Tectonism and Volcanism Study in the Minahasa Compartment of the North Arm of Sulawesi Related to Lahendong Geothermal Field, Indonesia

Abstract

Lahendong geothermal field is located in the northern arm of Sulawesi, in North Sulawesi Province of Indonesia. The arm consists of Lembeyan Ridge on the east and sedimentary environment on the west. The ridge comprises of tertiary andecite basalt volcanic rocks. Fault trending NE-SW and NW-SE are prominent structures in the arm as resulted from unique collision among Eurasian Plate in the north, Tomini Micro Plate in the south and North Sulawesi Arm. The younger structures found in the vicinity are Tondano and pangalombian lake caldera. These features are product of volcano-tectonic depression, oriented on the crustal scale NE-SW lineament.
The sedimentary formation comprises of pack stone and bound stone as shown by the three exploration wells in the north-west part of Lahendong geothermal field. The globigerina and globorotalia sp found in the formation suggest the relative age of Miocene period. The formation thickens to the north-west, indicating that the paleo-current flows to the south east. The east end of the basin is limited by the Lembeyan ridge. During the depositional process volcanic activities continuously erupt volcanic deposit in the vicinity as shown by Mount Klabat in the Northern part, Mount Manimporok and Rindengan in the Southern part. Therefore, inter-fingering between the volcanic products and the reef formation are common. In addition, these common inter-fingering which developed in the Miocene time, is supported by the existing modern volcanism of gunung Lokon-Mahawu in the north, gunung Soputan in the south, and modern reef of Bunaken.
This tectonic setting leads Lahendong as a unique geothermal field. The field currently produces 20 MWe and additional further development 40MW is now underway.