Baffin Bay Composite Tectono-Sedimentary Element

Baffin Bay formed as a result of continental extension during the Cretaceous, which was followed by sea floor spreading and associated plate drift during the early to middle Cenozoic. Formation of an oceanic basin in the central part of Baffin Bay may have begun from about 62 Ma in tandem with Labrador Sea opening but the early spreading phase is controversial. Plate-kinematic models suggests that from Late Paleocene the direction of sea floor spreading changed to N-S generating strike-slip movements along the transform lineaments, e.g. the Ungava Fault Zone and the Bower Fracture Zone, and structural complexity along the margins of Baffin Bay. The Baffin Bay Composite Tectono-Sedimentary Element (CTSE) represents a 3-7 km thick Cenozoic sedimentary and volcanic succession that has deposited over oceanic and rifted continental crust since active seafloor spreading began. The CTSE is subdivided into 5 seismic mega-units that have been identified and mapped using a regional seismic grid tied to wells and core sites. Thick clastic wedges of likely Late Paleocene to Early Oligocene age (mega-units E and D2) were deposited within basins floored by newly formed oceanic crust, transitional crust, volcanic extrusives and former continental rift basins undergoing subsidence. The middle-late Cenozoic is characterized by fluvial-deltaic sedimentary systems, hemipelagic strata and aggradational sediment bodies deposited under the influenced of ocean currents (mega-units D1, C and B). The late Pliocene to Pleistocene interval (mega-unit A) displays major shelf margin progradation associated with ice-sheet advance-retreat cycles resulting in accumulation of trough-mouth fans and mass-wasting deposits products in the oceanic basin. The Baffin Bay CTSE has not produced discoveries although a hydrocarbon potential may be associated with Paleocene source rocks. Recent data have improved the geological understanding of Baffin Bay although large data and knowledge gaps remain.

Thermo-tectonic development of the Wandel Sea Basin, North Greenland

The Carboniferous–Palaeogene Wandel Sea Basin of eastern North Greenland (north of 80°N, east of 40°W) is an important piece in the puzzle of Arctic geology. It is particularly important for understanding how the Paleocene–Eocene convergence between Greenland, the Canadian Arctic and Svalbard relates to the compressional tectonics in the High Arctic, collectively known as the Eurekan Orogeny. In this study, we present apatite fission-track analysis (AFTA) data and review published vitrinite reflectance data combined with observations from the stratigraphic record to place firmer constraints on the timing of key tectonic events. This research study reveals a long history of episodic burial and exhumation since the collapse of the Palaeozoic fold belts in Greenland. Our results define pre-Cenozoic exhumation episodes in early Permian, Late Triassic, Late Jurassic and mid-Cretaceous times, each involving the removal of kilometre-scale sedimentary covers. Mid-Paleocene exhumation defines the timing of compression along the major fault zones during the first stage of the Eurekan Orogeny, after the onset of sea-floor spreading west of Greenland. Regional exhumation that began at the end of the Eocene led to the removal of most of a kilometre-thick cover that had accumulated during Eocene subsidence and involved a major reverse movement along the Harder Fjord Fault Zone, northern Peary Land. These events took place after the end of sea-floor spreading west of Greenland, and thus, represent post-Eurekan tectonics. Mid–late Miocene exhumation is most likely a consequence of uplift and incision across most of the Wandel Sea Basin study area. The preserved sedimentary sequences of the Wandel Sea Basin represent remnants of thicker strata that likely extended substantially beyond the present-day outline of the basin. We find that the present-day outline of the basin with scattered sedimentary outliers is primarily the result of fault inversion during Eurekan compression followed by deposition and removal of a kilometre-thick overburden.

Icelandic-type crust enigma solved

Although on the mid-Atlantic extensional plate boundary, the crust beneath Iceland is unlike any produced by sea-floor spreading 1,2. It is up to 40 km thick – 6-7 times thicker than typical oceanic crust 3,4, its seismic velocity gradients are inconsistent with a solely mafic petrology, its lower part has a density approaching that of the mantle, and lithosphere thickness is up to 100 km. Furthermore, downward continuation of surface high thermal gradients predict partial melt in the lower crust that is at odds with the subsolidus state detected by seismic measurements. For the last ~ 50 years it has been assumed that its unusually large thickness results from excess magma production in a hot source 5 but it cannot explain these observations. We model jointly the seismic and thermal data and show that they are consistent with stretched continental crust 6 overlain by a few kilometres of young flood basalts. This resembles a volcanic passive margin under construction. It is mechanically feasible 7 and compatible with the composition of Icelandic lavas. This solution is the first proposed that can explain the geophysical properties of Icelandic-type crust. It has major implications for Atlantic Ocean opening, the structure of passive margins, extent of continental crust in the oceans, natural resources and limits of national seaboards.

Tromsø - Bjørnøya Composite Tectono-Sedimentary Element

The Tromsø - Bjørnøya composite tectono-sedimentary element in the southwestern Barents Sea comprises strata of Late Paleozoic - Paleocene age. Since the Paleozoic Caledonian orogeny, the structural evolution of the CTSE is mainly related to extension, culminating in Late Jurassic - Early Cretaceous hyperextension. Some compressive deformation observed during Late Cretaceous - Paleogene times may relate to activity in the North Atlantic prior to the Early Eocene onset of sea floor spreading between Norway and Greenland.The sedimentary succession may be up to 14 km thick. It comprises Late Paleozoic continental facies, followed by carbonates, evaporites and eventually cherts and marine clastic material. The overlying Triassic - Paleocene succession is entirely siliciclastic, reflecting Triassic - Middle Jurassic deltaic and shallow marine conditions followed by deeper marine conditions during Late Jurassic - Paleocene times.Primary reservoirs are encountered in the latest Triassic - Middle Jurassic succession, with secondary reservoirs found in Late Jurassic - Early Cretaceous syn-rift succession, and in Paleocene strata. The primary source rock for petroleum is of Late Jurassic - Early Cretaceous age. Other source rocks include strata of Triassic and Barremian age, and a recently observed unit of Cenomanian - Early Turonian age.

Icelandia

<p>The NE Atlantic formed by complex, piecemeal breakup of Pangea in an environment of structural complexity. North of the present-day latitude of Iceland the ocean opened by southward propagation of the Aegir ridge. South of the present-day latitude of Iceland breakup occurred along the proto-Reykjanes ridge which formed laterally offset by ~ 100 km from the Aegir ridge to the north. Neither of these new breakup axes were able to propagate across the east-westerly striking Caledonian frontal thrust region which formed a strong barrier ~ 400 km wide. As a result, while sea-floor spreading widened the NE Atlantic, the Caledonian front region could only keep pace by diffuse stretching of the continental crust, which formed the aseismic Greenland-Iceland-Faroe ridge. The magmatic rate there was similar to that of the ridges to the north and south and so the stretched continental crust is now blanketed by thick mafic flows and intrusions. The NE Atlantic also contains a magma-inflated microcontinent – the Jan Mayen Microplate Complex, and an unknown but probably large amount of stretched continental crust blanketed by seaward-dipping reflectors in the passive margins of Norway and Greenland. The NE Atlantic thus contains voluminous continental crust in diverse forms and settings. If even a small portion of the sunken continental material contiguous with the Greenland-Iceland-Faroe ridge is included the area exceeds a million square kilometers, an arbitrary threshold suggested to designate a sunken continent. We have called this region Icelandia. The conditions and processes that funneled large quantities of continental crust into the NE Atlantic ocean are common elsewhere. This includes much of the North and South Atlantic oceans including both the seaboards and the deep oceans. Nor are such processes and outcomes confined to oceans bordered by passive margins. They are also found around the Pacific rims where subduction is in progress. Indeed, these conditions and processes likely are generic to essentially all the world's oceans and are potentially also informed by observations from intracontinental extensional regions and land-locked seas.</p>

Insights into the Red Sea area from magnetic and gravity analysis

<p>We explore the lithosphere structure of the Red Sea using gravity and magnetic data.</p><p>We re-processed marine data form past surveys conducted during the 70’s and the 80’s, available at the NGDC database. By correcting the magnetic measurements according to the DGRF (definitive magnetic reference field), leveling and replacing the long wavelengths with satellite data (LCS1 model) we managed to generate a consistent magnetic anomaly map for the entire length of the Red Sea that is composed of 10 different surveys and contain overs 100,000 measuring points. The magnetic anomaly map highlights structural differences between the southern, central and northern parts of the Red Sea.</p><p>Using forward gravity approach, constrains from seismic, wells and petrophysical data, and by integrating insights from magnetic analysis, we define the lithospheric model of the Red Sea to address key questions regarding rifting, sea floor spreading and transition processes.  For example, the southern parts of the Red Sea are characterized by shallow and wide asthenosphere upwelling, while in the axial trough lithosphere is thin with thicknesses of less than 15 km. The lithosphere thickness increase asymmetrically towards the rift shoulders. In general, the lithosphere is thicker on the eastern sides than on the western sides. In the central parts of the Red Sea, the lithosphere structure is not significantly different from the southern parts, however, asthenosphere upwelling is slightly narrower. In northern parts of the Red Sea asthenosphere upwelling significantly narrows and focused mainly beneath the axial trough and the lithosphere is thicker. This architecture reflects the currently transition from continental rifting (in the north) to oceanic seafloor spreading (in the south) in the Red Sea.</p>

Geological archive of the onset of plate tectonics

Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780–2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700–2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.

A Geologist Reflects on a Long Career

Fifty years ago Jason Morgan and I proposed what is now known as the theory of plate tectonics, which brought together the ideas of continental drift and sea floor spreading into what is probably their final form. I was twenty-five and had just finished my PhD. The success of the theory marked the beginning of a change of emphasis in the Earth sciences, which I have spent the rest of my career exploring. Previously geophysicists had principally been concerned with using ideas and techniques from physics to make measurements. But the success of plate tectonics showed that it could also be used to understand and model geological processes. This essay is concerned with a few such efforts in which I have been involved: determining the temperature structure and rheology of the oceanic and continental lithosphere, and with how mantle convection maintains the plate motions and the long-wavelength part of the Earth's gravity field. It is also concerned with how such research is supported.

Probably the Best Theory on Earth

The magnetic bar-code on the ocean floor provides convincing evidence of moving continents, yet, as with the discovery of the structure of DNA, few are convinced—at first. Drilling in the deep oceans and geochemical work at mid-ocean ridges provides further evidence in support of the Vine–Matthews Hypothesis. Application of the hypothesis to data collected in the Pacific and Atlantic Oceans establishes sea-floor spreading as the process that creates new oceans and, in conjunction with reversals of the geomagnetic field, stamps the bar-code into the rocks beneath the sea bed.