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Tectonophysics
No full textTexto completo. Acesso restrito. p. 163–188Heat flow at 170 locations in the Central Tertiary basin of Sumatra was determined
from thermal gradients obtained from the extrapolated oil well bottom hole formation
temperature and the assumed temperature of 80°F at the surface. The effective thermal
conductivity of the whole rock column, by which the gradient is multiplied to get the
heat flow was calculated from measurements on 273 specimens of the geologic section
and inspection of 92 well logs. For the whole basin the gradient averaged 3.71 i- l.O4’F/
100 ft (67,6’C/km) the conductivity 4.83 i: 0.31 meal ‘C-l cm-l set-l, giving an average
heat flow of 3.27 ?: 0.93 10s6 cal crne2 set-i which is about twice the world average. The
gradient and the heat flow vary inversely with the depth of the wells most of which
bottom in the pre-Tertiary basement. This may result from the basement rocks being
several times more conductive than the sediments. Mocef calculations on a narrow heatflow
anomaly which rises from a base level of 3.2 HFU to 8.8 HFU suggest that it can be
caused by the intrusion less than 55,000 years ago of an igneous plug or Iaccolith no
deeper than 3 km and 2.2 to 4.6 km wide.
Using the gradients from the SEAPEX Geothermal Gradient Map and assuming a conductivity
of 5 meal cm-l ‘C-l set- l, the heat flow in the North Sumatra basin, the South
Sumatra Basin, Sunda Strait and West Java is 2.5 HFU, while in Java east of 1lO”E longitude
it drops to 1.9 HFU. Since subduction off Sumatra dates back at least to the Cretaceous,
compression of the Asian plate against the Benioff zone is preventing the opening
of a back-arc basin. This does not preclude the possibility of occasional periods of crustal
tension corresponding perhaps to episodes of transgression which allow magma to rise
into the rocks underlying the basin.Salvado
The signature of the earthquake cycle at subduction zones
No full textRecent megathrust events taught us a lot about the dominant physical processes, particularly about re-locking, afterslip, and mantle relaxation. The observations show complex spatial and temporal patterns in crustal deformation and displacement, and significant differences between different margins. The main question is what causes these differences. I use geodynamic models to isolate the geodetic and geological signature of the megathrust cycle. A global review of pre-, co- and post-seismic geodetic observations, and of their fit to the model predictions, indicates that similar physical processes are active at different margins, and differences in the observations are controlled by their stage in the earthquake cycle. The model results provide a possible explanation for puzzling observations, of normal faulting aftershocks and tensile cracking of the overriding plate. The ratio of the loading and relaxation time scales exerts a critical control on post-seismic relaxation. The Tohoku and Sumatra margins therefore undergo a protracted post-seismic relaxation period. The Chilean margin has a short post-seismic relaxation period even if the mantle viscosity is similar to other regions. I find that geodetic observations may deceitfully suggest weak locking of some margins, e.g., the west Alaska margin
Seismic data reveal eastern Black Sea Basin structure
Full text linkRifted continental margins are formed by progressive extension of the lithosphere. The development of these margins plays an integral role in the plate tectonic cycle, and an understanding of the extensional process underpins much hydrocarbon exploration. A key issue is whether the lithosphere extends uniformly, or whether extension varies\ud
with depth. Crustal extension may be determined using seismic techniques. Lithospheric extension may be inferred from the waterloaded subsidence history, determined from\ud
the pattern of sedimentation during and after rifting. Unfortunately, however, many rifted margins are sediment-starved, so the subsidence history is poorly known.\ud
To test whether extension varies between the crust and the mantle, a major seismic experiment was conducted in February–March 2005 in the eastern Black Sea Basin (Figure 1), a deep basin where the subsidence history is recorded\ud
by a thick, post-rift sedimentary sequence. The seismic data from the experiment indicate the presence of a thick, low-velocity zone, possibly representing overpressured sediments. They also indicate that the basement and\ud
Moho in the center of the basin are both several kilometers shallower than previously inferred. These initial observations may have considerable impact on thermal models of the petroleum system in the basin. Understanding\ud
the thermal history of potential source rocks is key to reducing hydrocarbon exploration risk. The experiment, which involved collaboration between university groups in the United Kingdom, Ireland, and Turkey, and BP and\ud
Turkish Petroleum (TPAO), formed part of a larger project that also is using deep seismic reflection and other geophysical data held by the industry partners to determine the subsidence history and hence the strain evolution of\ud
the basin
Evolving plate boundaries in the Aegean–Anatolian region
No full textMy thesis focuses on evolving and (geologically) short-lived plate boundary segments, their segmentation processes and geological imprints in the eastern Mediterranean. In Chapter 2, I investigate the nature/type of the plate boundary between the eastern Aegean region and the Africa plate. The work involves an integrative analysis of geological and geophysical information. I conclude that these surface observations document that the “Pliny-Strabo trench” is a predominantly strike-slip plate boundary. My interpretation is that this plate boundary represents an expression of slab tearing related to an active STEP (c.f. Figure 1.1). The paper represents the first detailed account of surface deformation related to a STEP fault, and constitutes a novel contribution to the understanding of the relation between deep processes and (near-) surface deformation, a key topic in geodynamic research. In Chapter 3, I investigate the location and nature of currently active plate boundaries and other major faults in the southern Anatolia-Aegean region, in the transition region from the Hellenic Arc to the Cyprus Arc. The question is particularly relevant for accessing earthquake hazard. I use mechanical models based on the finite element method. I explore various options for these faults, most of them proposed in the scientific literature, to explore how they would affect the deformation at locations where there are actual observations. The (mis)fit between model predictions and observations allows us to conclude that the active plate boundary is located offshore. The research question that I address in Chapter 4 is what the cause is of deformation in one of the seismically most active fault zones in Europe, the Kefalonia Transform Fault. I present results from a recent full-waveform tomographic model which particularly improves our understanding of the structure of the upper few hundred kilometers of the Earth. The cause of the deformation along the Kefalonia Transform Fault is likely rooted in a fragmented slab that we image for the first time. The geometry of the slab fragment leads me to conclude that it became disconnected from the larger Hellenic slab around 5 Ma, at about the time of opening of the Gulf of Corinth in the overriding plate, which suggests a highly interesting causal relation
T. Reischmann [Tectonophysics 473, 53–68 (doi:10.1016/j.tecto.2008.10.028)]
No full textThe work by Koglin et al. (Koglin, N., Kostopoulos, D., Reichmann, T.,
2009. Geochemistry, petrogenesis and tectonic setting of the Samothraki
mafic Suite, NE Greece: Trace-element, isotopic and zircon age
constraints. Tectonophysics 473, 53-68. doi:
10.1016/j.tecto.2008.10.028), where the authors have proposed to nullify
the scenario presented by Bonev and Stampfli (Bonev, N., Stampfli, G.,
2008. Petrology, geochemistry and geodynamic implications of Jurassic
island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic
low-grade sequence, eastern Rhodope, Bulgaria. Lithos 100, 210-233) is
here Put under discussion. The arguments for this proposal are reviewed
in the light of available stratigraphic and radiometric age constraints,
geochemical signature and tectonics of highly relevant Jurassic
ophiolitic suites occurring immediately north of the Samothraki mafic
suite. Our conclusion is that the weak arguments and the lack of
knowledge on the relevant constraints from the regional geologic
information make inconsistent the Proposal and the model of these
authors. (C) 2009 Elsevier B.V. All rights reserved
A-type granitoids from the Eastern Pontides, NE Turkey: Records for generation of hybrid A-type rocks in a subduction-related environment
No full textThe Eastern Pontides is characterized by the many of intrusive bodies formed throughout the late Mesozoic-early Cenozoic. Most of these are I-type granitoids, but here, we present for the first time an A-type pluton from the region to assess source characteristics and geodynamic implications. The A-type Pirnalli pluton has a SHRIMP zircon U-Pb age of 81.2 +/- 1 Ma. It is composed of granite, syenite and quartz monzonite, and its enclaves are monzonitic in composition with elevated Ga/Al ratios and low Mg# (<42). The pluton is dominantly metaluminous (A/CNK = 0.88 to 1.00) and belong to shoshonitic and ultra-potassic series. The samples are highly enriched in LREE and show significant negative Eu (Eu/Eu* = 0.33 to 0.92), Ba, Nb, Sr and Ti anomalies in the spidergrams. The host rocks and their enclaves posses quite similar Sr-Nd isotopic compositions (I-Sr = 0.70693 to 0.70736, epsilon(Nd) (81 Ma) = -2.6 to -2.0, T-DM = 0.94 to 1.12 Ga), pointing to a lower crustal parental magma with a minor contribution of lithospheric mantle. We hypothesize that upwelling of asthenosphere triggered melting of chemically enriched upper mantle and basic magma formed. Melting of lower crust was provided by the underplating of this basic magma. Mixing between lower crust- and mantle-derived melts at depths of lower crust appears to be most reasonable petrogenetic process responsible for generation of the pluton. Sr-Nd isotope modeling suggests mixing of 82-90% of the lower crustal-derived melt with similar to 10-18% of the mantle-derived melt. Then the hybrid melt ascended to shallower crustal level and underwent a limited fractionation process to generate a variety of rock types. Our data also suggest that the A-type Pirnalli pluton likely formed at an extensional environment of active continental margin throughout the late Cretaceous. Ongoing extension then led to opening of Black Sea as a back-arc basin further north of the Eastern Pontides. (C) 2011 Elsevier B.V. All rights reserved.Geochemistry & GeophysicsSCI(E)EI0ARTICLE208-22453
On the forces that drive and resist deformation of the south-central Mediterranean: a mechanical model study
Full text linkThe geodynamics of the Mediterranean comprises a transitional setting in which slab rollback and plate convergence compete to shape the region. In the central Mediterranean, where the balance of driving and resisting forces changes continuously and rapidly since the Miocene, both kinematic and seismo-tectonic observations display a strong variation in deformation style and, therefore possibly, lithospheric forces. We aim to understand the current kinematics in southern Italy and Sicily in terms of lithospheric forces that cause them. The strong regional variation of geodetic velocities appears to prohibit such simple explanation. We use mechanical models to quantify the deformation resulting from large-scale Africa-Eurasia convergence, ESE retreat of the Calabrian subduction zone, pull by the Aegean slab, and regional variations in gravitational potential energy (topography). A key model element is the resistance to slip on major regional fault zones. We show that geodetic velocities, seismicity and sense of slip on regional faults can be understood to result from lithospheric forces. Our most important new finding is that regional variations in resistive tractions are required to fit the observations, with notably very low tractions on the Calabrian subduction contact, and a buildup towards a significant earthquake in the Calabrian fore-arc. We also find that the Calabrian net slab pull force is strongly reduced (compared to the value possible in view of the slab’s dimensions) and that trench suction tractions are negligible. Such very small contributions to the present-day force balance in the south-central Mediterranean suggest that the Calabrian arc is now further transitioning towards a setting dominated by Africa-Eurasia plate convergence, whereas during the past 30 Myrs slab retreat continually was the dominant factor
Gateway exchange, climatic forcing and circulation of the Mediterranean Sea during the late Miocene: A model perspective
No full textOceanen transporteren - en fungeren als opslag van - grote hoeveelheden warmte, zout, en andere chemische verbindingen, waaronder CO2. Ze zijn daarom een belangrijk onderdeel van het aardse klimaatsysteem. Gezien de huidige bezorgdheid over het veranderende klimaat, is het cruciaal om een goed begrip te hebben van het functioneren van oceaancirculatie. Veranderingen in de circulatie en chemische samenstelling van de oceaan zijn veelal terug te zien in de sedimenten die afgezet worden op de oceaanbodem. Niet alleen het type sediment wordt bepaald door zulke veranderingen; de chemische samenstelling en fossielinhoud van het sediment worden er ook door beïnvloed. Op deze wijze vormen de afgezette sedimenten “het geologische archief” van genoemde veranderingen. Het bestuderen van dit archief is een manier om inzicht te verkrijgen in de processen die de oceaancirculatie aandrijven. De circulatie en sedimentatie in door land ingesloten bekkens zijn bijzonder gevoelig voor veranderingen in het klimaat; dit maakt deze bekkens uitermate geschikt om klimaatverandering te bestuderen. De gevoeligheid voor veranderingen in het klimaat is een gevolg van de beperkte grootte van de bekkens en de gelimiteerde interactie met de open oceaan. Het bekendste voorbeeld van een door land ingesloten bekken is de Middellandse Zee, met zijn ligging tussen het Europese en het Afrikaanse continent. Circulatie in de Middellandse Zee wordt aangedreven door de uitwisseling van water met de Atlantische Oceaan en door de atmosferische condities in het Mediterrane gebied en zijn omgeving, zoals winden, verdamping, neerslag en resulterende zoetwater-instroom van rivieren. Op dit moment is de Straat van Gibraltar de enige zeestraat die de Middellandse Zee en de Atlantische Oceaan met elkaar verbindt; in het verleden is deze verbinding gecompliceerder geweest. De wateruitwisseling door een zeestraat wordt sterk beïnvloed door de zeestraat-bathymetrie; hierdoor was het mogelijk dat tektonische veranderingen in het gebied rond Gibraltar gevolgen hadden voor de grootte van de wateruitwisseling. Genoemde atmosferische condities worden sterk beïnvloed door de intensiteit van de inkomende zonnestraling, die op haar beurt afhangt van de baan van de Aarde en positie van de rotatieas van de Aarde ten opzichte van de zon. Het is het samenspel van klimaat en tektoniek dat leidt tot veranderingen in de circulatie in de Middellandse Zee en dat zijn weerslag vindt in het marien-geologische archief. Het herkennen en onderscheiden van de individuele invloed van de twee drijfveren is lastig maar belangrijk voor het verbeteren van ons begrip van oceaancirculatie. De sedimenten die zijn afgezet in de Middellandse Zee in het laatste (d.w.z. jongste) deel van het Mioceen (het Messinien, van 7,25 tot 5,33 miljoen jaar geleden) vertonen een grote variabiliteit in hun samenstelling. Sedimenten kenmerkend voor afzetting in een open oceaan worden afgewisseld door lagen met een hoge organische inhoud. 5.97 miljoen jaar geleden werd deze afwisseling onderbroken door de afzetting van evaporieten (vooral gips en steenzout). Rondom de gehele Middellandse Zee zijn gipsafzettingen uit deze tijd gevonden en kilometers dikke lagen steenzout zijn verborgen onder de huidige zeebodem. Het uitzonderlijke geologische gebeuren dat geleid heeft tot de afzetting van deze evaporieten staat bekend als de Messinien Zoutcrisis en vond plaats tussen 5,97 en 5,33 miljoen jaar geleden. Deze relatief korte periode van evaporiet-afzetting is, ondanks het onderzoek van generaties van wetenschappers, nog steeds één van de grootste mysteries in de geologische geschiedenis. Voortbouwend op een groot aantal waarnemingen en een uitgebreid kwalitatief inzicht in het laat-Mioceen, heeft mijn promotieonderzoek als doel het verbeteren van het kwantitatieve begrip van de invloed van de grootte van de verbindende zeestraat tussen de Middellandse Zee en de Atlantische oceaan en van het klimaat op circulatie en zoutgehalte in de Middellandse Zee. Dit wordt bereikt door bestaande geologische/geochemische waarnemingen te combineren met een theoretische en model-gedreven aanpak van fysische aard. In dit proefschrift ontwikkel ik (1) een theoretische benadering van de relatie tussen zeestraatgrootte en bekkensaliniteit, (2) een vernieuwende aanpak, gebruik makend van meerdere modellen, om een schatting te maken van het zoetwaterbudget (relatie tussen neerslag, rivier-input en verdamping) van de Middellandse Zee in het Mioceen, (3) een gesimplificeerd model van de oceaancirculatie van de Middellandse Zee, dat de ruimtelijke verdeling van saliniteit in het bekken in eerste orde verklaart. De verkregen resultaten kunnen als volgt kort worden samengevat: Om een zoutgehalte in de Middellandse Zee in stand te kunnen houden dat groter is dan het huidige, moet de verbinding via de zeestraat beperkter (ondieper of smaller, of langer, of een combinatie hiervan) geweest zijn dan de huidige Straat van Gibraltar. Hoewel tijdens het laat-Mioceen de zoetwateraanvoer door de Afrikaanse rivieren mogelijk veel groter was (waarschijnlijk door afwatering in de Middellandse Zee van het destijds zeer grote Chad Meer), was het netto zoetwaterbudget van de Middellandse Zee vergelijkbaar met het huidige. Deze resultaten leiden tot de conclusie dat de Messinien Zoutcrisis voornamelijk op gang gebracht is doordat tektonische processen de verbinding van de Middellandse Zee met de Atlantische Oceaan drastisch verkleind hebben. Mijn onderzoek toont aan dat onder deze omstandigheden betreffende wateruitwisseling en zoetwaterbudget de Mediterrane waterkolom sterk gelaagd geweest kan zijn. Dit resultaat werpt nieuw licht op algemeen aanvaarde percepties van de Messinien Zoutcrisis en levert een nieuwe kwantitatieve basis voor toekomstige studies. De behaalde proces-gerelateerde resultaten zijn niet alleen zinvol voor de Middellandse Zee als case study gebied; tezamen met de geïntegreerde onderzoeksstrategie ontwikkeld in dit proefschrift zullen zij naar verwachting bijdragen tot verdieping van inzicht in oceaancirculatie en sedimentatie in andere vergelijkbare gebieden (tegenwoordige of in het geologische verleden) en in oceaancirculatie, in het algemeen
Signature of slab fragmentation beneath Anatolia from full-waveform tomography
Full text linkWhen oceanic basins close after a long period of convergence and subduction, continental collision and mountain building is a common consequence. Slab segmentation is expected to have been relatively common just prior to closure of other oceans in the geological past, and may explain some of the complexity that geologists have documented in the Tibetan plateau also. We focus on the eastern Mediterranean basin, which is the last remainder of a once hemispherical neo-Tethys ocean that has nearly disappeared due to convergence of the India and Africa/Arabia plates with the Eurasia plate. We present new results of full-waveform tomography that allow us to image both the crust and upper mantle in great detail. We show that a major discontinuity exists between western Anatolia lithosphere and the region to the east of it. Also, the correlation of geological features and the crustal velocities is substantially stronger in the west than in the east. We interpret these observations as the imprint in the overriding plate of fragmentation of the neo-Tethys slab below it. This north-dipping slab may have fragmented following the Eocene (about 35 million years ago) arrival of a continental promontory (Central Anatolian Core Complex) at the subduction contact. From the Eocene through the Miocene, slab roll-back ensued in the Aegean and west Anatolia, while the Cyprus–Bitlis slab subducted horizontally beneath central and east Anatolia. Following collision of Arabia (about 16 million years ago), the Cyprus–Bitlis slab steepened, exposing the crust of central and east Anatolia to high temperature, and resulting in the velocity structure that we image today. Slab fragmentation thus was a major driver of the evolution of the overriding plate as collision unfolded
Tectonophysics Perspectives on Integrated, Coordinated, Open, Networked (ICON) Science
No full textThis article is composed of two independent opinion pieces about the state of integrated, coordinated, open, and networked (ICON) principles (Goldman et al., 2021, https://doi.org/10.1029/2021EO153180; Goldman et al., 2022, https://doi.org/10.1029/2021ea002099) in Tectonophysics and discussion on the opportunities and challenges of adopting them. Each opinion piece focuses on a different topic: (a) global collaboration, technology transfer and application, reproducibility, and data sharing and infrastructure; and (b) field, experimental, remote sensing, and real-time data research and application. Within tectonophysics science, ICON-FAIR principles are starting to be adopted and implemented, however they have not become frequent and there are still plenty of opportunities for further development. During the last decade, standardization reduced fragmentation, facilitated openly available databases, and enabled different modeling methods to be combined. On the other hand, integration and coordination remained insufficient as exemplified by numerous geophysical interpretation programs running on different platforms, lacking the proper documentation and with diverse output formats. We agree that adapting the principles of ICON-FAIR brings high efforts and risks, but in the end, it has great benefits and potential in the tectonophysics community.Publishede2021EA0021441T. Struttura della TerraJCR Journa
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