Ícaro Silva, from Ciências ULisboa: “The Almansor River Migmatites are a very important window of information”

Rocks around 340 million years old have been recognised as a Geosite of National Interest. This recognition results from more than two decades of research carried out by Ciências ULisboa and the University of Évora.

Around 340 million years ago, long before the current configuration of the continents, the region where Montemor‑o‑Novo is located today was undergoing profound geological transformations. Along the Almansor River, some of the marks of that ancient past have been preserved. The Almansor River Migmatites have been recognised as a Geosite of National Interest and included in the National Inventory of Geological Heritage, a recognition that highlights the scientific, educational and heritage value of this outcrop. For Ícaro Silva, lecturer at the Department of Earth Sciences and Energy at Ciências ULisboa, these outcrops are “a very important window of information” for understanding the processes involved in the formation of continental crust in an orogenic environment.

A 340 million years old “Portuguese Stone Soup”

But what, after all, are migmatites? “Migmatites are those rocks found at the boundary between metamorphic rocks […] and magmatic rocks,” explains Ícaro Silva. Their formation is associated with a drastic increase in temperature in the crust, which caused profound changes in the original rocks and, subsequently, processes of selective or partial melting. The result is a rock with a very distinctive appearance. To explain it simply, the researcher compares migmatites to a “sopa da pedra” (“portuguese stone soup”), in which the melted, granite‑like material surrounds fragments of rock that resisted melting.

In the stretch of the Almansor River known as Vale Paraíso, these structures are exceptionally well preserved, allowing the characteristics of migmatites to be observed in their place of formation. The outcrop also has landscape and heritage value, reinforcing its scientific and educational importance. It is precisely this preservation that makes it possible to study an important part of Earth’s geological history. According to Ícaro Silva, “around 340 million years ago, in the Carboniferous period, these rocks were formed through processes of partial melting at temperatures of around 800 °C and at relatively shallow depths (11–14 km).” The formation of these rocks took place during a period marked by the collision between the Gondwana and Laurussia continents, which would contribute to the formation of the supercontinent Pangaea and the Variscan mountain range.

The conditions recorded in the migmatites are particularly relevant for understanding how continental crust forms. The existence of very high temperatures at relatively shallow depths over a prolonged period constitutes, in the researcher’s words, “a case study that changes our perception of how crust forms in a continental collision regime.”

From research to the valorisation of the territory

The classification now awarded is the result of more than two decades of research carried out by teams from Ciências ULisboa and the University of Évora, but also of sustained work in training and scientific outreach. Over the past 20 years, the Almansor River Migmatites and other areas along the river have been the setting for activities aimed at students, teachers and the wider community. Among the initiatives developed was the project “A Escola e o Rio” (“The School and the River”), which involved lower‑secondary pupils from the Montemor‑o‑Novo School Group in activities that brought together Science and Art. For Ícaro Silva, scientific research should not remain confined to the academic community. “Every scientist, at some point in their life, should feel the call to communicate science to the community,” he says. “It is the best way to value and showcase our work, thereby attracting new talent to the sciences.”

The classification stems from the Collaboration Protocol signed in 2024 between Ciências ULisboa, the University of Évora and the Municipality of Montemor‑o‑Novo, which has promoted the inventory, valorisation and dissemination of the municipality’s geological heritage. For the researcher, this closer relationship between science, territory and community is also a way of “contributing to scientific literacy.”

The recognition of the Almansor River Migmatites therefore represents a new step in valuing and preserving this natural heritage, bringing it closer to schools, students and the wider community. For Ícaro Silva, it is also “the beginning of a broader and more ambitious process”, paving the way for new initiatives to promote this geological heritage.