Indo-Myanmar Ranges Research Articles

A multi-proxy provenance study of Eocene to Oligocene sandstones in the Salin Sub-basin, Myanmar

The Salin Sub-basin, Myanmar, contains up to 15,000 m of Cenozoic sediments, but their provenance remains ambiguous. Here, a multi-proxy provenance study that employed Raman Spectroscopy-assisted heavy mineral analysis, light mineral petrography, and U-Pb detrital zircon geochronology, is used to identify source areas and sediment pathways of nine samples from three formations of Eocene to Oligocene age. The heavy mineral assemblages are diverse and highly immature and indicate that sediments were principally provided from a range of igneous and metamorphic lithologies, with some recycling of older sediments. The metamorphic basement rocks in northern Myanmar are identified as a source in all three formations, suggesting that the headwaters of the sedimentary pathway were situated in this area. Detrital zircons overwhelmingly yield Cretaceous and Palaeogene ages. A population of Late Cretaceous and Palaeocene zircons could indicate input from the Mogok Metamorphic Belt, or a currently buried section of the Wuntho-Popa Arc; the diminishing of this signal by the end of the Rupelian suggests reduction in transport from the former, or burial of the latter. Late Cretaceous grains exhibit rounded and euhedral morphologies, suggesting input from recycled Wuntho-Popa Arc material via the sediments of the Chin Hills, and direct input from the Wuntho-Popa Arc, respectively. A persistent Palaeoproterozoic and Triassic signal in the Shwezetaw and Padaung Formations suggests provenance in the Pane Chuang Formation of the Indo-Myanmar Ranges, showing that by the early-mid Oligocene, the ranges were topographically prominent enough to be an important source of sediment for the Central Myanmar Basin.

Dextral transpressional shearing and strike-slip partitioning developments in the Central Myanmar Basin during the collision between the India Plate and West Myanmar Block

Central Myanmar Basin (CMB) lies between the two major strike-slip faults: Sagaing Fault to the east and Kabaw Fault to the west. Central Volcanic Line of Myanmar emplaced en-echelon array of P-shears along the fault zone, which was active dextral as surrounding major faults at a low angle about 15° to the shear zone boundary. CMB was developed as strike-slip partitioned transpression model as proposed in this study. The transprsession tectonic is common with oblique convergence subduction as well as collision of India Plate to West Myanmar Block, especially effects on the CMB. Structural evidence are occurred as en-echelon folding and fracturing by satellite photos, field observation and 3D strain ellipsoid construction showing plane strain by pure shear upon ideal strike-slip with simple shear. In this study, two types of transpression distinguished as homogeneous and strike-slip partitioning which are developed within the frame of the strike-slip fault with progressive deformation. Under the condition of the strike-slip partitioned transpression, strain partitioning is distinctly occurred together with progressive deformation and reactivation of pre-existing structures such as cylindrical fold to double plunging fold, normal fault to oblique slip fault and positive flower structure. Deformation process related to the India Plate movement deduced the period of Late Miocene and Pliocene-Pleistocene based on the structural analysis in Rakhine Coastal region, western Myanmar. During the period between the Late Miocene to Pliocene-Pleistocene, pre-existing ophiolite zone in the Indo-Myanmar Ranges (IMR) was split up different zones by the Sagaing Fault displacement, accompanied to the West Myanmar Block movement with India Plate subduction. Accordance with the Sagaing Fault displacement and group of mud volcanoes shifting, the CMB moved northward about 450km with displacement rate 5–7cm per annum by the 45–50°convergent angle of India Plate collision to Eurasia Plate. Transpression deformation of northward compression was developed in the CMB, simultaneously on the other side transtension as pull-apart basin was formed by Andaman Sea opening at the south on the Sagaing Fault. During the Miocene time, collision of India Plate to Eurasia Plate was principal and caused the deformation at northern border the India, in which India Plate moved both in northwards and rotated anti-clockwise, whereas West Myanmar Block together with Sibumasu Block rotated clockwise becoming final closure of the northeasternmost Assam and Myanmar regions. During the Oligocene time, deposition of the shallow marine Barail formation in the Bengal Basin and shallow marine to continental shelf sequences in the CMB started as twin trough. This study provides the transpression deformation in the CMB and related regions during syn- and post-collision of India Plate to West Myanmar Block with position and kinematic structural interpretation.

Sedimentary provenance of the Plio-Pleistocene Nicobar Fan: Complex sourcing revealed through Raman spectroscopy heavy mineral analysis

The Nicobar Fan lies within the north-eastern Indian Ocean between the Ninety-East Ridge and Sunda Arc. The fan forms part of the Bengal–Nicobar Fan System and is among the oldest and largest submarine fans on Earth. Previous U–Pb zircon studies of the Nicobar and Bengal fans indicate the Himalaya as the dominate sediment source, making these fans a major Cenozoic sink for uplifted Himalayan sediment. However, the northwards moving Indian Plate, coupled with mid-Pleistocene collision of the Ninety-East Ridge with the Sunda Arc, has shutdown many sediment pathways linking the Himalaya and Nicobar Fan. Here we use big data Raman spectroscopy heavy mineral analysis along with U–Pb zircon data to better define sediment source regions for the Nicobar Fan during the Plio-Pleistocene following the shutdown of sediment delivery. The detrital zircon spectra for the Plio-Pleistocene Nicobar Fan from this study are consistent with previous work indicating that the original sources of these zircons can be found within both the Greater and Tethyan Himalaya, the Gangdese Arc, and the Indo-Myanmar Ranges. However, the heavy mineral data indicate that a large proportion of sediment has been derived from a more complex array of sources. This is coupled with an abundance of low- and moderate-stability minerals (e.g., amphibole, apatite, clinopyroxene), which are unlikely to have been transported large distances. Suggesting that proximal sources have delivered the majority of lower-stability heavy minerals into the Plio-Pleistocene Nicobar Fan. We show that from the Pleistocene onwards direct sediment delivery into the Nicobar Fan from the Himalaya was largely shutdown, with sediment instead shedding off the uplifting Indo-Myanmar Ranges, the Andaman–Nicobar Accretionary Ridge, and the westwards propagating Ayeyarwady River. This study shows that extensive uplift along the northern Sunda Arc is recorded in the Nicobar Fan alongside the previously reported Himalayan record.

Tectono-magmatic evolution of Tethyan oceanic lithosphere in supra subduction zone fore arc regime: Geochemical fingerprints from crust-mantle sections of Naga Hills Ophiolite

The Naga Hills Ophiolite (NHO) belt in the Indo-Myanmar range (IMR) represents a segment of Tethyan oceanic crust and upper mantle that was involved in an eastward convergence and collision of the Indian Plate with the Burmese Plate during the Late Cretaceous-Eocene. Here, we present a detailed petrological and geochemical account for the mantle and crustal sections of NHO, northeastern India to address (i) the mantle processes and tectonic regimes involved in their genesis and (ii) their coherence in terms of the thermo-tectonic evolution of Tethyan oceanic crust and upper mantle. The NHO suite comprises well preserved crustal and mantle sections discretely exposed at Moki, Ziphu, Molen, Washelo and Lacham areas. The ultramafic-mafic lithologies of NHO are mineralogically composed of variable proportions of olivine, orthopyroxene, clinopyroxene and plagioclase. The primary igneous textures for the mantle peridotites have been overprinted by extensive serpentinisation whereas the crustal section rocks reflect crystal cumulation in a magma chamber. Chondrite normalised REE profiles for the cumulate peridotite-olivine gabbro-gabbro assemblage constituting the crustal section of NHO show flat to depleted LREE patterns consistent with their generation from depleted MORB-type precursor melt in an extensional tectonic setting, while the mantle peridotites depict U-shaped REE patterns marked by relative enrichment of LREE and HREE over MREE. These features collectively imply a dual role of depleted MORB-type and enriched arc-type mantle components for their genesis with imprints of melt-rock and fluid-rock interactions. Tectonically, studied lithologies from NHO correspond to a boninitic to slab-proximal Island Arc Tholeiite affinity thereby conforming to an intraoceanic supra subduction zone (SSZ) fore-arc regime coherent with the subduction initiation process. The geochemical attributes for the crustal and mantle sections of NHO as mirrored by Zr/Hf, Zr/Sm, Nb/Ta, Zr/Nb, Nb/U, Ba/Nb, Ba/Th, Ba/La and Nd/Hf ratios propound a two-stage petrogenetic process: (i) a depleted fore arc basalt (FAB) type tholeiitic melt parental to the crustal lithologies was extracted from the upwelling asthenospheric mantle at SSZ fore-arc extensional regime thereby rendering a refractory residual upper mantle; (ii) the crust and upper mantle of the SSZ fore arc were progressively refertilised by boninitic melts generated in response to subduction initiation and slab-dehydration. The vestiges of Tethyan oceanic lithosphere preserved in NHO represent an accreted intra-oceanic fore arc crust and upper mantle section which records a transitional geodynamic evolution in a SSZ regime marked by subduction initiation, fore arc extension and arc-continent accretion.

Pattern of active tectonic deformation across the Churachandpur-Mao thrust zone of Manipur Hills, Indo-Myanmar range, NE India: Inferences from geomorphic features and indices

The Churachandpur-Mao thrust (CMT) in Indo-Myanmar Range (IMR) is known to be tectonically active, but nevertheless the extent and pattern of activities on it and effects thereof on the surrounding region has not been determined as yet. We herein present the results of our tectonic geomorphological investigations on these aspects across a long stretch of CMT zone spanning western Imphal intermontane valley and enclosing frontal mountains. The NNE-SSW trending CMT and NW-SE trending Sekmai fault have subdivided the area into four tectonic blocks. Geomorphic features in conjunction with statistically analyzed Mountain-front Sinuosity Index (Smf), Stream Length-Gradient Index (SL), Hypsometric Integral (HI), Drainage Basin Asymmetry factor (AF), and Transverse Topography Symmetry Factor (T) reveal variations in nature and extent of tectonic activities, and thus the pattern of surface deformation in these tectonic blocks. Tectonic blocks to the north of Sekmai fault are experiencing more intense activities than the tectonic blocks to the south of Sekmai fault. North of the Sekmai fault, the CMT's footwall is experiencing the most intense activity and thus severe surface deformation in the area, whereas the tectonic activity in the CMT's hanging wall here is only intense in the northern part. To the south of Sekmai fault, while the hanging wall of the CMT is experiencing relatively moderate tectonic activities, the footwall of the CMT is experiencing moderate to intense tectonic activities in different parts, being most intense close to the Sekmai fault. Tectonic activities have caused an overall southward down-tilting of the CMT's footwall to the north of Sekmai fault, and overall northward down-tilting of the remaining three tectonic blocks. Evidently, the tectonic activities and thus the pattern of active surface deformation in the CMT zone of the area is significantly influenced by the transverse Sekmai fault.

Geology, structure and lithostratigraphic framework of the Rakhine Coastal Ranges in western Myanmar: Implications for the collision of the India Plate and West Myanmar Block

Termination of the eastward subduction of the Indian Plate is inferred to be latest Eocene in age in the north-easternmost Assam and Myanmar regions, followed by the collision of the Indian continent with the Asia Plate. This event is typically represented by the underthrusting of the Middle and Upper Eocene Sylhet Formation, which was deposited on the western margin of India Plate, beneath the Eocene Disang Formation, while the northern margin of India collided against Eurasia and Tibet along a zone, which lies south of the Triassic-Jurassic deep-marine sediments and Yarlung ophiolite in the latest Eocene. Later movement of the Naga and Disang Thrusts to the east suggests convergence between the Burma and Indian Plates, as both moved northwards and India rotated anti-clockwise after the collision. The stratigraphic records indicate that an early Oligocene emplacement of the deep-marine sedimentary sequence on the India plate, probably within 10 Ma interval age during the India-Asia collision, and moved northwards. Oblique convergence could also have resulted from possible clockwise rotation of SE Asia relative to the Indian Plate accompanying the eastward translation of South China along strike-slip faults. The deformation of western and southern Myanmar is still active today with under-thrusting related to subduction. The basement of the Indian Plate below the Indo-Myanmar Ranges is moving towards the north with respect to the rest of Asia. This study provides the syn- and post-deformation history of Neogene siliciclastic sequences of the Rakhine Coastal Ranges in western Myanmar allowing structural and kinematic interpretation of the oblique subduction and collision history. The growth of these folds and faults and associated uplift were resulted from the tectonic processes and evolution in which the Burma Plate was wedged in the subduction zone and dragged towards the north with the Indian Plate between internal N-S trending right-lateral shearing and external E-W shortening.

Eocene foraminifers of the Naga Hills of Manipur, Indo-Myanmar Range (IMR): Implications on age and basin evolution

The Disang Group incorporates the oldest Cenozoic clastic sedimentary rocks that crop out in a series of NNE–SSW trending ridges and valleys throughout much of the Naga Hills. The stratigraphic position of this unit is not well constrained due to a paucity of definitively recognisable, in situ fossils. We report forty-four species attributable of twenty-eight genera. Based on our new reported foraminiferal assemblages, we refine the age and paleoenvironmental interpretations for the Upper Disang Formation. We recognize Planktonic Foraminiferal Zones E14-16 correlative to upper middle Eocene to upper Eocene in the Upper Disang Formation within the Naga Hills. A basin model for this lithological unit involving an upper bathyal bathymetry, rapidly shallowing in a restricted basin with slump deposits where anoxic conditions prevailed is proposed based on field observations, foraminiferal assemblages, and published data.

Thermal history of Early Jurassic eclogite facies metamorphism in the Nagaland Ophiolite Complex, NE India: New insights into pre-Cretaceous subduction channel tectonics within the Neo-Tethys

Eclogite from two locations in a fossil accretionary complex now exposed in Nagaland, NE India, at the northern end of the Indo-Myanmar ranges, provides the oldest evidence for Neo-Tethyan subduction along the Yarlung-Tsangpo suture zone. Metamorphic texture, mineral composition, peak metamorphic P-T estimates, reconstructed metamorphic P-T paths, and U–Pb zircon ages from three eclogite samples collected near Mokie and Thewati villages collectively reveal snapshots of a c. 205–172 Ma subduction burial-exhumation cycle in the eastern Neo-Tethys. The Thewati eclogite records a clockwise metamorphic P-T path involving: (1) prograde metamorphism traversing the epidote blueschist facies and culminated in peak eclogite facies conditions at 25–28 kbar and ~650 °C; (2) an early retrograde stage involving decompression with cooling in the eclogite facies at ~18.3 kbar and 630 °C; followed by (3) cooling through the epidote blueschist, transitional lawsonite blueschist and greenschist facies to ~6 kbar and 300 °C. Circa 189–185 Ma peak metamorphism is inferred for the Mokie and Thewati eclogites, and was accompanied by an apparently low thermal gradient (~7–8 °C/km). Such conditions and the clockwise P-T path are associated with a tectonic scenario involving cold mature subduction within the Neo-Tethys in Nagaland. This is thus the first comprehensive dataset of an Early Jurassic subduction channel (with respect to present geographic co-ordinates) for the eastern margin of the Neo-Tethyan suture. The Nagaland samples offer a critical record of a pre-Cretaceous subduction system within the Neo-Tethys, which incorporated an Early-Middle Jurassic Andean-type convergent margin extending along the southern Eurasian margin from Pakistan to the Indo-Myanmar Ranges.

Evaluation of hydrochemical data using multivariate statistical methods to elucidate heavy metal contamination in shallow aquifers of the Manipur valley in Indo-Myanmar Range

Descriptive statistics, factor analysis, correlation matrices, and cluster analysis are used to gain insights on hydrochemical processes and contamination in the shallow aquifers of Manipur valley. Groundwater has remained as a prime source of water supply for a population of nearly 3 million people living in this valley. Sixteen variables (pH, ORP, TDS, Ti, V, Cr, Cu, Ge, As, Rb, Sr, Nb, Mo, Hf, Ta, and W) are monitored from 28 shallow wells. Mean pH and TDS values (6.8 and 800 mg/l, respectively) suggest fresh quality water in terms of its acidity, alkalinity, or salinity. Oxidation reduction potential values (mean − 6.75 mV) indicate dissolution of metals in anoxic condition. The order of abundance of metals is Sr > As > Rb > Ti > Cu > V > Cr > Mo > Ge > W > Hf > Ta > Nb. Sr, As, Cr, Cu, and Mo are elevated than the WHO limit. Elevation of Sr is attributed to weathering of gypsum, evaporite, and rock salt which reflects in factor 5 of the factor analysis. Factors 2 represents Cr, As, and Mo elevations and signifies geogenic weathering from ultramafic rocks of Manipur Ophiolite Melange Zone. Factor 3 represents Rb, V, and Cu elevations owing to natural weathering of clay and Fe-oxyhydroxides along with dissociation of solid organic carbons. Factor 4 is related to a reduced environment under low pH condition. Factor 1 reflects dissolution of Nb, Hf, Ta, and Ti under anoxic environment as insoluble oxides. Analysis on Pearson correlation and hierarchical clustering strongly support observation made by factor analysis. Thus, the present study shows the accountability of multivariate statistical techniques in interpreting and delineating the sources of contaminations in shallow groundwater.

Ichnological Significance of Upper Disang Formation and Lower Barail Formation (Late Eocene to Early Oligocene) of Nagaland, Northeast India, in the Indo-Myanmar Ranges

ABSTRACT The Upper Disang-Lower Barail Transition Sequences of Nagaland in northeast India, Indo-Myanmar Ranges (IMR) are found to preserve reasonably diverse biological sedimentary structures. Three ichnofacies were observed, Skolithos ichnofacies consisting of Bergaueria hemispherica, Gyrochorte comosa, Ophiomorpha nodosa, Skolithos linearis and Thalassinoides paradoxicus; Cruziana ichnofacies – Curvolithus simplex, Scolicia plana, Scolicia strozzii, Scolicia vertebralis, Treptichnus pedum, Taenidium diesingi and Palaeophycus tubularis; and Nereites ichnofacies – Chondrites targionii and Paleomeandron elegans. Presence of Skolithos and Cruziana ichnofacies suggest well oxidising, substrate rich depositional environment in the foreshoreface to offshore setting in general; and an overall possible fluctuation in the depositional bathymetry which is supported by the presence of Nereites ichnofacies in horizons alternating with Skolithos and Cruziana ichnofacies. The depositional system is proposed to be proximal to distal hyperpycnal-delta-fed turbidite system. Observation of sand spherules also suggests possibility of shoreline as one of the depositional environments.

Subduction-related Manipur Ophiolite Complex, Indo-Myanmar Ranges: elemental and isotopic record of mantle metasomatism

Abstract This study reports, for the first time, Sr and Nd isotope ratios from the mafic rocks in the Manipur Ophiolite Complex (MOC), along with new elemental abundances to show the subduction zone influence. The initial 87 Sr/ 86 Sr ratios (for t = 127 Ma) range from 0.705230 to 0.709734. The initial 143 Nd/ 144 Nd and ɛ Nd t ( t = 127 Ma) range from 0.512611 to 0.512900 and +2.7 to +8.3, respectively. The high field strength element (HFSE) ratios vary widely, with Nb/Ta ranging from c. 3 to 18 and Zr/Hf ranging from 20 to 41, indicating fluid–rock interaction in the presence of rutile. The correlated variation in the Nd and Sr isotope ratios and the HFSEs, including TiO 2 , reflects the variation in the slab-derived fluids. The light rare earth element (LREE) enriched and flat patterns yielded by the mafic rocks are modelled by varying the degree of melting of the fluid-metasomatized mantle. The subsequent influx of the slab-derived fluid at a greater depth caused the re-melting of the previously depleted wedge to produce the LREE-depleted patterns. We propose that the geochemical variation recorded in the MOC rocks indicates the changing nature of fluid metasomatism of the mantle wedge across the subduction zone with time.

Morphotectonics and neotectonic activity of the Schuppen Belt of Mokokchung, Nagaland, India

A stretch of the schuppen belt, trending NE-SW in the western sector of the Indo-Myanmar Ranges, represents a tectonically active zone. Deformed Quaternary deposits and various geomorphic features lend evidence for the same. In a portion of the footwall block of the Sanis-Chongliyimsen Thrust, the Nazira Sandstone of the Tipam Group of Mio-Pliocene age is thrust over tilted Quaternary fluvial deposits near Tzudikong, with a displacement of more than 2 m along the plane of the thrust fault. Deformed Quaternary deposits such as tilted terraces and faulted Quaternary sediments are indicative of ongoing tectonic activity in the area. The sediments are tilted towards the southeast by varying degrees (21°–39°) similar to the trend of stream migrations observed at four locations in and around Tuli. In some sections, faulting has not only affected the underlying bedrock but also deformed the overlying fluvial sediments. An important morphotectonic feature representing tectonic movement along the Kongan Thrust is evident from drainage migration in the hanging wall block of the thrust. The stream has migrated towards the southeast as a result of NW verging along the Kongan Thrust, which has left behind a trail of palaeochannels. Numerous palaeochannels, mostly linear in nature, associated with the scarp of the terrace, are indicative of migration of the river. Stream migrations suggest that the two anticlines noted in the study area are possibly growing in the present tectonic regime. Multiple levels of strath terraces lend evidence to tectonic pulses in the study area, each strath representing a tectonic phase. Lineaments have been extensively mapped in the area, out of which, around 70% are parallel to the regional NE-SW trend and the other 30% are approximately perpendicular to this trend. Any movement along the NW-SE plane may be normal faults. The mountain front sinuosity index of the emerging mountain front is close to 1, which is indicative of a relatively active mountain front. Steam length gradient index and steepness index correspond with each other, with high values in the thrust zones, which is indicative of a neotectonically active region.

The State of Wetlands of the Manipur Valley in Northeast India in View of Changing Time

The Manipur valley is located as an intramontane basin filled with alluviums of fluvio-lacustrine origin of Quaternary age in the Indo-Myanmar Range of Northeast India. The valley is confined between 24°16′ and 25°2′ North latitudes and 93°41′ and 94°9′ East longitudes covering an area of ~1920km2 with a population of more than 2 million people. This valley is mainly occupied by wetlands like ponds, swamps, paleochannels, lakes, agricultural fields and flood plains. Historically, these wetlands have been emotionally relating to cultural and ritual activities, fortification and recreational activities since the beginning of the Manipuri culture. To assess the quality of these wetland waters, several hydrochemical parameters like pH, Temperature, TDS, EC, ORP, HCO3, CO3, SO4, Cl, Na, K, Mg, Ca, PO4, F, H4SiO4, Ti, V, Cr, Cu, Ge, As, Rb, Sr, Nb, Mo, Hf, Ta, W were determined. The analysis suggests that the water is fresh and suitable for human consumption as well as and flora and fauna adaptation. Presently, the wetlands are used for water supplies for domestic, irrigation, industrial purposes and fish production. The rapid urbanization, massive increase in population, local climate change cause significant diminishing and shrinkage of these wetlands and thus creating a cultural gap as the ritual activities around these surface water bodies are no more practiced. Further, mismanagement and negligence on the treatment of domestic solid waste deteriorate the quality. Artificial eutrophication coupled with climate change as it reduces oxygen level and increases acidic level in the wetland waters further worsen the quality leading to the extinction of some fish species from these waters. Therefore, it is high time to avoid demolishing these wetlands and rejuvenate them to maintain the age old socio-cultural relationship it bears.

A hydrogeochemical approach to evaluate the occurrence and source of salinization in the shallow aquifers of the southeastern Imphal valley in the Indo-Myanmar range of Northeast India

The Imphal valley is an intramontane basin confined within an anticlinorium of several anticlines and synclines in the Disang Group of rocks of Tertiary age. This valley of more than 2 million people is occupied by fluvio-lacustrine deposits of Quaternary age and is located in the central part of the Indo-Myanmar range of Northeast India. The hydrogeochemical parameters of temperature, pH, ORP, TDS, Na, Cl, Br, Ba, B, Sr, Li, δ18O, HCO3, K, Mg, Ca, NO3, PO4, SO4 in 173 samples using ion-chromatograph, ICP (AES), ICP (OES), ICP (MS) and 37 dugwells were studied to understand the occurrence and origin of salinization process for the first time. The order of abundance of ions is identified as HCO3 > Na > Cl > Ca > Mg > K > NO3 > PO4 > Sr > Br > B>Ba > Li > SO4. Five hydrochemical facies (Na–Cl, Ca–Mg–HCO3, Na–HCO3, Ca–Mg–HCO3–Cl and Ca–Mg–Cl) represent the types of waters. The saline-dominated water types (Na–Cl and Na–HCO3) represent piedmont and the rest of the facies represent alluvial plain and flood plain groundwaters. Durov’s diagram reveales initial and intermediate stages of groundwater evolution. Isotope δ18O, Gibbs diagram and ions scatter plots suggest evaporation and crystallization processes leading to halite encrustation in the Disang shales. Negative Eh, low NO3 and the absence of SO4 indicates reduced condition coupled with rich dissolve organic matters leading to elevation of salts in soils around piedmont where the rock type is exclusively of the Disang shales. Trilinear plot, correlation matrix and water table flow analysis suggest salinization of groundwater originates in piedmont groundwater and disseminates towards alluvial plain and flood plain along the flow path.

Mineralogy, geochemistry, and melt evolution of the Kalaymyo peridotite massif in the Indo-Myanmar Ranges (western Myanmar), and tectonic implications

We present new whole-rock major, trace, and platinum group element (PGE) and mineral chemistry data from the Kalaymyo peridotite massif in the central part of the Indo-Myanmar Ranges (western Myanmar) and discuss its mantle melt evolution. The Kalaymyo peridotites consist mainly of harzburgites, which show typical porphyroclastic or coarse-grained equigranular textures. They are composed of olivine (forsterite, Fo = 89.8–90.5), orthopyroxene (enstatite, En 86–91 , wollastonite, Wo 1–4 , ferrosilite, Fs 8–10 ; Mg# = 89.6–91.9), clinopyroxene (En 46–49 Wo 47–50 Fs 3–5 ; Mg# = 90.9–93.6), and spinel (Mg# = 67.1–78.9; Cr# = 13.5–31.5), and have relatively homogeneous whole-rock compositions with Mg#s of 90.1–90.8 and SiO 2 (41.5–43.65 wt%), Al 2 O 3 (1.66–2.66 wt%), and CaO (1.45–2.67 wt%) contents. They display light rare earth element (LREE)–depleted chondrite-normalized (CN) REE patterns with (La/Yb) CN = 0.04–0.21 and (Gd/Yb) CN = 0.40–0.84, and show a slight enrichment from Pr to La with (La/Pr) CN in the range of 0.98–2.36. The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic (Pd/Ir) CN ratios (1.15–2.36). Their calculated oxygen fugacities range between the quartz-fayalite-magnetite (QFM) oxygen buffers, QFM–0.57 and QFM+0.90. These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees (5%–15%) of partial melting at a mid-oceanic ridge environment. The observed enrichment in LREE and Pd was a result of their reactions with enriched mid-oceanic ridge basalt–like melts percolating through these already depleted residual peridotites. The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges therefore represent mid-oceanic ridge–type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward-migrating subduction-accretion system along the eastern margin of India.

Resolving the conundrum in origin of the Manipur Ophiolite Complex, Indo-Myanmar range: Constraints from Nd isotopic ratios and elemental concentrations in serpentinized peridotite

Major, trace and rare earth element (REE) abundances along with Nd isotopic ratios are measured in serpentinized peridotite samples from the Manipur Ophiolite Complex (MOC), Indo-Myanmar range (IMR). An attempt is made to resolve the conundrum caused by apparently contradictory petrogenetic models and tectonic settings reported in literature. Nd isotope ratios, reported for the first time, range from −7.6 to +10.4 in epsilon units in the whole-rock samples of serpentinized harzburgite and lherzolite. Variation of La/Yb with εNdt is consistent with the progressive addition of a subduction derived fluid to a depleted mantle source. Literature data from the mafic extrusive, intrusive and ultramafic rocks together with new data generated during this study can be explained by a two stage petrogenetic model. Non-modal dynamic melting in the mantle-wedge subsequent to the mixing of fluids derived from the subducted slab explains the observed range of elemental abundances in the MOC mafic and ultramafic rocks. This model also explains the observed variability of Nb and Th in the mafic rocks without invoking different sources for the different types of rocks. Taking into account field, petrographic and geochemical evidences, we propose, that MOC comprises a buoyant fore-arc-mantle-wedge system along with the subducted slab that was obducted during the terminal stage of subduction of the Neotethys below the Burmese plate.

Chapter 4 Geological and tectonic evolution of the Indo-Myanmar Ranges (IMR) in the Myanmar region

The Indo-Myanmar Ranges (IMR) of Myanmar, also known as the Indo-Burman Ranges (IBR) or the Western Ranges, extend from the East Himalayan Syntaxis (EHS) southwards along the eastern side of the Bay of Bengal to the Andaman Sea, comprising the Naga Hills Tract in the north, the Chin Hills in the middle and the Rakhine (Arakan) Yoma in the south. The IMR is economically important; major discoveries of oil and gas have been made in the Bay of Bengal to the west of the Rakhine Yoma, and there are several occurrences of chromite and nickel deposits (e.g. Webula, Mwetaung in Chin State) and submarine volcanic-hosted massive sulphide deposits (e.g. Laymyetna in Ayerwaddy Region). The IMR occupies a complex tectonic zone as the southeastwards continuation of the Indian–Asian collision belt in Tibet and Assam, and lies north of the active subduction zone of the Sunda–Andaman arc (Figs 4.1 & 4.2). The IMR occurs along the western margin of the Myanmar Microplate, also known as the Burmese Platelet or the West Myanmar Terrane or Block, situated between the Eurasian Plate to the east and the Indian Plate to the west (e.g. Fitch 1972; Curray et al. 1979; Mukhopadhyay & Dasgupta 1988; Pivnik et al. 1998; Bertrand & Rangin 2003; Shi et al. 2009; Baxter et al. 2011; Garzanti et al. 2013; Soibam et al. 2015). The West Myanmar Block has been also described as a forearc sliver, bounded on the west by a subduction zone and a strike-slip margin, on the east by a strike-slip fault (Sagaing Fault), on the south by a spreading centre and on the north by a compressional plate boundary (Curray et al. 1979; Pivnik et al. 1998; Nielsen et al. 2004). Fig. 4.1. Tectonic map of Myanmar region …

Chapter 5 Arakan Coastal Ranges in western Myanmar, geology and provenance of Neogene siliciclastic sequences: implications for the tectonic evolution of the Himalaya–Bengal System

Supplementary material : Preparation and analysis of samples with appendices are available at https://doi.org/10.6084/m9.figshare.c.3860926 Neogene clastic sequences preserved in the western part of Indo-Myanmar Ranges provide detrital information that document the erosional and unroofing history of the eastern Himalayas and the Burmese Arc during the Indian–Asian collision. All of the sedimentological and provenance data link the syntectonic sedimentation and sequential evolution of the Bengal Basin, a remnant ocean basin south of the eastern Himalayas and, at the time of formation, a palaeo-incised valley in the eastern trough of the Central Myanmar Tertiary Basin. To the east lies the Sagaing Fault and the Mogok Belt, and further east the Shan–Thai Block. Modal analysis of the Lower Miocene sandstones of the Baronga Islands, Arakan Coastal Ranges shows that they are rich in both monocrystalline and polycrystalline quartz, sub-angular to subrounded feldspars and lithic fragments including metamorphic rock fragments with minor basaltic fragments, suggesting the onset of uplift, erosion and unroofing of the eastern Himalayas and Indo-Myanmar Ranges. Since the Early Miocene, sediments were deposited in twin gulfs separated by the uplifted Indo-Myanmar Ranges. In the Middle Miocene there was a major change in the provenance of the Neogene sediments of the Arakan Basin and the Central Tertiary Basin of Myanmar. Since the Early Miocene, basement uplift of the Mogok Belt in the east and the Gangaw Ranges of the upper Irrawaddy Basin in the western part of the Asian Plate, as well as the initiation of river systems, supplied orogenic detritus to the south (Allen et al. 2008; Kyi Khin et al. 2014; Robinson et al. 2014; Licht et al. 2015). Middle Miocene sandstones from both areas are rich in sub-angular monocrystalline quartz, chert and argillites with small amounts of feldspar and metamorphic lithic fragments, suggesting a relatively low …

Chapter 23 Gem deposits of Myanmar

The aim of this chapter is to review the locations, mineralogy and briefly the origins of the major gem deposits in Myanmar. Myanmar is fortunate in containing world-class gem deposits, such as the finest pigeon's-blood-coloured ruby from the Mogok Stone Tract in Mandalay Division, the Mong Hsu ruby deposit in Shan State and imperial coloured jadeite jade from Kachin State (Fig. 23.1). For the purposes of description the gemstone deposits in Myanmar are classified into: (1) primary hard-rock deposits in which the gemstones are hosted in the rocks in which they were crystallized or in their weathered products; and (2) secondary deposits in which the gemstones have been weathered out of their original (primary) host rock, transported and deposited as placer deposits in alluvial sediments. Fig. 23.1. Locations of the Jade Mine, Mogok Stone Tract and Mong Hsu areas and the tectonic zones in Myanmar: 1, the Arakan (Rakhine) coastal strip; 2, Indo-Myanmar Ranges; 3, Western Inner-Myanmar Tertiary Basin; 4, Central Volcanic Belt (Central Volcanic Line); 5, Eastern Inner-Myanmar Tertiary Basin; 6, Shan-Tenasserim Massif (map modified after Bender 1983; Khin Zaw 1989, 1990; Khin Zaw et al. 2015). Small white circles represent extinct or dormant Tertiary volcanoes. Examples of the primary-type gems are ruby in marble (Mogok, Mong Hsu and Sagyin), sapphire in syenite pegmatite, syenite and nepheline syenite (Mogok) and jadeite in serpentinized peridotite (Tawmaw). Other precious gemstones from primary deposits include spinel in marble (Mogok), peridot in dunite/peridotite (Mogok), topaz, aquamarine, tourmaline, quartz, etc. in pegmatite (Mogok, Mong Hsu and Momeik) and kyanite in quartzite (Moehnyin). Rare gemstones are often found in primary gem deposits in the Mogok Stone Tract and include johachidolite and hackmanite from pegmatites, painite from leucogranite and skarn, pollucite, petalite, phenakite, pezzottaite, monazite, danburite, jeremejevite and hambergite from pegmatites in the Momeik area. …

Chapter 2 Active tectonics of Myanmar and the Andaman Sea

Burma (Myanmar) is situated along the obliquely colliding eastern margin of the Indian Plate (Fig. 2.1). It connects the ongoing India–Asia collision along the Himalayan Range in the north to the newly formed oceanic crust in the Andaman Sea in the south, via the active plate margin along the dextral Sagaing Fault and subduction along the Burma Seismic Zone. The active tectonics of Myanmar are controlled by the combination of: (1) the continuing northwards penetration of India into Asia, ongoing since the initial collision and closing of the Tethyan ocean c. 50 Ma; (2) the active dextral shear along the right-lateral Sagaing strike-slip fault, and region to the west across the Indo-Burma Ranges or Indo-Myanmar Ranges (IMR); (3) the active eastwards-dipping Burma Seismic Zone that indicates subduction of a downgoing plate to depths of >150 km; (4) the clockwise rotation around the Eastern Himalayan Syntaxis and a series of arcuate strike-slip faults (e.g. Nanting and Wanding faults) in the northern Shan Plateau; and (5) the active extensional and strike-slip tectonics in the back-arc Andaman Sea. In this paper we review the active tectonics of this region and discuss the interactions and driving mechanisms of deformation in and around Myanmar. Fig. 2.1. Seismotectonic map of Myanmar (Burma) and surroundings. Faults are from Taylor & Yin (2009) with minor additions and adjustments. GPS vectors show velocities relative to a fixed India from Vernant et al. (2014), Gahalaut et al. (2013), Maurin et al. (2010) and Gan et al. (2007). Coloured circles indicate M w > 5 earthquakes from the EHB catalogue. Grey events are listed for depths 100 km. The band of yellow and red earthquakes beneath the Indo-Burman Ranges represents the Burma Seismic Zone. The dashed black line …