Reconstruction of Subduction and Back‐Arc Spreading in the NW Pacific and Aleutian Basin: Clues to Causes of Cretaceous and Eocene Plate Reorganizations

Abstract

The Eocene (~50–45 Ma) major absolute plate motion change of the Pacific plate forming the Hawaii‐Emperor bend is thought to result from inception of Pacific plate subduction along one of its modern western trenches. Subduction is suggested to have started either spontaneously, or result from subduction of the Izanagi‐Pacific mid‐ocean ridge, or from subduction polarity reversal after collision of the Olyutorsky arc that was built on the Pacific plate with NE Asia. Here we provide a detailed plate‐kinematic reconstruction of back‐arc basins and accreted terranes in the northwest Pacific region, from Japan to the Bering Sea, since the Late Cretaceous. We present a new tectonic reconstruction of the intraoceanic Olyutorsky and Kronotsky arcs, which formed above two adjacent, oppositely dipping subduction zones at ~85 Ma within the north Pacific region, during another Pacific‐wide plate reorganization. We use our reconstruction to explain the formation of the submarine Shirshov and Bowers Ridges and show that if marine magnetic anomalies reported from the Aleutian Basin represent magnetic polarity reversals, its crust most likely formed in an ~85‐ to 60‐Ma back‐arc basin behind the Olyutorsky arc. The Olyutorsky arc was then separated from the Pacific plate by a spreading ridge, so that the ~55‐ to 50‐Ma subduction polarity reversal that followed upon Olyutorsky‐NE Asia collision initiated subduction of a plate that was not the Pacific. Hence, this polarity reversal may not be a straightforward driver of the Eocene Pacific plate motion change, whose causes remain enigmatic.

Izanagi-Pacific ridge subduction revealed by a 56 to 46 Ma magmatic gap along the northeast Asian margin

“…However, the apparent lack of magmatic evidence for early Cenozoic Izanagi-Pacific ridge subduction south of Japan (i.e., in South China and southeast Asia) suggests that the modeled >5000 km slab detachment of Seton et al (2015) may be overestimated by more than a factor of two. Furthermore, studies to the north of our area suggest that Izanagi-Pacific ridge subduction was limited to the south of southern Sakhalin (Vaes et al, 2019), which would further shorten a slab detachment. The geodynamic viability of a much shorter (i.e., ∼1500 km length from this study) Izanagi-Pacific ridge-trench intersection for producing a ca.…”

Magmatic Forcing of Cenozoic Climate?

“…Starting at ~39 Ma, large volumes of magmas were erupted from several volcanic centers in the Basin and Range, where magmatism ended by ~33 Ma (Gans, ), in remarkable synchronicity with the final phases of latest Eocene climate cooling. Ophiolite emplacement on Kamchatka and the Kuriles and the subsequent onset of subduction along the Aleutian and the Kuril trenches following arc‐continent collision in Kamchatka and, farther south, along the Izu‐Bonin‐Marianas trench over a length comparable to that of the Neo‐Tethyan margin occurred around ~50 Ma (e.g., Konstantinovskaia, ; Ishizuka et al, ; Domeier et al, ; Vaes et al, ; Figure ). However, intraoceanic subduction zones commonly involve small amounts of carbon emissions because few carbonate sediments are subducted (e.g., Johnston et al, ), either due to the distance from the continents or because intraoceanic trenches are typically deeper than the carbonate compensation depth.…”

History of Subduction Polarity Reversal During Arc‐Continent Collision: Constraints From the Andaman Ophiolite and its Metamorphic Sole

“…For instance, the arrival of the Ontong-Java Oceanic Plateau in the Vitiaz Trench led to the formation of the New Hebrides subduction zone in the Vitiaz/Melanesian Arc (Hall, 2002;Knesel et al, 2008). Subduction polarity reversal following arc-continent collision was also proposed in the Aleutian Arc (Vaes et al, 2019) or to form the modern Kamchatka subduction zone (Domeier et al, 2017;Konstantinovskaia, 2001;Shapiro & Solov'ev, 2009;Vaes et al, 2019). Modern examples where polarity reversal may be ongoing are the Banda Arc in Timor (e.g., Breen et al, 1989;Harris, 2006;Tate et al, 2015), Taiwan (Chemenda et al, 2001), or the Solomon Arc (Cooper & Taylor, 1985;Cooper & Taylor, 1987).…”