Himanshu Sachan | Wadia Institute Of Himalayan Geology (original) (raw)
Papers by Himanshu Sachan
Journal of the Geological Society of India
A detailed mineral chemistry and geothermobarometry of the Deccan volcanic covered Neoarchean cry... more A detailed mineral chemistry and geothermobarometry of the Deccan volcanic covered Neoarchean crystalline basement rocks is presented, pierced by KLR-1 borehole, drilled in the Killari region of Maharashtra, which was a site of major earthquake disaster in 1993, killing almost 10,000 people. The present study provides unequivocal evidence that the entire drilled basement is mainly made up of tonalite/granodiorite and amphibolite/granulite. They contain hornblende, clinopyroxene, plagioclase, biotites and minor orthopyroxene, apart from accessories like ilmenite, magnetite, pyrite, titanite, zoisite, clinozoisite and epidote. Compositionally, amphibole conform to ferropargasite, magnesiohastingsite, ferro-edenite and edenite. Similarly, the clinopyroxenes correspond to diopside and orthopyroxenes to clino-enstatite. Further, biotites are found to be magnesium and iron-rich, while feldspars correspond mainly to albite and orthoclase. Bulk rock chemistry and mineral chemistry of amphibole and biotites indicate calc-alkaline nature of the rock associated with high oxygen fugacity, that may have been formed in subduction zone related environments as evidenced by geochemical data and tectonic discrimination diagrams. Geothermobarometric studies carried out on amphibolite and granulite, indicate that the underlying basement was subjected to metamorphic temperatures between 540 and 860°C and pressure, 5 to 7 kb, corresponding to 15–21 km depth. Petrographically, these rocks appear deformed, retrogressed and metasomatized by halogen-rich mantle-derived CO2 and brought to the surface by continued geodynamic process of uplift and erosion, even before the onset of Deccan volcanism.
Journal of the Geological Society of India, Aug 1, 2018
Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effe... more Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effects of diagenetic process such as compaction, cementation and dissolution on reservoir properties. The average framework composition of Ridge sandstone is Q 80 F 17 L 3 , medium-to coarse grained and subarkose to arkose. Syndepositional silty to clayey matrix (3% average) is also observed that occurs as pore filling. The diagenetic processes include compaction, cementation and precipitation of authigenic cements, dissolution of unstable grains and grain replacement and development of secondary porosity. The major cause of intense reduction in primary porosity of Ridge sandstone is early cementation which include silica, carbonate, iron, kaolinite, illite, smectite, mixed layer illite-smectite and chlorite, which prevents mechanical compaction. The plots of COPL versus CEPL and IGV versus total cement suggest the loss of primary porosity in Ridge sandstone is due to cementation. Cements mainly iron and carbonate occurs in intergranular pores of detrital grains and destroys porosity. The clay mineral occurs as pore filling and pore lining and deteriorates the porosity and permeability of the Ridge sandstone. The reservoir quality of the studied sandstone is reduced by clay minerals (kaolinite, illite, smectite, mixed layer illitesmectite, chlorite), carbonate, iron and silica cementation but on the other hand, it is increased by alteration and dissolution of the unstable grain, in addition to partial dissolution of carbonate cements. The potential of the studied sandstone to serve as a reservoir is strongly related to sandstone diagenesis. INTRODUCTION Sandstone diagenesis is of great importance in understanding the reservoir quality of sandstone. The reservoir quality is controlled by composition (Ehrenberg, 1990; Bloch, 1991), texture (Scherer, 1987; Atkins and McBride, 1992) and diagenetic processes (Lundegard, 1992). Diagenesis is also controlled by factors such as texture, detrital composition, environment of deposition and associated lithology (Burley et al., 1985; Morad et al., 2000). The detrital composition can influence the reservoir quality of sandstone by conditioning the pathway of both physical and chemical diagenesis (Bloch, 1994). The intraformational variations in the detrital composition of sandstone results in significant heterogeneity in reservoir quality of sandstone. The importance of compaction, both mechanical and chemical is regarded as less capable than cementation (Houseknecht, 1987; McDonald and Surdam, 1984; Lundegard, 1992). The effect of cementation on sandstone porosity is estimated easily i.e. the pore spaces are filled with cement and are observed in sandstone (Ehrenberg, 1995). Kachchh basin, in general constitutes a potential site for petroleum exploration. Scientists have worked on the prospects of hydrocarbon in Kachchh basin (Biswas and Deshpande, 1983). However, the understanding of the diagenetic controls on the reservoir of the Jurassic Jumara dome Ridge sandstone from the Kachchh basin is not thoroughly studied. Reservoir quality is one of the key controls on the efficient exploration of reservoir, and therefore, it is important to have a detailed understanding of the various diagenetic controls and their effects. The aim of the present study is to have a detailed diagenetic analysis. The analysis was undertaken to provide data that will help in understanding diagenesis with a goal on various diagenetic controls and reservoir quality of Ridge sandstone. GEOLOGICAL BACKGROUND The Kachchh basin is a pericratonic basin in the west of Indian peninsula (Biswas, 1987). The Kachchh basin covers entire Kachchh district in Gujarat state and extends between latitude 22°30' and 24°3 0' N and longitude 68° and 72° E (Fig.1). The Kachchh basin was formed due to rifting and counters clockwise rotation of Indian plate in the late Triassic/early Jurassic (Biswas, 1987). The basin is bordered by subsurface Nagarparker Massif in the north, Radhanpur-Barmer arch in the east and Kathiawar uplift towards the south (Biswas, 1982). Mesozoic sediments in the Kachchh basin range in age from Bajocian to Albian (Table 1) lay unconformably on the Precambrian basement (Bardhan and Datta, 1987). Mesozoic sediments are the rift fill sediments and constitute the major part of the basin fill (Biswas, 2002). Basin configuration was controlled by primordial fault pattern in the basement rocks (Biswas, 1977). The Mesozoic rocks are exposed in the Kachchh mainland, Wagad, Bela, Khadir, Patcham and Chorar islands in the great Rann of Kachchh ranging in age from middle Jurassic to lower Cretaceous. In the Kachchh mainland at Jumara dome mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic dominating Chari Formation (Bathonian to Oxfordian) are exposed. Jumara hills lie on the western flank of Kachchh mainland near great Rann of Kachchh and these hills form a dome which is doubly plunging anticline. Jumara dome located nearly 80 km NW of Bhuj. Geologically, the Jumara dome is famous locality in the Mesozoic strartigraphy of Kachchh for its abundant mega fossils and good Jurassic exposures. The lower part of the Jumara dome is represented by the Jumara Coral Limestone Member of Jhurio Formation, followed upward by the Echinoderm Packstone Member of Jhurio Formation, above this Spongy Limestone Member of Patcham Formation followed by Grey Shale Member of Chari Formation followed by Ridge Sandstone Member of Chari Formation overlain by Gypsiferous Shale Member of Chari Formation and on the top Dhosa Oolite Member of Chari Formation (Fig.2). SAMPLES AND METHODOLOGY The study is based on a total twenty samples representing different levels of measured litho-stratigraphic section at Jumara dome (Fig.2). The analytical techniques applied are thin section petrography, scanning
Journal of Asian Earth Sciences, Nov 1, 2022
Contributions to Mineralogy and Petrology, Jun 1, 2022
Carbonates and Evaporites, Dec 10, 2022
Journal of Asian Earth Sciences, Feb 1, 2023
Journal of Geological Society of India, 1996
The fluid inclusion study in quartz overgrowth in the siliciclastics of Neoproterozoic Nagthat Fo... more The fluid inclusion study in quartz overgrowth in the siliciclastics of Neoproterozoic Nagthat Formation reveals that the quartz cementation took place in the range of 80°C to 130°C with a salinity range of 0.82 to 9.18 wt. % NaCl. The microthermometric data, combined with petrographic and geologic evidences pennitted to constrain the nature of cementing fluids and source of cement. The silica for quartz cementation was derived partly from both the internal source (quartz and feldspar dissolution) and external source (pore fluids). It can be further suggested that the quartz cementation in the lower stratigraphic level (near the Chandpur Formation) is mainly by marine water while in the upper stratigraphic level (near the Blaini Formation), meteoric water has played an important role for the same.
International Journal of Earth Sciences, 2021
The evolutionary nature of the Neoarchean basement, concealed below 66 Ma Deccan Large Igneous Pr... more The evolutionary nature of the Neoarchean basement, concealed below 66 Ma Deccan Large Igneous Province, remains largely unknown. We present here detailed results of integrated geoscientific investigations, carried out on 43 basement cores that cover an entire 270 m thick column, penetrated by the KLR-1 deep scientific borehole, drilled in the epicentral zone of 1993 Killari earthquake (Maharashtra, India). They dominantly contain high velocity-high density, halogen-rich, retrogressed and metasomatized amphibolite to granulite facies mid-crustal rocks, with intercalations of TTG, which were subjected to temperatures between 540 and 860 °C and pressure 5–7 kb, equating to 15–21 km emplacement depth. The granitic-gneissic layer, typical of the upper crust, appears absent. Geochemically, these iron-rich rocks are characterized by wide variation in which SiO2, MgO and FeOT contents vary from 45.12 to 69.96 wt% (avg. 58.11 wt%), 0.18–11.95 wt% (avg. 4.22 wt%), and 0.34–22.92 wt% (avg. 9.01 wt%) respectively. Measured FeOT contents are even higher than the normal lower crust. The granulite rocks exhibit tholeiite affinity, while amphibolite (which dominate the lithology) and TTG rocks show calc-alkaline character. Further, chondrite and primitive mantle normalized plots, show consistent and complimentary REE patterns (except in HREE), with negative Eu anomalies and LILE enrichment, indicating source rock fractionation. Well-marked depletion in Nb–Ta, Zr–Hf, subordinate depletion in Sr and Ba, and their distinct calc-alkaline to tholeiite character, indicate their subduction zone/arc-related affinity. In addition, large-scale crust-mantle interaction and pervasive metasomatism, have led to considerable alteration to the basic fabric of the rock thereby making it weak and characterized by reduced velocities due to biotitization and substantial Fe-enrichment. Quite likely, earthquake nucleation in intraplate stable regions may have a close link with mantle metasomatism.
Journal of African Earth Sciences, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Geological Journal, 2017
Sapphirine‐bearing granulite from Usilampatti in the Madurai block of southern India preserves a ... more Sapphirine‐bearing granulite from Usilampatti in the Madurai block of southern India preserves a variety of mineral textures and reactions that help in reconstructing a three‐stage metamorphic evolution. Corroded biotite, sillimanite and quartz inclusions within garnet represent relics from the prograde history. Peak metamorphic conditions were attained with the development of sapphirine + quartz in textural equilibrium (Stage 1). This was followed by nearly isothermal decompression, leading to the formation of sapphirine + cordierite at Stage 2. Subsequent retrograde hydration (Stage 3) is only locally evident. Using the Perple_X software and the model system NCKFMASH, the peak P‐T conditions were estimated from core compositions, and the retrograde evolution was deduced from rim or symplectite compositions of different minerals as computed by isopleths of XMg garnet, XCa garnet, XMg orthopyroxene, XMg sapphirine and XMg biotite. The P‐T conditions for Stage 1 thus obtained, and su...
Current Science, 2016
ACKNOWLEDGEMENTS. We thank Director, CSIR-CIMFR for permission to publish the paper. Thanks are d... more ACKNOWLEDGEMENTS. We thank Director, CSIR-CIMFR for permission to publish the paper. Thanks are due to Ministry of Mines (Govt of India) for partial funding. The work forms part of the Ph D thesis of the first author. Acknowledgement is due to the Indian School of Mines and other personnel for help.
European Journal of Mineralogy, Mar 29, 2004
... Evidence for deep subduction Himanshu K. SACHAN 1 ,* , Barun K ... Earth. Planet. Sci. Lett.,... more ... Evidence for deep subduction Himanshu K. SACHAN 1 ,* , Barun K ... Earth. Planet. Sci. Lett., 171, 720.[CrossRef]. Wain, A. (1997): New evidence for coesite in eclogite and gneisses: defining an ultrahigh-pressure province in the western gneiss region of Norway. ...
International Geology Review, 2003
Page 1. 49 International Geology Review, Vol. 45, 2003, p. 4969. Copyright © 2003 by VH Winston ... more Page 1. 49 International Geology Review, Vol. 45, 2003, p. 4969. Copyright © 2003 by VH Winston & Son, Inc. All rights reserved. 0020-6814/03/645/49-21 $10.00 Carbonate-Bearing UHPM Rocks from the Tso-Morari Region, Ladakh, India: Petrological Implications ...
Geological Magazine, Jul 15, 2009
Fluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phas... more Fluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phases present during ultrahigh-pressure metamorphism. The subduction-related coesite-bearing eclogites of the Tso Morari Complex, Himalaya, contain five major types of fluids identified by microthermometry and Raman spectroscopy. These are: (1) high-salinity brine, (2) N 2 , (3) CH 4 , (4) CO 2 and (5) low-salinity aqueous fluids. These fluids were trapped during both deep subduction and exhumation processes. The coesite-bearing rocks are inferred to have been buried to a depth of > 120 km, where they experienced ultrahigh-pressure metamorphism. The fluid-rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica-carbonate assemblages in eclogite. High salinity brine, N 2 and CH 4 inclusions are remnants of prograde and peak metamorphic fluids, whereas CO 2 and low-salinity aqueous fluids appear to have been trapped late, during uplift. The high-salinity brine was possibly derived from subducted ancient metasedimentary rocks, whereas the N 2 and CH 4 fluids were likely generated through chemical breakdown of NH 3-bearing K minerals and graphite. Alternatively, CH 4 might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks. High density CO 2 is associated with matrix minerals formed during granulite-facies overprinting of the ultrahigh-pressure eclogite. During retrogression to amphibolitefacies conditions, low-salinity fluids were introduced from external sources, probably the enclosing gneisses. This source enhances salinity differences as compared to primary saline inclusions. The subducting Indian lithosphere produced brines prior to achieving maximal depths of > 120 km, where fluids were instead dominated by gaseous phases. Subsequently, the Indian lithosphere released CO 2rich fluids during fast exhumation and was then infiltrated by the low-salinity aqueous fluids near the surface through external sources. Elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions.
Earth and Planetary Science Letters, May 1, 2007
The Nidar Ophiolite Complex (NOC) within the Indus Suture Zone in Eastern Ladakh, India, represen... more The Nidar Ophiolite Complex (NOC) within the Indus Suture Zone in Eastern Ladakh, India, represents a suprasubduction zone (SSZ) ophiolite from a fore-arc setting. The lower part of the ophiolite sequence is comprised of ultramafic upper mantle rocks that are Mg-rich (Fo in olivine N 90-92) and contain 2-7% Cr-spinel. Pure-methane (CH 4) fluid inclusions occur in olivine from partially serpentinized harzburgite and dunite from the NOC. Homogenization temperatures range from −160°C to − 108°C, and freezing behavior combined with Raman analyses indicate that the inclusions contain no other gaseous species. The majority of the inclusions appear to be of secondary origin although some isolated inclusions of indeterminate origin were observed. CH 4 in the Nidar ophiolite was generated as a by-product of serpentinization of ultramafic rocks in the mantle wedge above the subducting slab, coupled with the complete consumption of water during hydration of serpentine. The presence of the lizardite polymorph of serpentine is consistent with formation in a rock-dominated system (low water activity) that was being deformed in a non-isotropic stress environment. The observed fluid inclusion isochores suggest various degrees of reequlibration during the history of the rocks, with the more extreme (high P) isochores most closely approximating the serpentinization conditions during prograde metamorphism at temperatures b 600°C and pressures in excess of about 2 kbars. These results support previous studies that have shown that early-formed fluid inclusions in mantle-derived rocks may be preserved during tectonic uplift to the surface and maintain the original mantle chemical signature.
Lithosphere, Jun 1, 2012
The Karakoram fault zone is a dextral strike-slip fault bounded by the Pangong and Tangtse strand... more The Karakoram fault zone is a dextral strike-slip fault bounded by the Pangong and Tangtse strands on its NE and SW fl anks, respectively. In the Tangtse shear zone, the microstructures of mylonitic leucogranite exhibit superposition of high-temperature deformation followed by low-temperature deformation. The mylonites show fl uid immiscibility, containing brine and carbonic inclusions. The occurrence of carbonicand brine-rich inclusions in the oscillatory-zoned plagioclase indicates that they were trapped during the formation of the leucogranite. Eventually, these fl uids recorded a near-isobaric drop in temperature down to <450 °C at the amphibolite-greenschist facies transition, when the zone of fl uid mixing was established. The 40 Ar-39 Ar biotite ages indicate that the area cooled down to 400-350 °C over 10.34-9.48 Ma, and this period also coincides with a major phase of fl uid infi ltration and trapping of secondary reequilibrated carbonic and saline-aqueous inclusions. The 10.34-9.80 Ma period recorded a low-temperature deformation at greenschist conditions, when the involved fl uid evolved following a near-isobaric path at ~2 kbar. Subsequently, between 9.80 Ma and 9.48 Ma, the sudden drop in pressure (1.75-0.5 kbar) caused by mylonites produced reequilibrated fl uid inclusion textures. These observations suggest that the Karakoram fault zone rocks show a single progressive deformation event with bimodal fl uid evolution, in which the carbonic-and brine-rich inclusions were available prior to hightemperature deformation during the initiation of the Karakoram fault zone. The trapping of secondary inclusions between 10.34 Ma and 9.48 Ma with pressure decrease of ~2-0.5 kbar yields an average uplift rate of 1 mm yr-1 for the Karakoram fault zone.
Journal of the Geological Society of India
A detailed mineral chemistry and geothermobarometry of the Deccan volcanic covered Neoarchean cry... more A detailed mineral chemistry and geothermobarometry of the Deccan volcanic covered Neoarchean crystalline basement rocks is presented, pierced by KLR-1 borehole, drilled in the Killari region of Maharashtra, which was a site of major earthquake disaster in 1993, killing almost 10,000 people. The present study provides unequivocal evidence that the entire drilled basement is mainly made up of tonalite/granodiorite and amphibolite/granulite. They contain hornblende, clinopyroxene, plagioclase, biotites and minor orthopyroxene, apart from accessories like ilmenite, magnetite, pyrite, titanite, zoisite, clinozoisite and epidote. Compositionally, amphibole conform to ferropargasite, magnesiohastingsite, ferro-edenite and edenite. Similarly, the clinopyroxenes correspond to diopside and orthopyroxenes to clino-enstatite. Further, biotites are found to be magnesium and iron-rich, while feldspars correspond mainly to albite and orthoclase. Bulk rock chemistry and mineral chemistry of amphibole and biotites indicate calc-alkaline nature of the rock associated with high oxygen fugacity, that may have been formed in subduction zone related environments as evidenced by geochemical data and tectonic discrimination diagrams. Geothermobarometric studies carried out on amphibolite and granulite, indicate that the underlying basement was subjected to metamorphic temperatures between 540 and 860°C and pressure, 5 to 7 kb, corresponding to 15–21 km depth. Petrographically, these rocks appear deformed, retrogressed and metasomatized by halogen-rich mantle-derived CO2 and brought to the surface by continued geodynamic process of uplift and erosion, even before the onset of Deccan volcanism.
Journal of the Geological Society of India, Aug 1, 2018
Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effe... more Ridge sandstone of Jurassic Jumara dome of Kachchh was studied in an attempt to quantify the effects of diagenetic process such as compaction, cementation and dissolution on reservoir properties. The average framework composition of Ridge sandstone is Q 80 F 17 L 3 , medium-to coarse grained and subarkose to arkose. Syndepositional silty to clayey matrix (3% average) is also observed that occurs as pore filling. The diagenetic processes include compaction, cementation and precipitation of authigenic cements, dissolution of unstable grains and grain replacement and development of secondary porosity. The major cause of intense reduction in primary porosity of Ridge sandstone is early cementation which include silica, carbonate, iron, kaolinite, illite, smectite, mixed layer illite-smectite and chlorite, which prevents mechanical compaction. The plots of COPL versus CEPL and IGV versus total cement suggest the loss of primary porosity in Ridge sandstone is due to cementation. Cements mainly iron and carbonate occurs in intergranular pores of detrital grains and destroys porosity. The clay mineral occurs as pore filling and pore lining and deteriorates the porosity and permeability of the Ridge sandstone. The reservoir quality of the studied sandstone is reduced by clay minerals (kaolinite, illite, smectite, mixed layer illitesmectite, chlorite), carbonate, iron and silica cementation but on the other hand, it is increased by alteration and dissolution of the unstable grain, in addition to partial dissolution of carbonate cements. The potential of the studied sandstone to serve as a reservoir is strongly related to sandstone diagenesis. INTRODUCTION Sandstone diagenesis is of great importance in understanding the reservoir quality of sandstone. The reservoir quality is controlled by composition (Ehrenberg, 1990; Bloch, 1991), texture (Scherer, 1987; Atkins and McBride, 1992) and diagenetic processes (Lundegard, 1992). Diagenesis is also controlled by factors such as texture, detrital composition, environment of deposition and associated lithology (Burley et al., 1985; Morad et al., 2000). The detrital composition can influence the reservoir quality of sandstone by conditioning the pathway of both physical and chemical diagenesis (Bloch, 1994). The intraformational variations in the detrital composition of sandstone results in significant heterogeneity in reservoir quality of sandstone. The importance of compaction, both mechanical and chemical is regarded as less capable than cementation (Houseknecht, 1987; McDonald and Surdam, 1984; Lundegard, 1992). The effect of cementation on sandstone porosity is estimated easily i.e. the pore spaces are filled with cement and are observed in sandstone (Ehrenberg, 1995). Kachchh basin, in general constitutes a potential site for petroleum exploration. Scientists have worked on the prospects of hydrocarbon in Kachchh basin (Biswas and Deshpande, 1983). However, the understanding of the diagenetic controls on the reservoir of the Jurassic Jumara dome Ridge sandstone from the Kachchh basin is not thoroughly studied. Reservoir quality is one of the key controls on the efficient exploration of reservoir, and therefore, it is important to have a detailed understanding of the various diagenetic controls and their effects. The aim of the present study is to have a detailed diagenetic analysis. The analysis was undertaken to provide data that will help in understanding diagenesis with a goal on various diagenetic controls and reservoir quality of Ridge sandstone. GEOLOGICAL BACKGROUND The Kachchh basin is a pericratonic basin in the west of Indian peninsula (Biswas, 1987). The Kachchh basin covers entire Kachchh district in Gujarat state and extends between latitude 22°30' and 24°3 0' N and longitude 68° and 72° E (Fig.1). The Kachchh basin was formed due to rifting and counters clockwise rotation of Indian plate in the late Triassic/early Jurassic (Biswas, 1987). The basin is bordered by subsurface Nagarparker Massif in the north, Radhanpur-Barmer arch in the east and Kathiawar uplift towards the south (Biswas, 1982). Mesozoic sediments in the Kachchh basin range in age from Bajocian to Albian (Table 1) lay unconformably on the Precambrian basement (Bardhan and Datta, 1987). Mesozoic sediments are the rift fill sediments and constitute the major part of the basin fill (Biswas, 2002). Basin configuration was controlled by primordial fault pattern in the basement rocks (Biswas, 1977). The Mesozoic rocks are exposed in the Kachchh mainland, Wagad, Bela, Khadir, Patcham and Chorar islands in the great Rann of Kachchh ranging in age from middle Jurassic to lower Cretaceous. In the Kachchh mainland at Jumara dome mixed carbonate-siliciclastic succession is represented by the Jhurio and Patcham formations and siliciclastic dominating Chari Formation (Bathonian to Oxfordian) are exposed. Jumara hills lie on the western flank of Kachchh mainland near great Rann of Kachchh and these hills form a dome which is doubly plunging anticline. Jumara dome located nearly 80 km NW of Bhuj. Geologically, the Jumara dome is famous locality in the Mesozoic strartigraphy of Kachchh for its abundant mega fossils and good Jurassic exposures. The lower part of the Jumara dome is represented by the Jumara Coral Limestone Member of Jhurio Formation, followed upward by the Echinoderm Packstone Member of Jhurio Formation, above this Spongy Limestone Member of Patcham Formation followed by Grey Shale Member of Chari Formation followed by Ridge Sandstone Member of Chari Formation overlain by Gypsiferous Shale Member of Chari Formation and on the top Dhosa Oolite Member of Chari Formation (Fig.2). SAMPLES AND METHODOLOGY The study is based on a total twenty samples representing different levels of measured litho-stratigraphic section at Jumara dome (Fig.2). The analytical techniques applied are thin section petrography, scanning
Journal of Asian Earth Sciences, Nov 1, 2022
Contributions to Mineralogy and Petrology, Jun 1, 2022
Carbonates and Evaporites, Dec 10, 2022
Journal of Asian Earth Sciences, Feb 1, 2023
Journal of Geological Society of India, 1996
The fluid inclusion study in quartz overgrowth in the siliciclastics of Neoproterozoic Nagthat Fo... more The fluid inclusion study in quartz overgrowth in the siliciclastics of Neoproterozoic Nagthat Formation reveals that the quartz cementation took place in the range of 80°C to 130°C with a salinity range of 0.82 to 9.18 wt. % NaCl. The microthermometric data, combined with petrographic and geologic evidences pennitted to constrain the nature of cementing fluids and source of cement. The silica for quartz cementation was derived partly from both the internal source (quartz and feldspar dissolution) and external source (pore fluids). It can be further suggested that the quartz cementation in the lower stratigraphic level (near the Chandpur Formation) is mainly by marine water while in the upper stratigraphic level (near the Blaini Formation), meteoric water has played an important role for the same.
International Journal of Earth Sciences, 2021
The evolutionary nature of the Neoarchean basement, concealed below 66 Ma Deccan Large Igneous Pr... more The evolutionary nature of the Neoarchean basement, concealed below 66 Ma Deccan Large Igneous Province, remains largely unknown. We present here detailed results of integrated geoscientific investigations, carried out on 43 basement cores that cover an entire 270 m thick column, penetrated by the KLR-1 deep scientific borehole, drilled in the epicentral zone of 1993 Killari earthquake (Maharashtra, India). They dominantly contain high velocity-high density, halogen-rich, retrogressed and metasomatized amphibolite to granulite facies mid-crustal rocks, with intercalations of TTG, which were subjected to temperatures between 540 and 860 °C and pressure 5–7 kb, equating to 15–21 km emplacement depth. The granitic-gneissic layer, typical of the upper crust, appears absent. Geochemically, these iron-rich rocks are characterized by wide variation in which SiO2, MgO and FeOT contents vary from 45.12 to 69.96 wt% (avg. 58.11 wt%), 0.18–11.95 wt% (avg. 4.22 wt%), and 0.34–22.92 wt% (avg. 9.01 wt%) respectively. Measured FeOT contents are even higher than the normal lower crust. The granulite rocks exhibit tholeiite affinity, while amphibolite (which dominate the lithology) and TTG rocks show calc-alkaline character. Further, chondrite and primitive mantle normalized plots, show consistent and complimentary REE patterns (except in HREE), with negative Eu anomalies and LILE enrichment, indicating source rock fractionation. Well-marked depletion in Nb–Ta, Zr–Hf, subordinate depletion in Sr and Ba, and their distinct calc-alkaline to tholeiite character, indicate their subduction zone/arc-related affinity. In addition, large-scale crust-mantle interaction and pervasive metasomatism, have led to considerable alteration to the basic fabric of the rock thereby making it weak and characterized by reduced velocities due to biotitization and substantial Fe-enrichment. Quite likely, earthquake nucleation in intraplate stable regions may have a close link with mantle metasomatism.
Journal of African Earth Sciences, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Geological Journal, 2017
Sapphirine‐bearing granulite from Usilampatti in the Madurai block of southern India preserves a ... more Sapphirine‐bearing granulite from Usilampatti in the Madurai block of southern India preserves a variety of mineral textures and reactions that help in reconstructing a three‐stage metamorphic evolution. Corroded biotite, sillimanite and quartz inclusions within garnet represent relics from the prograde history. Peak metamorphic conditions were attained with the development of sapphirine + quartz in textural equilibrium (Stage 1). This was followed by nearly isothermal decompression, leading to the formation of sapphirine + cordierite at Stage 2. Subsequent retrograde hydration (Stage 3) is only locally evident. Using the Perple_X software and the model system NCKFMASH, the peak P‐T conditions were estimated from core compositions, and the retrograde evolution was deduced from rim or symplectite compositions of different minerals as computed by isopleths of XMg garnet, XCa garnet, XMg orthopyroxene, XMg sapphirine and XMg biotite. The P‐T conditions for Stage 1 thus obtained, and su...
Current Science, 2016
ACKNOWLEDGEMENTS. We thank Director, CSIR-CIMFR for permission to publish the paper. Thanks are d... more ACKNOWLEDGEMENTS. We thank Director, CSIR-CIMFR for permission to publish the paper. Thanks are due to Ministry of Mines (Govt of India) for partial funding. The work forms part of the Ph D thesis of the first author. Acknowledgement is due to the Indian School of Mines and other personnel for help.
European Journal of Mineralogy, Mar 29, 2004
... Evidence for deep subduction Himanshu K. SACHAN 1 ,* , Barun K ... Earth. Planet. Sci. Lett.,... more ... Evidence for deep subduction Himanshu K. SACHAN 1 ,* , Barun K ... Earth. Planet. Sci. Lett., 171, 720.[CrossRef]. Wain, A. (1997): New evidence for coesite in eclogite and gneisses: defining an ultrahigh-pressure province in the western gneiss region of Norway. ...
International Geology Review, 2003
Page 1. 49 International Geology Review, Vol. 45, 2003, p. 4969. Copyright © 2003 by VH Winston ... more Page 1. 49 International Geology Review, Vol. 45, 2003, p. 4969. Copyright © 2003 by VH Winston & Son, Inc. All rights reserved. 0020-6814/03/645/49-21 $10.00 Carbonate-Bearing UHPM Rocks from the Tso-Morari Region, Ladakh, India: Petrological Implications ...
Geological Magazine, Jul 15, 2009
Fluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phas... more Fluid inclusions trapped in coesite-bearing rocks provide important information on the fluid phases present during ultrahigh-pressure metamorphism. The subduction-related coesite-bearing eclogites of the Tso Morari Complex, Himalaya, contain five major types of fluids identified by microthermometry and Raman spectroscopy. These are: (1) high-salinity brine, (2) N 2 , (3) CH 4 , (4) CO 2 and (5) low-salinity aqueous fluids. These fluids were trapped during both deep subduction and exhumation processes. The coesite-bearing rocks are inferred to have been buried to a depth of > 120 km, where they experienced ultrahigh-pressure metamorphism. The fluid-rock interaction provides direct evidence for fluid derivation during a deep subduction process as demonstrated by silica-carbonate assemblages in eclogite. High salinity brine, N 2 and CH 4 inclusions are remnants of prograde and peak metamorphic fluids, whereas CO 2 and low-salinity aqueous fluids appear to have been trapped late, during uplift. The high-salinity brine was possibly derived from subducted ancient metasedimentary rocks, whereas the N 2 and CH 4 fluids were likely generated through chemical breakdown of NH 3-bearing K minerals and graphite. Alternatively, CH 4 might have been formed by a mixed fluid that was released from calcareous sediments during subduction or supplied through subducted oceanic metabasic rocks. High density CO 2 is associated with matrix minerals formed during granulite-facies overprinting of the ultrahigh-pressure eclogite. During retrogression to amphibolitefacies conditions, low-salinity fluids were introduced from external sources, probably the enclosing gneisses. This source enhances salinity differences as compared to primary saline inclusions. The subducting Indian lithosphere produced brines prior to achieving maximal depths of > 120 km, where fluids were instead dominated by gaseous phases. Subsequently, the Indian lithosphere released CO 2rich fluids during fast exhumation and was then infiltrated by the low-salinity aqueous fluids near the surface through external sources. Elemental modelling may improve quantitative understanding of the complexity of fluids and their reactions.
Earth and Planetary Science Letters, May 1, 2007
The Nidar Ophiolite Complex (NOC) within the Indus Suture Zone in Eastern Ladakh, India, represen... more The Nidar Ophiolite Complex (NOC) within the Indus Suture Zone in Eastern Ladakh, India, represents a suprasubduction zone (SSZ) ophiolite from a fore-arc setting. The lower part of the ophiolite sequence is comprised of ultramafic upper mantle rocks that are Mg-rich (Fo in olivine N 90-92) and contain 2-7% Cr-spinel. Pure-methane (CH 4) fluid inclusions occur in olivine from partially serpentinized harzburgite and dunite from the NOC. Homogenization temperatures range from −160°C to − 108°C, and freezing behavior combined with Raman analyses indicate that the inclusions contain no other gaseous species. The majority of the inclusions appear to be of secondary origin although some isolated inclusions of indeterminate origin were observed. CH 4 in the Nidar ophiolite was generated as a by-product of serpentinization of ultramafic rocks in the mantle wedge above the subducting slab, coupled with the complete consumption of water during hydration of serpentine. The presence of the lizardite polymorph of serpentine is consistent with formation in a rock-dominated system (low water activity) that was being deformed in a non-isotropic stress environment. The observed fluid inclusion isochores suggest various degrees of reequlibration during the history of the rocks, with the more extreme (high P) isochores most closely approximating the serpentinization conditions during prograde metamorphism at temperatures b 600°C and pressures in excess of about 2 kbars. These results support previous studies that have shown that early-formed fluid inclusions in mantle-derived rocks may be preserved during tectonic uplift to the surface and maintain the original mantle chemical signature.
Lithosphere, Jun 1, 2012
The Karakoram fault zone is a dextral strike-slip fault bounded by the Pangong and Tangtse strand... more The Karakoram fault zone is a dextral strike-slip fault bounded by the Pangong and Tangtse strands on its NE and SW fl anks, respectively. In the Tangtse shear zone, the microstructures of mylonitic leucogranite exhibit superposition of high-temperature deformation followed by low-temperature deformation. The mylonites show fl uid immiscibility, containing brine and carbonic inclusions. The occurrence of carbonicand brine-rich inclusions in the oscillatory-zoned plagioclase indicates that they were trapped during the formation of the leucogranite. Eventually, these fl uids recorded a near-isobaric drop in temperature down to <450 °C at the amphibolite-greenschist facies transition, when the zone of fl uid mixing was established. The 40 Ar-39 Ar biotite ages indicate that the area cooled down to 400-350 °C over 10.34-9.48 Ma, and this period also coincides with a major phase of fl uid infi ltration and trapping of secondary reequilibrated carbonic and saline-aqueous inclusions. The 10.34-9.80 Ma period recorded a low-temperature deformation at greenschist conditions, when the involved fl uid evolved following a near-isobaric path at ~2 kbar. Subsequently, between 9.80 Ma and 9.48 Ma, the sudden drop in pressure (1.75-0.5 kbar) caused by mylonites produced reequilibrated fl uid inclusion textures. These observations suggest that the Karakoram fault zone rocks show a single progressive deformation event with bimodal fl uid evolution, in which the carbonic-and brine-rich inclusions were available prior to hightemperature deformation during the initiation of the Karakoram fault zone. The trapping of secondary inclusions between 10.34 Ma and 9.48 Ma with pressure decrease of ~2-0.5 kbar yields an average uplift rate of 1 mm yr-1 for the Karakoram fault zone.