A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Sukheswala, R. N.
- Deccan Traps and Associated Rocks of the Bassein Area
Authors
1 Department of Geology, St. Xavier's College, Bombay, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 3 (1962), Pagination: 125-146Abstract
The area of Bassein lies 30 miles north of Bombay. Within a compass of about 150 square miles the rocks encountered here are basalt flows and dykes, dolerite dykes, ·diorites, thin veins of aplite, a single dyke of camptonite and pyroclasts.
An explanation is offered for the origin of felsic rocks of differing composition. It is suggested that the initial rhyolitic magma is not a product of differentiation of Deccan basalt but originated as a result of partial fusion of the sialic crust during long continued ascent and outpouring of vast volume of basalt lavas.
Rocks of dioritic composition are described, and it has been shown that the diorite and its associates like meladiorite. leucodiorite, granophyre, andesite. etc., are the result of contamination of rhyolite magma with the country rock dolerite. In support of this, chemical, microscopic and field evidences are cited. Thin stringers of aplite are considered to be the residual liquid product of the contaminated rhyolite magma.
Detailed optical investigations on the pyroxenes and feldspars of basalts and dolerites are carried out. While pyroxene is mainly augite, pigeonite and/or orthopyroxene are conspicuous by their absence. Important minerals of various other rock types are also described.
- Nepheline Syenite in the Deccan Traps of Jawhar, Bombay
Authors
1 Geology Department, St. Xavier's College, Bombay, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 7 (1966), Pagination: 86-91Abstract
The paper records the occurrence of nepheline syenite noticed as a narrow vertical dyke in the Deccan Trap area near Khuded, about 90 miles north-east of Bombay. A full description is given of the nepheline syenite, including its physical, chemical and optical characters; and on the basis of these data, the mode of origin of this nepheline syenite and its age relationship with reference to the adjacent Deccan basalts are discussed.- Rare Earth Element Geochemistry of Basalt-Spilite Association of Bombay and Carlsberg Ridge-A Preliminary Study
Authors
1 Indian Insntute of Technology, Powai, Bombay-400076, IN
2 Bhabha Atomic Research Center, Trombay, Bombay-400085, IN
3 St. Xavier's College, Bombay-400 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 20, No 10 (1979), Pagination: 517-519Abstract
No Abstract.Full Text
- Fenitized Sandstones in Amba Dongar Carbonatites, Gujarat, India
Authors
1 Geology Department, St. Xavier's College, Bombay 400 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 22, No 8 (1981), Pagination: 368-374Abstract
Potash fenitization of sandstones of Amba Dongar carbonatite-complex was described earlier by Deans et al. in 1972. The present work mainly deals with newly found soda-fenites in carbonatites, rich in aegirine-augite, aegirine, albite and orthoclase. The chemistry of potash fenites and soda fenites (new analyses) reveals two trends in Amba Dongar fenites; (i) 'normal fenitization' in which both soda and potash have been added and (ii) predominantly potash fenitization leading to the development of potash fenites. The fenitlzing solutions were supplied by the carbonatite magmas (both sovite and ankeritic carbonatite).- Igneous Complex of Mount Girnar, Saurashtra, Gujarat - A Reappraisal
Authors
1 Geology Department, St. Xavier's College, Bombay 400 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 23, No 1 (1982), Pagination: 13-18Abstract
Mount Girnar is a major igneous plutonic complex which intruded into the basalts towards the close of the Deccan Trap period. The rock types identified in this complex are gabbros (tholeiitic and alkalic), diorites, lamprophyres, alkali-syenites and rhyolites. The parent gabbroic magma is shown to have given rise in sequence to diorites, lamprophyres and alkali-syenites. The rhyolite, though earlier considered a product of differentiation, is now believed to be an independent magma without any genetic link with the gabbro and its variants.
On scanning through available literature, however, it became apparent that the chemical/petrographic data were at variance with the crystallization differentiation hypothesis proposed by earlier workers to account for the varying rock types. To overcome these difficulties it is thought that the 'fenitization' model proposed here can better explain the formation of the different rock types. During the geological history of Mount Girnar, at least three different types of genetically unrelated gabbroic, rhyolitic and syenitic magmas erupted independently at different periods. The highly volatile-charged alkali-syenite magma which came last, was responsible in bringing about metasomatic changes (Na-fenitization) in the earlier formed rocks. It was the process of fenitization that gave rise to rock types such as alkali-gabbro, diorites and lamprophyres. The rhyolitic rocks developed out of an independent rhyolite magma.
- Layered Gabbro of the Igneous Complex of Phenai Mata, Gujarat State
Authors
1 Geology Department, St. Xavier's College, Bombay, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 10, No 2 (1969), Pagination: 177-187Abstract
Phenai Mata hill (Lat. 22°8'N., Long. 73°55'E.), believed to be a composite plug, is successively filled by basalt, gabbro, granophyre and nepheline syenite. The paper focusses attention on the layered character of the gabbro. Rhythmic layering is due to the repetition of thick anorthositic and gabbroic layers. Cryptic layering is marked by extreme variation in anorthite content of plagioclase. The differentiation trend is established by the chemical and petrographic studies of samples collected at regular intervals. Up to 600 feet the enrichment is towards both iron and alkali, after which the gabbro (tholeiitic) differentiates to a granitic residuum.- Occurrence of Rhyolytic Tuffs at Deep Sea Drilling Project Site 219 on the Laccadive Ridge
Authors
1 National Institute of Oceanography, IN
2 Geology Department, St. Xavier's College, Bombay, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 4 (1976), Pagination: 539-546Abstract
A study of thin sections from the lower and middle parts of Unit V (Paleocene) from Site 219shows that these largely consist of acidic or rhyolitic tuffs. The overlying limestones in Unit V (Paleocene) and Unit IV (Lower Eocene) also contain tuffaceous material in varying proportions. Albite/oligoclase forms the phenocrysts as also needles in the groundmass of these tuffs and tuffaceous material in limestones. The euhedral fresh felspars suggest that the source of activity was nearby and possibly most of the activity was subaqueous rather than subaerial. Similar acidic tuffs in the Deccan Traps have been reported particularly from the West Coast of India. The acidic tuffs at site 219 are of the same age as the Deccan Traps and may represent a late phase of Deccan Trap activity on the Laccadive Ridge before its subsidence and separation from peninsular India.- Carbonatite Kimberlite Complexes of India
Authors
1 St. Xavier's College, Bombay, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 4 (1976), Pagination: 429-438Abstract
No Abstract.Full Text