Dyke swarms - time markers of crustal evolution - IDC5

75 Pages·2005·6.37 MB·English

by  Arto Luttinen

FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

FIFTH INTERNATIONAL DYKE CONFERENCE
"Dyke swarms - time markers of crustal evolution"

Pohtimolampi Wilderness Hotel -
Polar Circle - Rovaniemi - Finland
31 June – 3 August 2005

PRE-CONFERENCE FIELD TRIP A GUIDEBOOK:

Southern and Central Finland

edited by
Luttinen, A.V.
Department of Geology
P.O.Box 64, FIN-00014 University of Helsinki

Vuollo, J.I.
Geological Survey of Finland
P.O.Box 77 FIN-96101 Rovaniemi

ISBN 951-690-927-2
FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND
FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Organising Committee
Dr. Jouni Vuollo (Geological Survey of Finland)
Dr. Satu Mertanen (Geological Survey of Finland)
Prof. Olav Eklund (University of Turku)
Prof. Eero Hanski (University of Oulu)
Dr. Hannu Huhma( Geological Survey of Finland)
Dr. Pentti Hölttä (Geological Survey of Finland)
Dr. Arto Luttinen (University of Helsinki)
Prof. Tapani Rämö (University of Helsinki)
Dr. Saku Vuori (Geological Survey of Finland)

IDC5 Congress Office
Ms. Marja-Leena Porsanger & Ms. Päivi Mäkikokkila (Rovaniemi-Lapland Con-
gresses, University of Lapland)

Sponsors

Scientific
Geological Survey of Finland
Large Igneous Provinces Commission
University of Oulu
University of Helsinki
University of Turku

Technical sponsors
Geological Survey of Finland
University of Oulu
University of Helsinki
University of Turku
Tulikivi
Kivikeskus

Financial sponsors
Academy of Finland
Geological Survey of Finland
City of Rovaniemi & Municipality of Rovaniemi
European Diamonds PLC
Scandinavian Gold Limited
Kiviteollisuusliitto
FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Table of contents

Introduction i
Itinerary and stop descriptions ii

Proterozoic mafic dyke swarms of southern and central Finland 1
1. General geological background 1
2. Mafic magmatism 4
2.1. Rifting and breakup of the Archaean craton (2.5–2.0 Ga) 4
~2.45 Ga dyke swarms 4
~2.32 Ga dyke swarm and intrusions 5
~2.2 Ga layered sills and dykes 5
~2.1 Ga dyke swarms 5
~1.98 Ga dyke swarm 6
2.2. Seafloor spreading (1.95 Ga) 6
2.3. Rapakivi-related mafic magmatism (1.7–1.4 Ga) 7
Plutons 7
Dyke swarms and basalts 7
2.4. Rifting at 1.2 Ga 8
2.5. Dyke emplacement related to Sveconorwegian orogny (~1.1 Ga) 9
2.6. Dykes related to the Caledonides (~430 Ma) 9
2.7. Palaeozoic kimberlite magmatism 10
Day 1 – STOPS 1.1. – 1.3. 11
Day 2 – STOPS 2.1. – 2.10. 15
Day 3 – STOPS 3.1. – 3.3. 23
Day 4 – STOPS 4.1. – 4.4. 26
Day 5 – STOPS 5.1. – 5.9. 37
Day 6 – STOPS 6.1. – 6.8. 53
References 59
FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Introduction

This fieldtrip was organized as a part of the 5th International Dyke Conference to be held in
Rovaniemi, Finland, July 31 – August 3 (Fig. 1). The purpose of the excursion is to highlight the
geology of various Proterozoic dyke systems, including diabase dyke swarms, the Åva ring com-
plex, microtonalites, kimberlites, and dykes belonging to the Jormua ophiolite complex, in southern
and central Finland.
We depart from Helsinki downtown on July 26. On our 300 km drive to Rauma, we will first
examine the ~1.65 Ga Kopparnäs dyke. In the afternoon we make two stops in order to study the so-
called Postjotnian 1.2 Ga dolerite sills and dykes in the Satakunta region. We stay overnight in
Rauma.
On July 27, we take a ferry to the Åland archipelago. Our first target is the 500 m wide 1.6 Ga
old bimodal Korsö dyke in the Åland–Åboland dyke swarm. In the afternoon we focus on the bi-
modality between granite and shoshonitic magmas and related lamprophyre dykes in the post-
collisional 1.8 Ga Åva ring complex. We stay overnight in Uusikaupunki.
The main objective of the third day, July 28, is driving some 500 km to the east. Along our
way, we make quick stops to examine the ~1.7 Ga Häme swarm; one dyke near Orivesi contains
well-preserved basaltic glass. We recover from the strenuous drive in our peaceful lodging at
Kivennapa.
We begin our fourth excursion day, July 29, by examining ~1.85 Ga microtonalite dykes at
Kivennapa and then continue with Finnnish kimberlites at Kaavi. In the afternoon, we visit the
Tulikivi quarry and factory (soapstone products) in Nunnanlahti. We spend the night in Koli.
On July 30, we focus on the ~2 Ga dykes in the Koli area and Varpaisjärvi. We also visit the
Finnish Rock Centre at Juuka before arriving at our lodging in Kajaani.
On July 31, we visit some of the key outcrops of the Early Proterozoic Jormua Ophiolite
complex in the morning and then head towards Rovaniemi. A quick stop to examine the oldest rock
of Europe at Siurua will make the 300 km transit more bearable. We will arrive at the conference
venue, Rovaniemi, in time to participate to the IDC5 ice-breaker party at the Pohtimolampi Wilder-
ness Hotel.

Arto Luttinen and Jouni Vuollo
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FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Itinerary and stops

DAY 1 - 26 JULY:

07:45 Name call at Hotel Arthur, Helsinki
08:00 Minibuses leave for Kopparnäs
11:00 Lunch at Mustio Castle
12:00 Fieldtrip in Satakunta area
18:00 Lodging and dinner at Hotel Kalatorin Majatalo, Rauma

DAY 2 - 27 JULY:

07:00 Breakfast at Kalatorin Majatalo
08:00 Minibuses leave for Åva
11:05 Ferry to Brändö, Åland
11:40 Fieldtrip and lunch on Brändö
18:30 Ferry to mainland
21:00 Lodging and dinner at Hotel Aquarius, Uusikaupunki

DAY 3 - 28 JULY:

07:00 Breakfast at Hotel Aquarius
08:00 Minibuses leave for fieldtrip
11:00 Fieldtrip and lunch in Orivesi area
18:00 Lodging, sauna, dinner, and lecture at Hotel Kivennapa

DAY 4 - 29 JULY:

07:00 Breakfast at Hotel Kivennapa
08:00 Fieldtrip starts at Kivennapa
09:00 Minibuses leave for Kaavi
09:30 Fieldtrip in the Kaavi area
14:00 Lunch and guided tour at Tulikivi, Nunnanlahti
17:30 Lodging and dinner at Hotel Koli

DAY 5 - 30 JULY:
07:00 Breakfast at Hotel Koli
08:00 Fieldtrip at Kaunisniemi
13:00 Lunch and guided tour at Finnish Rock Centre, Juuka
15:00 Fieldtrip at Varpaisjärvi
18:00 Lodging and dinner at Hotel Kajaani

DAY 6 - 31 JULY:
06:30 Breakfast at Hotel Kajaani
07:30 Minibuses leave for Jormua
08:00 Fieldtrip and lunch in Jormua region
13:00 Minibuses leave for Rovaniemi
18:00 Arrival at Conference venue
19:00 Ice-breaker party
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FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Stop descriptions

26.7.2005 (Guide: Arto Luttinen –University of Helsinki)
Stop 1.1. Kopparnäs dyke (AL)
Stop 1.2. Hinnerjoki crosscutting dyke (AL)
Stop 1.3. Reposaari dyke (AL)

27.7.2005 (Guide: Olav Eklund –University of Turku)
Stop 2.1. Ring dykes near Björnholma (OE)
Stop 2.2. Bimodal lamprophyre–granite dykes at Åva harbour (OE)
Stop 2.3. Roof pendants, monzonite-granite interactions, pegmatites (OE)
Stop 2.4. Thin tholiitic dykes south of Brändö (OE)
Stop 2.5. Korsö dyke (OE)
Stop 2.6. Leuconorite and labradorite megacrysts (OE)
Stop 2.7. Vesicular granite, hybrid, and snow-flake plagioclase (OE)
Stop 2.8. Gabbroic autoliths (OE
Stop 2.9. Pyterlitic rapakivi granite (OE)
Stop 2.10. Järppilä quartz-feldspar porphyry dyke (OE)

28.7.2005 (Guide: Arto Luttinen –University of Helsinki)
Stop 3.1. Proterozoic basaltic glass in Orivesi dykes (AL)
Stop 3.2. Flow-differentiated Vehkajärvi dyke (AL)
Stop 3.3. Quartzite cobbles in Maijaanvuori dyke (AL)

29.7.2005 (Guides: Matti Tyni; Olli Äikäs –Geological Survey of Finland)
Stop 4.1. Microtonalite dykes at Kivennapa (OÄ)
Stop 4.2. Kimberlite boulders (MT)
Stop 4.3. Kimberlite pipe 2 (MT)
Stop 4.4. Tulikivi soapstone factory

30.7.2005 (Guides: Jouko Parviainen and Jouni Vuollo –Geological Survey of Finland)
Stop 5.1. Olivine (-chromite) cumulate (JV)
Stop 5.2. Layered olivine, chromite, and clinopyroxene cumulates (JV)
Stop 5.3. Clinopyroxenite (JV)
Stop 5.4. Magnetite clinopyroxenite and magnetite gabbro (JV)
Stop 5.5. Layered and laminated magnetite gabbro (JV)
Stop 5.6. Granophyre, marginal types, and basement granite (JV)
Stop 5.7. The 1.97 Ga dyke (JV)
Stop 5.8. The Finnish Stone Centre, Juuka
Stop 5.9. Varpaisjärvi dyke (JP)

31.7.2005 (Guides: Hannu Huhma, Asko Kontinen and Katja Lalli –Geological Survey of Finland)
Stop 6.1. Clinopyroxenite and hornblendite-garnetite dykes (AK)
Stop 6.2. “OIB” metalamprophyre and “E-MORB” dykes (AK)
Stop 6.3. Sheeted dykes (AK)
Stop 6.4. Harzburgite and metarodingitic gabbro dyke (AK)
Stop 6.5. Gabbros, ferrogabros and plagiogranites (AK)
Stop 6.6. Podiform chromitite (AK)
Stop 6.7. Pillow lavas (AK)
Stop 6.8. The oldest rock of Europe at Siurua (HH, KL)

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FIFTH INTERNATIONAL DYKE CONFERENCE 31.7 – 3.8.2005 – ROVANIEMI, FINLAND

Figure 1. General geology of southern and central Finland showing the areas to be visited.
Red star depicts the conference venue at Hotel Pohtimolampi.

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FIFTH INTERNATIONAL DYKE CONFERENCE 31.7. – 3.8.2005 – ROVANIEMI, FINLAND

Proterozoic mafic dyke swarms of southern and central Finland

1. General geological background

The Finnish bedrock makes up roughly one third of the Fennoscandian Shield. The bedrock
is divided into an Archaean complex (3.50–2.50 Ga) in the north and east and an Early Proterozoic
(1.92–1.77 Ga) Svecofennian domain which dominates in the central and southern Finland (Fig. 1).
The Archaean basement is mainly composed of ~2.7 Ga granodiorites and tonalities and
interfingered ~2.8 Ga greenstone belts. The 2.58 Ga Siilinjärvi carbonatite complex near Kuopio is
among the oldest carbonatites world-wide.
A sequence of continental sediments and lavas, designated as the Karelian Supergroup, was
deposited on the Archaean basement during successive periods of rifting within the Archaean
craton. At the base there are felsic lavas (Sumi), followed by immature conglomerates, sandstones
and intermediate volcanites (Sariola). Subsequently, a thick aluminium-rich weathered crust was
developed, which indicates low-latitude palaeoposition of the Archaean continent. The hiatus is
overlain by recycled weathered material and quartz-rich sediments (Kainuu) which were deposited
in fluvial systems in small grabens and on the flanks of Archaean crustal blocks. Advanced rifting
led to sedimentation of up to 3–4 km thick quartz-rich sandstones in fluvial and shallow marine
environments (Jatuli) and, finally, marine clay-rich sandstones, clays, iron formations, and
metalligenous black schists (Kaleva).
The Archaean basement and the sedimentary cover were repeatedly intruded by mafic
plutons and dykes during the Early Proterozoic time (2.50–1.98 Ga). Based on current
geochronological data, the intrusions may represent six, or possibly seven, distinctive magmatic
events and indicate periodic intracontinental rifting with intervals of ~50–100 Ma between
subsequent rifting events. These rifting events culminated in the formation of a passive continental
margin as the Archaean craton broke up at ~2 Ga. The now-separated “western” cratonic block has
not been identified, although Archaean blocks in northern Sweden may represent reassembled parts
of it. Obducted remnants of oceanic crust (eg. 1.95 Ga Jormua ophiolite) manifest a transition from
continental rift-related magmatism to seafloor spreading after the break up.
Isotope geological studies have established a suture between the Archaean and the
Svecofennian domains. The origin and evolution of the 1.9–1.8 Ga Svecofennian orogenic crust
has remained somewhat controversial. The Svecofennian domain of central and southern Finland
has been traditionally divided into three tectonic units based on lithological criteria and U-Pb
zircon age data. These units form 1) the primitive arc complex of central Finland adjacent to the
Archaean craton, 2) the accretionary arc complex of central and western Finland, and 3) the
accretionary arc complex of southern Finland (e.g. Korsman et al., 1997; Nironen, 1997) (Fig. 2).
Much of the accretionary arc complex of central and western Finland is occupied by the 40 000
km2 Central Finland Granitoid Complex (Elliott et al., 1998; Nironen et al., 2000). The generally
accepted concept of a semi-continuous Svecokarelian/Svecofennian orogeny has been recently
rejected by Lahtinen et al. (2003) who have put forward a more complex orogenic model for the
Early Proterozoic evolution of the Svecofennian domain. The model involves >2.0 Ga
microcontinents, pre-1.92 Ga island arcs, and 1.90–1.82 arcs that accreted to the Archaean craton
to form the Fennoscandian Shield. The following pre-1.92 Ga components have been proposed:
Karelian, Kola and Norrbotten Archaean cratons; Keitele, Bergslagen and Bothnia >2.0 Ga
microcontinents; Kittilä ~2.0 Ga island arc; and Savo, Knaften, Inari and Tersk ~1.95 Ga island
arcs. The assembly of the cratons and microcontinents at 1.92–1.88 Ga to form a larger
Fennoscandian continental plate was followed by a continental extensional stage along the
Archaean-Proterozoic boundary and in the central part of the continent at 1.88–1.85 Ga. Collisions
of Fennoscandia with Sarmatia and Amazonia have been envisaged at 1.85–1.79 Ga. The orogenic
cycle was terminated by an orogenic collapse and stabilization stage (1.79–1.77 Ga).
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