Avoluminous magmatic complexw asemplaced int he Vøringa ndM øreb asins duringP aleocene/Eocenec ontinentalr iftinga ndb reak-up int he NE Atlantic.Thisintrusivee vent hashad asignificant impactondeformation,source-rock maturation andfluid flow inthe basins. Intrusivecomplexesandassociated hydrothermalv ent complexeshaveb eenm apped on aregional2 Dseismic dataset( c .1500 00 km) andon one large 3Dsurvey. The extent ofthe sill complexisatleast 800 00 km 2 ,withanestimated totalvolumeof0.9 to 2.8 £ 10 4 km 3 .The sheetintrusions aresaucer-shaped inu ndeformed basins egments. The widthso fthe saucers becomelargerw ithi ncreasinge mplacement depth.Morevaried intrusion geometriesaref oundi n structured basinsegments. Some734hydrothermalvent complexeshavebeenidentified,although itisestimated that2-3000 vent complexesarepresent int he basins. The vent complexesarelocated abovesills andwere formed asad irectconsequence ofthe intrusivee vent byexplosivee ruption ofg ases,liquidsandsediments, formingup to 11 kmwide craters atthe seafloor. The largest vent complexesarefoundinbasinsegments with deeps ills (3-9kmp alaeodepth). Moundsandseismic seepanomaliesl ocated abovethe hydrothermalv ent complexess uggest thatt he vent complexeshaveb eenr e-used for verticalfluid migration longa ftert heir formation. The intrusivee vent mainly tookplace just prior to,or during, the initialp haseofmassiveb reak-up volcanism (55.0-55.8Ma). Thereisalso evidence for aminor UpperPaleocenevolcanic event documented by the presence of20 vent complexest erminatingi nt he UpperPaleocenesequence andthe localp resence of extrusivevolcanic rockswithinthe Paleocenesequence.Volcanic processesanddeposits mayhaveastrongimpactonthe structureandgeodynamic development ofcontinentalmargins and associated sedimentary basins. The identification ofvolcanic deposits andthe evaluation oftheirimpacto nt he marginhistory are, thus,two important aspects ofpetroleum exploration of continentalrifted margins. Significant attention has,overt he past decade, beendevoted to studieso fe xtrusiveprocessesand deposits on volcanic rifted margins (e.g.Eldholm etal .1 989; Menzies etal. 2002; White etal .2 003). However,petroleum explorationists will commonly encounterintrusivec omplexes beforetheyencounterextrusivevolcanic rocksw hent heym ove from shallow-watert odeep-waterareas. Deep-waterexplorationists,therefore, need to know how to recognize, interpretand risk-evaluatei ntrusivec omplexes.The frontierVøringa ndM øreb asins off mid-Norwayare classicalexampleso fi ntruded volcanic basins located on arifted volcanic margin( e.g.Skogseid etal .1 992; Skogly 1998;Berndt etal .2 000; Brekke 2000; Gernigon etal .2 003). The volcanic activity inthesebasins wasassociated withLatePaleocenerifting andc ontinentalbreak-up int he NE Atlantic.Similarintrusive basinprovincesarelocated alongthe entireEuropeanNE Atlantic margin(e.g.Gibb &Kanaris-Sotiriou 1988;Bell &Butcher2002; Smallwood&Maresh2002) andonshoreincentral-east Greenland (e.g.Larsen&M arcussen1 992; Price etal .1 997).Sill comp...
The full gradient tensor is presently not measured routinely onboard airplanes or on land. This paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available. We suggest that, in addition to producing for example standard total field anomaly maps, the invariants of the tensor be mapped. Strikes of magnetic or gravimetric structures may be determined from minimizing the power in the first row and column of the tensor. Invariants can be looked upon as nonlinear filters enhancing sources with big volumes. Their lateral resolution is superior to that of the field proper and, for a given resolution, the flight altitude and separation between flight lines can be increased compared with the standard mode of operation. In airborne surveys the distance between flight lines is normally much larger than the height above the ground. This may introduce severe aliasing effects in the direction perpendicular to the flight lines. By increasing the flight altitude, aliasing effects are reduced at the expense of lateral resolution which, however, may be improved by mapping the tensor invariants in addition to the magnetic field. The estimated gradient tensor from total field magnetic data over the Siljan impact region shows that the magnetic properties of the area are very nonuniform even from a height of 430 m above the topography. The nonlinear filters discriminate major anomalies into separate units.
Voluminous volcanism characterized Early Tertiary continental break-up on the mid-Norwegian continental margin. The distribution of the associated extrusive rocks derived from seismic volcanostratigraphy and potential field data interpretation allows us to divide the Møre, Vøring and Lofoten-Vesterålen margins into five segments. The central Møre Margin and the northern Vøring Margin show combinations of volcanic seismic facies units that are characteristic for typical rifted volcanic margins. The LofotenVesterålen Margin, the southern Vøring Margin and the area near the Jan Mayen Fracture Zone show volcanic seismic facies units that are related to small-volume, submarine volcanism. The distribution of subaerial and submarine deposits indicates variations of subsidence along the margin. Vertical movements on the mid-Norwegian margin were primarily controlled by the amount of magmatic crustal thickening, because both the amount of dynamic uplift by the Icelandic mantle plume and the amount of subsidence due to crustal stretching were fairly constant along the margin. Thus, subaerial deposits indicate a large amount of magmatic crustal thickening and an associated reduction in isostatic subsidence, whereas submarine deposits indicate little magmatic thickening and earlier subsidence. From the distribution of volcanic seismic facies units we infer two main reasons for the different amounts of crustal thickening: (1) a general northward decrease of magmatism due to increasing distance from the hot spot and (2) subdued volcanism near the Jan Mayen Fracture Zone as a result of lateral lithospheric heat transport and cooling of the magmatic source region. Furthermore, we interpret small lateral variations in the distribution of volcanic seismic facies units, such as two sets of Inner Seaward Dipping Reflectors on the central Vøring Margin, as indications of crustal fragmentation.
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