The Christmas Cove Dyke of coastal Maine, USA, and regional sources for Early Mesozoic flood basalts in northeastern North America

 A large Early Mesozoic quartz tholeiite dyke has been mapped discontinuously for 190 km in southern coastal Maine, USA. Including its type locality at Christmas Cove (South Bristol, Maine, USA), the dyke has features of a generally ENE strike; dip usually steep to the SSE but abruptly turning very shallow in short sections; and widths of 9 to 35 m. The dyke rock has a distinctive cross-columnar field appearance, and a subophitic to micro-porphyritic texture with abundant Ti-bearing augite, calcic plagioclase, scattered euhedral orthopyroxene phenocrysts, and coarse-grained glomerophyric clumps of augite with plagioclase. Several 40Ar/39Ar whole-rock dates for this and associated regional dykes are close to 201 Ma, in agreement with ages of other Early Mesozoic dykes and basalts of the Central Atlantic Magmatic Province (CAMP). The geographic position, age, whole-rock chemistry, and petrography indicate that the Christmas Cove Dyke is co-magmatic or contiguous with the Higganum-Holden Dyke of southern New England, which was a source for the Talcott Basalt of the Early Mesozoic Hartford rift basin. The dyke system is a 700-km long fissure source for the earliest rift basin basalts preserved in northeastern North America, and it virtually connects the Hartford Basin and the Fundy Basin in Atlantic Canada. The Caraquet Dyke of New Brunswick and central Maine may be co-magmatic with the Buttress Dyke and Holyoke Basalt of southern New England, but lava from it is not preserved in Atlantic Canada or Maine.

Triassic Basin Stratigraphy at Grand Manan, New Brunswick, Canada

The island of Grand Manan (Canada) in the southwestern Bay of Fundy has the only exposed strata and basalt of the Grand Manan Basin, a mainly submerged Early Mesozoic riſt basin about 30 km wide by 70 km long. The basin is bounded on the southeast by the west-dipping Red Point Fault, which bisects the island, and on the northwest by a submarine border fault marked by the Murr Escarpment, a bathymetric feature that parallels the coast of Maine (USA). A fault-bounded horst of Ediacaran to Cambrian rocks separates the Grand Manan Basin from the much larger Fundy Basin to the east. The Ashburton Head, Seven Days Work, and Southwest Head members of the end-Triassic Dark Harbour Basalt cover most of western Grand Manan with a total thickness around 240 m. Up to 12 m of sub-horizontal grey mudstone and fine-grained red sandstone of the Dwellys Cove Formation are exposed along the western shoreline beneath the basalt. Coarse red arkosic sandstone a few metres thick at Miller Pond Road rests on a basement of Late Ediacaran rocks east of the basin. Exposures of the Dwellys Cove and Miller Pond Road formations are at the top and bottom, respectively, of several km (?) of sub-horizontal Late Triassic clastic basin strata, juxtaposed by the eastern border fault. Extending from beneath the Miller Pond Road sandstone, a level surface of low relief forms much of the eastern island and its archipelago, which may be interpreted as a relict Late Triassic peneplain that was beneath the Mesozoic strata. RÉSUMÉ L’île Grand Manan (Canada) au sud‑ouest de la baie de Fundy possède la seule strate et basalte qui affleure du bassin de Grand Manan, un bassin d’effondrement en bonne partie submergé du début du Mésozoïque qui fait environ 30 km de large sur 70 km de long. Ce bassin est bordé au sud-est par la faille de Red Point qui présente en pend-age vers l’ouest et qui traverse l’île de part en part, et au nord‑ouest, par une faille de bordure sous‑marine marquée par l’escarpement Murr, une structure bathymétrique qui longe la côte du Maine (É.‑U.). Un horst bordé par une faille et composé de roches de la période comprise entre Ediacara et le Cambrien sépare le bassin de Grand Manan du bassin de Fundy, beaucoup plus vaste, à l’est. Les membres de Ashburton Head, de Seven Days Work et de Southwest Head de la formation de basalte de Dark Harbour, de la fin du Trias, recouvrent la plus grande partie de l’ouest de l’île Grand Manan, et leur épaisseur totale serait d’environ 240 m. Des roches de mudstone gris subhorizontal et de grès rouge à grains fins de la Formation de Dwellys Cove dont l’épaisseur peut atteindre 12 m affleurent le long du rivage occidental, sous le basalte. Une couche de grès arkosique rouge grossier de quelques mètres d’épaisseur sur Miller Pond Road repose sur un socle de roches de la fin d’Ediacara, à l’est du bassin. Des affleurements des Formations de Dwellys Cove et de Miller Pond Road sont observés respectivement au sommet et à la base de la strate subhorizontale de plusieurs kilomètres (?) d’un bassin de roches clastiques de la fin du Trias, en juxtaposition avec la faille de bordure orientale. Sous le grès de Miller Pond Road, une surface de niveau en terrain peu accidenté se prolonge et compose la plus grande portion de la partie est de l’île et de son archipel, ce qui pourrait suggérer la présence d’une ancienne pénéplaine du Trias tardif qui se trouvait sous la strate du Mésozoïque. [Traduit par la redaction

PETROLOGY AND AGE OF THE LEPREAU RIVER DYKE, SOUTHERN NEW BRUNSWICK, CANADA: SOURCE OF THE END-TRIASSIC FUNDY GROUP BASALTS

A large dyke of quartz-tholeiitic gabbronorite has been mapped for 59 km in southern New Brunswick, Canada, between Lepreau River in the northeast and Indian Island in the southwest. Scattered outcrops occur along a positive aeromagnetic lineament, providing a dyke strike of N42E overall (segments N30E to N72E), dips of 80 to 90NNW, and widths of 4 to 30 m. A new 40Ar/39Ar plagioclase age of 201.67 0.35 Ma for the Lepreau River Dyke is similar to dates for the massive North Mountain Basalt in the Fundy Basin to the east. The dyke is associated with the Ministers Island and Christmas Cove dykes, which are indistinguishable in chemistry, petrology, and probable age, and we regard them as segments of the same co-magmatic dyke system. In addition, their petrology is similar to that of the basalts of the adjacent Early Mesozoic Fundy and Grand Manan basins. We propose that the Lepreau River and associated dykes were sources for the regional basin basalts, which in turn are part of the Central Atlantic Magmatic Province (CAMP) that overlaps the Triassic-Jurassic boundary and associated mass extinction event.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The Christmas Cove Dyke of coastal Maine, USA, and regional sources for Early Mesozoic flood basalts in northeastern North America

A large Early Mesozoic quartz tholeiite dyke has been mapped discontinuously for 190 km in southern coastal Maine, USA. Including its type locality at Christmas Cove (South Bristol, Maine, USA), the dyke has features of a generally ENE strike; dip usually steep to the SSE but abruptly turning very shallow in short sections; and widths of 9 to 35 m. The dyke rock has a distinctive cross-columnar field appearance, and a subophitic to micro-porphyritic texture with abundant Ti-bearing augite, calcic plagioclase, scattered euhedral orthopyroxene phenocrysts, and coarse-grained glomerophyric clumps of augite with plagioclase. Several 40Ar/39Ar whole-rock dates for this and associated regional dykes are close to 201 Ma, in agreement with ages of other Early Mesozoic dykes and basalts of the Central Atlantic Magmatic Province (CAMP). The geographic position, age, whole-rock chemistry, and petrography indicate that the Christmas Cove Dyke is co-magmatic or contiguous with the Higganum-Holden Dyke of southern New England, which was a source for the Talcott Basalt of the Early Mesozoic Hartford rift basin. The dyke system is a 700-km long fissure source for the earliest rift basin basalts preserved in northeastern North America, and it virtually connects the Hartford Basin and the Fundy Basin in Atlantic Canada. The Caraquet Dyke of New Brunswick and central Maine may be co-magmatic with the Buttress Dyke and Holyoke Basalt of southern New England, but lava from it is not preserved in Atlantic Canada or Maine