Large scale Variscan granitoid intrusion throughout Europe: a lateral geochronological trend? K. Oud BSc Thesis, Faculty of Earth Sciences, Utrecht University, July 2006 Abstract Large scale granitoid intrusion during the Variscan orogeny (370 to 250 Ma) in Europe above subduction zones of that time is assumed to be the result of a heat pulse due to slab detachment. This would show from a lateral trend in age of emplacement of all granitic bodies, migrating through the complete Variscan fold belt, and thus, a younging direction perpendicular to the former subduction zones. To test this, an inventory of intrusion ages (on the basis of U Pb, Rb Sr and K Ar analysis), typology (I or S type) and location of 70 granitic bodies in the European Variscan fold belt, from the Armorican Massif to the Bohemian Massif, was made. From the collected data, no lateral trend in age is observed. However, a trend in age parallel to former subduction zones is shown in most massifs, with a younging direction towards the thrusting vergence. This is probably the result of nappe stacking. In the Armorican Massif and Massif Central, granites are all S type, which is probably the cause of continental subduction. In central Europe, the typology is mixed S and I type, which can be caused by subduction of either continental or oceanic lithosphere. 1. Introduction result of the ‘usual’ heat and melt generation attributed to subduction The Variscan orogeny yielded a large processes. However, there is another number of granitoid intrusions throughout possibility of granite emplacement that all of the European Variscides. In all can be considered, which is not commonly orogenic events like subduction and mentioned in related studies. During the continental collision, the crust and mantle final stages of subduction, the subducted are subjected to extreme temperature and slab may break off and sink into the pressure conditions; thermal pulses astenosphere. This is called slab caused by such conditions are abundant. detachment (fig. 1) [Wortel and Spakman, These often result in heating of the crust 2000]. during burial, or decompression during late orogenic extension, and the subsequent melting of the crust and/or mantle which produces (granitic) magmas that intrude into the middle and upper crust. It has been shown that granitic magmas can have a rather varying ? composition, which means a derivation from differing source regions and source rocks [Chappell and White, 2001]. Therefore, the occurrence of granites in an orogenic belt is a reflection of its tectonothermal evolution and its deep structures and processes that are the least accessible and the worst exposed [Finger et al, 1997]. The massive occurrence of granites throughout the Variscan fold belt gives rise to the assumption of a large scale Fig. 1 . Slab detachment with possible thermal pulse along the entire Variscan granitic intrusion (indicated by the ‘?’). After suture. It is possible that this is just the Wortel and Spakman, 2000.
1 When a ‘cold’ slab detaches, it can be From previous studies concerning replaced by hot astenospheric material Variscan granites, I listed the ages of that creates a heat pulse underneath the intrusion from the granitic bodies, aiming overlying plate, which may cause to use the most reliable dating method magmatism [Wortel et al, 2003]. As is available. On the basis of geochemical shown by Wortel and Spakman [2000], information of the bodies involved, I slab detachment can take place during the determined whether they can be last stages of an orogeny, after ocean considered an I type or S type. All those closure and continent collision. With this data will be plotted in a geological map of process, the chance of breaking of the Europe and with this, it will be possible to slab along the entire plate boundary at see whether there is a trend in the age of once would be very small. Rather, the slab intrusion or not and thus, if the intrusion would start to break at a small area where of granites is the possible result of a heat applied stresses would overcome the pulse from slab detachment. strength of the plate segment. This fracture would then start to extend and migrate laterally along the plate 2. Geological and tectonothermal boundary. Consequently, one could expect background a similar lateral trend in the related heat pulse and granite emplacement, shown in The Variscan orogeny resulted from the crust above. Because it is shown by the collision of Euramerica (i.e. Laurentia, tomography [Bijwaard et al, 1998] that Baltica and Avalonia) and Gondwanaland the Variscan subducting slabs are no (Africa) which began in early Palaeozoic longer present under Europe, they must time (from 480 Ma, fig. 2). It meant the have detached. It is suggested by Franke subduction of a part of the latter continent [2000] that at least at some places in the under Euramerica. The suture was Variscan belt, subducting slabs broke off completed during the late with subsequent rising of astenospheric Carboniferous/early Permian (250 Ma) and material and formation of granitic melts. formed the supercontinent Pangaea This paper aims to test whether the [Stanley, 1999]. large scale granite intrusion during the The northern margin of Gondwanaland Variscan orogeny was caused by a heat was very fragmented and the collision pulse from slab detachment. For this area was therefore composed of purpose, I made an inventory of the ages continental microplates, separated by a and typology of the granitic intrusions in system of ridges and troughs, basins and the Variscan massifs in Europe, from the oceanic rifts [Pin, 1990b]. These terranes Armorican to the Bohemian Massif. were the origin of the European
Fig. 2. Schematic map showing the world and its continents, microplates and oceans during Middle Silurian (from Scotese [2003]).
2 Variscan fold belt; they drifted northward southern margins of the Rheinisches from Gondwanaland, colliding with the Schiefergebirge and the Harz. The basin northern continents. This is shown in was closed during the Early Carboniferous. several zones by the occurrence of thick The Variscan collision yielded large sequences of marine sediment and small scale (thin skinned) nappe thrusting and but extensive occurrences of eclogites, (thick skinned) crustal stacking and the originated from MOR basalts which show Precambrian basement of the ridges fused that the rifting at least must have reached with thick layers of sediment and ocean a narrow ocean stage [Franke, 1989]. floor of rift basins from Early Palaeozoic There are several hypotheses about time. The thrusting caused large scale the exact composition and evolution of the Barrovian type (med T/med P) regional microplates involved in the suture, but metamorphism, most extensive in the geological and palaeomagnetic evidence interior of the Moldanubian zone. During indicates that the two largest terranes, the late Early Carboniferous the process of Avalonia and Armorica, were the nappe stacking stopped because of foundations of the Variscan fold belt. dextral wrenching of Gondwana relative to These microplates are said to be Euramerica, which in turn led to dextral composed of several smaller terranes [Tait transpressional and transtensional et al, 1997] and are believed to be tectonics [Arthaud and Matte, 1977]. attached to Baltica and Laurentia before During this process, large parts of the the large collision between Gondwana and Moldanubian zone were affected by severe Euramerica. Also, two main oceanic basins high T/low P metamorphism. Also, the – each consisting of several smaller anti parallel subducted mantle slabs oceanic basins – are recognized: the possibly joined and became detached, Iapetus ocean between Avalonia, Baltica which caused the rise of astenospheric and Laurentia and the Rheic ocean material and therefore a large scale between Avalonia and Gondwana [Matte, intrusion of post tectonic granites [Franke, 2001]. Closing of the first caused the 2000] (fig. 3, the red areas in the Caledonian orogeny in western and massifs). This hypothesis will be tested in northern Europe during middle Silurian to this paper. early Devonian (430 Ma to 370 Ma). The During the Late Carboniferous and Variscan orogeny was caused by the Permian, post orogenic uplift and closure of the Rheic Ocean. extension of the Variscan crust occurred. The generally believed theory for the In the Late Carboniferous, along the composition of the European Variscan fold southern margins of the fold belt, there belt is that it consists of two large might have been some renewed subduction zones which originated before subduction of oceanic crust and accretion the collision in the ridge trough system of terranes, which had sheared of from described above. A southern, northward Gondwanaland while this was drifting dipping system by which the Massif westward. However, it is not clear what Central and intra Alpine oceans were their exact relationship was before these closed (the Moldanubian zone, fig. 3) and terranes were deformed by the Alpine more to the north a southward dipping orogeny in the Mesozoic and Tertiary system which led to the closure of the [Finger et al, 1997]. Saxothuringian and Rhenohercynian basins. This closure began during late Ordovician to early Devonian time, first 3. Granitoids involving oceanic crust, followed by subduction of continental crust during the 3.1 Intrusion
Late Carboniferous. Contrasting with this Granite intrusions occur when heat or convergence is the opening of the water is added to the mantle or crust – Rhenohercynian basin during the having various geodynamic causes such Devonian. This is possibly caused by back that it melts and rises to intrude shallower arc spreading due to the northward crust. Granitic melts (magmas) can be subduction of oceanic crust further to the formed either through the addition of south [Franke, 1989]. Traces of the volatiles (i.e. water) in the mantle, opening of this basin can be found at the decompression of the crust or mantle or
3 Fig. 3. Map showing the main geological and tectonic units of the Variscan fold belt in Europe (after Franke, 1989; Finger et al, 1997). AM: Armorican Massif, MC: Massif Central, RS: Rheinisches Scheifergebirge, H: Harz, O: Odenwald, V: Vosges, SW: Schwarzwald (Black Forest), BM: Bohemian Massif. heat transfer from rising magma rocks (I type) [Chappell and White, [Marshak, 2001]. When hydrated crust, 2001]. Partial melting of metasedimentary e.g. marine sediments, is buried during source rocks is a process called anatexis subduction it is heated rapidly and or ultrametamorphism. Igneous source dehydrates, which causes melting of the rocks that have not been weathered at the rock. Extending the crust causes rapid surface can produce I type granitoids, pressure decrease, while the temperature which also can be created from crystal can remain equal. This decompression fractionation of magmas. A third type of leads to melting of the rock, as is also the granite is recognized by Loiselle and case with heating of the crust by a simple Wones [1979], which is related to mantle increase in temperature, for example by plumes and is thus called A type heat transfer from rising magma in the (anorogenic). surrounding crust. Another form of In determining whether a granite body decompression melting can be caused by can be considered S type or I type, slab detachment. When a portion of a several methods are used. This often can subducting slab breaks away, it sinks into be difficult, because the boundaries the mantle and the overlying portion of between the two are not always very the crust is suddenly exposed to a heat precise. Granites can be distinguished by pulse from the mantle which rises to their chemical composition and mineral replace the ‘cold’ slab and, as a content. Also, some workers use field consequence, may melt because of criteria, but those will not be used in this decompression [Wortel et al, 2003]. paper. I type granitoids are rich in sodium and calcium, which is characteristic for a 3.2 Typology and classification large input from the mantle or lower crust, whereas S types are Na poor and rich in A subdivision made in 1974 by aluminium, which results from a large Chappell and White for classification of input from metasedimentary rocks and are granites is now commonly considered as a thus crust derived. These chemical good measure and distinguishes two types properties of S type granitoids are due to of granites. These are the result from the fact that during sedimentary partial melting of different kinds of source fractionation, Na is removed into sea rocks: (meta)sedimentary source rocks water (and evaporates) and Ca into (S type) and older, pre existing igneous carbonates, which means a relative
4 enrichment in Al in the main sedimentary primitive igneous rocks. S types typically stack. In this paper, the molar have a δ 18 O ratio higher than 9‰,
Al 2O3/(Na 2O+K 2O+CaO) ratio is used a whereas I types have a value that is lower few times. For I types, this ratio is less than 9‰, which gives a very clear than 1.1, whereas for S types it is larger distinction [O’Neill and Chappell, 1977]. than 1.1. This is logical because of the I type and S type granitoids are also high Al and low Na content in sedimentary characterised by different mineral rocks. assemblages, because of their differences Furthermore, because sediment is rich in source material. The most important in SiO 2, S type granitoids have also a high difference is the absence of muscovite in SiO 2 content – between 65% and 74% I types and its presence in S types. which means they are more felsic in Hornblende is generally present in most I composition and are usually light types, but is absent in more felsic S types coloured. I types are lower in SiO 2 content [Chappell and White, 2001]. – 53% and higher – and have therefore a composition which ranges from felsic to mafic, being granitic to tonalitic, and are 3.3 Tectonic setting consequently richer in Mg and Fe and darker in colour. Granitoids that contain Both I type and S type granitoids form less than 65% SiO 2 can be considered to in subduction settings, wherein S types be I type [from ‘Granites’]. occur as a result of melting of the higher Also very important are various crust (supracrustal) and I types from isotopic compositions, wherein Sr 87 /Sr 86 melting of the lower crust and high mantle ratios, εNd values and oxygen isotopic (infracrustal) [from ‘Granites’]. In ‘normal’ ratios are the most important for continental collision, i.e. the suture classification of granitoids. It is shown that between two continental plates, mostly S in S type granitoids, strontium is more types occur because of thickening of the radiogenic [Chappel and White, 2001], continental crust, which yields higher with initial Sr 87 /Sr 86 ratios of 0.708 to temperatures and thus melting of the 0.720. I type granitoids give initial crust (fig. 4a). In subduction settings Sr 87 /Sr 86 ratios of 0.704 to 0.712. As can wherein oceanic crust is involved, more I be seen, there is a significant overlap type granitic intrusions occur. This is between the initial isotopic compositions because the subduction of oceanic crust of the S and I type, which makes yields metamorphosis of the subducting distinction sometimes difficult. Isochron slab, which results in the release of plots give a regular linear set of points for volatiles in it, and melting of the lower I type granitoids while for S types, the lithosphere above it as a consequence of points are scattered over a large area. heat transfer. This causes the formation of This variation in initial Sr 87 /Sr 86 ratios more I type granitoids (fig. 4b), together within a single igneous body would be the with S types. Magmatic underplating as a result from a heterogeneous source result of slab detachment generally material [Chappell and White, 2001]. produces I type granitoids. This is Another ratio that is often used in because the hot mantle material that related papers are Neodymium isotopic replaces a cold slab melts because of values. These are expressed as εNd, which decompression. is the deviation of the 143 Nd/144 Nd ratio Post orogenic collapse is often related from its present day average value in the to slab detachment. After the formation of earth. For I type granitoids, εNd ranges an orogenic belt, either compression from +3.5 to 8.9 and for S types it ceases or the slab slowly detaches. This ranges from 5.8 to 8.8. For this paper, results in extension and collapse of the the εNd ratio is not used very much, crust, thinning of the lithosphere and because the overlap is often too large for subsequent rise of the asthenosphere, determining the type of granite. In which cause decompression melting and contrast, the δ 18 O ratio of granitoids is melting from the increased heat flux. Both used quite often. The δ18 O ratio of S type post orogenic S type and I type granitoids and I type granitoids reflects the fact that are produced by this tectonic setting (fig. sedimentary rocks are richer in O 18 than 5).
5
Fig. 4a and b. The formation of S type granitoids in continent continent collision and of I type granitoids in ocean continent collision. From ‘Granites’. Fig. 5. The formation of granitoids as a result of post orogenic collapse of an orogenic belt. From ‘Granites’. 4. Dating methods the ratio between present parent and daughter isotopes and by calculating the In determining the age of time needed to produce that ratio. emplacement of a granitic body, several Complications occur when the amount of dating methods are commonly used, all daughter isotopes is not zero from the based on the radioactive decay of certain start. This amount is always calculated isotopes present in minerals in the rock. carefully, mostly by determining the Radioactive isotopes (parent isotopes) different amounts of parent and daughter decay to daughter isotopes at a certain isotopes present in different minerals in rate per year. Every isotope has a the rock and by comparing those. constant and characteristic rate, Ages of granitic intrusions in this paper expressed as its half life: the time at were based mostly on dating by Uranium which half of the amount of parent isotope Lead and Rubidium Strontium methods. has decayed to its daughter isotope. Potassium Argon and Argon Argon were In slowly cooling igneous bodies, like used only in case of lack of one of the granites, various minerals start to former dating methods, because they are crystalllize at various temperatures. This less accurate for this purpose; they closure temperature (i.e. the temperature measure cooling temperatures which are at which isotopes do not exchange freely somewhat too low for cooling granites between minerals in the fluid anymore; [Begemann et al, 2001; Min et al, 2000]. they become locked in the mineral) is the Radiometric dating based on the decay start of the radioactive decay of the of 238 U and 235 U to 206 Pb and 207 Pb, isotope and thus the start of the dating respectively, nowadays gives the most clock [Bennington]. Knowing the decay reliable result. It is one of the earliest rate of an isotope allows one to determine methods, and hence, its decay constants the age of crystallization of the involved are intensively studied, particularly in mineral and thus, to a certain extent, the zircon. The occurrence of this mineral in age of intrusion and cooling of an igneous felsic igneous rocks is widespread and it is body. Granitic intrusions start to extremely resistant to isotopic resetting crystallize at about 800 oC or lower [from (the resetting of the radioactive clock ‘Bowen’s reaction series’ (BRS)]. The age through a reheating event like of the intrusion is measured by calculating metamorphism) [Begemann et al, 2001].
6 This is because the closure temperature of data was available, ages from Rb Sr and zircon is around 850±50 oC [from ‘BRS’], K Ar analysis were taken. The ages and which makes it the perfect representation characteristics of all granites are given in for the cooling age of the igneous body in Table 1. which it is present. A problem occurs In two geologic maps that cover the when the zircon originates from an older area, all Variscan granitic intrusions were granite from which the clock has not been indicated. A division in age was made, reset. This would give much older ages. indicated with different colours, which However, taking more samples and differs slightly from the division made by compare their ages will reduce the effect Finger et al [1997], because this gives a of this risk. clearer overview. The intervals were The decay of Rubidium 87 to chosen between 370 and 330 Ma, 330 and Strontium 87 is mostly measured from 300 Ma and 300 Ma and younger. With hornblende, biotite and muscovite, which this division plotted in different shades of have closure temperatures of about 700 pink (the lighter, the younger the granite) oC, 600 oC and 500 oC, respectively on the intrusions in the map, it turned out [‘BRS’]. 87 Rb/87 Sr analysis is because of to be more clear and easier to determine these lower closure temperatures a trend. Bodies of unknown age are somewhat less accurate than U Pb plotted in blue. The age of intrusion is also analysis. indicated on the map, together with its 40 K/ 40 Ar and 40 Ar/ 39 Ar dating are the uncertainty interval. These are indicated least accurate of the three. This is for a with green or red, in which green stands major part because there is much for I type and red for S type, which discussion about the exact decay makes it possible to see if this division constants of 40 K and 40 Ar. Also, the closure also shows a trend. Granitic intrusions temperature from the used minerals is from which it is not certain whether they relatively low for the cooling of a granitic can be considered as I or S type have body. Biotite and muscovite are used the ages indicated in blue. most, together with K feldspar, which has a closure temperature of about 500 oC. Another important remark to this method 5.1 Armorican Massif and Vendée is the fact that Ar is a gas and is thus present in the form of bubbles in the rock. From the Armorican Massif and the It can be quite easy for a gas to escape Vendée area southwest of it, 15 data from the original rock to other rocks or points were obtained (fig. 6). All the ages the atmosphere, which means that the of granites from the Vendée area were ratio of parent and daughter isotopes can determined on the basis of K Ar analysis. be changed, and not only by decay of In the Armorican Massif, ages were parent isotopes [Bennington]. obtained through Rb Sr analysis. Here, Variscan granites intruded particularly in the south, in the north most granitic 5. Data analysis bodies intruded during pre Variscan time (the early Palaeozoic and Precambrian), A total of 70 data points in granites but one Variscan body is clearly present in was collected, 40 in the Armorican Massif, the north. All granites are S types, but in Vendée, Massif Central and Vosges and 30 the Vendée, the typology is not clear. In in the Black Forest, Odenwald, Harz and age, a rather clear trend can be seen. It the Bohemian Massif, which are mostly in shows a younging direction to the the Moldanubian and, to a lesser extent, southwest, over the whole width. in the Saxothuringian zone (figs. 6 to 9). Remarkable is the fact that the age of The Rhenohercynian does not have any intrusion runs parallel to the subduction Variscan granitic intrusions, except for the zone of the Massif Central suture. North of Brocken granite in the Harz. From each this range, there are a few granites that granitic body considered, its age and have no determined age or type. North of typology were determined. For as far as that is the Ploumanac’h granite, which lies possible, ages obtained on the basis of U directly on the former southward Pb analysis were taken, but when no U Pb
7 # name lat lon type age err (+/- dating reference (N) (E) (Ma) Ma)) method 1 Odenwald 4959 846 I 369 5 K Ar Todt (1995) 2 Stare Sedlo/ Mirotice 4931 1418 I 373 5 U Pb Kosler (1993) 3 Sazava suite 4949 1444 I 350 12 U Pb (E) Holub (1997) 4 Leuchtenberg granite 4938 1217 I/S 342 6 U Pb Kohler (1996), Behrmann (1997), (Siebel (1995a)) 5 Falkenberg granite 4950 1216 S 311 4 Rb Sr Siebel (1995a), Wendt (1989) 6 Mitterteich granite 4955 1214 S 310 6 Rb Sr Siebel (1995b), Siebel (2003) 9 Weinsberg granite 0 0 I/S 318 4 Finger (1995) 10 Leuchtenberg granite 4947 1212 I/S 325 2 Rb Sr, Pb Siebel (1995a), Siebel Pb (2003) 11 Rastenberger 4835 1520 I 338 2 U Pb Klotzli (1996), Vellmer granodiorite (1994) 12 Scharding granite 4828 1341 S 319 6 U Pb Finger (1997), Frasl (1991) 13 Eisgarn granite 4858 1506 S 327 4 U Pb Vellmer (1994), Frasl (1991) 14 Malsburg granite 4745 746 I/S 328 6 U Pb Schaltegger (2000), Todt (1976) 15 St. Blasien granite 4746 806 I/S 333 2 U Pb Schaltegger (2000) 16 Barhalde granite 4750 808 S 332 3 U Pb Schaltegger (2000) 17 Albtal granite 4739 804 I/S 334 3 U Pb Schaltegger (2000) 18 Oberkirch granite 4829 802 I/S 320 5 Rb Sr Hoefs (1983) 19 Forbach granite 4843 824 S 293 3 Rb Sr von Drach (1974) 20 Triberg granite 4813 816 S 325 6 U Pb, Rb Schleicher (1994) Sr 21 Karkonosze/Reichenber 5048 1508 I 328/3 12/14 Rb Sr/U Oberc (2005), Kroner g granite 04 Pb (E) (1994) 22 Brocken granite 5146 1040 A 295 3 U Pb Baumann (1991) 23 Eibenstock 5028 1238 S 297 8 U Pb Kempe (2004) SHRIMP 24 Kirchberg 5037 1228 I/S 330/3 5/7 U Pb/Rb Kempe (2003), Forster 10 Sr (1999) 25 G1 5005 1202 I/S 325/3 /14 Rb Sr Irber (1997), Besang 10 (1976) 26 G2 5010 1200 S 305/2 /7 Rb Sr Irber (1997), Besang 91 (1976) 27 G3 4958 1150 S 305/2 /4 Rb Sr Irber (1997), Besang 88 (1976) 28 G4 5001 1150 S 290/2 /6 Rb Sr Irber (1997), Besang 85 (1976) 30 Bor 4946 1246 I/S 332 8 U Pb Siebel (1997) 31 Rozvadov 4940 1240 S 304 19 Rb Sr Siebel (1997) 32 Karlsbad/ Karlovy Vary 5010 1256 I 303 7 ? Cathro (2005) batholith 33 Meissen 5111 1330 I 328 8 U/Pb Nasdala (1999), Wenzel (1997) 34 (Molkenrain rhyolite) 4749 706 338 5 U/Pb Schaltegger (1996) 35 Ballons granite 4749 654 I 340 3 U/Pb Schaltegger (1996) 36 Northern Vosges granite 4822 711 I 331 5 U/Pb Schaltegger (1997) 37 Borne granite 4428 400 310 10 U/Pb Talbot (2004) 38 Velay granite 4441 416 301 5 U/Pb Ledru (2001) 39 Margeride granite 4445 332 S 323/3 12/7 Rb Sr/U Ledru (2001), 34 Pb 40 Rocles granite 4429 410 318 3 U/Pb Be Mezeme (2006) 41 Mt Lozere 4427 340 S? 285 15 Rb Sr Vialette (1977) 42 Tournon 4457 454 337 13 Rb/Sr Ledru (2001) 43 St Sylvestre 4613 133 S 324 4 U Pb Turpin (1990) 44 Gueret 4615 151 S 355 10 Rb Sr Turpin (1990) 45 Millevaches 4602 149 S 345 12 Rb Sr Turpin (1990) 46 Luzy granite 4649 404 S 300 4 Rb Sr Rolin (1991) 47 Settons granite 4708 417 340 5 Rb Sr Rolin (1991) 48 Lormes/Pierre qui Vire 4718 404 S 324 8 Rb Sr/U Rolin (1991), Duthou granite Pb (1984) 49 Chateau Chinon granite 4706 354 301 7 U/Pb Rolin (1991), Carpena (1984)
8 50 Ussel granite 4525 225 S 327 3 Rb Sr Vialette (1973) 51 Echassieres granite 4613 259 312 8 Rb Sr Faure (2002) 52 Pouzol Servant granite 4608 258 330 9 Rb Sr Faure (2002) 53 St Gervais granite 4602 250 349 8 Rb Sr Pin (1990a) 54 Aigoual St Guiral Liron 4404 335 S 285 5 Rb Sr Sinclair (1993) granite 55 Bois Noirs Madeleine 4558 344 S 330 10 Rb Sr Pin (1990a), Vialette St Julien la Vetre (1973) 56 Blond 4603 57 S 318 13 U Pb Alexandrov (2002) 57 Crevant 4631 153 S 312 Rb/Sr Pin (1990a) 58 St Dier 4540 330 S 330 Rb Sr Pin (1990a) 59 Ploemeur leucogranite 4743 324 S 304 6 Rb/Sr Bernard Griffiths (1985) 60 Lizio granite 4752 237 S 338 13 Rb/Sr Bernard Griffiths (1985) 61 Pontivy Rostrenen 4801 315 S 344 8 Rb/Sr Bernard Griffiths (1985) granite 62 Point du Raz granite 4802 435 S 310 20 Rb/Sr Bernard Griffiths (1985) 63 Quimper granite 4759 410 S 318 7 Rb/Sr Bernard Griffiths (1985) 64 Questembert granite 4742 235 S 329 21 Rb/Sr Bernard Griffiths (1985) 65 Pont l'Abbe granite 4752 416 S 305 6 Rb/Sr Bernard Griffiths (1985) 66 Sarzeau granite 4731 250 S 300 10 Rb/Sr Bernard Griffiths (1985) 67 Ploumanac'h granite 4847 328 S 290 10 68 Les Cerqueux de 4656 42 309 K/Ar Ries (1979) Maulevrier 69 Poiroux 4630 127 296 K/Ar Ries (1979) 70 St Aubin le Cloud 4638 22 321 K/Ar Ries (1979) 71 Les Clouzeaux 4633 116 297 K/Ar Ries (1979) 72 Noirlieu 4654 30 328 K/Ar Ries (1979) 73 L'Ecarpiere 4701 107 306 K/Ar Ries (1979) Table 1 . Ages and characteristics of all listed granites. Numbers correspond to numbers on the maps. Another possible trend in intrusion age can also be seen. This is in the southern line of granites of the Armorican Massif. Granite bodies in this line range gradually from 310 Ma in the northwest, to 300 Ma in the southeast, thus, perpendicular to the subduction zone. 5.2 Massif Central The Massif Central exposes much of the Variscan basement dominated by granitic intrusions. It yielded a list of 22 granites (fig. 7). More than half of the ages of those were obtained on the basis of Rb Sr analysis, some in combination with U Pb data (Table 1). For nine granitic bodies it was not possible to determine its type, however, the largest part of the other intrusions turned out to be S type. As can be seen in the map, older Fig. 6. Variscan granitoids with age of granites appear somewhat in the middle intrusion and type in the Armorican Massif and of the Massif Central, as younger granites Vendée. Scale 1 : 4 100 000. appear more towards the edges. The youngest intrusions, again, are in the south. In the (south)western and –eastern subduction zone north of the Armorican rims are quite some intrusions that have Massif. no determined age. However, for the
9 Fig 8. Age and type of intrusions in the Vosges, Black Forest and Odenwald. Scale 1 : 5 100 000. west to east directed younging trend can be seen in the two areas together, as in the Armorican Massif. The north and south Fig. 7. Age and type of granitic intrusions of both areas are bounded by the two in the Massif Central. Scale 1 : 4 100 000. former subduction zones that define the Moldanubian zone. actual data available, there is, as in the The Odenwald lays just south of the Armorican Massif, a general trend in suture zone between the Rhenohercynian younging direction shown parallel to the and Saxothuringian zone. It only yields MC suture. There are a few exceptions; one data point, from which the age is i.e. in the southeast and northeast. Here based on K Ar analysis. This lies too far are two granitic bodies that are older than from the other two areas to include it in the observed trend. the observation of a possible trend, also because it does not lie in the Moldanubian zone. 5.3 Vosges, Black Forest and Odenwald 5.4 Bohemian Massif and Harz From the Vosges, Black Forest and Odenwald 11 data points are collected, The Bohemian Massif and Harz yielded which are not all shown in the map a total of 22 data points, from which one because of similar results in nearby in the Brocken granite in the Harz (fig 9). intrusions (fig. 8). The ages of the Ages are determined on the basis of either intrusions are mostly based on U Pb U Pb or Rb Sr analysis. Most granites are analysis and they have different typology. S types or the type is not clear. The The Vosges and Odenwald have I type Brocken granite lays just north of the granitoids, whereas the Black Forest has former subduction zone between the two (known) S type granitoids, the rest is Rhenohercynian and Saxothuringian. It is not determined. the only granite which is considered to be Here, a trend in younging direction is A type and thus does not fit in a not very clear. In the Black Forest, subduction setting. granites become younger to the north and In the Bohemian Massif, a somewhat there also is a somewhat older granite in northwest/southeast directed trend in the south. In the Vosges, there are only younging direction can be seen, with the two granites measured, thus, a trend can oldest granites occurring in the middle not be considered. However, a somewhat part. This is approximately the same trend
10 scraped of by the overlying crust, with subsequent formation of several thrusts behind each other, so that accretion on the overlying plate occurs [van Hinsbergen et al, 2005]. When this happens, the nappes that subduct behind the frontal one subsequently form igneous intrusions too, only further away from and at a later time than this nappe. This process would show a similar kind of trend as is observed in the Variscan massifs, which would imply that during the Variscan orogeny, nappe stacking and accretion of the overlying crust occurred in most of the subduction zones described in Fig. 2. This is also mentioned by Finger et al [1997]. Especially in the Armorican Massif it is clearly shown; here, the slab subducted to the northeast, and along the entire zone, granitic intrusions become younger to the opposite direction, i.e. the thrusting vergence which is towards the southwest. In the other Variscan massifs, Fig. 9. Granites in the Harz (upper left) and the process of nappe stacking can be seen Bohemian Massif. Scale 1 : 2 200 000. less clearly from the intrusion of granites, because a trend in younging direction is as is shown in areas considered less evident. Though, in most of the previously. However, this trend is not as massifs, it is present. In the middle of the clear as, for example, in the Armorican Massif Central, the MC suture bends to the Massif. Here, a few granites differ from northeast, which is also shown in the the general trend: at the southeastern trend in intrusions. The youngest and northwestern rim, two granites are intrusions are present in the (south)west, much older as should be expected and in south, and (south)east of the massif, and the north, two granites are situated the intrusions are older to the north. somewhat separated from the others and The Vosges and Black Forest lay in do not fully fit in with the other results. between two former subduction zones Also, at the southwestern rim there is a which are directed towards each other to reasonable number of granites that the north and south [Franke, 1989; Finger remain undetermined. et al, 1997]. Therefore, when following the trend observed in previous massifs, a trend in younging direction to the north 6. Discussion and south of both massifs would be expected. This is indeed the case, but not All granitic intrusions in the Variscan very clear, possibly because the areas and fold belt lay above suture zones that thus the amount of data are just too formed the Variscan fold belt. The trends small. In the Odenwald, the granitic in age of intrusion in the areas considered intrusion lies somewhat south of the turn out to show a younging direction in boundary of the suture zone between the the direction of the vergence of the Rhenohercynian and Saxothuringian in thrusting and parallel to the former which subduction occurred to the south. subduction zone. This can logically not be As a result, it is logical that this granitic the result of a heat pulse migrating body intruded here. perpendicular to the zone caused by slab In the Bohemian Massif, the observed detachment. trend can have the same cause as is the A possible cause for this is a process case for the Vosges and Black Forest. called nappe stacking. In subduction When the former northward subduction zones, parts of the subducting crust are zone south of the Moldanubian zone is
11 continued to the Bohemian Massif – which subduction zones, which do not exist is, however, not clearly shown yet from anymore nowadays, as is shown by previous studies , again, two subduction tomography by Bijwaard et al [1998]. zones were directed towards each other. Thus, the slabs must have detached, but In between, older granites would occur without resulting heat pulse. and younger granites occur to the outside, Some remarks that can be made to parallel to the subduction zones. This is this study are the following. Very exactly observed from the collected data. important to take into consideration is the On the basis of the typology of the accuracy of some of the collected data, granites, no clear conclusion can be especially in case of the dating methods. drawn. The Armorican Massif and Massif K Ar dating is less precise as U Pb dating Central consist entirely of S type in the dating of granites. Unfortunately, in granitoids, the rest of the massifs have some of the areas, like the Vendée, there mixed typology and granites from which were no other data available. For the the type is not clear. It is possible that the Vendée this probably does not matter that suture zones of the first two, i.e. the MC much because the age of all granites in suture, were of continent continent the area is based on the same method, collision type, whereas the other massifs thus, it is all right if granites within the were (partly) of ocean continent collision area are compared, unless there was an type. Clear evidence for this assumption is event of metamorphism after the not given in related studies. Matte [2001] intrusion. However, if dating methods states that France is built from the within areas differ, comparison of Armorican microplate, which is a intrusion ages in the concerned area continental plate that was attached to becomes less accurate. Here, ages of Euramerica during the Middle Devonian granites on the basis of differing dating (approximately 375 Ma). Yet, there is methods do not seem to show much some discussion about the time of the varying results. Though, for further suture between Armorica and Gondwana studies, I would recommend the usage of and the exact configuration of the similar dating methods, and especially the microplates and oceanic basins in usage of U Pb analysis in the dating of between. This information is essential for granitic intrusions. conclusions about the assumption above. The uncertainty in determining the However, in the light of the fact that the type of a granitic intrusion is also an Variscan collision area was built from important remark. This determination can microplates and oceanic basins, it is very be quite difficult because boundaries likely that alternating subduction of between ratios that distinguish S and I oceanic and continental lithosphere has type often have an overlap to a certain taken place. extent. In seeking a trend in typology, it The occurrence of a migrating heat can be a large problem, however, in this pulse as a result of slab detachment paper it is not the most important issue. during or after the Variscan orogeny is not proven on the basis of the gained results. A trend in intrusion age perpendicular to a 7. Conclusions former suture zone is observed almost nowhere. There are two areas where such With the analysis of 70 granites a trend can be observed to a certain throughout the Variscan fold belt (from extent. This is in the Armorican Massif and the Armorican Massif to the Bohemian – to a lesser extent – in the Vosges/Black Massif), the hypothesis that the enormous Forest area. Here, a heat pulse as a result scale on which granitic intrusions occur of slab detachment may have occurred. would be the result of a heat pulse from However, the observed perpendicular slab detachment was investigated. Ages of trends in younging direction stay within intrusion obtained from different dating the uncertainty boundaries of the dating methods – U Pb, Rb Sr and K Ar – turn methods. This makes the occurrence of a out to show rather reliable results, from heat pulse due to migrating slab which the following can be concluded. detachment in the Variscan orogeny not It shows that there is no trend in certain. Yet, it is clear that there were ageing of granitic intrusions perpendicular
12 to the suture zones in which they intrude. is the only A type, which can be the result Only in the Armorican Massif and the from post orogenic extension. Vosges/Black Forest area, a possible trend in younging direction perpendicular to the suture zone and thus the possibility of a References heat pulse can be observed. However, all the ages stay within the same uncertainty "Granites." boundaries. This, together with the www.geology.wisc.edu/courses/g203/pdf/g203c lass21.pdf . absence of such a trend in other massifs, "Bowen's reaction series." proves that slab detachment in the www.bookrags.com/sciences/earthscience/bow Variscan – which must have occurred – ens reaction series woes 01.html . did not go together with a heat pulse from Alexandrov, P., Ruffet, G., Cheilletz, A. (2002) . "Muscovite recrystallization and saddle shaped the astenosphere migrating along the 40 Ar/ 39 Ar age spectra: Example from the Blond plate boundary and resulting granite (Massif Central, France)." Geochimica et decompression melting of the lithosphere Cosmochimica Acta 66 (10): 1793 1807. and intrusion of granites. Arthaud, F., Matte, P. (1977) . "Late Paleozoic strike slip faulting in southern Europe and northern Only convincing trends in younging Africa: result of a right lateral shear zone direction parallel to the former subduction between the Appalachians and the Urals." zones are shown, all in the direction of the Geological Society of America Bulletin 88 : thrusting vergence. This is probably 1305 1320. Baumann, A., Grauert, B., Mecklenburg, S., Vinx, R. caused by nappe stacking or continental (1991) . "Isotopic age determinations of accretion, in which parts of the crust crystalline rocks of the Upper Harz Mountains, subduct under previous subducted crust: a Germany." Geologische Rundschau 80 (3): 669 migrating subduction zone with 690. Be Mezeme, E., Cocherie, A., Faure, M., Legendre, subsequent migrating intrusion of O., Rossi, Ph. (2006) . "Electron microprobe granites. In a tectonic setting with many monazite geochronology of magmatic events: small microplates and oceanic basins, as examples from Variscan migmatites and in the Variscan, this process is very likely. granitoids, Massif Central, France." Lithos 87 : 276 288. Especially in the Armorican Massif, the Begemann, F., Ludwig, K.R., Lugmair, G.W., Min, K., trend in younging direction in the direction Nyquist, L.E., Patchett, P.J., Renne, P.R., Shih, of the vergence is clearly shown. In other C.-Y., Villa, I.M., Walker, R.J. (2001). "Call for massifs, it is also present, though less an improved set of decay constants for geochronological use." Geochimica et clear due to some missing data. In the Cosmochimica Acta 65 (1): 111 121. Bohemian Massif, were probably two slabs Behrmann, J. H., Tanner, D.C. (1997). subducted towards each other, the "Carboniferous tectonics of the Variscan younging of granites is also directed basement collage in eastern Bavaria and western Bohemia." Geologische Rundschau towards both vergences of thrusting, the 86 (Suppl.): S15 S27. oldest granites are present in between. Bennington, J. B . "Radiometric dating of the rock In all massifs, data differing from the record." general trend in is possibly caused by http://people.hofstra.edu/faculty/j_b_benningto n/ 2cnotes/dating.html . small differences or errors in dating Bernard-Griffiths, J., Peucat, J.J., Sheppard, S., methods. Vidal, P. (1985). "Petrogenesis of Hercynian The typology of granites shows that leucogranites from the souhern Armorican the Armorican Massif and the Massif Massif: contribution of REE and isotopic (Sr, Nd, Pb and O) geochemical data to the study of Central are entirely of S type. This would source rock characteristics and ages." Earth and imply a more continent continent collision Planetary Science Letters 74 (2 3): 235 250. type of subduction. However, this is not Besang, C., Harre, W., Kreuzer, H. (1976). clearly shown from related studies, "Radiometrische Datierung, geochemische und petrographische Untersuchungen der because workers have some discussion Fichtelgebirgsgranite." Geologisches Jahrbuch about the exact tectonic setting and Reihe E E8 . configuration before the Variscan orogeny. Bijwaard, H., Spakman, W., Engdahl, E.R. (1998). It turns out that other massifs have no “Closing the gap between regional and global travel time tomography.” Journal of clear trend in typology. They have mixed Geophysical Research B: Solid Earth 103 (B12): types, which can be caused both by 30025 30078. continent continent and ocean continent Carpena, J., Doubinger, J., Guerin, R., Juteau, T., collision. The Brocken granite in the Harz Monnier, M. (1984). "Le volcanisme acide de l'Ouest Morvan dans son cadre géologique. Caractérisation géochimique, structurala et
13 chronologie de mise en place." Bulletin granite (Erzgebirge, Germany)." Contributions Société Géologique de France 7: 839 859. to Mineralogy and Petrology 145 : 107 118. Cathro, R. J. (2005). "Joachimsthal, Czech Republic." Kempe, U., Bombach, K., Matukov, D., Schlothauer, CIM Bulletin . T., Hutschenreuter, J., Wolf, D., Sergeev, S. Chappell, B. W., White, A.J.R. (2001). "Two (2004). "Pb/Pb and U/Pb zircon dating of contrasting granite types: 25 years later." subvolcanic rhyolite as a time marker for Australian Journal of Earth Sciences 48 : 489 Hercynian granite magmatism and Sn 499. mineralisation in the Eibenstock granite, Duthou, J. L., Cantagrel, J.M., Didier, J., Vialette, Y. Erzgebirge, Germany: Considering effects of (1984). "Palaeozoic granitoids from the French zircon alteration." Mineralium Deposita 39 : Massif Central: age and origin studied by the 646 669. 87 Rb 87 Sr system." Physics of the Earth & Klötzli, U. S., Parrish R.R. (1996). "Zircon U/Pb and planetary Interiors 35 (1 3): 131 144. Pb/Pb geochronology of the Rastenberg Faure, M., Monié, P., Pin, C., Maluski, H., Leloix, C. granodiorite, South Bohemian Massif, Austria." (2002). "Late Visean thermal event in the Mineralogy and Petrology 58 : 197 214. Northern part of the French Massif Central: new Košler, J., Aftalion, M., Bowes, D.R. (1993). "Mid late 40 Ar/ 39 Ar and Rb Sr isotopic constraints on the Devonian plutonic activity in the Bohemian Hercynian syn orogenic extension." Massif: U Pb isotopic evidence from the Staré International Journal of Earth Sciences 91 (1): Sedlo and Mirotice gneiss complexes, Czech 53 75. Republic." Neues Jahrbuch für Mineralogie Finger, F., Clemens, J.D. (1995). "Migmatization and Monatshefte : 417 431. "secondary" granitic magmas: effects of Köhler, H., Hölzl, St. (1996). "The age of the emplacement and crystallization of "primary" Leuchtenberg granite (NE Bavaria, Germany); A granitoids in Southern Bohemia, Austria." revision on account of new U Pb zircon ages." Contributions to Mineralogy and Petrology 120 : Neues Jahrbuch für Mineralogie Monatshefte : 311 326. 212 222. Finger, F., Roberts, M.P., Haunschmid, B., Kröner, A., Hegner, E., Hammer, J., Haase, G., Schermaier, A., Steyrer H.P. (1997) . "Variscan Bielicki, K.H., Krauss, M., Eidam, J. (1994). granitoids of Central Europe: their typology, "Geochronology and Nd Sr systematics of potential sources and tectonothermal relations." Lusatian granitoids: significance for the Mineralogy and Petrology 61 (1 4): 67 96. evolution of the Variscan orogen in east central Förster, H. J., Tischendorf, G., Trumbull, R.B., Europe." Geologische Rundschau 83 : 357 376. Gottesmann, B. (1999). "Late collisional Ledru, P., Courrioux, G., Dallain, C., Lardeaux, J.M., granites in the Variscan Erzgebirge, Germany." Montel, J.M., Vanderhaeghe, O., Vitel, G. Journal of Petrology 40 (11): 1613 1645. (2001). "The Velay dome (French Massif Franke, W. (1989). "Tectonostratigraphic units in the Central): melt generation and granite Variscan fold belt of central Europe." Geological emplacement during orogenic evolution." Society of America Special Paper 230 : 67 90. Tectonophysics 342 : 207 237. Franke, W. (2000). "The mid European segment of Loiselle, M. C., Wones, D.R. (1979). "Characteristics the Variscides: Tectonostratigraphic units, and origin of anorogenic granites." Geological terrane boundaries and plate tectonic Society of America, Abstracts 11 : 468. evolution." Geological Society Special Marshak, S. (2001). Earth: Portrait of a planet , W.W. Publication (179): 35 56. Norton & Company. Frasl, G., Finger, F. (1991). "Geologisch Matte, P. (2001). "The Variscan collage and orogeny petrographische Exkursion in der (480 290 Ma) and tectonic definition of the österreichischen Teil des Südböhmischen Armorica microplate: a review." Terra Nova 13 : Batholiths." Berichte der Deutschen 122 128. Mineralogischen Gesellschaft 3(2): 23 40. Min, K., Mundil, R., Renne, P.R., Ludwig, K.R. Hoefs, J., Emmermann, R. (1983). "The oxygen (2000). "A test for systematic errors in 40 Ar/ 39 Ar isotope compostion of Hercynian granites and geochronology through comparison with U/Pb pre Hercynian gneisses from the Schwarzwald, analysis of a 1.1 Ga rhyolite." Geochimica et SW Germany." Contributions to Mineralogy and Cosmochimica Acta 64 (1): 73 98. Petrology 83 : 320 329. Nasdala, L., Wenzel, T., Pidgeon, R.T., Kronz, A. Holub, F. V., Cocherie, A., Rossi, P. (1997). (1999). "Internal structures and dating of "Radiometric dating of granitic rocks from the complex zircons from Meissen Massif Central Bohemian Plutonic Complex (Czech monzonites, Saxony." Chemical Geology 156 : Republic): constraints on the chronology of 331 341. thermal and tectonic events along the O'Neill, J. R., Chappel, B.W. (1977). "Oxygen and Moldanubian Barrandian boundary." Comptes hydrogen isotope relations in the Berridale Rendus de l'Academie des Sciences, Paris 325 : batholith." Journal of the Geological Society of 19 26. London 133 : 559 571. Irber, W., Förster, H.J., Hecht, L., Möller, P., Oberc-Dziedzic, T., Pin, C., Kryza, R. (2005). "Early Morteani, G. (1997). "Experimental, Palaeozoic crustal melting in an extensional geochemical, mineralogical and O isotope setting: petrological and Sm Nd evidence from constraints on the late magmatic history of the the Izera granite gneisses, Polish Sudetes." Fichtelgebirge granites (Germany)." International Journal of Earth Sciences 94 : Geologische Rundschau 86 : S110 S124. 354 368. Kempe, U. (2003). "Precise electron microprobe age Pin, C., Duthou, J.-L. (1990a). "Sources of Hercynian determination in altered uraninite: granitoids from the French Massif Central: consequences on the intrusion age and the Interferences from Nd isotopes and metallogenic significance of the Kirchberg consequences for crustal evolution." Chemical
14 Geology 83 : 281 296. Rundschau 86 : 585 598. Pin, C. (1990b). "Variscan oceans, ages, origins and Talbot, J. Y., Martelet, G., Courrioux, G., Chen, Y., geodynamic implications inferred from Faure, M. (2004). "Emplacement in an geochemical and radiometric data." extensional setting of the Mont Lozère Borne Tectonophysics 177 : 215 227. granitic complex (SE France) inferred from Ries, A. C. (1979). "Variscan metamorphism and K comprehensive AMS, structural and gravity Ar dates in the Variscan fold belt of S Brittany studies." Journal of Structural Geology 26 : 11 and NW Spain." Journal of the Geological 28. Society of London 136 (1): 83 103. Todt, W. A. (1976). "Zirkon U/Pb Alter des Rolin, P., Stussi, J.-M. (1991). "Decrochements Malsburg Granits vom Süd Schwarzwald." intracrusteaux et intrusions granitiques Neues Jahrbuch für Mineralogie Monatshefte : carboniferes dans le Morvan (Massif Central 532 544. francais)." Bulletin Societe Geologique de Todt, W. A., Altenberger, U., von Raumer, J.F. France 162 : 123 130. (1995). "U Pb data on zircons for the thermal Schaltegger, U., Schneider, J.L., Maurin, J.-C., Corfu, peak of metamorphism in the Variscan F. (1996). "Precise U Pb chronometry of 345 Odenwald, Germany." Geologische Rundschau 340 Ma old magmatism related to syn 84 : 466 472. convergence extension in the Southern Vosges Turpin, L., Cuney, M., Friedrich, M., Bouchez, J.-L., (Central Variscan Belt)." Earth and Planetary Aubertin, M. (1990). "Meta igneous origin of Science Letters 144 : 403 419. Hercynian peraluminous granites in N.W. Schaltegger, U. (1997). "Magma pulses in the French Massif Central: implications for crustal Central Variscan Belt: episodic melt generation history reconstructions." Contributions to and emplacement during lithospheric thinning." Mineralogy and Petrology 104 : 163 172. Terra Nova 9: 242 245. van Hinsbergen, D. J. J., Hafkenscheid, E., Spakman, Schaltegger, U. (2000). "U Pb geochronology of the W., Meulenkamp, J.E., Wortel, R. (2005). Southern Black Forest Batholith (Central "Nappe stacking resulting from subduction of Variscan Belt): timing of exhumation and oceanic and continental lithosphere below granite emplacement." International Journal of Greece." Geology 33 (4): 325 328. Earth Sciences 88 : 814 828. Vellmer, C., Wedepohl, K.H. (1994). "Geochemical Scharbert, S. (1998). "Some geochronological data characterization and origin of granitoids from from the South Bohemian Pluton in Austria: a the South Bohemian Batholith in Lower critical review." Acta Universitatis Carolinae Austria." Contributions to Mineralogy and Geologica 42 (1): 114 118. Petrology 118 : 13 32. Schleicher, H. (1994). "Collision type granitic melts Vialette, Y. (1973). "Age des granites du Massif in the context of thrust tectonics and uplift Central." Bulletin Société Géologique de history (Triberg granite complex, Schwarzwald, France 7(3 4): 260 270. Germany)." Neues Jahrbuch für Mineralogie, Vialette, Y., Sabourdy, G. (1977). "Age et origine des Abhandlungen 166 (2): 211 237. granitoïdes du Mont Lozère dans le Massif Scotese, C. R. (2003). "Paleomap Project." Central français." Compte Rendu Sommaire des www.scotese.com . Seances : 127 129. Siebel, W. (1995(a)). "Anticorrelated Rb Sr and K Ar von Drach, V., Lippolt, H.J., Brewer, M.S. (1974). age discordances, Leuchtenberg granite, NE "Rb Sr Altersbestimmungen an Graniten des Bavaria, Germany." Contributions to Mineralogy Nordschwarzwalds." Neues Jahrbuch für and Petrology 120 (2): 197 211. Mineralogie, Abhandlungen 123 (1): 38 62. Siebel, W. (1995(b)). "Constraints on a Variscan von Quadt, A., Finger, F. (1991). "Geochronologische granite emplacement in north east Bavaria, Untersuchungen im österreichischen Teil des Germany: further clues from a petrogenic study Südböhmischen Batholiths: U Pb Datierungen of the Mitterteich granite." Geologische an Zirkonen, Monaziten und Xenotimen des Rundschau 84 : 384 398. Weinsberger Granits." Berichte der Deutschen Siebel, W., Trzebski, R., Stettner, G., Hecht. L., Mineralogischen Gesellschaft 3: 281. Casten, U., Höhndorf, A., Müller, P. (1997). Wendt, I., Wendt, J.I., Carl, C. (1989). "U/Pb whole "Granitoid magmatism of the NW Bohemian rock and mineral dating of the Falkenberg massif revealed: gravity data, composition, age granite in northeast Bavaria." Earth and relations and phase concept." Geologische Planetary Science Letters 94 : 236 244. Rundschau 86 : S45 S63. Wenzel, T., Mertz, D.F., Oberhänsli, R., Becker, T., Siebel, W., Chen, F., Satir, M. (2003). "Late Variscan Renne, P.R. (1997). "Age, geodynamic setting, magmatism revisited: new implications from and mantle enrichment processes of a K rich Pb evaporation zircon ages on the emplacement intrusion from the Meissen massif (northern of redwitzites and granites in NE Bavaria." Bohemian massif) and implications for related International Journal of Earth Sciences 92 : 36 occurerences from the mid European Her 53. cynian." Geologische Rundschau 86 : 556 570. Sinclair, A.J., Macquar J.C., Rouvier, H. (1993). "Re Wortel, M. J. R., Spakman, W. (2000). "Subduction evaluation of lead isotopic data, southern Massif and Slab Detachment in the Mediterranean Central, France." Mineralium Deposita 28 (2): Carpathian Region." Science 290 : 1910 1917. 122 128. Wortel, M. J. R., van Bergen, M.J., van de Zedde, Stanley, S.M. (1999). Earth System History , W.H. D.M.A., Spakman, W. (2003). "Continental Freeman Publishers. collision, slab detachment and K rich magma Tait, J. A., Bachtadse, V., Franke, W., Soffel, H.C. tism: central southern Italy as a type example." (1997). "Geodynamic evolution of the European EGS AGU EUG Joint Assembly, Abstracts Variscan fold belt: palaeomagnetic and from the meeting held in Nice, France, 6 11 geological constraints." Geologischen April 2003 abstract #11281 .
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