Continental extension of northern Gondwana margin in the Eastern Himalaya: Constraints from geochemistry and U–Pb zircon ages of mafic intrusives in the Siang window, Arunachal Himalaya, India

We report new U–Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende $+$ Fe–Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by $(\mathrm{La}/\mathrm{Yb})_{\mathrm{N}} = 2.65-3.99$. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12–28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U–Pb ages of 521.50 $\sim$ 2.53 Ma and 568 ${\pm }$ 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent

Continental extension of northern Gondwana margin in the Eastern Himalaya: Constraints from geochemistry and U–Pb zircon ages of mafic intrusives in the Siang window, Arunachal Himalaya, India

We report new U–Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende $+$ Fe–Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by $(\mathrm{La}/\mathrm{Yb})_{\mathrm{N}} = 2.65-3.99$. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12–28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U–Pb ages of 521.50 $\sim$ 2.53 Ma and 568 ${\pm }$ 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent

Application of machine learning algorithms in landslide susceptibility mapping, Kali Valley, Kumaun Himalaya, India

The study focuses on the preparation of landslide susceptibility maps in the Kali River valley, Kumaun Himalaya using three machine learning algorithms, namely K-nearest neighbour (KNN), random forest (RF) and extreme gradient boosting (XGB). Fifteen landslide conditioning factors (LCFs) were selected and an inventory of 368 landslides was used for the analysis. Multicollinearity analysis using the variation inflation factor, tolerance and Pearson correlation coefficient (PCC) depicted less to no similarity between all factors. Evaluation of variable importance suggests LCFs such as slope, elevation and distance to thrust contributed significantly and consistently for all three models. Model accuracy was determined and compared using the area under the receiver operating characteristic curve and other statistical signifiers like accuracy, sensitivity, F-measure, accuracy, specificity and recall. The results show that the ensemble algorithms, XGB and RF, yield higher accuracy of approximately 85% compared to the KNN model with 81% accuracy

Perennial to ephemeral transformation of a Lesser Himalayan watershed

Under a changing climate, the Sub-Himalayan ecosystems are likely to experience marked transformations in hydrological, biogeochemical and biophysical processes. To explore this, we have been observing various hydrometeorological parameters in a completely rain-fed sub-Himalayan watershed (Salla Rauetella Watershed) since 1991. We noted a changing trend for some of the hydrometeorological parameters over the 22-yr period. While the annual air temperature has increased significantly, the annual rainfall also shows an increasing trend with a higher probability of increased rainfall intensity. The run-off data show a peculiar trend that the watershed has been transforming itself from a perennial to an ephemeral system, despite an increasing trend of rainfall magnitudes. This is primarily attributed to the increasing trends of rainfall intensities exceeding the infiltration capacities of the soil which trigger large but high-intensity run-off events with dry spells in other periods, which makes the river ephemeral. We infer a likely dynamic change in the run-off-generation mechanism which warrants the need for a more precise and rigorous observationcum- measurement strategy of ecohydrological processes in Himalayan ecosystems, supported with modelling and remote sensing approaches. This will help identify the optimal headwater treatment measures for augmenting groundwater to sustain the rainfed streams of the Himalaya under a changing climate. [ABSTRACT FROM AUTHOR] Copyright of Current Science (00113891) is the property of Indian Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract