The HMS OWEN with captain Hall and chief scientist G. Evans landed in
December 1960 on the St. Peter’s and St. Paul’s Rock’s islets. J.D.H. Wiseman, a
known specialist in land-based ophiolite complexes, accompanied the expedition.
Wiseman (1966) found the rocks from the islets unusual when compared to other
peridotites because of their mineralogical peculiarity. He noted the presence of
abundant hornblende, a hydrated silicate mineral, and called the rocks ‘‘Challengerites’’, after the first discoveries made by the HMS CHALLENGER
expedition.
The ‘‘volcanic versus metamorphic’’ origin of the rocks from the St. Peter’s and
St. Paul’s islets has long been debated by geologists. Washington (1930) proposed
that the origin of the rocks was from deep seated and deformed plutonic rocks.
Tilley (1947) made further detailed studies of this expedition and suggested that
the rocks forming the Islets were dynamically emplaced during the uplift of deepseated material. Indeed, the presence of deformed and metamorphosed peridotite
transformed into mylonite was observed, and this could very well indicate extreme
pressure conditions.
More recently, Melson and Thompson (1973) published the first complete and
comprehensive descriptions of the rocks forming the Islets and compared them to
the samples collected from surrounding underwater structures during the Atlantis
II’s twentieth cruise in 1966. Russian expeditions with the R.V. AKADEMIC
NIKOLAJ STRAKHOV from the Geological Institute of the USSR Academy of
Science also visited the area of the St. Paul’s Rocks in 1988 and in 2000. Professor
Leonid Dimitriev (1985) studied the material in detail and made the most accurate
description of the mylonite samples from the St. Paul’s Rocks submarine massif.
Leonid stated that it is likely that the emplacement of mylonite, which is high
temperature, probably around 800–900 °C, is the result of a plastic deformation of
the upper mantle (Turner and Verhoogen 1960).
The St. Paul’s Rocks Islets revisited in 1997–1998
One goal of our St. Paul’s Rocks cruise also called St. Paul’s cruise was to follow
in the paths of the HMS BEAGLE and HMS CHALLENGER adventures and
therefore to land on the islets in order to carry out geological reconnaissance with
sampling stations and scientific observations. The main objectives were to collect
oriented samples and drill cores for paleo-magnetic studies. Bertrand Sichler had
brought a hand-carried coring device that could drill holes a few centimeters deep
into the rocks. Thus, a landing expedition on the islets of the St. Peter’s and St.
Paul’ Rocks was programmed. On January 3, 1998, we sent a zodiac (inflatable
boat) with four people from the scientific team: Eulalia Gracia from the University
of Barcelona (Spain), Bertrand Sichler (IFREMER), Thierry Juteau (University of
Brest) and Ronan Apprioual (IFREMER) who was in charge of handling the
zodiac and assisting the three geologists in their venture. A hand radio was
St. Peter and St. Paul’s Rock’s Islets
283
December 1960 on the St. Peter’s and St. Paul’s Rock’s islets. J.D.H. Wiseman, a
known specialist in land-based ophiolite complexes, accompanied the expedition.
Wiseman (1966) found the rocks from the islets unusual when compared to other
peridotites because of their mineralogical peculiarity. He noted the presence of
abundant hornblende, a hydrated silicate mineral, and called the rocks ‘‘Challengerites’’, after the first discoveries made by the HMS CHALLENGER
expedition.
The ‘‘volcanic versus metamorphic’’ origin of the rocks from the St. Peter’s and
St. Paul’s islets has long been debated by geologists. Washington (1930) proposed
that the origin of the rocks was from deep seated and deformed plutonic rocks.
Tilley (1947) made further detailed studies of this expedition and suggested that
the rocks forming the Islets were dynamically emplaced during the uplift of deepseated material. Indeed, the presence of deformed and metamorphosed peridotite
transformed into mylonite was observed, and this could very well indicate extreme
pressure conditions.
More recently, Melson and Thompson (1973) published the first complete and
comprehensive descriptions of the rocks forming the Islets and compared them to
the samples collected from surrounding underwater structures during the Atlantis
II’s twentieth cruise in 1966. Russian expeditions with the R.V. AKADEMIC
NIKOLAJ STRAKHOV from the Geological Institute of the USSR Academy of
Science also visited the area of the St. Paul’s Rocks in 1988 and in 2000. Professor
Leonid Dimitriev (1985) studied the material in detail and made the most accurate
description of the mylonite samples from the St. Paul’s Rocks submarine massif.
Leonid stated that it is likely that the emplacement of mylonite, which is high
temperature, probably around 800–900 °C, is the result of a plastic deformation of
the upper mantle (Turner and Verhoogen 1960).
The St. Paul’s Rocks Islets revisited in 1997–1998
One goal of our St. Paul’s Rocks cruise also called St. Paul’s cruise was to follow
in the paths of the HMS BEAGLE and HMS CHALLENGER adventures and
therefore to land on the islets in order to carry out geological reconnaissance with
sampling stations and scientific observations. The main objectives were to collect
oriented samples and drill cores for paleo-magnetic studies. Bertrand Sichler had
brought a hand-carried coring device that could drill holes a few centimeters deep
into the rocks. Thus, a landing expedition on the islets of the St. Peter’s and St.
Paul’ Rocks was programmed. On January 3, 1998, we sent a zodiac (inflatable
boat) with four people from the scientific team: Eulalia Gracia from the University
of Barcelona (Spain), Bertrand Sichler (IFREMER), Thierry Juteau (University of
Brest) and Ronan Apprioual (IFREMER) who was in charge of handling the
zodiac and assisting the three geologists in their venture. A hand radio was
St. Peter and St. Paul’s Rock’s Islets
283