FIGURE 1. Geological distribution map for basalts from Sangxiu Formation in the central segment of Tethyan Himalayas. a. Tectonic location (modified from Mahoney et al. 2002). b. Distributions (after Pan Gui-tang et al. 2004, in press). c. Geological map for studied area (Regional Geological report (1: 250, 000) for Luoza County, 2003, unpublished) Sangxiu Formation, which is only distributed in the Yangzuoyong Tso area (south to Lhasa, Figure 1b), is a special stratum unit that is mainly characterized by volcanic interlayers. Tectonically, it is located in the eastern part of central segment of Tethyan Himalayas, and paleogeography belongs to the northern margin of Greater India. Here one finds not only the southern transitional part of space-time framework of the central-eastern Yarlung Zangbo ophiolitic melange zone, but also the supposedly the extended end-point of Ninetyeast Ridge (Figure 1a). The age of the Sangxiu Fm is from Late Jurassic to Early Cretaceous, which is constrained by fossils, though precise isotopic age of basaltic magmatic effusion is not known at present. Regionally, the Rajmahal traps on eastern Indian margin are explained by the consequences of early activity of the Kerguelen hotspot (Kent et al. 2002), and the track of Kerguelen hotspot since 120 Ma was interpreted from Rajmahal traps via Ninetyeast Ridge to the Kerguelen hotspot (O’Neill et al. 2003). If the early volcanic activity of the Kerguelen hotspot is extended much farther to the north and northeast, can this hotspot influence the volcanic activity in Tethyan Himalayas− the northern margin of Greater India during Late Jurassic to Early Cretaceous? The goal of this paper is to show our recent work on the geochemical and isotopic compositions and to discuss the characteristics of magmatic source, especially to shed light on the petrogenetic processes and to suggest a possible genetic relationship with Kerguelen hotspot in the light of systemically petrological and geochemical data (including REE, incompatible trace element and isotopic data) for basalts from Sangxiu Fm in Tethyan Himalayas. Stratigraphy and petrography The underlying stratum of Sangxiu Fm is the Late Jurassic Weimei Fm., which is mainly consists of quartz sandstones and dark grey argillaceous rocks with high content of quartz, shallow water ripple marks and relic fossils, is thought to the sedimentary records of shore-shallow sea (Jiang et al. 2003). The overlying stratum is the Early Cretaceous Jiabula Fm. that is characterized by accumulates of collapse and turbid sediments. The lower parts of Sangxiu Fm are mainly composed of apogrites, conglomerates, the middle parts are mainly basalts and shales gripped, and the upper parts are aleuritic shales and calcipulverite lens gripped. The massive, amygdaloidal, pillow basalts can be observed in different outcrops. The phenocrysts (about 5-10%) in basalts are mainly consist of plagioclase and pyroxene, which have experienced variable degree of alteration and metamorphism, however, the original textures appear to have been preserved; the plagioclase groundmass also underwent partly alteration; the accessory mineral assemblages include ilmenite, titanite and magnetite.