Sapphirine granulites from Panasapattu,Eastern Ghats belt,India:Ultrahigh-temperature metamorphism in a Proterozoic convergent plate margin

We report equilibrium sapphirine ＋ quartz assemblage in biotite-orthopyroxene-garnet granulites from a new locality in Panasapattu of Paderu region in the Eastern Ghats granulite belt, which provide new evidence for ultrahigh-temperature （UHT） metamorphism at 1030-1050 ℃ and 10 kbar in this region. The development of migmatitic texture, stabilization of the garnet-orthopyroxene- plagioclase-K-feldspar association, prograde biotite inclusions within garnet and sapphirine as well as sapphirine and cordierite inclusions within garnet in these granulites indicate that the observed peak assemblages probably formed during prograde dehydration melting of a Bt-Sill-Qtz assemblage, and constrain the prograde stage of the p--T path. The core domains of orthopyroxene porphyroblasts have up to w（Al203） 9.6%, which suggest that the temperatures reached up to 1150 ~C suggesting extreme crustal metamorphism. These conditions were also confirmed by the garnet-orthopyroxene thermobar- ometery, which yields a p--T range of 1012--960 ~C and 9.4 kbar. The p--T phase topologies computed using isochemical sections calculated in the model system Na20-CaO-K20--FeO-MgO-A1203-SiO2 --H2O （NCKFMASH） for metapelites, garnet-free sapphirine granulites and garnet-bearing sapphirine granulites match the melt-bearing assemblages observed in these rocks. Isochemical sections constructed in the NCKFMASH system for an average sub-aluminous metapelite bulk composition, and contoured for modal proportions of melt and garnet, as well as for the compositional isopleths of garnet, predict phase and reaction relations that are consistent with those observed in the rocks. Garnet and orthopyroxene contain Ti-rich phlogopite inclusions, suggesting formation by prograde melting reactions at the expense of phlogopite during ultrahigh-temperature conditions. These p--T results underestimate ＇peak＇ condi- tions, in part as a result of the modification of garnet compositions in the domains where some melt was retained. The post-peak evolution is constrained by a succession of melt-present reactions that occur at p 〈 10 kbar, inferred from micro-structural relations among various minerals. After high-temperature decompression from the metamorphic peak, the p--T path followed a near isobaric cooling stage to T 〈 900℃. The UHT rocks investigated in this study occur within a continental collision suture which witnessed prolonged subduction-accretion history prior to the final collision. We correlate the extreme metamorphism and the stabilization of UHT mineral assemblages to heat and volatile input from an upwelled asthenosphere during subduction--collision tectonics in a Proterozoic convergent plate margin.

Structure and floristic composition of tree stand in tropical forest in the Eastern Ghats of northern Andhra Pradesh, India

The changes in species composition, abundance and forest stand structure were analyzed across altitudinal regimes in tropical forests of Eastern Ghats of northern Andhra Pradesh, India. Three 1-ha plots were established with one each in low, medium and high altitudes. A total of 153 species, 2129 stems （709 stems .ha^-1） of ≥10 cm girth were enumerated. Species richness and diversity pattern varied along altitudinal gradient and increased with the altitude. Species richness varied from 52 to 110 species-ha^-1 and stand density from 639 to 836 stems.ha^-1 with average basal area of 34.39 m^2.ha^-1. Shannon-Wiener index （H＇） ranged from 4.55 to 5.17. Low altitude （i.e., Site 1） is dominated byXylia xylocarpa （59.22） and Lagerstroemia parviflora （23.90）, medium altitude （i.e., Site 2） by Xylia xylocarpa （45;50） Bursera serrata （17.29）, and high altitude （i.e., Site 3） has Schleichera oleosa （28.25） Pterocarpus marsupium （26.55） as predominant species. Taxonomically, Rubiaceae （12 species）, Fabaceae （12）, Euphorbiaceae （11）, Rutaceae （7） and Lanraceae （7） were dominant families. Density-wise, Fabaceae, Combretaceae, Euphorbiaceae, Anacardiaceae and Myrtaceae were abundant. Thus, conservation assessment based on altitudinal regimes and the information on species structure and function can provide baseline information for monitoring and sustaining the biodiversity.

Differences in Tree Species Diversity and Soil Nutrient Status in a Tropical Sacred Forest Ecosystem on Niyamgiri Hill Range,Eastern Ghats,India

We have quantitatively analyzed the tree species diversity with respect to soil nutrient status in three sites of a sacred forest ecosystem of Niyamgiri hill range, Eastern Ghats, India. Extensive field surveys and sampling were conducted in 3 sites of the hill range： Site 1 Pterocarpus dominated forest （PTF） （19°40＇02.2＇＇ N and 83°21＇23.1＇＇ E）, Site 2 Mangifera dominated forest （MAF） （19°40＇02.8＇＇ N and 83°21＇40.8＇＇ E） and Site 3 Mixed forest （MIF） （19°36＇47.1＂ N and 83°21＇02.7＇＇ E）. A total of 28 families, 42 genera, 46 tree species, and 286 individual trees were recorded on an area of0.6 ha. Tree density varied between 470 and 49o individuals ha and average basal area between 3.16 and l0.04 m2 ha-1. Shannon Index （H＇） ranged from 2.34 to 4.53, Simpson＇s Index ranged from 0.07 to o.09, and equitability Index ranged from 0.7 to 1.34. The number of individuals was highest in the girth at breast height （GBH） class of 50-7o cm. The soil nutrient status of the three forest types was related to tree species diversity. The soil pH value of the three sites reflected the slightly acidic nature of the area. Species diversity was positively correlated with organic carbon and phosphorus and negatively with nitrogen, EC and pH. The results of the current study may be helpful to further develop a conservation planfor tree species in tropical sacred forest ecosystems.

Diversity, distribution and resource values of woody climbers in tropical forests of southern Eastern Ghats, India

We investigated the distribution and resource values of liana species assessed in six hill complexes of southern Eastern Ghats, India. 143 liana species （DBH （diameter at breast height） ≥1.5 cm） and 32,033 liana individuals were recorded from 110 transects （0.5 ha each covering 55 ha area） in the study sites. The resource values of lianas were broadly categorized into ecological and economic importance. About 90% （129） of liana species and 96% （30,564） of liana individuals were established ecological/economic values. Fruit rewards provided by 76 species and 20,325 individuals constituted the major resource of ecological importance. 82 species and 21,457 liana individuals are of economic importance as medicine, edible fruits, edible and medicinal values, and yet others are used for different domestic purposes including furniture, fuel wood, rope making etc.. Ecologically, the prevalence of succulent diaspores in lianas of Indian Eastern Ghats indicates the animal dependence of many liana species for dispersal and underlines the need for a holistic and whole-forest conservation approach in maintaining forest biodiversity.

Ancient terrane boundaries as probable seismic hazards: A case study from the northern boundary of the Eastern Ghats Belt, India

In the eastern part of the Indian shield, late Paleozoic-Mesozoic sedimentary rocks of the Talchir Basin lie precisely along a contact of Neoproterozoic age between granulites of the Eastern Ghats Mobile Belt （EGMB） and amphibolite facies rocks of the Rengali Province. At present, the northern part of the basin experiences periodic seismicity by reactivation of faults located both within the basin, and in the Rengali Province to the north. Detailed gravity data collected across the basin show that Bouguer anomalies decrease from the EGMB （~＋15 mGal）, through the basin （^-10 mGal）, into the Rengali Province （^-15 mGal）. The data are consistent with the reportedly uncompensated nature of the EGMB, and indicate that the crust below the Rengali Province has a cratonic gravity signature. The contact between the two domains with distinct sub-surface structure, inferred from gravity data, coincides with the North Orissa Boundary Fault （NOBF） that defines the northern boundary of the Talchir Basin. Post-Gondwana faults are also localized along the northern margin of the basin, and present-day seismic tremors also have epicenters close to the NOBF. This indicates that the NOBF was formed by reactivation of a Neo- proterozoic terrane boundary, and continues to be susceptible to seismic activity even at the present-day.

Geochronological Constraints for Boundary Shear Zones between Eastern Ghats Province and Bastar Craton: Implication for the Formation of Granulites and Their Exhumation History

Shear zones in the boundary between Eastern Ghats Province (EGP) and the cratons of Singhbhum in the north and Bastar in the west provide an excellent opportunity to study the tectonics of shear zone development and its timing in relation to the evolutionary history of the granulite suites. Detailed structural, microfabric and quartz C-axis patterns revealed a high temperature shear zone, at the western boundary between EGP and Bastar Craton (BC) around Paikmal. Petrological studies in this shear zone indicated decompression coeval with stretching in the sheared granulites. Geochronological constraints provided here indicate rapid exhumation of deep seated granulites in this boundary shear zone;the timing also is late in relation to the long-lived thermal (granulite formation) event in the EGP. Additionally, our geochronological data demonstrated the ~1600 Ma event in the Eastern Ghats Belt (EGB) involving sedimentation, magmatism, metamorphism and crustal anatexis, as a significant world event.

Apatite Microstructure and Composition in Manganese Formation of Eastern Ghats, Orissa, India

Apatite grains in a stratabound manganese ore body from Eastern Ghats in Leliguma, Koraput district south Orissa, India were studied under optical and electron microscope. Apatite shows bimodal occurrence: one associated with granite/pegmatitic phase and other with manganese phase, and exhibits different microstructure and composition. Apatite in pegmatitic association (occurring as inclusion in quartz and feldspar) is small in size and occurs as subhedral grains having irregular boundaries and poor in manganese content (MnO: 0.16%). Apatite associated with manganese mineral phases (cryptomelane / romanechite) is mostly euhedral, relatively larger in size, contains higher manganese value, and exhibits some peculiar features like twinning, zoning, overgrowth, and occasionally contains inclusion of quartz and feldspar grains. Apatite grains occurring as inclusions within quartz and feldspar are of hydrothermal origin and formed along with pegmatitic minerals. Such apatite is almost devoid of manganese but relatively enriched in Sr, F and LREE content. The apatite in manganese mineral association formed during supergene process. The apatite of latter generation appears as idiomorphic crystals;contains up to 6.85% of MnO in solid solution and shows relatively higher HREE values. The higher HREE values may be due to its derivation from stratiform Mn-ore bodies and associated granitised rock during remobilization, solution and precipitation of Mn –rich fluid along structurally weak planes resulting in development of a stratabound ore body.

Secular evolution of continental crust: recorded from massif-type charnockites of Eastern Ghats belt, India

It is reasonably well established that the Earth has substantially cooled from the Archean to the pre-sent and hence the sites, rates and pro- cesses of crust formation must have changed through geo-logic time. Archean and Proterozoic granitic rocks are the principal record of such changes. Massif-type charnockites in the Eastern Ghats granulite belt, India, of Archean and Proterozoic ages mirror the changing conditions and/or processes of continental crust for- mation. Though both can be explained by dehydration melting of mafic rocks, the conditions differ. Potasium and rubidium rich Proterozoic charnockites have significant negative Eu ano- maly indicating melting at shallow depths in the stability field of plagioclase. In contrast, sodium and strontium rich Archean charnockites with less LREE enrichment and less depletion in Eu indicate melting at greater depths in the stability field of garnet or amphibole.

Geochemistry of Major Oxides in Host Rocks in Vizianagarm Manganese Ores Belt (A.P.), India

The abundance, distribution trends and significance of the major oxides in the host rocks in Vizianagarm Manganese Ores Belt (A.P.) (between N latitude 18°12' and 18°30' and E longitudes 83°20' and 83°45'), 15 samples of host rocks from different localities of the area under study were collected and analyzed for major oxides. We describe here in major oxides geochemistry of host rocks and manganese ore deposits associated with Precambrian Khondalite and Charnockite in Vizianagarm Manganese Ores Belt (A.P.): 1) Preponderance of SiO2 over Al2O3;2) Dominance of K2O and CaO over Na2O;3) Abnormally high concentration of phosphorus and a positive relationship of P2O5 with CaO and Ti contents;4) Manganese increases with increases of iron, lime and soda and vice versa, 5) CaO increases with the increases of Al2O3, Ti, K2O and vice versa.?High P2O5content in these manganese ores appears to be the result of precipitation from secondary manganese rich solutions containing dissolved phosphorus from the P2O5 enriched host rocks.?Another source of P2O5 may be the associated granitic and pegmatitic intrusions. Elements like K, Na, Ca, Mg, Co, Ni, Pb and Zn etc. appear to be mostly concentrated in the Mn-minerals viz. psilomelane, cryptomelane, hollandite and pyrolusite and related secondary phases [1] and [2]. Stratigraphically, the study area includes within a thick succession of Precambrian Group belonging to the Khondalite and Charnockite Groups of Dharwar Supergroup, that form a part of Eastern Ghat Complex of India. The manganiferous rocks that have been encountered in the Vizianagarm Manganese Ores Belt (A.P.) India are known as Kodurites.

Provenance studies on the heavy mineral placers along the coastal deposits of Odisha,eastern India

The coastal deposits along the eastern part of the Indian Peninsula are known for the high abundance of heavy minerals. The present study, as discussed here, has been undertaken along the southwestern coastal part of Odisha, India, adjoining the charnockite-migmatite zone of the Eastern Ghat Mobile Belt(EGMB). The composition of the placers along the study area is primarily controlled by the detritus from the proximal hinterland rock type(s). The weathering index has been established based on the grain morphology, major element concentration and radioelement ratios. Petrological characteristics and grain morphology of monazite, zircon, ilmenite and rutile have been presented respectively, and their implications are discussed. The provenance study of these coastal placers is based on the abundance of rare earth elements(REE) and radioactive elements in the placer sands and the rock types in the study area. The tectonic implications are based on the major element abundance of the beach sands.