scholarly journals Mechanisms of overburden deformation associated with the emplacement of the Tulipan sill, mid-Norwegian margin

2017 ◽  
Vol 5 (3) ◽  
pp. SK23-SK38 ◽  
Author(s):  
Tobias Schmiedel ◽  
Sigurd Kjoberg ◽  
Sverre Planke ◽  
Craig Magee ◽  
Olivier Galland ◽  
...  
Keyword(s):  
Host Rock ◽  
Shear Failure ◽  
Sedimentary Basins ◽  
Rock Deformation ◽  
3D Seismic ◽  
Elastic Bending ◽  
Hydrocarbon Maturation ◽  
Dome Structure ◽  
Well Data ◽  
Host Rocks

The emplacement of igneous intrusions into sedimentary basins mechanically deforms the host rocks and causes hydrocarbon maturation. Existing models of host-rock deformation are investigated using high-quality 3D seismic and industry well data in the western Møre Basin offshore mid-Norway. The models include synemplacement (e.g., elastic bending-related active uplift and volume reduction of metamorphic aureoles) and postemplacement (e.g., differential compaction) mechanisms. We use the seismic interpretations of five horizons in the Cretaceous-Paleogene sequence (Springar, Tang, and Tare Formations) to analyze the host rock deformation induced by the emplacement of the underlying saucer-shaped Tulipan sill. The results show that the sill, emplaced between 55.8 and 54.9 Ma, is responsible for the overlying dome structure observed in the seismic data. Isochron maps of the deformed sediments, as well as deformation of the younger postemplacement sediments, document a good match between the spatial distribution of the dome and the periphery of the sill. The thickness [Formula: see text] of the Tulipan is less than 100 m, whereas the amplitude [Formula: see text] of the overlying dome ranges between 30 and 70 m. Spectral decomposition maps highlight the distribution of fractures in the upper part of the dome. These fractures are observed in between hydrothermal vent complexes in the outer parts of the dome structure. The 3D seismic horizon interpretation and volume rendering visualization of the Tulipan sill reveal fingers and an overall saucer-shaped geometry. We conclude that a combination of different mechanisms of overburden deformation, including (1) elastic bending, (2) shear failure, and (3) differential compaction, is responsible for the synemplacement formation and the postemplacement modification of the observed dome structure in the Tulipan area.

Tectonic stress controls saucer-shaped sill geometry and emplacement mechanism

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 898-902
Author(s):  
R.J. Walker ◽  
S.P.A. Gill
Keyword(s):  
Host Rock ◽  
Shear Failure ◽  
Sedimentary Basins ◽  
Tectonic Stress ◽  
Tensile Failure ◽  
Magma Source ◽  
Primary Control ◽  
Base Length ◽  
Source Pressure ◽  
Emplacement Mechanism

Abstract Saucer-shaped sills are common in sedimentary basins worldwide. The saucer shape relates to asymmetric sill-tip stress distributions during intrusion caused by bending of the overburden. Most saucer-shaped sill models are constructed using a magma-analogue excess source pressure (Po) to drive host-rock failure, but without tectonic stress. Here we present axisymmetric finite-element simulations of radially propagating sills for a range of tectonic stress (σr) conditions, from horizontal tension (σr < 0) to horizontal compression (0 < σr). Response to σr falls into four regimes, based on sill geometry and failure mode of the host rock. The regimes are considered in terms of the ratio of tectonic stress versus magma source pressure R = σr/Po: (I) initially seeded sills transition to a dike during horizontal extension (R < 0); (II) with R increasing from 0 towards 1 (compressive σr), sill base length increases and sill incline decreases; (III) where 1 < R < 2, sill base length relatively decreases and sill incline increases; and (IV) where R > 2, sills grow as inclined sheets. Sills in regimes I–III grow dominantly by tensile failure of the host rock, whereas sills in regime IV grow by shear failure of the host rock. Varying σr achieves a range of sill geometries that match natural sill profiles. Tectonic stress therefore represents a primary control on saucer-shaped sill geometry and emplacement mechanism.

Porosity channeling and fracturing in fluid over-pressure zones

2020 ◽  
Author(s):  
Daniel Koehn ◽  
Sandra Piazolo ◽  
Till Sachau ◽  
Renaud Toussaint
Keyword(s):  
Effective Stress ◽  
Shear Failure ◽  
Sedimentary Basin ◽  
Fluid Pressure ◽  
Sedimentary Basins ◽  
Horizontal Layer ◽  
Mean Stress ◽  
Porosity Evolution ◽  
Hydrocarbon Maturation ◽  
Approach Zero

<p>It is important to understand the effects of fluid over-pressure in rocks because gradients in over-pressure can lead to failure of rocks and expulsion of fluids. Examples are hydro-fracturing in engineering as well as fluid generation during hydrocarbon maturation, metamorphic reactions or over-pressure below seals in sedimentary basins. In order to have an understanding of the complexity of effective stress fields, fracture, failure and fluid drainage the process was studied with a dynamic hydro-mechanical numerical model. The evolution of fluid pressure build up, fracturing and the dynamic interaction between solid and fluid is modeled. Three scenarios are studied: fluid pressure build up in a sedimentary basin, in a confined zone and in a horizontal layer that is offset by a fault. Results indicate that the geometry of the fluid-overpressure zone has a first order control on the patterns including porosity evolution and fracturing. If the over-pressure develops below a seal in a sedimentary basin, the effective differential and mean stress approach zero and the horizontal and vertical effective stresses flip in orientation leading to horizontal hydro-factures or breccia zones. If the over-pressure zone is confined vertically as well, the standard effective stress model develops with the effective mean stress decreasing while the differential stress remains mainly constant. This leads to semi-vertically aligned extensional and conjugate shear failure at much lower over-pressures than in the sedimentary basin. A perfectly aligned horizontal layer that increases in fluid pressure internally leads to a horizontal hydro-fracture within the layer. A faulted layer develops complex multi-directional failure with the fault itself being a location of early fracturing followed by brecciation of the layer itself. All simulations undergo a phase transition in porosity evolution with an initially random porosity reducing its symmetry and forming a static porosity wave with an internal dilation zone and the development of dynamic porosity channels within this zone that drain the over-pressure. Our results show that patterns of fractures, hence fluid release, that form due to high fluid overpressures can only be successfully predicted if the geometry of the geological system is known, including the fluid overpressure source and the position of seals and faults that offset source layers and seals.</p>

scholarly journals Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology

Minerals ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 195 ◽  
Author(s):  
Wenheng Liu ◽  
Xiaodong Liu ◽  
Jiayong Pan ◽  
Kaixing Wang ◽  
Gang Wang ◽  
...  
Keyword(s):  
Host Rock ◽  
Inductively Coupled Plasma ◽  
Magma Mixing ◽  
Coarse Grained ◽  
Calc Alkaline ◽  
Quartz Crystals ◽  
Alkaline Rocks ◽  
Mafic Enclaves ◽  
Normal Zoning ◽  
Host Rocks

The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 5.2 Ma (MSWD (mean standard weighted deviation)= 1.5, n = 14) and 432.8 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period.

Compositional variation in the chevkinite group: new data from igneous and metamorphic rocks

2009 ◽  
Vol 73 (5) ◽  
pp. 777-796 ◽  
Author(s):  
R. Macdonald ◽  
H. E. Belkin ◽  
F. Wall ◽  
B. Baginski
Keyword(s):  
Electron Microprobe ◽  
Host Rock ◽  
Metamorphic Rocks ◽  
Compositional Variation ◽  
Temperature Range ◽  
Wide Range ◽  
Host Rocks ◽  
Cation Sites ◽  
Dominant Cation

AbstractElectron microprobe analyses are presented of chevkinite-group minerals from Canada, USA, Guatemala, Norway, Scotland, Italy and India. The host rocks are metacarbonates, alkaline and subalkaline granitoids, quartz-bearing pegmatites, carbonatite and an inferred K-rich tuff. The analyses extend slightly the range of compositions in the chevkinite group, e.g. the most MgO-rich phases yet recorded, and we report two further examples where La is the dominant cation in the A site. Patchily- zoned crystals from Virginia and Guatemala contain both perrierite and chevkinite compositions. The new and published analyses are used to review compositional variation in minerals of the perrierite subgroup, which can form in a wide range of host rock compositions and over a substantial pressure- temperature range. The dominant substitutions in the various cation sites and a generalized substitution scheme are described.

Competence and lithostratigraphy of host rocks govern kimberlite pipe morphology

2018 ◽  
Vol 55 (2) ◽  
pp. 130-137
Author(s):  
David E. Newton ◽  
Amy G. Ryan ◽  
Luke J. Hilchie
Keyword(s):  
Host Rock ◽  
Sedimentary Rock ◽  
Kimberlite Pipe ◽  
Crystalline Rock ◽  
Experimental Results ◽  
Compressed Air ◽  
Unconsolidated Sediments ◽  
Final Shape ◽  
Class 1 ◽  
Host Rocks

We use analogue experimentation to test the hypothesis that host rock competence primarily determines the morphology of kimberlite pipes. Natural occurrences of kimberlite pipes are subdivided into three classes: class 1 pipes are steep-sided diatremes emplaced into crystalline rock; class 2 pipes have a wide, shallow crater emplaced into sedimentary rock overlain by unconsolidated sediments; class 3 pipes comprise a steep-sided diatreme with a shallow-angled crater emplaced into competent crystalline rock overlain by unconsolidated sediments. We use different configurations of three analogue materials with varying cohesions to model the contrasting geological settings observed in nature. Pulses of compressed air, representing the energy of the gas-rich head of a kimberlitic magma, are used to disrupt the experimental substrate. In our experiments, the competence and configuration of the analogue materials control the excavation processes as well as the final shape of the analogue pipes: eruption through competent analogue strata results in steep-sided analogue pipes; eruption through weak analogue strata results in wide, shallow analogue pipes; eruption through intermediate strength analogue strata results in analogue pipes with a shallow crater and a steep-sided diatreme. These experimental results correspond with the shapes of natural kimberlite pipes, and demonstrate that variations in the lithology of the host rock are sufficient to generate classic kimberlite pipe shapes. These findings are consistent with models that ascribe the pipe morphologies of natural kimberlites to the competence of the host rocks in which they are emplaced.

scholarly journals EFFECTS OF IGNEOUS INTRUSION ON THE MINERALOGICAL CONTENT OF IRATI FORMATION, PARANÁ BASIN, IN SAPOPEMA (PR), SOUTHERN BRAZIL

2019 ◽  
Vol 4 (3) ◽  
pp. 350-360
Author(s):  
Werlem Holanda ◽  
Anderson Costa dos Santos ◽  
Camila Cardoso Nogueira ◽  
Luiz Carlos Bertolino ◽  
Sérgio Bergamaschi ◽  
...  
Keyword(s):  
Host Rock ◽  
Mineral Assemblage ◽  
Sedimentary Basins ◽  
Southern Brazil ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mineralogical Association ◽  
Irati Formation ◽  
Igneous Intrusions ◽  
Rock Association

Igneous intrusions in sedimentary basins are commonly related with mineralogical association changes in host-rock. At Sapopema region (Paraná State, southern Brazil), an extensive diabase sill (associated to Serra Geral Formation) was emplaced in pelitic-carbonate succession during post-Triassic. The sedimentary host-rock association includes mostly shale, siltstone and carbonate of the Permian Irati Formation. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) data revealed that heat transfer was not enough to cause modifications in mineral assemblage of the Taquaral Member (quartz + albite + muscovite + illite + kaolinite + chlorite). However, mineralogical content from Assistência Member presented changes probably caused by the intrusion of diabase sill (talc + pyrophyllite + calcite). Talc and calcite were formed due to the reaction between dolomite and quartz, while pyrophyllite was the product of reaction between kaolinite and quartz. EFEITOS DA INTRUSÃO IGNEA NA COMPOSIÇÃO MINERALÓGICA DA FORMAÇÃO IRATI, BACIA DO PARANÁ, SAPOPEMA (PR), SUL DO BRASIL ResumoAs intrusões ígneas em bacias sedimentares dão origem em geral a alterações mineralógicas da rocha hospedeira. Na região de Sapopema (Estado do Paraná, sul do Brasil), uma extensa soleira de diabásio (associada à Formação Serra Geral) pós-Triássica, foi intrudida numa sucessão sedimentar constituída por pelitos e carbonatos. A associação de rochas sedimentares hospedeiras, era principalmente constituída por folhelho, siltito e carbonato da Formação Irati, do Permiano. Dados de difração de raios X (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS) revelaram que a transferência de calor não foi suficiente para causar modificações na composição mineralógica do membro Taquaral (quartzo + albita + moscovita + ilita + caulinita + clorita). No entanto, o conteúdo mineralógico do Membro Assistência apresentou alterações, provavelmente causadas pela intrusão do diabásio (talco + pirofilita + calcita). O talco e a calcita foram formados devido à reação entre dolomita e quartzo, enquanto a pirofilita foi o produto da reação entre a caulinita e o quartzo. Palavras-chave: Bacia Sedimentar. Intrusões Ígneas. Metamorfização de sedimentos. Reações mineralógicas. XRD. SEM / EDS.

scholarly journals Permeability Changes Resulting from Quartz Precipitation and Dissolution around Upper Crustal Intrusions

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-19 ◽  
Author(s):  
Samuel W. Scott ◽  
Thomas Driesner
Keyword(s):  
Host Rock ◽  
Permeability Reduction ◽  
Rock Permeability ◽  
Permeability Changes ◽  
Order Of Magnitude ◽  
Porosity And Permeability ◽  
Fluid Convection ◽  
Flow Heat ◽  
Primary Porosity ◽  
Host Rocks

It has long been recognized that quartz precipitation from circulating hydrothermal fluids may reduce porosity and permeability near intrusions. However, the magnitude of permeability changes and potential feedbacks between flow, heat transfer, and quartz precipitation/dissolution remain largely unquantified. Here, we present numerical simulations of fluid convection around upper crustal intrusions which explicitly incorporate the feedback between quartz solubility and rock permeability. As groundwater is heated to ~350°C, silica dissolves from the host rock, increasing porosity and permeability. Further heating to supercritical conditions leads to intensive quartz precipitation and consequent permeability reduction. The initial host rock permeability and porosity are found to be main controls on the magnitude and timescales of permeability changes. While the permeability changes induced by quartz precipitation are moderate in host rocks with a primary porosity ≥ 0.05, quartz precipitation may reduce rock permeability by more than an order of magnitude in host rocks with a primary porosity of 0.025. Zones of quartz precipitation transiently change locations as the intrusion cools, thereby limiting the clogging effect, except for host rocks with low initial porosity. This permeability reduction occurs in timescales of hundreds of years in host rocks with initial high permeability and thousands of years in host rocks with intermediate permeability.

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