December 2012 LIP of the Month

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The ~2.44 Ga LIP in the Fennoscandian shield

Laura S. Lauri1, Perttu Mikkola2 and Tuomo Karinen3

1Geological Survey of Finland, P.O. Box 77, FI-96101Rovaniemi, Finland, laura.lauri@gtk.fi

2Geological Survey of Finland, P.O.Box 1237, FI-70211 Kuopio, Finland

3Mustavaaran Kaivos Oy, Kaarnatie 36, FI-90530 Oulu, Finland

Introduction

The nucleus of the Fennoscandian shield formed during the Archean Eon between 3.6 Ga and 2.7 Ga (Hölttä et al., 2008 and references therein). By the end of the Archean the continental crustal fragment comprising the present Karelian and Belomorian domains and most probably also the Kola domain had formed a stable craton that may have been joined to the Archean cratonic domains of the present Canadian shield.

At the Archean–Proterozoic transition the Fennoscandian craton experienced two distinct periods of extension during which voluminous amounts of mafic magma intruded the crust, forming mafic layered intrusions (Fig. 1). The first Paleoproterozoic magmatic event in the Fennoscandian shield is seen only in the Kola Domain, where ca. 2.5 Ga mafic layered intrusions are found in the central and northern part of the Kola Peninsula (Amelin et al., 1995). If the age for the first event is correct it is coeval with the Mistassini dykes of the Superior craton and dykes of the North Atlantic craton (e.g., Ernst and Bleeker, 2010; Nilsson et al. 2010, and references therein). The younger, shield-wide magmatic event took place at ca. 2.44 Ga, forming a large igneous province with both mafic and silicic intrusions, diabase dykes and coeval volcanic rocks (Lauri et al., 2012a and references therein). The younger magmatic phase in Fennoscandia is coeval with other large igneous provinces in other cratons, such as the ~2.48-2.45 Ga Hearst-Matachewan dykes and the East Bull Lake intrusion of the southern Superior craton (Heaman, 1997; Corfu and Easton, 2000; Buchan and Ernst, 2004; Easton et al., 2010; Ernst and Bleeker, 2010), and the 2.45 Ga Weeli Wolli- Woongarra event of the Pilbara craton (Barley et al. 1997); and is slightly older than the 2.42 Ga Scourie dykes of Scotland (Heaman and Tarney, 1989).


Figure 1 Simplified geologic map of the northern part of the Fennoscandian shield (modified from Lauri et al., 2012a). 2.45-2.39 Ga A-type intrusions: 1 - Kynsijärvi, 2 - Nuorunen, 3 - Pussisvaara, 4 - Rasinkylä, 5 - Ryysyranta, 6 - Tuliniemet, 7 - Rasimäki.

The ~2.44 Ga LIP

The global magmatic event at ~2.44 Ga is perhaps best documented in the Fennoscandian shield, which hosts numerous A-type granite plutons coeval with the more voluminous mafic layered intrusions, diabase dykes and associated volcanic rocks with early Paleoproterozoic ages (2.50 – 2.39 Ga). The following descriptions are largely based on the review of Lauri et al. (2012a) and references therein.

Silicic intrusions

At least seven granitic and syenitic intrusions and numerous silicic dykes with ages between 2.45–2.39 Ga (Luukkonen, 1988; Buiko et al., 1995; Vaasjoki et al., 1999; Lauri and Mänttäri, 2002; Mikkola et al., 2010) are known in the Karelian province of the Fennoscandian shield. Only two of the intrusions, the syenitic Kynsijärvi in Finland and the granitic Nuorunen in Russia, are situated in the immediate vicinity of mafic layered complexes (Fig. 1). Near the other granitic plutons further south the ~2.44 Ga mafic magmatism is present only as diabase dykes (Vuollo and Huhma, 2005 and references therein).

The ~2.44 Ga silicic intrusions are small plutons that sharply cross-cut their Archean country rocks (Fig. 2). The largest known intrusion of this type in Finland is the Tuliniemet pluton in Kuhmo that is almost 10 km in diameter (Luukkonen, 1988), all other intrusions are smaller. According to Luukkonen (1988), the largest Tuliniemet intrusion shows rapakivi texture in the central parts. The smaller intrusions are commonly porphyritic in texture. Most of the ~2.44 Ga intrusions are undeformed. Only the westernmost intrusions (Rasinkylä, Pussisvaara and Rasimäki) have been somewhat deformed during the Svecofennian orogeny at 1.89-1.87 Ga (Mikkola et al., 2010).


Figure 2 Lithologic maps of some of the 2.44 Ga felsic plutons in the Fennoscandian shield. (a) lithologic map and (b) aeromagnetic grayscale image of the Kynsijärvi syenite, (c) Pussisvaara, Rasinkylä and Ryysyranta plutons (Mikkola et al., 2010), (d) Tuliniemet intrusions (Luukkonen, 1988). Coordinates in (a), (b) and (d) in Finnish KKJ.

The ~2.44 Ga granitic intrusions are nearly devoid of xenoliths and inherited zircons. The main minerals are porphyritic K-feldspar, quartz, plagioclase, and biotite. Typical accessory minerals include zircon, apatite, allanite, and fluorite. The intrusions may be divided into magnetic (Nuorunen, Pussisvaara, Ryysyranta, Rasinmäki and the Kynsijärvi syenite) and non-magnetic (Tuliniemet, Rasinkylä) groups; the magnetic intrusions contain accessory magnetite (Mikkola et al., 2010). The Kynsijärvi syenite differs from other intrusions in containing mesoperthitic alkali feldspar, quartz, and ferro-edenitic amphibole as the major minerals (Lauri and Mänttäri, 2002). Secondary stilpnomelane is also present in Kynsijärvi, whereas the most common secondary minerals in the granitic intrusions are muscovite and chlorite. The granite porphyry dykes have euhedral phenocrysts of K-feldspar (microcline), plagioclase (oligoclase), and blue quartz in a fine-grained groundmass (Luukkonen, 1988).

Geochemically the ~2.44 Ga silicic intrusions are silica-rich (> 70 wt.%), high-Fe# (0.76–0.96) rocks that are weakly peraluminous to metaluminous. They have high contents of Zr, Ga, Nb, and REE except Eu (Fig. 3). The intrusions are classified as within plate granites in the diagram of Pearce et al. (1984) and A-type in the diagrams of Eby (1992) and Dall’Agnol and Oliveira (2007). All ~2.44 Ga silicic intrusions have initial Nd isotope compositions that suggest their being derived from local Archean crust (Fig. 4).


Figure 3 The ~2.44 Ga felsic intrusions classified in the diagrams of (A) Pearce et al. (1984), ORG - ocean ridge granites, VAG - volcanic arc granites, syn-COLG - syn-collisional granites, WPG - within plate granites, (B) Eby (1992), and (C) Dall'Agnol and Oliveira (2007). (D) K/Na ratio, (E) Chondrite-normalized REE diagram, and (F) Primitive mantle normalized spider diagram of the ~2.44 Ga felsic intrusions. Normalizing values in (E) from Taylor and McLennan (1985) and (F) from Sun and McDonough (1989). Data on Bushveld granites from Kleemann and Twist (1989) in A-D and Hill et al. (1996) in E-F. Modified from Lauri et al. (2012a).


Figure 4 Initial epsilon-Nd vs. age diagram of the ~2.44 Ga felsic and mafic intrusions. Modified from Lauri et al. (2012a).

Mafic intrusions

Mafic layered intrusions of ~2.44 Ga age are found in northern Finland, Russian Karelia and Kola Peninsula (Fig. 1). Most of the intrusions were emplaced along the contact between the Archean basement and the overlying supracrustal rocks that seem to be of nearly similar age as the mafic layered complexes (see Lauri et al., 2012a and references therein). The roof contacts of some intrusions have been eroded and many of the intrusions have been fragmented into separate blocks by tectonic movements.

The mafic layered intrusions of ~2.44 Ga age may be structurally divided into the marginal series and the layered series, which may show a discordant contact with each other. Some of the intrusions seem to have crystallized from a single batch of magma whereas others show multiple injections of primitive magma, which Alapieti and Lahtinen (2002) called “megacyclic units”. The megacyclic units are seen as the reappearance of ultramafic cumulates within the more evolved rock types in the crystallization sequence.

The parental magma compositions of the mafic layered intrusions may be approximated from the chilled margins (Table 1) or associated diabase dykes of similar age (Karinen, 2010). For the ~2.44 Ga intrusions of the Fennoscandian shield, two compositionally different parental magma types have been proposed (Lahtinen et al., 1989; Alapieti et al., 1990; Saini-Eidukat et al., 1997; Vogel et al., 1998); the first type is characterized by relatively high MgO and Cr content, intermediate SiO2 and low TiO2 and referred to as boninitic. The second, tholeiitic type, has low MgO and Cr and intermediate SiO2 contents. Nd isotope composition of the mafic layered intrusions has been constrained to slightly below chondritic values at ~2.44 Ga (Fig. 4; Lauri et al., 2012a and references therein).

Table 1. Parental magma compositions of the ~2.44 Ga mafic layered intrusions in Finland.

Sample

1

2

3

4

5

SiO2

52.8

50.7

53.57

53.96

51.7

TiO2

0.24

0.22

0.28

0.23

0.31

Al2O3

13.2

14.2

16.61

16.54

17.00

Fe2O3tot

9.08

7.85

7.89

8.22

7.27

MnO

0.16

0.14

0.13

0.12

0.13

MgO

14.1

14.7

9.16

9.72

9.91

CaO

9.01

11.6

9.82

10.05

11.3

Na2O

1.81

1.22

2.55

2.44

2.55

K2O

0.53

0.22

0.54

0.10

0.56

P2O5

0.03

0.02

0.02

0.02

0.03

 

 

 

 

 

 

Cr

3290

3330

464

310

217

Ni

230

270

218

160

24

V

-

-

102

98

-

Zr

27

25

24

39

27

 

 

 

 

 

 

Mg#

80.4

82.6

75.7

77.5

78.6

1 – average Penikat MCU1 (Penikat intrusion; Alapieti et al., 1990), 2 – average Narkaus MCU1 (Portimo complex; Alapieti et al., 1990), 3 – lower chilled margin, sample 259-TTK-00 (Koillismaa intrusion, Porttivaara block; Karinen, 2010), 4 – lower chilled margin, sample U0144l-72 (Koillismaa intrusion, Kuusijärvi block; Juopperi, 1976), 5 – average Penikat MCU4 (Penikat intrusion; Alapieti et al., 1990).

The ~2.44 Ga diabase dykes have been divided into five subgroups with based on their composition and the trends of the dykes (Vuollo and Huhma, 2005 and references therein). Diabase dykes of ~2.44 Ga age are widespread all over the Archean Fennoscandia. They have been studied especially for the paleomagnetic reconstructions of the Fennoscandian shield (Mertanen et al., 1999, 2006).

Volcanic rocks

Volcanic rocks with ~2.44 Ga ages are widespread all over the northern part of the Fennoscandian shield, following the areal distribution of the mafic layered intrusions. In Finland the earliest Paleoproterozoic volcanic rocks are grouped into the Salla group (Lehtonen et al., 1998), which consists of intermediate and silicic volcanic rocks that have been extruded on top of the Archean gneissic basement. The type locality for the Salla group is in the Salla area in eastern Lapland, where they form a sequence of well-preserved metavolcanic rocks (Manninen, 1991). The hanging-wall volcanic rocks of the Koillismaa, Akanvaara and Koitelainen mafic layered intrusions have been correlated with the Salla group and the age of the volcanic phase has been constrained to 2.49-2.44 Ga based on several age determinations (Manninen et al., 2001; Räsänen and Huhma, 2001; Lauri et al., 2003, 2012b). Some ~2.44 Ga volcanic rocks are also found in Russia associated with the Oulanka and Imandra layered intrusions (Amelin et al., 1995).

In the Koillismaa area the volcanic rocks of the Salla group form the roof of the mafic layered intrusion (Lauri et al., 2003). The stratigraphic sequence in the Koillismaa area starts with a thick, possibly pyroclastic rhyodacite unit overlain by less voluminous rhyolitic and andesitic lavas. Contrary to the coeval mafic and silicic intrusions the ~2.44 Ga volcanic rocks are not strictly bimodal in composition, instead they form a series of intermediate and silicic rocks ranging from basaltic andesite to rhyolite (Fig. 5). The rhyodacite in Koillismaa (Sirniövaara fm in Fig. 5) shows some A-type geochemical features such as high total alkali content, Fe/Mg, Ga/Al, Zr, REE, and a negative Eu anomaly (Lauri et al., 2003). Initial Nd isotope composition of the volcanic rocks in Koillismaa is close to the values measured from the layered intrusions, with initial εNd values at 2440 Ma ranging between -1.1 and -2.5 (Lauri et al., 2006).


Figure 5 Volcanic rocks of the Salla group in Koillismaa classified in the diagram of Winchester and Floyd (1977). Light blue field: Salla group rocks in the Salla greenstone belt (Manninen, 1991) Modified from Lauri et al. (2003).

Conclusions

The current interpretation of the tectonic evolution of the Fennoscandian shield during the Archean-Proterozoic transition is that the earliest Paleoproterozoic extensional event was first seen as volcanic eruptions that were followed by the emplacement of the mafic layered complexes between the Archean gneisses and the overlying volcanic rocks. The rifting does not seem to have proceeded to actual seafloor spreading stage at this time.

References

Alapieti, T.T., and Lahtinen, J.J., 2002. Platinum-Group Element Mineralization in the Layered Intrusions of Northern Finland and the Kola Peninsula, Russia. In: Cabri, L.J. (Ed.), The Geology, Geochemistry, Mineralogy and Mineral Beneficiation of Platinum-Group Elements. Special Volume 54, Canadian Institute of Mining, Metallurgy and Petroleum, 507–546.

Alapieti, T.T., Filén, B.A., Lahtinen, J.J., Lavrov, M.M., Smolkin, V.F. and Voitshekovsky, S.N., 1990. Early Proterotzoic Layered Intrusions in the Northeastern Part of the Fennoscandian Shield. Mineralogy and Petrology 42, 1–22.

Amelin, Yu. V., Heaman, L.M. and Semenov, V.S., 1995. U–Pb geochronology of layered mafic intrusions in the eastern Baltic Shield: implications for the timing and duration of Paleoproterozoic continental rifting. Precambrian Research 75, 31–46.

Barley, M.E., Pickard, A.L., and Sylvester, P.J., 1997. Emplacement of a large igneous provinces as a possible cause of banded iron formation 2.45 billion years ago. Nature, 385, 55-58.

Buiko, A.K., Levchenkov, O.A., Turchenko, S.I., and Drubetskoi, J.R., 1995. Geologija I izotopnoje datirovanije ranneproterozoiskogo sumiisko-sarioliiskogo kompleksa Severnoi Karelii (Paanajarvi-Tsipringskaja struktura). Stratigrafija Geologicheskaja korreljatsija T.3 (4), 16–30. (in Russian)

Buchan, K.L., and Ernst, R.E., 2004. Diabase dyke swarms and related units in Canada and adjacent regions. Geological Survey of Canada Map No. 2022A, scale 1:5,000,000, with accompanying booklet.

Corfu, F. and Easton, R,M., 2000. U–Pb evidence for polymetamorphic history of Huronian rocks within the Grenville front tectonic zone east of Sudbury, Ontario, Canada. Chemical Geology 172, 149–171.

Dall’Agnol, R. and Oliveira, D.C., 2007. Oxidized, magnetite-series, rapakivi-type granites of Carajás, Brazil: Implications for classification and petrogenesis of A-type granites. Lithos 93, 215–233.

DePaolo, D.J., 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Proterozoic. Nature 291, 684–687.

Devaraju, T.C., Viljoen, R.P., Sawkar, R.H. and Sudhakara, T.L., 2009. Mafic and Ultramafic Magmatism and Associated Mineralization in the Dharwar Craton, Southern India. Journal of the Geological Society of India 73, 73–100.

Easton, R.M., James, R.S. and Jobin-Bevans, L.S., 2010. Geological Guidebook to the Paleoproterozoic East Bull Lake Intrusive Suite Plutons at East Bull Lake, Agnew Lake and River Valley, Ontario: A Field Trip for the 11th International Platinum Symposium. Ontario Geological Survey, Open File Report 6253.

Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644.

Heaman, L.M., 1997. Global mafic magmatism at 2.45 Ga: Remnants of an ancient large igneous province?: Geology, 25 (4), 299-302.

Heaman, L.M. and Tarney, J., 1989. U-Pb baddeleyite ages for the Scourie dike swarm, Scotland: evidence for two distinct intrusion events. Nature 340, 705–708.

Hill, M., Barker, F., Hunter, D. and Knight, R., 1996. Geochemical Characteristics and Origin of the Lebowa Granite Suite, Bushveld Complex. International Geology Review 38, 195–227.

Hölttä, P., Balagansky, V., Garde, A.A., Mertanen, S., Peltonen, P., Slabunov, A., Sorjonen-Ward, P. and Whitehouse, M., 2008. Archean of Greenland and Fennoscandia. Episodes 31, 13–19.

Juopperi, H., 1976. Kuusijärvi-Lipeävaaran alueen kallioperä. Unpublished M.Sc. Thesis, University of Oulu, Department of Geology, 87 p. (in Finnish)

Karinen, T., 2010. The Koillismaa Intrusion, northeastern Finland – evidence for PGE reef forming processes in the layered series. Geological Survey of Finland, Bulletin 404, 176 p.

Kleemann, G.J. and Twist, D., 1989. The Compositionally-zoned Sheet-like Granite Pluton of the Bushveld Complex: Evidence Bearing on the Nature of A-type Magmatism. Journal of Petrology 30(6), 1383–1414.

Lahtinen, J.J., Alapieti, T.T., Halkoaho, T.A.A., Huhtelin, T.A. and Iljina, M.J., 1989. PGE mineralization in the Tornio-Näränkävaara layered intrusion belt. In: Alapieti, T.T. (Ed.), 5th International Platinum Symposium, August 4-11, 1989, Espoo, Finland. Guide to the post-symposium field trip. Geological Survey of Finland, Guide 29, 43–58.

Lauri, L.S. and Mänttäri, I., 2002. The Kynsijärvi quartz-alkali feldspar syenite, Koillismaa, eastern Finland – silicic magmatism associated with 2.44 Ga continental rifting. Precambrian Research 119, 121–140.

Lauri, L.S., Karinen, T. and Räsänen, J., 2003. The earliest Paleoproterozoic supracrustal rocks in Koillismaa, northern Finland – their petrographic and geochemical characteristics and lithostratigraphy. Bulletin of the Geological Society of Finland 75(1-2), 29–50.

Lauri, L.S., Mikkola, P. and Karinen, T., 2012a. Early Paleoproterozoic felsic and mafic magmatism in the Karelian province of the Fennoscandian shield. Lithos 151, 74–82.

Lauri, L.S., Huhma, H. and Lahaye, Y., 2012b. New age constraints for the Paleoproterozoic felsic volcanic rocks associated with the Koillismaa intrusion, Finland. In: Mertanen, S., Pesonen, L.J. and Sangchan, P. (Eds.), Supercontinen Symposium 2012, September 25-28, 2012, University of Helsinki, Finland: Programme and abstracts, 78-79.

Lauri, L.S., Rämö, O.T., Huhma, H., Mänttäri, I. and Räsänen, J., 2006. Petrogenesis of silicic magmatism related to the ~2.44 Ga rifting of Archean crust in Koillismaa, eastern Finland. Lithos 86, 137–166.

Lehtonen, M., Airo, M-L., Eilu, P., Hanski, E., Kortelainen, V., Lanne, E., Manninen, T., Rastas, P., Räsänen, J. and Virransalo, P., 1998. Kittilän vihreäkivialueen geologia, Lapin vulkaniittiprojektin raportti. Summary: The stratigraphy, petrology and geochemistry of the Kittilä greenstone area, northern Finland. A report of the Lapland Volcanite Project. Geological Survey of Finland, Report of Investigation 140, 144 p. (in Finnish, with English summary)

Luukkonen, E.J., 1988. Moisiovaaran ja Ala-Vuokin kartta-alueen kallioperä. Summary: Pre-Quaternary rocks of the Moisiovaara and Ala-Vuokki map-sheet areas. Geological map of Finland 1:100 000, Explanation to the maps of Pre-Quaternary rocks, sheets 4221 and 4423+4441. Geological Survey of Finland, 90 p. (in Finnish, with English summary)

Manninen, T., 1991. Sallan alueen vulkaniitit, Lapin vulkaniittiprojektin raportti. Summary: Volcanic rocks in the Salla Area, northeastern Finland. A report of the Lapland Volcanite Project. Geological Survey of Finland, Report of Investigation 104, 97 p. (in Finnish, with English summary)

Manninen, T., Pihlaja, P. and Huhma, H., 2001. U-Pb geochronology of the Peurasuvanto area, northern Finland. In: Vaasjoki, M. (Ed.), Radiometric age determinations from Finnish Lapland and their bearing on the timing of Precambrian volcano-sedimentary sequences. Geological Survey of Finland, Special Paper 33, 189–200.

Mertanen, S., Halls, H.C., Vuollo, J.I., Pesonen, L.J. and Stepanov, V.S., 1999. Paleomagnetism of 2.44 Ga mafic dykes in Russian Karelia, eastern Fennoscandian Shield – implications for continental reconstructions. Precambrian Research 98, 197–221.

Mertanen, S., Vuollo, J.I., Huhma, H., Arestova, N.A. and Kovalenko, A., 2006. Early Paleoproterozoic–Archean dykes and gneisses in Russian Karelia of the Fennoscandian Shield–New paleomagnetic, isotope age and geochemical investigations. Precambrian Research 144, 239–260.

Mikkola, P., Kontinen, A., Huhma, H. and Lahaye, Y., 2010. Three Paleoproterozoic A-type granite intrusions and associated dykes from Kainuu, East Finland. Bulletin of the Geological Society of Finland 82, 81–100.

Nilsson, M.K.M., Söderlund, U., Ernst, R.E., Hamilton, M., Scherstén, A., Armitage, P.E.B., 2010. Precise U-Pb baddeleyite ages of mafic dykes and intrusions in southern West Greenland and implications for a possible reconstruction with the Superior craton. Precambrian Research, 183, 399-415, doi: 10.1016/j.precamres.2010.07.010.

Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25, 956–983.

Räsänen, J. and Huhma, H., 2001. U-Pb datings in the Sodankylä schist area, central Finnish Lapland. In: Vaasjoki, M. (Ed.), Radiometric age determinations from Finnish Lapland and their bearing on the timing of Precambrian volcano-sedimentary sequences. Geological Survey of Finland, Special Paper 33, 153–188.

Saini-Eidukat, B., Alapieti, T.T., Thalhammer, O.A.R. and Iljina, M.J., 1997. Siliceous high-magnesium parental magma compositions of the PGE-rich early Palaeoproterozoic layered intrusion belt of northern Finland. In: Rongfu, P. (Ed.), Proceedings, 30th International Geological Congress 9, 177–197.

Sun, S.S. and McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geological Society Special Publications 42, 313–345.

Taylor, S.R. and McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. 312 pp.

Vaasjoki, M., Taipale, K. and Tuokko, I., 1999. Radiometric ages and other isotopic data bearing on the evolution of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland. In: Studies related to the Global Geoscience Transects/SVEKA Project in Finland. Bulletin of the Geological Society of Finland 71 (1), 155–176.

Vogel, D.C., Vuollo, J.I., Alapieti, T.T. and James, R.S., 1998. Tectonic, stratigraphic, and geochemical comparison between ca. 2500-2400 Ma mafic igneous events in the Canadian and Fennoscandian Shields. Precambrian Research 92, 89–116.

Vuollo, J. and Huhma, H., 2005. Paleoproterozoic mafic dikes in NE Finland. In: Lehtinen, M., Nurmi, P.A. and Rämö, O.T. (Eds.), Precambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Elsevier B.V., Amsterdam, pp. 195–236.

Winchester, J.A. and Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology 20, 325–343.