles spanning approximately -1220 km and~1120 kmrespectively along Delhi - Chandigarh - Kiratpur - Sundernagar - Kullu - Manali - Keylong - Sarchu- Pang - Rumtse- Upshi - Igu - Leh - Khardung La - Panamik, Igu - Karu - Chang la - Durbuk profiles across all major structural elements of NW Himalaya were duly processed and interpreted. Additionally, we include here gravity and magnetic profiles across Indus Tsangpo Suture Zone (ITSZ) along Mahe- Sumdo - Tso Morari. Spectral analysis of projected gravity and magnetic data on straight profiles followed by data decomposition led to main profiles and its components. It is done by our own software. Then, our Stabilized Analytical Signal algorithm is applied on all projected gravity and magnetic data and its components leading to estimates of depth and horizontal coordinates of anomaly sources. Continuous Wavelet Transform (CWT) method is applied to gravity and pseudo-gravity data and its components, thereby leading to comprehensive depth stacks. Based on Phillips (2010), Analytical Signal of complete gravity, magnetic and pseudo-gravity anomalies and its components along Delhi - Panamik, Delhi - Durbuk and Mahe - Sumdo - Tso Morari profiles allowed us to asses the dip of thrust sheets and faults coinciding with surface geological formations. By considering all the inputs, crustal structure models were derived from gravity and magnetic data along Delhi - Panamik profile. Our gravity derived crustal structure equally emphasizes the deepening of Moho below Higher Himalaya to around 65 km and it shallows up under Aravallis to 40 km. The decollement in both sections (gravity and magnetic cases) is around 9 - 12 km on an average. Partially melt zone is inferred below Higher Himalaya zone in gravity derived crustal structure section. The importance of variable density in terrain correction (Sastry et al., 2005) is illustrated in our Mahe - Sumdo - Tso Morari profile. Additionally, presence of ophiolites within Ladakh batholith is also inferred in our analysis of total field intensity anomaly data along Rumtse - Upshi -Igu - Leh - Khardung la - Panamik, Rumtse - Upshi -Igu - Karu - Chang la - Durbuk profiles.