A story with millions of years
The rock age and landscape shape are not the same question.
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The work of A. Almeida refers to a dating of the complex of Cabeceiras de Basto by the uranium-chumbo method, using the minerals zircon and monazite. The result cited is a minimum age of 311 ± 1 million years. It is a geological reference to the rock formation studied: it does not date the construction of a wall, nor establishes when a hillside has acquired the form that we see today.
The article integrates the minutes of the V National Congress of Geology, published in 1998. Upon reaching the value, Almeida refers to a work of geochronology with other authors, indicated in the bibliography. This chain of references allows us to understand where the number comes from: it is a result of investigation, not an age estimated by the color or size of the grains.
Reading a landscape forces you to separate time scales. One thing is the age attributed to the rocky complex; another, the transformation of relief; another, the moment when a stone was used in a construction. The three stories can cross on the same wall, but need different evidence.
Three questions for the same stone
Open an option and choose the story.
What do you see in the grains?
The size of the crystals allows comparing textures without dating the stone to the eye.
Granite also changes grain →How does the landscape change?
The history of relief adds processes to the observation of the rock.
The mountains is also read in stone →How does the stone enter the village?
The use of granite in construction opens another scale of time and human work.
Granite also draws the village →
Source and context
Accessed: . Editorial summary; the date of consultation is not the date of the facts.