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This study analysed frost heave lands in the cold arid Leh-Ladakh region of the Himalaya, India through semi-detail field survey and remote sensing. Most of these sites are highland grasslands occurring along the alluvial plains of rivers in the Leh and Nubra valleys. The study identified the occurrence of some unique frost heave patterns whose morphometry varied from simple, isolated to complex ones with elongated, coalesced and superimposed bedforms. These lands can be further subdivided into vegetated and degraded types. The degraded forms exhibited several cracks, dry, collapsed and slump structures. Invasion of Cirsium arvense over native grass species, soil salinity and feeding pressure by livestock have been identified as major land degradation factors. C. arvense has replaced the native vegetation on frost heaves and has allowed Carex species to grow, which is known to degrade and deplete the pasture ecology. [ABSTRACT FROM AUTHOR]

We report new U--Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, easternHimalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende Å 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 (La/Yb)N Æ 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 § 2.53 Ma and 568 § 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. [ABSTRACT FROM AUTHOR]