page_title: Geology of the Iberian Peninsula
section_title: Galicia-Trás-os-Montes Zone
hierarchical_section_title: Geology of the Iberian Peninsula / Iberian Massif / Galicia-Trás-os-Montes Zone
caption_attribution_description: Galego: Ribeira Sacra. Río Sil. Lugo. Galiza
context_page_description: The geology of the Iberian Peninsula consists of the study of the rock formations on the Iberian Peninsula, which includes Spain, Portugal, Andorra, and Gibraltar. The peninsula contains rocks from every geological period from the Ediacaran to the Quaternary, and many types of rock are represented. World-class mineral deposits are also found there.
  The core of the Iberian Peninsula consists of a Hercynian cratonic block known as the Iberian Massif. On the northeast this is bounded by The Pyrenean fold belt, and on the southeast it is bounded by the Betic Fold mountain chain. These two fold chains are part of the Alpine belt. To the west, the peninsula is delimited by the continental boundary formed by the opening of the Atlantic Ocean. The Hercynian Fold belt is mostly buried by Mesozoic and Cenozoic cover rocks to the east, but nevertheless outcrops through the Iberian Chain and the Catalan Coastal Ranges.
context_section_description: The Galicia-Trás-os-Montes Zone is a bean-shaped tectonic unit in the northwest corner of Spain and northeast Portugal (Trás-os-Montes). It has also been called the allochthonous complexes. The zone consists of a nappe stack which is highly metamorphosed. It was formed by the collision of the Iberian Plate with a thinned piece of crust from another continent called the Meguma terrane. There are five units in the stack. At the lowest level are high pressure, low temperature metamorphosed rocks.  Second is an ophiolite.  Third is the lower part of a continental crust which has been metamorphosed to high temperature with high pressure. Fourth is a layer of sediments derived from weathering land with low-grade metamorphism. There is also an underlying Ediacaran and early Paleozoic layer called the autochthenous sequence. Metamorphism of the allochthenous nappe occurred 390–380 Ma in the Middle Devonian. This is possibly from the Rheic Ocean. Finally, above this are other schists called the schistose domain of Galicia-Trás-os-Montes or Para-autochthenon. There are five oval shaped masses of mafic to ultramafic rocks making up the ophiolite. These are the Cabo Ortegal, Ordes, Lalín, Bragança and Morais Massifs. Each of these are in a syncline and are surrounded by Silurian metamorphic rocks with an inward-dipping thrust zone forming the boundary. The kinds of rock in the mafic massifs are schists, gneiss, amphibolite, metagabbro, granulite, eclogite, and serpentine. The Ordes Massif dates from 380 to 390 Ma, and represents part of the Rheno-Hercynian Ocean as part of an accretionary wedge. It became joined to the European Hunic Terrane between the Channel Block and the allochthenous nappe. It has a corresponding block, the Lizard complex in southwest England. The Cabo Ortegal complex is dated around 345–340 Ma and is the remains of a Paleo-Tethys Ocean mid-oceanic ridge
  The Malpica-Lamego line is a shear zone forming a line running north–south on the west side of the Galicia-Trás-os-Montes Zone.  It is 275 km long and associated with intrusions of granodiorite.  There is over 10 km of vertical offset along the shear zone.
caption: The Galician Massif mountains surrounding the Sil River in Lugo, Galicia.
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