IGC 33 Field Excursion 35 & Regional symposium EUR-05

Dear colleagues,

The deadline for abstracts for ICG33 in Oslo is Friday 29th – see 
http://www.33igc.org

For those interested in early Caledonian tectonism and magmatism, we call 
your attention to a pre-IGC field excursion 35: “Pre-Scandian Tectonic and 
Magmatic Evolution of the Helgeland Nappe Complex, Uppermost Allochthon” 
and the companion IGC Regional Symposium: “EUR-05: Pre-collisional 
evolution of the Caledonian-Appalachian orogen.”

The 5-day pre-conference field excursion will present the geologic 
development of the Helgeland Nappe Complex (HNC), the structurally highest 
nappe complex in the Norwegian Caledonides. Because the HNC did not 
undergo ultra-high-pressure (UHP) metamorphism before or during the 
Scandian event, its component nappes retain a pre-Scandian history that is 
much easier to read than in rocks that underwent UHP metamorphism. A 
consensus has emerged that the HNC nappes represent tectonostratigraphic 
terranes that formed on the western side of the Iapetus Ocean basin. 
Therefore, a better understanding of the deposition, tectonic history, 
metamorphism, and magmatic activity of the nappes will improve out 
understanding of geologic evolution of the western side of Iapetus. The 
goals of the excursion are to (1) introduce the nappe structure of the 
HNC, the nature of known basement rocks, the provenance of (meta)
sedimentary deposits, and the timing of metamorphism, (2) study examples 
of pre-Scandian magmatic activity (Bindal Batholith; Leka ophiolite), 
magma emplacement, and magma sources/contamination, (3) study the history 
and timing of deformation of the HNC, (4) study the evidence for post-
Scandian exhumation of the HNC, and (5) place all of this information into 
a broad tectonic context.

Field trip organizers: Calvin Barnes, Carol Frost, Øystein Nordgulen 
(contact person), Aaron Yoshinobu Tore Prestvik & Håkon Austrheim.  
This is an excellent opportunity to see superb geology in a one of the 
most beautiful fjord landscapes in Norway.  Part of the excursion will 
take place in the Vega Islands World heritage Site - see also: 
http://whc.unesco.org/en/list/1143  and 
http://www.verdensarvvega.no/english.htm.  

For those interested, a copy of the Excursion guide (pdf-file) can be 
obtained from [log in to unmask] 

IGC Regional Symposium EUR-05: Pre-collisional evolution of the Caledonian-
Appalachian orogen

The classic Caledonian—Appalachian orogeny was preceded by a complex 
history of basin and volcanic arc formation, sedimentation, and magmatism 
in the ancient Iapetus ocean basin. These various tectonic elements were 
amalgamated, deformed and metamorphosed during pre-Scandian orogenic 
events (Taconian, Grampian, etc.). Recent geological, geochronological, 
and geochemical investigations in Scandinavia, the British Isles, 
Greenland, Newfoundland, and the U.S. have indicated that some pre-
Scandian terranes that are now widely dispersed share strikingly similar 
sediment provenance and metamorphic, magmatic, and tectonic histories. In 
contrast, other terranes are geologically distinct. Whether these 
distinctive characteristics are due to isolated sediment provenance, etc. 
or result from a distant origin of the terranes is commonly unclear.

The advent of rapid dating of detrital zircons, the increasing abundance 
of isotopic data for (meta) igneous and sedimentary rocks, and the large 
number of high-precision U-Pb ages of plutons and volcanic rocks now 
permits much more precise reconstructions of pre-Scandian geologic 
activity throughout the Caledonian—Appalachian orogen. These new data and 
tectonic reconstructions invite comparison of pre-Scandian terranes, in 
hopes of gaining a better understanding of sediment dispersal patterns, 
tectonic activity, styles of magmatism, and thermal evolution that 
accompanied closure of Iapetus.

We invite contributions that address all aspects of the pre-Scandian 
evolution of the Caledonian—Appalachian orogen in Scandinavia, the British 
Isles, North America, and Greenland.

Symposium organizers: David Roberts ([log in to unmask]), Øystein 
Nordgulen ([log in to unmask]), Aaron Yoshinobu 
([log in to unmask]), Carol Frost ([log in to unmask]), & Calvin Barnes 
([log in to unmask]).

Best wishes,
Øystein Nordgulen,
Geological Survey of Norway
N-7491 Trondheim – Norway (www.ngu.no)