New paleomagnetic results on $$\sim $$2367 Ma Dharwar giant dyke swarm,Dharwar craton,southern India: implications for Paleoproterozoic continental reconstruction

Here we report new paleomagnetic results and precise paleopole position of the extensional study on \(\sim \)2367 Ma mafic giant radiating dyke swarm in the Dharwar craton, southern India. We have sampled 29 sites on 12 dykes from NE–SW Karimnagar–Hyderabad dykes and Dhone–Gooty sector dykes, eastern Dharwar craton to provide unambiguous paleomagnetism evidence on the spectacular radiating dyke swarm and thereby strengthening the presence of single magmatic event at \(\sim \)2367 Ma. A total of 158 samples were subjected to detailed alternating field and thermal demagnetization techniques and the results are presented here along with previously reported data on the same dyke swarm. The remanent magnetic directions are showing two components, viz., seven sites representing four dykes show component (A) with mean declination of \(94{{}^{\circ }}\) and mean inclination of \(-\,70{{}^{\circ }}\) (\(\hbox {k}=87\), \(\upalpha _{95}=10{{}^{\circ }}\)) and corresponding paleopole at \(16{{}^{\circ }}\hbox {N}\), \(41{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=15{{}^{\circ }}\) and \(\hbox {dm}=17{{}^{\circ }}\)) and 22 sites representing 8 dykes yielded a component (B) with mean declination of \(41{{}^{\circ }}\) and mean inclination of \(-\,21{{}^{\circ }}\) (\(\hbox {k}=41\), \(\upalpha _{95}=9{{}^{\circ }}\)) with a paleopole at \(41{{}^{\circ }}\hbox {N}\), \(200{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=5{{}^{\circ }}\) and \(\hbox {dm}=10{{}^{\circ }}\)). Component (A) results are similar to the previously reported directions from the \(\sim \)2367 Ma dyke swarm, which have been confirmed fairly reliably to be of primary origin. The component (B) directions appear to be strongly overprinted by the 2080 Ma event. The grand mean for the primary component (A) combined with earlier reported studies gives mean declination of \(97{{}^{\circ }}\) and mean inclination of \(-\,79{{}^{\circ }}\) (\(\hbox {k}=55\), \(\upalpha _{95}=3{{}^{\circ }}\)) with a paleopole at \(15{{}^{\circ }}\hbox {N}\), \(57{{}^{\circ }}\hbox {E}\) (\(\hbox {dp}=5{{}^{\circ }}\), \(\hbox {dm}=6{{}^{\circ }}\)). Paleogeographical position for the Dharwar craton at \(\sim \)2367 Ma suggests that there may be a chance to possible spatial link between Dharwar dykes of Dharwar craton (India), Widgemooltha and Erayinia dykes of Yilgarn craton (Australia), Sebanga Poort Dykes of Zimbabwe craton (Africa) and Karelian dykes of Kola-Karelia craton (Baltica Shield).     

Geochemical assessment of fluoride enrichment and nitrate contamination in groundwater in hard-rock aquifer by using graphical and statistical methods

This systematic study was carried out with objective to delineate the various sources responsible for \(\hbox {NO}_{3}^{-}\) contamination and \(\hbox {F}^{-}\) enrichment by utilizing statistical and graphical methods. Since Central Ground Water Board, India, indicated susceptibility of \(\hbox {NO}_{3}^{-}\) contamination and \(\hbox {F}^{-}\) enrichment, in most of the groundwater, \(\hbox {NO}_{3}^{-}\) and \(\hbox {F}^{-}\) concentration primarily observed \({>}45\) and \({>}1.5~\hbox {mg/L}\), respectively, i.e., higher than the permissible limit for drinking water. Water Quality Index (WQI) indicates \({\sim }22.81\%\) groundwater are good-water, \({\sim }71.14\%\) groundwater poor-water, \({\sim }5.37\%\) very poor-water and 0.67% unsuitable for drinking purpose. Piper diagram indicates \({\sim }59.73\%\) groundwater hydrogeochemical facies are Ca–Mg–\(\hbox {HCO}_{3 }\) water-types, \({\sim }28.19\%\) Ca–Mg–\(\hbox {SO}_{4}\)–Cl water-types, \({\sim }8.72\%\) Na–K–\(\hbox {SO}_{4}\)–Cl water-types and 3.36% Na–K–\(\hbox {HCO}_{3 }\) water-types. This classification indicates dissolution and mixing are mainly controlling groundwater chemistry. Salinity diagram indicate \({\sim }44.30\%\) groundwater under in low sodium and medium salinity hazard, \({\sim }49.66\%\) groundwater fall under low sodium and high salinity hazard, \({\sim }3.36\%\) groundwater fall under very-high salinity hazard. Sodium adsorption ratio indicates \({\sim }97\%\) groundwater are in excellent condition for irrigation. The spatial distribution of \(\hbox {NO}_{3}^{-}\) indicates significant contribution of fertilizer from agriculture lands. Fluoride enrichment occurs in groundwater through the dissolution of fluoride-rich minerals. By reducing the consumption of fertilizer and stress over groundwater, the water quality can be improved.     

Moisture rainout fraction over the Indian Ocean during austral summer based on $$^{18}\hbox {O}/{}^{16}\hbox {O}$$ ratios of surface seawater,rainwater at latitude range of 10°N–60°S

Oxygen isotope ratios (\(^{18}\hbox {O}/^{16}\hbox {O}\)) of surface seawater and rainwater samples from the Indian Ocean region (10°N–60°S) during austral summer collected onboard ORV Sagar Nidhi during 2011–2013 have been measured along with salinity, sea surface temperature and relative humidity. The rainwater is isotopically lighter (by \(4.6\pm 2.7\permille )\) compared to the equilibrium condensation of the vapour arising from the seawater at the ambient condition. The isotopic composition of the vapour at high altitude responsible for the rain formation at the sampling location is estimated from a global atmospheric water isotope model (IsoGSM2). The apparent deficit of \(\sim \)5\(\permille \) can be explained by invoking a high degree of rainout (on average, about 70% of the overhead atmospheric moisture) during transport of the source vapour to the sampling location undergoing a Rayleigh fractionation. The required rainout fraction is higher (\(\sim \)80%) in the latitude belt 40°–60°S compared to the equatorial belt (\(\sim \)60%). The pattern of variation in the rainout fraction with latitude is consistent with the well-known evaporation/precipitation processes in the Indian Ocean.     

Early Neoarchaean A-type granitic magmatism by crustal reworking in Singhbhum craton: Evidence from Pala Lahara area,Orissa

Several volumetrically minor \(\sim \)2.8 Ga anorogenic granites and rhyolites occur along the marginal part of the Singhbhum craton whose origin and role in crustal evolution are poorly constrained. This contribution presents petrographic, geochemical, zircon U–Pb and trace element, and mineral chemical data on such granites exposed in the Pala Lahara area to understand their petrogenesis and tectonic setting. The Pala Lahara granites are calc-alkaline, high-silica rocks and define a zircon U–Pb age of 2.79 Ga. These granites are ferroan, weakly metaluminous, depleted in Al, Ca and Mg and rich in LILE and HFSE. They are classified as A2-type granites with high Y/Nb ratios. Geochemical characteristics (high \(\hbox {SiO}_{2}\) and \(\hbox {K}_{2}\hbox {O}\), very low MgO, Mg#, Cr, Ni and V, negative Eu anomaly, flat HREE and low Sr/Y) and comparison with melts reported by published experimental studies suggest an origin through high-temperature, shallow crustal melting of tonalitic/granodioritic source similar to the \(\sim \)3.3 Ga Singhbhum Granite. Intrusion of the Pala Lahara granites was coeval with prominent mafic magmatism in the Singhbhum craton (e.g., the Dhanjori mafic volcanic rocks and NNE–SSW trending mafic dyke swarm). It is suggested that the \(\sim \)2.8 Ga A-type granites in the Singhbhum craton mark a significant crustal reworking event attendant to mantle-derived mafic magmatism in an extensional tectonic setting.     

Indian summer monsoon forcing on the deglacial polar cold reversals

The deglacial transition from the last glacial maximum at \(\sim \)20 kiloyears before present (ka) to the Holocene (11.7 ka to Present) was interrupted by millennial-scale cold reversals, viz., Antarctic Cold Reversal (\(\sim \)14.5–12.8 ka) and Greenland Younger Dryas (\(\sim \)12.8–11.8 ka) which had different timings and extent of cooling in each hemisphere. The cause of this synchronously initiated, but different hemispheric cooling during these cold reversals (Antarctic Cold Reversal \(\sim \)3\(^{\circ }\hbox {C}\) and Younger Dryas \(\sim \)10\(^{\circ }\hbox {C}\)) is elusive because \(\hbox {CO}_{2}\), the fundamental forcing for deglaciation, and Atlantic meridional overturning circulation, the driver of antiphased bipolar climate response, both fail to explain this asymmetry. We use centennial-resolution records of the local surface water \(\delta ^{18}\hbox {O}\) of the Eastern Arabian Sea, which constitutes a proxy for the precipitation associated with the Indian Summer Monsoon, and other tropical precipitation records to deduce the role of tropical forcing in the polar cold reversals. We hypothesize a mechanism for tropical forcing, via the Indian Summer Monsoons, of the polar cold reversals by migration of the Inter-Tropical Convergence Zone and the associated cross-equatorial heat transport.     

Characteristics of global strong earthquakes and their implications for the present-day stress pattern

Earthquakes occurred on the surface of the Earth contain comprehensive and abundant geodynamic connotations, and can serve as important sources for describing the present-day stress field and regime. An important advantage of the earthquake focal mechanism solution is the ability to obtain the stress pattern information at depth in the lithosphere. During the past several decades, an increasing number of focal mechanisms were available for estimating the present-day stress field and regime. In the present study, altogether 553 focal mechanism data ranging from the year 1976 to 2017 with Mw \(\ge \)7.0 were compiled in the Global/Harvard centroid moment tensor (CMT) catalogue, the characteristics of global strong earthquakes and the present-day stress pattern were analyzed based on these data. The majority of global strong earthquakes are located around the plate boundaries, shallow-focus, and thrust faulting (TF) regime. We grouped 518 of them into 12 regions (Boxes) based on their geographical proximity and tectonic setting. For each box, the present-day stress field and regime were obtained by formal stress inversion. The results indicated that the maximum horizontal principal stress direction was \(\sim \)N–S-trending in western North America continent and southwestern Indonesia, \(\sim \)NNE–SSW-trending in western Middle America and central Asia, \(\sim \)NE–SW in southeastern South America continent and northeastern Australia, \(\sim \)NEE–SWW-trending in western South America continent and southeastern Asia, \(\sim \)E–W-trending in southeastern Australia, and \(\sim \)NW–SE-trending in eastern Asia. The results can provide additional constraints to the driving forces and geodynamic models, allowing them to explain the current plate interactions and crustal tectonic complexities better.     

Comparison of earthquake source characteristics in the Kachchh Rift Basin and Saurashtra horst,Deccan Volcanic Province,western India

Seismic source parameters of small to moderate sized intraplate earthquakes that occurred during 2002–2009 in the tectonic blocks of Kachchh Rift Basin (KRB) and the Saurashtra Horst (SH), in the stable continental region of western peninsular India, are studied through spectral analysis of shear waves. The data of aftershock sequence of the 2001 Bhuj earthquake (\(M_{w}\) 7.7) in the KRB and the 2007 Talala earthquake (\(M_{w}\) 5.0) in the SH are used for this study. In the SH, the seismic moment (\(M_{o})\), corner frequency \((f_{c})\), stress drop (\(\varDelta \sigma \)) and source radius (r) vary from \(7.8\times 10^{11}\) to \(4.0\times \)10\(^{16}\) N-m, 1.0–8.9 Hz, 4.8–10.2 MPa and 195–1480 m, respectively. While in the KRB, these parameters vary from \(M_{o} \sim 1.24 \,\times \, 10^{11}\) to \(4.1 \times 10^{16}\) N-m, \(f_{c }\sim \) 1.6 to 13.1 Hz, \(\varDelta \sigma \sim 0.06\) to 16.62 MPa and \(r \sim 100\) to 840 m. The kappa (K) value in the KRB (0.025–0.03) is slightly larger than that in the SH region (0.02), probably due to thick sedimentary layers. The estimated stress drops of earthquakes in the KRB are relatively higher than those in SH, due to large crustal stress concentration associated with mafic/ultramafic rocks at the hypocentral depths. The results also suggest that the stress drop value of intraplate earthquakes is larger than the interplate earthquakes. In addition, it is observed that the strike-slip events in the SH have lower stress drops, compared to the thrust and strike-slip events.     

Lithologic boundaries from gravity and magnetic anomalies over Proterozoic Dalma volcanics

Dalma volcanics (DVs) has intruded the older Singhbhum Group of Metapelites. Despite DVs being rich in mineralisation, its boundaries are not clearly demarcated. Gravity and magnetic surveys have been attempted for mapping the boundaries in DVs. These surveys were made in the northern fringe of the DVs over an area of \(\sim \)0.70 \(\hbox {km}^{2}\) along 13 parallel lines at 50 m spacing. The data was acquired at \(\sim \)25 \(\hbox {m}\) spacing. The surveys were taken for determination of lithological boundaries, depths and nature of causative source using Euler depth solutions and radially averaged power spectrum (RAPS). Residual anomaly maps of gravity and magnetic intensity show the same trend as that of Bouguer gravity anomaly and total magnetic intensity anomaly map indicating towards shallow sources. The magnetic map in general follows the same pattern as that of gravity anomaly maps. The map shows coincident high gravity and magnetic anomalies. These anomalies together with resistivity signatures confirm that the northern fringe of DVs hosts volcanogenic massive sulphide settings. The Euler depth solution delineated the lateral boundaries and nature of the source. It seems that the source is of spherical nature lying within a depth range of 25–40 m. The obtained lithological (vertical) units from RAPS are between Lower DVs, Upper DVs and Singhbhum Group Metapelites at depths of \(\sim \)15, \(~\sim \)25 and \(\sim \)40 \(\hbox {m}\), respectively. The metallogeny is associated with the Upper DVs and the corresponding delineated lithological (vertical) unit is indicative of the top of the ore body. Good agreement is observed with the geological succession from the drilling data and resistivity data. The findings suggest that the northern fringe of DVs could be a preferred target for drilling.     

Correlation analyses of effects of temperature on physical and mechanical properties of clay

In determining the physical and mechanical parameters of clay, it is sometimes necessary to determine them indirectly from other parameters since they cannot be measured directly from laboratory or field tests. In order to determine the effect of temperature on the behavior of clay, an indirect approach is used here by analyzing the changes of mass (\(\Delta m\)), density (\(\rho\)), porosity (\(\phi\)), P-wave velocity (\({v_p}\)), thermal conductivity (\(\lambda\)), specific heat capacity (c), resistivity (R) and uniaxial compressive strength (f) of clay from eastern China for a temperature range between 20 and 800 °C. The results indicate that temperature has a significant effect on these parameters. Comparisons between \(\Delta m\) and \(\rho\), \(\Delta m\) and \({v_p}\), \(\rho\) and \({v_p}\), \(\phi\) and \(\lambda\), \({v_p}\) and f, R and f show a linear change among these parameters,whereas the relationships among \(\Delta m\) and \(\phi\), \(\phi\) and \({v_p}\), \(\phi\) and R, \({v_p}\) and \(\lambda\), \(\phi\) and f are exponential. It is difficult to obtain these relationships by using regression analysis with high levels of accuracy. Further refinement is therefore required.     

Effect of solar flare on the equatorial electrojet in eastern Brazil region

The effect of solar flare, sudden commencement of magnetic storm and of the disturbances ring current on the equatorial electrojet in the Eastern Brazil region, where the ground magnetic declination is as large as \(20^{^{\circ }}\hbox {W}\) is studied based on geomagnetic data with one minute resolution from Bacabal during November–December 1990. It is shown that the mean diurnal vector of the horizontal field was aligned along \(2{^{\circ }}\hbox {E}\) of north at Huancayo and \(30{^{\circ }}\hbox {W}\) of north at Bacabal during the month of December 1990. Number of solar flares that occurred on 30 December 1990 indicated the direction of solar flare related \(\Delta H\) vector to be aligned along \(5{^{\circ }}\hbox {E}\) of north at Huancayo and \(28{^{\circ }}\hbox {W}\) of north at Bacabal. This is expected as the solar flare effects are due to the enhanced conductivity in the ionosphere. The SC at 2230 UT on 26 November 1990 produced a positive impulse in \(\Delta X\) and negative impulse in \(\Delta Y\) at Bacabal with \(\Delta H\) vector aligned along \(27{^{\circ }}\hbox {W}\) of north. At Huancayo the \(\Delta H\) vector associated with SC is aligned along \(8{^{\circ }}\hbox {E}\) of north, few degrees east to the alignment of the diurnal vector of H. The magnetic storm that followed the SC had a minimum Dst index of –150 nT. The corresponding storm time disturbance in \(\Delta X\) at Huancayo as well as at Bacabal were about –250 nT but \(\Delta Y\) at Bacabal was about +70 nT and very small at Huancayo, that give the alignment of the H vector due to ring current about \(16{^{\circ }}\hbox {W}\) of north at Bacabal and almost along N–S at Huancayo. Thus alignment of the \(\Delta H\) vector due to ring current at Bacabal is \(14{^{\circ }}\hbox {E}\) of the mean direction of \(\Delta H\) vector during December 1990. This is consistent with the direction of ring current dependent on the dipole declination at the ring current altitude which is about \(5{^{\circ }}\hbox {W}\) of north over Bacabal and the deviation of declination due to the ring current during disturbed period given by the angle (\(\psi \)-D).     

Fission-track evidence of tectonic evolution in the northwestern Qaidam Basin,China

Fission-track dating was conducted on zircons and apatites from 11 cores of the upper Xiaganchaigou Formation and lower Shangganchaigou Formation (northwestern Qaidam Basin). The obtained apatite fission-track age is 3.1–61.9 Ma, and the zircon fission-track age is 49.2–123.5 Ma. Although the average apatite age is consistent with ages predicted from the stratigraphy, nine of the 11 apatite fission-track ages have \(\hbox {P}(\upchi ^{2}) < 5\%\), indicating that the grains experienced heterogeneous annealing after sedimentation. The average zircon age is greater than that indicated by stratigraphy, and all eight zircon fission ages have \(\hbox {P}(\upchi ^{2})>5\%\), exhibiting consistent characteristics and indicating that zircons retain provenance age information after burial. From the zircon and apatite ages, the fission-track length distribution, and the geological setting, the northwestern Qaidam Basin has experienced two tectonothermal events since the Late Mesozoic, at \(39.1 \pm 9.3\) to \(133.7\,\pm \,6.6\,\hbox {Ma}\) and \(1.2 \pm 0.6\) to \(32.0\,\pm \,3.0\,\hbox {Ma}\). The earlier (39.1–133.7 Ma) tectonothermal event resulted from the initial collision of the Indian and Eurasian plates. As a consequence of the collision, the Altyn Tagh fault, which forms the northwestern boundary of the Qaidam Basin, began to develop. Subsequently, uplift of the Altyn Tagh mountains began and the northwestern depression of the Qaidam Basin started to form. The later (1.2–32.0 Ma) tectonothermal event resulted from further collision of the Indian and Eurasian plates along the Yarlung Tsangpo suture zone. Strata in the Qaidam Basin were further deformed by transpression in this period and this period played a crucial role in petroleum accumulation.     

Phase diagram and thermodynamic properties of AIPO<Subscript>4</Subscript> based on first-principles calculations and the quasiharmonic approximation

We calculated the phase diagram of \(\hbox {AlPO}_{4}\) up to 15 GPa and 2,000 K and investigated the thermodynamic properties of the high-pressure phases. The investigated phases include the berlinite, moganite-like, \(\hbox {AlVO}_{4},\, P2_1/c\), and \(\hbox {CrVO}_{4}\) phases. The computational methods used include density functional theory, density functional perturbation theory, and the quasiharmonic approximation. The investigated thermodynamic properties include the thermal equation of state, isothermal bulk modulus, thermal expansivity, and heat capacity. With increasing pressure, the ambient phase berlinite transforms to the moganite-like phase, and then to the \(\hbox {AlVO}_{4}\) and \(P2_1/c\) phases, and further to the \(\hbox {CrVO}_{4}\) phase. The stability fields of the \(\hbox {AlVO}_{4}\) and \(P2_1/c\) phases are similar in pressure but different in temperature, as the \(\hbox {AlVO}_{4}\) phase is stable at low temperatures, whereas the \(P2_1/c\) phase is stable at high temperatures. All of the phase relationships agree well with those obtained by quench experiments, and they support the stabilities of the moganite-like, \(\hbox {AlVO}_{4}\), and \(P2_1/c\) phases, which were not observed in room-temperature compression experiments.     

Characterisation of a garnet population from the Sikkim Himalaya: insights into the rates and mechanisms of porphyroblast crystallisation

The compositional zoning of a garnet population contained within a garnet-grade metapelitic schist from the Lesser Himalayan Sequence of Sikkim (India) provides insight into the rates and kinetic controls of metamorphism, and the extent of chemical equilibration during porphyroblast crystallisation in the sample. Compositional profiles across centrally sectioned garnet crystals representative of the observed crystal size distribution indicate a strong correlation between garnet crystal size and core composition with respect to major end-member components. Systematic steepening of compositional gradients observed from large to small grains is interpreted to reflect a progressive decrease in the growth rate of relatively late-nucleated garnet as a result of an increase in interfacial energies during progressive crystallisation. Numerical simulation of garnet nucleation and growth using an equilibrium approach accounting for chemical fractionation associated with garnet crystallisation reproduces both the observed crystal size distribution and the chemical zoning of the entire garnet population. Simulation of multicomponent intracrystalline diffusion within the population indicates rapid heating along the pressure–temperature path, in excess of 100 \(^{\circ }\)C Myr\(^{-1}\). Radial garnet growth is correspondingly rapid, with minimum rates of 1.4 mm Myr\(^{-1}\). As a consequence of such rapid crystallisation, the sample analysed in this study provides a close to primary record of the integrated history of garnet nucleation and growth. Our model suggests that nucleation of garnet occurred continuously between incipient garnet crystallisation at \(\sim\)520 \(^{\circ }\)C, 4.5 kbar and peak metamorphic conditions at \(\sim\)565 \(^{\circ }\)C, 5.6 kbar. The good fit between the observed and predicted garnet growth zoning suggests that the departure from equilibrium associated with garnet nucleation and growth was negligible, despite the particularly fast rates of metamorphic heating. Consequently, rates of major element diffusion in the intergranular medium during garnet crystallisation are interpreted to have been correspondingly rapid. It is, therefore, possible to simulate the prograde metamorphic history of our sample as a succession of equilibrium states of a chemical system modified by chemical fractionation associated with garnet crystallisation.     

Characteristics of surface ozone in Agra,a sub-urban site in Indo-Gangetic Plain

In the present study, measurements of surface ozone (\(\hbox {O}_{3}\)) and its precursors (NO and \(\hbox {NO}_{2}\)) were carried out at a sub-urban site of Agra (\(27{^{\circ }}10'\hbox {N}\), \(78{^{\circ }}05'\hbox {E}\)), India during May 2012–May 2013. During the study period, average concentrations of \(\hbox {O}_{3}\), NO, and \(\hbox {NO}_{2}\) were \(39.6 \pm 25.3\), \(0.8 \pm 0.8\) and \(9.1 \pm 6.6 \, \hbox {ppb}\), respectively. \(\hbox {O}_{3}\) showed distinct seasonal variation in peak value of diurnal variation: summer \({>}\) post-monsoon \({>}\) winter \({>}\) monsoon. However, \(\hbox {NO}_{2}\) showed highest levels in winter and lowest in monsoon. The average positive rate of change of \(\hbox {O}_{3}\) (08:00–11:00 hr) was highest in April (16.3 ppb/hr) and lowest in August (1.1 ppb/hr), while average negative rate of change of \(\hbox {O}_{3}\) (17:00–19:00 hr) was highest in December (–13.2 ppb/hr) and lowest in July (–1.1 ppb/hr). An attempt was made to identify the \(\hbox {VOC--NO}_{\mathrm{x}}\) sensitivity of the site using \(\hbox {O}_{3}/\hbox {HNO}_{3}\) ratio as photochemical indicator. Most of the days this ratio was above the threshold value (12–16), which suggests \(\hbox {NO}_{\mathrm{x}}\) sensitivity of the site. The episodic event of ozone was characterized through meteorological parameters and precursors concentration. Fine particles (\(\hbox {PM}_{2.5}\)) cause loss of ozone through heterogeneous reactions on their surface and reduction in solar radiation. In the study, statistical analyses were used to estimate the amount of ozone loss.     

Fluid inclusion,geochemical, Rb–Sr and Sm–Nd isotope studies on tungsten mineralized Degana and Balda granites of the Aravalli craton,NW India

Granitic plutons occurring within and to the west of the Delhi Fold Belt in the Aravalli craton, northwestern India are the result of widespread felsic magmatism during Neoproterozoic, some of which are associated with greisen and skarn tungsten deposits. In this paper, we present the result of our study on fluid inclusions, geochemistry and geochronology of two such tungsten mineralized granite plutons at Degana and Balda, and interpret the nature of ore fluid, and petrogenesis and age of these mineralized granites. Fluid inclusion study reveals coexistence of moderate and hyper-saline aqueous fluid inclusions along with aqueous-carbonic inclusions, suggesting their origin due to liquid immiscibility during fluid–rock interaction. Geochemically, the granites are peraluminous, Rb enriched, Sr and Ba depleted and highly differentiated. The Rb–Sr isotopic systematics yielded \(795\pm 11\) Ma for Balda granite and \(827\pm 8\) Ma for Degana granite. We show that major phase of widespread granitoid magmatism and mineralization during the Neoproterozoic (840–790 Ma) in NW India is coeval with breakup of the Rodinia supercontinent and infer a causal relationship between them.     

Modeling competing hydraulic fracture propagation with the extended finite element method

We present an extended finite element framework to numerically study competing hydraulic fracture propagation. The framework is capable of modeling fully coupled hydraulic fracturing processes including fracture propagation, elastoplastic bulk deformation and fluid flow inside both fractures and the wellbore. In particular, the framework incorporates the classical orifice equation to capture fluid pressure loss across perforation clusters linking the wellbore with fractures. Dynamic fluid partitioning among fractures during propagation is solved together with other coupled factors, such as wellbore pressure loss (\(\Delta p_w\)), perforation pressure loss (\(\Delta p\)), interaction stress (\(\sigma _\mathrm{int}\)) and fracture propagation. By numerical examples, we study the effects of perforation pressure loss and wellbore pressure loss on competing fracture propagation under plane-strain conditions. Two dimensionless parameters \(\Gamma = \sigma _\mathrm{int}/\Delta p\) and \(\Lambda = \Delta p_w/\Delta p\) are used to describe the transition from uniform fracture propagation to preferential fracture propagation. The numerical examples demonstrate the dimensionless parameter \(\Gamma \) also works in the elastoplastic media.     

Shear Behaviors of the Binary Structural Plane

Binary-medium contact interfaces widely exist in rock engineering. They have significant impacts on the safety of rock engineering due to their poor shear behavior. A material of different strength is produced by pouring mortar of a different sand-to-cement ratio on the top of a rock-like mortar material (with the ratio of 1:1), thereby forming a binary-medium structural plane. Then, direct shear test is performed on the structural plane by applying different normal stresses. The shear strength parameters of the structural plane (cohesion \(c\) and friction angle \(\varphi\)) are obtained from the Mohr–Coulomb criterion. Moreover, the mechanical behaviors of the structural plane are compared with the unitary-medium specimen in the shearing process. A similar shear stress–shear displacement rule is observed in the shearing process. However, the peak and residual shear strengths of the binary structural plane are far lower than those of the unitary ones. The difference between the unitary and binary planes at cohesion \(c\) decreases with the increasing sand–cement ratio, whereas a up-down trend is observed in the friction angle \(\varphi\) with the increasing sand-to-cement ratio. When the upper and lower parts of the structural plane are different in sand-to-cement ratio, the cohesion \(c\) of the structural plane slightly increases with the increasing ratio of the upper specimen. However, when the two parts are identical in ratio, the cohesion of the structural plane reaches the peak, and its friction angle \(\varphi\) substantially increases with the increasing ratio of the upper part.     

Micromechanical Modeling of Yield in Isotropic Non-Cohesive Particulate Materials

We perform a micromechanical analysis of general isotropic non-cohesive particulate materials idealized as three-dimensional random assemblies of uniform spheres with a simple linear elastic inter-particle contact force law and inter-particle Coulomb friction law. We obtain analytical relationships between the inter-particle friction coefficient \(\mu\) (or inter-particle friction angle \(\phi _\mu = \tan ^{-1} \mu\)) on the microscale and the material friction angle \(\phi\) on the macroscale. Our micromechanical analysis directly employs force and moment equilibrium (together with compatibility and the contact constitutive assumptions noted) rather than energy methods, and thus can account for the effects of particle rotation, and in particular the effects of mechanisms or zero-energy modes due to particle rotation. To explore the effects of particle rotation, we perform analyses with particle rotation either allowed or prohibited. To validate the analytical results obtained here, we compare the \(\phi\) versus \(\phi _\mu\) curves determined theoretically to those obtained by the discrete element method (DEM) for six randomly packed specimens of 3430–29, 660 uniform spherical elements with uniform inter-element Coulomb friction in Fleischmann et al. in Geotech Geol Eng 32(4):1081–1100, (2014). The \(\phi\) versus \(\phi _\mu\) curves derived here show remarkable agreement with those obtained via DEM simulations in Fleischmann et al. in Geotech Geol Eng 32(4):1081–1100, (2014), especially for the case in which particle rotation is not artificially restrained.     

The geochemical and petrological characteristics of prenatal caldera volcano: a case of the newly formed small dacitic caldera,Hijiori, Northeast Japan

Evaluating the magma depth and its physical properties is critical to conduct a better geophysical assessment of magma chambers of caldera volcanoes that may potentially cause future volcanic hazards. To understand pre-eruptive conditions of a magma chamber before its first appearance at the surface, this paper describes the case of Hijiori caldera volcano in northeastern Japan, which emerged approximately 12,000 years ago at a place where no volcano ever existed. We estimated the depth, density, bulk modulus, vesicularity, crystal content, and bulk H\(_2\)O content of the magma chamber using petrographic interpretations, bulk and microchemical compositions, and thermodynamic calculations. The chemical mass balance calculations and thermodynamic modeling of the erupted magmas indicate that the upper portion of the Hijiori magmatic plumbing system was located at depths between 2 and 4 km, and had the following characteristics: (1) pre-eruptive temperature: about 780 \(^{\circ }\)C; (2) bulk magma composition: 66 ± 1.5 wt% SiO\(_{2}\); (3) bulk magmatic H\(_2\)O: approximately 2.5 wt%, and variable characteristics that depend on depth; (4) crystal content: \(\le\)57 vol%; (5) bulk modulus of magma: 0.1–0.8 GPa; (6) magma density: 1.8–2.3 g/cm³; and (7) amount of excess magmatic H\(_2\)O: 11–32 vol% or 48–81 mol%. The range of melt water contents found in quartz-hosted melt inclusions (2–9 wt%) suggests the range of depth phenocrysts growth to be wide (2\(\sim\)13 km). Our data suggest the presence of a vertically elongated magma chamber whose top is nearly solidified but highly vesiculated; this chamber has probably grown and re-mobilized by repeated injections of a small amount of hot dacitic magma originated from the depth.     

Strain responses of frozen clay with thermal gradient under triaxial creep

Thermal gradient is one of the main features for the temperature distribution in artificial frozen shaft lining (FSL). The time-dependent strain responses and the corresponding heterogeneity characteristics of frozen soils with thermal gradient are of potential significance for stability assessment and prediction of FSL, especially of the FSL embedded in thick alluvium. A series of triaxial creep tests were carried out on frozen saturated clay under various thermal gradients and creep stresses. The experimental results indicated that the triaxial creep curves for frozen clay with thermal gradient exhibit viscous characteristics, and the creep rate \(\Delta \varepsilon_{\text{a}} /\Delta t\) decreases with the increase in creep time \(t\) and decrease in thermal gradient. The stress–strain curve under different \(t\) showed that the creep stress has a marked growth when axial strain \(\varepsilon_{\text{a}} \le 1\,\%\). However, when \(\varepsilon_{\text{a}} \ge 1\,\%\), the growth rate decreases gradually. The deviation between measured radial strain \(\varepsilon_{\text{r}}^{\text{m}}\) under the middle specimen section height SSH and the calculated radial strain \(\varepsilon_{\text{r}}^{\text{c}}\) from the volumetric strain increases following a unified equation with the increase in axial strain. The radial strain \(\varepsilon_{\text{r}}^{\text{f}}\) for frozen clay with thermal gradient after experiment increases with the increase in SSH, and the slope of \( \varepsilon_{\text{r}}^{\text{f}} - {\text{SSH}} \) curve is significantly dependent on the thermal gradient and creep stress. The variation of \(\varepsilon_{\text{r}}^{\text{m}} - \varepsilon_{\text{r}}^{\text{c }}\) during experiment and \(\varepsilon_{\text{r}}^{\text{f}}\) distribution after experiment are the macro-responses of internal micro-heterogeneities in frozen soils induced from thermal gradient, and are closely related to strain rate and its variation. These observations and findings provide an insight into the creep mechanism and the estimation method of creep deformation for frozen soils with thermal gradient.