Die syn- bis post-magmatische Entwicklung des Mauna Kea/Hawaii, USA : Interpretation geophysikalischer Bohrlochdaten und petrophysikalischer Kerndaten aus der Tiefbohrung 'Hawaii Scientific Drilling Project, HSDP-2'

In 1999, an extensive logging program with standard logging tools was run by the GFZ Potsdam in the scientific drillhole ‘Hawaii Scientific Drilling Program - HSDP-2’ on the island of Hawaii/USA. Measurements of electrical resistivity, gamma-ray activity, and Vp-velocity were performed in an open-hole environment from 550 - 2720 mbsl (meter below sea level). The drilled section comprises basaltic formations of subaerial and submarine environment of various amount, morphology, and physical properties. Additionally, a broad range of petrophysical, geochemical, and petrographical core measurements were carried out. The present study deals with the interpretation of the logging data with regard to the primary and secondary evolution of the volcano Mauna Kea. This is achieved in different steps, namely (1) a re-classification of the current lithostratigraphic profile on the basis of the log data, (2) the combination of various core measurements and logging data, and finally (3) by setting up a volcano model, which integrates all information into an overall picture of the volcano evolution. Downhole measurements in HSDP-2 drillhole revealed many unexpected effects within geochemically similar rock types. Data recorded in different lithostratigraphic and/or structural environment of the drilled subaerial and submarine lava flows were influenced by secondary processes. Fluid flow, brecciation, and the evolution of alteration minerals lead to deviating results in gamma-ray and resistivity measurements. Data from downhole measurements were generally corrected for environmental influences. The re-classification of the current lithological profile resulted in a modified lithostratigraphic column. This column represents a differentiation of the drilled section into nine larger units, named log units LU 1 - 9. These log units show clearly distinguishable petrophysical features, which are connected to primary lithology as well as to secondary effects, such as compaction or alteration. For the detection of possible fluid pathway zones porosity and permeability profiles were calculated, applying an integration of conductivity and permeability measurements on cores with downhole resistivity measurements. Beside a gradual decrease of porosity and permeability with depth, the application revealed seven porosity/permeability transitions, which are related to lithological as well as hydrostratigraphical changes. These 'bounds' correlate with an Illite/Smectite as well as with a Smectite/Smectite-Zeolite border based on alteration mineral research results, and with a so-called alteration index performed on the basis of the spectral gamma-ray. Generally, the correlations of various events point to a relatively lithological independence of alteration phases. The overall combination and integration of the information from the various measurements leads to the perception that the shield volcano Mauna Kea, although almost at the end of its life-cycle, is still subject to and highly influenced by ongoing changes. These changes among which the observed fluid flow along permeable basalt and breccia zones is recently the most important one, have a deep impact on the entire volcano evolution.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2005

Author dc:creator

• Buysch, Arno

Contributors dc:contributor

• Clauser, Christoph

• info:eu-repo/classification/ddc/550
• Geowissenschaften
• Hawaii
• Mauna Kea
• Geologie
• Petrophysik
• Well Log Analysis
• Porosität
• Permeabilität
• Elektrofazies

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123735%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62145