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Wex, Sebastian, Neil S. Mancktelow, Friedrich Hawemann, Alfredo Camacho i Giorgio Pennacchioni. "Inverted distribution of ductile deformation in the relatively “dry” middle crust across the Woodroffe Thrust, central Australia". Solid Earth 9, nr 4 (11.07.2018): 859–78. http://dx.doi.org/10.5194/se-9-859-2018.
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Abstract. Thrust fault systems typically distribute shear strain preferentially into the hanging wall rather than the footwall. The Woodroffe Thrust in the Musgrave Block of central Australia is a regional-scale example that does not fit this model. It developed due to intracontinental shortening during the Petermann Orogeny (ca. 560–520 Ma) and is interpreted to be at least 600 km long in its E–W strike direction, with an approximate top-to-north minimum displacement of 60–100 km. The associated mylonite zone is most broadly developed in the footwall. The immediate hanging wall was only marginally involved in the mylonitization process, as can be demonstrated from the contrasting thorium signatures of mylonites derived from the upper amphibolite facies footwall and the granulite facies hanging wall protoliths. Thermal weakening cannot account for such an inverse deformation gradient, as syn-deformational P–T estimates for the Petermann Orogeny in the hanging wall and footwall from the same locality are very similar. The distribution of pseudotachylytes, which acted as preferred nucleation sites for shear deformation, also cannot provide an explanation, since these fault rocks are especially prevalent in the immediate hanging wall. The most likely reason for the inverted deformation gradient across the Woodroffe Thrust is water-assisted weakening due to the increased, but still limited, presence of aqueous fluids in the footwall. We also establish a qualitative increase in the abundance of fluids in the footwall along an approx. 60 km long section in the direction of thrusting, together with a slight decrease in the temperature of mylonitization (ca. 100 °C). These changes in ambient conditions are accompanied by a 6-fold decrease in thickness (from ca. 600 to 100 m) of the Woodroffe Thrust mylonitic zone.
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Camacho, A., B. Simons i P. W. Schmidt. "Geological and palaeomagnetic significance of the Kulgera Dyke Swarm, Musgrave Block, NT, Australia". Geophysical Journal International 107, nr 1 (październik 1991): 37–45. http://dx.doi.org/10.1111/j.1365-246x.1991.tb01154.x.
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Hawemann, Friedrich, Neil S. Mancktelow, Sebastian Wex, Alfredo Camacho i Giorgio Pennacchioni. "Pseudotachylyte as field evidence for lower-crustal earthquakes during the intracontinental Petermann Orogeny (Musgrave Block, Central Australia)". Solid Earth 9, nr 3 (9.05.2018): 629–48. http://dx.doi.org/10.5194/se-9-629-2018.
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Abstract. Geophysical evidence for lower continental crustal earthquakes in almost all collisional orogens is in conflict with the widely accepted notion that rocks, under high grade conditions, should flow rather than fracture. Pseudotachylytes are remnants of frictional melts generated during seismic slip and can therefore be used as an indicator of former seismogenic fault zones. The Fregon Subdomain in Central Australia was deformed under dry sub-eclogitic conditions of 600–700 °C and 1.0–1.2 GPa during the intracontinental Petermann Orogeny (ca. 550 Ma) and contains abundant pseudotachylyte. These pseudotachylytes are commonly foliated, recrystallized, and cross-cut by other pseudotachylytes, reflecting repeated generation during ongoing ductile deformation. This interplay is interpreted as evidence for repeated seismic brittle failure and post- to inter-seismic creep under dry lower-crustal conditions. Thermodynamic modelling of the pseudotachylyte bulk composition gives the same PT conditions of shearing as in surrounding mylonites. We conclude that pseudotachylytes in the Fregon Subdomain are a direct analogue of current seismicity in dry lower continental crust.
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Kelly, Nigel M., Geoffrey L. Clarke i Simon L. Harley. "Monazite behaviour and age significance in poly-metamorphic high-grade terrains: A case study from the western Musgrave Block, central Australia11Abbreviations: After Kretz, 1983." Lithos 88, nr 1-4 (maj 2006): 100–134. http://dx.doi.org/10.1016/j.lithos.2005.08.007.
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Macnae, James, Xiuyan Ren i Tim Munday. "Stripping induced polarization effects from airborne electromagnetics to improve 3D conductivity inversion of a narrow palaeovalley". GEOPHYSICS 85, nr 5 (7.07.2020): B161—B167. http://dx.doi.org/10.1190/geo2019-0396.1.
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The electrical conductivity distribution within wide palaeochannels is usually well-mapped from airborne electromagnetic data using stitched 1D algorithms. Such stitched 1D solutions are, however, inappropriate for narrow valleys. An alternative option is to consider 2D or 3D models to allow for finite lateral extent of conductors. In airborne electromagnetic data within the Musgrave block near the well-studied Valen conductor, strong induced polarization (IP) and superparamagnetic (SPM) effects make physical property and structure estimation even more uncertain for deep channel clays, particularly those whose channel widths are comparable to their depth of burial. We developed a recursive data fitting algorithm based on dispersive thin sheet responses. The separate IP and SPM components of the fit provide near-surface chargeability and SPM distributions, and the associated electromagnetic (EM) fit provides stripped data with monotonic decays compatible with a simple nondispersive conductivity model. The validity of this stripped data prediction was tested through a comparison of 1D conductivity-depth imaging and 3D inversion applied to the original data and the stripped data. Due to the forked geometry of the deep conductivity structure in the region we investigated, we successfully used 3D rather than 2D inversion to predict the conductivity distribution related to the EM data. We recovered from the stripped data a continuous conductivity structure consistent with a branching, clay-filled palaeovalley under cover.
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Fan, Xiao-Ping, Yi-Cheng He, Cong-Jie Yang i Jun-Fei Wang. "Evaluation of crustal inhomogeneity parameters in the southern Longmenshan fault zone and adjacent regions". Journal of Seismology 24, nr 6 (19.08.2020): 1175–88. http://dx.doi.org/10.1007/s10950-020-09949-w.
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AbstractBroadband teleseismic waveform data from 13 earthquakes recorded by 70 digital seismic stations were selected to evaluate the inhomogeneity parameters of the crustal medium in the southern Longmenshan fault zone and its adjacent regions using the teleseismic fluctuation wavefield method. Results show that a strong inhomogeneity exists beneath the study region, which can be divided into three blocks according to its structure and tectonic deformation features. These are known as the Sichuan-Qinghai Block, the Sichuan-Yunnan Block, and the Mid-Sichuan Block. The velocity fluctuation ratios of the three blocks are approximately 5.1%, 3.6%, and 5.1% in the upper crust and 5.1%, 3.8%, and 4.9% in the lower crust. The inhomogeneity correlation lengths of the three blocks are about 10.1 km, 14.0 km, and 10.7 km in the upper crust and 11.8 km, 17.0 km, and 11.8 km in the lower crust. The differences in the crustal medium inhomogeneity beneath the Sichuan-Yunnan Block, the Sichuan-Qinghai Block, and the Mid-Sichuan Block may be related to intensive tectonic movement and material flow in the crust and upper mantle.
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Smethurst, M. A., i J. C. Briden. "Palaeomagnetism of Silurian Sediments In W Ireland: Evidence For Block Rotation In the Caledonides". Geophysical Journal International 95, nr 2 (1.11.1988): 327–46. http://dx.doi.org/10.1111/j.1365-246x.1988.tb00472.x.
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White, R. W., Roger Powell i G. L. Clarke. "The interpretation of reaction textures in Fe-rich metapelitic granulites of the Musgrave Block, central Australia: constraints from mineral equilibria calculations in the system K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3". Journal of Metamorphic Geology 20, nr 1 (11.01.2002): 41–55. http://dx.doi.org/10.1046/j.0263-4929.2001.00349.x.
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Bache, Francois, Paul Walshe, Juergen Gusterhuber, Sandra Menpes, Mattilda Sheridan, Sergey Vlasov i Lance Holmes. "Exploration of the south-eastern part of the Frontier Amadeus Basin, Northern Territory, Australia". APPEA Journal 58, nr 1 (2018): 190. http://dx.doi.org/10.1071/aj17221.
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The Neoproterozoic to Late Paleozoic-aged Amadeus Basin is a large (~170 000 km2) east–west-trending basin, bounded to the south by the Musgrave Province and to the north by the Arunta Block of the Northern Territory. Commercial oil and gas production is established in the northern part of the basin but the southern part is still a frontier exploration area. Vintage and new seismic reflection data have been used with well data along the south-eastern Amadeus Basin to construct a new structural and depositional model. Three major phases of deformation controlling deposition have been identified. The first phase is characterised by a SW–NE trending structural fabric and is thought to be older than the deposition of the first sediments identified above basement (Heavitree and Bitter Springs formations). The second phase corresponds to the Petermann Orogeny (580–540 Ma) and trends in a NW–SE orientation. The third phase is the Alice Springs Orogeny (450–300 Ma) and is oriented W–E to WNW–ESE in this part of the basin. This tectono-stratigraphic model involving three distinct phases of deformation potentially explains several critical observations: the lack of Heavitree reservoir at Mt Kitty-1, limited salt movements before the Petermann Orogeny (~300 Ma after its deposition) and salt-involved structures that can be either capped by the Petermann Unconformity and overlying Cambrian to Devonian sediments, or can reach the present day surface. Finally, this model, along with availability of good quality seismic data, opens new perspectives for the hydrocarbon exploration of the Amadeus Basin. Each of the tectonic phases impacts the primary petroleum system and underpins play-based exploration.
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Xu, Wenjing, Xisheng Xu, Yuejun Wang i Matthew Jacek Brzozowski. "The effects of mafic-felsic magma interaction on magma diversity: insights from an early Paleozoic hornblendite-quartz monzonite suite in the South China block". Mineralogy and Petrology 114, nr 1 (7.01.2020): 71–90. http://dx.doi.org/10.1007/s00710-019-00692-w.
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Yin, Rong, Li Han, Xiao-Long Huang, Jie Li, Wu-Xian Li i Lin-Li Chen. "Textural and chemical variations of micas as indicators for tungsten mineralization: Evidence from highly evolved granites in the Dahutang tungsten deposit, South China". American Mineralogist 104, nr 7 (1.07.2019): 949–65. http://dx.doi.org/10.2138/am-2019-6796.
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Abstract The Dahutang tungsten deposit, located in the Yangtze Block, South China, is one of the largest tungsten deposits in the world. Tungsten mineralization is closely related to Mesozoic granitic plutons. A drill core through a pluton in the Dalingshang ore block in the Central segment of the Dahutang tungsten deposit shows that the pluton is characterized by multi-stage intrusive phases including biotite granite, muscovite granite, and Li-mica granite. The granites are strongly peraluminous and rich in P and F. Decreasing bulk-rock (La/Yb)N ratios and total rare earth element (ΣREE) concentrations from the biotite granite to muscovite granite and Li-mica granite suggest an evolution involving the fractional crystallization of plagioclase. Bulk-rock Li, Rb, Cs, P, Sn, Nb, and Ta contents increase with decreasing Zr/Hf and Nb/Ta ratios, denoting that the muscovite granite and Li-mica granite have experienced a higher degree of magmatic fractionation than the biotite granite. In addition, the muscovite and Li-mica granites show M-type lanthanide tetrad effect, which indicates hydrothermal alteration during the post-magmatic stage. The micas are classified as lithian biotite and muscovite in the biotite granite, muscovite in the muscovite granite, and Li-muscovite and lepidolite in the Li-mica granite. The Li, F, Rb, and Cs contents of micas increase, while FeOT, MgO, and TiO2 contents decrease with increasing degree of magmatic fractionation. Micas in the muscovite granite and Li-mica granite exhibit compositional zonation in which Si, Rb, F, Fe, and Li increase, and Al decreases gradually from core to mantle, consistent with magmatic differentiation. However, the outermost rim contains much lower contents of Si, Rb, F, Fe, and Li, and higher Al than the mantle domains due to metasomatism in the presence of fluids. The variability in W contents of the micas matches the variability in Li, F, Rb, and Cs contents, indicating that both the magmatic and hydrothermal evolutions were closely associated with W mineralization in the Dahutang deposit. The chemical zoning of muscovite and Li-micas not only traces the processes of W enrichment by magmatic differentiation and volatiles but also traces the leaching of W by the fluids. Therefore, micas are indicators not only for the magmatic–hydrothermal evolution of granite, but also for tungsten mineralization.
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Sattarvand, Javad, i Christian Niemann-Delius. "A New Metaheuristic Algorithm for Long-Term Open-Pit Production Planning / Nowy meta-heurystyczny algorytm wspomagający długoterminowe planowanie produkcji w kopalni odkrywkowej". Archives of Mining Sciences 58, nr 1 (1.03.2013): 107–18. http://dx.doi.org/10.2478/amsc-2013-0007.
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Paper describes a new metaheuristic algorithm which has been developed based on the Ant Colony Optimisation (ACO) and its efficiency have been discussed. To apply the ACO process on mine planning problem, a series of variables are considered for each block as the pheromone trails that represent the desirability of the block for being the deepest point of the mine in that column for the given mining period. During implementation several mine schedules are constructed in each iteration. Then the pheromone values of all blocks are reduced to a certain percentage and additionally the pheromone value of those blocks that are used in defining the constructed schedules are increased according to the quality of the generated solutions. By repeated iterations, the pheromone values of those blocks that define the shape of the optimum solution are increased whereas those of the others have been significantly evaporated.
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Wadsworth, W. J. "Silicate mineralogy of the Behelvie cumulates, N E Scotland". Mineralogical Magazine 55, nr 378 (marzec 1991): 113–19. http://dx.doi.org/10.1180/minmag.1991.055.378.09.
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AbstractUltramafic, troctolitic and gabbroic rocks at the northern end of the Belhelvie layered intrusion display progressive cryptic variation over a stratigraphic thickness of approximately 800 m in steeply-dipping cumulates, which young from W to E. This variation is shown by olivine (Fo87−77), orthopyroxene (En87−79), clinopyroxene (Ca45Mg48Fe7 to Ca44.5Mg45.5Fe10) and plagioclase (An81−75). The Belhelvie succession is believed to be equivalent to the poorly-exposed and structurally complex Insch Lower Zone. A laterally impersistent hypersthene-gabbro unit within the main sequence is re-interpreted as a downfaulted block of slightly more evolved cumulates. A repeat sequence of peridotites, troctolites and gabbros on the eastern side of the intrusion, and separated from the underlying main succession by a thin septum of country rock, is believed to represent a fresh influx of magma.
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Ismagilov, F. R., M. K. Dzheksenov i A. V. Kurochkin. "Technology for Block Design of a Gas Treatment Plant for Oil Blow-Off to Remove Hydrogen Sulfide". Chemical and Petroleum Engineering 56, nr 7-8 (listopad 2020): 633–37. http://dx.doi.org/10.1007/s10556-020-00820-w.
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Hashemi, Seyed Ahmad, Bahram Rezai, Mohammad Reza Tavakoli Mohammadi i Sepideh Javanshir. "Characterization and Concentration Studies of Jalal Abad Iron Mine / Charakterystyka I Badania Koncentracji W Kopalni Rud Żelaza Jalal Abad". Archives of Mining Sciences 58, nr 3 (1.09.2013): 729–45. http://dx.doi.org/10.2478/amsc-2013-0051.
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Abstract Characterization and determination of liberation degree are the first stages of ore dressing. Block 4 of Jalal Abad mine, Kerman province, Iran, has three kinds of iron ores; D1, D2 and D3, with different grades. In this research, chemical analysis, mineralogy, liberation degree and magnetic enrichment studies were done by XRF, XRD, microscopic sections and Davis tube, respectively. The results indicated that D1, D2 and D3 had average iron grades of 58, 52 and 38%, respectively. The minerals of Magnetite, Hematite, Dolomite, Calcite and Quartz were distinguished. Average liberation degree was estimated about 500 μm by Microscopic studies. The results of magnetic tests showed that iron grade of D1, D2 and D3 concentrates increased to 70.46, 63.98 and 45.37%, respectively. The optimization of blending was investigated for production of accumulated concentrate with desirable iron grade (68%) using MATLAB software.
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Frontera, T., A. Concha, P. Blanco, A. Echeverria, X. Goula, R. Arbiol, G. Khazaradze, F. Pérez i E. Suriñach. "DInSAR Coseismic Deformation of the May 2011 M<sub>w</sub> 5.1 Lorca Earthquake (southeastern Spain)". Solid Earth 3, nr 1 (2.04.2012): 111–19. http://dx.doi.org/10.5194/se-3-111-2012.
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Abstract. The coseismic superficial deformation at the region of Lorca (Murcia, southeastern Spain) due to the Mw 5.1 earthquake on 11 May 2011 was characterized by a multidisciplinary team, integrating information from DInSAR, GPS and numerical modelling techniques. Despite the moderate magnitude of the event, quantitative information was obtained from the interferometric study of a pair of TerraSAR-X images. The DinSAR results defined the trace of the fault plane and evidenced uplift of the hanging wall block in agreement with the estimated deformation obtained through an elastic rupture dislocation numerical model. Meanwhile for the footwall block, interferometric results showed that tectonic deformation is masked by an important subsidence related to groundwater extraction previously identified at the area of study. Horizontal crustal deformation rates and velocity vectors, obtained from GPS stations existent at the area, were also coherent with the tectonic setting of the southern margin of the Iberian Peninsula and with the focal mechanism calculated for the Lorca event. The analysis of a continuous GPS site in Lorca showed good agreement with the horizontal N–S direction component relative to the numerical model and tectonics of the region. This is the first time at this seismic active area that a multi-technique analysis has been performed immediately after the occurrence of a seismic event, comparing the existing deformation data with a theoretical numerical model based on estimated seismic rupture dislocation.
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Wu, Chenglong, Tao Xu, Yinshuang Ai, Weiyu Dong i Long Li. "XKS splitting-based upper-mantle deformation in the Jiaodong Peninsula records the boundary between the North China Craton and South China Block". Geophysical Journal International 222, nr 2 (9.05.2020): 956–64. http://dx.doi.org/10.1093/gji/ggaa224.
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SUMMARY The Jiaodong Peninsula consists of the Jiaobei massif and the Northern Sulu UHP massif. These are separated by the Wulian suture zone (WSZ), a key region for understanding the collision between the North China Craton (NCC) and South China Block (SCB). To interpret this collisional zone, a broad-band seismic profile of 20 stations was installed across the WSZ. Shear wave splitting analysis of teleseismic data revealed a contrast in the splitting patterns beneath different structural zones of the Jiaodong Peninsula. The anisotropic structures of the Jiaobei massif and Northern Sulu UHP massif can be explained by a single anisotropic layer model with WNW-ESE or E-W oriented fast directions. In the WSZ, splitting parameters exhibit pronounced variation in backazimuths indicating a two-layer anisotropy pattern. The lower layer exhibits a WNW-ESE fast direction consistent with that observed in the other two regions. Because the fast direction is generally parallel to the present-day direction of Pacific plate subduction, the anisotropy most likely represents asthenospheric return flow in the big mantle wedge caused by Pacific plate subduction. The upper layer exhibits an NE fast direction, that is, parallel to faulting associated with the WSZ. The lithosphere may preserve fossilized anisotropy induced by the Late Triassic collision of the NCC and SCB even after subsequent destruction and thinning from the Late Mesozoic to Cenozoic. We infer that the WSZ represents a lithospheric-scale structural boundary between the NCC and SCB.
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Lee, Tien‐Chang, Thomas L. Henyey i Brian N. Damiata. "A simple method for the absolute measurement of thermal conductivity of drill cuttings". GEOPHYSICS 51, nr 8 (sierpień 1986): 1580–84. http://dx.doi.org/10.1190/1.1442208.
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We present a method for absolute measurement of thermal conductivity of drill cuttings. The simplicity of the apparatus makes it suitable for nondestructive use of cuttings and for sample sizes too small to be measured with a needle probe. Because the measurement is absolute, no calibration standards are required. Samples are placed in a Plexiglas cup with a lid containing an electric heat source. The base of the cup is placed in good thermal contact with an aluminum‐block heat sink. Upward and radial heat losses are minimized with styrofoam insulation surrounding the cup. The accuracy of the method was estimated by cross‐measurement of selected samples with a well‐calibrated needle probe. Results indicate that errors in measurement are less than 5 percent for sample conductivities greater than 0.8 W/m ⋅ K if the heat loss through the styrofoam insulation is accounted for. Reproducibility is typically within 3 percent. An axisymmetric finite‐element model which simulates the temperature distribution of the measurement apparatus further demonstrates its viability.
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Ni, Pei, Guo-Guang Wang, Wen-Sheng Li, Zhe Chi, Su-Ning Li i Yan Gao. "A review of the Yanshanian ore-related felsic magmatism and tectonic settings in the Nanling W-Sn and Wuyi Au-Cu metallogenic belts, Cathaysia Block, South China". Ore Geology Reviews 133 (czerwiec 2021): 104088. http://dx.doi.org/10.1016/j.oregeorev.2021.104088.
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Pautov, Leonid A., Atali A. Agakhanov, Vladimir Yu Karpenko, Yulia A. Uvarova, Elena Sokolova i Frank C. Hawthorne. "Rinkite-(Y), Na2Ca4YTi(Si2O7)2OF3, a seidozerite-supergroup TS-block mineral from the Darai-Pioz alkaline massif, Tien-Shan mountains, Tajikistan: Description and crystal structure". Mineralogical Magazine 83, nr 03 (29.06.2018): 373–80. http://dx.doi.org/10.1180/mgm.2018.122.
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AbstractRinkite-(Y), ideally Na2Ca4YTi(Si2O7)2OF3, is a new rinkite-group (seidozerite-supergroup) TS-block mineral from the Darai-Pioz alkaline massif, Tian-Shan mountains, Tajikistan. The mineral is of hydrothermal origin. It occurs as aggregates (up to 1.5 cm long) of acicular crystals 0.1–1.0 mm thick, and as separate elongated columnar, flattened-prismatic crystals up to 1 cm long with rectangular or rhombic sections up to 0.5 mm across. Associated minerals are quartz, aegirine, microcline, neptunite, pectolite, calcite, eudialyte-group minerals, fluorite, titanite, turkestanite, kupletskite, galena, albite and pyrochlore-group minerals. Crystals are transparent and colourless to occasionally white, with a vitreous lustre. Rinkite-(Y) has a white streak, uneven, conchoidal fracture and does not fluoresce under a cathode or ultraviolet light. Cleavage is very good on {100}, no parting was observed, Mohs hardness is ~5, and it is brittle, Dmeas. = 3.44(2) g/cm3, Dcalc. = 3.475 g/cm3. It is biaxial (+) with refractive indices (λ = 590 nm) α = 1.662(2), β = 1.666(2), γ = 1.685(5); 2Vmeas. = 50(3) and 2Vcalc. = 49.7°. It is nonpleochroic. Rinkite-(Y) is monoclinic, space group P21/c, a = 7.3934(5), b = 5.6347(4), c = 18.713(1) Å, β = 101.415(2)° and V = 764.2(2) Å3. The six strongest reflections in the X-ray powder diffraction data [d(Å), I, (hkl)] are: 3.057, 100, (006, $\bar{2}$12, 210); 2.688, 28, (016); 9.18, 24, (002); 2.929, 17, ($\bar{2}$13, 211); 3.559, 15, (104, 014) and 2.783, 14, (021). The empirical formula calculated on 18 (O + F) is Na2.11(Ca3.74Sr0.03Mn0.03)Σ3.80(Y0.50Nd0.16Ce0.16Gd0.07Dy0.06Sm0.05Pr0.03La0.03${\rm U}_{0.01}^{{\rm 4 + }} {\rm )}_{\Sigma 1.07}{\rm (T}{\rm i}_{0.85}{\rm N}{\rm b}_{0.17}{\rm W}^{6+}_{0.01}{\rm T}{\rm a}_{0.01}{\rm )}_{\Sigma 1.04}\left( {{\rm S}{\rm i}_{4.03}{\rm O}_{14}} \right){\rm O}_{1.40}{\rm F}_{2.60}$ with Z = 2. The ideal formula is Na2Ca4YTi(Si2O7)2OF3. The crystal structure was refined on a twinned crystal to R1 = 4.59% on the basis of 1489 unique reflections (F > 4σF) and is a framework of TS (Titanium-Silicate) blocks. The TS block consists of HOH sheets (H – heteropolyhedral, O – octahedral) parallel to (100). In the O sheet, the Ti-dominant [6]MO1 site ideally gives 1 Ti apfu. The [8]MO2 and [6]MO3 sites are ideally occupied by Na and (NaCa) apfu. In the H sheet, the [7]MH site is occupied by Ca1.13Y0.50REE0.37, (REE = rare-earth element), ideally (CaY), <MH–φ> = 2.415 Å and the [7]AP site is occupied by Ca1.81REE0.19, ideally Ca2, <AP–φ> = 2.458 Å. The MH + AP sites ideally give (Ca3Y) apfu. The MH and AP polyhedra and Si2O7 groups constitute the H sheet. Linkage of H and O sheets via common vertices of MH and AP polyhedra and Si2O7 groups with MO1–3 polyhedra results in a TS block. The TS block in rinkite-(Y) exhibits linkage 1 and stereochemistry typical for the rinkite group (Ti = 1 apfu) of the seidozerite supergroup. For rinkite-(Y), the ideal structural formula of the form AP2MH2MO4(Si2O7)2$ \left( {{\rm X}_{\rm M}^{\rm O} } \right)_2\left( {{\rm X}_{\rm A}^{\rm O} } \right)_2{\rm is }\;\left( {{\rm C}{\rm a}_3{\rm Y}} \right){\rm Na}\left( {{\rm NaCa}} \right){\rm Ti}\left( {{\rm S}{\rm i}_2{\rm O}_7} \right)_2\left( {{\rm OF}} \right){\rm F}_2 $ with Z = 2. The mineral is named rinkite-(Y) as it is structurally identical to rinkite-(Ce) and Y is the dominant rare-earth element.
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Zhang, Zhi-Gang, Yan-Bao Liu, Hai-Tao Sun, Wei Xiong, Kai Shen i Quan-Bin Ba. "An alternative approach to match field production data from unconventional gas-bearing systems". Petroleum Science 17, nr 5 (18.05.2020): 1370–88. http://dx.doi.org/10.1007/s12182-020-00454-w.
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Abstract Nowadays, the unconventional gas-bearing system plays an increasingly important role in energy market. The performances of the current history-matching techniques are not satisfied when applied to such systems. To overcome this shortfall, an alternative approach was developed and applied to investigate production data from an unconventional gas-bearing system. In this approach, the fluid flow curve obtained from the field is the superposition of a series of Gaussian functions. An automatic computing program was developed in the MATLAB, and both gas and water field data collected from a vertical well in the Linxing Block, Ordos Basin, were used to present the data processing technique. In the reservoir study, the automatic computing program was applied to match the production data from a single coal seam, multiple coal seams and multiple vertically stacked reservoirs with favourable fitting results. Compared with previous approaches, the proposed approach yields better results for both gas and water production data and can calculate the contributions from different reservoirs. The start time of the extraction for each gas-containing unit can also be determined. The new approach can be applied to the field data prediction and designation for the well locations and patterns at the reservoir scale.
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Shulgin, Alexey, Jan Inge Faleide, Rolf Mjelde, Asbjørn Breivik i Ritske Huismans. "Crustal domains in the Western Barents Sea". Geophysical Journal International 221, nr 3 (24.04.2020): 2155–69. http://dx.doi.org/10.1093/gji/ggaa112.
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SUMMARY The crustal architecture of the Barents Sea is still enigmatic due to complex evolution during the Timanian and Caledonian orogeny events, further complicated by several rifting episodes. In this study we present the new results on the crustal structure of the Caledonian–Timanian transition zone in the western Barents. We extend the work of Aarseth et al. (2017), by utilizing the seismic tomography approach to model Vp, Vs and Vp/Vs ratio, combined with the reprocessed seismic reflection line, and further complemented with gravity modelling. Based on our models we document in 3-D the position of the Caledonian nappes in the western Barents Sea. We find that the Caledonian domain is characterized by high crustal reflectivity, caused by strong deformation and/or emplacement of mafic intrusions within the crystalline crust. The Timanian domain shows semi-transparent crust with little internal reflectivity, suggesting less deformation. We find, that the eastern branch of the earlier proposed Caledonian suture, cannot be associated with the Caledonian event, but can rather be a relict from the Timanian terrane assemblance, marking one of the crustal microblocks. This crustal block may have an E–W striking southern boundary, along which the Caledonian nappes were offset. A high-velocity/density crustal body, adjacent to the Caledonian–Timanian contact zone, is interpreted as a zone of metamorphosed rocks based on the comparison with global compilations. The orientation of this body correlates with regional gravity maxima zone. Two scenarios for the origin of the body are proposed: mafic emplacement during the Timanian assembly, or massive mafic intrusions associated with the Devonian extension.
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Torne, Montserrat, Ivone Jiménez–Munt, Jaume Vergés, Manel Fernàndez, Alberto Carballo i Margarete Jadamec. "Regional crustal and lithospheric thickness model for Alaska, the Chukchi shelf, and the inner and outer bering shelves". Geophysical Journal International 220, nr 1 (7.10.2019): 522–40. http://dx.doi.org/10.1093/gji/ggz424.
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SUMMARY This study presents for the first time an integrated image of the crust and lithospheric mantle of Alaska and its adjacent western shelves of the Chukchi and Bering seas based on joint modelling of potential field data constrained by thermal analysis and seismic data. We also perform 3-D forward modelling and inversion of Bouguer anomalies to analyse density heterogeneities at the crustal level. The obtained crustal model shows northwest-directed long wavelength thickening (32–36 km), with additional localized trends of thicker crust in the Brooks Range (40 km) and in the Alaska and St Elias ranges (50 km). Offshore, 28–30-km-thick crust is predicted near the Bearing slope break and 36–38 km in the northern Chukchi Shelf. In interior Alaska, the crustal thickness changes abruptly across the Denali fault, from 34–36 to the north to above 30 km to the south. This sharp crustal thickness gradient agrees with the presence of a crustal tectonic buttress guiding block motion west and south towards the subduction zone. The average crustal density is 2810 kg m−3. The denser crust, up to 2910 kg m−3, is found south of the Denali Fault likely related to the oceanic nature of the Wrangellia Composite Terrane rocks. Offshore, less dense crust (<2800 kg m−3) is found along the sedimentary basins of the Chukchi and Beaufort shelves. At LAB levels, there is a regional SE–NW trend that coincides with the current Pacific Plate motion, with a lithospheric root underneath the Brooks Range, Northern Slope, and Chuckchi Sea, that may correspond to a relic of the Chukotka-Artic Alaska microplate. The obtained lithospheric root (above 180 km) agrees with the presence of a boundary of cold, strong lithosphere that deflects the strain towards the South. South of the Denali Fault the LAB topography is quite complex. East of 150°W, below Wrangellia and the eastern side of Chugach terranes, the LAB is much shallower than it is west of this meridian. The NW trending limit separating thinner lithosphere in the east and thicker in the west agrees with the two-tiered slab shape of the subducting Pacific Plate.
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Gao, Wei, Ruizhong Hu, Albert H. Hofstra, Qiuli Li, Jingjing Zhu, Keqiang Peng, Lan Mu, Yong Huang, Jianwen Ma i Qiang Zhao. "U-Pb Dating on Hydrothermal Rutile and Monazite from the Badu Gold Deposit Supports an Early Cretaceous Age for Carlin-Type Gold Mineralization in the Youjiang Basin, Southwestern China". Economic Geology 116, nr 6 (1.09.2021): 1355–85. http://dx.doi.org/10.5382/econgeo.4824.
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Abstract The Youjiang basin on the southwestern margin of the Yangtze block in southwestern China is the world’s second largest Carlin-type gold province after Nevada, USA. The lack of precise age determinations on gold deposits in this province has hindered understanding of their genesis and relation to the geodynamic setting. Although most Carlin-type gold deposits in the basin are hosted in calcareous sedimentary rocks, ~70% of the ore in the Badu Carlin-type gold deposit is hosted by altered and sulfidized dolerite. Although in most respects Badu is similar to other Carlin-type gold deposits in the province, alteration of the unusual dolerite host produced hydrothermal rutile and monazite that can be dated. Field observations show that gold mineralization is spatially associated with, but temporally later than, dolerite. In situ secondary ion mass spectrometry (SIMS) U-Pb dating on magmatic zircon from the least altered dolerite yielded a robust emplacement age of 212.2 ± 1.9 Ma (2σ, mean square of weighted deviates [MSWD] = 0.55), providing a maximum age constraint on gold mineralization. The U-Th/He ages of detrital zircons from hydrothermally mineralized sedimentary host rocks at Badu and four other Carlin-type gold deposits yielded consistent weighted mean ages of 146 to 130 Ma that record cooling from a temperature over 180° to 200°C and place a lower limit on the age of gold mineralization in the basin. Hydrothermal rutile and monazite that are coeval with gold mineralization have been identified in the mineralized dolerite. Rutile is closely associated with hydrothermal ankerite, sericite, and gold-bearing pyrite. It has high concentrations of W, Fe, V, Cr, and Nb, as well as growth zones that are variably enriched in W, Fe, Nb, and U. Monazite contains primary two-phase fluid inclusions and is intergrown with gold-bearing pyrite and hydrothermal minerals. In situ SIMS U-Pb dating of rutile yielded a Tera-Wasserburg lower intercept age of 141.7 ± 5.8 Ma (2σ, MSWD = 1.04) that is within error of the in situ SIMS Th-Pb age of 143.5 ± 1.4 Ma (2σ, MSWD = 1.5) on monazite. These ages are ~70 m.y. younger than magmatic zircons in the host dolerite and are similar to the aforementioned U-Th/He cooling ages on detrital zircons from hydrothermally mineralized sedimentary host rocks. We, therefore, conclude that the Badu Carlin-type gold deposit formed at ca. 144 Ma. The agreement of the rutile and monazite ages with the U-Th-He cooling ages of Badu and four other Carlin-type gold deposits in the Youjiang basin suggests that ca. 144 Ma is representative of a regional Early Cretaceous Carlin-type hydrothermal event formed during back-arc extension.
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Andersson, Joel B. H., Tobias E. Bauer i Edward P. Lynch. "Evolution of structures and hydrothermal alteration in a Palaeoproterozoic supracrustal belt: Constraining paired deformation–fluid flow events in an Fe and Cu–Au prospective terrain in northern Sweden". Solid Earth 11, nr 2 (17.04.2020): 547–78. http://dx.doi.org/10.5194/se-11-547-2020.
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Abstract. An approximately 90 km long Palaeoproterozoic supracrustal belt in the northwestern Norrbotten ore province (northernmost Sweden) was investigated to characterize its structural components, assess hydrothermal alteration–structural geology correlations, and constrain a paired deformation–fluid flow evolution for the belt. New geological mapping of five key areas (Eustiljåkk, Ekströmsberg, Tjårrojåkka, Kaitum West, and Fjällåsen–Allavaara) indicates two major compressional events (D1 and D2) have affected the belt, with each associated with hydrothermal alteration types typical for iron oxide–apatite and iron oxide Cu–Au systems in the region. Early D1 generated a regionally distributed, penetrative S1 foliation and oblique reverse shear zones that show a southwest-block-up sense of shear that formed in response to NE–SW crustal shortening. Peak regional metamorphism at epidote–amphibolite facies broadly overlaps with this D1 event. Based on overprinting relationships, D1 is associated with regional scapolite ± albite, magnetite + amphibole, and late calcite alteration of mafic rock types. These hydrothermal mineral associations linked to D1 structures may form part of a regionally pervasive evolving fluid flow event but are separated in this study by crosscutting relationships. During D2 deformation, folding of S0–S1 structures generated F2 folds with steeply plunging fold axes in low-strain areas. NNW-trending D1 shear zones experienced reverse dip-slip reactivation and strike-slip-dominated movements along steep, E–W-trending D2 shear zones, producing brittle-plastic structures. Hydrothermal alteration linked to D2 structures is a predominantly potassic–ferroan association comprising K-feldspar ± epidote ± quartz ± biotite ± magnetite ± sericite ± sulfides. Locally, syn- or post-tectonic calcite is the main alteration mineral in D2 shear zones that intersect mafic rocks. Our results highlight the importance of combining structural geology with the study of hydrothermal alterations at regional to belt scales to understand the temporal–spatial relationship between mineralized systems. Based on the mapping results and microstructural investigations as well as a review of earlier tectonic models presented for adjacent areas, we suggest a new structural model for this part of the northern Fennoscandian Shield. The new model emphasizes the importance of reactivation of early structures, and the model harmonizes with tectonic models presented by earlier workers based mainly on petrology of the northern Norrbotten area.
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Leitch, C. H. B., P. van der Heyden, C. I. Godwin, R. L. Armstrong i J. E. Harakal. "Geochronometry of the Bridge River Camp, southwestern British Columbia". Canadian Journal of Earth Sciences 28, nr 2 (1.02.1991): 195–208. http://dx.doi.org/10.1139/e91-019.
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Mineralization at the Bralorne mesothermal gold vein deposit is closely related to a suite of early Late Cretaceous to early Tertiary dykes. Premineral albitite dykes (91.4 ± 1.4 Ma by U–Pb on zircons) and postmineral lamprophyre dykes (43.5 ± 1.5 Ma by K–Ar on biotite) set definite age limits on the mineralizing event. A late intra- to post-mineral green hornblende dyke set (85.7 ± 3.0 Ma by K–Ar on hornblende) that forms a transitional series to the albitites may further restrict the age. Thus, mineralization occurred long after emplacement of the host Bralorne intrusions, dated as Early Permian (minimum age of approximately 270 ± 5 Ma by U–Pb on zircons, 284 ± 20 Ma by K–Ar on hornblende, and 40Ar/39Ar plateau at 276 ± 31 Ma). Lithologically similar intrusions 20 km to the north near Gold Bridge are also Early Permian (287 ± 20 Ma by K–Ar on hornblende and 320 ± 80 Ma by a Rb–Sr whole-rock isochron). Geochronology, radiogenic and stable isotopes, and fluid-inclusion studies suggest that there were several pulses of mineralizing activity adjacent to and east of the Coast Plutonic Complex (CPC). Decreasing temperatures and younger age of mineralization with increasing distance from the CPC imply that plutons of the CPC were the main heat source responsible for mineralization. The main pulses were about 90 Ma for mesothermal Au–Ag–As ± W,Mo mineralization at Bralorne near the CPC, ranging outwards to 65 Ma for Ag–Au–Sb–As ± Hg mineralization at the Minto and Congress deposits, to 45 Ma for Ag–Au epithermal mineralization at Blackdome, 100 km east of the CPC.The Bralorne intrusions may have been emplaced below the sea floor in a spreading-ridge oceanic environment, as suggested by the petrology of the intrusive suite, which includes serpentinized ultramafite, hornblende diorite, and soda granite (trondhjemite), typical of an ophiolite association. The chemistry of volcanic rocks mapped as Cadwallader Group, which host these intrusive bodies, is transitional from mid-ocean-ridge basalts to island-arc tholeiite, suggesting a back-arc-basin setting. Gradational contact relations between the hornblende diorite and the volcanic rocks suggest that the diorite intruded its own volcanic products. Intrusive contacts of the diorite with adjacent elongate ultramafic bodies imply that the ultramafic rocks are of Permian or older age and had been structurally emplaced into crustal levels by the time of diorite intrusion. In the Bralorne fault block the Bralorne intrusions appear to cut the adjacent Cadwallader and Bridge River groups, implying an Early Permian or older age for at least parts of these groups. Thus, rocks mapped as Cadwallader Group in the Bralorne area could be distinct from and older than lithologic equivalents exposed elsewhere, although they are similar in terms of their petrology and major- and trace-element chemistry.
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Hansen, Torsten Hundebøl, Ole Rønø Clausen i Katrine Juul Andresen. "Thick- and thin-skinned basin inversion in the Danish Central Graben, North Sea – the role of deep evaporites and basement kinematics". Solid Earth 12, nr 8 (4.08.2021): 1719–47. http://dx.doi.org/10.5194/se-12-1719-2021.
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Abstract. Using borehole-constrained 3D reflection seismic data, we analyse the importance of sub-salt, salt, and supra-salt deformation in controlling the geometries and the kinematics of inverted structures in the Danish Central Graben. The Danish Central Graben is part of the failed Late Jurassic North Sea rift. Later tectonic shortening caused mild basin inversion during the Late Cretaceous and Paleogene. Where mobile Zechstein evaporites are present, they have played a significant role in the structural evolution of the Danish Central Graben since the Triassic. Within the study area, Jurassic rifting generated two major W- to SW-dipping basement faults (the Coffee Soil Fault and the Gorm–Tyra Fault) with several kilometres of normal offset and associated block rotation. The Coffee Soil Fault system delineates the eastern boundary of the rift basins, and within its hanging wall a broad zone is characterized by late Mesozoic to early Paleogene shortening and relative uplift. Buttressed growth folds in the immediate hanging wall of the Coffee Soil Fault indicate thick-skinned inversion, i.e. coupled deformation between the basement and cover units. The western boundary of the inverted zone follows the westward pinch-out of the Zechstein salt. Here, thin-skinned folds and faults sole out into Zechstein units dipping into the half-graben. The most pronounced inversion structures occur directly above and in prolongation of salt anticlines and rollers that localized shortening in the cover above. With no physical links to underlying basement faults (if present), we balance thin-skinned shortening to the sub-salt basement via a triangle zone concept. This implies that thin Zechstein units on the dipping half-graben floor formed thrust detachments during inversion while basement shortening was mainly accommodated by reactivation of the major rift faults further east. Disseminated deformation (i.e. “ductile” at seismic scales) accounts for thin-skinned shortening of the cover units where such a detachment did not develop. The observed structural styles are discussed in relation to those found in other inverted basins in the North Sea Basin and to those produced from physical model experiments. Our results indicate that Zechstein units imposed a strong control on structural styles and kinematics not only during rift-related extension but also during basin inversion in large parts of the Danish Central Graben. Reactivated thin-skinned faults soling out into thin Triassic evaporite units within the carapace above Zechstein salt structures illustrate that even thin evaporite units may contribute to defining structures during tectonic extension and shortening. We thus provide an updated and dedicated case study of post-rift basin inversion, which takes into account the mechanical heterogeneity of sub-salt basement, salt, and supra-salt cover, including multiple evaporite units of which the Zechstein is the most important.
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Camacho, Alfredo, i John D. Fitz Gerald. "Misidentification of oxide phases and of twinned kyanite: implications for inferred P-T histories of the Musgrave Block, central Australia". Journal of the Virtual Explorer 35 (2010). http://dx.doi.org/10.3809/jvirtex.2011.00275.
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Wang, Yuan, Changsong Lin, Yanda Sun, Jingyan Liu, Hao Li, Haiquan He, Qinglong Wang i in. "Depositional sequences and microfacies of Lower Carboniferous strata in the Marsel block of the Chu-Sarysu Basin, Southern Kazakhstan". Carbonates and Evaporites 35, nr 2 (18.03.2020). http://dx.doi.org/10.1007/s13146-020-00573-w.
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