Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life

Abstract

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life. This article is part of a discussion meeting issue 'Serpentine in the Earth system'.

Keywords: Mariana trench; evolution of life; exhumed microbes; serpentinite mud volcanism; subducted cretaceous seamounts.

Figure 1.

Colour-contoured bathymetry map of Mariana forearc area (inset: regional map) lit from northwest. Forearc serpentinite mud volcanoes drilled to date are labelled. Conical Smt. (ODP Leg 125—Sites 778, 779 and 780); Asùt Tesoru Smt. (IODP Exp. 366 - Sites U1493, U1494, U1495, U1496); Fantangisña Smt. (IODP Exp. 366—Sites U1497, U1498); Yinazao Smt. (IODP Exp. 366—Sites U1491, U1492); and South Chamorro Smt. (ODP Leg 195—Site 1200). Black dots are positions of all earthquakes from 1900 to 2017 at depths of 0–50 km (NEIC database). Black dashed line is Mariana Trench axis. Large box on map at left is area of map on right. Small red box at 12.5°N, 147°E indicates location of figure 2a. (Map created by N.C. Becker). (Online version in colour.)

Figure 2.

(a) Colour-contoured bathymetry map of Mariana Trench area (small red box at ∼12.5°N, 147°E in figure 1), lit from northwest (cool/dark colours are deep, warm/light colours are shallower). White asterisks show positions of ROV Dives 4 [1] and 16 [1] at approximately 20°N. Black dashed line is Mariana Trench axis. (b) ROV video grab of oblique view of reef sequences on ROV Dive 4 on the deep inner slope of Mariana Trench (light layers are massive reef deposits (rudists, figure 3), darker layers are mainly bivalve fossils). Debris chutes and intervening sharp ridges are from submarine mass-wasting. (c) ROV video grab of oblique view on ROV Dive 16 of Cretaceous reef sequences on Pacific Plate Cretaceous guyot, light layers are massive reef deposits and rudists ( figure 3 for scale) and darker layers are mainly bivalve fossils. (Online version in colour.)

Figure 3.

(a–c) Video grabs of fossils observed on ROV video on Fryer Guyot (Dive 16 [1]). (d–f) Video grabs of fossils observed on ROV video on Mariana Trench inner slope (Dive 4 [1]). (Fossil identifications verified by S. Stanley, personal communication, 2017).

Figure 4.

(a) Core section of metabasite (U1496B-10F-2 W, 6–8 cm). (b) Photomicrograph in plane-polarized light of metabasite in (a) with euhedral-subhedral titanaugite (Cpx) and plagioclase (Pl) with equigranular texture. Labelled, altered plagioclase shows relict albite twin. (c) Provenance plot of vanadium versus titanium/1000 [54] for metamorphosed basalts recovered from the IODP Exp. 366 Sites labelled in legend on figure. The points shown by circles were analysed by pXRF (shipboard, hand-held XRF), others were analysed as labelled (tables 2 and 3). Arc, Island arc tholeiitic basalt; MORB; mid-ocean ridge basalt; Alkalic/OIB,  ocean island basalt.

Figure 5.

Plots of shore-based whole-rock Inductively coupled plasma mass spectrometry (ICP MS) analyses of trace element abundances. (a) C1 chondrite normalized rare earth elements; four of five samples are LREE-enriched, one is LREE-depleted. (b) Samples normalized to N-MORB for five metabasites, all (except U1498-21R-1, 54 cm, a MORB) show OIB compositional trends. Shown for comparison in both plots are a representative forearc basalt [55] and an average ocean island basalt (OIB) [52]. Normalizing values from Sun and McDonough (1989) [55]. For data, see table 2.

Figure 6.

Imagery of microprobe element maps of the alkalic metabasite sample IODP U1496B-8X-CC-W, 33 to 41 cm, showing blueschist facies paragenesis with aragonite occurring as an interlocking mineral with lawsonite and phengite replacing a plagioclase crystal (elongate rectangle in centre of image. (a) Backscatter image of the polished, carbon-coated thin section (Lws, lawsonite; Arg, aragonite and Ph, phengite). (b) Aluminium elemental map of the same region as (a) showing Al distribution at margins of the aragonite crystal in orange. (c) Calcium elemental map of the same region as (a) showing Ca distribution in the aragonite crystal in orange. (d) Potassium elemental map of the same region as (a) showing K distribution ubiquitously distributed in former groundmass (green and blue phases surrounding the aragonite crystal are phengite and Na pyroxene, respectively) of alkalic ocean island basalt as tiny, scattered points of orange. (Analyst: Y. Ichiyama). (Online version in colour.)

Figure 7.

(a) Miogypsina rudstone cobble with larger lithoclasts and coralline, red-algal grainstone) matrix from Yinazao Seamount flank drill core. (b) Photomicrograph (plane-polarized light) of U1491C-2H-CC, 1–7 cm at 25 mbsf (see text for description). ca, coralline red algae; ech, echinoderms; pel, Peloide (all micritic round clasts); ef, encrusting foraminiferan; npo, neopycnodontid oyster). (Analyst: W. Kurz). (Online version in colour.)

Figure 8.

Idealized west–east cross-section of various Mariana forearc settings, including the relative positioning of serpentinite mud volcanoes and representative cored materials from each setting [3] (top figure modified after Fryer et al. [5]). (Online version in colour.)