Pictorial remanent magnetization retrieved from the Santo Domingo Convent (Isthmus of Tehuantepec, Oaxaca, Mexico): An attempt to directly date mural paintings based on geomagnetic field variation

Abstracts A detailed magnetic mineralogy and archaeomagnetic investigation was performed on thirty-two red mural painting samples belonging to the colonial Santo Domingo Convent in Oaxaca (Southern Mesoamerica). Systematic magnetic experiments included continuous thermomagnetic curves, hysteresis cycles, acquisition of isothermal remanence and step-wise alternating field demagnetization of the pictorial remanent magnetization (PiRM). Titanium-poor titanomagnetite seems to act as responsible for major part of pictorial remanent magnetization while heating and cooling curves show marked irreversibility and high thermal instability. Although all samples were demagnetized by means of alternating fields up to 90 mT, only seven of them provided reasonably well-grouped paleodirections yielding following mean values: Inclination = 35.2°, Declination = 2.3°, α95 = 4.8° and k = 161. According to the probability density function obtained by means of the global geomagnetic model SHA.DIF.14 K, the possible elaboration date of the painting layer under study is estimated between 1684 CE and 1744 in accordance with historical documents. Despite low success rate, the described methodology deserves to be considered for dating of wide range of red mural paintings worldwide.