Mike Coffin | University of Tasmania (original) (raw)

Papers by Mike Coffin

Geology, 1986

Abstract New geophysical data confirm the existence of marked structural and morphological differ... more Abstract New geophysical data confirm the existence of marked structural and morphological differences between the northern and southern sectors of the Kerguelen Plateau. A major sedimentary basin (Raggatt Basin) covers an area of at least 30 000 km 2 on the eastern part of the southern plateau. A deep oceanic basin (Labuan Basin) with extremely rough basement lies adjacent to the southeastern flank of the plateau. We suggest that this may be the former western extension or conjugate feature of the Diamantina zone ...

Journal of Geophysical Research: Solid Earth, 2001

We use multichannel seismic data, gravity, and subsidence modeling, in conjunction with plate rec... more We use multichannel seismic data, gravity, and subsidence modeling, in conjunction with plate reconstructions, to evaluate the crustal origin and composition of the Kerguelen Plateau. Predominantly oceanic crust of the southern and parts of the central Kerguelen Plateau appears to include continental fragments related to the breakup of India and Antarctica; these fragments may have been metamorphosed during emplacement of the main plateau. The upper crust is basaltic, the middle crust is intrusive mafic rock and intruded continental crust, and the lower crust is a plagioclase-rich metamorphic rock. The Labuan Basin crust is predominantly oceanic with stranded Kerguelen Plateau fault blocks. High-density lower crust in the Labuan Basin is probably composed of serpentinized peridotites formed during slow rifting and spreading. Plate reconstruction models indicate opening between eastern Broken Ridge and southern Kerguelen Plateau at ~90 Ma, heralding the formation of the Labuan Basin and Diamantina Zone; crustal attenuation and slow accretion of oceanic crust continued until the Australian and Antarctic plates separated at C 18 time (-40 Ma). Plate reconstructions of the free-air gravity field indicate that the Naturaliste Plateau fits against Antarctica and that Elan Bank and India were juxtaposed until ~110 Ma. Both Naturaliste Plateau and Elan Bank are probable microcontinents. A ~1 km positive residual depth anomaly in the oceanic basins adjacent to the plateau, along with the positive geoid anomaly centered beneath the northern Kerguelen Plateau, imply that the lithosphere is partially dynamically supported by an upwelling hot asthenosphere of the Kerguelen hot spot. 1. Introduction The Kerguelen Plateau in the southern Indian Ocean (Figure 1) is one of the world's two most voluminous large igneous provinces (LIPs) [Coffin and Eldholm, 1994]. Oceanic plateaus form by massive, transient magmatic activity, commonly attributed to mantle plumes, which is typically followed by continuous, but less voluminous magmatism [Coffin and Eldholm, 1994]. LIPs associated with the Kerguelen Plateau and the conjugate Broken Ridge include the Bunbury Basalts in SW Australia (130/123 Ma) [Frey et al., 1996], the Rajmahal Traps (116 Ma) [Kent et al., 1997], the Naturaliste Plateau (-100 Ma), and Ninetyeast Ridge (82-38 Ma) (Figure 1); all are possibly related to the breakup of the Indian, Australian and the Antarctic plates [Mahoney et al., 1983; Frey et al., 2000]. The' Kerguelen Plateau, in contrast to many smaller, subaerially-emplaced oceanic LIPs (e.g., Iceland, Hawaiian Ridge), is characterized by well-developed sedimentary basins that contain detailed records of its early erosional and subsidence history. The most prominent among these basins are the Raggatt Basin and the Banzare Bank on the southern plateau, the Labuan Basin

Geochemistry, Geophysics, Geosystems, 2003

Microcontinents appear to commonly form on young continental margins close to hot spots, but diff... more Microcontinents appear to commonly form on young continental margins close to hot spots, but difficulties in understanding their geology and evolution have inhibited assessment of their global distribution and significance. Thick volcanic accumulations in areas affected by hot spot magmatism only complicate the issue. Elan Bank, a large western salient of the Kerguelen Plateau, is a microcontinent that originally lay between India and Antarctica in Gondwana. Recent regional plate tectonic reconstructions suggest that during Gondwana breakup, Elan Bank and India initially separated from Antarctica, and Elan Bank became isolated in the Southern Ocean via a ridge jump to the north between Elan Bank and India. In Albian time (108 Ma), voluminous magmatism attributed to the Kerguelen hot spot overprinted and radically altered the original microcontinent and its surroundings. Recent ODP investigations, deep seismic reflection data, and a wide-angle seismic line on Elan Bank allow us to gain the first insight into the feature's integrated crustal structure and geological evolution and the adjacent continent-ocean transition zone. Our analysis shows that Elan Bank's crust is at least 16 km thick. The upper igneous crust consists of a 2-3 km thick layer with seismic velocities ranging from 4.4 to 5.9 km/s that can be interpreted as the result of accumulation of lava flows originating from the Kerguelen hot spot. Seismic velocities at the base of the crust are as low as 6.6 km/s, which is consistent with a fragment of thinned continental crust 14 km thick. A high velocity body, located at depths of 5 to 10 km, could be interpreted as plutonic rocks emplaced during the major regional magmatic episode. On the basis of deep seismic reflection data, we interpret extensional structures beneath the volcanic flows. In Albian time, when the area was affected by the Kerguelen hot spot, volcaniclastic material and lava flows accumulated in faulted grabens and basins both on the bank and within the continent-ocean transition zone to the south, creating the appearance of flat, unstructured basement. The seismic structure and inferred composition of Elan Bank revealed by this study contribute to our understanding of microcontinent formation as well as provide a template for identifying microcontinents in accreted terranes and mountain belts.

Geology, 1995

Multibeam bathymetric and geophysical data reveal a major strike-slip fault that extends along th... more Multibeam bathymetric and geophysical data reveal a major strike-slip fault that extends along the summit of the Puysegur Ridge east of the Puysegur Trench. The northward structural development of this ridge-trench system illustrates the evolution of an incipient subduction zone along a transform plate boundary that has been subjected to increasing transverse shortening during the past 10 m.y. At the southern end of the trench, where subduction has not yet started, the Puysegur Ridge has a narrow (4 0 km) steepsided cross section, and the axial strike-slip fault separates a shallow (125-625 m), flattopped eastern crest from a deeper (400-1600 m) western crest; these characteristics indicate differential uplift during the initial stage of shortening. On the lower plate an incipient, 5.2-km-deep trench developed in conjunction with normal and reverse faults, suggesting strong interplate coupling across the trench. Northward, the ridge broadens linearly to 80 km wide, its western flank has locally collapsed, and the ridge summit has subsided, possibly by 1.5 km, suggesting that the interplate coupling decreases and that a Benioff zone is being formed. Concomitant to the northward ridge evolution, the trench deepens to 6.2 kni and normal fault throws increase along its outer wall, indicating greater flexure of the downgoing plate.

Geophysical Monograph Series, 2000

Large Igenous Provinces (LIPs) constitute broad areas, >10 5 km 2 , of mafic volcanic and ... more Large Igenous Provinces (LIPs) constitute broad areas, >10 5 km 2 , of mafic volcanic and plutonic rocks erupted over ∼10 6 yr. Compared with plate dimensions, LIPs are smaller, localized features; they form both in plate interiors and at plate boundaries. LIPs originate in the ...

Investigación y ciencia, 1993

Información del artículo Grandes provincias ígneas.

Earth and Planetary Science Letters, 2000

Oceanic plateaus form by mantle processes distinct from those forming oceanic crust at divergent ... more Oceanic plateaus form by mantle processes distinct from those forming oceanic crust at divergent plate boundaries. Eleven drillsites into igneous basement of Kerguelen Plateau and Broken Ridge, including seven from the recent Ocean Drilling Program Leg 183 (1998^99) and four from Legs 119 and 120 (1987^88), show that the dominant rocks are basalts with geochemical characteristics distinct from those of mid-ocean ridge basalts. Moreover, the physical characteristics of the lava flows and the presence of wood fragments, charcoal, pollen, spores and seeds in the shallow water sediments overlying the igneous basement show that the growth rate of the plateau was sufficient to form subaerial landmasses. Most of the southern Kerguelen Plateau formed at V110 Ma, but the uppermost submarine lavas in the northern Kerguelen Plateau erupted during Cenozoic time. These results are consistent with derivation of the plateau by partial melting of the Kerguelen plume. Leg 183 provided two new major observations about the final growth stages of the Kerguelen Plateau. 1: At several locations, volcanism ended with explosive eruptions of volatilerich, felsic magmas; although the total volume of felsic volcanic rocks is poorly constrained, the explosive nature of the eruptions may have resulted in globally significant effects on climate and atmospheric chemistry during the late-stage, subaerial growth of the Kerguelen Plateau. 2: At one drillsite, clasts of garnet^biotite gneiss, a continental rock, occur in a fluvial conglomerate intercalated within basaltic flows. Previously, geochemical and geophysical evidence has been used to infer continental lithospheric components within this large igneous province. A continental geochemical signature in an oceanic setting may represent deeply recycled crust incorporated into the Kerguelen plume or continental fragments dispersed during initial formation of the Indian Ocean during breakup of Gondwana. The clasts of garnet^biotite gneiss are the first unequivocal evidence of continental crust in this oceanic plateau. We propose that during initial breakup between India and Antarctica, the spreading center jumped northwards transferring slivers of the continental Indian plate to oceanic portions of the Antarctic plate.

First Break, Jun 1, 2005

Integrirani program oceanskog busenja (IODP), međunarodna suradnja geoznanstvenika, oceanologa i ... more Integrirani program oceanskog busenja (IODP), međunarodna suradnja geoznanstvenika, oceanologa i bioznanstvenika, objavio je plan istraživanja za 2005. i 2006. godinu. Busit ce se karbonatna izdignuca u bazenu Porcupine u podmorju jugoistocne Irske, na pasivnim kontinentalnim rubovima u Meksickom zaljevu, na Tahitiju i u podmorju otoka Vancouver.

First Break, 2004

Building upon the successes of previous scientific ocean drilling programmes, the IODP offers sci... more Building upon the successes of previous scientific ocean drilling programmes, the IODP offers scientists worldwide unprecedented opportunities to address a vast array of scientific problems in all submarine settings. The scientific advisory structure of the proposal-driven IODP recently planned the inaugural drilling expeditions, targeting critical scientific problems in the eastern Pacific, central Arctic, and north Atlantic Oceans in 2004 and 2005 (Figure 1, Table 1). Co-led by Japan and the United States, with initial significant contributions from ...

Eos, Transactions American Geophysical Union, 1992

Eos, Transactions American Geophysical Union, 2011

The Ontong Java Plateau (OJP; see Figure 1a), in the western equatorial Pacific Ocean, is one of ... more The Ontong Java Plateau (OJP; see Figure 1a), in the western equatorial Pacific Ocean, is one of the largest oceanic plateaus on Earth, covering 1.86 million square kilometers—equivalent to roughly one third of the contiguous United States [Coffin and Eldholm, 1994]. This voluminous plateau is thought to have formed about 120 million years ago and to have caused significant global environmental changes; however, a consensus has not been reached on how the OJP formed. Competing theories include formation through a mantle plume, a meteor impact, and fast spreading ridges. Detailed knowledge of the OJP's crustal and upper mantle structure is necessary to help distinguish among existing models and to develop new models of how the OJP formed. Previous seismic studies acquired data by exploding charges at the ocean's surface and, through seismic analyses of travel times, deducing horizons of reflections and refractions below the ocean floor. However, most of these studies used rel...

Tectonophysics, 1990

Your selection(s) could not be saved due to an internal error. Please try again. ... Received 1 S... more Your selection(s) could not be saved due to an internal error. Please try again. ... Received 1 September 1988. Accepted 3 February 1989. Available online 9 April 2003. ... Deep crustal reflections, appearing at two-way times of 6–20 s, are characterised by a low signal-to-noise ratio and a low-frequency content (~ 5–30 Hz). Optimising the visibility of these reflections requires that: 1. ... (3) the shot spacing be as snail as possible. ... An airgun array simulation program was used to investigate the effect of operating a 10-gun array at different depths. It ...

From November 1980, through January 1981, R/V Vema cruises 3618 and 3619 were devoted to studying... more From November 1980, through January 1981, R/V Vema cruises 3618 and 3619 were devoted to studying the evolution of the East African continental margin and the western Somali basin. Multiand single-channel seismic reflection, sonobuoy reflection/refraction, gravity, magnetics and echosounding data were collected on these cruises. We show prominent features on one of the multichannel seismic lines (line 84V, location in Figure 1) which demonstrate important processes affecting the passive continental margin of ...

Episodes of magmatism have resulted in the emplacement of LIP's including CFB and associated... more Episodes of magmatism have resulted in the emplacement of LIP's including CFB and associated intrusive provinces; volcanic passive margins; oceanic plateaus; submarine ridges; ocean basin flood basalts; and seamount groups. In the oceanic realm, high-quality seismic data and a few scientific drill holes have shown that volcanic margins and oceanic plateaus comprise extensive constuctions of extrusive igneous rock. In some cases volcanic margins and oceanic plateaus share temporal, spatial, and compositional characteristics ...

Geochimica et Cosmochimica Acta Supplement, Sep 1, 2003

AGU Fall Meeting Abstracts, Dec 1, 2004

Mantle plumes are upwellings of large volumes of mantle material in focused conduits, the leading... more Mantle plumes are upwellings of large volumes of mantle material in focused conduits, the leading ends of which are referred to as plume heads. Large igneous provinces (LIPs) are suspected to form from magmatism resulting from plume head decompression melting, but, evidence for this theory for the origins of LIPs is mixed. We have now reached the point of having either to modify the theory to fit characteristics of individual LIPs or to abandon the theory and search for a more unifying explanation. A ...