Informatics Publishing Limited

J. Ratnakar ¹, C. Leelanandam ²

Affiliations
1 Department of Geology, Post-Graduate College of Science, Osmania University, Saifabad, Hyderabad - 500 004, IN
2 Department of Geology, Osmania University, Hyderabad - 500 007, IN

Abstract

The ferrosyenites of Sivamalai (Tamil Nadu, South India) contains ortho- and clinopyroxenes in addition to fayalitic olivine, quartz, palgioclase, orthoclase perthite and opaques. The orthopyroxene occurs as (a) submicroscopic rim around fayalite, (b) exsolved (001) and (100) lamellae within clinopyroxene and (c) discrete blebs close to clinopyroxene. The composition of orthopyroxene among the analysed samples varies from eulite to orthoferrosilite and that of clinopyroxene from ferroaugite to ferrohedenbergite. The ortho- and clinopyroxenes individually exhibit systematic intraspecimen and intralintergranular variations of Fe and Mg, with a restricted range of Ca. The Fe/(Fe+Mg) ratios in the pyroxenes (0.966-0.722) indicate their consistency iron-rich nature, and the orthopyroxenes, in particular. are among a few extremely iron-rich ones reported.

The occurrence of orthopyroxene lamellae within clinopyroxenes of ferrosyenites of Sivamalai is a diagnostic feature of slow cooling of a tholeiitic magma. The two compositional trends defined by the pyroxenes in the quadrilateral suggest strongly fractionated nature of the liquid. The mineral assemblage fayalite+quartz+ferrosilite-rich orthopyroxene suggests a minimum P of 6 kb. The Sivamalai pyroxenes are considered to have formed at -740°C and 7 kb. These pyroxenes are presumably crystalllized from a Fe-rich acidic liquid under low fO₂, moderate to high P and increasing SiO₂.

Keywords

Pyroxenes, Ferrosyenites, Sivamalai, Tamil Nadu.

Full Text

     

V. Madhavan ¹, C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad-503007, A.P., IN

Abstract

The rocks of the Elchuru alkaline pluton are broadly classified into (a) mafic-rich alkaline rocks and (b) leucocratic alkaline rocks. Field and petrographic observations suggest that these alkaline rocks constitute a differentiated series which conformably intruded the pre-existing gneisses. The occurrence of mafic-rich alkaline rocks points to a magmatic origin of the pluton and its abyssal Source.

Full Text

   

C. Leelanandam ¹, K. Krishna Reddy ²

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500007, IN
2 Geological Survey of India, Patna 800 013, IN

Abstract

The Uppalapadu alkaline pluton is predominantly composed of hypersolvus nepheline syenites containing biotite as the sole ferromagnesian mineral. Hornblendesyenites and orthopyroxene-bearing hornblende-syenites are the associated rock types. The pluton is enveloped by a variety of rock types such as amphibolites, gabbros, and granitic rocks.

Full Text

     

V. Madhavan ¹, C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500 007, IN

Abstract

The oblong alkaline pluton at Elchuru is constituted of shonkinite, malignite, nepheline syenite (foyaite and pulaskitic foyaite) and nepheline gneiss (including litchfieldite and mariupolite); the bulk of the pluton is, however, made up of nepheline syenite and nepheline gneiss. These alkaline rocks are emplaced conformably and permissively by a simple mechanism of dilation of the surrounding country rocks under tensional stress. During emplacement, the pluton deformed its own nearly solid periphery producing an outer ring of nepheline gneiss with subsolvus assemblage which surrounds the central core of nepheline syenite with hypersolvus assemblage.

The field, petrographic and geochemical studies, when viewed together, suggest that all the rocks of the pluron arc comagmatic and that nepheline syenites (and nepheline gneisses) are the differentiated products of a basic alkaline magma. The present study has shown that the alkaline magma remained strongly undersaturated throughout the differentia tion process.

The agpaitic coefficient of these rocks is very near to, but invariably less than unity. In tune with their miaskitic chemistry, these rocks show low Na₂O/K₂O and Fe₂O₃/FeO ratios and a generally lower content of MgO, TiO₂ and MnO. The contents of Sr and Ba are very high and with differentiation the ratios Ba/Sr and Sr/Ca fall whereas K/Ba ratio rises. The uniformly higher KJRb ratios of these rocks suggest a deep seated source for the magma.

Full Text

     

H. Sarvothaman ¹, C. Leelanandam ²

Affiliations
1 Geological Survey of India, Samchi, Bhutan, IN
2 Department of Geology, Osmania University, Hyderabad 500 007, IN

Abstract

The model compositions of the Archaean granitic (s.1.) rocks of the Medak area in Andhra Pradesh correspond to tonalite, quartz diorite, granodiorite. adamellite, quartz monzodiorite, granite (s.s.) and alkali feldspar granite. The granitic units show retrograde effects such as albitic rims around plagioclase at K-feldspar contacts, and inclusions of chlorite, epidote and ores in hornblende; anti-rapakivi mantling of plagioclase by K-feldspar is common; K-feldspars show incipient microclinisation. The diagnostic mineral parageneses of the granitic units indicate an overall metamorphism under greenschist facies conditions though locally culminating in amphibolite facies.

The major oxide chemistry reveals that the granitic rocks are divisible into three types. (i) tonalite-quartz diorite suite; (ii) calc-alkaline granites; and, (iii) potassic granites. Tonalites and quartz diorites seem to have formed from a melt which is produced by partial melting from a potassium-depleted sub-crustal (or a mantle) source; the melts of calc-alkaline and potassic granites are probably produced by repeated anatexis from an early sialic crustal source.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology. Osmania University, Hyderabad 500007, IN

Abstract

The Prakasam alkaline province is essentially composed of three major nepheline syenite plutons at Elchuru, Purimetla and Uppalapadu, and one silica-oversaturated (syenite and quartz syenite) pluton at Settupalle. These four post-orogenic plutons, all occurring in the Prakasam District of Andhra Pradesh, display dissimilar internal structures and variable rock associations; they are almost exclusively salic and generally show evidence of passive emplacement.

The gross petrographic characteristics of the individual plutons are presented, and a generalised discussion on the petrogenetic aspects is included. The undersaturated and oversaturated syenites of the province are supposed to have formed from a critically undersaturated hornblende syenite magma by branching differentiation mechanism. The gabbros represent tholeiitic magmatism preceding the emplacement of alkaline rocks, and the ferrosyenites represent the final product of a closed system fractionation (with Jow fO₂) of magma that gave rise to gabbro-anorthosite complexes.

The geological setting of the plutons is portrayed and the tectonic significance of the province, especially in its regional context, is highlighted. The feldspathoidal plutons of the province are conspicuously confined to an extremely narrow linear belt which is close to the known basement fracture zone, with which the major Bouguer gravity axis runs in close paralJelism ; this belt lies at the junction between two (granitegreenstone and gneiss-granulite) terrains.

The localisation of feldspathoidaI plutons at the western margin of the middle Proterozoic mobile belt and their absence in the cratonic region is significant. The over-all development of the mobile belt is speculated in the light of currently fashionable tectonic models. Crustal shortening and thickening of the mobile belt due to collision tectonics, predate the emplacement of the alkaline plutons; the lithosphere controls the character of the magmatism, and pre-existing abyssal faults determine the location of alkaline magmatism.

Full Text

     

N. P. Subrahmanyam ¹, C. Leelanandam ²

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, AMD Complex, Begumpet, Hyderabad 500 016, IN
2 Department of Geology, Osmania University, Hyderabad 500 007, IN

Abstract

The Toa layered suite ranges from feldspalhic peridotites to gabbros and gabbroic anorthosites. This suite differs from the Mer and MusaIa plutons in having coarse-grained cumulophyric rocks (with ubiquitous olivine) and scanty feldspathoidal dikes.

Observed features are traceable to the high H₂O content and high H₂O/CO₂ ratio of the parental liquid. High H₂O content has reduced the viscosity of the magma by many orders of magnitude and facilitated rapid crystallization and settling of crystals leading to the formation of coarse-grained cumulophyric suite of rocks. With its selective reactivity to Si-O-Si bridges, H₂O has depressed the activities of the saturated components (ab, or and qz) in the magma and led to the crystallization of considerable amounts of olivine from the silica-undersaturated components and consequently of feldspars (instead of feldspathoids). The depression of the liquidus of albite has facilitated the crystallization of more calcic feldspars leading to the formation of gabbroic anorthosites. A model of pulsed emplacement of magma is proposed to account (1) for the differing H₂O and CO₂ contents of the parental liquids of the Musala, Mer and Toa plutons, and (2) for the three different trends of differentiation in the three plutons which gave rise to an amazing variety of rock types in the Mundwara Complex.

Keywords

Alkaline Rocks, Toa Pluton, Mundwara Complex, Rajasthan.

Full Text

     

H. Sarvothaman ¹, C. Leelanandam ²

Affiliations
1 Precambrian Geology Division, Geological Survey of India, Bandlaguda, P.O : Saroornagar, Hyderabad 500 660, IN
2 Department of Geology, Osmania University, Hyderabad 500007, IN

Abstract

Predominant rocks in the Medak-Nizamabad segment in Andhra Pradesh are of a granodiorite-adamellite-granite (GAG) suite; the Alumina Saturation Indices or the molar Al₂O₂/(CaO + Na₂O + K₂O) of these units indicate that they arc metaluminous. This suite contains inclusions of a peraluminous tonalite-trondhjemite (IT) suite. A younger peraluminous suite of K-rich granite, granite (s.s.) and adamellite (KGA) intrudes the metaluminous GAG suite and the peraluminous IT suite; a body of alkaline granite intrudes the peraluminous granites.

The tonalite-trondhjemite protoliths of the ca. 3000 Ma old gneisses of Kamataka are peraluminous, and the granites associated with them metaluminous. The Closepet granite activity began with the emplacement of mctaluminous granites, followed by the intrusion of peraluminous granites.

Partial melting (at lower to middle crustal levels) of charnockites, mafic granulites and basic lithologies may have generated the melts of metaluminous and alkaline granites. The ca. 3000 Ma old peraluminous granites are suggested to have formed by partial melting of basic rocks such as basalt and amphibolite under water-excess condition at lower crustal levels. Metaluminous granites, greenstone lithologies and the ca. 3000 Ma old peraluminous gneisses are the precursors for the peraluminous components of the Closepet granite and the KGA suite of Andhra Pradesh. The alkaline granite of Medak-Nizamabad is post-collisional and is emplaced in a rift-free setting.

Keywords

Granites, Peraluminous, Metaluminous. Alkaline, A/CNK, Andhra Pradesh, Karnataka, Dharwar Craton.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500007, IN

Abstract

The fayalite-bearing ferrosyenites in the Prakasam district of Andhra Pradesh are distinctly unique as they strangely contain not only the ferrosilitic orthopyroxene but also Iate aIrnandine-rich garnet, the two minerals which are totally alien to similar rocks occurring elsewhere in the world. Symplectic, vermicular, granular and coronal garnet (with intergrowth of quartz) occurs in insignificant amounts with sporadic distribution around ore, orthopyroxene, clinopyroxene, hornblende and fayalitic olivine when they are in contact with feldspar (occasionally with intervening and incomplete rim of quartz), All the garnet-forming reactions might have resulted due to falling temperature. High and variable silica activity, local variations in f₀₂ and rate of cooling may explain many of the observed textural features.

The electron microprobe analyses of almandine-rich garnets suggest two independent substitutions have taken place, one involving Ca and Mn, and the other involving (Ca+Mn) and Fe. The minor chemical variations in garnet are significantly controlled by its habit. Textural features, and inter- and intra-granular compositional variations in garnet even within a single specimen reflect its disequilibrium formation.

Keywords

Ferrosyenites, Garnet Habit, Compositional Variation, Andhra Pradesh.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad-500007, IN

Abstract

The clinopyroxenes from the ferrosyenites in the Prakasam district of Andhra Pradesh are characterized by their subcalcic nature, enrichment in Fe with concomitant impoverishment in Mg, and low amounts of (calculated) Fe³⁺, Na, Al and Ti - features which specifically typify their subalkaline (tholeiitic) parentage. The acmite component is insignificantly low in the analyzed clino-pyroxenes (Na_3.60-5.74 Mg_10.01-27.09 Fe_67.17-85.16) and bears no relationship whatsoever either with the hedenbergite component or with the calculated Fe³⁺ content. The results of the Fe³⁺ calculations were suspect, especially when the mineral analyses show low SiO₂, low totals, Si+Al<2, and total cations more than 4 per formula unit of 6 oxygens. These strongly coloured green clinopyroxenes, commonly mistaken as sodium-rich acmitic pyroxenes, are indeed sodium-poorferro-augites and ferro-hedenbergites. The high Fe/Mg ratios in the clinopyroxenes (2.4-8.2; Ca_43.3-45.6Mg_5.8-16.0Fe_39.6-50.5), coupled with the extremely high Fe/Mg ratios in the coexisting olivines (35.5-61.8; Fa_97.3-98.5) and orthopyroxenes (3.6-11.8; FS_78.2-91.3) are an indication of the very highly fractionated nature of the magma. Clinopyroxenes of comparable chemical characteristics are reported from ferrosyenitic rocks elsewhere in the world, which in contrast to these of the Prakasam district, are not cospatial with (feldspathoidal) alkaline rocks. The occurrence of ferrosyenites, containing Fe-rich orthopyroxene (eulite-ferrosilite) and inverted pigeonite, in the vicinity of alkaline rocks in the Prakasam district, is interpreted as purely fortuitous and merely coincidental, not having any genetic or causative relationship.

Keywords

Ferrosyenites, Prakasam District, Andhra Pradesh, Mineral Chemistry.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500 007, IN

Abstract

Almost all the feldspaihoidal alkaline complexs of the Eastern Ghat granulite belt are virtually restricted to its western margin, arid are significantly confined to the junction zone between the catonic and mobile belt regions. The presence of subordinate amounts of quartz syenite in preponderantly nephe1ine syenite plutons is ascribed, among other causes, to the dominant role of crustal contamination by initially undersaturated magmas. The not-so-common ferrosye nites, though cospatial, are not comagmatic with nepheline syenites. White ferrosyenites represent the late stage derivatives of tholeiitic magmas, nepheline syenites correspond to the end stage differentiation products of malignites/melteigites. The so-called "alkalic stamp" for rocks purported to be gabbros, in the vicinity of alkaline plutons, is realised as merely a myth. The longevity or propensity for rejuvenation of alkaline magmatism and carbonatite emplacements of mantle origin, in abyssal faults, is fairly well established. The possibility of the presence of isotopically distirict subcontinental mantle reservoirs in a part of the belt is discussed. Some general characteristics of the feldspathoidal complexes are summarized the need for studying them on modern lines to understand their precise petrogenetic schemes and exact crystallization histories is outlined.

Keywords

Alkaline Complexes, Igneous Petrology, Eastern Ghats, Nepheline Syenites, Ferrosyenites.

Full Text

     

E. V. S. S. K. Babu ¹, C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad 500007, IN

Abstract

Pigeonites are typically absent in slowly cooled plutonic rocks, and ortho-pyroxene is totally unkown in alkaline rocks. Ferrosyenites and ferrornonzosyenites of the Chimakurti (Andhra Pradesh) and Sivamalai (Tamil Nadu) areas in south India contain both ortho- and clino-pyroxenes exhibiting various exsolution and inversion textures. The present study on these textures demonstrates the rare presence of 'inverted pigeonites' suggesting very high initial crystallization temperatures for the host rocks and also offers unambiguous evidence for the sub-alkaline (tholeiitic) nature of the host rocks.

Keywords

Inverted Pigeonite, Ortho- and Clino-Pyroxenes, Ferrosyenites.

Full Text

     

J. Ratnakar ¹, C. Leelanandam ², R. Natarajan ³

Affiliations
1 Department of Geology, Post-Graduate College of Science, Osmania University, Safiabad, Hyderabad-500 004, IN
2 Department of Geology, Osmania University, Hyderabad-500 007, IN
3 National Geophysical Research Institute, Hyderabad-500 007, IN

Abstract

The electron microprobe analysis of olivines from the ferrosyenites of Sivamalai shows that they are extremely rich in iron with Fa_96.4-Fa_93.9. The restricted range of Fe²⁺:Mg:Mn values and high Fe²⁺/Mg ratios amongst the analysed samples suggest that parental liquids underwent high degree of fractionation. Association of fayalitic olivine, orthopyroxene, inverted pigeonite and quartz in the ferrosyenites of Sivamalai strongly suggests their tholeiitic nature.

Full Text

   

K. Vijaya Kumar ¹, C. Leelanandam ²

Affiliations
1 School of Earth Sciences, SRTM University, Nanded - 431 606, IN
2 House No. 12-13-205/1, Street No. 2, Tarnaka, Hyderabad - 500 017, IN

Abstract

The Proterozoic Eastern Ghats Belt (EGB) along the east coast of India exposes deep segments of the continental crust, and is considered as a deeply eroded remnant of the present-day Himalayan-type setting. The EGB registers crustal growth of the Indian plate on its eastern side. Precambrian sutures in this poly-metamorphosed and multiply-deformed belt are recognized by the presence of ophiolites (containing unequivocal sheeted dykes and plagiogranite), shear zones, ultrahigh-T metamorphism, massif-type anorthosites and more significantly, by the presence of deformed alkaline rocks and carbonatites (DARCs). The southern segment of the EGB, around Kondapalli (Andhra Pradesh), records the entire gamut of processes from Palaeoproterozoic rifting to Grenvillian/Pan-African collision. The first convergence event that operated between 2 and 1.6 Ga is yet to be identified in other parts of the EGB. The mafic and felsic granulites of Kondapalli exhibit trace element characteristics typical of subduction-related magmatic arcs and the Kondapalli Layered Complex (KLC) is construed as an arc-ischolar_main complex in the deeply eroded Eastern Ghats orogen.

We postulate that the evolution of the EGB involved two distinct episodes of convergence, both being initiated by the onset of continental rifting. In our favoured model, the first rifting event at ~ 2.0 Ga along the eastern margin of the Indian plate, initiated the formation of an Atlantic-type continental margin, which was later converted into an Andeantype continental margin by convergent plate motion at ~1.85 Ga. Final culmination by continent-continent collision was possibly completed by 1.55 Ga. The second episode of rifting between 1.5-1.35 Ga, along the eastern margin of the thickened arc crust, facilitated the emplacement of alkaline rocks and carbonatites (ARCs). The exact timing of the Mesoproterozoic basin inversion and conversion of ARCs into DARCs - either during Grenvillian or Pan-African orogeny - remains elusive.

Keywords

Rifting, Collision, Suture, Arc Magmatism, ARCs-DARCs, Eastern Ghats Belt, India.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad - 500 007, IN

Abstract

This communication is aimed at evaluating the compositional relationships between the minerals and host charnockitic rocks from Kondapalli and to demonstrate that the composition of any particular ferromagnesian mineral in the granulites is controlled not by the whole rock chemistry alone but by the amount and actual composition of all other coexisting ferromagnesian minerals and also of the ore minerals.

Full Text

   

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad - 500 007, IN

Abstract

Though fayalite + quartz association is common in a variety of rocks, it is extremely rare with orthopyroxene and virtually non~existent with orthopyroxene + garnet. Hence the fayalite-ferrosilite-ferrohedenbergite( almandine-rich)garnet-quartz-bearing ferrosyenites in the Prakasam district (A.P.) are deemed as singularly exceptional and amazingly unique (Leelanandam, 1993a). The main purpose of this communication is to present electron microprobe analyses of the extremely iron-rich olivines (Fa_97.29 - Fa_99.78) from these unusual rocks and to comment on the relevant petrogenetic implications.

Full Text

   

M. Narsimha Reddy ¹, E. V. S. S. K. Babu ², C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad - 500 007, IN
2 Present address National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN

Abstract

The Inukurti Anorthosite Complex (IAC) forms a small elliptical dome (15 x 10 km) within the Archaean metamorphosed volcano-sedimentary sequences of the Nellore Schist Belt (NSB) The IAC comprises dominantly of anorthositic rocks, which are cut by mafic sills and dykes, volumetncally insignificant lenses and bands of dionte occur along its periphery All the rocks are deformed and metamorphosed under amphibohte-facies conditions but exhibit relict magmatic textures despite metamorphic recrystallisation and deformation The minerals from anorthosites diontes and amphibohtes exhibit compositional characteristics distinct to each group

Garnet-hornblende plagioclase-quartz equilibria from the IAC indicate a narrow range of metamorphic equilibration temperature between 644 and 570 °C, but a broad range of pressure between 76 and 27 kbar Geothermobarometry on zoned garnet porphyroblasts indicates that the rocks of the IAC were subjected to decompression of the order of about 5 kbar from 76 to 27 kbar related to rapid exhumation

Keywords

Anorthosite, Dionte Amphibohte, Geothermobarometry, Amphibohte facies, Inukurti Complex, Nellore schist belt, Andhra Pradesh.

Full Text

     

K. Vijaya Kumar ¹, K. Rathna ¹, C. Leelanandam ²

Affiliations
1 School of Earth Sciences, SRTM University, Nanded 431 606, IN
2 House No. 12-13-205/1, Street No. 2, Tarnaka, Hyderabad 500 017, IN

Abstract

Understanding the origin and growth of continental crust is a fundamental problem in geological sciences. Two distinct ways in which the continental crust grows include horizontal (subduction) and vertical (plume/extension) accretions. As the mantle reservoirs in these two tectonic settings are generated and/or modified by contrasting processes, the erupted melts offer clues on the nature of these divergent mantle sources. Trace element geochemistry is a robust tool to quantitatively model the mantle sources, melting mechanisms and relative roles of mantle and crust in the petrogenesis of magmatic rocks, which ultimately lead us to unravel the origin of continental crust.

The present study portrays growth of the continental crust in the Proterozoic Eastern Ghats Belt, SE India. Mafic magmas within the Palaeoproterozoic Kondapalli-Kandra region illustrate subductionrelated island arc basalt-type geochemical signatures whereas alkali basaltic magmas in the Mesoproterozoic Prakasam continental rift-zone display ocean island basalt-type characteristics. Calculated mantle sources for subduction-zone and rift-related magmas display distinctly different geochemical traits. Mesoproterozoic gabbroic magmas in the Prakasam rift-zone exhibit geochemical signatures akin to the subduction-related mafic melts. This dichotomy of continental crust produced by intra-plate processes exhibiting plate-margin signatures advocates that we possibly have overestimated the proportion of continental crust generated above subduction zones.

Keywords

Continental-Rift, Eastern Ghats Belt, Geochemistry, Mafic Magmas, Mantle Sources, Subduction Zone.

Full Text

   

C. Leelanandam ¹, K. Vijaya Kumar ¹

Affiliations
1 School of Eartli Sciences, Swanni Ramanand Teerth Marathwada University, Nanded - 431 606, IN

Abstract

Tiie Kondapalli Layered Complex (KLC) is a minor mafic-ultramafic intrusion occurring in the charnockitic region of the Eastern Ghats Mobile Belt (EGMB). it consists dominantly of gabbroic and anorthositic rocks, with subordinate ultramafic rocks (orthopyroxenite, websterite, cliriopyroxenite, harzburgite and dunite), which are associated with chromitite. The components of the KLC are grouped into two series: (1) Chromitite-Ultramafic Rock Series (CURS), and (2) Gabbro-Anorthosite Layered Series (GALS); some mafic gabbros belong to CURS. A profound petrological and geochemical hiatus exists between the primitive CURS and evolved GALS, which constitute a regressive intrusive sequence, it is shown that the REE abundances and chondrite-normalized patterns of 27 rocks from the KLC are controlled by the dominant cumulus minerals and variable amounts of trapped melt. The cumulate anorthositic and gabbroic rocks of the GALS are classified into those showing (1) positive Eu anomaly (An I and Gb I), (2) no Eu anomaly (An II and Gb II), and (3) negative Eu anomaly (Gb III). The whole-rock REE compositions possibly record the evolution of the "associated" liquids. Calculated associated liquid compositions, when viewed in conjunction with the available mineralogical, petrological and geochemical data of CURS and GALS, strongly suggest a two-magma genesis for the Kondapalli Layered Complex.

Keywords

Rare Earth Elements, Cumulates, Associated Liquids, Petrogenesis, Kondapalli Layered Complex, Andhra Pradesh.

Full Text

     

K. Krishna Reddy ¹, J. Ratnakar ², C. Leelanandam ³

Affiliations
1 Geological Survey of India, Bandlaguda, Hyderabad-500 660, IN
2 Department of Geology, Post-Graduate College of Science, Osmania University, Hyderabad-500 004, IN
3 Department of Geology, Osmania University, Hyderabad-500 007, IN

Abstract

The Proterozoic Uppalapadu alkaIine complex (1348±41 Ma) in the Prakasam province of Andhra Pradesh is predominantly composed of nepheline syenite, hornblende syenite and quartz syenite, all of which represent an alkaline series. The pluton is closely associated with tholeiitic gabbro and ferrosyenite representing a sub-alkaline series. Geochemical characters suggest that the rocks of the alkaline series were formed by the differentiation of the hydrous alkaline basaltic magma under high P_H2O, whereas those of the sub-alkaline series were formed by differentiation of an anhydrous olivine tholeiitic magma under low fO₂ (reducing) conditions. Quartz syenite (an offshoot in the alkaline series) is formed either by fractionation of K-feldspar, ferrohastingsite and/or biotite under high P_H2O conditions or by crustal contamination of critically saturated syenitic liquids.

Keywords

Petrochemistry, Proterozoic, Alkaline Complex, Andhra Pradesh.

Full Text

     

C. Leelanandam ¹

Affiliations
1 Department of Geology, Osmania University, Hyderabad - 500 007, IN

Abstract

The primary purpose of this communication is to present a comparative picture of the chemically analyzed and normatively computed compositions of ortho-pyroxenes (En contents) and plagioclase feldspars (An contents) from the charnockitic rocks of Kondapalli in Andhra Pradesh.

Full Text