Internal and external geodynamics: plate tectonics, magmatism, metamorphism and deformation
This domain tests how the exam frames Earth dynamics as one system: plate-scale tectonics driving deformation, magmatism and metamorphism, and surface processes shaping relief. Andalusia is the natural case study, because the Betic Cordillera records Mesozoic rifting, Cenozoic convergence between Eurasia and Africa, and late-orogenic extension.
Plate tectonic framework
- Iberia lies on the Eurasian plate; convergence with Africa (Nubia) since the Late Cretaceous proceeds at roughly 4-5 mm/yr, partitioned along the Azores-Gibraltar and Alboran-Rif systems.
- The Betic-Rif arc formed by subduction of Tethyan lithosphere, slab rollback and detachment; delamination of thickened mantle lithosphere helped generate late-orogenic extension and the Alboran Sea basins.
- Present seismicity concentrates in the Betics and the Gulf of Cadiz: a slow, distributed boundary, not a single strike-slip fault.
Deformation
- Stress (compression, tension, shear) produces strain: brittle folds and faults at shallow levels, ductile folds and foliation at depth.
- The Betics stack thrust sheets: Internal Zones (Nevado-Filabride, Alpujarride, Malaguide) with Alpine metamorphism; External Zones (Prebetic, Subbetic) with thin-skinned thrusts; and the Campo de Gibraltar flysch nappes.
- The Guadalquivir Basin is a foreland basin filled with Miocene molasse.
Magmatism and metamorphism
- Magma composition reflects source and differentiation; calc-alkaline suites (Cabo de Gata, Alboran) record subduction-related and post-collisional melting.
- Metamorphic facies are pressure-temperature fields; Nevado-Filabride prograde paths record high-P conditions (eclogite, blueschist) followed by decompression.
- External geodynamics - weathering, erosion, transport and deposition - is controlled by climate, lithology and relief, producing karst, fluvial incision and coastal landforms.
Worked example
A Subbetic limestone thrusts over Lower Miocene marls. What does this establish? The thrust must postdate deposition of the marls (cross-cutting relationship), so shortening is at least early Miocene. The limestone is allochthonous, so its Jurassic fossils do not date the underlying basin, and the contact is tectonic rather than stratigraphic. This is how a thrust is distinguished from an unconformity.
Traps that cost marks
Assuming every Betic structure is compressional, when extension is well documented; naming a metamorphic facies as if it were a rock; treating a nappe contact as conformable; forgetting that erosion rates depend on climate as well as uplift.
Key points
- Convergence, rollback and delamination explain both compression and extension in the Betics.
- Internal and External Zones differ in metamorphism and thrust style.
- Facies indicate P-T conditions, not specific rock names.
- Thrust contacts postdate the youngest rocks they cut.
- Surface processes link tectonics to relief and sedimentation.