Palaeogene Continental to Oceanic Magmatism on the SE Greenland Continental Margin at 63°N: a Review of the Results of Ocean Drilling Program Legs 152 and 163 (original) (raw)
Related papers
Journal of Petrology, 2000
mantle melting zone, accompanied by an increase in the average Drilling along a 63°N transect off SE Greenland during Ocean degree of melting with time from >4% to >12%. These modest Drilling Program (ODP) Legs 152 and 163 recovered a succession degrees of melting imply mantle temperatures only >100°C hotter of volcanic rocks representing all stages in the break-up of the than normal upper mantle. Upwelling mantle must therefore have volcanic rifted margin. The rocks range from pre-break-up continental been fed dynamically to the melt zone to generate the igneous crust tholeiitic flood basalt, through syn-break-up picrite, to truly oceanic of 18 km thickness deduced from seismic and gravity studies. Nbasalt forming the main part of the seaward-dipping reflector MORB-like magmas dominated the earliest part of the succession sequence (SDRS). All the lava flows recovered from the transect although a few flows of 'Icelandic' basalt were erupted in the prewere erupted in a subaerial environment. 40 Ar-39 Ar dating shows break-up phase. In contrast, the post-break-up magmas had an that the earliest magmas were erupted at >61 Ma and has Icelandic mantle source. This suggests that the developing head of confirmed that the main part of the SDRS was erupted during C24r the ancestral Iceland plume was compositionally zoned, with a core (56-53 Ma) following continental break-up. Magma represented by of Icelandic mantle surrounded by a thick outer zone of hot, depleted the pre-break-up lava flows was stored in crustal reservoirs where upper mantle. it evolved by fractional crystallization and assimilation of continental crust. Trace element and radiogenic isotope data show that the contaminant changed, through time, from lower-crustal granulite to a mixture of granulite and amphibolite, suggesting storage of magma at progressively shallower levels in the crust. The degree of contamination declined rapidly as break-up proceeded, and the youngest rocks sampled in the transect are uncontaminated by continental basement. Variation of, for example, Sc/Zr and Sm/ KEY WORDS: flood basalt; geochemistry; Greenland; Palaeogene; Sr-Nd-Pb isotopes Lu through the succession suggests a shallowing of the top of the * Corresponding
Polyphase magmatism during the formation of the northern East Greenland continental margin
Tectonics
New marine geophysical data acquired across the partly ice-covered northern East Greenland continental margin highlight a complex interaction between tectonic and magmatic events. Breakup-related lava flows are imaged in reflection seismic data as seaward dipping reflectors, which are found to decrease in size both northward and southward from a central point at 75°N. We provide evidence that the magnetic anomaly pattern in the shelf area is related to volcanic phases and not to the presence of oceanic crust. The remnant magnetization of the individual lava flows is used to deduce a relative timing of the emplacement of the volcanic wedges. We find that the seaward dipping reflectors have been emplaced over a period of 2-4 Ma progressively from north to south and from landward to seaward. The new data indicate a major post-middle Eocene magmatic phase around the landward termination of the West Jan Mayen Fracture Zone. This post-40-Ma volcanism likely was associated with the progressive separation of the Jan Mayen microcontinent from East Greenland. The breakup of the Greenland Sea started at several isolated seafloor spreading cells whose location was controlled by rift structures and led to the present-day segmentation of the margin. The original rift basins were subsequently connected by steady-state seafloor spreading that propagated southward, from the Greenland Fracture Zone to the Jan Mayen Fracture Zone.
40Ar/39Ar geochronology of the West Greenland Tertiary volcanic province
Earth and Planetary Science Letters, 1998
Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A 40 Ar= 39 Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that ¾80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60:5 š 0:4 Ma). Minimum estimates of magma production rates (1:3 ð 10 4 km 3 year 1 km 1) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to < 0:7 ð 10 4 km 3 year 1 km 1 (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British-Irish province. This is interpreted as manifesting the impact and rapid (>1 m=year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at ¾62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at ¾55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.
1998
The lavas drilled during Ocean Drilling Program Leg 152 on the southeast Greenland Margin cover almost the whole compositional variation found in the North Atlantic volcanic province, ranging from picrites to dacites. Evidence for high-MgO melts, indicating a hotter than normal (plume) mantle is now found in several widespread areas, regardless of the distance to the assumed plume center. In most areas of the North Atlantic, several parallel fractionation trends are present, indicating several independent magma types and magma generation events. Fe-and Ti-enriched fractionated three-phase cotectic basalts are characteristic of the North Atlantic province but are not present at the southeast Greenland Margin except for one young sill. The Tertiary basalts are richer in FeOT and poorer in Na 2 O than normal mid-ocean-ridge basalts (MORB), indicating melting of hot plume material under a continental/lithospheric lid. The lavas from the southeast Greenland Margin, the Hatton Bank Margin, and the British Isles apparently formed from less hot mantle than the rest. Parts of this southern mantle were more depleted in incompatible elements than the mantle in other areas. The lavas from Hatton Bank and Site 918 have unusually high Sc contents, unparalleled in modern MORBs. All seaward-dipping reflector sequences drilled up to now (Vøring Margin, Hatton Margin, southeast Greenland Margin) include crustally contaminated rocks in the oldest parts of the sequences. Thick Tertiary dacite successions formed only over the peripheral parts of the mantle plume head. The crustal contaminant at the southeast Greenland Margin is similar to that in the British Isles and Kangerlussuaq and is in strong contrast to the crustal component in the Hatton Bank lavas. This is in accordance with the situation of these areas in different Precambrian structural and age provinces in the North Atlantic region.
Proceedings of the Ocean Drilling Program. Scientific results, 1998
The lavas drilled during Ocean Drilling Program Leg 152 on the southeast Greenland Margin cover almost the whole compositional variation found in the North Atlantic volcanic province, ranging from picrites to dacites. Evidence for high-MgO melts, indicating a hotter than normal (plume) mantle is now found in several widespread areas, regardless of the distance to the assumed plume center. In most areas of the North Atlantic, several parallel fractionation trends are present, indicating several independent magma types and magma generation events. Fe-and Ti-enriched fractionated three-phase cotectic basalts are characteristic of the North Atlantic province but are not present at the southeast Greenland Margin except for one young sill. The Tertiary basalts are richer in FeOT and poorer in Na 2 O than normal mid-ocean-ridge basalts (MORB), indicating melting of hot plume material under a continental/lithospheric lid. The lavas from the southeast Greenland Margin, the Hatton Bank Margin, and the British Isles apparently formed from less hot mantle than the rest. Parts of this southern mantle were more depleted in incompatible elements than the mantle in other areas. The lavas from Hatton Bank and Site 918 have unusually high Sc contents, unparalleled in modern MORBs. All seaward-dipping reflector sequences drilled up to now (Vøring Margin, Hatton Margin, southeast Greenland Margin) include crustally contaminated rocks in the oldest parts of the sequences. Thick Tertiary dacite successions formed only over the peripheral parts of the mantle plume head. The crustal contaminant at the southeast Greenland Margin is similar to that in the British Isles and Kangerlussuaq and is in strong contrast to the crustal component in the Hatton Bank lavas. This is in accordance with the situation of these areas in different Precambrian structural and age provinces in the North Atlantic region.
Seismic volcanostratigraphy of the NE Greenland continental margin
Geological Society, London, Special Publications
The Early Eocene continental break-up between the NE Greenland and the mid-Norwegian-SW Barents Sea margins was associated with voluminous magmatism and led to the emplacement of massive volcanic complexes including wedges of seawards-dipping reflections (SDR). We study the distribution of these break-up-related volcanic rocks along the NE Greenland margin by revisiting existing seismic reflection data and comparing our observations to betterstudied segments of the conjugate margin. Seismic facies types match between the conjugate margins and show strong lateral variations. Seaward-dipping wedges are mapped offshore East Greenland, the conjugate to the Vøring continental margin. The geophysical signature of the SDRs becomes less visible towards the north, as it does along the conjugate Lofoten-Vesterålen margin. We suggest that the Traill Ø volcanic ridge is a result of plume-ridge interactions formed between approximately 54 and 47 Ma. North of the East Greenland Ridge, strong basement reflections conjugate to the Vestbakken Volcanic Province are interpreted as lava flows or 'spurious' SDRs. We discuss our findings in conjunction with results from seismic wide-angle experiments, gravity and magnetic data. We focus on the spatial and temporal relationships of the break-up volcanic rocks, and their structural setting in a late rift and initial oceanic drift stage.
Geological Society, London, Special Publications, 2009
Eo-to Mesoarchaean greenstone belts (e.g. 3800-3700 Ma Isua, c. 3075 Ma Ivisaartoq, 3071 Ma Qussuk) occur within orthogneisses of the southern West Greenland Craton. Greenstone belts are composed mainly of metavolcanic rocks with minor ultramafic and sedimentary schists. Compositionally, volcanic rocks are dominantly tholeiitic basalts, boninites, and picrites, with minor intermediate to felsic volcanic rocks. These greenstone belts appear to have formed in convergent margin geodynamic settings. Detailed field observations, contrasting ages, and metamorphic and structural histories suggest that this craton was assembled in several accretionary tectonothermal events, involving accretion of arcs, back-arcs, forearcs, and continental fragments by horizontal tectonics. The Superior Province of Canada was also built by the amalgamation of oceanic and continental fragments ranging in age from 3700 to 2650 Ma, during five discrete tectonothermal events over 40 Ma between 2720 and 2680 Ma. The Neoarchaean (2750-2670 Ma) Wawa greenstone belts are composed of tectonically juxtaposed fragments of oceanic plateaux, oceanic island arcs, back-arcs, and siliciclastic trench turbidites. Following juxtaposition, these diverse lithologies were collectively intruded by syn-to post-kinematic granitoids with subduction zone geochemical signatures. Oceanic island arc lavas are easily distinguished from oceanic plateau counterparts because they possess positively fractionated rare earth element (La/Sm cn . 1 and Gd/Yb cn . 1) and high field strength element depleted (Nb/Th pm , 1; Nb/La pm , 1) patterns. In addition, the island arc association includes pyroclastic rocks that are rare to absent in the oceanic plateau volcanic association. Structural studies indicate that the Wawa greenstone belts underwent a complex history of deformation including thrusting, strike-slip faulting, and asymmetric folding. These belts constitute part of a c. 1000 km scale subduction-accretion complex that formed along an intra-oceanic convergent plate margin during trenchward migration of the magmatic arc axis. Several first-order geological observations on Archaean greenstone belts of SW Greenland and the Superior Province suggest that Phanerozoic-style plate-tectonic models can provide an elegant explanation for their structural, lithological, metamorphic and geochemical characteristics.
ODP Preliminary Report, 1993
The principal objectives of Leg 152 were to sample the basalts of the seaward-dipping reflector sequences (SDRS) on the continental margin of southeast Greenland and in the adjacent Irminger Basin. The leg aimed to achieve deep penetration (400 m) at one site on the featheredge of the SDRS and another deep site in the center of the sequence. Drilling of the cover sediments was aimed at recording the subsidence history of the margin and the paleoceanographic development of this part of the North Atlantic. Four sites (914-917) were drilled on the shelf in 500 m of water, and two on the continental rise in 1868 m (Site 918) and 2088 m (Site 919). Deep penetration (779 m) into the earliest basalts of the SDRS was achieved at Site 917, recording the nature of some of the earliest volcanism and the nature of the breakup unconformity and immediate substrata. Three lava series were identified, an Upper Series of picrites and high Mg-basalts, a Middle Series of dacites and evolved basalts and a Lower Series of basalts and rare olivine basalts. The middle and Upper Series are separated by thin fluvial sandstones. Flow thicknesses decrease systematically upsection. All three series appear to be derived by melting of a normal MORB-like depleted upper mantle. Contamination of the lavas by continental lithosphere was recognized in the trace element composition (high Ba, K, Sr) of the two lower series. Further basalt drilling at Site 918 showed that a MORB source was the source of all the magmatic melts during SDRS eruption. No evidence was found to implicate the presence of a chemically less depleted mantle plume, similar to that underlying the modern Icelandic hotspot, although the presence of large volumes of magma and picritic basalts clearly indicates the need for a thermally anomalous mantle source. Weathering horizons and intercalated sediments demonstrate that the lavas were erupted in a subaerial environment. Penetration of the basal breakup unconformity moreover indicates that the Greenland crust had been stretched, subsided and then uplifted into a subaerial environment prior to SDRS volcanism. Eruption rates were very high, with the whole 150-km-wide SDRS apparently having been produced during magnetic Chron 24r (latest Paleocene to early Eocene), spanning only 2.7 m.y. Gradual thermal cooling of the margin has resulted in gradual subsidence since that time. Sites 914-917 have remained at shelf depths probably due to buoyant underlying continental crust, while Site 918 subsided rapidly, as it lies east of the sharp ocean-continent transition. An influx of terrigenous turbidites in the Irminger Basin during the late Leg 152 Preliminary Report Page 8 Oligocene may reflect both a fall in eustatic sea level and the start of (flexural) uplift of the Greenland margin. Ridge-push from the Reykjanes Ridge may have instigated the uplift and is seen in the shape of boreholes measured by caliper logging tools. Development of glauconitic hardgrounds within middle Miocene chalks indicates a start to the flow of the cold North Atlantic Deep Water (NADW) at 13-11 Ma into the Irminger Basin over the subsiding Iceland-Greenland Ridge. Microfauna suggest a warm climate up to this time. The first occurrence of ice-rafted debris is in marine silts of 7 Ma (late Miocene). The provenance of dropstones clearly points to a previously unrecorded early glaciation of southern Greenland. The date predates other estimates of North Atlantic glaciation by about 3-4 Ma and may indicate that the later widespread North Atlantic glaciation nucleated in this area.