A Dyke Swarm and Crustal Flexure in East Greenland

Wager, L. R.; Deer, W. A.

doi:10.1017/s0016756800089226

Cited by 95 publications

(27 citation statements)

References 1 publication

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“…Larsen (1978) suggested that an offshore continuation of the East Greenland coastal dike swarm and flexure zone (e.g., Wager and Deer, 1938;Nielsen, 1978;Myers, 1980;Bird et al, 1988;Myers et al, 1993;Klausen et al, 1996) is present within this onlap zone. Seismic data (Larsen, 1990) and Leg 152 drilling confirmed the presence of a seaward-dipping flexure zone including rift lavas on top of continental crust.…”

Section: Detailed Setting Of Drilling Transectmentioning

confidence: 99%

Tectonism and volcanism at the southeast Greenland rifted margin: a record of plume impact and later continental rupture

Larsen¹,

Saunders²

1998

Proceedings of the Ocean Drilling Program

112

141

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During Ocean Drilling Program Leg 152, Sites 914 through 919 were drilled on the southeast Greenland Margin along a transect from the middle shelf into the adjacent deep-water Irminger Basin 500 km south of the Iceland hot-spot track (IcelandGreenland Ridge). Sites 915 through 918 penetrated the entire cover of postrift sediments, and three of these four sites sampled the volcanic basement of the seaward-dipping reflector sequences (SDRS). The landward featheredge of the SDRS was drilled at the most landward site, Site 917, where a 779.5-m-thick, south to southeastward dipping volcanic section was found to overlie steeply dipping, marine pre-rift sediments of unknown, possibly Cretaceous, age. The more seaward Site 915 (later deepened by Site 990) recovered two lava flows that are stratigraphically located above Site 917 and located within the oldest part of the main SDRS wedge. The central part of the SDRS wedge was penetrated at Site 918 in the Irminger Basin where a 120-mthick lava section was recovered below 1189 m of postrift sediments. A few sills and dikes were sampled. All other igneous units recovered were subaerially erupted and deposited lavas, some of which may have flowed over wet ground or into shallow water. Lavas at Site 917 display compositions ranging from picrite over olivine basalt to basalt, dacite, and acid tuffs. The younger lavas at Site 915 and Site 918 have a quite uniform composition similar to depleted Icelandic tholeiites. Two major successions are defined: the older Continental Succession and the younger Oceanic Succession. The Continental Succession comprises the Lower and Middle Series lavas at Site 917, and the Oceanic Succession comprises the Uppers Series lavas at Site 917 and the main SDRS series lavas at Sites 915 (and Site 990) and Site 918. The Oceanic Succession is separated from the Continental Succession by an unconformity and a thin sediment horizon. The Oceanic Succession shows strongly decreasing (to absent) continental contamination, a primary melting depth extending to a shallower level (spinel field), and, apart from the initial picritic Site 917 Upper Series, a much more uniform composition and a less depleted source than the Continental Sucession. The age of the reversely magnetized Continental Succession is approximately 61−60 Ma, possibly slightly older, and is related to magnetic Chron C26r (possibly C27r). The main part of the Oceanic Succession is 56−53 Ma (magnetic Chron C24r), with the oldest part extending into C25r. Except for six of the youngest lava flows in the Lower Series, the Continental Succession had a depleted (ambient asthenosphere?) mantle source, and magmas underwent considerable fractionation in crustal magma chambers. The Oceanic Succession, except for the initial Site 917 Upper Series, had a slightly less depleted mantle source. Tentative estimates of eruption rates vary from 1/11 k.y. within the Continental Succession to 1/670 yr within the main SDRS wedge. Likewise, the total magmatic flux is estimated to vary from (maximum) 0.22...

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Section: Detailed Setting Of Drilling Transectmentioning

confidence: 99%

Tectonism and volcanism at the southeast Greenland rifted margin: a record of plume impact and later continental rupture

Larsen¹,

Saunders²

1998

Proceedings of the Ocean Drilling Program

112

141

View full text Add to dashboard Cite

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“…The margin-parallel flexure zone is close to the coast from about 66° to 68°N where it parallels the East Greenland coastal dike swarm (Wager and Deer, 1938;Nielsen, 1978;Larsen, 1978;Myers, 1980;Karson et al, 1994). Shallow seismic data along the EG63 transect indicate the presence of landward-dipping normal faults bounding blocks of seaward-dipping reflectors (lavas) within the flexure zone.…”

Section: Coast-parallel Crustal Flexure Zonementioning

confidence: 99%

Crustal structure along the Leg 152 drilling transect

Larsen¹,

Dahl‐Jensen²,

Hopper³

1998

Proceedings of the Ocean Drilling Program

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Seismic data, drilling data, and gravity data define a 40-km-wide continent-ocean transition (COT) below the outer half of the 70-to 80-km-wide shelf along the Leg 152 drilling transect. The seismic data include a detailed grid of shallow high-resolution seismic data; a regional grid of conventional multichannel seismic data (including sonobuoy refraction data); and a deep crustal, vertical incidence multichannel seismic profile. Below the outer shelf, the top of the Precambrian crust off southeast Greenland dips through a normally faulted, seaward-facing flexure zone below the landward feather edge of the seaward-dipping reflector sequence (SDRS), which is subaerially erupted basaltic lavas. Associated with the flexure zone, the continental crust thins from approximately 28 km thick to almost zero over a maximum distance of 40 km. Variations in present-day crustal thickness are much less because of accretion of thick igneous crust during breakup. Most of the thinning of the continental crust takes place within only 25 km from the mid-shelf flexure zone. Within this zone, landward-dipping normal faults are present in the upper continental crust, indicating that thinning was accommodated by fault-related crustal extension. Lower crustal thinning appears to be of a different nature and may be related to "intrusive" underplating. The seismically defined COT is consistent with a distinct development from initially continental to oceanic volcanism observed in the boreholes. The new igneous SDRS crust seems to be 20−22 km thick, including at least 5 km of lava in the upper crust. Deep reflections located below the COT at 30−35 km depth may represent a pillow of thick (10 km or more) underplated material or intra-mantle reflections from a residual mantle.

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“…Penecontemporaneous plutonic activity produced numerous layered gabbro intrusions along the unconformity between the sedimentary rocks and basalts and the underlying gneisses. In the present day coastal region, faulting rotated igneous layering and other structures, as gabbroic plutonism ceased (Wager & Deer, 1938; and sea-floor spreading began. Sporadic gabbroic and syenitic plutonism continued until 35 Ma (Brooks & Nielsen, 1982;Deer, Kempe & Jones, 1984;Nielsen, 1987;Noble, Macintyre & Brown, 1988).…”

Section: Geology Of the Gabbro Complex 2a Regional Settingmentioning

confidence: 99%

Petrology and geochemistry of the Kruuse Fjord Gabbro Complex, East Greenland

Arnason

Bird

Bernstein³

et al. 1997

Geol. Mag.

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The Kruuse Fjord Gabbro Complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies. It was emplaced into Archaean continental crust of East Greenland during early Tertiary rifting of Greenland from Eurasia. The work to date has identified an outer gabbro series and an inner troctolite series, and these are separated by a narrow zone of trondhjemitic intrusions. In the southeast, the partially crystallized cumulates of the gabbro series were intruded by a lenticular, ultramafic pluton 800 m in thickness. Volumetrically minor, syenite–trachyandesite net-veined dykes and later, diabase dykes cross-cut the plutonic rocks. Structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure.The gabbro series is composed of a marginal gabbro unit, about 20 m wide, bordering more than a 2 km thickness of layered olivine and magnetite gabbro cumulates. The marginal gabbro is interpreted to be chilled magma. The layered cumulates are the product of repeated injections of magma that fractionated in an open-system magma chamber. Anorthositic and troctolitic layers in the lower part of the sequence may represent inputs of magma and suggest that the order of cumulus mineral crystallization was (1) plagioclase (An39–85), (2) olivine (Fo46–82), (3) augite (Wo28–47En39–58Fs8–18 ) and (4) magnetite. The disappearance of cumulus magnetite and a reversal in mineral compositions at 1.5 km from the base of the succession suggests a major input of magma occurred at this height. In the troctolite series, the composition of cumulus minerals, mineral crystallization sequence and style of emplacement are similar to those in the gabbro series. The ultramafic pluton is composed of coarse-grained wehrlite, olivine melagabbro and troctolite that were formed by at least three injections of magma. The typical mineral crystallization sequence was (1) cumulus chromite and olivine (Fo84–88); (2) poikilitic chrome diopside (Wo29–51En43–63Fs3–13 ); and (3) intercumulus plagioclase (An75–90), phlogopite, apatite and localized disseminated sulphides containing Au and platinum-group elements.Comparison of crystallization sequences and the major and trace element compositions of clinopyroxene suggests that the gabbroic and troctolitic rocks formed from a magma represented by the chilled marginal gabbro, a tholeiitic basalt magma similar to E-MORB, whereas the ultramafic rocks formed from a magma that was relatively enriched in incompatible trace elements and volatiles. The association of these two magma types is an example of bimodal mafic–ultramafic magmatism in a rifting environment.

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A Dyke Swarm and Crustal Flexure in East Greenland

Cited by 95 publications

References 1 publication

Tectonism and volcanism at the southeast Greenland rifted margin: a record of plume impact and later continental rupture

Tectonism and volcanism at the southeast Greenland rifted margin: a record of plume impact and later continental rupture

Crustal structure along the Leg 152 drilling transect

Petrology and geochemistry of the Kruuse Fjord Gabbro Complex, East Greenland

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