KineDyn: Thermo-Mechanical Method for Validation of Seismic Interpretations with Dynamic Forward Models 

2021 ◽  
Author(s):  
Iskander Muldashev ◽  
Marta Pérez-Gussinyé ◽  
Mário Neto Cavalcanti de Araújo ◽  
Zhonglan Liu
Keyword(s):  
Lower Crust ◽  
Dynamic Mode ◽  
Surface Process ◽  
Upper Crust ◽  
Physical Processes ◽  
Rifted Margins ◽  
Non Linear ◽  
Kinematic Modelling ◽  
History Of ◽  
Rifted Margin

<p>Rifts and rifted margins result from interaction of several physical processes, which produce a range of crustal structures, subsidence histories, and sedimentary architectures. Study of these processes in academia and industry includes kinematic modelling (i.e. cross-section restoration, backstripping) combined with simple thermomechanical models and dynamic modelling. In kinematic models, the thinning of the lower crust and mantle is kinematically imposed in the form of pure shear, which contradicts natural non-linear viscous behavior. Although, kinematic modelling can provide a crustal thinning profile, heatflow estimates, subsidence rates etc., imposed extension of the lower crust and mantle might strongly impact the result. On the other hand, a dynamic approach allows to model the whole range of possible physical processes, but it cannot be used to model particular extension histories.<br>Here, we show a new modelling technique, namely KineDyn, to combine the advantages of the above-mentioned approaches into a single modelling framework. Our method employs full non-linear visco-elasto-plastic rheology, surface process of erosion and sediment transport, decompression melting of the mantle, and serpentinization of mantle rocks. Faults are introduced as weak planes in the upper crust, in order to simulate faulting during the model run. In our approach, faults are initially controlled by prescribed initial locations, offsets and timings, while the rest of the model is resolved in a fully dynamic mode. Since fault planes are much weaker than the surrounding upper crust, extension of the model naturally leads to slip on the faults. We demonstrate that faults modelled this way reproduce a natural behavior, including rotation due to flexure and unloading of the fault plane. <br>In order to reconstruct the evolution of an existing rift or rifted margin we model extension of the lithosphere with controlled faulting. To do this we use the interpreted spatio-temporal evolution of the faulting from a seismic profile to guide the evolution of the dynamic model. After a trial-and-error process, where we correct the faults’ locations, the thicknesses of layers, surface process’s parameters, initial thermal gradient etc., we obtain the model that best fits the observations. Thus, KineDyn gives, in effect, the same results as existing section restoration techniques (i.e. the potential history of faulting) and forward modeling techniques (i.e. the likely history of sedimentation, thinning, heat flow and subsidence), while simultaneously taking into account non-linear interactions between processes occurring during rifting. <br>In this work we show the methodology, examples, tests and benchmarks of the technique. Finally, we present applications of KineDyn for the following rifts and rifted margins: Malawi Rift, East African Rift System, hyper-extended West Iberia Margin, and ultra-wide Santos-Benguela Rifted Margin.</p>

Granitic batholiths: from pervasive and continuous melting in the lower crust to discontinuous and spaced plutonism in the upper crust

2006 ◽  
Vol 97 (4) ◽  
pp. 311-324 ◽  
Author(s):  
Jean Louis Vigneresse
Keyword(s):  
Lower Crust ◽  
Magma Mixing ◽  
Tectonic Setting ◽  
Continuous Process ◽  
Chemical Compositions ◽  
Upper Crust ◽  
Linear Processes ◽  
Non Linear ◽  
Thermally Driven ◽  
Two Phases

ABSTRACTThe generation of granitic magmas begins with melting in the lower crust, under active participation of the underlying mantle. Thermally driven, melting is a pervasive and continuous process that develops over a wide region. In contrast, the building of a granitic pluton is highly discontinuous in time and space. Several inputs of magma, sometimes with a different chemical compositions, are focused toward a region where they accumulate, forming a large pluton, often separated by some 50 km from an adjacent one. The switch from a continuous to a discontinuous process represents a fundamental point of magma generation. It gives place to the modified model m(M-SAE), in which the mantle (m) and Melting (M) are separated from the Segregation (S), Ascent (A) and Emplacement (E) modes. Discontinuities result from non-linear processes that develop during segregation and ascent of the magma. They rely on the non-linear rheology of partially molten rocks. Thresholds control the change from a solid-like to liquid-like behaviour of the magma. In between, the rheology exhibits sudden jumps between states. Because two phases continuously coexist (matrix and melt), strain is highly partitioned between them. This may induce highly discontinuous melt segregation, which needs both pure and simple shear to develop. Melt focusing is controlled by the viscosity contrast between the two phases. It gives rise to different compaction lengths depending on the region, a partially melting source or a nearly brittle crust, where it develops. Because ascent and emplacement are discontinuous in time, this allows the crust to relax, avoiding the room problem for a pluton intruding the upper crust. Intermediate magma chambers could develop with different temperature and magma composition. They could be the place of enhanced magma mixing. Finally, the stress conditions, which differ for each tectonic setting, influence the shape of the granitic body.

scholarly journals Melt volume at Atlantic volcanic rifted margins controlled by depth-dependent extension and mantle temperature

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gang Lu ◽  
Ritske S. Huismans
Keyword(s):  
Numerical Models ◽  
Potential Temperature ◽  
Analytical Prediction ◽  
Natural Systems ◽  
Passive Margins ◽  
Margin Width ◽  
Rifted Margins ◽  
Mantle Potential Temperature ◽  
Mantle Temperature ◽  
Rifted Margin

AbstractBreakup volcanism along rifted passive margins is highly variable in time and space. The factors controlling magmatic activity during continental rifting and breakup are not resolved and controversial. Here we use numerical models to investigate melt generation at rifted margins with contrasting rifting styles corresponding to those observed in natural systems. Our results demonstrate a surprising correlation of enhanced magmatism with margin width. This relationship is explained by depth-dependent extension, during which the lithospheric mantle ruptures earlier than the crust, and is confirmed by a semi-analytical prediction of melt volume over margin width. The results presented here show that the effect of increased mantle temperature at wide volcanic margins is likely over-estimated, and demonstrate that the large volumes of magmatism at volcanic rifted margin can be explained by depth-dependent extension and very moderate excess mantle potential temperature in the order of 50–80 °C, significantly smaller than previously suggested.

scholarly journals Learning dominant physical processes with data-driven balance models

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jared L. Callaham ◽  
James V. Koch ◽  
Bingni W. Brunton ◽  
J. Nathan Kutz ◽  
Steven L. Brunton
Keyword(s):  
Nonlinear Optics ◽  
Unsupervised Learning ◽  
History Of Science ◽  
Traditional Approach ◽  
Data Driven ◽  
Mechanistic Models ◽  
Physical Processes ◽  
History Of ◽  
Separation Of Scales ◽  
Geophysical Fluids

AbstractThroughout the history of science, physics-based modeling has relied on judiciously approximating observed dynamics as a balance between a few dominant processes. However, this traditional approach is mathematically cumbersome and only applies in asymptotic regimes where there is a strict separation of scales in the physics. Here, we automate and generalize this approach to non-asymptotic regimes by introducing the idea of an equation space, in which different local balances appear as distinct subspace clusters. Unsupervised learning can then automatically identify regions where groups of terms may be neglected. We show that our data-driven balance models successfully delineate dominant balance physics in a much richer class of systems. In particular, this approach uncovers key mechanistic models in turbulence, combustion, nonlinear optics, geophysical fluids, and neuroscience.

Results of a seismic reflection survey across the fault zone between the Thompson nickel belt and the Churchill Tectonic Province, northern Manitoba

1981 ◽  
Vol 18 (1) ◽  
pp. 13-25 ◽  
Author(s):  
A. G. Green
Keyword(s):  
Fault Zone ◽  
Lower Crust ◽  
Seismic Reflection ◽  
High Amplitude ◽  
Small Scale ◽  
Upper Crust ◽  
Travel Times ◽  
Reflection Point ◽  
Point Data ◽  
Amplitude Reflection

Approximately 11 km of four-fold common reflection point data have been recorded across a region that spans the contact fault zone between the Thompson nickel belt and the Churchill Tectonic Province. From these data it is shown that the upper crust in this region and, to a lesser extent, the lower crust are characterized by numerous scattered events that originate from relatively small-scale features. Within the Thompson nickel belt two extensive and particularly high-amplitude reflection zones, at two-way travel times of t = 5.0–5.5 s and t = 6.0–6.5 s, are recorded with apparent northwesterly dips of 0–20 °C. These reflection zones, which have a laminated character, are truncated close to the faulted contact with the Churchill Province. Both the contact fault zone and the Churchill Province in this region have crustal sections that are relatively devoid of significant reflectors. The evidence presented here confirms that the crustal section of the Thompson nickel belt is fundamentally different from that of the Churchill Tectonic Province.

Dynamics of the extension in the Fonualei Rift in the northern Lau Basin at 16 °S

2021 ◽  
Author(s):  
Anna Jegen ◽  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Udo Barckhausen ◽  
Ingo Heyde ◽  
...  
Keyword(s):  
Velocity Gradient ◽  
Lower Crust ◽  
Pacific Plate ◽  
P Wave ◽  
Upper Crust ◽  
Lau Basin ◽  
Australian Plate ◽  
The Pacific ◽  
Refraction Seismic ◽  
Roll Back

<p>The Lau Basin is a young back-arc basin steadily forming at the Indo-Australian-Pacific plate boundary, where the Pacific plate is subducting underneath the Australian plate along the Tonga-Kermadec island arc. Roughly 25 Ma ago, roll-back of the Kermadec-Tonga subduction zone commenced, which lead to break up of the overriding plate and thus the formation of the western Lau Ridge and the eastern Tonga Ridge separated by the emerging Lau Basin.</p><p>As an analogue to the asymmetric roll back of the Pacific plate, the divergence rates decline southwards hence dictating an asymmetric, V-shaped basin opening. Further, the decentralisation of the extensional motion over 11 distinct spreading centres and zones of active rifting has led to the formation of a composite crust formed of a microplate mosaic. A simplified three plate model of the Lau Basin comprises the Tonga plate, the Australian plate and the Niuafo'ou microplate. The northeastern boundary of the Niuafo'ou microplate is given by two overlapping spreading centres (OLSC), the southern tip of the eastern axis of the Mangatolu Triple Junction (MTJ-S) and the northern tip of the Fonualei Rift spreading centre (FRSC) on the eastern side. Slow to ultraslow divergence rates were identified along the FRSC (8-32 mm/a) and slow divergence at the MTJ (27-32 mm/a), both decreasing southwards. However, the manner of divergence has not yet been identified. Additional regional geophysical data are necessary to overcome this gap of knowledge.</p><p>Research vessel RV Sonne (cruise SO267) set out to conduct seismic refraction and wide-angle reflection data along a 185 km long transect crossing the Lau Basin at ~16 °S from the Tonga arc in the east, the overlapping spreading centres, FRSC1 and MTJ-S2, and extending as far as a volcanic ridge in the west. The refraction seismic profile consisted of 30 ocean bottom seismometers. Additionally, 2D MCS reflection seismic data as well as magnetic and gravimetric data were acquired.</p><p>The results of our P-wave traveltime tomography show a crust that varies between 4.5-6 km in thickness. Underneath the OLSC the upper crust is 2-2.5 km thick and the lower crust 2-2.5 km thick. The velocity gradients of the upper and lower crust differ significantly from tomographic models of magmatically dominated oceanic ridges. Compared to such magmatically dominated ridges, our final P-wave velocity model displays a decreased velocity gradient in the upper crust and an increased velocity gradient in the lower crust more comparable to tectonically dominated rifts with a sparse magmatic budget.</p><p>The dominance of crustal stretching in the regional rifting process leads to a tectonical stretching, thus thinning of the crust under the OLSC and therefore increasing the lower crust’s velocity gradient. Due to the limited magmatic budget of the area, neither the magnetic anomaly nor the gravity data indicate a magmatically dominated spreading centre. We conclude that extension in the Lau Basin at the OLSC at 16 °S is dominated by extensional processes with little magmatism, which is supported by the distribution of seismic events concentrated at the northern tip of the FRSC.</p>

scholarly journals New evidence for upper Permian crustal growth below Eifel, Germany, from mafic granulite xenoliths

2021 ◽  
Vol 33 (2) ◽  
pp. 233-247
Author(s):  
Cliff S. J. Shaw
Keyword(s):  
Rare Earth ◽  
Lower Crust ◽  
Volcanic Field ◽  
Upper Permian ◽  
Primitive Mantle ◽  
Magmatic Temperature ◽  
Heavy Rare Earth Elements ◽  
History Of ◽  
Granulite Xenoliths ◽  
West Eifel

Abstract. Granulite xenoliths from the Quaternary West Eifel Volcanic Field in Germany record evidence of magmatism in the lower crust at the end of the Permian. The xenoliths sampled two distinct bodies: an older intrusion (ca. 264 Myr old) that contains clinopyroxene with flat, chondrite-normalised rare earth element (REE) profiles and a younger (ca. 253 Myr old) intrusion that crystallised middle-REE-rich clinopyroxene. The younger body is also distinguished based on the negative Sr, Zr and Ti anomalies in primitive mantle-normalised multi-element plots. REE-in-plagioclase–clinopyroxene thermometry records the magmatic temperature of the xenoliths (1100–1300 ∘C), whereas Mg-in-plagioclase and Zr-in-titanite thermometry preserve an equilibration temperature of ca. 800 ∘C. These temperatures, together with a model of the mineral assemblages predicted from the composition of one of the xenoliths, define the pressure of crystallisation as ∼1 GPa. The xenoliths also preserve a long history of reheating events whose age ranges from 220 to 6 Myr. The last of these events presumably led to breakdown of garnet; formation of symplectites of orthopyroxene, plagioclase and hercynite; and redistribution of heavy rare earth elements into clinopyroxene. The data from the West Eifel granulite xenoliths, when combined with the existing data from granulites sampled in the East Eifel, indicate that the lower crust has a long a complex history stretching from at least 1.6 Ga with intrusive events at ca. 410 and 260 Ma and reheating from the Triassic to late Miocene.

Thermodynamic constraints on assimilation of silicic crust by primitive magmas

2021 ◽  
Author(s):  
Jussi S Heinonen ◽  
Frank J Spera ◽  
Wendy A Bohrson
Keyword(s):  
Phase Equilibria ◽  
Lower Crust ◽  
Primitive Mantle ◽  
Upper Crust ◽  
Basaltic Composition ◽  
Primitive Magma ◽  
Partial Melts ◽  
Thermodynamic Limits ◽  
Melt Composition ◽  
Lower Crustal

<p>Some studies on basaltic and more primitive rocks suggest that their parental magmas have assimilated more than 50 wt.% (relative to the initial uncontaminated magma) of crustal silicate wallrock. But what are the thermodynamic limits for assimilation by primitive magmas? This question has been considered for over a century, first by N.L. Bowen and many others since then. Here we pursue this question quantitatively using a freely available thermodynamic tool for phase equilibria modeling of open magmatic systems — the Magma Chamber Simulator (MCS; https://mcs.geol.ucsb.edu).</p><p>In the models, komatiitic, picritic, and basaltic magmas of various ages and from different tectonic settings assimilate progressive partial melts of average lower, middle, and upper crust. In order to pursue the maximum limits of assimilation constrained by phase equilibria and energetics, the mass of wallrock in the simulations was set at twice that of the initially pristine primitive magmas. In addition, the initial temperature of wallrock was set close to its solidus at a given pressure. Such conditions would approximate a rift setting with tabular chambers and high magma input causing concomitant crustal heating and steep geotherms.</p><p>Our results indicate that it is difficult for any primitive magma to assimilate more than 20−30 wt.% of upper crust before evolving to intermediate/felsic compositions. However, if assimilant is lower crust, typical komatiitic magmas can assimilate more than their own weight (range of 59−102 wt.%) and retain a basaltic composition. Even picritic magmas, more relevant to modern intraplate settings, have a thermodynamic potential to assimilate 28−49 wt.% of lower crust before evolving into intermediate/felsic compositions.</p><p>These findings have important implications for petrogenesis of magmas. The parental melt composition and the assimilant heavily influence both how much assimilation is energetically possible in primitive magmas and the final magma composition. The fact that primitive mantle melts have potential to partially melt and assimilate significant fractions of (lower) crust may have fundamental importance for how trans-Moho magmatic systems evolve and how crustal growth is accomplished. Examples include generation of siliceous high-magnesium basalts in the Precambrian and anorogenic anorthosite-mangerite-charnockite-granite complexes with geochemical evidence of considerable geochemical overprint from (lower) crustal sources.</p>

Rift inheritance controls the switch from thin- to thick-skinned thrusting and basal décollement re-localization at the subduction-to-collision transition

2021 ◽  
Author(s):  
Stefano Tavani ◽  
Pablo Granado ◽  
Amerigo Corradetti ◽  
Giovanni Camanni ◽  
Gianluca Vignaroli ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Complete Removal ◽  
Lower Plate ◽  
Accretionary Wedge ◽  
Convergent Margins ◽  
Middle Crust ◽  
Rifted Margins ◽  
Thrust System ◽  
Structural Levels ◽  
Rifted Margin

In accretionary convergent margins, the subduction interface is formed by a lower plate décollement above which sediments are scraped off and incorporated into the accretionary wedge. During subduction, the basal décollement is typically located within or at the base of the sedimentary pile. However, the transition to collision implies the accretion of the lower plate continental crust and deformation of its inherited rifted margin architecture. During this stage, the basal décollement may remain confined to shallow structural levels as during subduction or re-localize into the lower plate middle-lower crust. Modes and timing of such re-localization are still poorly understood. We present cases from the Zagros, Apennines, Oman, and Taiwan belts, all of which involve a former rifted margin and point to a marked influence of inherited rift-related structures on the décollement re-localization. A deep décollement level occurs in the outer sectors of all of these belts, i.e., in the zone involving the proximal domain of pre-orogenic rift systems. Older—and shallower—décollement levels are preserved in the upper and inner zones of the tectonic pile, which include the base of the sedimentary cover of the distal portions of the former rifted margins. We propose that thinning of the ductile middle crust in the necking domains during rifting, and its complete removal in the hyperextended domains, hampered the development of deep-seated décollements during the inception of shortening. Progressive orogenic involvement of the proximal rift domains, where the ductile middle crust was preserved upon rifting, favors its reactivation as a décollement in the frontal portion of the thrust system. Such décollement eventually links to the main subduction interface, favoring underplating and the upward motion of internal metamorphic units, leading to their final emplacement onto the previously developed tectonic stack.

How seismicity relates to lithospheric heterogeneity in the Alps

2021 ◽  
Author(s):  
Ajay Kumar ◽  
Cameron Spooner ◽  
Magdalena Scheck-Wenderoth ◽  
Mauro Cacace
Keyword(s):  
Lower Crust ◽  
Convergence Rates ◽  
Upper Rhine Graben ◽  
Topographic Effects ◽  
Relative Role ◽  
Upper Crust ◽  
Radiogenic Heat ◽  
First Order ◽  
Tectonic Inheritance ◽  
The Alps

<p>The Alps mountains and its forelands consist of a heterogeneous lithosphere, comprised of a multitude of tectonic blocks from different tectonic provinces with different thermo-physical properties. Patterns of seismicity distribution are also observed to vary significantly throughout the region. However, the relationship between seismicity and lithospheric heterogeneity has been often overlooked in previous studies. We present an overview of recent results that have attempted to address these questions through the use of integrated 3D modelling techniques, thereby including: (i) a gravity and seismic data constrained, 3D, density structural model of the lithosphere; (ii) a 3D thermal model constrained against available wellbore temperature data; and,  (iii) a 3D rheological model of the long-term lithospheric strength and effective viscosities. Our models support the existence of a first-order correlation between the distribution of seismicity (laterally and with depth) and the strength of the lithosphere, with the former being clustered mainly within weaker domains. Beneath the Alps, observed upper-crustal level (i.e., unimodal) seismicity correlates with a weaker lithosphere where plate strength is controlled by the thick crustal root. Whereas in the southern foreland, weaker zones are found preferentially around the stronger Adriatic indenter while in the northern foreland they are located in the crust beneath the the Upper Rhine Graben (URG). We found that this correlation is primarily controlled by resolved thermal gradients and is a function of the tectonic inheritance setting (e.g., UGR), crustal architecture (e.g., thickness of sediments, upper and lower crust) and LAB depth. Sediment thickness and topographic effects controls the shallow thermal filed (0 – 10 km) whereas the deeper thermal field is controlled by the thickness of felsic upper crust (higher radiogenic heat contribution), the mafic lower crust (less radiogenic heat contribution) and basal thermal boundary condition from LAB depth. Seismicity is bounded by specific isotherms, 450 <sup>o</sup>C in the crust and < 600 <sup>o</sup>C in the mantle, except in regions where slabs are imaged by seismic tomography models. This is in contrast to the recent proposition that convergence velocity is a first-order factor controlling seismicity in an orogen rather than its architecture. Fast convergence rates (e.g., Himalayas) have been related to the subduction of the cold crust to deeper crustal depths thereby leading to a deepening of the brittle  domain and to a bimodal (i.e., upper and lower crust) seismicity character. In contrast, slow convergence (e.g., Alps) is thought to lead to a hotter ductile lower crust thus limiting brittle deformation within the upper crust. We therefore end our contribution by opening a discussion on the relative role of convergence rates and lithospheric heterogeneities, inherited and/or developed during orogenesis, in controlling the seismicity. In doing so we carry out a comparison between observed seismicity and lithospheric architecture in the other mountain ranges of the western Alpine-Himalayan collision zone where  convergence velocities are of a similar order of magnitudes as Alps, i.e., the Betics, the Pyrenees and the Apennines but where seismicity is observed to occur both at upper and lower crustal levels.</p>

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