Abstract
We use freely available Google satellite data, instrumental seismicity, fault plane solutions, and previously mapped structural and geological maps to identify new fault zones in central Borneo. We have mapped a number of ~NW-SE trending dextral strike-slip faults and ~NE-SW to ~N-S trending sinistral strike-slip fault zones. The geomorphic expression of faulting is shown by the well-developed triangular facets, fault rupture scarps, truncated sedimentary beds, topographic breaks, displaced ridges, deflected streams, faulted Plio-Pleistocene volcanic deposits, and back-tilted Holocene to Recent sedimentary deposits. Some of the mapped faults are actively growing, and show text-book examples of dextral and sinistral offset, which ranges from ~450 m to tens of km. The dextral strike-slip fault systems are clearly developed in the central and eastern portions of Borneo where they cut through the folded sedimentary sequences for >220 km. The ~NE-SW to ~N-S trending sinistral strike-slip faults are dominantly developed in the eastern portion of central Borneo for >230 km. The geomorphic expression of faulting is clear and the fault scarps are ~SE facing for the sinistral fault system, and ~NE facing for the dextral fault system. The age of the faulting is constrained by the cross-cutting relationship where the fault cuts through Plio-Pleistocene volcanic deposits for >30 km, which suggests a neotectonic nature of faulting. The strike-slip fault systems that we have mapped here provide the first geomorphic evidence of large-scale strike-slip faulting in Borneo and suggest the presence of a major sinistral strike-slip fault that runs for >900 km through the center of Borneo, and forms a backbone onto which most of the mapped structures root. The mapped structures clearly suggest that plate tectonic forces dominantly control the geological structures that we have mapped and support the regional oblique convergence that is oblique with respect to the major trend of the Crocker Range, which forms the spine of the Borneo Island.
Highlights
Fifteen years ago, the bulk of the geological setting of Borneo Island was poorly known because of inaccessibility to its dense tropical rainforest
The mapped structures clearly suggest that plate tectonic forces dominantly control the geological structures that we have mapped and support the regional oblique convergence that is oblique with respect to the major trend of the Crocker Range, which forms the spine of the Borneo Island
The fault mapped by us (e.g., [15,55]) is instead arguably evidence of a major sinistral strike-slip fault system that might explain the existence of extension in NW Borneo, and this could be responsible for the large scale pattern of faulting that is mapped in Borneo, and we propose that the tectonic forces are largely responsible for deformation in Borneo that ~NW-SE directed regional oblique compression is driving the deformation seen in Borneo (Figures 13 and 14)
Summary
The bulk of the geological setting of Borneo Island was poorly known because of inaccessibility to its dense tropical rainforest This has changed with the advancement of technology, with the freely available satellite data which provide a digital platform to conduct geological studies in the region [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. A great variety of satellite data and high-resolution satellite imagery enable geologic, geomorphic, and tectonics investigators to acquire such data over smaller or large areas and gain a more comprehensive understanding of the Earth’s dynamic nature of landforms [16] This methodology reduces the limitations of traditional geological mapping in an area that is politically complex or inaccessible [17,18,19]. Geosciences 2018, 8, x FOR PEER REVIEW available Google terrain view provides a much better platform to map geomorphic landforms on regions in Borneo makes it difficult to map it by using high-resolution images, and the freely a scale significant to terrain our work [14,15,19,20,21,22,23,24,25,26,27]).
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