Robertson, Alastair H. F. (2007): Evidence of continental breakup from the Newfoundland rifted margin (Ocean Drilling Program Leg 210); Lower Cretaceous seafloor formed by exhumation of subcontinental lithosphere and the transition to seafloor spreading. Texas A&M University, Ocean Drilling Program, College Station, TX, United States, In: Tucholke, Brian E., Sibuet, Jean-Claude, Klaus, Adam, Arnaboldi, Michela, Delius, Heike, Engstrom, Anna V., Galbrun, Bruno, Gardin, Silvia, Hiscott, Richard N., Karner, Garry D., Ladner, Bryan C., Leckie, R. Mark, Lee, Chao-Shing, Manatschal, Gianreto, Marsaglia, Kathleen M., Pletsch, Thomas K., Pross, Joerg, Robertson, Alastair H. F., Sawyer, Dale S., Sawyer, Derek E., Shillington, Donna J., Shirai, Masaaki, Shryane, Therese, Stant, Sharon Audra, Takata, Hiroyuki, Urquhart, Elspeth, Wilson, Chris, Zhao, Xixi, Proceedings of the Ocean Drilling Program; scientific results; drilling the Newfoundland half of the Newfoundland-Iberia transect; the first conjugate margin drilling in a nonvolcanic rift; covering Leg 210 of the cruises of the Drilling Vessel JOIDES Resolution; St. Georges, Bermuda, to St. John's, Newfoundland; sites 1276 and 1277; 6 July-6 September 2003, 210, georefid:2007-087762

Drilling of the distal Newfoundland margin at Ocean Drilling Program Site 1277 recovered part of the transition between exhumed subcontinental mantle lithosphere and normal mid-ocean-ridge basalt (NMORB) volcanism perhaps related to the initiation of seafloor spreading, which may have occurred near the Aptian/Albian boundary, coincident with the final separation of subcontinental mantle lithosphere. Subcontinental mantle lithosphere was recovered near the crest of a basement high, the Mauzy Ridge. This ridge lies near magnetic Anomaly M1 and is inferred to be of Barremian age. The recovered section is dominated by serpentinized spinel harzburgite, with subordinate dunite and minor gabbroic intrusives, and it includes inferred high-temperature ductile shear zones. The serpentinite is capped by foliated gabbro cataclasite that is interpreted as the product of a major seafloor extensional detachment. The serpentinized harzburgite beneath is highly depleted subcontinental mantle lithosphere that was exhumed to create new seafloor within the ocean-continent transition zone. After inferred removal of overlying brittle crust, the detachment was eroded, producing multiple mass flows that were dominated by clasts of serpentinite and gabbro in a lithoclastic and calcareous matrix. Basaltic lavas were erupted spasmodically, mainly as sheet flows, with subordinate lava breccia, hyaloclastite, and possible pillow lava. The sedimentary-volcanic succession and the exhumed mantle lithosphere experienced later high-angle extensional fracturing and probably faulting. Extensional fissures opened incrementally and were filled with silt-sized carbonate, basalt-derived clastic sediment, and hyaloclastite, forming neptunian dykes and geopetal structures. Chemical analysis of representative basalts for major elements and trace elements were made using a high-precision, high-accuracy X-ray fluorescence method (utilizing increased count times) and by wholerock inductively coupled plasma-mass spectrometry that yielded additional evidence for rare earth elements. The analyses indicate N-MORB to slightly enriched compositions. The MORB was produced by relatively high degree melting of a fertile mantle source that differed strongly from the cored serpentinized peridotites. The basalts exhibit a distinct negative Nb anomaly on MORB-normalized plots that can be explained by prior extraction of melt from upper mantle that had previously been affected by subduction, possibly during closure of the Iapetus or Rheic oceans. In the proposed interpretation, mantle lithosphere was exhumed to the seafloor and experienced mass wasting to form serpentinite-rich mass flows. The interbedded MORB records the beginning of a transition to "normal" seafloor spreading. This interpretation takes into account drilling results from the Iberia-Galicia margin and the Jurassic Alps-Apennines.
West: -44.4700 East: -44.4700 North: 45.2400 South: 45.2400
Expedition: 103
Expedition: 149
Expedition: 173
Expedition: 210
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