EXECUTIVE SUMMARY (SDPRC) I EXECUTIVE SUMMARY I The SOPACMAPS Project was designed to investigate as much area as possible of the EEZs of the SOPAC member countries: Solomon Islands, Vanuatu, Fiji and Tuvalu.The main objectives were to map the bathymetry, investigate the resource potential and to study geological processes, including geological hazards. A total area of approximately 730,000 km2 was mapped during a total of 87 days at sea, using the Dual Multibeam Swath echo sounder on the research vessel l/Atalante, operated by IFREMER under contract to SOPAC and funded by the European Union. The data are a very important source of information for the understanding of the nature of the seafloor of the South Pacific, and establish an understanding of seafloor process and resources at a level which could not have been imagined as recently as 20 years ago. During the three legs of 29 days each, multibeam (bathymetry and acoustic imagery), 6- channel reflection seismic, magnetics, gravimetry and sub-bottom profiler data were collected along 439 profiles totalling 15,680 nautical miles. All data are of very fair to excellent quality. Preliminary reports and on-board processed charts at 1:250,000 scale were delivered to SOPAC shortly after each leg. Reprocessing of the data by IFREMER produced several sets of charts: navigation, bathymetry and acoustic imaging at 1:250,000 scale, and bathymetry, acoustic imaging and morpho-structural interpretation at 1:500,000 scale. Interpretation of the data, conducted for SOPAC by IFREMER and ORSTOM, produced comprehensive fmal reports focused on eight areas: - Central Solomon Trough, - Malaita Area, - Melanesian Arc Gap Area, - North New Hebrides Back Arc Area, - New Hebrides Intra-Arc Basin, - Pandora Bank Area, - Alexa/Charlotte Banks Area, - South Tuvalu Banks Area. &m Final Report - NNHBAA - SOPACMAPS [SDPRC] !' This report describes the North New Hebrides Back-Arc Area (NNHBAA) which is entirely located in Solomon Islands EEZ. A great deal of data are now accumulated especially over the back arc trough, the northwestern comer of the North Fiji Basin and the main structural structures such as the 9°30'S Ridge and the Duff Ridge. Owing to the multibeam EM 12 echosounder data, an accurate bathymetric map of the region has been drawn. The other data (seismic profiles, magnetics, gravimetry and acoustic imagery) and the conducted interpretation provide a better understanding of the regional geology as for applied objectives. Acquisition of new data such as high resolution multichannel seismic lines for petroleum prospection is not necessary because the bathymetric map shows some sedimentary basins under ..~ a too great water depth for actual petroleum working. \' In the field of living potential resources, it could be interesting to prospect bathymetric highs such as the Duff Islands Ridge, the Reef Islands and the volcanic arc which may be good sites for deep sea fishes population. In the field of mineral resources, the real potentialities of that zone seem to be related to hydrothermalism. Three zones could constitute in evidence active hydrothermal sites (the active volcanic island are, the 9°30'S Ridge and the back arc trough) but chemical measurements, sampling and photographs observations are now necessary to confirm the existence and location of mineral deposits. Geological hazards are important in the area; they are related to small tsunamis due to submarine slides but also and mainly to volcanic activity and earthquakes. t" -, ""'" &m Final Report - NNHBAA - SOPACMAPS CONTENTS (SDPRC) ; I CONTENTS I EXECUTIVE SUMMARY CONTENTS ..........................................................................................................................•...•.... 1 CHAPTER 1 - INTRODUCTION 1-1 1.1 - SOPACMAPS Project presentation '" 1-1 1.2 - Preliminary notes 1-2 1.2.1 - Sheet assemblage 1-2 ( 1.2.2 - Specific aspects relative to the coastline .....................................•...................... 1-3 CHAPTER 2 - GEOLOGICAL FRAMEWORK 2·1 2.1 - Regional setting: the Southwest Pacific 2-1 2.1.1 - Present plate boundaries ..................................................•................................. 2-1 2.1.2 _SUbduction of the Pacific Plate 2-1 2.1.3 - Subduction of the Indo-Australian Plate 2-7 2.1 .4 - The active marginal basins ................................................................................• 2-8 2.2 - The New Hebrides Island Arc ........................................................................•....•.............. 2-9 2.3 - Geological setting of Solomon Islands .......................................................•.................... 2-14 2.3.1 - The Solomon Islands Arc ....................................•............................................. 2-14 2.3.1.1 _ Plates Reconstruction and the Solomon Islands Arc •......................•.. 2-14 2.3.1.2 - Morphology ...............................................................•......................... 2-15 2.3.1.3 - Seismicity ......................................................•......•...........................•. 2-15 2.3.1.4 - Crustal structure 2-17 2.3.1.5 - Geodynamic evolution ..............................................•......................... 2-18 2.3.1.6 - Sedimentary deposition and vertical evolution ..........•....•................... 2-19 2.3.1.7 - Plio-Pleistocene volcanism .........•..............................................•........ 2-20 2.3.2 - The Melanesian Arc Gap (MAG) .............................................................•......... 2-21 2.3.3 - The North New Hebrides Back Arc Area (NNHBAA) 2-23 2.3.3.1 - Regional Geography 2-23 2.3.3.2 - Geological framework/Previous works 2-23 2.3.3.3 - Petrology and age ...............................................•.............................. 2-26 2.4 - Tectonic setting of the Melanesian Borderland .........................•..................................... 2-28 2.4.1 - The North Fiji Basin 2-28 2.4.2 - The Fiji Platform, The Fiji Fracture Zone and the northern part of the Lau Basin 2-31 2.4.3 - The Vitias Trench lineament 2-33 2.4.4 - The Melanesian Border Plateau 2-36 ~ Final Report - NNHBAA - SOPACMAPS . page i (SDPRCl CHAPTER 3 - DATA ANALYSIS 3-1 3.1 - Previous work 3-1 3.2 - Bathymetry 3-2 3.3 - Imagery 3-5 3.4 - Seismic reflection profiles 3-6 3.5 - Magnetism 3-12 3.6 - Gravimetry '" 3-14 CHAPTER 4 - GEOLOGICAL SyNTHESiS 4-1 4.1 - The Duff Ridge 4-1 4.2 - The northern domain 4-1 4.3 - The eastern domain (North Fiji Basin) 4-2 4.4 - The western domain 4-3 4.5 - Geological hazards 4-3 CHAPTER 5 - POTENTIAL RESOURCES 5·1 5.1 - Uving Resources 5-1 5.1.1 - Preliminary considerations , 5-1 5.1.2 - SOPACMAPS results ...............................................................•.......................... 5-4 5.2 - Mineral Resources 5-4 5.2.1 - Polymetallic nodules 5-4 5.2.2 - Polymetallic crusts 5-5 5.2.3 - Hydrothermal sulfides ..............•.......................................................................... 5-6 5.3 - Oil Potential 5-7 CHAPTER 6 • CONCLUSIONS 6-1 6.1 - Geology •............................................................................................................................ 6-1 6.2 - Resources 6-1 CHAPTER 7 - SURVEY EQUIPMENT 7-1 7.1 - Data processing on board RIV L'Ataiante 7-2 7.2 - Bathymetry and imagery processing 7-4 7.2.1 - Bathymetry 7-4 7.2.2 - Post-processing navigation 7-5 7.2.3 - Post-processing EM 12 Dual bathymetric data 7-5 7.2.4 - EM12 Dual image processing 7-6 7.2.5 - Setting up of the celerity files 7-6 7.3 - Seismic reflection 7-8 7.3.1 - Seismic Reflection on AN L'Ataiante 7-9 ~ Final Report- NNHBAA - SOPACMAPS _, page 11 (SOPRC] 7.3.2 - G.1. Gun - Model 150 7-9 7.3.3 - Air gun principle 7-11 7.3.4 - Compressor 7-12 7.3.5 - Streamer Specifications 7-13 7.3.6 - Recording data 7-13 7.4 - Instrumentation 7-14 a) Barringer magnetometer 7-15 b) Bodenseewerk seagravimeter system KSS 30 7-16 c) 3.5 kHz hull-mounted sub-bottom protiler 7-20 d) Ocean-meteorology station 7-22 e) Acoustic Doppler current protiler (VM-ADCP) 7-27 f) Thermo-salinometer - CTD+ 100 7-29 CHAPTER 8 • ENCLOSURES 8·1 ENCLOSURE 1 - Staff 8-2 ENCLOSURE 2 - Cruise chronology 8-6 ENCLOSURE 3 - Logbook 8-19 ENCLOSURE 4 - Environmental conditions 8-32 ENCLOSURE 5 - Document table 8-41 ENCLOSURE 6 - Profile table .................................................•.................................... 8-46 ENCLOSURE 7 - Bibliography .....................................................•............................... 8-58 &m Final Report - NNHBAA - SOPACMAPS ... page ill (SDPRC) LIST OF FIGURES Fig. 1.1 - General navigation map of SOPACMAPS - Leg 1 1-6 Fig.1.2 - General navigation map of SOPACMAPS - Leg 2 1-7 Fig. 1.3 - General navigation map of SOPACMAPS - Leg 3 1-8 Fig. 1.4 - General sheet assemblage (1/250,000) 1-9 Fig. 1.5 - General sheet assemblage (1/500,000 and details) 1-10 Fig. 2.1 - General map of the Southwest Pacific region 2-2 Fig. 2.2 - Morphotectonic map of the Southwest Pacific 2-3 Fig.2.3a - Shallow seismicity of the Southwest Pacific 2-4 Fig.2.3b - Intermediate and deep seismicity of the Southwest Pacific 2-5 Fig.2.4 - Proposed quantitative model for present-day relative motions in the Southwest Pacific 2-6 Fig.2.5 - Bathymetric map of the New Hebrides Arc and location of the NHIAB sheet 2-10 Fig.2.6 - Sedimentary basins and faults in the central and northern New Hebrides Arc 2-11 Fig.2.7 - Place names, tectonic features and bathymetry of the central and western Solomon Islands area