Kathleen Crane

Haakon Mosby Mud Volcano provides unusual example of venting

A seafloor mud volcano north of Norway is presenting researchers with an uncommon example of venting and is raising important questions. Seafloor aqueous vents, gas vents, mud volcanoes, and mud diapirs are found in a variety of geological settings. However, scientists did not expect to discover venting at the northern site, now known as the Haakon Mosby Mud Volcano (HMMV). It is considered especially unusual because of its Arctitc Location (72°N), its development largely within glacial marine sediments, and its lack of association either with salt tectonics or with plate subduction. Further, the volcano is posing questions for investigators about the relationship of methane generation and mud volcanism to thick, rapidly deposited sediments; sediment failure; and gas hydrates (GH).

Methane seep community of the Håkon Mosby mud volcano (the Norwegian Sea): composition and trophic aspects

The Håkon Mosby mud volcano (the Norwegian Sea, depth c. 1250 m) was studied in July 1998 by a joint Russian–German–USA–Norwegian expedition on the 40th cruise of the RV Akademik Mstislav Keldysh using the two Mir submersibles. The benthic community is dominated by two species of symbiotrophic pogonophores, Sclerolinum contortum (more abundant) and Oligobrachia haakonmosbiensis. The biomass of S. contortum reaches at least 435 g m ; for O. haakonmosbiensis the value is 350 g m . Different benthic organisms form associations with each species of pogonophore. The total list of known benthic fauna includes 46 species. A zoarcid fish, Lycodes squamiventer, is a common member of the benthic community. Bacterial mats are found over an extensive part of the crater. The background benthic community is much poorer and is dominated by ophiuroids (Ophiocten gracilis, Ophiopleura borealis). Pycnogonids (Collossendeis proboscidea), buccinid gastropods and asteroids are also present. Stable carbon isotope data showed significant depletion of C in both species of pogonophores: in S. contortum δ C was up to −48.3‰, in O. haakonmosbiensis the value varied from −51.1 to −56.1‰. It can be suggested that the methane carbon contributes to the nutrition of the pogonophoran O. haakonmosbisensis. Carbon isotopes also revealed incorporation of non‐photosynthetic carbon into local trophic webs: δ C in Metacaprella horrida (amphipod) showed −44.9‰, in the tube‐dwelling polychaete (Amphinomidae) −40.6‰. In the bacterial mat δ C varied from −17.6 to −53.0.

Rifting in the northern Norwegian‐Greenland Sea: Thermal tests of asymmetric spreading

The analysis of heat flow, seismic, and topographic data collected in the northern Norwegian-Greenland Sea reveals an asymmetric evolution of the Eurasian and North American plates. These data are compared to predictions from three kinematic models of extension which produce asymmetry about the Knipovich Ridge: (1) uniform asymmetric pure shear, (2) lithospheric simple shear, and (3) rift/ridge jumping. The data are consistent with a range of deformation scenarios, from one ridge jump occurring at about 25 m.y. after the initiation of spreading to continuous asymmetric extension. The simple shear model can match the data only when a detachment fault dips more steeply than 45° under Svalbard. Tectonic and heat flow evidence suggests that asymmetry may have evolved from a combination of all three models. When the Mohns Ridge (propagating to the east) encountered the preexisting northward trending Spitsbergen Shear Zone, the direction of ridge propagation shifted to the north, being influenced by the abrupt change in the regional stress field at the shear zone-ridge axis intersection. As a result, the nascent Knipovich Ridge entered into and propagated along the shear zone. Consequently, formerly active shear faults became the new detachment surfaces along which new crust is minted and asymmetrically extended. The high level of deviatoric stress about the Mohns and Knipovich Ridge intersection may cause a gradual eastward migration of the Knipovich Ridge, resulting in multiple zones of magma intrusion. “Off-axial” bands of high heat flow and volcanism located along the Barents Sea and Svalbard margin, along the Yermak Plateau, and on continental Svalbard just southeast of the Yermak Plateau may be evidence for this migration. Propagation from the Nansen Ridge may have entered the same shear zone from the north, explaining the creation of the small Molloy Ridge and off-axis volcanism on the Yermak Plateau.

Thermal implications for the evolution of the spitsbergen transform fault

Abstract Heat flow taken between Svalbard and Greenland reveal three thermal provinces: 1. (1) the Molloy Ridge within the Spitsbergen Transform, 2. (2) the Yermak Plateau 3. (3) the northeastern margin of Svalbard (Nordaustlandet). The Molloy Ridge is a short spreading segment and the average heat flow is much above the Sclater et al. (1971), cooling curve but agrees with values from the Norwegian-Greenland Sea. An additional zone of intrusion identified by heat flow lies to the northwest of the Molloy Ridge. It straddles both the visible fracture zone and part of the Yermak Plateau. A thermal boundary lies between the warm western segment of the Yermak Plateau and the shelf off Nordaustlandet. If the thermal subsidence of the western Yermak Plateau can be traced to the latest heating episode then it is likely that the crust is similar to oceanic in composition and not older than 13 m.y. (approximately 20 m.y. younger than the northeastern segment of the plateau). Plate rotation shows that there was no room for the western segment of the plateau prior to anomaly 7. We postulate that the original transform is associated with the Hornsund Fault zone. In response to deviatoric stress across the oblique ridge-transform system, the Nansen Ridge propagated southwestward aborting the old transform trace, and shifted to its present position. It is suggested that this propagation and migration of the ridge-transform system across a zone of extensional deviatoric stress allowed the massive intrusion of basalt forming the Western Yermak Plateau. The propagation phenomenon coincides with large-scale Tertiary volcanic activity on Svalbard. Readjustment and migration of the oblique transform is still taking place. As the transform-ridge system is liberated from continental constraints, the migration rate will diminish as orthogonality is approached.

Structural evolution of the East Pacific Rise axis from 13°10′N to 10°35′N: interpretations from SeaMARC I data

In 1983 the SeaMARC I and the Sea Beam systems imaged the East Pacific Rise (EPR) and the Clipperton Transform Fault from 13°10′N to 9°50′N revealing both magmatic and tectonic segmentation along the rise axis. Tectonic segments are defined by an undulating axial zone of extension which widens and narrows at an average wavelength of 45 km. In addition, axial fissure-fault-density and -length curves reveal wavelengths of 30 and 56 km. The narrowest axial zones, < 0.5 km in width, correspond to regions of hydrothermal activity and are located atop regional morphologic highs quasi-harmonically spaced at 155 km. These highs define the major magma centers on the rise axis about which seamounts cluster. Superimposed on the intermediate-wavelength highs are smaller highs (from 10 to 50 km in length) which are truncated by overlapping spreading centers (OSCs) at their distal edges. The rise axis widens near OSCs while it narrows and disappears near the Clipperton Transform Fault suggesting that transforms and OSCs have different origins. Imagery on and adjacent to a few OSCs reveals that in some cases OSCs migrate along the axis forming relict off-axial structural traces at oblique angles (285°–330°) to the axis. Off-axial fault density and length curves have wavelengths similar to the axial curves. However, fault densities to the west of the axis are somewhat antisymmetric to fissure-fault densities on the axis. In contrast, faults to the east of the axis nearly mimic fissure-fault density and length curves on the axis suggesting that the fracture pattern is controlled by the state of deviatoric stress in the adjacent Cocos Plate to the east. The data suggest that large deep-seated magma diapirs may dominate the magmatic segmentation of the EPR generating dynamically supported 155 km wavelength highs. Smaller, shallower magma cupulas may rise as fingers to the seafloor above the large diapirs. Where the magma erupts may be a factor of the thin skin tectonic segmentation of the rise axis formed in response to the state of deviatoric stress in the upper crust. Small OCSs may form at crustal weak points and may migrate in response to magma body movement along the axis. The instability of both the magmatic and tectonic segmentation is apparent from the oblique alignment of both seamount chains and relict OSCs with their present-day counterparts.

Thermal Evolution of the Western Svalbard Margin

The northern Norwegian-Greenland Sea opened up as the Knipovich Ridge propagated from the south into the ancient continental Spitsbergen Shear Zone. Heat flow data suggest that magma was first intruded at a latitude of ≈75° N around 60 m.y.b.p. By 40–50 m.y.b.p. oceanic crust was forming at a latitude of 78° N. At ≈12 m.y.b.p. the Hovgård Transform Fault was deactivated during a northwards propagation of the Knipovich Ridge. Spreading is now in its nascent stages along the Molloy Ridge within the trough of the Spitsbergen Fracture Zone. Spreading rates are slower in the north than the south. For the Knipovich Ridge at 78° N they range from 1.5–2.3 mm yr-1 on the eastern flank to 1.9–3.1 mm yr-1 on the western flank. At a latitude of 75° N spreading rates increase to 4.3–4.9 mm yr-1.Thermal profiles reveal regions of off-axial high heat flow. They are located at ages of 14 m.y. west and 13 m.y. east of the northern Knipovich Ridge, and at 36 m.y. on the eastern flank of the southern Knipovich Ridge. These may correspond to episodes of increased magmatic activity; which may be related to times of rapid north-wards rise axis propagation.The fact that the Norwegian-Greenland Sea is almost void of magnetic anomalies may be caused by the chaotic extrusion of basalts from a spreading center trapped within the confines of an ancient continental shear zone. The oblique impact of the propagating rift with the ancient shear zone may have created an unstable state of stress in the region. If so, extension took place preferentially to the northwest, while compression occurred to the southeast between the opening, leaking shear zone and the Svalbard margin. This caused faster spreading rates to the northwest than to the southeast.

The distribution of geothermal fields along the East Pacific Rise from 1310? N to 820? N: Implications for deep seated origins

In 1983 a combined SeaMARC I, Sea Beam swath mapping expedition traversed the East Pacific Rise from 13°20′ N to 9°50′ N, including most of the Clipperton Transform Fault at 10°15′ N, and a chain of seamounts at 9°50′ N which runs obliquely to both the ridge axis and transform fault trends. We collected temperature, salinity and magnetic data along the same track. These data, combined with Deep-Tow data and French hydrocasts, are used to construct a thermal section of the rise axis from 13°10′ N to 8°20′ N.Thermal data collected out to 25 km from the rise axis and along the Clipperton Transform Fault indicate that temperatures above the rise axis are uniformly warmer by 0.065°C than bottom water temperatures at equal depths off the axis. The rise axis thermal structure is punctuated by four distinct thermal fields with an average spacing of 155 km. All four of these fields are located on morphologic highs. Three fields are characterized by lenses of warmed water ≈ 20 km in length and ≈ 300 m thick. Additional clues to hydrothermal activity are provided in two cases by high concentrations of CH4, dissolved Mn and 3He in the water column and in another case by concentrations of benthic animals commonly associated with hydrothermal regions.We use three methods to estimate large-scale heat loss. Heat flow estimates range from 1250 MW to 5600 MW for one thermal field 25 km in length. Total convective heat loss for the four major fields is estimated to lie between 2100 MW and 9450 MW. If we add the amount of heat it takes to warm the rest of the rise axis (489 km in length) by 0.065.°C, then the calculated axial heat loss is from 12,275 to 38,525 MW (19–61% of the total heat theoretically emitted from crust between 0 and 1 m.y. in age).

Thermal variations in the gregory rift of southern Kenya (

Abstract A compilation of thermal and seismic data collected over the last sixty years allows one to infer that tectonic phenomena and heat emanation could be linked in an oscillatory mode up and down the Kenyan part of the East African Rift. The seismic period is approximately 20–30 years during which time the loci of maximum intensity earthquakes move in a rhythmic pattern from south to north and back to south. Temperatures measured from hot springs also fluctuate over this time span increasing or decreasing in different sections of the rift. Spatial variations were measured by infrared radiometers from low altitude aircraft or high-altitude satellites. These reveal that individual thermal springs ranging from 35°C to 80°C, warm up greater than 5 km2 of the lake bottom of Magadi (only a slightly active thermal region which, however, yields greater then 300 MW). The heated area is large enough to detect by satellite imagery, making it possible to monitor the heat budget and flux over time and relate it to tectonic activity in the rift.

Heat flow and hydrothermal vents in Lake Baikal, U.S.S.R.

The processes that generate thinning, extension, and finally rifting of continental crust are often assumed to be either “active” or “passive.” There are two major continental rifting provinces active in the world today: the East African Rift and the Baikal Rift in Siberia. Many authors suspect that the Baikal Rift formed in response to the India-Eurasia collision, which deformed the lithosphere in central Asia creating the Himalayas in the south and an extensional province in Siberia [Molnar and Tapponier, 1975; Tapponier and Molnar, 1979; Zonenshain and Savostin, 1981]. Others believe that the Baikal Rift is primarily an active phenomenon, citing updoming around Lake Baikal and the presence of Cenozoic volcanics as an example of slightly elevated partial melting in the asthenospheric material underneath the lake [Artemyev and Artyushkov, 1971; Zorin, 1971, 1981; Puzyrev et al., 1974; Logatchev et al., 1983].

Rescuing the former Soviet Union's marine data

Until recently, the Arctic was thought of as remote and pristine, far removed from the environmental problems that plague the industrial and agricultural lands of the lower latitudes. The Cold War cloaked many activities in the region under a curtain of secrecy and for most of the world, the Arctic remained largely out of sight and out of mind. Information released in 1992 on the deliberate dumping of nuclear materials in shallow Siberian-Arctic Seas [Handler, 1992; 1993a,b] elicited a strong response among the countries that ring the Arctic. Materials dumped included 16 nuclear reactors—six of which had fuel rods intact—and over 10,000 containers of lower-level radioactive waste.