Alteration effects on petrophysical properties of subaerial flood basalts: Site 990, Southeast Greenland margin

Cerney, Brian; Bücker, C.; Nilsen, Odd G.

doi:10.2973/odp.proc.sr.163.105.1999

Cited by 13 publications

(20 citation statements)

References 1 publication

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“… Poisson's ratio against P ‐wave velocity for serpentinites (black), basalts (white) and gabbro (grey) samples; crosses indicate altered basalts. Measurements from Miller & Christensen (1997) (squares), Christensen (1978) (triangles), Christensen (1966) (circles), Christensen & Shaw (1970) (diamonds), Salisbury & Christensen (1978) (hexagons), Planke et al (1999) (inverted triangles), Christensen (1996) (stars), Johnston & Christensen (1997) (crosses) and seismically defined for basalts (‘v’) Minshull (1993) and made at 60 MPa (0.6 kbar), the approximate lithostatic pressure at 5 km below basement, and ambient temperature except for Christensen (1996) and Johnston & Christensen (1997), which were made at 200 MPa. The range of V p vs. Poisson's ratio for 50–120 km in this velocity model (Fig.…”

Section: Discussionmentioning

confidence: 99%

From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK

Bullock

Minshull

2005

Geophysical Journal International

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S U M M A R YWe present a 169-km wide-angle velocity model across the Goban Spur rifted margin, southwest of the UK. A 120-km-wide intermediate region is identified between the first clear seafloor spreading magnetic anomaly (anomaly 34r) and thinned continental crust, where velocities increase from 4.5 km s −1 to 6.8 km s −1 in the top 4 km beneath acoustic basement. At depth it can be divided into a region where a 1.5-km-thick high-velocity layer (7.2-7.6 km s −1 ) exists and a region where this layer is absent but velocities of ∼7 km s −1 are present. Wide-angle PmP arrivals are observed across the whole of the intermediate region but a normal incidence reflection Moho is not present.Based on these velocities and combined with seismic reflection, gravity and magnetic modelling along this transect we interpret the intermediate region to consist of a 70 km wide zone of exhumed mantle with high Poisson's ratio at top basement (>0.34), an extremely low topographic expression and a high-velocity deep layer. Empirical relationships between velocity and degree of serpentinization suggest that serpentinite content decreases with depth from 100 per cent at top basement to <25 per cent from 5-7 km into basement. The observed magnetic anomaly is best fit by a thin magnetized layer (1 km) of magnetization 2-3 A m −1 . The intense magnetization may be due to magnetite formation during a prolonged interaction of serpentinite with sea water. Between this exhumed mantle and anomaly 34r is a 50-km-wide region raised 400 m above the adjacent exhumed mantle, consisting of a series of basement ridges. Poisson's ratio is not well defined in this region, which may be composed of anomalous oceanic crust or exhumed mantle.

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Section: Discussionmentioning

confidence: 99%

From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK

Bullock

Minshull

2005

Geophysical Journal International

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“…Viereck et al 1988). The potential field anomalies associated with SDRS arise from measured magnetic susceptibilities on basaltic lavas averaging between 1000 and 5000 3 10 À5 SI, and densities of around (2.8-3.0) 3 10 3 kg m À3 (Eldholm et al 1989;Planke et al 1999). Petrologically and geochemically, the lavas are overwhelmingly dominated by normal mid-ocean ridge basalt (N-MORB) tholeiites, with minor dacite and andesite derived from crustal melting and assimilation (Viereck et al 1988;Crawford & von Rad 1994).…”

Section: Characteristics Of Modern Seaward-dipping Reflector Sequencesmentioning

confidence: 99%

“…Major long-wavelength gravity and magnetic highs under the Cambrian Warburton Basin represent a further likely subsurface extension (Meixner et al 1999). Crawford & von Rad (1994) and Planke et al (1999). Approximate continent-ocean boundary (COB) shown in red.…”

Section: Late Neoproterozoic Volcanic Rocks In Southeastern Australiamentioning

confidence: 99%

Fossil seaward-dipping reflector sequences preserved in southeastern Australia: a 600 Ma volcanic passive margin in eastern Gondwanaland

Direen

Crawford

2003

JGS

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Evidence for a c. 600 Ma rifted passive margin in eastern Australia exists in the form of multiple belts of mafic volcanic rocks preserved along the western margin of the Tasman Fold Belt System, and giving rise to elongate magnetic anomalies. Outcrop, drillhole and geophysical evidence points to piles of lavas, volcaniclastic and intrusive rocks up to 6 km thick, extending for strike lengths of hundreds of kilometres in individual segments. The distinctive, unifying characteristics of these piles are apparent common formation ages (600-580 Ma), presence of early more landward transitional alkaline basalts, and more seaward abundant rift tholeiites, with high-temperature picrites and olivine-rich basalts at most localities. Despite later structural reorganization, these belts have close geochemical, geometric and lithological affinities with Mesozoic seaward-dipping reflector sequences along the North Atlantic, and northwestern Australian volcanic passive margins, and strongly imply the formation of a volcanic passive margin in eastern Gondwanaland at the close of the Neoproterozoic. Recognition of this event has implications for the position of an implied earlier rifted margin related to the break-up of Rodinia around 780 Ma. A rifting event at 600 Ma in eastern Gondwanaland helps explain both the lack of evidence for volcanism from Rodinia break-up, and a widespread 600 Ma population of inherited zircons within rocks of the Lachlan Orogen, which developed outboard of the passive margin in earliest Palaeozoic time.

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“…(a) Simplified schematic displaying the four-arm caliper response to common borehole conditions (followingReinecker et al, 2003). (b) Basics of televiewer imaging of borehole features.…”

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Understanding volcanic facies in the subsurface: a combined core, wireline logging and image log data set from the PTA2 and KMA1 boreholes, Big Island, Hawai`i

et al. 2019

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Abstract. To help understand volcanic facies in the subsurface, data sets that enable detailed comparisons between down-hole geophysical data and cored volcanic intervals are critical. However, in many cases, the collection of extended core intervals within volcanic sequences is rare and often incomplete due to challenging coring conditions. In this contribution we outline and provide initial results from borehole logging operations within two fully cored lava-dominated borehole sequences, PTA2 and KMA1, on the Big Island of Hawai`i. Data for spectral gamma, magnetic susceptibility, dipmeter resistivity, sonic, total magnetic field, temperature and televiewer wireline logs were successfully acquired for the open hole interval ca. 889 m to 1567 m within the PTA2 borehole. Spectral gamma was also collected from inside the casing of both wells, extending the coverage for PTA2 to the surface and covering the interval from ca. 300 to 1200 m for KMA1. High-quality core material was available for both boreholes with almost complete recovery which enabled high-resolution core-to-log integration. Gamma data are generally low commonly in the range ca. 7–20 gAPI but are shown to increase up to API of ca. 60 with some intrusions and with increases in hawaiite compositions in the upper part of PTA2. Velocity data are more variable due to alteration within porous volcanic facies than with burial depth, with a general degrease down-hole. The high-resolution televiewer data have been compared directly to the core, enabling a comprehensive analysis of the variations in the televiewer responses. This has enabled the identification of key features including individual vesicles, vesicle segregations, strained vesicles, chilled margins, rubble zones, intrusive contacts and pāhoehoe lobe morphologies, which can be confidently matched between the televiewer data and the full diameter core. The data set and results of this study include findings which should enable improved borehole facies analysis through volcanic sequences in the future, especially where down-borehole data and images but no core are available.

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Alteration effects on petrophysical properties of subaerial flood basalts: Site 990, Southeast Greenland margin

Cited by 13 publications

References 1 publication

From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK

From continental extension to seafloor spreading: crustal structure of the Goban Spur rifted margin, southwest of the UK

Fossil seaward-dipping reflector sequences preserved in southeastern Australia: a 600 Ma volcanic passive margin in eastern Gondwanaland

Understanding volcanic facies in the subsurface: a combined core, wireline logging and image log data set from the PTA2 and KMA1 boreholes, Big Island, Hawai`i

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