@article {6868, title = {Basalts from the Chukchi Borderland: 40Ar/39Ar Ages and Geochemistry of Submarine Intraplate Lavas Dredged from the Western Arctic Ocean}, volume = {125}, year = {2020}, month = {May 11}, publisher = {American Geophysical Union}, abstract = {

Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mantle plume based on geophysics and meager geochemical evidence. Basaltic samples dredged from Chukchi Borderland within the basin have produced minimum 40Ar/39Ar ages for eruption at ca. 118-112 Ma, ca. 105-100 Ma and ca. 90-70 Ma, which we use to constrain tectonic models for basin opening. Major-oxide and trace-element concentrations, and Sr, Nd, and Hf isotopic ratios of the lavas show that the ca. 118-112 Ma samples from Northwind Ridge are tholeiites (low-Ti tholeiite I) with low degrees of rare-earth-element (REE) fractionation, high overall HREE and Mg$\#$, which suggests magma derivation from a garnet-free source followed by minor crystal fractionation. Strontium, Nd and Hf isotope systematics for these lavas, and ratios of highly incompatible trace elements, point toward a lithospheric source. Eruptions at ca. 105-100 Ma and ca. 90-70 Ma, both at Healy Spur, produced two types of lavas: low-Ti tholeiite II \– which are generally older than high-Ti tholeiite \– both common in continental flood basalt (CFB) provinces, and both with trace-element abundance patterns typifying a garnet-free source, and significant crystal fractionation for the high-Ti tholeiite. The isotope characteristics for both groups are common features of asthenospheric sources. Composition-time relationships for the lavas suggest inception of melting in the sub-continental lithospheric mantle (SCLM) \– probably due to introduction of a heat source by a plume \– followed later (at ca. 105-100 Ma and ca. 90-70 Ma) by asthenospheric melting possibly triggered by plume rise.

}, doi = {https://doi.org/10.1029/2019JB017604}, author = {Mukasa, S B and Andronikov, A and Brumley, K and Larry A Mayer and Andrew A. Armstrong} } @proceedings {5704, title = {Alpha / Mendeleev Ridge and Chukchi Borderland 40Ar/39Ar Geochronology and Geochemistry: Character of the First Submarine Intraplate Lavas Recovered from the Arctic Ocean}, volume = {17}, year = {2015}, month = {April 12 - 17}, address = {Vienna, Austria}, abstract = {

At least three episodes of magmatic activity have been recognized on the basis of 40Ar/39Ar age determinations in the submarine basaltic samples dredged, drilled or grabbed with a manipulation arm from Alpha / Mendeleev Ridge and Chukchi Borderland of the Arctic Ocean by US Coast Guard Icebreaker Healy, in August-September 2008, and Russian research vessel Captain Dranitsin in August-October 2012: ca. 112 Ma, ca. 100 Ma and ca. 85-73 Ma. Major-oxide and trace-element concentrations, and Pb, Sr, Nd, and Hf isotopic ratios of the recovered lavas provide important constraints on the composition and sources for the original melts. Lavas erupted at ca. 112 Ma (Group 1) have alkali basalt major-oxide compositions. Their low degree of rare-earth-element (REE) fractionation (CeN/YbN = 1.7-2.5), combined with high overall HREE (22-24 times chondrite) and Mg$\#$ ~54, suggest derivation from a garnet-free source followed by only minimal crystal fractionation for this group. Pb-Sr-Nd-Hf isotopic systematics of the lavas (206Pb/204Pb = 18.73-18.79; 207Pb/204Pb = 15.54-15.56; 208Pb/204Pb = 38.28-38.35; 143Nd/144Nd = 0.512594-0.512610; 87Sr/86Sr = 0.709458-0.709601; 176Hf/177Hf = 0.283224), together with ratios of highly incompatible trace elements (Th/Ce = 0.09-0.11; Ce/Nb = 2.58-3.09; Th/Nb = 0.24-0.33), point toward a lithospheric source for the magmas. Eruptions at ca. 100 Ma and 85-73 Ma produced two types of lavas: low-Ti tholeiitic basalts - LT, and high-Ti alkali basalts - HT, both assigned to Group 2. This distribution of low- and high-Ti lavas is common in continental flood basalt (CFB) provinces elsewhere, and has been attributed to plume activity in some studies. The trace-element abundance patterns for these Group 2 Arctic lavas are also very similar to those of CFBs elsewhere. Their low degrees of REE fractionation (CeN/YbN = 2.0-3.3) accompanied by progressively decreasing Mg$\#$s (from 53 to 33) suggest a garnet-free source, with the derivative magmas experiencing significant crystal fractionation prior to eruption. Both LT and HT basalts have Sr, Nd and Hf isotope ratios that fall between MORB and Bulk Silicate Earth (143Nd/144Nd = 0.512669-0.512919; 87Sr/86Sr = 0.703820-0.704764; 176Hf/177Hf = 0.283128-0.283191), and are thus characterized as depleted, most likely originating in a subcontinental asthenospheric source. Contamination of these lavas with small amounts of lithospheric components is a distinct possibility. HT basalts, generally the younger of the two lava types in Group 2, are more depleted in their Nd and Sr isotopic compositions than the older LT basalts. Measured Pb-isotopic ratios plot mostly along and above the Northern Hemisphere Reference Line or NHRL (206Pb/204Pb = 18.59-19.37; 207Pb/204Pb = 15.55-15.60; 208Pb/204Pb = 38.31-38.99). Volume estimates between the Group 1 and Group 2 lavas are not yet possible to determine. However, the composition-time relationships for the lavas suggest inception of melting in the Amerasia Basin\ 

}, url = {http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8291-2.pdf}, author = {Mukasa, S B and Larry A Mayer and Aviado, Kimberly and Bryce, Julie and Andronikov, A and Brumley, K and Blichert-Toft, Janne and Petrov, Oleg and Shokalsky, Sergey} } @article {, title = {Petrography and U-pb, Detrital Zircon Geochronology of Metasedimentary Strata Dredged from the Chukchi Borderland, Amerasia Basin, Arctic Ocean}, year = {2010}, month = {Dec 13 - Dec 17}, chapter = {Fall Meeting}, address = {San Francisco, CA, USA}, keywords = {Other}, author = {Brumley, K and Miller, E L and Larry A Mayer and Andronikov, A and Wooden, J L and Dumitru, T A and Elliott, B and Gehrels, G E and Mukasa, S B} } @article {3508, title = {Recent Mapping and Sampling on the Chukchi Borderland and Alpha/Medeleev Ridge}, volume = {89}, number = {53}, year = {2008}, month = {Dec 15 - 19}, address = {San Francisco, CA, USA}, keywords = {Other}, author = {Larry A Mayer and Brumley, K and Andronikov, A and Dale N Chayes and Andrew A. Armstrong and Brian R Calder and John K Hall and Clyde, W C and Bothner, W A and James V. Gardner} } @article {5000, title = {Recent Mapping and Sampling on the Chukchi Borderland and Alpha/Medeleev Ridge}, year = {2008}, month = {December 2008}, address = {San Francisco, CA, United States}, author = {Larry A Mayer}, editor = {Brumley, K} } @article {, title = {First Recovery of Submarine Basalts from the Chukchi Borderland and Alpha/Mendeleev Ridge, Arctic Ocean}, volume = {89}, number = {53}, year = {2007}, month = {Dec 10 - Dec 14}, pages = {2123-2124}, chapter = {Fall Meeting}, address = {San Francisco, CA, USA}, keywords = {Other}, author = {Andronikov, A and Mukasa, S B and Larry A Mayer and Brumley, K} }