NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 173

Caledonian anatexis of Grenvillian crust: a U/Pb study of Albert I Land, NW Svalbard

Per Inge Myhre, Fernando Corfu & Arild Andresen

Myhre, P.I., Corfu, F. & Andresen, A.: Caledonian anatexis of Grenvillian crust: a U/Pb study of Albert I Land, NW Svalbard. Norwegian Journal of Geology, Vol. 89, pp. 173-191. Trondheim 2008. ISSN 029-196X.

Dating by U-Pb ID-TIMS of zircon, titanite and monazite has been carried out on orthogneiss, granite and migmatite from Albert I Land Terrane, Northwest Svalbard, to investigate the origin of this terrane and its role within the North Atlantic Caledonides. Detrital zircons in a migmatized metasedimentary rock of the Smeerenburgfjorden Complex indicate deposition after about 1070 Ma. Zircon and titanite from orthogneiss within the same complex yield an upper intercept age of 967.9 ± 4.7 Ma interpreted to date crystallization of the igneous protolith. Monazite ages of 419.7 ± 0.5 Ma from the orthogneiss are interpreted to date Caledonian reworking. Other migmatite and granite samples of the Smeerenburgfjorden Com- plex record monazite growth during a 6–8 My long period commencing at c. 430 Ma. This period concluded with the intrusion of granitoids with ages of 421.7 ± 0.6 Ma and 418.8 ± 0.7 Ma. The latter is coeval with the Hornemantoppen Batholith emplaced at 418.4 ± 0.8 Ma. The identification of late Grenvillian (Rigolet) magmatic and Caledonian (Scandian) magmatic and metamorphic events, combined with other stratigraphic analogies, supports a link with Svalbard’s Nordaustlandet Terrane as well as with Laurentian terranes in NE Greenland and the Scandinavian Caledonides.

Per Inge Myhre, Department of Geosciences, University of Oslo N-0316 Oslo, Norway, now at Department of Geology, University of Tromsø, Dram- sveien 201, N–9037 Tromsø, Norway ([email protected]); Fernando Corfu and Arild Andresen, Department of Geosciences, University of Oslo N-0316 Oslo, Norway.

Introduction affinities of Svalbard’s Caledonian terranes is given by Gee & Teben`kov (2004). The evolution of the western The Svalbard archipelago consists of variably deformed belts remains, however, poorly understood. The present and metamorphosed pre-Devonian basement rocks study was aimed, therefore, at resolving the metamorphic unconformably overlain by Devonian or younger cover and plutonic evolution of Albert I Land, and at establish- rocks, which continue into the Barents Sea. The base- ing a more firm basis for tectonic correlations within the ment rocks have been referred to as the “Hecla Hoek” North Atlantic realm. unit (Harland 1971) and have traditionally been inter- preted to represent the northernmost segment of the Pal- aeozoic Caledonide orogen. The appearance of distinctly Regional geology different pre-Devonian provinces within Svalbard led Harland (1971) to subdivide the Hecla Hoek unit into an NW Composite Terrane and Biscayarhalvøya Terrane Eastern, a Central and a Western Province (Harland & Wright 1979) bounded by the Billefjorden, the Central– The NW Composite Terrane comprises the Biscayar- Western and the Svalbard–Greenland fault zones. The halvøya Terrane and the Albert I Land Terrane, separated different provinces have now been renamed the Eastern, by the Raudfjorden Fault (Fig. 1). The two terranes have the North-western and the South-western Terranes (Gee similar characteristics, as they both include Grenvillian & Teben’kov 2004), which we, in line with these authors, orthogneiss and Caledonian HT/LP metamorphic rocks consider to be composite. and granites. The Biscayarhalvøya Terrane, however, also contains an upper amphibolite to eclogite-facies There have been widespread debates on the affinity of complex, known as the Richardalen HP-Complex, (Gee the E Composite Terrane of Svalbard with terranes in 1966), and deformed upper Silurian–Devonian (“Old eastern Laurentia (NE-Greenland) (Gee et al. 1995, 1999; Red Sandstone”) deposits (McCann 2000), both absent Gee & Page 1994; Johansson et al. 2001, 2005; Lyberis from Albert I Land (with the exception of some possi- & Manby 1999; Witt et al. 1998). Similar relationships bly Devonian red beds within olistostromes; Thiedig & have also been proposed for the NW Composite Terrane, Manby 1992). The HP-complex has an inferred pro- based for the most part on the Neoproterozoic supra- tolith-age of 670–645 Ma (Gromet & Gee 1998; Peucat crustal record, but also on the nature of the metamorphic et al. 1989) and underwent HP-metamorphism in the rocks (Gromet & Gee 1998; Ohta et al. 2002; Peucat et Ordovician based on an U-Pb ID-TIMS titanite age al. 1989). A thorough review of the geology and terrane of c. 455 ± 5 Ma, and similar Ar/Ar-ages, from upper 174 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY amphibolite-facies felsic and mafic gneisses (Dallmeyer Albert I Land Terrane et al. 1990; Gromet & Gee 1998). A low-grade rock unit The Albert I Land Terrane encompasses the area north structurally interlayered with the high-pressure rocks of Kongsfjorden and west of the Raudfjorden Fault zone underwent metamorphism at 430 ± 3 Ma (Gromet & (Figs. 1 & 2). Recorded geological observations from the Gee 1998). South of the eclogite-bearing complex in the area date back to the first half of the 19th century (Blom- Biscayarhalvøya Terrane, Caledonian metamorphism strand 1864), and when systematic mapping efforts com- was characterized by upper amphibolite facies meta- menced in the 1960’s the main geological features were morphism with some areas experiencing partial melting already well known (Holtedahl 1913; Schetelig 1912). (Wyss et al. 1998).

Fig. 1. Bedrock map of Svalbard. RF: Raudfjorden Fault, BBF: Breibogen-Bockfjorden Fault, BF: Billefjorden Fault, EOF: Eolsletta Fault, M: Motalafjella blueschist, R: Richardalen eclogites. NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 175

The Albert I Land Terrane is made up of 3 main lithotec- banded gneisses include mafic and felsic varieties as well tonic units (Fig. 2): (i) the Smeerenburgfjorden Complex as quartzite, pelite, calc-silicate and marble layers, which consisting mainly of migmatites and para -and orthog- record upper amphibolite facies conditions (Bucher neisses, (ii) the metasedimentary Krossfjorden Group, 1981). Orthogneiss occurs within the Smeerenburgfjor- and (iii) Caledonian granitoids (Dallmann et al. 2002). den Complex as smaller or larger bodies, and those com- From field evidence it is clear that the Smeerenburgfjor- monly contain xenoliths of deformed pelitic and mafic den Complex comprises migmatized parts of the Kros- lithologies, remnants of the crust into which the orthog- sfjorden Group in addition to orthogneisses presumably neiss originally intruded. The map by Dallmann et al. equivalent to the substrate of the Krossfjorden Group. (2002) places the boundary between the Krossfjorden Therefore, the Smeerenburgfjorden Complex is both Group and the Smeerenburgfjorden Complex along the younger and older than the Krossfjorden Group, and this dashed line indicated in Fig. 2. study aims to resolve some of this complexity by dating the migmatites and orthogneisses, respectively. The Krossfjorden Group

The Smeerenburgfjorden Complex The Krossfjorden Group dominates the southern part of Albert I Land. It is subdivided into the Nissenfjella, Rocks assigned to the Smeerenburgfjorden Complex Signehamna and Generalfjella units (Gee & Hjelle 1966). (Fig. 2) include a wide variety of banded ortho- and The two lower units are dominated by metapelitic and paragneisses, and migmatites (Ohta et al. 1996). The metapsammitic rocks with some marbles, whereas the

Fig. 2. Geological map of Albert I Land Terrane with sample locations. 176 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY upper unit is dominated by marble. The age of deposi- matite-rich (Smeerenburgfjorden Complex) unit forms tion of the metasediments is not well constrained due to a N–S-trending horst between this fault and the Raudf- metamorphic overprint, lack of fossils and lack of dat- jorden fault zone, some 10 km to the east (Dallmann et able volcanic interlayers. The distribution of different al. 2002; Gjelsvik 1979). The appearance of the migma- rock units within the Krossfjorden Group is controlled titic rocks varies from veined melanosome-dominated by large-scale west vergent isoclinal folds and a set of migmatites (Fig 3a) to rocks dominated by granitic leu- younger NNW–SSE-trending faults. A penetrative N–S cosome with only scattered biotite-rich schlieren. The striking axial planar foliation (S1) is associated with the melanosome blocks in Fig. 3a are banded (± garnet) early formed isoclinal folds (D1), and in most places is mica–schists and quartzo-feldspatic rocks and could parallel to the original bedding (S0). The dip of the foli- represent an early deposited metasedimentary unit (pre- ation is variable and appears to be related to a younger cursor). The transition between leucosome-rich and leu- fold phase (D2). The mineral assemblages (micas ± gar- cosome-poor parts of the rock mass seems to be gradual net in schist) associated with the D1 event indicate defor- and not associated with structural discontinuities, sug- mation under upper greenschist to lower amphibolite gesting that different areas in the precursor rock were facies conditions. affected by different degrees of migmatization during the same event. Two samples of leucosome-rich granite were Late granitoids taken in order to constrain the timing of the migmati- zation. One of the samples (75) contains quartz, plagio- Numerous granitoid plutons occur within Albert I Land, clase, K-feldspar, biotite, minor muscovite and chlorite and their presence has traditionally been seen in con- and accessory monazite and zircon. The other sample nection with the widespread migmatization. Some gran- (72) has the same mineralogy but also contains partially ites have proved to be Silurian in age (Ohta et al. 2002) decomposed garnet. The garnet (together with some of but both Caledonian (Hjelle 1979) and pre-Caledonian the biotite and plagioclase) presumably represents the (Ohta et al. 2003; Ravich 1979) timing of the migmatiza- microscale equivalent to the mesoscale biotite schlieren tion have been proposed. The largest granite is the Hor- noted above. This petrographical evidence of xenocrys- nemantoppen batholith (Fig. 2), which intrudes all other tic material within the granitoid will be important in the lithologies and has yielded Rb/Sr whole-rock ages of 414 interpretation of monazite and zircon U-Pb-data later ± 10 Ma (Hjelle 1979) and 413 ± 5 Ma (Balasov et al. on. 1996). This pluton clearly cuts across the gneissic fabric, and also transects numerous granitic dykes and small Granodioritic orthogneiss, Krossfjorden granitoid plutons. A tentative interpretation is that the samples 46 and 38) granitic dykes represent coalescing neosomes emplaced in front of the ascending intrusions of the Horneman- A SW to NE section along inner Krossfjorden (Figs. 2 toppen batholith. & 4) exposes (i) west-dipping pelitic schist of the Kros- sfjorden Group (Signehamna unit), (ii) west-dipping Faults granodioritic orthogneiss, (iii) migmatite and (iv) two- mica granite. Two samples of orthogneiss were col- A number of NNW–SSE-trending extensional faults lected, no. 38 representing the SW-dipping orthogneiss cut the earlier formed D1 folds and cleavages. The most body seen in the central part of Fig. 4, and no. 46 occur- prominent one appears in the inner part of Kongsfjorden ring as a c. 1x2x2 m large xenolith within the two-mica where it brings the Krossfjorden Group against members granitic leucosomes farther to the NE. The in situ vari- of the Smeerenburgfjorden Complex (Fig. 2). Similarly ety (38) is rich in hornblende relative to biotite, and has oriented faults occur throughout the study area. In the titanite, epidote, apatite, allanite and zircon. The xeno- area around Kongsfjorden, some of these faults are asso- lith has biotite as the dominant mafic phase instead of ciated with olistostromal deposits (Fig. 2) of inferred hornblende; it contains zircon, monazite and apatite, Devonian age (Thiedig & Manby 1992), thus linking and common myrmekitic plagioclase-quartz-inter- them to a phase of Late Caledonian (Devonian) crustal growths on plagioclase-K-feldspar grain boundaries. extension. Both orthogneisses have granodioritic modal composi- tions.

Sample description Two-mica granite leucosome, Krossfjorden (sample 80)

Two-mica granite leucosome, Kongsfjorden The NE part of the Krossfjorden section (Fig. 4) is occu- (samples 72 and 75) pied by two-mica granite rich in xenoliths of mica-rich rocks and orthogneiss. In the c. 1 km wide transition In the innermost part of Kongsfjorden, migmatite zone between the orthogneiss and the two-mica granite gneisses of the Smeerenburgfjorden Complex are in the rock resembles a migmatite, with melanosome/leuco- faulted contact with isoclinally folded micaschists and some ratios of around 1. The melanosome in the migma- marbles of the Krossfjorden Group (Fig. 2). The mig- tite consists of mica-rich schist that occurs as schlieren NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 177

Fig. 3. (a): Veined migmatite of the Smeerenburgfjorden Complex in innermost Kongsfjorden, about 2 km north of the sample locality for samples 72 & 75. Banded melanosome (dark blocks) sit in a matrix of leucosome with a leucosome/ melanosome-ratio of less than 1. (b): Orthogneiss xenolith within granite; sample locality for 46. (c): Isoclinally folded psammitic layer within garnet-bearing mica schist of the Krossfjorden Group (east shore of Krossfjorden, west is to the left). (d): CL-images of analyzed zircons from sample 72.

Fig. 4. Cross section in inner Krossfjorden (Kollerfjorden; cf. Fig. 2) with sample locations. 178 P. I. Myhre et al.. NORWEGIAN JOURNAL OF GEOLOGY - - 12 24 27 33 30 16 13 14 14 10 24 22 39 31 21 40 1.1 2.2 1.4 8.6 4.4 0.6 2.7 9.5 0.6 6.9 0.6 0.6 3.0 1.0 1.1 0.1 0.7 0.3 3.5 1.1 1.4 3.7 1.9 -3.4 -0.5 -0.9 -0.2 -0.9 -0.1 -4.1 -2.3 -1.8 -0.9 -1.0 [%] Disc. 12 82 17 34 18 11 62 11 18 11 14 3.4 6.0 4.8 1.4 6.4 7.5 2.4 2.8 2.1 6.1 1.7 3.8 2.7 5.2 2.1 3.5 2.4 2.4 1.6 1.4 5.5 3.8 5.3 4.4 4.3 4.6 5.1 1.5 5.3 1.6 2.1 6.6 4.1 9.0 4.1 3.5 5.4 6.3 1.9 1.5 4.5 σ 2 [abs] 867 421 956 417 411 412 1002 950.4 956.3 423.8 927.8 938.7 406.7 953.5 717.2 422.2 946.8 637.3 420.6 421.9 957.0 951.1 963.9 916.3 419.6 418.1 422.7 420.0 428.1 423.0 416.7 470.5 430.1 429.4 947.0 812.8 419.3 417.7 426.1 Pb/ Pb 1299.0 1474.5 1366.9 1388.3 1302.3 1419.9 1364.7 1388.4 1555.5 1582.1 2697.0 1543.2 1351.2 207 206 - - 925.0 943.8 942.8 418.9 714.0 873.9 911.6 418.7 417.9 936.4 533.1 420.0 903.6 485.8 422.4 419.8 953.3 932.7 961.4 957.7 853.3 415.9 417.6 418.2 420.4 423.0 428.3 424.6 422.1 420.1 422.9 457.1 426.2 424.4 994.9 924.0 422.3 421.0 419.6 Pb/ U 1082.6 1398.0 1240.2 1282.7 1192.6 1306.5 1163.5 1207.3 1185.8 1293.9 2481.8 207 235 - - 6 893.2 940.9 937.0 418.0 666.1 852.7 900.5 418.4 978.3 419.9 929.2 491.0 419.6 886.0 454.3 422.7 419.4 951.7 924.9 964.0 955.0 829.2 415.2 417.5 993.6 418.4 420.0 423.5 428.3 427.1 421.9 421.5 424.0 454.5 425.4 423.5 841.2 914.4 422.8 421.6 418.4 Pb/ U 1348.5 1168.5 1220.6 1133.0 1238.6 1058.5 1108.6 1127.3 2227.7 Ages 206 238 - - 0.64 0.89 0.90 0.91 0.52 0.96 0.56 0.30 0.74 0.39 0.85 0.90 0.86 0.92 0.85 0.94 0.79 0.88 0.78 0.96 0.84 0.95 0.96 0.96 0.95 0.96 0.83 0.82 0.17 0.84 0.87 0.99 0.53 0.78 0.76 0.95 0.69 0.47 0.51 0.95 0.57 rho 0.93 0.80 0.78 0.71 0.99 0.67 0.94 0.97 0.74 - - σ 2 0.0031 0.0012 [abs] 0.00063 0.00052 0.00080 0.00030 0.00076 0.00028 0.00065 0.00033 0.00056 0.00018 0.00091 0.00016 0.00064 0.00013 0.00075 0.00015 0.00014 0.00013 0.00061 0.00065 0.00041 0.00066 0.00074 0.00035 0.00044 0.00050 0.00052 0.00038 0.00075 0.00023 0.00342 0.00019 0.00064 0.00021 0.00014 0.00028 0.00017 0.00014 0.00026 0.00015 0.00031 0.00017 0.00025 0.00167 0.00032 0.00014 0.00016 0.00015 - - 0.1613 0.4128 Pb/ U 0.14861 0.15715 0.15645 0.06699 0.10886 0.14142 0.14991 0.06705 0.16388 0.06730 0.15505 0.07915 0.23267 0.06726 0.14734 0.07301 0.06776 0.06722 0.15909 0.19873 0.15428 0.20846 0.19215 0.15968 0.21183 0.13727 0.17845 0.06653 0.18764 0.06692 0.16665 0.06706 0.19109 0.06732 0.06791 0.06870 0.06850 0.06764 0.06757 0.06799 0.07304 0.06822 0.06790 0.13939 0.15239 0.06779 0.06759 0.06706 206 238 - - 6 σ 0.011 0.010 0.045 0.015 0.011 0.031 0.015 0.012 0.046 0.010 0.032 0.020 2 0.0055 0.0026 0.0031 0.0083 0.0093 0.0046 0.0017 0.0087 0.0012 0.0081 0.0014 0.0014 0.0013 0.0060 0.0089 0.0047 0.0094 0.0094 0.0039 0.0062 0.0063 0.0073 0.0020 0.0030 0.0018 0.0017 0.0049 0.0029 0.0012 0.0039 0.0013 0.0029 0.0015 0.0030 0.0053 0.0013 0.0014 0.0015 [abs] - - 1.487 1.531 1.020 1.454 1.515 1.578 0.506 2.284 2.215 2.576 1.664 Pb/ Pb/ U 1.5332 0.5107 1.3646 0.5104 1.9043 0.5091 0.6904 2.9625 0.5123 1.4349 0.6136 0.5158 0.5120 1.5571 2.3919 1.5057 2.5371 2.2366 1.5682 2.6209 1.3172 2.1453 0.5088 0.5097 0.5129 10.522 0.5168 0.5247 0.5192 0.5154 0.5124 0.5166 0.5686 0.5215 0.5189 1.4843 0.5157 0.5138 0.5117 IsotopicRatios 207 235 - 5 848 146 620 203 389 118 382 916 935 5671 1534 4175 1061 1468 3050 4248 5133 2816 2305 3111 3541 4107 6508 1152 2860 2725 1581 7817 1766 1288 1752 4076 5187 1261 2180 8834 2766 4795 1710 1493 7073 7271 3976 Pb/ Pb 11672 10593 13381 13471 32275 20053 22763 42254 206 204 - - 25 16 12 26 27 95 13 10 1.8 1.8 0.7 1.0 8.5 1.1 6.1 6.0 1.5 0.6 5.7 1.2 3.2 4.7 1.5 2.3 0.8 1.8 0.7 0.6 0.6 2.1 1.1 1.0 1.0 0.2 1.1 0.9 1.8 1.0 0.8 3.9 2.3 2.4 7.2 0.7 1.4 0.8 0.5 2.0 117 18.2 [pg] - - 4 0.00 0.00 1.60 0.00 0.37 0.00 1.10 4.01 0.33 0.00 0.41 0.00 0.30 0.00 0.07 0.53 1.86 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 24.3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.08 23.8 0.15 0.01 0.41 0.35 0.00 0.00 0.00 0.00 1.68 0.50 0.36 0.00 0.00 Pbc [ppm] 3 - - 0.60 0.62 0.56 0.43 0.55 0.43 7.21 0.33 23.9 0.58 0.98 0.54 19.7 0.47 0.94 5.41 22.8 0.57 0.29 0.67 0.56 0.51 0.41 1.26 0.58 0.63 0.33 0.52 0.50 0.50 0.65 0.66 0.46 0.58 0.18 5.03 3.58 6.79 4.89 19.5 4.36 0.75 4.64 0.31 0.20 0.61 7.73 6.81 0.96 1.14 Th/U - - 19 70 53 44 73 74 38 162 259 658 625 223 299 169 576 458 511 528 246 354 114 711 177 378 249 631 135 177 262 261 995 153 354 151 504 513 993 200 323 408 169 237 676 U 1040 1704 1957 2252 1532 1002 4480 [ppm] 2 1 1 1 1 1 1 1 5 5 5 1 1 8 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 8 1 17 21 12 32 12 16 10 18 11 15 13 25 15 54 70 23 23 Wt. [ug] 1 Table 1: U-Pb-TIMS-results 1: Table Sample/mineral description 1:z= zircon, t = titanite, m=monazite, clr incl. = clear, = inclusion, eu. = euhedral, = pyramidal, pyr. l/w = lenght/width, [4]= of no. grains, (u/nu)= used /not used in age calculaton, 2: Weight isknown to within 10 %, 3: Th is modelled based on measured 208/206 Pb-ratio and 207/206Pb-age. 4:Pbc = total common Pb in sample (initial + blank) 5:Corrected for fractionation and blank 6: Corrected for fractionation, blank, spike and initial Pb.Coordinates are given in geographic datum WGS84 75:Two-mica granite leucosome, Kongsfjorden [pim04-75, N 79 00.32°, E 12 32.64°] z1prism, l/w 3-3.5 [1] (nu) z5 clr. prisms z5clr. l/w 4 [8] (u) z2short prism, l/w 2-3 [1] (nu) z6non-abraded [20] (nu) z1prisms w/melt incl. l/w 3-4 [4] (u) t1tit. > [5] (u) z3tips [6] (nu) 46:Granodioritic orthogneiss, Krossfjorden [pim04-46, N 78 18.43°, E 12 07.59°] m1few clear, incl. [3] (u) z2prism w/black incl. l/w 5 [3] (u) z4[30] (nu) z4prism, l/w 3-3.5 [1] (nu) m2turbid, w/incl. [4] (u) z3w/melt incl., l/w 5-6 [1] (nu) z5[30] (nu) m1small, light [1] (u) m3turbid, w/incl. [4] (u) z4prism w/bio. incl. l/w 3 [1] (u) 72:Two-mica granite leucosome, Kongsfjorden [pim04-72, 79 00.22° E 12 32.90°] z1prisms, l/w 2.5 [4] (nu) z1prism w/ melt incl. incl.& b. l/w 4 [1] (u) z2short prisms, l/w 1.5-2 [5] (nu) z2prism w/elongated melt incl. l/w 4-5 [1] (u) z34 tips [4] (nu) z3 prism w/elongated melt incl. l/w 4-5 [1] (u) z3 prism w/elongated melt incl. l/w 4-5 [1] (u) z4resorped [7] (nu) z4prism l/w 4 [2] (u) z30 mount prism, non abraded, l/w 2.5-3 [1] (nu) z30mount prism, non abraded, l/w 2.5-3 [1] (nu) 80:Two-mica granite leucosome, Krossfjorden [pim04-80, N 79 18.47°, E 12 07.88°] z1l/w 2-3 black incl. frag. [2] (nu) z37mount prism, non abraded, l/w 2.5-3 [1] (nu) z2l/w 4-5, some w/ melt incl [11] (u) z25 mount prism, non abraded, l/w 2.5-3 [1] (nu) z25mount prism, non abraded, l/w 2.5-3 [1] (nu) z3l/w 4-5, black incl. [1] (u) z36 mount prism, non abraded, l/w 2.5-3 [1] (nu) z36mount prism, non abraded, l/w 2.5-3 [1] (nu) z4l/w 4-5, some w/ melt incl [4] (u) z34mount prism, non abraded, l/w 2.5-3 [1] (nu) m1[5] (nu) m1[3] (u) m2[4] (nu) m2[8] (u) m3>[5] (nu) m3[1] (u) z5l/w 2-3 [1] (nu) m4[2] (u) 22:Grey granite, Smeerenburgfjorden [pim05-22, N 79 38.38°, 28.54°] E 11 z1prism l/w 3-4 w/ melt incl & black incl. [1] (nu) z5”211” no spike [1] (nu) z2 prism l/w 3-4 w/ melt incl no black incl. [1] (nu) [1] incl. black no incl melt w/ 3-4 l/w prism z2 38:Granodioritic orthogneiss, Krossfjorden [pim04-38, N 79 18.17°, E 12 03.17°] t1light [9] (u) z3prism l/w 3-4 w/ melt incl frgt. small [5] (nu) t2dark [7] (u) m1non-turbid, few incl. [16] (u) m2non-turbid, few incl. [15] (u) 19:Hornemantoppen batholith, Smeerenburgfjorden [pim05-19, N 79 38.30°, 33.66°] E 11 z1l/w 3-4, prisms [4] (u) z2l/w 3-4, prisms [1] (u) NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 179 - - 12 24 27 33 30 16 13 14 14 10 24 22 39 31 21 40 1.1 2.2 1.4 8.6 4.4 0.6 2.7 9.5 0.6 6.9 0.6 0.6 3.0 1.0 1.1 0.1 0.7 0.3 3.5 1.1 1.4 3.7 1.9 -3.4 -0.5 -0.9 -0.2 -0.9 -0.1 -4.1 -2.3 -1.8 -0.9 -1.0 [%] Disc. 12 82 17 34 18 11 62 11 18 11 14 3.4 6.0 4.8 1.4 6.4 7.5 2.4 2.8 2.1 6.1 1.7 3.8 2.7 5.2 2.1 3.5 2.4 2.4 1.6 1.4 5.5 3.8 5.3 4.4 4.3 4.6 5.1 1.5 5.3 1.6 2.1 6.6 4.1 9.0 4.1 3.5 5.4 6.3 1.9 1.5 4.5 σ 2 [abs] 867 421 956 417 411 412 1002 950.4 956.3 423.8 927.8 938.7 406.7 953.5 717.2 422.2 946.8 637.3 420.6 421.9 957.0 951.1 963.9 916.3 419.6 418.1 422.7 420.0 428.1 423.0 416.7 470.5 430.1 429.4 947.0 812.8 419.3 417.7 426.1 Pb/ Pb 1299.0 1474.5 1366.9 1388.3 1302.3 1419.9 1364.7 1388.4 1555.5 1582.1 2697.0 1543.2 1351.2 207 206 - - 925.0 943.8 942.8 418.9 714.0 873.9 911.6 418.7 417.9 936.4 533.1 420.0 903.6 485.8 422.4 419.8 953.3 932.7 961.4 957.7 853.3 415.9 417.6 418.2 420.4 423.0 428.3 424.6 422.1 420.1 422.9 457.1 426.2 424.4 994.9 924.0 422.3 421.0 419.6 Pb/ U 1082.6 1398.0 1240.2 1282.7 1192.6 1306.5 1163.5 1207.3 1185.8 1293.9 2481.8 207 235 - - 6 893.2 940.9 937.0 418.0 666.1 852.7 900.5 418.4 978.3 419.9 929.2 491.0 419.6 886.0 454.3 422.7 419.4 951.7 924.9 964.0 955.0 829.2 415.2 417.5 993.6 418.4 420.0 423.5 428.3 427.1 421.9 421.5 424.0 454.5 425.4 423.5 841.2 914.4 422.8 421.6 418.4 Pb/ U 1348.5 1168.5 1220.6 1133.0 1238.6 1058.5 1108.6 1127.3 2227.7 Ages 206 238 - - 0.64 0.89 0.90 0.91 0.52 0.96 0.56 0.30 0.74 0.39 0.85 0.90 0.86 0.92 0.85 0.94 0.79 0.88 0.78 0.96 0.84 0.95 0.96 0.96 0.95 0.96 0.83 0.82 0.17 0.84 0.87 0.99 0.53 0.78 0.76 0.95 0.69 0.47 0.51 0.95 0.57 rho 0.93 0.80 0.78 0.71 0.99 0.67 0.94 0.97 0.74 - - σ 2 0.0031 0.0012 [abs] 0.00063 0.00052 0.00080 0.00030 0.00076 0.00028 0.00065 0.00033 0.00056 0.00018 0.00091 0.00016 0.00064 0.00013 0.00075 0.00015 0.00014 0.00013 0.00061 0.00065 0.00041 0.00066 0.00074 0.00035 0.00044 0.00050 0.00052 0.00038 0.00075 0.00023 0.00342 0.00019 0.00064 0.00021 0.00014 0.00028 0.00017 0.00014 0.00026 0.00015 0.00031 0.00017 0.00025 0.00167 0.00032 0.00014 0.00016 0.00015 - - 0.1613 0.4128 Pb/ U 0.14861 0.15715 0.15645 0.06699 0.10886 0.14142 0.14991 0.06705 0.16388 0.06730 0.15505 0.07915 0.23267 0.06726 0.14734 0.07301 0.06776 0.06722 0.15909 0.19873 0.15428 0.20846 0.19215 0.15968 0.21183 0.13727 0.17845 0.06653 0.18764 0.06692 0.16665 0.06706 0.19109 0.06732 0.06791 0.06870 0.06850 0.06764 0.06757 0.06799 0.07304 0.06822 0.06790 0.13939 0.15239 0.06779 0.06759 0.06706 206 238 - - 6 σ 0.011 0.010 0.045 0.015 0.011 0.031 0.015 0.012 0.046 0.010 0.032 0.020 2 0.0055 0.0026 0.0031 0.0083 0.0093 0.0046 0.0017 0.0087 0.0012 0.0081 0.0014 0.0014 0.0013 0.0060 0.0089 0.0047 0.0094 0.0094 0.0039 0.0062 0.0063 0.0073 0.0020 0.0030 0.0018 0.0017 0.0049 0.0029 0.0012 0.0039 0.0013 0.0029 0.0015 0.0030 0.0053 0.0013 0.0014 0.0015 [abs] - - 1.487 1.531 1.020 1.454 1.515 1.578 0.506 2.284 2.215 2.576 1.664 Pb/ Pb/ U 1.5332 0.5107 1.3646 0.5104 1.9043 0.5091 0.6904 2.9625 0.5123 1.4349 0.6136 0.5158 0.5120 1.5571 2.3919 1.5057 2.5371 2.2366 1.5682 2.6209 1.3172 2.1453 0.5088 0.5097 0.5129 10.522 0.5168 0.5247 0.5192 0.5154 0.5124 0.5166 0.5686 0.5215 0.5189 1.4843 0.5157 0.5138 0.5117 IsotopicRatios 207 235 - 5 848 146 620 203 389 118 382 916 935 5671 1534 4175 1061 1468 3050 4248 5133 2816 2305 3111 3541 4107 6508 1152 2860 2725 1581 7817 1766 1288 1752 4076 5187 1261 2180 8834 2766 4795 1710 1493 7073 7271 3976 Pb/ Pb 11672 10593 13381 13471 32275 20053 22763 42254 206 204 - - 25 16 12 26 27 95 13 10 1.8 1.8 0.7 1.0 8.5 1.1 6.1 6.0 1.5 0.6 5.7 1.2 3.2 4.7 1.5 2.3 0.8 1.8 0.7 0.6 0.6 2.1 1.1 1.0 1.0 0.2 1.1 0.9 1.8 1.0 0.8 3.9 2.3 2.4 7.2 0.7 1.4 0.8 0.5 2.0 117 18.2 [pg] - - 4 0.00 0.00 1.60 0.00 0.37 0.00 1.10 4.01 0.33 0.00 0.41 0.00 0.30 0.00 0.07 0.53 1.86 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 24.3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.08 23.8 0.15 0.01 0.41 0.35 0.00 0.00 0.00 0.00 1.68 0.50 0.36 0.00 0.00 Pbc [ppm] 3 - - 0.60 0.62 0.56 0.43 0.55 0.43 7.21 0.33 23.9 0.58 0.98 0.54 19.7 0.47 0.94 5.41 22.8 0.57 0.29 0.67 0.56 0.51 0.41 1.26 0.58 0.63 0.33 0.52 0.50 0.50 0.65 0.66 0.46 0.58 0.18 5.03 3.58 6.79 4.89 19.5 4.36 0.75 4.64 0.31 0.20 0.61 7.73 6.81 0.96 1.14 Th/U - - 19 70 53 44 73 74 38 162 259 658 625 223 299 169 576 458 511 528 246 354 114 711 177 378 249 631 135 177 262 261 995 153 354 151 504 513 993 200 323 408 169 237 676 U 1040 1704 1957 2252 1532 1002 4480 [ppm] 2 1 1 1 1 1 1 1 5 5 5 1 1 8 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 8 1 17 21 12 32 12 16 10 18 11 15 13 25 15 54 70 23 23 Wt. [ug] 1 Table 1: U-Pb-TIMS-results 1: Table Sample/mineral description 1:z= zircon, t = titanite, m=monazite, clr incl. = clear, = inclusion, eu. = euhedral, = pyramidal, pyr. l/w = lenght/width, [4]= of no. grains, (u/nu)= used /not used in age calculaton, 2: Weight isknown to within 10 %, 3: Th is modelled based on measured 208/206 Pb-ratio and 207/206Pb-age. 4:Pbc = total common Pb in sample (initial + blank) 5:Corrected for fractionation and blank 6: Corrected for fractionation, blank, spike and initial Pb.Coordinates are given in geographic datum WGS84 75:Two-mica granite leucosome, Kongsfjorden [pim04-75, N 79 00.32°, E 12 32.64°] z1prism, l/w 3-3.5 [1] (nu) z5 clr. prisms z5clr. l/w 4 [8] (u) z2short prism, l/w 2-3 [1] (nu) z6non-abraded [20] (nu) z1prisms w/melt incl. l/w 3-4 [4] (u) t1tit. > [5] (u) z3tips [6] (nu) 46:Granodioritic orthogneiss, Krossfjorden [pim04-46, N 78 18.43°, E 12 07.59°] m1few clear, incl. [3] (u) z2prism w/black incl. l/w 5 [3] (u) z4[30] (nu) z4prism, l/w 3-3.5 [1] (nu) m2turbid, w/incl. [4] (u) z3w/melt incl., l/w 5-6 [1] (nu) z5[30] (nu) m1small, light [1] (u) m3turbid, w/incl. [4] (u) z4prism w/bio. incl. l/w 3 [1] (u) 72:Two-mica granite leucosome, Kongsfjorden [pim04-72, 79 00.22° E 12 32.90°] z1prisms, l/w 2.5 [4] (nu) z1prism w/ melt incl. incl.& b. l/w 4 [1] (u) z2short prisms, l/w 1.5-2 [5] (nu) z2prism w/elongated melt incl. l/w 4-5 [1] (u) z34 tips [4] (nu) z3 prism w/elongated melt incl. l/w 4-5 [1] (u) z3 prism w/elongated melt incl. l/w 4-5 [1] (u) z4resorped [7] (nu) z4prism l/w 4 [2] (u) z30 mount prism, non abraded, l/w 2.5-3 [1] (nu) z30mount prism, non abraded, l/w 2.5-3 [1] (nu) 80:Two-mica granite leucosome, Krossfjorden [pim04-80, N 79 18.47°, E 12 07.88°] z1l/w 2-3 black incl. frag. [2] (nu) z37mount prism, non abraded, l/w 2.5-3 [1] (nu) z2l/w 4-5, some w/ melt incl [11] (u) z25 mount prism, non abraded, l/w 2.5-3 [1] (nu) z25mount prism, non abraded, l/w 2.5-3 [1] (nu) z3l/w 4-5, black incl. [1] (u) z36 mount prism, non abraded, l/w 2.5-3 [1] (nu) z36mount prism, non abraded, l/w 2.5-3 [1] (nu) z4l/w 4-5, some w/ melt incl [4] (u) z34mount prism, non abraded, l/w 2.5-3 [1] (nu) m1[5] (nu) m1[3] (u) m2[4] (nu) m2[8] (u) m3>[5] (nu) m3[1] (u) z5l/w 2-3 [1] (nu) m4[2] (u) 22:Grey granite, Smeerenburgfjorden [pim05-22, N 79 38.38°, 28.54°] E 11 z1prism l/w 3-4 w/ melt incl & black incl. [1] (nu) z5”211” no spike [1] (nu) z2 prism l/w 3-4 w/ melt incl no black incl. [1] (nu) [1] incl. black no incl melt w/ 3-4 l/w prism z2 38:Granodioritic orthogneiss, Krossfjorden [pim04-38, N 79 18.17°, E 12 03.17°] t1light [9] (u) z3prism l/w 3-4 w/ melt incl frgt. small [5] (nu) t2dark [7] (u) m1non-turbid, few incl. [16] (u) m2non-turbid, few incl. [15] (u) 19:Hornemantoppen batholith, Smeerenburgfjorden [pim05-19, N 79 38.30°, 33.66°] E 11 z1l/w 3-4, prisms [4] (u) z2l/w 3-4, prisms [1] (u) 180 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY or blocks varying in size from less than a centimetre to reaches of the Smeerenburgfjorden system, about 4 km several meters, in some cases around 5 x 10 metres. The from the grey granite (22) described above. It is coarse- blocks, particularly the larger ones, generally have a pre- grained granite, with biotite as the main mafic phase. ferred orientiaton parallel to the NW-striking regional Feldspar is commonly euhedral, and plagioclase exhibits fabric, but random orientations are also quite common. magmatic zoning. Titanite and zircon occur as accessory The melanosome bears evidence of partial melting 1) in phases. the form of leucosome rims and/or layer-parallel dykelets associated with relatively intact mica-schist blocks, or 2) in the form of partially digested melanosome schlie- U-Pb (ID-TIMS) analyses ren consisting essentially of biotite. The granitic leuco- some bodies have no preferred orientation and range in Analytical Methods size from a few millimetres up to ten meters, forming a network of granitic dykelets, dykes and sills presumably The samples were crushed and separated using a Wilf- derived from coalescing magma derived from the pelites. ley table, magnetic separation and heavy liquid flotation. Sample 80 was taken from a fairly homogeneous granitic Mineral grains chosen for analysis were imaged using a dyke (Fig. 4). The sample contains quartz, zoned pla- camera attached to the optical microscope and in one gioclase, K-feldspar, equal amounts of biotite and mus- case (sample 72) by SEM. All mineral samples (except covite, some chlorite (as pseudomorphs after biotite), some grains from sample 38 & 72) were air-abraded, fol- minor opaque minerals and accessory monazite and lowing the procedure of Krogh (1982). Typically, some zircon. Some myrmekite occurs at plagioclase-K-feld- 1–10 crystals (in the case of zircon), usually weighing 2 spar grain boundaries. We consider this rock to repre- µg or less, were chosen for analysis (Table 1). Monazite sent the product of melting of rocks equivalent to the and titanite were usually analyzed as larger fractions, Krossfjorden Group metasediments, perhaps triggered sometimes up to 350 µg. The abraded crystals were by deeper-seated granitic intrusions and partly mixed cleaned with warm HNO3, acetone and water. Zircon with magma derived from depth. Further, we consider samples were dissolved in 10 drops HF + 1 drop HNO3 the melanosome bodies within the granite to represent in pressurized Teflon bombs at 190°C for 5 days. Titanite variably digested remnants of rocks equivalent to the was dissolved in HF (+HNO3), and monazite in HCl, in Krossfjorden Group metasediments. Savillex vials on a hotplate. All samples were spiked with a 205/202Pb-235U-tracer except some grains from samples 205 235 Grey granite, Smeerenburgfjorden (sample 22) 80, 72 and 75 which were spiked with a Pb- U-tracer. The 235U/205Pb-ratios of the two types of tracers were The northern reaches of the study area, around Smeeren- 119.49 (± 0.09%) and 119.34 (± 0.03%), respectively. burgfjorden (Fig. 2), are dominated by orthogneiss, mig- Zircon samples larger than about 5 µg and all titanite matite, and local paragneiss, and are intruded by granit- and monazite samples once dissolved were chemically oid plutons (Hjelle & Ohta 1974). The grey granite covers purified using micro-columns (procedure in Corfu 5-6 km2 near the Hornemantoppen Batholith in Bjørnf- 2004; Krogh 1973). Most zircon samples, however, were jorden, Smeerenburgfjorden area (Fig. 2). It intrudes the smaller than this and were measured without chemical Smeerenburgfjorden Complex and contains numerous purification. The samples were loaded on degassed Re xenoliths of folded pelitic rock, quartzite and orthog- filaments using a silica-gel described in Gerstenberger & neiss. It is itself intruded by the Hornemantoppen Batho- Haase (1997) and measured in a Finnigan MAT 262 mass lith. Sample 22 is a two-mica granite containing equal spectrometer in multicollector-mode on Faraday-cups, amounts of biotite and muscovite and accessory opaques, or in peak-jumping mode on an electron multiplier. At monazite and zircon. the start of each analytical day the NBS 982 U500+Pb- standard was analyzed to monitor the performance of the Hornemantoppen Batholith, Smeerenburgfjorden mass spectrometer and in particular the electron multi- (sample 19) plier. Data were reduced using the ROMAGE software developed by T. E. Krogh and L. Heaman with decay Named after the Norwegian geologist Hans Henrik Hor- constants from Jaffey et al. (1971). Isotopic fractionation neman (1878–1945) (Orvin 1991), the Hornemantop- was 0.1 %/a.m.u for Pb and 0.12 % for U, with uncertain- pen batholith has always been considered to represent ties of ± 0.06% for the Faraday multicollection-mode and the final stage of Caledonian magmatic activity in NW ± 0.1 for the electron multiplier. For samples spiked with Spitsbergen (Blomstrand 1864; Gee & Hjelle 1966; Schet- the 202/205Pb-tracer measured in multicollection mode, elig 1912). The intrusion covers some 125 km2, mainly the fractionation was calculated from the measured in the mountainous area south of Smeerenburgfjorden 202/205Pb-ratio normalized to the certified value. With (Fig. 2). The contact to the country rocks is sharp and this procedure, Pb fractionation values were between clearly intrusive, except in the NW where a semi brittle, 0.05–0.15%/a.m.u., with errors propagated from the SE-dipping shear zone separates the Hornemantoppen measurement uncertainty or ± 0.06% as a minimum granitoid from basement gneiss of the Smeerenburgfjor- default value. The data were corrected for 0.1 pg U, and den Complex. The dated sample is from the innermost 2 pg Pb blank, the latter with the following composi- NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 181

Fig. 5. Concordia diagram presenting U-Pb geochronological results. Error ellipses are 2σ. Black ellipses are zircon; grey ellipses are monazite or titanite. Ellipse labelling (z1, m1, etc.) refers to analysis labels in Table 1. 182 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY tion: 206/204Pb = 18.3 ± 2%, 207/204Pb = 15.555 ± 1%, 208/204Pb is a correlation between decreasing age and decreasing = 37.625 ± 2%. Initial Pb was corrected for using the U-content (Table 1) suggesting physical mixing of dif- Pb-evolution model of Stacey and Kramers (1975) at the ferent grain-specific or intragrain age domains on a finer age of the sample (with the same uncertainties as for the scale. blank). The corrected isotopic data were reduced using Isoplot version 3.00 (Ludwig 2003). All uncertainties are Zircons from the two samples have quite similar char- given at the 2 σ confidence level. acteristics, the majority of the crystals being stubby and euhedral to subhedral with low length/width-ratios. Commonly, the zircons consist of a small, rounded core Results with euhedral tips. There is a minor group of longer prisms with l/w-ratios of up to 3, and zircons from this Two-mica granite leucosome, Kongsfjorden group were used for most analyses except for two frac- (samples 72 and 75) tions of broken-off tips (75z3 and 72z3). Some grains from sample 04-72 were mounted in epoxy and imaged Monazite occurs as two main types: (1) pale yellow anhe- with the SEM to reveal possible cores. A few of the dral grains with resorbed rims, commonly with inclu- apparently core-free zircons (Fig. 3d) were then removed sions of other phases, and (2) pale yellow, euhedral to from the grain mount and analyzed. Most zircons have subhedral grains with few or no inclusions. Most ana- U-concentrations of 20 to 250 ppm, except the tips that lyzed grains were of the inclusion-free type except for have high levels of 600–700 ppm. The results cluster in m3, which contained a black inclusion. The results of 5 3 different groups. One group, representing the majority monazite analyses, 4 from sample 72, plot concordantly of the analyzed grains, yields variously discordant data or slightly reversely concordant with U-Pb ages varying with 207Pb/206Pb-ages of about 1300 to 1600 Ma (Fig. 5a). from 428.3 ± 1.7 Ma to 422.1 ± 0.8 Ma (Fig. 5b). There A second group, consisting of a single crystal with well

Fig. 6. Monazite BSE images from sample 72. (a–c): Partly decomposed monazite. The dark material surrounding the monazite is fine-grained chlorite. (d) euhedral monazite within feldspar. No decomposed rim. Abbreviations: b= biotite, z = zircon, m = monazite, q = quartz, f = feldspar. NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 183 developed euhedral growth zoning (z34, Fig. 3d), yields lization at a time between 428.3 ±1.0 and 422.1 ± 0.8 Ma. the oldest 207Pb/206Pb -age of c. 2700 Ma (plots beyond the This implies that the rock must have experienced a met- limits of Fig. 5a). Also some of the other grains seem to amorphic history leading up to the formation of leuco- be gravitating towards this Archean component (grains some capable of producing monazite. Relicts of this pro- z25 and z36) although Caledonian Pb loss from Meso- grade history are represented by macroscopic (schlieren, proterozoic grains can also explain their position. A third not studied) and microscopic (deeply embayed garnet group of two single grain analyses plot on a line between and strained dark brown biotite laths in thin section as c. 420 and 1070 Ma. described above) melanosomic enclaves within the two- mica granite leucosome. The interpretation of these data is not straightforward. The general scatter of the analyses likely reflects the Monazite is a product in several prograde reactions in presence of multiple generations of zircon combined pelites (with or without melt as a product). Some impor- with partial Pb loss. Analyses z25 and z36 record both tant monazite-forming reactions are the allanite-out the Grenvillian and Caledonian events. The latter is also reaction at around 550°C, a number of phase transitions indicated by monazite. Most of the other data points involving garnet-bearing pelites, and melting of apatite could be explained either by (1) minor zircon crystalliza- (Williams et al. 2007). An example of monazite dating tion at 420 Ma in a population dominated by older zir- of melt-forming reactions is presented by Hawkins & con xenocrysts, (2) a main zircon crystallizing event at Bowring (1999) for a Palaeoproterozoic leucosome from about 1070 Ma, with xenocrystic cores of Mesoprotero- the Grand Canyon. They showed that monazite grains zoic and older ages, and Pb loss at 420 Ma, or (3) a main thought to be igneous had ages spanning a 6 My interval, zircon crystallizing event between 1500 and 1800 Ma, the and interpreted this to reflect several episodes of melting hypothetical upper intercept ages of the palaeo-discordia of a pelite. Once formed, monazite thus retained its U-Pb line to 1070 Ma (e.g. the reference line in Fig. 5a), and age even if melting continued to occur in the rock. subsequent disruptions by variable Pb loss at 1070 and 420 Ma. The monazite data discussed below suggest that Since we cannot rule out that the euhedral feldspar/ the migmatite developed during the Caledonian orogeny quartz-hosted monazites observed in thin section are in a pelitic protolith. Accepting this, we must then con- Precambrian or that their U-Pb-systematics are reset, the clude that the zircon populations in the two samples are slight possibility still exists that the migmatite formed in dominantly xenocrystic and the scatter reflects mainly the Precambrian. However, our preferred interpretation derivation from multiple sources with ages mainly in the is that the oldest monazites represent prograde meta- 1800–1500 Ma range. A further implication is that the morphism in a pelitic protolith, starting at 428.3 ± 1.7 two grains on the 420–1070 Ma line set a maximum age Ma. Then, at around 422.1 ± 0.8 Ma, monazite grew as of deposition at c. 1070 Ma. a result of partial melting, either as a product of melt- producing reactions or as igneous monazite. Some of the A SEM thin section investigation shows that monazite monazites were incorporated into quartz and feldspar in sample 72 occurs in three settings (Fig. 6): 1) within as the neosome crystallized. This interpretation is sup- biotite grains; 2) at grain boundaries and triple junc- ported by zircon analyses z25 & z36, both of which have tions, generally between biotite, quartz or feldspar; 3) a Caledonian age component. within feldspar and quartz grains. In one case, a mona- zite sits next to a rounded zircon and a strained biotite Granodioritic orthogneiss, Krossfjorden lath (Fig. 6a). The monazites that are within quartz or (samples 46 and 38) feldspar are commonly subhedral or euhedral, and have fresh rims (Fig. 6d). The grains that occur within biotite The zircon populations of the two samples have the same or near grain boundaries, on the other hand, are often in characteristics, with the highest quality grains having a decomposed state surrounded by fine-grained chlorite relatively high length/width ratios of up to 3–6. Many (Fig. 6a–c). The occurrence of euhedral monazite within of these also have worm-like or elongate (parallel to the feldspar and quartz grains implies that the monazite age c-axis) melt inclusions, indicating a rapid and simple would constrain the crystallization of the feldspar and crystallization history (Corfu et al. 2003). Apart from this quartz, unless the monazite was reset after crystalliza- group of zircons, there are many cracked, metamict and/ tion. Resetting by Pb diffusion is unlikely because such or otherwise poor-quality grains. Titanite from sample a process is only efficient at temperatures of (above) 800 38 displays a range of colour varieties from colourless to °C (Gardés et al. 2006). At lower temperatures, resetting dark brown, and the grain size is between 100 to 200 µm. can occur by reprecipitation or mineral-fluid interaction The analyzed fractions were of the dark type. Monazite in the presence of magmatic or metamorphic fluids (Wil- occurs in sample 46 as 50-150 µm wide anhedral grains, liams et al. 2007). This is possible, but since we do not see often with inclusions and turbid interiors. All (but one) any components older than 428 Ma it would still mean analyses of zircons from both samples as well as titanite that the feldspar/quartz is of this age or younger. There- from the main orthogneiss body (38) plot on a discordia- fore, the most likely significance of the monazites within line anchored at 419 Ma with an upper intercept of 967.9 feldspar and quartz is that they date leucosome crystal- ± 4.7 Ma (MSWD = 4.6; Fig. 5c). The anchor point is 184 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY

Fig. 7. Tectonic model for the Scandian evolution of the Albert I Land Terrane. (a) Situation at the time of formation of ‘old’ metamorphic monazite in samples 72, 75 & 80. The subhorizontal wiggly line defines a monazite front at c. 430 Ma. (b) Evolution of the monazite front into a migmatization front and intrusion of granitic plutons at 424 – 418 Ma as defi- ned by the younger monazites from sample 72, 75, 80 and 46 and igneous zircon from samples 80, 22 and 19. (c): Inferred tectonic position of the Albert I Land Terrane within the Laurentian plate overriding Baltica in a westward subduction system. defined by 3 concordant monazite analyses from xeno- granite. This process is described in Bingen et al. (1996), lith sample 46 with a concordia-age of 419.7 ± 0.5 Ma when studying the amphibolite-granulite facies transi- (MSWD = 2.5; Fig. 5d). Note that the titanite (labelled tion in Sveconorwegian orthogneisses in south-western 38t1 & 38t2) from sample 38 plot on the discordia-line Norway. The consistency of the monazite ages shows that near the upper intercept, is only weakly affected by the the process of heating and final metamorphism of the Silurian overprint. One zircon analysis (38z6) is excluded xenolith occurred on a timescale shorter than the resolu- from the calculation because it was not abraded, and tion of U-Pb geochronology. falls slightly off the discordia line, probably due to post- Silurian Pb-loss. Late Pb-loss may also be the reason for Two-mica granite leucosome, Krossfjorden (80) analyses 38z3 and 46z4 falling slightly below the discor- dia-line, and exclusion of these two also improves the A large portion of the zircons in this sample occurs as MSWD to 2.7, but the age remains the same (967.6 ± 3.8 euhedral stubby crystals, often with turbid interiors and Ma, not shown). cores, or with tip overgrowths. Zircons of this type rep- resent inherited grains with variable degrees of over- The uniform behaviour of monazite in this sample is in growth. Apart from these evidently inherited zircons, contrast to that of samples 72 and 75 discussed above, there is a group of zircons with much higher aspect and 80 below, suggesting that the process that led to ratios, and many of these are clear with no turbid or the creation of monazite in the orthogneiss is of a dif- metamict domains. These grains locally also contain ferent character. The xenolith (46) is equivalent to the elongate melt inclusions and mineral inclusions such as main orthogneiss body (38) in terms of structure, age biotite and sulphides. Zircons from this group give a con- and chemical composition (except for somewhat higher cordia age of 418.8 ± 0.7 Ma based on 3 analyses (Fig. 5e)

SiO2), but the mineralogy is different; sample 38 has interpreted as the age of crystallization of the leucosome. abundant hornblende and minor amounts of apatite, A single zircon (z5, outside the area of Fig. 5e) is discor- titanite, epidote and allanite. In contrast, sample 46 has dant with a 207Pb/206Pb-age of c. 470 Ma, and a discordia no hornblende and titanite, but is richer in biotite and line through this point and the concordant analyses has has monazite. There are minor amounts of allanite and an upper intercept of 618 ± 76 Ma, hinting at a Neopro- apatite. Both samples are granitic to granodioritic in terozoic age of the inherited component. Monazite is composition and contain biotite. The mineralogy of the common, typically with a dark yellow to greenish colour two samples is consistent with breakdown of hornblende, and speckeled with minor dark, turbid domains and titanite, allanite and apatite in the less altered orthog- sulphide-inclusions. The 3 analyses are slightly reversely neiss (38) to form monazite, plagioclase and HREE-rich discordant (1–4 %) with 207Pb/235U-ages ranging from apatite as the xenolith (46) was incorporated into the 424.6 ± 1.9 and 423.0 ± 1.1 to 420.1 ± 2.6 Ma. By anal- NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 185

400 420 440 460 480 Ma

1.m 2. NW Composite terrane: 1. Albert I Land Terrane 6, 7, 8, 21, 22, 23, 24, 2. 80 3, 4, 17, 18 2.Ar 1, 2, 16 33 1. NW Composite terrane: 18, 20 16.Rb Biscayarhalvøya Terrane 5, 19 17.ec 32 18.Ar 17.m

SW Composite Terrane 9, 10, 11, 27, 28 19.Ar 29, 30, 31, 20.ec 12, 25, 26 19.Ar 18.HP (Ar & Rb) 19.Ar 18.HP (Ar) 13, 14, 15 18.HP (Ar & Rb) 70

E Composite Terrane: Nordaustlandet Terrane 6. Age, Ma 21. 6. 900 920 940 960 980 1. 2. NW Composite 22. terrane: 6. 3. 23. Albert I Land 6. 4. Terrane 2. 21. NW Composite terrane: Biscayarhalvøya Terrane 4. 22. 28. 24. 21. SW Composite Terrane 5. 24. 6. NE Greenland E Composite Terrane: Nordaustlandet Terrane 25. 26. 6.ex 9. 7.ex 27. 8. 6.

12. 7.ex 11. 12. 7. 29. 25. 12. 30. 7.ex 29.m 29. 8. 30. 6. 29. 26. 7. 6. 32. 29. 31. NE Greenland 12. 9.m 29. 10.m 30. 12. 10. 30. 11. 30. 12. 11. 30. 10.

32. 30. 31. 12. 30. 12. 33.ec N Scandinavia allochtons: Kalak-Seve Nappe 13. 14. 15. Fig. 8. Compilation of Grenvillian-Sveconorwegian and Caledonian age data from Svalbard and East Greenland. Some impor- tant ages from the Scandinavian allochthons are also plotted for comparison. References: 1: This study, 2: Ohta et al. (2002); 3: Peucat et al. (1989); 4: Ohta et al. (2003); 5: Balasov et al. (1995); 6: Johansson et al. (2004); 7: Johansson et al. (2000); 8: Gee et al. (1995); 9: Strachan et al. (1995); 10: Kalsbeek et al. (2000); 11: Watt et al. (2000); 12: Leslie & Nutman (2003); 13: Gerber (2006); 14: Kirkland et al. (2006); 15: Albrecht (2000); 16: Balasov et al. (1996); 17: Gromet & Gee (1998); 18: Dallmeyer et al. (1990); 19: Manecki et al. (1998); 20: Bernard et al. (1993); 21: Johansson et al. (2002); 22: Teben’kov et al. (1996); 23: Myhre et al. (2006); 24: Gee et al. (1999); 25: Nutman & Kalsbeek, unpublished data in Higgins et al. (2004); 26: Rehnstrøm (2007); 27: Kalsbeek et al. (2001); 28: Teben’kov et al. (2002); 29: Andresen et al. (2007); 30: Hartz et al. (2001); 31: Hartz et al. (2000); 32: Gilotti & McClelland (2005); 33: Gilotti et al. (2004). All data are U/Pb igneous ages except the ones labeled: m = metamorphic U-Pb age, Ec = U-Pb-age of high-pressure metamorphism, Ex = extrusive rock, (HP)Ar = (high pressure metamorphism) Ar/Ar data, (HP)Rb = (High pressure metamorphism) Rb/Sr-data. 186 P. I. Myhre et al.. NORWEGIAN JOURNAL OF GEOLOGY ogy with the leucosome samples described by Hawkins & Discussion Bowring (1999), and discussed in more detail above, we interpret this pattern to indicate monazite growth on the General implications prograde metamorphic path in the protolith that eventu- ally produced the granodioritic melt. In this particular The analytical data presented above, combined with field case the amount of melt generated at peak metamorphic observations, demonstrate the presence of two major conditions was large enough and had the appropriate phases of magmatic activity within the Albert I Land composition to allow igneous zircon to form at 418.8 ± Terrane: an early Neoproterozoic event at c. 968 Ma and 0.7 Ma. The older monazites were preserved owing to the a Late Silurian event between 430 and 418 Ma, terminat- low solubility of monazite in this type of magma (Wil- ing with emplacement of the Hornemantoppen batholith liams et al. 2007). at 418.4 ± 0.8 Ma. The former age is in agreement with zircon ages around 960 Ma reported for orthogneisses Grey granite, Smeerenburgfjorden (sample 22) of the Smeerenburgfjorden Complex (Ohta et al. 2002), determined using the Kober technique (Kober 1987). The zircons from the grey granite (sample 22) are domi- Similar granodioritic orthogneisses are also present in nated by stubby crystals with cores and overgrowths, many other places within the Smeerenburgfjorden Com- but there is also a minor population of slender, core- plex, thus suggesting that early Neoproterozoic mag- free prismatic grains. Such a grain with a mineral inclu- matic rocks were widespread in the NW Composite Ter- sion gave a concordia-age of 423.6 ± 1.5 Ma. A discor- rane (Fig. 8). dia line through this and a 40 % discordant second zir- con analysis (z2) had an upper intercept of about 1663 Ohta et al. (2002) preferred the interpretation that mig- Ma of uncertain significance. Monazites are pale yellow matization of the Smeerenburgfjorden Complex occurred anhedral to subhedral, and most are free of inclusions during the Grenvillian rather than during the Caledonian and turbid domains. The monazite data are slightly nega- orogeny. This proposal is not supported by our field obser- tively (reversely) discordant (two analyses), but their vations and geochronological data, which indicate instead 207Pb/235U-ages (422.3 and 421.0 Ma) overlap those of the a Caledonian age. The c. 1070 Ma upper intercept age of concordant zircon analysis. In detail, the zircon analysis presumed detrital zircons in sample 72 indicates that the gives a slightly older age than the monazites, and it may sedimentary protolith for this sample was younger than c. have a small component of inheritance. Therefore, we 1070 Ma and presumably Neoproterozoic. prefer to interpret the weighted average 207Pb/235U-age of monazite of 421.7 ± 0.6 Ma (MSWD = 4.1) as the time of The Scandian metamorphic and magmatic record of crystallization of the granite. Albert I Land

Hornemantoppen Batholith, Smeerenburgfjorden The metamorphic record (sample 19) Published data on the metamorphic conditions for Albert I Land indicate temperatures between 400 and Zircon crystals of this sample are mainly prisms with 700°C and mid-crustal pressures, generally increasing high l/w-ratios constituting a homogeneous population towards the north. In a study on marble lenses within the with some variation in degree of metamictization and the Smeerenburgfjorden Complex Bucher (1981) reported presence of cracks. Two small fractions of 1 and 4 zircons temperatures in excess of 600°C at an estimated pres- plot 1.4–1.9 % discordant with 206Pb/238U-ages of around sure of 4 kbar. For garnet-bearing pelites from the same 418 Ma, the same age as the overlapping titanite analysis. area Klaper (1986) found near-isobaric conditions of The two zircon analyses are well constrained analytically 5–6 kbar at 650° - 700°C, using garnet-plagioclase and and the isotopic ratios are essentially the same, thus the garnet-cordierite-sillimanite-quartz geobarometers and slight discordance is probably not due to inheritance as the garnet-biotite geothermometer. Further south, in a xenocrystic cores would have a tendency to affect each south-north profile from Kongsfjorden to the inner parts analysis differently. The discordance may be related of Krossfjorden, garnet mica-schists belonging to the to other causes, for example a bias in the U decay con- Krossfjorden Group gave temperature estimates increas- stant as discussed by Schoene et al. (2006). The best esti- ing from less than 400°C to more than 550°C (Lange & mate for the crystallization of the granite is the weighted Hellebrandt 1999). average 206Pb/238U-ages of the zircon and titanite analy- ses, which gives 418.4 ± 0.8 Ma. Zircon fractions z3 & Chronological model for metamorphism z4 contained an inherited component and plot c. 30 % and magmatism discordantly with an upper intercept between 1530 and Fig. 7 presents a conceptual tectonic model, which inte- 1830 Ma (Fig. 5g). grates the published metamorphic data with geochronol- ogy. It does not consider the timing of the folding. Nev- ertheless, because the granitic plutons are seemingly only affected by brittle deformation their age implies that duc- tile deformation in the area occurred prior to 420 Ma. In NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 187

Fig. 7a a monazite front is shown as a wiggly line in the Ediacaran deposits are also present in the SW Com- middle - upper crust. The front is defined by conditions posite Terrane, but not in the NW Composite Terrane, favourable for monazite-growth, i.e. prograde monazite– prompting Hjelle (1979) to consider the Krossfjorden in reactions as described above, and is controlled by pres- Group to be older than these deposits. In spite of the sure, temperature and reaction kinetics, REE-budgets good lithostratigraphic correlation between the Vet- and the degree of mineral-fluid interaction. The front eranen and Akademikerbreen Groups and the Krossf- is associated with metamorphic conditions within the jorden Group, with its pelites, psammites, marbles and range described in the literature for large areas of Albert I comparable thickness, the age of deposition at around Land. The timing of this situation at c. 430 Ma is defined 1 Ga inferred in this study implies that at least the lower by the older monazites in samples 72, 75 and 80. Fig. 7b parts of the Krossfjorden Group must be older Grenvil- shows the situation in the mid Silurian when metamor- lian deposits, with more affinity to the Brennevinsfjor- phism had progressed further. At this stage the monazite den Group. It is, however, possible that the upper part of front was replaced by a migmatization front defined by the Krossfjorden Group could be a younger sequence of crossing of major-phase liquidus curves. Where plutons Late Neoproterozoic age. were present, their roof forced the migmatization front upwards due to the associated heat influx. In those areas In terms of the Caledonian magmatic and metamorphic where the solidus curve was not crossed, the monazite history the various terranes of Svalbard show both simi- front would have persisted also at this stage, the timing is larities and differences (Fig. 8). One difference is the defined at 424 – 418 Ma by the younger monazites from abundance of Early Silurian ages (440-430 Ma) in the E samples 72, 75, 80 and 46 and igneous zircon from sam- and SW Composite Terranes and their apparent absence ples 80 and 22. Intrusion of the Hornemantoppen Batho- in the NW Composite Terrane. By contrast, both the E lith at 418.4 ± 0.8 Ma concluded the Scandian orogeny in and NW Composite Terranes have a well-documented Albert I Land. record of Late Silurian metamorphism and magma- tism. In Albert I Land this terminated at 418 Ma with Comparison of Albert I Land terrane with other Caledo- the emplacement of the Hornemantoppen Batholith. nian terranes in Svalbard Silurian magmatism did not affect the SW Composite Terrane. Grenvillian age magmatism has now been documented both in the E and NW Composite Terranes in Sval- The Late Grenvillian-Caledonian connection of terranes bard (Fig. 8). In the former, 960 to 930 Ma andesitic to of the north Atlantic margins rhyolitic volcanic rocks of the Svartrabben and Kapp Hansteen Groups were deposited unconformably on The presence in the Albert I Land Terrane, of Meso- an older sequence of turbiditic metasedimentary rocks proterozoic metasedimentary rocks with approximately (Brennevinsfjorden Group) filling a Mesoproterozoic Grenvillian depositional ages, a predominant Mesopro- basin the basement of which is unknown unknown (Gee terozoic provenance for this detritus, and 968 Ma meta- et al. 1995; Gee & Teben’kov 1996; Ohta 1982a, b). These plutonic rocks, resembles the situation observed in many volcanic rocks, together with coeval subvolcanic quartz– Caledonian terranes of the north Atlantic margins (Fig. porphyries and granitoid plutons, have been related to a 8). Besides the Nordaustlandet Terrane in Svalbard, these tectonomagmatic event along an active convergent con- also include allochthonous terranes of East Greenland, tinental margin (Gee & Teben’kov 1996; Johansson et al. the Kalak and Seve Nappe Complexes of Scandinavia 2000; 2005). No Grenvillian age migmatites were iden- (Fig. 8) and terranes in Scotland (Kirkland et al. 2007, tified. Isotopic data from the Grenvillian plutons indi- 2008a, b). Several of these areas also have Late Neopro- cate anatexis of older continental crust, most likely the terozoic sedimentary basins with clastic, carbonaceous Brennevinsfjorden Group (Johansson et al. 2000). The and tillitoid deposits (Nystuen et al. 2008). These, as close similarity in age (Fig. 8) and type of Grenvillian discussed above, may also be present in the upper, car- activity in the two composite terranes thus suggests that bonate-rich metasedimentary components of the Albert they may have been part of the same margin. I Land Terrane. These terranes were all involved in the Caledonian orogeny and in general show a similar pat- Post-Grenvillian erosion predated deposition of the tern with high-temperature - low pressure metamor- Neoproterozoic and Palaeozoic Murchisonfjorden and phism or migmatization as well as S-type granitic intru- Hinlopenstredet Supergroups in the E Composite Ter- sions. This is consistent with a tectonic position in the rane. The Murchisonfjorden Supergroup is dominated upper plate during the Silurian Scandian convergence by siliclastic deposits (Veteranen Group) in the lower (Gee 1975) during which the rocks belonging to Lauren- part, but also includes a thin carbonate horizon in the tia underwent widespread crustal melting and granitic middle. Various carbonates (Akademikerbreen Group) plutonism while the overridden Baltic plate descended constitute the upper part of the Murchisonfjorden to great depths where it interacted with mantle rocks and Supergroup. The overlying Polarisbreen Group of the was locally eclogitized, but experienced very little intru- Hinlopenstredet Supergroup is dominated by shale and sive activity (Fig. 7c). tillites. Tillite horizons and fossils characteristic of the 188 P. I. Myhre et al. NORWEGIAN JOURNAL OF GEOLOGY

Within this framework there are two possible paleogeo- Post-Scandian evolution graphical interpretations that could be applied to the After the final Scandian thermal imprint in the Albert I Albert I Land Terrane: (i) a linkage with northern Lau- Land Terrane, defined by the Hornemantoppen batho- rentia, or (ii) as a development outboard of the Grenville lith at 418.4 ± 0.8 Ma, deformation in Svalbard occurred orogen on the eastern Laurentian margin. only under low-grade metamorphic conditions. In the Devonian, the various terranes of Svalbard were juxta- The correlation with northern Laurentia suggested posed along the major fault systems shown in Fig. 1 into by Gee & Teben’kov (2004) is also considered in the their present configuration. Lateral escape tectonics (Gee most recent Rodinia reconstruction by Li et al. (2008), et al. 2001; Lyberis & Manby 1999) would allow some which places the E Composite Terrane to the north, areas of the orogen (i.e. Svalbard) to undergo low-grade away from the Amazonia-Laurentia-Baltica triple junc- deformation while eclogites were still being formed else- tion. Although the Albert I Land Terrane is not directly where, e.g. in northeast Greenland (Gilotti et al. 2004). considered in their reconstruction, it would likely be On paleogeographic reconstructions for the late Carbon- positioned close to the E Composite Terrane in a high- iferous, Svalbard occupies a position north of Greenland arctic connection in such a scenario. This arrange- (Torsvik & Cocks 2004). This position remained con- ment is based on a correlation with elements from the stant until the mid Tertiary when Svalbard moved south- Pearya Terrane and Ellesmere Island, although these east relative to Greenland during what is known as the are generally somewhat older and geochronologically West Spitsbergen –Eurekan orogeny. less well constrained than in Svalbard. These elements include the Cape Columbia Complex with 1060 ± 18 to 980 Ma and 926 Ma granitic rocks (Sinha & Frisch Conclusions 1976) and the 1037 +25/-20 Ma granites from the Deuc- hars Glacier Belt (Trettin et al. 1987). The main coun- Zircon, monazite and titanite from Albert I Land show terargument to such an arrangement is the need for a that the Krossfjorden Group is a Neoproterozoic sedi- hypothetical, late Grenville mobile belt at the northern mentary sequence deposited after 1070 Ma. A suite of margin of Laurentia. A derivation of the NW Compos- granitoid plutons intruded at 967.9 ± 4.7 Ma. Sedimen- ite Terrane from Ellesmere Island would also require tary and granitic rocks were then variously metamor- that these rocks underwent the Cambrian-Ordovician phosed and locally migmatized, forming the Smeeren- McClintock orogeny (Gee & Teben’kov 2004; Harland burgfjorden Complex, during a sequence of events & Wright 1979) for which there is, as yet, no clear evi- between about 430 and 418 Ma. Prograde metamorphic dence. Trettin (1991) points out that the McClintock monazite preserves a memory of the earliest metamor- orogeny corresponds in time to the Taconian orogeny phic reactions whereas the last stages of the evolution are and that the mafic complexes of the Pearya Terrane cor- recorded by both monazite and zircon in leucosomes and relate with the early ophiolites in Newfoundland and by the Hornemantoppen Batholith. The data and geo- Norway. It is thus also possible to invoke a “reverse” logical observations outline a situation identical to that correlation between the Pearya Terrane and the North observed in the East Greenland allochthons and locally Atlantic occurrences, meaning that Pearya originated also in some Scandian nappes, implying common deriva- farther southeast in Laurentia than its present position tions, most likely in the foreland of the Grenville orogen would suggest on the eastern margin of Laurentia.

The alternative is the hypothesis discussed, among oth- Acknowledgments - The fieldwork was financially supported by the ers, by Kirkland et al. (2007; 2008a) and favoured by us, Norwegian Polar Institute through “Arktisk stipend” granted to P. I. Myhre in 2004 & 2005. P. I. Myhre thanks Alexander Teben’kov for gui- where the NW and E Composite Terranes are placed dance in the field in 2004. Bernard Bingen and Chris Kirkland provi- alongside other north Atlantic terranes along a common ded constructive reviews. margin between Laurentia, Gondwana and Baltica. All the terranes involved have a strikingly common record for the period between 1050 and 950 Ma, involving the development of sedimentary basins, followed by volca- nic, plutonic and metamorphic activity between 980-930 Ma. This is known as the Rigolet phase (Rivers 1997) and according to Kirkland et al. (2007) this record is thought to reflect late Grenvillian arc activity preceded by the for- mation of a successor basin. This situation is compatible with Rodinia reconstructions (Condie 1997; Hoffman 1991; Weil et al. 1998). NORWEGIAN JOURNAL OF GEOLOGY Caledonian anatexis of Grenvillian crust 189

References arch 70(3-4), 215-234. Gee, D.G. & Page, L.M. 1994: Caledonian terrane assembly on Sval- Albrecht, L.G. 2000. Early structural and metamorphic evolution of bard; new evidence from 40Ar/39Ar dating in Ny Friesland. Ameri- the Scandinavian Caledonides: a study of the eclogite-bearing Seve can Journal of Science 294(9), 1166-1186. Nappe Complex at the Arctic Circle, Sweden, Lund University, 132 Gee, D.G. & Teben’kov, A.M. 1996: Two major unconformities bene- pp. ath the Neoproterozoic Murchisonfjorden Supergroup in the Cale- Andresen, A., Rehnstrøm, E.F. & Holte, M. 2007: Evidence for simul- donides of central Nordaustlandet, Svalbard. Polar Research 15(1), taneous contraction and extension at different crustal levels during 81-91. the Caledonian Orogeny in NE Greenland. Journal of the Geological Gee, D.G. & Teben’kov, A.M. 2004. Svalbard: A fragment of the Lau- Society of London 164(4), 869-880. rentian margin. In: D.G.P. Gee, V. L. 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