Geothermal exploration concepts can be improved at an early stage of exploration by assessing the petrophysical rock properties of samples from surface outcrops. The results can be used to better evaluate the proposed geothermal resource and exploration strategies for the region. Our study provides fundamental knowledge on thermohydraulic rock properties to help identify the heat transfer mechanisms associated with geothermal resources in the extensional tectonic settings of the Ambilobe and Ambanja areas in North Madagascar. Thermostratigraphic units were defined according to the thermofacies concept. The geology of both areas is predominantly Quaternary volcanics (mainly basalt) and Permian–Triassic sediments (mainly shale and sandstone) overlying a faulted and fractured Proterozoic metamorphic basement of gneiss and amphibolite. Normal faults related to graben structures, along which hot springs occur, are characteristic of this extensional regime. Permian sandstone and mica schist have the highest porosities, with values up to 0.10–0.11. The matrix permeability of sedimentary and basement rock formations varies from less than 1.0 \(\times\) 10^–19 to 1.1 \(\times\) 10^–14 m² (< 0.001 to 11 mD), while the average thermal conductivity is ~ 3.8 W m⁻¹ K⁻¹ and ~ 2.7 W m⁻¹ K⁻¹, respectively. Conductive heat transfer is expected for such low-permeability rocks, except where fractures form permeable conduits that promote forced convection driven by regional groundwater flow. Crustal-scale faults should be targeted for further geothermal exploration.

通过评估地表露头样品的岩石物理性质，可以在勘探的早期阶段改进地热勘探概念。结果可用于更好地评估该地区拟议的地热资源和勘探策略。我们的研究提供了关于热工水力岩石特性的基础知识，以帮助确定与北马达加斯加安比洛贝和安巴尼亚地区伸展构造环境中地热资源相关的传热机制。热地层单位是根据热相概念定义的。这两个地区的地质主要是第四纪火山岩（主要是玄武岩）和二叠纪-三叠纪沉积物（主要是页岩和砂岩），覆盖在片麻岩和角闪岩的断层和断裂的元古界变质基底上。与地堑构造相关的正断层，温泉沿其出现，是这种伸展状态的特征。二叠纪砂岩和云母片岩的孔隙度最高，可达 0.10-0.11。沉积岩和基底岩层的基质渗透率从小于 1.0 \(\times\)  10 ^–19 to 1.1  \(\times\)  10 ^–14  m ² (< 0.001 to 11 mD)，而平均热导率为 ~ 3.8 W m ^-1  K ^-1和 ~ 2.7 W m ^-1  K ^-1分别。对于此类低渗透性岩石，预期传导热传递，除非裂缝形成渗透性管道，促进区域地下水流驱动的强制对流。地壳规模的断层应成为进一步地热勘探的目标。