VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!

Browsing by Author "Hobbs, Richard W."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Analysis of a conductive heat flow profile in the Ecuador Fracture Zone
    Kolandaivelu, Kannikha Parameswari; Harris, Robert N.; Lowell, Robert P.; Alhamad, Ahmed; Gregory, Emma P. M.; Hobbs, Richard W. (2017-06)
    We report 18 new conductive heat flow measurements collected from a sediment pond located in the inactive part of the Ecuador Fracture Zone in the Panama Basin. The data were collected along an east-west transect coincident with a multi-channel seismic reflection profile that extends from ODP Hole 504B to west of the sediment pond. Conductive models indicate that heat flow should decrease from approximate to 400 mW m(-2) on the 1.5 Ma western plate to approximate to 200 mW m(-2) on the 6 Ma eastern plate; however the observed heat flow increases nearly linearly toward the east from approximately 140 mW m(-2) to 190 mW m(-2). The mean value of 160 mW m(-2) represents an average heat flow deficit of which we attribute to lateral advective heat transfer between exposed outcrops on the western and eastern margins of the sediment pond. We apply the well-mixed aquifer model to explain this eastwardly flow, and estimate a volumetric flow rate per unit length in the north-south direction of approximate to 400 +/- 250 m(2) yr(-1) through the basement aquifer. Using a Darcy flow model with the mean flow rate, we estimate permeabilities of similar to 10(-11) and 10(-12) m(2) for aquifer thicknesses of 100 and 1000 m, respectively. The estimated permeabilities are similar to other estimates in young oceanic upper crust and suggest that vigorous convection within the basement significantly modifies the thermal regime of fracture zones. Additional heat flow data are needed to determine the prevalence and importance of advective heat transfer in fracture zones on a global scale. (C) 2017 The Authors. Published by Elsevier B.V.
  • Thumbnail Image
    Evolution of heat flow, hydrothermal circulation and permeability on the young southern flank of the Costa Rica Rift
    Kolandaivelu, Kannikha Parameswari; Harris, Robert N.; Lowell, Robert P.; Robinson, Adam H.; Wilson, Dean J.; Hobbs, Richard W. (2020-01)
    We analyse 67 new conductive heat-flow measurements on the southern flank of the Costa Rica Rift (CRR). Heat-flow measurements cover five sites ranging in oceanic crustal age between approximately 1.6 and 5.7 Ma, and are co-located with a high-resolution multichannel seismic line that extends from slightly north of the first heat-flow site (1.6 Ma) to beyond ODP Hole 504B in 6.9 Ma crust. For the five heat-flow sites, the mean observed conductive heat flow is approximate to 85 mW m(-2). This value is approximately 30 per cent of the mean lithospheric heat flux expected from a half-space conductive cooling model, indicating that hydrothermal processes account for about 70 per cent of the heat loss. The advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults. Supercritical convection in Layer 2A extrusives occurs between 1.6 and 3.5 Ma, and flow through a thinly sedimented basement high occurs at 4.6 Ma. Advective heat loss diminishes rapidly between approximate to 4.5 and approximate to 5.7 Ma, which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages approximate to 65 +/- 10 Ma. At approximate to 5.7 Ma the CRR topography is buried under sediment with an average thickness of approximate to 150 m, and hydrothermal circulation in the basement becomes subcritical or perhaps marginally critical. The absence of significant advective heat loss at approximate to 5.7 Ma at the CRR is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as a result of mineral precipitation and original permeability at the time of formation. Permeability is a non-monotonic function of age along the southern flank of the CRR, in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge-axis magma supply and tectonic extension. Hydrothermal circulation in the young oceanic crust at the southern flank of CRR is affected by the interplay and complex interconnectedness of variations in permeability, sediment thickness, topographical structure, and tectonic and magmatic activities with age.