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The West Mariana Ridge, Western Pacific Ocean The West Mariana Ridge, western Pacifi c Ocean: Geomorphology and processes from new multibeam data James V. Gardner† University of New Hampshire, Center for Coastal & Ocean Mapping, 24 Colovos Road, Durham, New Hampshire 03824, USA ABSTRACT rine geologists and geophysicists (e.g., National and Uyeda, 1981; Kroenke et al., 1981; Fryer, Science Foundation [NSF] MARGINS Pro- 1996). In 2006 and 2007, the Center for Coastal The western fl ank of the West Mariana gram, Subduction Factory Experiment). In and Ocean Mapping at the University of New Ridge and the distal Parece Vela Basin have comparison, the western extension of this Hampshire conducted multibeam-echosounder been mapped for the fi rst time using a mod- system, the West Mariana Ridge (Fig. 1), has (MBES) surveys of the summit of West Mari- ern multibeam echosounder. The new data attracted only minor attention from the ma- ana Ridge, its western margin and the adjacent reveal the Ridge to be composed of 82 vol- rine community (Karig and Glassley, 1970; easternmost Parece Vela Basin in support of a canic peaks, of which 25 have summits with Fisher et al., 1971; Anderson, 1975; Hussong potential U.S. submission to the United Nations water depths of <1000 m and 11 have sum- mits with depths of <500 m deep. Five of the vol canoes have summit craters, and two 134°E 136°E 138°E 140°E 142°E 144°E 146°E 148°E are guyots ; the remaining 75 seamounts are peaked volcanoes. One volcanic peak has a summit water depth of 16 m, and two in the 24°N N DSDP 24°N central region have summits as shoal as ~7 m. 100 km ODP The erosional character of the volcanoes sug- gests a younging toward the south. The west- ern fl ank of the West Mariana Ridge is buried 22°N 22°N by a sediment apron that merges with the dis- M tal Parece Vela Basin. The sediment apron is Mariana a incised by a series of canyon-channel systems r W i Mariana a that head on the upper fl ank or summit of the 20°N Parece n 20°N e a Kyushu-Palau Ridge West Mariana Ridge and trend downslope to s a Vela t c the west. Several of the channels are sediment t M i Basin v fi lled with an incised thalweg, suggesting a 195-1201 59-451 e a r multiphase evolution to the channel systems. 18°N i 18°N 59-450 a None of the channels have a pelagic drape, n 59-449 6-53B a whereas the seafl oor adjacent to the chan- a r c Trough nels does, suggesting recent activity. The lack R i d of guyots, the apparent younging of the vol- 16°N Trench 16°N canoes to the south, and the youth of channel 59-448A g e Saipan activity suggest the West Mariana Ridge may 6-54 be either recently or is presently tectonically active with the evidence suggesting uplift. 14°N 14°N Guam INTRODUCTION The Mariana Trench, forearc, arc, and back- 12°N 12°N arc basin have all witnessed intense investi- gations during the past 40 years (e.g., Karig, 1971; Martinez and Fryer, 1995; Fryer, 1996; 134°E 136°E 138°E 140°E 142°E 144°E 146°E 148°E Stern et al., 2003). The seismically and vol cani- cally active Mariana arc and related subduction Figure 1. Regional map of the West Mariana Ridge and Parece Vela Basin. White polygon zone continue to be strong attractions for ma- outlines area mapped. Deep Sea Drilling Project (DSDP) leg site (yellow circles) and Ocean Drilling Program (ODP) sites (white circles). Background map from Smith and Sandwell †E-mail: [email protected] (1997). Inset shows location. GSA Bulletin; September/October 2010; v. 122; no. 9/10; p. 1378–1388; doi: 10.1130/B30149.1; 14 fi gures. 1378 For permission to copy, contact [email protected] © 2010 Geological Society of America Geomorphology of West Mariana Ridge Convention on the Law of the Sea (UNCLOS) surface and an extensive volcanic apron that (DTMs) of unknown pixel resolution of the for an extended continental shelf (Gardner et al., has buried much of the western fl ank of the vol- Mariana forearc, but their data do not extend 2006a). The bathymetry and 12-kHz acoustic canic edifi ce. In addition, a remarkable series of far enough to the west to adjoin the new MBES back scatter of the West Mariana Ridge, from well-developed (implying relatively young to data. The highest resolution bathymetry of this 13°20′N to 21°00′N and from the crest of the active) channel systems were found that incise region available prior to the MBES surveys is Ridge to the western margin where it merges the volcanic apron on the western fl ank of the the ~1.8 km/pixel–resolution satellite altimetry with the Parece Vela Basin in water depths of West Mariana Ridge. (Smith and Sandwell, 1997, 2004) (Fig. 2A). almost 5000 m has now been mapped almost The new MBES surveys are the fi rst high- At this rather coarse resolution, only the gross in its entirety (Gardner, 2006, 2008). The new resolution bathymetric maps of this large area morphology of the seafl oor geomorphology data reveal a series of isolated or coalesced vol- (>184,000 km2) of seafl oor in the western Pa- is resolved. Japan has conducted MBES map- canic seamounts, several of which rise along cifi c. Stern and Smoot (1998) published 200-m ping to the west, north, and, to some extent, the West Mariana Ridge crest almost to the sea contour maps and gridded digital terrain models to the east of the West Mariana Ridge, but not 21°N Stingray Shoal A B 1 Fig. 11A N N 20°N 50 km 50 km 2 3 Fig. 19°N 13A Fig. 4B 4 Fig. 7A 5 x 18°N Water depth (m) Fig. 13B 0 Fig. 6 1000 14 2000 Fig. 7 15A 3000 x 17°N 4000 Fig. 12 5000 8 Fig. 15B 16°N 9 10 15°N 11 Fig. 4A Fig. 8A 14°N Fig. 7B Fig. 11B Fig. 8B 144°E 141°E 142°E 143°E 144°E141°E 142°E 143°E Figure 2. Comparison of (A) Smith and Sandwell (1997) satellite altimetry bathymetry of mapped area and the (B) new multibeam bathymetry. Location for subsequent fi gures shown by white squares and white arrowheads with white dashed leaders. Black numbered arrowheads point to cross-chain volcanoes. Solid white line is location of high-resolution subbottom profi ler line. Geological Society of America Bulletin, September/October 2010 1379 Gardner of the Ridge proper, although their data are pres- velocity sensor. Instantaneous ship heave and the University of New Hampshire–developed ently not publicly available. The 100-m/pixel pitch and roll were recorded with an Applanix Geocoder software (Fonseca and Calder, 2005; resolution of the new MBES bathymetry grid POS/MV model 320 motion-reference unit, Fonseca and Mayer, 2007). provides a much more detailed view of the West and heading was provided by a Sperry model Mariana Ridge that resolves mesoscale (a few 39 gyro. The EM121A can compensate for GENERAL GEOMORPHOLOGY hundred meters) features (Fig. 2B). The focus of pitch and roll but not yaw. The Applanix this paper is to describe the geomorphology of POS/MV was interfaced with two Trimble The West Mariana Ridge separates two ba- the Ridge from the newly acquired MBES data Force 5 GRAM-S global positioning system sins—the Mariana Trough, a >3000-m-deep, from its crest to its western fl ank and propose (GPS) receivers using NavCom Defense Elec- actively spreading, backarc basin to the east processes that the geomorphology suggests tronics Starfi re SF2050R wide-area differential and the ~5000-m-deep Parece Vela Basin to the have modifi ed this margin. GPS that provide position fi xes with an accu- west (Fig. 1). The overall morphology of the racy of <±0.5 m. All horizontal positions are West Mariana Ridge is a gently arcuate SSE- Background georeferenced to the WGS84 ellipsoid, and ver- (at the north end) to SSW-trending (at the south tical referencing is to instantaneous sea level. end) edifi ce of single and coalesced submarine The West Mariana Ridge is the southwestern Seventy cross-line intersections provide an volcanic peaks (the term volcano is used inter- component of the Izu-Bonin-Mariana arc sys- evaluation of the precision of both the beam ray changeably with volcanic peak) along the Ridge tem. The arc system is nearly 3000 km long and tracing and the depth resolution of the EM121A crest and to the immediate west of the crest. The resides on the eastern edge of the Philippine Sea MBES. The mean depth error from the cross- West Mariana Ridge has a steep (10° to 14°) plate. Studies of the Mariana arc system sug- line analyses (n = 16,772,630 soundings) is east-facing fl ank thought to be a fault scarp that gest that the West Mariana Ridge is a remnant 0.07% for water depths from 2000 to 4900 m. resulted from the splitting of the active arc by arc (Karig, 1971, 1972) produced by Miocene The raw multibeam bathymetry and acous- backarc spreading in the Mariana Trough that backarc spreading in the Mariana Trough that is tic backscatter data were processed aboard began ~7 Ma (Hussong and Uyeda, 1981; Fryer, suspected to have separated from the West Mari- ship using the University of New Brunswick’s 1996; Stern et al., 2003).
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