The Geometry
and Evolution of the Sarulla Graben,
Hickman, Robert G.1, Pat P.
Dobson2, Marc Van Gerven3, Birean D. Sagala4,
Richard P. Gunderson5 (1) Structural Solutions, Houston, TX (2)
Lawrence Berkeley National Laboratory, Berkeley, (3) Solaria Corporation,
Fremont, (4) Chevron Geothermai Indonesia, Jakarta, Indonesia (5) Consultant,
Santa Rosa,
The
In contrast, field mapping, gravity
surveys, exploration wells and limited seismic demonstrate that, the two km
deep Sarulla graben does not fit standard models of strike-slip basins. The
basin has a half-graben profile and is internally cut by normal-dextral faults
that parallel a nearly linear part of the SFZ. The 35 km-long Sarulla graben
appears to have formed as a result of extension perpendicular to the major
strand of the SFZ. Within the graben the overall pattern of extension is
modified by sub-basin scale releasing and restraining bends.
Volcanic centers within the Sarulla area
include the Sibualbuali stratavolcano (~ 0.7-0.3 Ma), the Hopong caldera (~ 1.5
Ma), and the Namora-I-Langit dacitic dome field (0.8-0.1 Ma). These centers
generated the majority of the ash-flow tuffs and tuffaceous sediments filling
the Sarulla graben, and appear to have been localized by structural features of
the SFZ. Four significant geothermal systems within the Sarulla area are linked
to major faults and volcanic centers. In three of the systems, reservoir
permeability is dominated by faults and fractures within the SFZ. In the
fourth, permeability probably is locally influenced by faults, but highly
permeable fractures are widely distributed.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California