Evidence for Basement Reactivation during the Opening of the Labrador Sea from the Makkovik Province, Labrador, Canada: Insights from Field Data and Numerical Models

The onshore exposures adjacent to modern, offshore passive continental margins may preserve evidence of deformation from the pre-, syn-, and post-rift phases of continental breakup that allow us to investigate the processes associated with and controlling rifting and breakup. Here, we characterize onshore brittle deformation and pre-rift basement metamorphic mineral fabric from onshore Labrador in Eastern Canada in the Palaeoproterozoic Aillik Domain of the Makkovik Province. Stress inversion (1) was applied to these data and then compared to (2) numerical models of hybrid slip and dilation tendency, (3) independent calculations of the regional geopotential stress field, and (4) analyses of palaeo-stress in proximal regions from previous work. The stress inversion shows well-constrained extensional deformation perpendicular to the passive margin, likely related to pre-breakup rifting in the proto-Labrador Sea. Hybrid slip and dilatation analysis indicates that inherited basement structures were likely oriented in a favorable orientation to be reactivated during rifting. Reconstructed geopotential stresses illuminate changes of the ambient stress field over time and confirm the present paleo-stress estimates. The new results and numerical models provide a consistent picture of the late Mesozoic-Cenozoic lithospheric stress field evolution in the Labrador Sea region. The proto-Labrador Sea region was characterized by a persistent E–W (coast-perpendicular) extensional stress regime, which we interpret as the pre-breakup continental rifting that finally led to continental breakup. Later, the ridge push of the Labrador Sea spreading ridge maintained this general direction of extension. We see indications for anti-clockwise rotation of the direction of extension along some of the passive margins. However, extreme persistent N–S-oriented extension as indicated by studies further north in West Greenland cannot be confirmed.

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Tectonic stress patterns along the Vrancea subcrustal zone from the inversion of focal mechanisms data

10.5194/egusphere-egu21-15620 ◽

2021 ◽

Author(s):

Andreea Craiu ◽

Marius Craiu ◽

Mariu Mihai ◽

Elena Manea ◽

Alexandru Marmureanu

Keyword(s):

Stress Field ◽

Large Scale ◽

Fault Plane ◽

Numerical Models ◽

Moment Tensor ◽

Stress Inversion ◽

Slab Geometry ◽

Fault Plane Solutions ◽

Current Stress ◽

Stress Patterns

The Vrancea zone is an unique area with both crustal and intermediate-depth seismic activity and constitutes one of the most active seismic area in Europe.&#160; An intense and persistent seismicity is generated between 60 and 180 km depth, within a relic slab sinking nearly vertical in the Earth&#8217;s mantle due to the increasing of the stress state within this volume. At intermediate-depths, large magnitude events are frequent, i.e. four earthquakes with moment magnitudes (Mw) >7 occurred in the last century. An unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region.In this study, we evaluate the current stress field along the Vrancea subcrustal region by computing the fault plane solutions of 422 seismic events since January 2005. The continuous development of the National Seismic Network allows us to constrain the fault plane solutions and subsequently to evaluate the current stress field.The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the first one with the nodal planes oriented NE-SW parallel with the Carpathian Arc and the second one with the nodal planes oriented NW-SE perpendicular on the Carpathian Arc. The main axis of the moment tensor may indicate a predominant compressional stress field (Tpl>450 Ppl<450). Another characteristic of&#160; the Vrancea subcrustal zone is the tendency of the extension axis T to be almost vertical and the compression axis P being almost horizontal.The results of stress inversion indicate a dominant reverse faulting style, with an average stress regime index of 2.9. Other tectonic regimes were observed in the present dataset as normal and strike-slip but they are retrieved for a restrained number of events.The stress patterns obtained from formal stress inversion of focal mechanism solutions reveal many features of the current stress field that were not captured by large-scale numerical models.

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Seismogenesis in Eastern Canada

Seismological Research Letters ◽

10.1785/gssrl.59.4.219 ◽

1988 ◽

Vol 59 (4) ◽

pp. 219-225 ◽

Cited By ~ 3

Author(s):

H. S. Hasegawa

Keyword(s):

Labrador Sea ◽

Spreading Ridge ◽

Seismic Zone ◽

Eastern Canada ◽

Postglacial Rebound ◽

Mountain Ranges ◽

Moderate Seismicity ◽

Geophysical Processes ◽

Large Earthquakes ◽

Weak Zones

Abstract The pattern of seismicity in eastern Canada depends on the presence of weak zones from previous major tectonic orogenies and how these weak zones are reactivated by local and regional stress fields and geophysical processes. Within the Canadian Shield, away from seismotectonic trends, there is a low level of seismicity and earthquakes tend to be small, less than M5. However, along seismically active trends, earthquakes as large as M7 have occurred. The seismotectonic features fall into four main categories: positive (uplift) continental basement linears; grabens formed by old plate separation; passive rifted margins offshore; and extinct spreading ridges. Two of the positive seismotectonic trends are the Boothia Uplift-Bell Arch that transects the northeastern part of the craton and northeastern Baffin Island, where the effects of postglacial rebound on the upper crustal stress field are the most pronounced. The St. Lawrence Valley (and interconnecting grabens) is a seismically active graben system that contains the most seismically active region (the Charlevoix zone) in eastern Canada. The extinct spreading ridge along the Labrador Sea and the Mesozoic rifted margin along Baffin Bay and Labrador Sea contain clusters of moderate seismicity. There are diffuse zones of moderate seismicity over some geological provinces (e.g. Central Metasedimentary Belt in western Quebec) apart from major tectonic features, a confined seismic zone (within an intrusion) in the Miramichi region and seismicity at the intersection of faults in northern Ontario. In the Nahanni region, which is situated near the boundary between the northeast Cordillera and the Interior Platform, the commencement of a noteworthy earthquake sequence with magnitude up to Ms 6.9 indicates considerable stress-strain build-up over a large area. There is an anticline in the epicentral area that is bounded by thrust faults and mountain ranges. In order to enhance our understanding of causative factors of current seismicity, it is necessary to determine in greater detail the tectonic forces and geophysical processes that are reactivating pre-weakened faults along the seismotectonic trends and over broad, diffuse seismogenic regions. Some of these factors are the rate of stress build-up, stress concentration at the intersection of faults and between mountain ranges, residual stress, the role of pore fluids, individual block movement, whether this movement is due to postglacial rebound or to other underlying viscoelastic phenomena and the rate of sediment deposition along the continental slope. Paleoseismicity is useful not only for the reconstruction of old large earthquakes but also for providing insight as to why surface fault offsets have not been observed in regions where large earthquakes (and associated high rate of microseisrnicity) have occurred within the past several hundred years.

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An Open-Access Stress Magnitude Database for Germany

Safety of Nuclear Waste Disposal ◽

10.5194/sand-1-71-2021 ◽

2021 ◽

Vol 1 ◽

pp. 71-72

Author(s):

Sophia Morawietz ◽

Moritz Ziegler ◽

Karsten Reiter ◽

Keyword(s):

Stress State ◽

Stress Field ◽

Site Selection ◽

Selection Process ◽

Numerical Models ◽

Spatial Scales ◽

Damage Zone ◽

Hydraulic Permeability ◽

Stress Regime ◽

Migration Pathways

Abstract. The stress field in the Earth's crust plays a central role in the site-selection process for a deep geological repository for high-level nuclear waste. Site selection and construction planning must take into account several factors that are influenced by the stress state. These include the excavation damage zone, the hydraulic permeability of the host rock, the self-sealing capacity, the effects of seismic events and the possible reactivation of faults as migration pathways for fluids and radionuclides. Likewise, the initial stress state is of central importance for the long-term studies to prove site safety over 1 Ma. To obtain a continuous description of the current 3D stress state, 3D geomechanical numerical models are used. These models have to be calibrated with data on stress magnitudes to obtain robust predictions. One of the central goals of the SpannEnD project (Spannungsmodell Endlagerung Deutschland, http://www.spannend-projekt.de, last access: 31 October 2021) was to build the first comprehensive and publicly accessible stress magnitude database for Germany, including a quality ranking of the data compiled from different methods. This database is the logical extension of the database of the World Stress Map project, in which so far only information on stress orientations and the stress regime has been compiled systematically. We present this first compilation of stress magnitude data published and made available by Morawietz et al. (2020). The stress data density is generally low and heterogeneous, so that a model calibration at the scale of a site model is not possible. Therefore, the main objective of the SpannEnD project is to develop a 3D geomechanical numerical model for the whole of Germany. The resulting 3D stress field will provide the basis for regional and local models in a later phase of the site selection process. Details on this are presented in three complementary contributions in this symposium by Reiter et al., Röckel et al. and Ahlers et al. The new Geology Data Act (Geologie-Datengesetz) now allows access to considerably more data, which will be incorporated into an update of the database after assessment according to the defined quality criteria. This database extension will improve the reliability of the predictions of the geomechanical models on different spatial scales.

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Earthquakes along the Northwestern Boundary of the Labrador Sea

Seismological Research Letters ◽

10.1785/gssrl.63.4.587 ◽

1992 ◽

Vol 63 (4) ◽

pp. 587-602 ◽

Cited By ~ 2

Author(s):

Allison L. Bent ◽

Henry S. Hasegawa

Keyword(s):

Hot Spot ◽

Source Parameters ◽

Normal Fault ◽

Gravity Anomalies ◽

Tectonic Stress ◽

Passive Margin ◽

Labrador Sea ◽

Spreading Ridge ◽

Fault Plane Solutions ◽

Thrust Faulting

Abstract As in much of northeastern Canada, earthquakes in the Labrador Sea occur predominantly along the passive margin. Geologically and geophysically, this region is complex and consists of an extinct spreading ridge and transform faults, both oceanic and continental crust, a possible hot spot trace, and magnetic and gravity anomalies. We have studied five recent earthquakes in the magnitude 4.5 to 5.5 range to determine their source properties and to better understand how they fit into the seismotectonic framework of the region. A combination of body and surface wave analysis techniques were used to determine the source parameters. LS69, LS89 and PB89 were well recorded teleseismically, and thus their source properties are better constrained than those for LS86 and LS87, for which only a few teleseismic records were available and whose source parameters were determined more from first motions than by modeling. The two events (LS69, LS89) that occurred near the intersection of the extinct spreading ridge (and associated transform) and Mesozoic rifted margin are noteworthy in that the former is of the thrust-fault and the latter of the normal-fault type. Local structure and possibly post-glacial rebound could be the causative factors for the occurrence of normal and thrust faulting in the same area. The two events (LS86, LS87) that occurred along the continent ocean transition zone have fairly similar fault-plane solutions, and are both thrust-faulting events. The fifth event (PB89), which occurred in Payne Bay, is also a thrust-faulting event and could be associated with the Ungava Transform fault to the northeast, or the Cape Smith fold belt to the northwest. The focal depths of all five events lie between 10 and 15 km, and may be dominated by thermal effects. The observation that the deviatoric compression axis of all five earthquakes lies in the northwest (or equivalently in the southeast) quadrant is consistent with recent modeling efforts of the tectonic stress field in this region.

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40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/ggub.v184.5227 ◽

1999 ◽

pp. 19-29 ◽

Cited By ~ 3

Author(s):

Lotte Melchior Larsen ◽

David C. Rex ◽

W. Stuart Watt ◽

Philip G. Guise

Keyword(s):

Alkali Basalt ◽

Dyke Swarm ◽

Labrador Sea ◽

Precambrian Basement ◽

Stress Regime ◽

Southwest Coast ◽

Eastern Margin ◽

Step Heating ◽

Igneous Activity ◽

Break Up

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Melchior Larsen, L., Rex, D. C., Watt, W. S., & Guise, P. G. (1999). 40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea. Geology of Greenland Survey Bulletin, 184, 19-29. https://doi.org/10.34194/ggub.v184.5227 _______________ A 380 km long coast-parallel alkali basalt dyke swarm cutting the Precambrian basement in south-western Greenland has generally been regarded as one of the earliest manifestations of rifting during continental stretching prior to break-up in the Labrador Sea. Therefore, the age of this swarm has been used in models for the evolution of the Labrador Sea, although it has been uncertain due to earlier discrepant K–Ar dates. Two dykes from this swarm situated 200 km apart have now been dated by the 40Ar–39Ar step-heating method. Separated biotites yield plateau ages of 133.3 ± 0.7 Ma and 138.6 ± 0.7 Ma, respectively. One of the dykes has excess argon. Plagioclase separates confirm the biotite ages but yield less precise results. The age 133– 138 Ma is earliest Cretaceous, Berriasian to Valanginian, and the dyke swarm is near-coeval with the oldest igneous rocks (the Alexis Formation) on the Labrador shelf. A small swarm of alkali basalt dykes in the Sukkertoppen (Maniitsoq) region of southern West Greenland was also dated. Two separated kaersutites from one sample yield an average plateau age of 55.2 ± 1.2 Ma. This is the Paleocene–Eocene boundary. The swarm represents the only known rocks of that age within several hundred kilometres and may be related to changes in the stress regime during reorganisation of plate movements at 55 Ma when break-up between Greenland and Europe took place.

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ACTIVE STRESS FIELD OF THE SOUTHERN AEGEAN SEA SUBDUCTION AREA FROM FAULT-PLANE SOLUTIONS ON THE BASIS OF DIFFERENT STRESS INVERSION APPROACHES

Journal of Geodynamics ◽

10.1016/j.jog.2020.101813 ◽

2021 ◽

pp. 101813

Author(s):

Ch. Kkallas ◽

C.B. Papazachos ◽

E.M. Scordilis ◽

B.N. Margaris

Keyword(s):

Stress Field ◽

Fault Plane ◽

Aegean Sea ◽

Stress Inversion ◽

Fault Plane Solutions ◽

Active Stress

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Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

Geological Society London Memoirs ◽

10.1144/m57-2021-31 ◽

2021 ◽

pp. M57-2021-31

Author(s):

Harald Brekke ◽

Halvor S. S. Bunkholt ◽

Jan I. Faleide ◽

Michael B. W. Fyhn

Keyword(s):

Lower Jurassic ◽

Passive Margin ◽

Continental Margins ◽

Axial Line ◽

Continental Breakup ◽

The North ◽

Tectonic Development ◽

Definition Of ◽

Conjugate Margins ◽

Greenland Margin

AbstractThe geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

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Stress field characterisation in Nickel Rim South Mine using seismic stress inversion

Proceedings of the Eighth International Conference on Deep and High Stress Mining ◽

10.36487/acg_rep/1704_16_abolfazlzadeh ◽

2017 ◽

Cited By ~ 1

Author(s):

Yousef Abolfazlzadeh ◽

Stephen McKinnon

Keyword(s):

Stress Field ◽

Stress Inversion ◽

Seismic Stress

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Three-dimensional approach to understanding the relationship between the Plio-Quaternary stress field and tectonic inversion in the Triassic Cuyo Basin, Argentina

Solid Earth Discussions ◽

10.5194/sed-7-459-2015 ◽

2015 ◽

Vol 7 (1) ◽

pp. 459-494

Author(s):

L. Giambiagi ◽

S. Spagnotto ◽

S. M. Moreiras ◽

G. Gómez ◽

E. Stahlschmidt ◽

...

Keyword(s):

Stress Field ◽

Three Dimensional ◽

Sedimentary Basins ◽

Strike Slip ◽

Stress Regime ◽

Basin Inversion ◽

Structural Style ◽

Tectonic Inversion ◽

The Impact ◽

The Relationship

Abstract. The Cacheuta sub-basin of the Triassic Cuyo Basin is an example of rift basin inversion contemporaneous to the advance of the Andean thrust front, during the Plio-Quaternary. This basin is one of the most important sedimentary basins in a much larger Triassic NNW-trending depositional system along the southwestern margin of the Pangea supercontinent. The amount and structural style of inversion is provided in this paper by three-dimensional insights into the relationship between inversion of rift-related structures and spatial variations in late Cenozoic stress fields. The Plio-Quaternary stress field exhibits important N–S variations in the foreland area of the Southern Central Andes, between 33 and 34° S, with a southward gradually change from pure compression with σ1 and σ2 being horizontal, to a strike-slip type stress field with σ2 being vertical. We present a 3-D approach for studying the tectonic inversion of the sub-basin master fault associated with strike-slip/reverse to strike-slip faulting stress regimes. We suggest that the inversion of Triassic extensional structures, striking NNW to WNW, occurred during the Plio–Pleistocene in those areas with strike-slip/reverse to strike-slip faulting stress regime, while in the reverse faulting stress regime domain, they remain fossilized. Our example demonstrates the impact of the stress regime on the reactivation pattern along the faults.

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Tectonic stylolites as a valuable stress archive – new insights from Late Cretaceous intra-plate stresses in Europe

10.5194/egusphere-egu21-12586 ◽

2021 ◽

Author(s):

Saskia Köhler ◽

Daniel Koehn

Keyword(s):

Late Cretaceous ◽

Stress Inversion ◽

Stress History ◽

Tectonic Event ◽

Stress Regime ◽

Geological Processes ◽

First Results ◽

Roughness Analysis ◽

The Moment ◽

Short Time

The importance of paleostress analysis is dramatically increasing due to its application in diverse fields, such as sustainable exploration of resources, reservoir potential or storage sites. A good understanding of the subsurface geology, the geological stress-history and associated fracture and fault networks is essentially for these applications. Understanding of the complete paleostress history is not only of interest for applied research, but also for an understanding of the dynamics of geological processes in general. In recent years a diverse toolbox of stress inversion methods has been developed including stress inversion from tectonic stylolites (and slikolites). The pressure solution structures not only preserve the direction of the largest principle stress &#8211; they are an archive for the complete stress tensor and the absolute stress magnitude at the moment of their development. Here we present the first results of a systematic study of this upcoming method. For comparison we preformed roughness analysis of tectonic stylolites from Mesozoic limestone from SE Germany. In late Cretaceous the area was affected by shortening in a NE-SW direction, which is clearly illustrated by fault-slip analysis and the orientation of tectonic stylolites. During this tectonic event the stress regime changed from thrusting to strike-slip, with the sampled stylolites persevering the transition between these two stress events. With our preliminarily results we show that roughness analysis of tectonic stylolites enables us to record short time intervals during phases of contraction, and therefore offers crucial insights into stress history and tectonic processes with pulsating stress fields.

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