No abstract

Calderas represent morphological depressions several kilometers in diameter, and the unloaded crustal stresses they produce can form rapidly (e.g. Pinatubo, 1990) or slowly (e.g. Hawaii, 2018). Active calderas are known as sites of persistent magma intrusions, and yet the dynamics of their shallow plumbing system is not well constrained. We use scaled laboratory experiments to study how experimental intrusions are created beneath a caldera by injecting dyed water (magma analogue) into the base of an elastic gelatin solid (crust analogue) with a cylindrical cavity in its surface to mimic a caldera-like topography. The evolving dike geometry and stress field were qualitatively determined using polarized light, and digital image correlation allowed the incremental and total strain to be quantified by tracking passive-tracer particles in the gelatin that fluoresced in a thin 2D vertical laser sheet. Our results show that the unloaded stress field from a caldera can cause a divergence of vertical dikes, and leads to circumferential dikes and cone sheets. When the caldera was large the initially vertical dike became arrested, then grew laterally via circumferentially-propagating en echelon segments; these eventually joined to complete a cone sheet that was parallel to, but extended outside and beneath, the large caldera. When the caldera was small, a circumferential dike erupted, producing a short fissure which was outside, but parallel to, the caldera. We suggest that the distinct curved geometry, velocity, strain and stress characteristics of circumferential dikes and cone sheets can be used to interpret the origin and growth of post-caldera magmatism and the likelihood of eruption in caldera systems.

Geophysical survey techniques were carried out to identify the potential zones of manganese ore in Central Peninsular Malaysia. Electrical resistivity tomography and induced polarization (IP) geoelectrical methods have been used to identify the metal distribution and mineralization zones. Five geoelectrical survey profiles were deployed at the proposed site using pole-dipole array in the W-E direction with lengths of 400 m and 800 m. The results of the resistivity and IP inversion indicate the presence of well-correlated low resistivity (≤ 200 m) and high chargeability zones (≥ 10 ms) embedded in the varied weathered host rock as massive and disseminated ore bodies. The 3-D maps generated enabled the delineation of the conductive bodies orientation and mineral of interest distribution. Results of the geochemical analysis contributed to validating the site as a potential mineralized zone with a high concentration of manganese. The study suggests further geophysical investigations in the southern segment of the research area to produce a more consistent image of the subsurface structures, and conclusively identifying the extension of mineral deposits for the purpose of ore prospecting to aid drilling operations.

A geophysical survey has been carried out to assess the distribution of gold minerals at the Felda Chiku 3, Gua Musang district, Kelantan, Peninsular Malaysia. A 2-D geo-electrical resistivity imaging (ERI), combined with Induced Polarization (IP) method, and Oasis Montaj modelling were applied to delineate the potential conductive zones associated with sulphide mineralization. Most Peninsular Malaysia’s gold deposits occur in hydrothermal sulphides as discrete ore formations within the host rocks. A good correlation between the ERI and the IP profiles was observed during the interpretation of the model that successfully identifying the low resistive, and high chargeable sulphide zones, which correspond to the gold mineralization zones. The correlations could be linked to the conductive features at depth ranging from about 25 m - 135 m, trending along N-S directions. The study suggests further geo-electrical investigation to be carried out towards the south-western part of the area as more potential mineralized zones with N-S trends could be found in this region. Further studies would be able to give the extent of the gold deposits in Kelantan and by extension, allow for better informed mineral exploration and drilling operations to mine the gold in the region.

Prior to and during eruptions, magma is stored and transported within volcanic and igneous plumbing systems (VIPS) that comprise a network of magma reservoirs and sheet intrusions. The study of these VIPS requires the combination of knowledge from the fields of igneous petrology, geochemistry, thermodynamic modelling, structural geology, volcano geodesy, and geophysics, which express the physical, chemical, and thermal complexity of the processes involved, and how these processes change spatially and temporally. In this contribution, we review the development of the discipline of plumbing system studies in the past two decades considering three angles: (1) the conceptual models of VIPS and paradigm changes, (2) methodological advances, and (3) the diversity of the scientific community involved in VIPS research. We also discuss future opportunities and challenges related to these three topics.