Southernmost India Research Articles

Food and Shelter for the Itinerant Pilgrims: Maratha Chattrams in Southernmost India

A chattram, also called choultry, primarily refers to a wayside inn or resthouse for travelers, mostly pilgrims. They may halt here for a meal or for a few hours or even for a few days or weeks. Such chattrams were built almost throughout India by many kings and queens, ministers and merchants. Although there are copious references to such chattrams in ancient and medieval literature and inscriptions, actual specimens of such chattrams are limited in number. Many of them appear to have been destroyed during wars or in the course of later developments and constructions. In Tamil Nadu, in southern India, the Tanjavur Maratha dynasty (1676-1855) that ruled this region with Tanjavur as the capital, erected scores of such chattrams. Some of these chattrams have survived to this day. Many of these chattrams are massive and elegant buildings displaying innovative architectural features. Some of them also bear beautiful sculptures and wall paintings akin to those in the medieval temples of the region. Mainly based on archival and field researches, the present paper analyzes the historical, architectural and artistic importance of these chattrams and simultaneously, probes the role of these institutions in the socio-economic life of the Maratha period. The paper concludes with a brief account of the present-day condition of these chattrams and the ways in which they could be put to adaptive reuse according to the exigencies of contemporary times.

Evaluation of metals and trace elements in sediments of Kanyakumari beach (southernmost India) and their possible impact on coastal aquifers

Beach sediments of Kanyakumari at the southernmost India were evaluated for metals and trace elements and to assess their possible impact on coastal ecosystems. Positive correlations (except for Cd and Sr) between them indicated metamorphic lithologies and heavy mineral deposits as possible sources. Significant-extremely high enrichment and very high contamination of Th, Zr, Mo, Ti and U reflected the presence of different heavy minerals. The geo-accumulation index, however, mirrored their variable abundances at different sites. Association of Cd with P suggested the influence of anthropogenic solid waste from fishing industry. It might have caused >41-fold enrichment of Cd and the Fe- Mn-oxides possibly acted as scavengers for 13-fold enrichment of As compared to UCC. Concentrations of Zn and Cr between ERL and ERM in 13% and 93% of the samples, and Ni > ERM in 87% of sediments suggest their bioavailability to seawater with a potential risk for coastal aquifers.

Estimation of microplastics in sediments at the southernmost coast of India (Kanyakumari).

Increasing urbanization and anthropogenic activities of the last couple of decades have left significant amounts of plastic debris in both coastal and marine ecosystems. In this study, we estimated the abundance of microplastics (particle size < 5 mm) in the beach sediments of southernmost India at Kanyakumari by collecting sediments from harbors, coastal fishing villages/residential beaches, tourist beaches, and undisturbed coastal areas along the Indian Ocean. We recovered 343 particles (67% fiber and 33% fragment) from eight different stations by evaluating 50 g dry sediments (d.s.) from each location. All of them were secondary microplastics and most of them (i.e., 331 out of 343 particles) were transparent. Tourist beaches had the highest concentration (150 particles/50 g d.s.), followed by the harbors (99 particles/50 g d.s.). The undisturbed beach contained the least amount of microplastics, representing only 4.3% of the total recovered particles. Our study relates the abundance of microplastics to different degrees of anthropogenic activities. Further research, however, is required to identify the mechanism that influenced their transport and deposition in the coastal sediments as well as to evaluate the possible interaction between microplastic particles and marine ecosystems.

Isotopic systematics of zircon indicate an African affinity for the rocks of southernmost India

Southern India lies in an area of Gondwana where multiple blocks are juxtaposed along Moho-penetrating structures, the significance of which are not well understood. Adequate geochronological data that can be used to differentiate the various blocks are also lacking. We present a newly acquired SIMS U–Pb, Lu–Hf, O isotopic and trace element geochemical dataset from zircon and garnet from the protoliths of the Nagercoil Block at the very tip of southern India. The data indicate that the magmatic protoliths of the rocks in this block formed at c. 2040 Ma with Lu–Hf, O-isotope and trace element data consistent with formation in a magmatic arc environment. The zircon data from Nagercoil Block are isotopically and temporally distinct from those in all the other blocks in southern India, but remarkably correspond to rocks in East Africa that are exposed on the southern margin of the Tanzania–Bangweulu Block. The new data suggest that the tip of southern India has an African affinity and a major suture zone must lie along its northern margin. All of these blocks were finally brought together during the Ediacaran-Cambrian amalgamation of Gondwana where they underwent high to ultrahigh temperature metamorphism.

Zircon ages and Hf isotopic systematics reveal vestiges of Mesoproterozoic to Archaean crust within the late Neoproterozoic–Cambrian high-grade terrain of southernmost India

Late Neoproterozoic to Cambrian ages have been widely recorded from the Southern Granulite Terrain (SGT) of India and were correlated with global tectono-thermal (Pan-African) events associated with amalgamation of the Gondwana supercontinent. We report results of single zircon dating from a charnockite and a granitic augen–gneiss from the SGT using SHRIMP and evaporation techniques, complemented by zircon Hf isotopic systematics. The SHRIMP data for zircons in the charnockite are spread along a well-defined discordia line suggesting variably strong lead–loss during the late Neoproterozoic Pan-African event. A concordant grain yielded a 207Pb/206Pb age of 1893±13Ma, and the upper intercept of the discordia line for all analyses with Concordia is at 1881±14Ma. The concordant grain age is considered to most closely reflect the time of emplacement of the charnockite protolith. The imprecise lower Concordia intercept at 572±25Ma is likely to reflect Pb-loss during granulite-facies metamorphism. Evaporation of four zircons yielded consistent 207Pb/206Pb isotopic ratios at high evaporation temperatures of ca. 1598°C, suggesting an age of ca. 1450Ma. This date is clearly much younger than the SHRIMP result and suggests that the evaporated grains no longer contained their original, magmatic 207Pb/206Pb ratios but record strong Pb-loss as also shown by the SHRIMP data. Lu–Hf isotopic analysis of ten spots on zircon grains previously analyzed by SHRIMP II yielded strongly negative εHf(t)-values of −6.1 to −9.2 and mean Hf crustal residence ages of 2.95 to 3.14Ga.Eight grains from the augen–gneiss analyzed on SHRIMP II also show variable but considerable Pb-loss. A concordant grain yielded an age of 1557±16Ma, and the other grains define a discordia line with an upper Concordia intercept at 1553±21Ma. Two unzoned grains produced a combined mean 206Pb/238U age of 583±6Ma and reflect the high-grade late Neoproterozoic metamorphic event. A concordant 207Pb/206Pb age of 2043±13Ma was obtained for a xenocryst. Evaporation of five large zircons from this sample yielded a precise mean 207Pb/206Pb age of 1556.0±0.5Ma, identical to the result for the SHRIMP-dated concordant grain. Lu–Hf isotopic analysis of ten spots on zircon grains from where SHRIMP data were gathered yielded strongly negative εHf(t)-values of −6.0 to −17.0 and mean Hf crustal residence ages of 2.68 to 3.37Ga.Our results suggest that not all rocks in the so-called Pan-African domain of southern India are Neoproterozoic in age, and that there could be more Mesoproterozoic to Archaean crust hidden in the “sea” of Neoproterozoic granulites, granitoids and migmatites than so far recognized. The Hf isotopic data reveal both granitoid samples to be derived from crustal melts generated from Archaean continental crust, and the chemistry of these rocks is inherited from their ancient source. We compare the zircon ages with those of similar rocks in the Highland Complex of Sri Lanka and discuss their relevance as vestiges of an older continental terrain incorporated within the late Neoproterozoic–Cambrian collision belt of East Gondwana. In view of rock and age similarities we tentatively suggest links between the Indian Trivandrum and Madurai Blocks and the Sri Lankan Highland and Wanni Complexes.

Evolution of the continental crust in the Kerala Khondalite Belt, southernmost India: evidence from Nd isotope mapping, U–Pb and Rb–Sr geochronology

In order to decipher crustal genesis and evolution as well as to refine the metamorphic history of the Kerala Khondalite Belt (KKB), southernmost India, we have applied U–Pb monazite, Rb–Sr biotite-feldspar dating and Nd isotope geochemistry. The KKB belonged to an eastern Gondwana mobile belt that underwent ultra-high temperature metamorphism at Pan-African times. It is dominated by Nd model ages ranging between 2.0 and 3.0 Ga except at its northernmost boundary (the Achankovil Unit, AU), where Middle Proterozoic Nd model ages were recognised (1.3–1.6 Ga). The new data show, that these ages are not restricted to cordierite-bearing metasediments alone but can be found in other lithologies of the Achankovil Unit as well. Peak metamorphism occurred between 590 and 550 Ma as recorded by U–Pb dating of monazite from charnockites and garnet-biotite gneisses. Rb–Sr ages of minerals in pegmatite intrusions record cooling to ca. 400–500 °C by 490-470 Ma. Based on a systematic regional sampling, this contribution confirms and refines former models based on smaller datasets. The major issue is that the Kerala Khondalite Belt must have undergone an extremely slow cooling history (3–6 °C/Ma) comparable to the one described for Sri Lanka and Madagascar. Still such ultra-high temperatures associated to slow cooling processes cannot be satisfactorily fit into a common tectonic context.

The nature of the crust in southern India: Implications for Precambrian crustal evolution

We present crustal thickness and Poisson's ratio determinations from receiver function analyzes at 32 sites on the Archaean and Proterozoic terrains of South India. The crustal thickness in the late Archaean (2.5 Ga) Eastern Dharwar Craton varies from 34–39 km. Similar crustal thickness is observed beneath the Deccan Volcanic Province and the Cuddapah basin. The most unexpected result is the anomalous present‐day crustal thickness of 42–51 km beneath the mid‐Archaean (3.4–3.0 Ga) segment of the Western Dharwar Craton. Since the amphibolite‐grade metamorphic mineral assemblages (5–7 Kbar paleopressures) in this part of Western Dharwar Craton equilibrated at the depths of 15–20 km, our observations suggest the existence of an exceptionally thick (57–70 km) crust 3.0 Ga ago. Beneath the exhumed granulite terrain in southernmost India, the crustal thickness varies between 42–60 km. The Poisson's ratio ranges between 0.24–0.28 beneath the Precambrian terrains, indicating the presence of intermediate rock type in the lower crust. These observations of thickened crust suggest significant crustal shortening in South India during the Archaean.

Multiple Tectonothermal Events in the Granulite Blocks of Southern India Revealed from EPMA Dating: Implications on the History of Supercontinents

We report age data on zircon, monazite, uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern India using an electron microprobe technique. The rocks analysed in this study cover all of the major lithounits in these terrains and include garnet-bearing and garnet-free charnockites, garnet-biotite gneisses, khondalites, calc-silicate rocks, and a suite of orthogneisses (biotite gneiss, biotite-hornblende gneiss). Two pink metagranites representing the magmatic phase were also analysed. Zircons from the Madras Block yield well-defined isochrons at 2.5-2.6 Ga. Core to rim analyses of single zircon grains show age zoning with 2.6-2.9 Ga igneous cores mantled by 2.4-2.5 Ga rims. Detrital zircons show age up to ca. 3.2 Ga. Monazites in this block have cores and rims with 2.5-2.3 Ga. A suite of 19 samples from the Madurai Block brings out the multiple tectonothermal events in this terrain. Zircons from an orthogneiss yield well-defined isochrons at 1.7±0.1 Ga, 0.82±0.05 Ga and 0.58±0.04 Ga from core, inner rim and rim portions, respectively. Zircon grains in other rocks preserve either core or secondary growth ages at 0.8-1.0 Ga. Zircons in a pink metagranite from this block show sharply defined isochrons of 0.68±0.03 Ga for the core and 0.57±0.01 Ga for the secondary portion. A late Pan-African overprint is observed throughout this block with zircon rims, monazite, uraninite and huttonite yielding age values in the range of 0.45-0.60 Ga. Zircons from both the Trivandrum and Nagercoil blocks show a major tectonothermal event at 0.55 Ga with faint indications of previous tectonothermal events during 0.8-1.0 and 1.7-2.0 Ga. Monazite data from both the Trivandrum and Nagercoil blocks are essentially similar to those from the Madurai Block except for presence of relic monazite in the former. Our study confirms the notion that the Palghat-Cauvery Shear Zone marks the major terrain boundary between an Archean craton in the north and Proterozoic terrains in the south. It also strengthens the view of Paleoproterozoic accretion and Pan-African reworking of blocks south of this shear zone. The ages of production, accretion, and reworking in the terrains of southern India yield important information for the histories of Columbia (∼1.8-1.5 Ga), Rodinia (∼1.1-1.0 Ga), and Gondwana (∼0.6-0.5 Ga) supercontinents. The southern Indian terrains formed part of a worldwide network of orogenic belts that is centered around 1.8 Ga and outlines the configuration of Columbia. Accretion of terrains in the Madurai block to Archean rocks north of the Palghat-Cauvery Shear Zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the Eastern Ghats orogen of eastern India and the Rayner belt of coastal East Antarctica. Our data confirm earlier evidence that all of southernmost India underwent resetting of isotopic systems during the final accretion of Gondwana at the time of the Pan-African orogeny (∼0.5 Ga). The possibility that the Trivandrum and Nagercoil terrains accreted to the Madurai block after ∼0.7 Ga suggests that this Pan-African zone may also have involved accretion and closure of ocean basins. If that happened, then this zone may be the long-sought suture between East and West Gondwana.

Proterozoic crustal evolution of southernmost India and Sri Lanka

Abstract The Southern Granulite Terrain of India comprises four Proterozoic domains (from north to south): the Madurai Block, and the Achankovil, Ponmudi and Nagercoil Units. All but the Achankovil Unit share similarities with the Highland Complex of Sri Lanka: (1) evidence for Palaeoproterozoic crust formation (from U-Pb ages and 2.0–3.0 Ga Nd model ages); and (2) Pan-African ultrahigh-temperature metamorphism between 610 and 550 Ma. More specifically, the Ponmudi Unit and the Madurai Block share lithological and petrological characteristics with the low- P and high- P domains of the Highland Complex, respectively. The Achankovil Unit is correlated with the Wanni Complex of Sri Lanka on the basis of lithologies and Nd model ages (1.0–2.0Ga). These domains and the Vijayan and Kadugannawa Complexes of Sri Lanka represent Late Mesoproterozoic-Early Neoproterozoic crustal domains. Similarities in tectonic style, degree of metamorphism and Neoproterozoic U-Pb ages, suggest a common Pan-African tectonothermal evolution for the lower crustal domains of southern India, Sri Lanka and the Lützow-Holm Bay of Eastern Antarctica. Sri Lanka may have been located at the junction between the Mozambique Belt and a second belt partly involving areas that underwent a Grenvillian high-grade event during the formation of Rodinia. Madagascar shows a similar Pan-African metamorphic overprint, but is located in a different position and lacks the influence of the second belt. Alternative views are discussed.

A Pan-African ‘Humite Epoch’ in East Gondwana: implications for Neoproterozoic Gondwana geometry

The plate geometries during Neoproterozoic time have been reconstructed using humite occurrences for the first time. These occurrences are also used to demonstrate the hitherto undocumented humite epoch dominated by extremely water-rich, fluorinated, fluid activity during the Pan-African event. Humite-bearing marbles occur in the Kerala Khondalite Belt of southernmost India, South Madagascar, Sri Lanka and the Lutzow–Holm Complex of East Antarctica. These occurrences prompt a fit of these areas with the Tanzania–Mozambique region of Africa and suggest an intercontinental humite epoch coeval with the waning stages of Pan-African activity extending from the Lutzow–Holm complex of East Antarctica upto the East African Orogen along the eastern flanks of the Mozambique Belt. The modified Smith and Hallam fit of continents finds support in this study.

Teleseismic tomographic evidence for contrasting crust and upper mantles in south Indian Archaean terrains

We compare the velocity structure of the crust and upper mantle of the Archaen granulite terrain of southernmost India with that of the Archaean granite-greenstone (Dharwar craton) terrain just to the north, through P-wave teleseismic travel time measurements. The teleseismic rays recorded by a coarse network of 11 portable seismic stations show an anomalous pattern of late arrivals (delays) over the granulite terrain in contrast to fast arrivals on the Dharwar craton. Such a pattern of time residuals amongst these Archaean terrains, which have remained inert in the last 2 Ga, may indicate the presence of compositional heterogeneity within the crust and upper mantle beneath them. Three-dimensional P-wave velocity tomography using teleseismic rays from a variety of azimuths indicates the existence of contrasting P-wave crust and upper-mantle velocity patterns: (1) in the crust (0–40 km) the western Dharwar craton and the granulite terrain have lower velocity (up to −3%) compared with the higher velocity (1–3%) observed over the eastern Dharwar craton, and (2) in the upper mantle (40–177 km), there is 2–3% lower velocity beneath the granulite terrain compared with the western Dharwar craton. The existence of such lateral velocity variation in the crust and upper mantle, and its preservation since late Archaean times, points to the presence of possibly thick and chemically distinct lithospheres that did not participate in mantle convection.

Zircon geochronology of anatectic melts and residues from a highgrade pelitic assemblage at Ihosy, southern Madagascar: evidence for Pan-African granulite metamorphism

AbstractWe report U—Pb and207Pb/206Pb zircon ages for a granulite facies gneiss assemblage exposed in a large quarry at Ihosy, southern Madagascar. The granulites are derived from pelitic to arkosic sediments and attained equilibrium conditions at 650–700°C and 4–5 kbar. HigherP—Tconditions of 750–800°C and 6 kbar in the presence of low water activities have led to dehydration melting processes. The formation of granitic melts, which (partly) moved away from their source region, intruded into upper parts of the metapelitic gneisses as small granitic veins and left behind granulitic garnet-cordierite-quartz bearing rocks. Detrital zircons in a sample of metapelite and a sample of quartzofeldspathic gneiss yielded ages between ˜720 and ˜1855 Ma, suggesting a chronologically heterogeneous source region and a depositional age of less than ˜720 Ma for these rocks. High-grade metamorphism and anatexis are documented by zircon ages between 526 ±34 and 557 ±2 Ma with a mean age of about 550 Ma. The broad lithologies, metamorphic grades and ages recorded in the Ihosy rocks are similar to those in the Wanni Complex of northwestern Sri Lanka and in high-grade assemblages of southernmost India and support the contention that all these terrains were part of the Mozambique belt which formed as a result of collision of East and West Gondwana in latest Precambrian time.

Microstrain stability of Peninsular India 1864–1994

We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994) in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin, which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of the 19th century GTS survey.

Nd isotopic evidence for the position of southernmost Indian terranes within East Gondwana

Sm-Nd model ages of orthopyroxene-bearing massif charnockites from the Cardamom Hills Massif and adjoining supracrustal rocks from the Kerala Khondalite Belt in southernmost India are used to infer some of the relationships within these rocks and between them and neighboring areas. Most of these rocks have model ages of 2.1–2.8 Ga with most charnockites in the range 2.2–2.6 Ga. Thus, 3.0–3.4 Ga Archean rocks to their north did not contribute material to either suite and the two suites may have been juxtaposed after formation of the supracrustal rocks. The similarity of Sm-Nd isotope systems in the two units studied here supports an argument that the massif charnockites were the primary sole source of the detritus incorporated into the supracrustal rocks. A cordierite gneiss, representative of a relatively minor lithology in the supracrustal belt, has a model age of ∼ 1.3 Ga. The protolith of this gneiss not only formed from much younger material than the rest of the belt but also formed significantly after the other metasedimentary rocks. The source material of the gneiss protolith may have been located in the Wanni and Vijayan Complexes of Sri Lanka. The overlap of the model ages of rocks in this area and those in the Highland Complex of Sri Lanka supports the notion that these two sets of rocks were joined to each other in Gondwana. They belong to a belt that ran from Antarctica through Sri Lanka and India into Madagascar. This belt was involved in Pan-African tectono-metamorphism, as reflected in the ∼ 550 Ma age of the last, granulite-forming, event throughout the belt.

Metamorphic P-T Conditions of the Kerala (South India) Khondalite Belt, a Granulite Facies Supracrustal Terrain

The Khondalite Belt of southernmost India is an immense section of granulite facies metasediments of probable early Proterozoic age. Dominant rock types are migmatized khondalites (garnet-sillimanite $$\pm$$ cordierite metapelites), acid biotite-garnet graphitic gneisses and charnockites (quartzofeldspathic gneisses with orthopyroxene). Throughout much of southern Kerala, the biotite gneisses are in a state of arrested conversion to charnockite. Partially decrepitated $$CO_{2}$$ inclusions in quartz at the Ponmudi mixed biotite gneiss-charnockite quarry have significant $$CH_{4}$$ and/or $$N_{2}$$ and are texturally late. The probable sequence of events in metasediments was (1) migmatization, (2) charnockite formation, (3) symplectitic cordierite formation, and (4) late $$CO_{2}$$ entrapment. Phase equilibrium diagrams of anatexis in aluminous systems and Fe-Mg exchange between garnet and biotite indicate metamorphic temperatures of 650-850°C for the khondalites. Temperatures based on garnet-orthopyroxene...