Saint Peter and Saint Paul Archipelago
The St. Peter and St. Paul's Rocks ( portugies.: Penedos de São Pedro e São Paulo ) is a about 960 km off the northeastern coast of Brazil in the Atlantic area, this small group of bare rock islands. Meteorological terms, the approximately 100 km north of the Equator located archipelago is year-round in the intertropical convergence zone.
Geography
The group measures about 250-300 m in diameter and is at its highest point ( on the largest island Belmonte) 18 m high. It has a total area of 1.3 ha (0.013 km ²). The closest island is about 625 km south-west Fernando de Noronha location.
The island group includes the following islands:
- Island Belmonte ( of Southwest, southwest ): 5380 m²
- Challenger island (São Paulo, southeast ): 3000 m²
- Island Nordeste (São Pedro, north-east ): 1440 m²
- Eiland Cabral ( Noroeste, northwest ): 1170 m²
- Eiland South ( Sul, south ): 943 m²
And small rock like Beagle Rocha and Rocha Pillar to the north, Cambridge to the east and Rocha Rocha Rocha Coutinho and Erebus in the south. In none of the islands there are fresh water.
Geomorphology
The St. Peter and St. Paul's rocks are the head of a large sub- sea survey in an east-west direction and 90 in the north-south direction 21 kilometers long along the 3000 m isobath. In plan, this sigmoidal shaped, high morphological forms in about a verkipptes to the right " S", whose north and south sides is constructed of east-west oriented ridge structures. The North back with him seated island group is higher than the southern ridge and rises above sea level. The southern ridge reaches almost 1400 meters water depth. Between the two back a grave breach, which is lower than 2700 meter runs.
The geologically interpreted as Megamullion high structure belongs to the northern edge of the 90 kilometer-wide, 080 N - trending St. Paul Fracture Zone, which gradually displaced the Mid-Atlantic Ridge to a total of 550 kilometers to the east. The northern, only a maximum of 25 km-wide segment of the archipelago, has a left-sided offset of 280 km alone. The north ridge is immediately adjacent to the northernmost transform fault within the fault zone. The Mid-Atlantic Ridge is located about 120 kilometers to the west, until he staggered to the east segment is 160 kilometers.
Geology
In contrast to most of the islands in the Atlantic, such as Iceland, Jan Mayen, the Azores, Ascension and Tristan da Cunha which are all purely volcanic origin, pass the St. Peter and St. Paul's rocks of ultramafic mantle rock ( peridotite ). Due to the close proximity of the fault zone bounding the northern edge of the fault peridotite was strongly tektonisiert, mylonitisisiert and metasomatic transformed into serpentinite. The north ridge is crossed by numerous, steeply dipping faults in east-west direction, which simultaneously have a suspensory component in addition to right-sided offset and thus explain the tectonic Aufpressung the archipelago. The faults are occasionally accompanied by gabbroic intrusions, and lavas occurred to them from 1200 meters water depth.
The south adjoining grave fault zone is underlain by slightly deformed, serpentinitisiertem peridotite. It contains basaltic lavas and Doleritintrusionen. The grave fault system is likely to have originated as a pull- apart.
The southern ridge is how the trench from the undeformed, serpentinitisiertem peridotite. On its northern side, platform -like sponge colonies have settled in the south and sediments were left, which formed a consolidated, calcareous crust coating on the serpentinites.
Inside the Challenger Island, a 40 x 70 meter large bag is preserved with Quaternary sediments - the St. Peter and St. Paul - formation. The formation is divided into two units, the Atobás Members in the footwall and hanging wall Viuvinhas - members. The Atobás Members shall be discordant with a Transgressionskonglomerat of angular to rounded Peridotitgeröllen over the peridotite base. The Klastengröße reduced the slope ends on conglomeratic arenite towards coarse to medium Areniten (sand fraction). The sedimented after a hiatus Viuvinhas Members consists of Kalkareniten contain remanufactured clasts of biogenic origin. It also sets a konglomeratisch and then loses the slope ends at Klastengröße.
The Saint Peter and Saint Paul - formation provides evidence of seismic events during their deposition. Three major events can be identified:
- At the end of Atobás - Members: the unit was tilted to southeast and fractures opened in the substructure. The discordant following Viuvinhas Members must also have been affected seismically, as there are up to 1 meter blocks in its base conglomerate.
- At the end of Viuvinhas - Members: the entire coating in the St. Peter and St. Paul lineup was adjusted tectonically.
- After the end of sedimentation: severe disruption of the base, which by pauste up into the formation and reveals himself as areas of different incidence.
Also jungpleistozäne to Holocene Abrasionsterrassen can be seen on the St. Peter and St. Paul's Rocks. So polymictic beach pebbles found at levels 3, 6, 9 and 15 meters, roughly comparable with the situation in Fernando de Noronha Archipelago. They illustrate a jerky lifting of the archipelago in the upper Quaternary. Thus, the terraces of the six can - and 9 -meter levels are associated with the Flandrium ( Holocene ) and are old in about 6000 years. Is calculated from this quite a high elevation rate of 1.5 millimeters per year. Age dating with the radiocarbon method of fossil corals provided comparable results. The Mantelperidotit likely to have been raised at normal oceanic crustal thickness of 10 kilometers. This means that the uplift in front of about 7 million years BP began. The actual island stage was only reached in the Upper Pleistocene 100,000 to 200,000 years ago.
Political affiliation
Brazil has built on the islands a beacon and a lodge for military personnel and researchers. Administratively, they are part of the Brazilian state of Pernambuco, although nearer to the mainland of the State of Rio Grande do Norte.
Wildlife
On the rocks breed birds such as Brown Booby (Sula leucogaster ), Noddiseeschwalben ( Anous stolidus ) and Small Noddiseeschwalben ( Anous minutus), also there Red crabs live ( Grapsus grapsus ).
Events
- The islands were visited by Charles Darwin on February 16, 1832 during his expedition on the Beagle.