History and mechanism of eruption of soda-rhyolite and alkali basalt, Socorro Island, Mexico

1966 ◽  
Vol 29 (1) ◽  
pp. 453-479 ◽  
Author(s):  
W. B. Bryan
Keyword(s):  
Alkali Basalt ◽  
Socorro Island

40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea

1999 ◽  
pp. 19-29 ◽  
Author(s):  
Lotte Melchior Larsen ◽  
David C. Rex ◽  
W. Stuart Watt ◽  
Philip G. Guise
Keyword(s):  
Alkali Basalt ◽  
Dyke Swarm ◽  
Labrador Sea ◽  
Precambrian Basement ◽  
Stress Regime ◽  
Southwest Coast ◽  
Eastern Margin ◽  
Step Heating ◽  
Igneous Activity ◽  
Break Up

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Melchior Larsen, L., Rex, D. C., Watt, W. S., & Guise, P. G. (1999). 40Ar–39Ar dating of alkali basaltic dykes along the southwest coast of Greenland: Cretaceous and Tertiary igneous activity along the eastern margin of the Labrador Sea. Geology of Greenland Survey Bulletin, 184, 19-29. https://doi.org/10.34194/ggub.v184.5227 _______________ A 380 km long coast-parallel alkali basalt dyke swarm cutting the Precambrian basement in south-western Greenland has generally been regarded as one of the earliest manifestations of rifting during continental stretching prior to break-up in the Labrador Sea. Therefore, the age of this swarm has been used in models for the evolution of the Labrador Sea, although it has been uncertain due to earlier discrepant K–Ar dates. Two dykes from this swarm situated 200 km apart have now been dated by the 40Ar–39Ar step-heating method. Separated biotites yield plateau ages of 133.3 ± 0.7 Ma and 138.6 ± 0.7 Ma, respectively. One of the dykes has excess argon. Plagioclase separates confirm the biotite ages but yield less precise results. The age 133– 138 Ma is earliest Cretaceous, Berriasian to Valanginian, and the dyke swarm is near-coeval with the oldest igneous rocks (the Alexis Formation) on the Labrador shelf. A small swarm of alkali basalt dykes in the Sukkertoppen (Maniitsoq) region of southern West Greenland was also dated. Two separated kaersutites from one sample yield an average plateau age of 55.2 ± 1.2 Ma. This is the Paleocene–Eocene boundary. The swarm represents the only known rocks of that age within several hundred kilometres and may be related to changes in the stress regime during reorganisation of plate movements at 55 Ma when break-up between Greenland and Europe took place.

Bafliaz volcanics, NW Himalaya: origin of a bimodal, tholeiite and alkali basalt suite

1994 ◽  
Vol 114 (3-4) ◽  
pp. 217-234 ◽  
Author(s):  
M.I. Bhat ◽  
P. Le Fort ◽  
T. Ahmad
Keyword(s):  
Alkali Basalt ◽  
Nw Himalaya

scholarly journals Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 23-36
Author(s):  
Tomoaki Morishita ◽  
Naoto Hirano ◽  
Hirochika Sumino ◽  
Hiroshi Sato ◽  
Tomoyuki Shibata ◽  
...  
Keyword(s):  
Partial Melting ◽  
Sea Of Japan ◽  
Alkali Basalt ◽  
Spinel Peridotite ◽  
The Sea Of Japan ◽  
Low Degree ◽  
Tsushima Basin ◽  
Arc Setting ◽  
Element Enrichment ◽  
Back Arc

Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.

scholarly journals Phylogenetic Position and Generic Placement of The Socorro Wren (Thryomanes Sissonii)

The Auk ◽  
2005 ◽  
Vol 122 (1) ◽  
pp. 50-56 ◽  
Author(s):  
Juan E. Martínez Gómez ◽  
Brian R. Barber ◽  
A. Townsend Peterson
Keyword(s):  
Mitochondrial Dna ◽  
Dna Sequences ◽  
Species Complex ◽  
Taxonomic Classification ◽  
Phylogenetic Position ◽  
Base Pairs ◽  
House Wren ◽  
Taxonomic History ◽  
Socorro Island ◽  
Nd2 Gene

Abstract Since early in its taxonomic history, placement of the Socorro Wren (Thryomanes sissonii) has been an object of contention. Of particular interest is its current placement in the genus Thryomanes, which makes that genus ditypic and leads to an odd biogeographic scenario for the Socorro Wren's colonization of Socorro Island. We assessed its phylogenetic position by analyzing 516 base pairs of mitochondrial DNA sequences from the ND2 gene of this species and 14 additional wren taxa. Contrary to its present placement, the Socorro Wren is nested phylogenetically within the House Wren species complex, being placed as sister to the clade Troglodytes aedon + T. musculus. The current hypothesis (i.e. sister to Thryomanes bewickii) is strongly invalidated by our analysis. Our analyses indicate that the most appropriate taxonomic classification for the Socorro Wren is Troglodytes sissonii. Posición Filogenética y Ubicación Genérica de Thryomanes sissonii

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