Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya,Northeast India

The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics （47%--56% w（SiO2））, with subordinate felsic volcanics （67%--75% w（SiO2））. The felsic volcanics are dacitic to rhyolitic in composition and are typically en- riched in LREE （La/SmN = 3.09--3.90） with high REE contents （256--588 ppm）, moderately fraction- ated REE patterns （CeN/YbN = 6.54--9.52） and pronounced negative Eu anomalies （Eu/Eu＊ = 0.55-- 0.72）. Wide variations in Rb/Zr, K/Rb and La/Sm ratios suggest that they were derived from magmas which were randomly contaminated with crustal material. Chemical characteristics and petrogenetic modelling indicate that the dacites were generated by ~ 15% partial melting of a mafic source leaving a residue with 55% plagioclase, 14% orthoclase, 18% clinopyroxene, 5% orthopyroxene, 8% hornblende. The silica-rich rhyodacites and rhyolites were derived from a dacite magma source by a higher degree （〉45%） fractional crystallization of an assemblage consisting of 70% plagioclase, 12% clinopyroxene, 7% amphibole and 11% magnetite. The associated LREE-LILE enrichment and pronounced negative anomalies for HFSE （Nb, E and Ti） exhibited by these felsic volcanics are characteristic of continental rift volcanism, implying that they were emplaced during lithospheric extension.

Diversity, Invasion Status and Usages of Alien Plant Species in Northeastern Hilly State of Tripura: A Confluence of Indo-Barman Hotspot

The present study has explored the first authentic catalogue of the alien flora of the foot Himalayan hilly region along with their diversity, uses, various ecological aspects and invasion status. Environmentally similar south and tropical American aliens are higher in numbers in this region. A total of 216 plant species under 158 genera belonging to 58 families have been compiled in this catalogue. This alien flora occupies ~14.5% of the state flora, while 3.47% is invasive. Families having a large number of alien species are Asteraceae followed by Caesalpiniaceae and Solanaceae. Most of the alien species (61.57%) are of American origin followed by Asia (15.28%) and African continent (12.04%). Life form analysis shows that herbs (42.6%) are dominated alien. Among all the aliens, 67 species are used as ornamental plant, followed by 50 medicinally useful plants. In the state neutralized aliens are (36.57%) followed by invasive alien (24.07%). The present study also reports five alien species for the first time from the study site. This base line study would be the foundation for further advance studies on the invasion ecology and for the future assessment and management of invasive species in this biodiversity rich zone. Present work obviously helps in the agricultural sector of the state as well as the country and gives a clue for further introduction of new species in the country.

Diversity of Middle Eocene Coralline Red Algae from the Prang Limestone(Shella Formation) of Jaintia Hills, Meghalaya, NE Himalaya, India with special emphasis on palaeoenvironment

Palaeocene-Eocene carbonates of shallow marine sequence belonging to Shella Formation of Jaintia Group are well developed in the south of the Jaintia Hills, Meghalaya and represent an excellent outcrop of shelf sediments in North Eastern Himalaya, India. These outcrops are exposed along the southern fringe of Shillong Plateau. The Prang Limestone is the uppermost lithostratigraphic unit of the Shella Formation within the Jaintia Group. It is overlain by sand-shale alternation of the Kopili Formation and underlain by the Narpuh Sandstone. A rich assemblage of larger foraminifera including Nummulites, Discocyclina etc. has been recorded earlier from the Prang Limestone and based on the foraminiferal assemblage, a Middle Eocene to Early Late Eocene age has been assigned to the Prang Limestone. Thin section analysis of the Prang Limestone revealed the abundance of well preserved coralline red algae along with other well preserved and significant biogenic elements. Morpho-taxonomical study reveals that the algal flora is represented by seven species belonging to the families Hapalidiaceae(Subfamily: Melobesioideae), Corallinaceae(Subfamily: Mastophoroideae) and Sporolithaceae. The dominance of melobesioid and mastophoroid forms is the characteristic feature of this algal assemblage. Coralline algae occur mostly in encrusting growth form with orbitoid foraminifera and occasionally the coralline algae form rhodoliths. On this basis of algal forms it can be inferred that they thrived in a shallow, warm, shelf environment of normal salinity.