Home About us Contact
|
Home About us Contact | ||
|
|
||
Indian Ridge (indian + ridge)
Selected AbstractsMicrobial diversity of a sulphide spire located in the Edmond deep-sea hydrothermal vent field on the Central Indian RidgeGEOBIOLOGY, Issue 2 2003Joost Hoek ABSTRACT A culture-independent molecular phylogenetic survey was carried out for a bacterial and archaeal community of a mineralized crust coating a sulphide spire, which was collected from the Edmond vent field (23° S, 69° E, 3300 m depth) on the Central Indian Ridge. Small-subunit rRNA genes (16S rDNA) were amplified from environmental DNA by PCR utilizing Bacteria-specific, and Archaea-specific 16S rDNA primers. PCR products were cloned and 26 bacterial and nine archaeal unique sequence types (phylotypes) were identified from 150 clones analysed by restriction fragment length polymorphism, representing eight and four distinct lineages, respectively. The majority (>90%) of the bacterial phylotypes group with the ,-Proteobacteria and confirms the global prevalence of ,-Proteobacteria in deep-sea hydrothermal environments. Among the ,-Proteobacteria, >40% of the phylotypes were closely related to the recently isolated deep-sea vent thermophilic chemolithoautotrophic sulphur-reducer, Nautilia lithotrophica. A single bacterial sequence was nearly identical (99% similarity) to the thermophilic hydrogen-oxidizing Hydrogenobacter thermolithotrophum, and is the first report of Hydrogenobacter at deep-sea hydrothermal vents. A majority (97%) of the archaeal phylotypes grouped with the ,Deep-sea Hydrothermal Vent Euryarchaeotal Group', a phylogenetic lineage of uncultured Archaea that have only been reported from other deep-sea hydrothermal vents on the Mid-Atlantic Ridge, East Pacific Rise, Juan de Fuca Ridge, Isu,Ogasawara Arc, Okinawa Trough and the Manus Basin. A single sequence was closely related to the hyperthermophilic sulphur-reducing Thermococcales frequently found in diverse deep-sea vent environments. Scanning electron micrographs of the mineralized crust reveal abundant filamentous, rod and coccoidal forms encased in sulphur and sulphide mineral precipitate, suggesting that the thermophilic chemolithoautorophs and sulphide-producing heterotrophs may influence the architecture and sulphur cycling of the sulphide spire. [source] Refined spreading history at the Southwest Indian Ridge for the last 96 Ma, with the aid of satellite gravity dataGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005A. Bernard SUMMARY The spreading history of the oceans is modelled mostly by using magnetic anomalies and the fracture zone geometry. The high-quality, satellite-derived gravity data, that became available in recent years, reveal the details of fracture zones, which can be used as flow lines to control spreading models. We have applied this approach to the Southwest Indian Ridge (SWIR) in order to refine its spreading history. This is particularly useful for the period of complex spreading between magnetic anomalies 33 and 23, where the magnetic anomalies alone cannot resolve the detailed spreading history. We find four main stages in the spreading history of the SWIR since 96 Ma, including two that were not noted previously, between 96 Ma and anomaly 33 (76.3 Ma) and between anomalies 23o (51.7 Ma) and 18o (40.1 Ma; o denotes old boundaries of normal magnetization period). We also find that the start of the period of complex spreading was at anomaly 33, somewhat earlier than previously proposed. We discuss the characteristics of the extension that the old transform faults underwent during the complex spreading phase, in response to the counterclockwise rotation of spreading. New transform faults appeared at that time, considerably widening the transform zones. [source] Glass and Mineral Chemistry of Northern Central Indian Ridge Basalts: Compositional Diversity and Petrogenetic SignificanceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009Dwijesh RAY Abstract: The glass and mineral chemistry of basalts examined from the northern central Indian ridge (NCIR) provides an insight into magma genesis around the vicinity of two transform faults: Vityaz (VT) and Vema (VM). The studied mid-ocean ridge basalts (MORBs) from the outer ridge flank (VT area) and a near-ridge seamount (VM area) reveal that they are moderately phyric plagioclase basalts composed of plagioclase (phenocryst [An60,90] and groundmass [An35,79]), olivine (Fo81,88), diopside (Wo45,51, En25,37, Fs14,24), and titanomagnetite (FeOt,63.75 wt% and TiO2,22.69 wt%). The whole-rock composition of these basalts has similar Mg# [mole Mg/mole(Mg+Fe2+)] (VT basalt: ,0.56,0.58; VM basalt: ,0.57), but differ in their total alkali content (VT basalt: ,2.65; VM basalt: ,3.24). The bulk composition of the magma was gradually depleted in MgO and enriched in FeOt, TiO2, P2O5, and Na2O with progressive fractionation, the basalts were gradually enriched in Y and Zr and depleted in Ni and Cr. In addition, the ,REE of magma also increased with fractionation, without any change in the (La/Yb)N value. Glass from the VM seamount shows more fractionated characters (Mg#: 0.56,0.57) compared to the outer ridge flank lava of the VT area (Mg#: 0.63,0.65). This study concludes that present basalts experienced low-pressure crystallization at a relatively shallow depth. The geochemical changes in the NCIR magmas resulted from fractional crystallization at a shallow depth. As a consequence, spinel was the first mineral to crystallize at a pressure >10 kbar, followed by Fe-rich olivine at <10 kbar pressure. [source] | ||||||||||