The Google Image pics of Pijao I saw left me thinking, “Oh wow, this looks like a Swiss village, I gotta go there!” And right I was. Pijao is the perfect answer of the Andes Cordillera Central to a village in Switzerland. The cows look a bit different and there’s no Matterhorn shooting up into the sky in the distance, but as I said, I’m not fussy.
Wikipedia falls flat on its face in English with regard to information on Pijao, so we’re going to the Spanish page (here) and I’ll do some translation:
Pijao se encuentra ubicado dentro de la región fisiográfica denominada Región Andina, en la subregión de la Cordillera Central, contando con tres tipos de paisaje: montaña, piedemonte y valle.
El paisaje de Montaña se encuentra al oriente del municipio, sector del eje de la cordillera, construida sobre rocas metamórficas del complejo Cajamarca donde predominan los esquistos verdes y se observan rasgos característicos de estructuras geológicas como la falla de San Jerónimo. El paisaje de Piedemonte se encuentra en la parte occidental del municipio, constituido por depósitos fluviovolcánicos, rocas ígneas y algunas con recubrimiento de cenizas volcánicas. El paisaje de Valle se presenta en el sector de Barragán, Los Balsos y Río Lejos, conformado por aluviones recientes de relieve relativamente plano.
[Pijao is located in the physiographical region called the Andes Region, a subregion of the Cordillera Central, which has three types of terrain: mountains, piedmont and valley.
The mountain terrain is to the East of the municipality, in the axis of the range, lying above metamorphic rock of the Cajamarca complex in which green schists predominate. The San Jerónimo fault is also observable in the terrain. The piedmont terrain is also in the eastern part of the municipality and includes volcanic riverine deposits, igneous rocks and some coverage by volcanic ash. The valley terrain is found in the sectors of Barragán, Los Balsos and Río Lejos, formed by alluvial deposits of recent origin that are relatively flat in relief.]
Looks like a whole lotta something’s been going on there — tectonic uplift, volcanic activity, weathering, it’s a geological partaay. I always find it fascinating to know something about what’s under the things I see — I can’t say the green schists leaped to my attention but it’s nice to know they’re there. Somewhere. It’s like knowing a friend’s birthday — you’d feel something was missing if you had no idea when it was. If you read my post on living with the geology around us, you know that I purvey geological information in the suavest manner possible. I could be shoving information your way of this type (webpage here):
Late Jurassic terrane collision in the northwestern margin of Gondwana (Cajamarca Complex, eastern flank of the Central Cordillera, Colombia)
Medium-grade metabasites and metapelites from the Cajamarca Complex (Central Cordillera of Colombia) are in fault contact with the Jurassic Ibague batholith and show a penetrative foliation, locally mylonitic, suggesting intense dynamic–thermal metamorphism. The amphibolites are composed of calcic amphibole + epidote + plagioclase + quartz plus rutile + titanite + apatite + carbonate as accessory phases. Chlorite and albite appear as retrograde replacements. The metapelites are mainly composed of phengite + quartz + garnet + chlorite, plus epidote + albite + apatite + titanite + haematite as accessory phases. Bulk geochemistry of the amphibolites indicates basaltic protoliths with a mid-ocean ridge basalt (MORB) signature, although enrichment in the mobile large-ion lithophile elements compared to MORB suggests pre- and/or syn-metamorphic alteration by fluids. Peak pressure–temperature determinations for both types of rocks are similar, ranging 550–580°C and 8 kbar (approximately 26 km depth and an apparent geothermal gradient of 22°C/km). 40Ar-39Ar dating of amphibole from two amphibolite samples and one phengitic mica from a pelitic schist yielded plateau ages of 146.5 ± 1.1 Ma and 157.8 ± 0.6 Ma, and 157.5 ± 0.4 Ma, respectively. These Late Jurassic ages contrast with previously published (Permian)Triassic ages of metamorphism in the Cajamarca Complex. Taken together, our data indicate tectonic-driven burial of oceanic supracrustal sequences down to mid-crustal depths during Late Jurassic times and are best explained as the result of terrane collision-related metamorphism and deformation in a fore-arc/volcanic-arc environment of the active western margin of Gondwana rather than as a result of Jurassic thermal–metamorphic resetting of a (Permian)Triassic metamorphic sequence during intrusion of the Jurassic Ibague batholith. Our results represent the first report of Jurassic terrane collision tectonics involving supracrustal oceanic rocks in the northwestern margin of Gondwana in Colombia.
It’s riveting stuff, I’m about to hyperventilate. Gondwana! Wow! Too cool. But we’ve already established that we’re just after the pretty stuff, so let’s get to the pics. 🙂