scholarly journals New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland

2021 ◽  
pp. jgs2021-066
Author(s):  
A. Tamas ◽  
R.E. Holdsworth ◽  
J.R. Underhill ◽  
D.M. Tamas ◽  
E.D. Dempsey ◽  
...  
Keyword(s):  
Early Cretaceous ◽  
Fault Reactivation ◽  
Rift System ◽  
Seismic Reflection Data ◽  
Structural Inheritance ◽  
Basin Scale ◽  
Calcite Veins ◽  
Moray Firth ◽  
Supplementary Material ◽  
Orcadian Basin

The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic-Early Cretaceous with the widespread development of major NE-SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly due to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U-Pb geochronology have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip N-S to NNE-SSW-striking Devonian growth faults are recognised that have undergone later dextral reactivation during NNW-SSE extension. The U-Pb calcite dating of a sample from the syn-kinematic calcite veins associated with this later episode shows that the age of fault reactivation is 131.73 ± 3.07 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5635432

New insights into the kinematics and timing of superimposed rifting events through integration of offshore data, onshore fieldwork and U-Pb geochronology: Inner Moray Firth Basin, Scotland

2020 ◽  
Author(s):  
Alexandra Tamas ◽  
Robert Holdsworth ◽  
John Underhill ◽  
Kenneth McCaffrey ◽  
Eddie Dempsey ◽  
...  
Keyword(s):  
Seismic Data ◽  
Upper Jurassic ◽  
Fault Reactivation ◽  
Full Potential ◽  
Rift Basin ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
Moray Firth ◽  
Orcadian Basin ◽  
3D Seismic Data

<p>Keywords: inherited structures, fault reactivation, U-Pb geochronology</p><p>The E-W striking Inner Moray Firth Basin (IMFB) lies in the western part of the North Sea trilete rift system formed mainly in the Upper Jurassic. The IMFB has experienced a long history of superimposed rifting with plenty of uplift and fault reactivation during Cenozoic. The basin is overlying the Caledonian basement, the pre-existing Devonian-Carboniferous (Orcadian Basin) and a regionally developed Permo-Triassic basin. The potential influence of older structures related to the Orcadian Basin on the kinematics of later basin opening has received little attention, partly due to the poor resolution of seismic reflection data at depth or sparse well data.</p><p>By integrating onshore fieldwork with the interpretation of 2D and 3D seismic data and U-Pb geochronology of syndeformationally grown calcite we provide new insights into the kinematic opening of the basin as well as the role of pre-existing Devonian-Carboniferous (Orcadian) basin structures.</p><p>The Jurassic opening of the rift basin is known to be associated with major NE-SW trending faults. New detailed mapping of offshore 3D seismic data revealed that at a smaller scale en-echelon E-W to NE-SW trending faults, en-echelon N-S to NNE-SSW and NW-SE fault arrays coexist. This suggests an oblique-sinistral component associated with the major NE-SW rift basin trends. This correlates with onshore findings, which suggest that the inherited Orcadian fault systems (mainly N-S to NE-SW) have been dextrally reactivated. Sinistral WNW-SSE to NW-SE striking faults and associated transtensional folds are also present in the Devonian rocks. This later deformation is consistently associated with calcite mineralization (e.g. slickenfibers, calcite tensile veins or Riedel shear fractures). New U-Pb dating of the calcite mineralization, related to the reactivated faults, shows that the age of fault reactivation is 153 ± 0.68 Ma (Upper Jurassic).</p><p>The integration of fieldwork with subsurface interpretations and absolute dating techniques has provided better constraints on superimposed basin development, as well as explaining complexities that have hitherto been ignored. This can reduce subsurface uncertainties regarding the structural evolution of the basin and unlock the full potential of the area and significantly enhance future exploration programs.</p>

scholarly journals Zircon U-Pb and Pyrite Re-Os Isotope Geochemistry of ‘Skarn-Type’ Fe-Cu Mineralization at the Shuikoushan Polymetallic Deposit, South China: Implications for an Early Cretaceous Mineralization Event in the Nanling Range

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 480
Author(s):  
Shengbin Li ◽  
Yonghua Cao ◽  
Zeyou Song ◽  
Dan Xiao
Keyword(s):  
Contact Zone ◽  
Early Cretaceous ◽  
South China ◽  
Isotope Geochemistry ◽  
Time Interval ◽  
Mean Square ◽  
Geochronological Data ◽  
Nanling Range ◽  
Calcite Veins ◽  
Os Isotope

The Shuikoushan deposit is an economic ‘skarn-type’ polymetallic Pb-Zn deposit in South China. The deposit is located at the southern margin of the Hengyang basin in the northern part of the Nanling Range. Recently, economic Fe-Cu mineralization that occurs spatially connected to skarns along the contact zone between the granodiorite and limestones was discovered in the lower part of this deposit. Detailed zircon U-Pb geochronological data indicate that the granodiorite was emplaced at 153.7 ± 0.58 Ma (Mean Square of Weighted Deviates (MSWD) = 2.4). However, the pyrite Re-Os isochron age reveals that Fe-Cu mineralization formed at 140 ± 11 Ma (MSWD) = 8.1), which post-dates the emplacement of the granodiorite, as well as the previously determined timing of Pb-Zn mineralization (157.8 ± 1.4 Ma) in this deposit. Considering that Fe-Cu mineralization was connected with the contact zone and also faults, and that sulfide minerals commonly occur together with quartz and calcite veins that crosscut skarns, we interpret this mineralization type as being related to injection of post-magmatic hydrothermal fluids. The timing of Fe-Cu mineralization (140 ± 11 Ma) is inconsistent with a long-held viewpoint that the time interval of 145 to 130 Ma (e.g., Early Cretaceous) in the Nanling Range is a period of magmatic quiescence with insignificant mineralization, the age of 140 Ma may represent a new mineralization event in the Nanling Range.

First evidence for tooth-tooth occlusion in a ctenochasmatid pterosaur from the Early Cretaceous Jehol Biota

2021 ◽  
pp. SP521-2021-141
Author(s):  
Chang-Fu Zhou ◽  
Xinyue Wang ◽  
Jiahao Wang
Keyword(s):  
Early Cretaceous ◽  
Feeding Strategy ◽  
Three Dimensional ◽  
Tooth Wear ◽  
First Record ◽  
Jehol Biota ◽  
Content Type ◽  
Dimensional Reconstruction ◽  
Supplementary Material ◽  
Ct Data

AbstractCtenochasmatid pterosaurs flourished and diversified in the Early Cretaceous Jehol Biota. Here, a partial mandible of Forfexopterus is described based on a three-dimensional reconstruction using high-resolution X-ray Computed Tomography (CT) data. The first nine pairs of functional teeth of the rostral dentition revealed along with their replacements. The functional teeth are evenly arranged with a tooth density of 2.2 teeth/cm. The tooth crown is distinctly reduced from its base to the tip, and framed by two weak ridges, possibly as a pair of vestigial carinae. The replacement teeth are sharp and pointed, and have erupted slightly against the medial surface of the functional teeth. Surprisingly, tooth wear is observed in this specimen, the first record of tooth-tooth occlusion in ctenochasmatids. The wear facets exhibit high-angled lingual and lower-angled labial facets, implying a tooth-tooth occlusion in pterosaur clade. This discovery indicates that the Jehol ctenochasmatids possibly employed a more active feeding strategy than other filter-feeding pterosaurs (e.g. Ctenochasma, Pterodaustro, Gnathosaurus).Supplementary material at https://doi.org/10.6084/m9.figshare.c.5722060

Three-dimensional geometry and growth of a basement-involved fault network developed during multiphase extension, Enderby Terrace, North West Shelf of Australia

2021 ◽  
Author(s):  
Hongdan Deng ◽  
Ken McClay
Keyword(s):  
Three Dimensional ◽  
Sedimentary Basins ◽  
Fault Reactivation ◽  
Late Triassic ◽  
Seismic Reflection Data ◽  
North West ◽  
Reflection Data ◽  
Data Volume ◽  
Vertical Linkages ◽  
Fault Network

<div>Basement fault reactivation, and the growth, interaction, and linkage with new fault segments are fundamentally three-dimensional and critical for understanding the evolution of fault network development in sedimentary basins. This paper analyses the evolution of a complex, basement-involved extensional fault network on the Enderby Terrace on the eastern margin of the Dampier sub-basin, NW Shelf of Australia. A high-resolution, depth-converted, 3D seismic reflection data volume is used to show that multiphase, oblique extensional reactivation of basement-involved faults controlled the development of the fault network in the overlying strata. Oblique reactivation of the pre-existing faults initially led to the formation of overlying, en échelon Late Triassic – Middle Jurassic fault segments that, as WNW–directed rifting progressed on the margin, linked by breaching of relay ramp to form two intersecting fault systems (F1 and F2-F4). Further reactivation in the Latest Jurassic – Early Cretaceous (NNW–SSE extension) produced an additional set of en échelon fault arrays in the cover strata. The final fault network consists of main or principal faults and subordinate or splay faults, together with branch lines that link the various components. Our study shows that breaching of relay ramps and/or vertical linkages produces vertical and horizontal branch lines giving complex final fault geometries. We find that repeated activity of the basement-involved faults tends to form continuous and planar fault architectures that favor displacement transfer between the main constituent segments along strike and with depth.</div>

scholarly journals Structural controls on the location, geometry and longevity of an intraplate volcanic system: the Tuatara Volcanic Field, Great South Basin, New Zealand

2020 ◽  
Vol 177 (5) ◽  
pp. 1039-1056
Author(s):  
Thomas B. Phillips ◽  
Craig Magee
Keyword(s):  
Volcanic Field ◽  
Auckland Volcanic Field ◽  
Seismic Section ◽  
Volcanic System ◽  
Seismic Reflection Data ◽  
Content Type ◽  
Reflection Data ◽  
3D Geometry ◽  
Plumbing Systems ◽  
Supplementary Material

Intraplate volcanism is widely distributed across the continents, but the controls on the 3D geometry and longevity of individual volcanic systems remain poorly understood. Geophysical data provide insights into magma plumbing systems, but, as a result of the relatively low resolution of these techniques, it is difficult to evaluate how magma transits highly heterogeneous continental interiors. We use borehole-constrained 2D seismic reflection data to characterize the 3D geometry of the Tuatara Volcanic Field located offshore New Zealand's South Island and investigate its relationship with the pre-existing structure. This c. 270 km2 field is dominated by a dome-shaped lava edifice, surrounded and overlain by c. 69 volcanoes and >70 sills emplaced over 40 myr from the Late Cretaceous to Early Eocene (c. 85–45 Ma). The Tuatara Volcanic Field is located above a basement terrane boundary represented by the Livingstone Fault; the recently active Auckland Volcanic Field is similarly located along-strike on North Island. We suggest that the Livingstone Fault controlled the location of the Tuatara Volcanic Field by producing relief at the base of the lithosphere, thereby focussing lithospheric detachment over c. 40 myr, and provided a pathway that facilitated the ascent of magma. We highlight how observations from ancient intraplate volcanic systems may inform our understanding of active intraplate volcanic systems, including the Auckland Volcanic Field.Supplementary material: Interpreted seismic section showing well control on stratigraphic interpretation is available at https://doi.org/10.6084/m9.figshare.c.5004464

scholarly journals Outcrop-scale manifestations of reactivation during multiple superimposed rifting and basin inversion events: the Devonian Orcadian Basin, northern Scotland

2020 ◽  
Vol 178 (1) ◽  
pp. jgs2020-089 ◽  
Author(s):  
A.M. Dichiarante ◽  
R.E. Holdsworth ◽  
E.D. Dempsey ◽  
K.J.W. McCaffrey ◽  
T.A.G. Utley
Keyword(s):  
Structural Complexity ◽  
Structural Data ◽  
Dominant Group ◽  
Content Type ◽  
Basin Inversion ◽  
Supplementary Material ◽  
Group 2 ◽  
Orcadian Basin ◽  
East West ◽  
Group 1

The Devonian Orcadian Basin in Scotland hosts extensional fault systems assumed to be related to the initial formation of the basin, with only limited post-Devonian inversion and reactivation. However, a recent detailed structural study across Caithness, underpinned by published Re–Os geochronology, shows that three phases of deformation are present. North–south- and NW–SE-trending Group 1 faults are related to Devonian ENE–WSW transtension associated with sinistral shear along the Great Glen Fault during the formation of the Orcadian Basin. Metre- to kilometre-scale north–south-trending Group 2 folds and thrusts are developed close to earlier sub-basin-bounding faults and reflect late Carboniferous–early Permian east–west inversion associated with dextral reactivation of the Great Glen Fault. The dominant Group 3 structures are dextral oblique NE–SW-trending and sinistral east–west-trending faults with widespread syndeformational carbonate mineralization (± pyrite and bitumen) and are dated using Re–Os geochronology as Permian (c. 267 Ma). Regional Permian NW–SE extension related to the development of the offshore West Orkney Basin was superimposed over pre-existing fault networks, leading to local oblique reactivation of Group 1 faults in complex localized zones of transtensional folding, faulting and inversion. The structural complexity in surface outcrops onshore therefore reflects both the local reactivation of pre-existing faults and the superimposition of obliquely oriented rifting episodes during basin development in the adjacent offshore areas.Supplementary material: Stereographic projections of compiled structural data from individual fieldwork localities are available at https://doi.org/10.6084/m9.figshare.c.5115228

MARGIN-SCALE, BASEMENT-INVOLVED COMPARTMENTALISATION OF AUSTRALIA'S NORTH WEST SHELF: A PRIMARY CONTROL ON BASIN-SCALE RIFT, DEPOSITION AL AND REACTIVATION HISTORIES

1999 ◽  
Vol 39 (1) ◽  
pp. 40 ◽  
Author(s):  
G.W. O'Brien ◽  
M. Morse ◽  
D. Wilson ◽  
P. Quaife ◽  
J. Colwell ◽  
...  
Keyword(s):  
Transition Zone ◽  
Fault Reactivation ◽  
Small Displacement ◽  
Driving Mechanism ◽  
Fracture System ◽  
Primary Control ◽  
North West ◽  
Seal Failure ◽  
Lithospheric Flexure ◽  
Basin Scale

Australia's North West Shelf is segmented into four discrete margin-scale compartments which have distinct rift and reactivation histories. Two of the margin segments, the Carnarvon and Bonaparte compartments, are very wide (500–600 km), marginal plateau systems, whereas the other two segments, the Canning and Browse compartments, are narrower and steeper. The boundaries between individual rift compartments appear to be controlled by Proterozoic fracture systems.The Browse-Bonaparte transition zone is a major, northwest-trending Proterozoic fracture system which has a series of igneous intrusions along its length. These intrusions are located where the fracture system is cut by younger, northeast-trending extensional faults. This transition zone is a margin-scale fault relay zone, with intense fault overlap along the transition resulting in the zone being a long-lived, syn-rift high. Moreover, the transition zones between adjacent wide and narrow margins are prime locations for the entry point of siliciclastics into the rift or post-rift margin system. As a result, well-developed channel systems often cut through these boundaries and high quality reservoirs (particularly low-stand fans) are developed.Neogene fault reactivation, associated with convergence of the Australasian and Eurasian plates, is evident along the North West Shelf. The style of this reactivation is, however, closely controlled by the margin- scale architecture. In the Browse and Carnarvon basins, Neogene inversion is common, but at the leading edge of the collisional system, the Bonaparte compartment, the fault style is exclusively extensional. It appears that lithospheric flexure, associated with localised foreland development (i.e. the Timor Trough), has been the driving mechanism for the extensional faulting within the Bonaparte compartment. Crustal convergence seems to have been accommodated completely by thrusting on the northwestern margin of Timor and by foreland formation. In contrast, the Browse and Carnarvon compartments lacked a 'buffering' foreland system and, being adjacent to rigid and thin oceanic crust which transmits stress well over long distances, the inversional stresses were transmitted directly into these compartments.As a result of these margin-scale processes, the Bonaparte compartment is characterised by a thin regional seal (often 100 ms) on Neogene extensional faults—a combination which strongly favours fault seal failure and trap breach. In contrast, the Browse compartment is characterised by thick seals and small displacement Neogene faults, and thus the probability of fault seal failure is much less.

Formation of wide-blocky calcite veins by extreme growth competition

2020 ◽  
pp. jgs2020-104
Author(s):  
Liene Spruženiece ◽  
Michael Späth ◽  
Janos L. Urai ◽  
Estibalitz Ukar ◽  
Michael Selzer ◽  
...  
Keyword(s):  
High Resolution ◽  
Growth Rates ◽  
Polarized Light ◽  
Wall Rock ◽  
Scattered Electron ◽  
Thin Sections ◽  
Content Type ◽  
Calcite Veins ◽  
Supplementary Material ◽  
Electron Back Scattered Diffraction

Liassic limestones on the coast of Somerset in the UK contain dense arrays of calcite microveins with a common, but poorly understood microstructure, characterized by laterally wide crystals that form bridges across the vein. We investigated the mechanisms of formation and evolution of these ‘wide-blocky’ vein microstructures using a combination of high-resolution analytical methods, including virtual petrography, optical cathodoluminescence and scanning electron microscopy techniques (e.g. energy-dispersive X-ray spectrometry, back-scattered electron imaging, cathodoluminescence and electron back-scattered diffraction), laboratory experiments and multiphase field modelling. Our results indicate that the studied veins formed in open, fluid-filled fractures, each in a single opening and sealing episode. As shown by the optical and electron back-scattered diffraction images, the vein crystals grew epitaxially on grains of the wall rock and we hypothesize that their growth rates differed depending on whether the crystals were on a wall rock grain substrate that fractured intergranularly (slow growth rates) or transgranularly (rapid growth rates). Our multiphase field models support this hypothesis, showing that wide, blocky crystals only form where there are significant differences in the growth rate and are dependent on the type of seed grain. These results provide strong evidence for extreme growth competition, a process that we propose controls vein-filling in many micritic carbonate reservoirs, as well as demonstrate that the characteristics of the fracture wall can affect the filling processes in syntaxial veins.Supplementary material: The description and images of the studied thin sections are available at https://doi.org/10.6084/m9.figshare.c.5172371. High-resolution optical microscopy mosaics (under plane-polarized- and crossed polarized light) of the thin section collection in PetroScan file format are available on request from the authors.

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