Research ArticleGEOCHEMISTRY

An Early Cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean

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Science Advances  30 Oct 2020:
Vol. 6, no. 44, eabb4340
DOI: 10.1126/sciadv.abb4340
  • Fig. 1 Geographical overview and sample locality.

    (A) The ultraslow-spreading Gakkel Ridge extends for ca. 1800 km from the northwest coast of Greenland to the northern coast of Siberia and is located in the Eurasia basin. The Western Gakkel Ridge region is highlighted as a white square, and a zoomed-in view is provided in (B). The Western Gakkel Ridge region is divided, here, in the WVZ and the SMZ. The purple and red dots represent the sample locality of the basalts from the WVZ and SMZ, respectively. The exact location of each sample is provided in table S1. The maps were made using GeoMapApp (www.geomapapp.org).

  • Fig. 2 Trace element pattern and chemical proxies of past subduction influence.

    (A) The average trace element composition of the basalts from the Western Gakkel Ridge region is plotted relative to N-MORB showing an enrichment in fluid mobile elements (Ba and Sr), similar to BABBs. The similarity to BABB is further supported by (B) and (C). A detailed trace element plot can be found in fig. S1. Data for N-, D-, and E-MORB and BABB are plotted for comparison and taken from Gale et al. (63) (B), and (C) basalts from the Western Gakkel Ridge region show a pronounced enrichment in Ba and 87Sr/86Sr (up to 0.7037) compared to MORBs from the Atlantic and Pacific, similar to active island-arc and back-arc basins, such as the Lau and Mariana back-arc basin. High 87Sr/86Sr, Ba/Yb, and Ba/Nb ratios are explained by partial melting of a fluid-enriched mantle source. SMZ basalts tend to have higher Ba/Yb and lower Ba/Nb than WVZ basalts, implying a higher degree of source enrichment. Atlantic/Pacific MORB and Mariana BABB and Lau BABB data, plotted here for comparison, are compiled from Gale et al. (63). MORB data from the pacific include all values from ridge segments ranging between 15°N and 33°S and from the Atlantic ranging between 30°N and 30°S. Literature data from WVZ and SMZ are compiled from Gale et al. (63) and Goldstein et al. (14).

  • Fig. 3 Sr-Ba-Th systematics versus 208Pb/204Pb of the Western Gakkel Ridge basalts.

    (A) Distinct Sr composition of the Western Gakkel Ridge basalts compared to Atlantic/Pacific MORB. (B) Ba-Th versus 208Pb/204Pb shows similarities to Sr-Pb systematics. Western Gakkel Ridge basalts plot in the same range as BABB from the Lau basin and Marianas. Atlantic MORB data range from 30°N to 30°S, whereas the Pacific MORB data comprise solely data from the Eastern Pacific Rise ranging from 12°N to 30°S. Mariana and Lau BABB data were compiled from Gale et al. (63). The literature data for the WVZ and the SMZ are compiled from Gale et al. (63) and Goldstein et al. (14). Sr and Pb data for this study are provided in table S2.

  • Fig. 4 Ba/Th in MORB from the Western Gakkel Ridge region.

    Distribution of Ba/Th of the Western Gakkel Ridge MORBs (SMZ and WVZ) compared with global MORB data (A) and BABB (B). Ba/Th in SMZ basalts is higher than that in WVZ basalts, and Ba/Th in both ridge segments tend to be high compared to the global MORB distribution. Western Gakkel Ridge basalts, however, show a considerable overlap with Ba/Th in basalts erupted in active back-arc basins. MORB data are from Jenner and O’Neill (64), and BABB data are from Gale et al. (63) including Lau and Mariana BABB data. The gray bar represents the average Ba/Th concentration of MORB and BABB. Atlantic/Pacific MORB and Mariana BABB and Lau BABB data, plotted here for comparison, are compiled from Gale et al. (63). MORB data from the Pacific include all values from ridge segments ranging between 15°N and 33°S and from the Atlantic ranging between 30°N and 30°S. Literature data from the WVZ and the SMZ are compiled from Gale et al. (63) and Goldstein et al. (14).

  • Fig. 5 Paleogeography of the circum-Arctic region.

    Paleogeographic reconstructions show the Arctic region during the closure of the SAO at 130 Ma (top) and the present day (bottom). Top: During the closure and subduction of the SAO, mélange diapirs ascend into the mantle wedge, forming the Koyukuk-Nutseyn (KYK) volcanic arc at 145 to 130 Ma, which also led to the opening of the Amerasia basin (AM), which operated until 120 Ma as back-arc basin (50). The bottom panel at present-day shows the location of the SAO suture zone at 142 Ma (onset of subduction) and at 130 Ma (closure of SAO subduction). The red areas highlight the areas of the large igneous provinces. The orange rectangle in the paleo-reconstruction models highlights the sample locality, and on the right of the present day is our suggested model. Mélange diapirs, resultant from the SAO subduction, stay buoyant in the upper mantle and became integrated into the source of the Western Gakkel Ridge region. The slab of the SAO subduction resides at a depth of ~1300 km in the lower mantle (23). All paleogeographic reconstructions can be reproduced using pyGPlates (www.gplates.org).

  • Fig. 6 Th-Nb/Yb covariation diagram and Pb isotope systematics.

    (A) Th-Nb/Yb [after Pearce (65)] shows global MORB–ocean island basalt (OIB) array (diagonal gray bar). The orange and dark blue arrows indicate Th/Yb data trends (at a given Nb/Yb) for Lau and Mariana BABB. Many Gakkel Ridge MORBs exceed Th/Yb in the MORB-OIB array at a given Nb/Yb, indicating Th enrichment. MORB data are compiled from Jenner and O’Neill (64). (B) Elevated mantle Th contents (higher ΔTh/Nb) contribute to high mantle Th/U, producing positive Δ208Pb*/206Pb*. ΔTh/Nb is the deviation from the lower boundary of the MORB-OIB array, and Δ208Pb*/206Pb* is the difference in 208Pb/206Pb from the NHRL (see the Supplementary Materials for calculation). Mariana and Lau BABB, as well as literature data for the WVZ and the SMZ, are compiled from Gale et al. (63). Indian, Atlantic, and Pacific MORB data are compiled from Gale et al. (63). Atlantic MORB data comprise data from 30°N to 30°S and the Pacific MORB data from 12°N to 30°S, respectively.

Supplementary Materials

  • Supplementary Materials

    An Early Cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean

    Marianne Richter, Oliver Nebel, Roland Maas, Ben Mather, Yona Nebel-Jacobsen, Fabio A. Capitanio, Henry J. B. Dick, Peter A. Cawood

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    • Supplementary Notes S1 and S2
    • Figs. S1 to S5
    • Tables S1 and S2
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