Izu-Bonin-Mariana Rear Arc: The Missing Half of the Subduction Factory

4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, 1.5 km west of Ocean Drilling Program (ODP) Site 792, and at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including distinctive black glassy mafic ash layers that may record large-volume eruptions on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better recovery on the black glassy mafic ash layers and enclosing sediments and to better constrain the thickness of the mafic ash layers. IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the IzuBonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory”; this was because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear part of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent core recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and cored to 1806.5 mbsf

Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin

Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-εNd(0), 143Nd/144Nd, 147Sm/144Nd, and Sm-Nd Depleted Mantle Model ages-TDM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits εNd(0) average value of −10.5, TDM = 1.4 Ga and 143Nd/144Nd = 0.512103, while the Core 7620 shows εNd(0) average value of −17.5, TDM = 1.8 Ga and 143Nd/144Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620

Table_2_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.XLSX

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_3_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Table_1_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.XLSX

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_2_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p

Image_1_Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin.JPEG

<p>Based on radiogenic isotope systems of neodymium [Epsilon Neodymium-ε_Nd(0), ¹⁴³Nd/¹⁴⁴Nd, ¹⁴⁷Sm/¹⁴⁴Nd, and Sm-Nd Depleted Mantle Model ages-T_DM] from current and previous data of continental rocks and associated sediments, this work provides the provenance of Holocene sediments from the Southwestern Atlantic Margin. The isotopic variability reported along the cores 7616 and 7620 are related to paleoceanographic and paleoclimatic changes. Further, we display the first Nd radiogenic isotope system distribution map of the study area. The map is the result of the principal component and clustering analyses of data compiled from the Ribeira belt, Luís Alves craton, and Paraná basin rocks. Differences in Nd isotopic signatures allowed the distinction between the sediment sources of the cores. The Core 7616 exhibits ε_Nd(0) average value of −10.5, T_DM = 1.4 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.512103, while the Core 7620 shows ε_Nd(0) average value of −17.5, T_DM = 1.8 Ga and ¹⁴³Nd/¹⁴⁴Nd = 0.51177. The relative more radiogenic Nd ratios from the Core 7616 are associated to the contribution of sediments from the Paraná basin, nevertheless less radiogenic values are observed along the Core 7616 between ~2,000 and 1,800 cal. yr BP. We have attributed the lower Nd ratios, recorded during this interval, to the decreasing influence from the Rio de la Plata estuary in the Core 7616. Remarkable less radiogenic Nd ratios are also recorded in the Core 7620 during the late Holocene. The intensification of the NE winds and the South America Summer Monsoon (SASM) enhanced the terrigenous input from the Paraíba do Sul River and southwards sediment transport by the Brazil Current (BC), providing higher contribution of less radiogenic metasediments from the Paraíba do Sul geotectonic domain to the Core 7620.</p