Relationships between intermediate and acidic rocks in orogenic granitoid suites: petrological, geochemical and isotopic (Sr, Nd, Pb) data from Capo Vaticano (southern Calabria, Italy)

('heroical Geologt,, 92 ( t 991 ) 153-176 Elsevier Science Publishers B.V., A m s t e r d a m

153

Relationships between intermediate and acidic rocks in orogenic granitoid suites: petrological, geochemical and isotopic (Sr, Nd, Pb ) data from Capo Vaticano (southern Calabria, Italy) A. Rottura a, A. Del Moro b, L. Pinarelli h, R. Petrini b, A. Peccerillo c, A. Caggianelli d G.M. Bargossi a and G. P i c c a r r e t a ~ Dipartimento di Scienze Mineralo~iche, Universttd di Bologna, 1-40126 Bolo,~na, lta/r u lstituto di Geocronologia e Geochimica Isotopica del ('. N. R., 1-56100 Pisa, lta/v c lstituto di Scienze della Terra, Univet~ita di Me~sina, 1-98160 Messina-Sant 'Agata, Italy d Dipartimento Geomineralogico, Universita di Bari, 1- 70 124 Bari, Italy ~ lstituto di Chimica Agraria, Universitb della Basilicata, 1-851 O0 Potenza, ltaly (Received February 16. 1990: revised and accepted September 15. 1990)

ABSTRACT Rottura, A., Del Moro, A., Pinarelli, L., Petrini, R., Peccerillo, A., Caggianelli, A., Bargossi, G.M. and Piccarreta, G., 1991. Relationships between intermediate and acidic rocks in orogenic granitoid suites: petrological, geochemical and isotopic (Sr, Nd, Pb) data from Capo Vaticano (southern Calabria, Italy). In: A. Peccerillo (Guest-Editor), Geochemistry of Granitoid Rocks. Chem. Geol., 92:153-176. Major, trace element and isotopic data are reported for Hercynian granodiorites and tonalites from Capo Vaticano, Calabria, with the aim of clarifying the relationships between acidic and intermediate lithologics in orogenic intrusive suites. These granodiorites (SiO2 = 70.5%-73.5%) are peraluminous, relatively depleted in Rb, U, Th, and Pb, and display a large variation in many geochemical and isotopic parameters. REE show fractionated, cross-cutting chondrite-normalizcd patterns with small but significant negative Eu anomalies. Initial (290 Ma) Sr and Nd, and present-day Pb isotope ratios are: (87Sr/S6Sr)29o=0.7105-0.7110; (143Nd/144Nd)29o---0.51175-0.51221; 2°6pb/2°4pb= i8.35-18.50: 2(~TPb/2°4pb= 15.64-15.76: 2°Spb/2°4pb-- 38.51-39.03. Pb isotope ratios determined for separated feldspars show similar 2¢)6pb/2°4pb and :~°Spb/2°apb and higher 2°7pb/2°4pb ratios compared to the present-day values for the whole rock. The tonalites (SiO2= 57.6%-67.3%) are typically calc-alkaline in composition and most of them are weakly peraluminous. They display large heterogeneities in trace-element abundances, REE patterns and Nd and Pb isotope ratios, both between and within individual intrusive units. Sr, Nd and Pb isotopic compositions display a range of values close to that of the associated granodiorites (SVSr/86Sr)29o= 0.7099-0.7111: (143Nd/]a4Nd) 2~o= 0.51185-0.51224: 2()"pb/2°4pb = 18.3118.56; 2°Tpb/2°apb = 15.65-15.72; 2°spb/2°4pb = 38.41-39.59. The obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage. Likewise, many petrological, geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process, such as crystal-liquid fractionation or assimilation- fractional crystallization (AFC), and point to a different genesis for the two rock types. An origin of the granodiorites by the mixing of two separate acidic melts, one of crustal anatectic origin and one probably deri,,ed from an intermediate magma by crystal/liquid fractionation or AFC, is suggested by the data presented. The tonalites appear to have been generated by interaction of a marie magma with crustal end-member( s ) with isotopic and geochemical signatures similar to those of the granodiorites. The large involvement of crustal material in the genesis of the Capo Vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks. However. a contribution from mantie components is also indicated by petrological and geochemical data, as well as by the occurrence of marie enclaves commonly present in the tonalites. Nevertheless, the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids.

0 0 0 9 - 2 5 4 1 / 9 1 / $ 0 3 . 5 0 © 1991 Elsevier Science Publishers B.V. All rights reserved.

154

1. Introduction The genesis and evolution of granitoid suites represent one of the most complex problems of igneous petrology and a range of genetic hypotheses, ranging from classical fractional crystallization to melt-restite unmixing, have been proposed. Recent geochemical and isotopic investigations have provided a wealth of data which have made it increasingly clear that the majority of granitoid suites actually result from interaction between mantle and crustal components (e.g., Allbgre and Ben Othman, 1980: DePaolo, 1981a; Pankhurst et al., 1988; Pickett and Wasserburg, 1989). However, the relative roles played by crustal and mantle material are still a matter of discussion. In some granitoid suites elemental and isotopic variations point to fractional crystallization processes accompanied by a moderate interaction with the crust (e.g., Del Moro et al., 1983: Beckinsale et al., 1985); while in other cases the contribution of the crustal material appears to be the dominant factor in the genesis of the granitoids (e.g., Frost and O'Nions, 1985" Downes and Duthou, 1988; Liew et al., 1989). In this context, the relationship between intermediate and acidic rocks associated in space and time in many intrusive orogenic complexes is of particular importance. In fact, while for the former a clear contribution from both mantle and crust is often obvious, the acidic rocks are more ambiguous and it is debated whether they derive from intermediate magmas by continuing AFC or fractional crystallization, or are generated by crustal anatexis. A particularly interesting area for investigating these problems is the Capo Vaticano promontory, where intermediate tonalites and acidic granodiorites of Hercynian age form a normally zoned intrusive body. In this paper we report major, trace element and isotopic

~. ROTTLTRAETAL. data for these rocks and discuss their possible genesis, focusing in particular on the problem of the relationship between acidic and intermediate magmas.

2. Geological setting The Capo Vaticano promontory (CVP) is located in southern Calabria and forms part of the so-called Calabrian Arc, an arcuate Alpine belt linking the Apennines and the Maghrebian chain of Sicily (Fig. 1 ). Along the Calabrian Arc, a segment of the Hercynian chain of SW Europe outcrops; it consists largely of Palaeozoic, and possibly Precambrian, basement terrains (very low grade to granulite-facies metamorphites) intruded by late-Hercynian granitoids, more or less overprinted by Alpine tectogenesis (e.g., Amodio Morelli et al., 1976: Scandone, 1982; Bouillin et al., 1986). The CVP forms an horst separated from the Serre massif by the NE-SW trending Mesima graben. It consists of strongly to weakly foliated calc-alkaline granitoids, intermediate to acidic in composition, emplaced in late-Hercynian times (Rottura et al., 1990). Tectonic overprints of Alpine or Apenninic age (Del Moro et al., 1986; Schenk, 1989) affected the granitoids, producing local mylonite bands discordant to the rock foliation, and the widespread rejuvenation of mineral ages ( K/Ar and R b / S r mica apparent ages in the range 267128 Ma, cf. Civetta et al., 1973; Del Moro et al., 1986; Laurenzi et al., 1986). The area studied is crossed by fault zones, some of which may have played an important role in the uplift of the plutonic complex. The WNW- and ENE-trending lineaments correspond to two important regional trends, also recognized offshore and related to wrench tectonics which affected the Central Mediterranean area since the Middle-Upper Miocene (Boccaletti et al., 1984 and references).

RELATI()NSHIPS BETWEENINTERMEDIATEAND ACIDICROCKSIN OROGENICGRANITOIDSUITES

155

N

7

Briatico

I-7-] 6 0

1 2 Krn

3

~a5

Parghelia

4 ii

CapoVaticano

~ • S, M a r i a

...

:.;I:i
v ~. ......; /VVVv vv VV VV VV VV V V VVvVvVvV v V V( VVV

3

...... ...>

[ 751 2

•

.

TYRRHENIA~ SEA

I

V

!:7

:;(: i

.

Capo

L

_

~,

_

_

_

t+-%+/Td/ / ) _o ~,

T o r r e di I o p p o l o

Nicotera Marir

./7

F ......

VV VXI V V V V

l~

Km

0

10

20

~

%

V--~s HGM LGM

Maghrebide

Fig. 1. Geological sketch map of the Capo Vaticano promontory showing the distribution of the granitoid units: l = kinzigitic gneisses; 2 = loppolo tonalites; 3 = S. Maria quartz diorites and tonalites; 4 = Briatico tonalites; 5 = Capo Vaticano (sensu stricto ) tonalites and (a) granodiorites; 6 = two-mica porphyritic granodiorites; 7= uppermost M iocene-Quaternary deposits: ,~= faults. Inset shows location of the study area in the Calabrian Arc: S = sediments: G=granitoids: L(;M= lowto medium-grade metamorphites; H G M = high-grade metamorphites.

3. Granitoid types and field occurrence

The Capo Vaticano granitoids outcrop discontinuously beneath the uppermost Miocene-Quaternary deposits, over an area of about 270 km 2 (Fig. 1). Towards the northwest, they are bordered by high-grade metapelites (kinzigitic gneisses) which represent the upper part of the Serre lower crustal section (Maccarrone et al., 1983; Schenk, 1984). The granitoids consist of prevailing (65 vol.%) biotite-dominated tonalites, and subordinate ( 35 vol.%) two-mica + Al-silicate bearing porphyritic granodiorites. The tonalites are strongly foliated in the northern and southern

part of the promontory, and different facies have been distinguished: the Briatico, S. Maria and Ioppolo tonalites (Rottura et al., 1986, 1990). Weakly foliated tonalites (Capo Vaticano-type ) intruded by the granodiorites, make up the core of the promontory. Minor cummingtonite-hornblende, and locally garnetbearing, quartz diorites occur in the S. MariaIoppolo area (Clarke et al., 1990). The tonalites typically contain biotite-hornblende-bearing microgranitoid enclaves of quartz dioritic to tonalitic composition. In the granodiorites, in contrast, only ram- to cm-sized metasedimentary enclaves occur, in addition to xenoliths of the host intrusives. Aplite and pegma-

156

rite dikes crosscut all the granitoids; synplutonic basic dikes are lacking. The granitoids were emplaced during late- to post- main Hercynian deformation events. In particular, the strongly foliated tonalites and the quartz diorites intruded earlier into the kinzigitic gneisses (biotite-garnet-sillimanite migmatitic paragneisses), inducing some partial melting in the country rocks (Caggianelli et al., 1991; Rottura et al., 1990). An emplacement at P conditions ranging between 3.5 and 5.5 kbar can be inferred, on the basis of the PT - t path of the Serre lower crustal section (Schenk, 1989), field relations, and the total A1 content of hornblende from the tonalites (Rottura et al.. 1990). The weakly foliated tonalites and the granodiorites were intruded later in a brittle domain. An approximate estimate of the age of intrusion is furnished by a U / P b zircon age of 295 + 2 Ma on a tonalite from the Serre (Schenk, 1980). Moreover, tonalite samples from CV plot along linear trends in the 87Sr/S6Sr vs. 87Rb/S6Sr diagram, giving an age around 285 Ma (Laurenzi et al., 1986). As to foliation of the Capo Vaticano granitoids, a magmatic origin is favoured by microstructural and mesostructural evidence (e.g.. Paterson et al., 1989), although the presence of an episode of regional deformation during emplacement cannot be excluded.

¢. R( ) T T U R A IZT AL.

composition as follows: AlVa=0.53-0.65; AI Iv = 2.42-2.50 atoms p.f.u.; F e J (Fet + Mg) =0.49-0.55. The amphiboles are magnesiohornblendes tending to tschermakitic hornblendes. They have total A1 contents of about 1.92 atoms p.f.u., while A1v~ and Ti are in the range 0.5-0.7 and 0.10-0.14 atoms p.f.u., respectively. KD values for Fe-Mg exchange between coexisting hornblende and biotite are 1.04, on the average (Rottura et al., 1990). The granodiorites (modal classification in Fig. 2) are porphyritic and show some preferred orientation of the K-feldspar megacrysts. They consist of quartz, euhedral plagioclase (both unzoned and oscillatory or normally zoned), perthitic microcline, redbrown biotite (8 vol.%, on the average) and muscovite (3 vol.%). Minor sillimanite (mainly fibrolite needles in muscovite) and sporadic, poikilitic Fe-Mn-rich garnet are also present. Apatite, zircon, monazite (identified by electron microprobe) and ilmenite are c o m m o n accessory phases. Small (up to 2 cm ) micaceous clots, often with a regular polygonal shape, characteristically occur in the granodioQ

4. Petrographic characteristics and mineralogy The tonalites consist of early-crystallized zoned plagioclase ( A n 5 6 _ 3 s ) , often associated in synneusis and forming cumulus-like clots, biotite (21 vol.%, on the average) with or without hornblende ( < 5 vol.% present in 13% to 60% of the rocks in the different facies; Rottura et al., 1986) and scarce interstitial microcline. Apatite, allanite (idiomorphic or rimmed by colourless magmatic epidote), ilmenite, zircon and sphene are the accessory phases. Biotites from the tonalites have an A1 and Fe

A

P

Fig. 2. QAP modal diagram for the Capo Vaticano twomica porphyritic granodioriles ( horizontal lines: n = 30) and biotite + hornblende tonalites (oblique lines; n = 94, after Rottura et al., 1986). a , h=calc-alkaline trondhjcmitic (low-K) and granodioritic ( m e d i u m - K ) trends, respectively, after Lameyre and Bowden ( 1982 ).

RELA'FIONSHIPS BETWEEN INTERMEDIATEAND ACIDIC ROCKS IN OROGENIC GR&N1TOIDS( IIIES

l 57

scent on the cotectic plagioclase+ quartz surface, prior to crystallization of K-feldspar. This is consistent with experimental phase relations and crystallization kinetics in model and natural granite systems (e.g., Swanson, 1977; Winkler, 1979; Winkler and Schultes, 1982 ). Plagioclase core compositions (G.M. Bargossi and A. Rottura, unpublished data) in granodiorites are typically An3v 31 (An43 in sample PA28), while that of rims ranges be-

rites. These consist of diablastic aggregates of muscovite (with some relicts of fibrolite inclusions) and green-brown biotite, with minor plagioclase and subhedral apatite hosting numerous inclusions. The occurrence in the granodiorites of euhedral plagioclase, biotite and quartz (flquartz) crystals as inclusions in subhedral to euhedral K-feldspar megacrysts, testifies to an early crystallization along a liquid line of deTABLE I

Major, trace and rare earth element abundances of selected samples from the Capo Vaticano two-mica porphyritic granodiorites PA21 SiO: TiO2 AI20~ Fe20~ MnO MgO CaO Na20 K20 P2Os L.O.I. A/CNK ~ V Rb Sr Y Zr Nb Ba

68.30 0.27 17.30 2.45 0.09 0.61 1.87 3.63 4.64 0.18 0.66 1.21 15 119 303 16 132 11 1291

PA44 70.49 0.40 15.26 2.96 0.09 0.86 2.80 3.29 3.33 0.07 0.44 1.09 24 80 353 20 211 12 1386

PA28 70.65 0.30 15.57 2.36 0.09 0.64 2.12 3.44 3.98 0.16 0.71 1.13 17 97 357 15 166 9 1689

U Th Pb

0.5 1.4 10

0.8 2.4 12

1.1 1.4 12

La Ce Nd Sm Eu Gd Dy Er Yb Lu

15 41 26 7.7 1.7 7.5 7.1 3.5 2.7 0.44

21 50 22 5.2 1.6 4.6 4.1 2.1 1.8 0.31

12 36 22 6.1 1.6 5.9 5.2 2.7 2.5 0.45

CVl4 70.83 0.31 15.59 2,46 0.07 0.91 1,76 3.06 3.40 0.23 1.38 1.32 13 105 256 15 135 13 1062 n.d, n.d. n.d. 43 90 39 7.1 1.3 6.0 4.0 1.7 1.2 0.2

PA3 70.87 0.35 15.65 2.76 0.09 0.76 2.62 3.79 2.26 0.16 0.69 1.16 22 51 282 17 166 9 596

CV85-16 70.95 0.40 15.22 3.07 0.09 0.97 2.60 3.42 2.36 0.08 0.83 1.18

89 331 24 247 18 861

CV40 71.15 0.40 14.82 2.80 0.07 1.19 2.79 3.43 2.40 0.17 0.78 1.12 28 65 342 20 198 10 893

1.3 5.6 12

1.1 9.0 10

n.d. n.d. n.d.

29 67 32 7.3 1.7 6.3 5.6 2.7 2.2 0.35

73 145 57 11.1 1.7 7.0 3.9 1,5 1.4 0.22

64 133 58 10.5 1,7 8.9 6.1 2.8 2,2 0.41

PAl0 72.06 0.36 14.26 2.65 0.09 0.83 2.48 3.14 3.35 0.16 0.62 1.07 28 56 298 20 167 7 1388 1.2 20.9 17

PAl3 72.33 0.27 15.07 2.12 0.09 0.51 1.66 3.34 3.84 0.17 0.60 1.18 13 99 218 18 134 14 619 1.2 9.6 9

76 54 151 112 56 45 9.2 7.2 1.8 1.8 6.8 5.4 4.0 2.9 2.0 1.3 1.6 1.0 0.24 0.20

CV85-15 72.39 0.28 15.35 2.04 0.09 0.39 1.68 3.21 3.56 0.12 0.9(/ 1.25

114 251 20 126 10 946

PAl2 73.07 1/.28 14.28 2.35 0.09 0.57 1.90 3.25 3.45 0.11 1"/.64 1.14 17 72 260 17 139 9 899

PA27 73.18 (I.21 14.08 1.91 0.09 0.51 1.66 3.08 4.39 0.07 (I.82 1.09 14 I11 205 33 119 14 894

1.4 6.1 10

1.5 9.9 16

1,3 10.6 14

46 92 35 7.2 1,3 4.8 3.2 1.4 1,3 0.23

36 77 32 7.2 1,6 6.6 6.4 3.3 2.9 0.47

38 81 33 6.6 1.6 59 43 2,1 1.8 0.31

a = mol. A1203/(CaO + Na20 + K20 ). Total Fe as Fe203; n.d. = n o t determined. Major elements in wt.%; trace elements in ppm. REE data for samples CV85-15 and CV85-16 are from Rottura et al. ( 1990 ).

~,. ROTTURA ET AL.

158

tween An27 and An17. Reverse zoning was sometimes observed. Plagioclases enclosed in K-feldspar are, characteristically, bordered by a late-stage albite rim. Zoned plagioclase (An32_20) in very felsic rock samples, and large K-feldspars enclosing ovoids of earlier K-feldspars, have been observed (Monni, 1990). Similar characteristics have been considered as suggestive of magma mixing (e.g., Hibbard, 1981).

Biotites from the granodiorites have compositions characterized by A1 (AlVa=0.60 0.91; A l l y : 2 . 5 0 - 2 . 6 5 atoms p.f.u.) and Fe,/ ( F e , + M g ) (0,60-0.67) values higher than those of the tonalites, and appreciable Ti contents (0.30 atoms p.f.u., on average). Muscovite chemistry is characterized by ( 1 ) variable Ti contents ( < 0.20, mainly in the range 0.030.10 atoms p.f.u, based on 22 oxygens), and (2) low phengitic and biotitic substitutions

TABLE 11 Major, lrace and rare earth element abundances of selected samples from the Capo Vaticano biolite _+hornblende lonalites (major elements in wt%, trace elements in p p m ) Briatico Unit

SiO2 TiO2

A1203 Fe203 MnO MgO Ca() Na20 K20 P205 L.O.I. A/CN K V Rb Sr Y Zr Nb Ba U Th Pb La Ce Nd Sm Eu Gd Tb Dy Er Yb Lu

Capo Vaticano Unit

CV222

CV 185

CV43

CV20

CV85-1

CV240

CV30

CV22

CV25

CV33

VC37

57.64 0.93 18.06 6.66 0.11 4.28 6.07 2.30 2.44 0.30 1.21 1.04 128 71 302 31 148 13 705

59.59 0.96 17.41 6.71 0.09 3.40 4.94 2.73 2.68 0.23 1.26 1.06 119 83 302 9 198 19 841

61.14 0.74 17.88 5.39 0.11 2.51 5.54 2.82 2.23 0.29 1.35 1.04 95 93 333 22 164 20 709 18.6 2.1 25 60 122 53 9.9 1.4 8.1

62.95 0.78 16.86 5.74 0.08 3.15 4.58 2.28 2.50 0.19 0.88 1.13 91 73 299 9 173 16 776 10.6 2.8 31 55 108 44 6.5 1.5

61.61 0.82 16.43 6.28 0.09 3.04 4.84 2.61 2.43 0.24 1.61 1.04 118 83 255 27 167 15 765 12.0 3.0 25 21 46 21 5.2 1.4

62.25 0.73 16.91 5.68 0.08 2.39 4.86 2.82 2.43 0.20 1.65 1.05 104 84 271 26 156 14 699 13.9 2.8 25 44 85 38 7.1 1.3 5.6

64.34 0.67 16.27 5.15 0.09 2.23 4.46 2.95 2.72 0.18 0.93 1.02 71 89 295 28 170 11 842 14.0 2.3 27 69 136 53 8.0 1.5 6.8

67.26 0.60 15.40 4.64 0.09 1.78 3.32 2.88 2.90 0.16 0.97 1. I 1 57 88 285 26 214 15 802

74 103 39 8.3 1.4

60.48 0.84 17.07 6.27 0.14 3.36 5.53 2.52 2.40 0.24 1.15 1.01 114 70 283 23 171 14 739 23.0 2.3 27 31 69 35 8.0 1.8 8.1

64.47 0.70 15.95 5.15 0.08 2.41 4.47 2.88 2.17 0.19 1.52 1.05 86 76 276 15 157 12 684

43 76 45 12.3 1.6

60.40 0.78 17.72 5.58 0.12 2.61 5.89 2.91 2.17 0,19 1,62 0.99 106 89 340 26 194 15 722 22.1 2.5 23 71 139 61 11.1 1.8 8.6

1.5

0.6 4.4 1.8 1.4 0.25

7.1 3.4 2.6 0.49

4.7 1.8 1.3 0.22

3.6 1.6 1.3 0.20

3.8 1.9 1.4 0.31

3.3 0.39

1,2 n.d.

0.5

0.9 0.17

1.0

3.1 0.45

13 28 13 3.2 1.4 0.5

1.9 0.31

Total Fe as Fe203; n . d . = not detected. REE data for samples CV222, CV43, CV85-1, CV240, CV30, CV25, CV33, CV37, CV852, CV302, CV85-9, CV85-6 and CV85-8 are from Rottura et al. (1990).

RELATI()NSHIPS BETWEEN INTERMEDIATEAND ACIDIC ROCKS IN OROGENIC GRANITOII) SUITES

159

1981 ). Zircon crystals are similar in typology to zircons from aluminous granites (Rottura et al., 1990).

(octahedral occupancy and Si, in the range 4.03-4.08 and 6.10-6.26 atoms p.f.u., respectively). On the whole, these data are similar to those reported for biotites and muscovites from two-mica+Al-silicate bearing granites (e.g., Clarke, 1981; Miller et al., 1981; Monier and Robert, 1986; Rottura et al., 1990). Garnet shows an Alm76 PYs SpI4 Andr2 composition, similar to that of typical plutonic igneous garnets (e.g., Miller and Stoddard,

5. Whole-rock geochemistry

5.1. Sampling and experimental techniques Our sampling focused on unsheared rock types. The analyzed samples show only minor

S. Maria Unit

loppolo Unit

('V85-2

CV85-3

CV302

CV85-9

CV85-8

CV85-6

CV85-13

CV405

CV85-10

CV332

CV319

58.15 1.01 17.63 7.28 0.13 3.59 5.70 2.71 2.40 0.26 1.15 1.01 140 89 279 35 203 14 954

58.77 0.82 19.41 5.08 0.11 2.62 6.92 3.30 1.84 0.21 0.91 0.96 99 61 370 25 191

60.12 0.85 17.74 6.19 0.13 2.87 5.87 2.80 1.98 0.21 1.25 1.02 119 72 296 39 193 15 692 15.5 2.0 34 15 40 27 7.5 1.5 7.9

60.51 0.83 18.14 5.49 0.11 2.60 5.77 3.09 1.92 0.29 1.25 1.03 112 66 355 19 138 14 731

60.95 0.84 16.94 6.24 0.13 2.92 5.76 2.74 2.11 0.26 1.13 0.98 122 77 278 41 182 14 827

62.14 0.72 17.41 5.37 0.14 2.72 5.63 2.79 1.59 0.24 1.25 1.05 108 68 311 31 180 18 666

59.53 0.93 17.42 6.23 O. 13 3.10 6.10 2.63 2.19 0.32 1.37 0.98 125 81 328 28 186 15 762

59.40 0.84 17.83 6.07 0.08 3.30 5.99 2.65 2.07 0.19 1.48 1.02 121 72 330 32 220 15 708 21.6 2.6 27

61.86 0.70 17.27 4.84 O. 12 2.53 4.86 3.12 1.94 0.31 2.45 1.07 105 93 295 20 183 17 754

64.54 0.62 16.21 5.16 0.07 2.80 4.92 2.79 1.84 0.14 0.91 1.04 115 64 303 27 146 9 555

64.88 0.68 16.48 4.84 0.09 2.13 4.43 2.92 2.41 0.17 0.78 1.07 80 84 297 28 196 14 642 16.3 2.6 27 41 76 37 6.6 1.5

666 7 1.6 15 21 46 23 4.7 1.5 4.6

8 22 15 5.1 1.4 4.8

11 30 21 5.4 1.4 5.7

15 36 23 5.7 1.3 5.9

0.8 3.8 1.9 1.5 0.32

7.6 3.6 2.7 0.43

4.7 2.3 2.0 0.29

5.4 2.8 2.4 0.41

5.3 2.3 1.5 0.25

2.1 0.26

160

alteration effects, similar to those commonly described from granitic rocks, a n d / o r microscopic evidence of solid-state mineral deformation (e.g., undulatory extinction, kinking, fracturing) which are widespread throughout the Calabrian Arc. Only the tonalite sample CV85-9 is moderately sheared. Major- and trace-element analyses were performed by X R F procedures (described by Rottura, 1985); MgO and Na20 were determined by AAS and loss on ignition (LOI) gravimetrically. REE, U and Th concentrations were determined by inductively coupled plasma (ICP) spectrometry, and have uncertainties of +_5% ( _+ 16% for Lu) and +_ 10%, respectively; Pb concentrations were determined by AAS and have uncertainties of _+7%. Major, trace and REE concentrations are listed in Tables 1 and 2. Rb, Sr and Pb isotopic data were acquired on a TH5 Varian MAT single collector mass spectrometer. Rb and Sr concentrations were obtained by conventional I.D. analyses; the uncertainty in the STRb/S6Sr ratio is + 1.5%. Replicate analyses of NBS 987 SrCO3 standard over a period of two years gave a mean SVSr/86Sr ratio of 0.71028 _+5 (2a, n = 23 ). The Pb isotopic composition was determined following the method described in Pinarelli et al. (1989). Total procedure blanks were 3-6 ng. Lead isotope ratios were corrected for a mass fractionation of 0.13% per mass unit based on repeated analyses of the NBS 981 c o m m o n Pb standard. The reproducibility (95% C.L.) is estimated to be +0.1% for the 2°7pb/2°4pb and 2°6pb/2°apb ratios and +2% for the 2°Spb/2°4pb ratio. Average values obtained for the NBS 981 standard are: 2°6pb/2°4pb= 16.899, 2°7pb/2°4pb= 15.443 and 2°8pb/2°4pb--36.541 ( n = 11). Nd isotopic compositions were determined using an ISOMASS 54E mass spectrometer. Data acquisition and reduction followed the procedures of Ludwig (1987). The obtained 14~Nd/144Ndratios were normalized to the La Jolla standard value--0.51186. The reported

,\. ROTT{ !RA ET AI..

uncertainties represent in-run statistics at 95% C.L. The 147Sm/144Nd ratio used for calculating age-corrected Nd values has an uncertainty of +_7% on the basis of quoted errors for ICP determinations of Sm and Nd contents.

5.2. Major, trace and rare earth element data The analyzed rocks range in composition from intermediate ( 8 i 0 2 = 5 6 . 7 % ) to acidic (SIO2=73.6%). Most of the samples are fairly peraluminous with A / C N K (alumina saturation index see Table 1), increasing towards acidic compositions; a few metaluminous samples occur among the tonalites (Fig. 3 ). On AFM, calc-alkali ratio-silica, and N a 2 0 - K 2 0 CaO diagrams the rocks follow calc-alkaline trends. The major elements generally display regular variation trends on Harker diagrams. However, large scattering is observed for K20 and, especially, Na20. In addition, the granodiorites and tonalites seem to define distinct trends with different slopes on an A1203 vs. SiO2 diagram (Fig. 4). The trace elements show very complex variation patterns. A large scattering of values is generally observed in all rock types and also within single intrusive masses. Rb ranges from 61 to 93 p p m in tonalites and does not display 1.4 AJCNK &

1.3 1.2

•

,~

•

AA

AA

1.1 1,0

I:]"O~O ~ 0

0.9 55

zx

S102

[]

60

65

70

75

Fig. 3. Molar AI203/(CaO-I-Na20-FK2() ) vs. SiO2 for Capo Vaticano granitoids. Solid triangles = two-mica porphyritic granodiorites; d i a m o n d s = Briatico tonalites; triangles=Capo Vaticano (sensu stricto) tonalites; circles=S. Maria tonalite; squares=Ioppolo tonalites. Tonalite data are partially from Rottura el al. (1990).

R E L A T I O N S H I P S B E T W E E N I N T E R M E D I A T E ,AND A C I D I C R O C K S 1N O R O G E N I C G R . a . N I T O I D S U I T E S

12

l0 1

20 AI203

Ti02

1,0

o

19

O

0

o

08

~

o

06

"'~£3

0

°°

18 17 z~

O

0

16

A

•

,#

AA

•

15

,=%

04 14 02 55

i

i

L

60

65

70

,

75

13 55

i

i

i

60

65

70

75

4 K20

N ~

0

0

O

d~

O

A

o

[] •

A A

Z~

o

t 0 °

&

0

o

[] 0

2 55

i

L

60

65

i

1

70

75

120

55

[]

0

i

i

i

60

65

70

75

70

75

400 Sr

Rb •

0

• &

oo

I O0

• 0

0

eon~3~O &

80

g¢. 0o

o÷+~ 0

0

60

°

+,

6~.o

"~%%

•

300

O

•.

A

A&

0

o~)

A

°" &

[]

"*&

A

O

[]

0

40

' 60

55

i

'

70

65

75

300

200 55

i

i

6O

65

1800 Zr

Ba

1600 1400

200

o

8

°°

"

. o ~;o%o °o

A

•

t

1200

•,

o

1000

o

0

&A

800 •

0 o

100 55

•4L

o

i

i

i

60

65

70

Si02

0

.~. b0

600

n

75

400 55

o

' 60

' 65

-'~ o

70

Si02

Fig. 4. Selected Harker diagrams for major and trace elements in Capo Vaticano granitoids. Symbols as in Fig. 3.

75

162

A. R ( ) T T U R A

120 - -

400 Sr

Rb

0

• oo

100

~ h-~~~,. o 80

*•

0 0

o

[] °

•

(~0

.

o

~;

•

D•

$~"- -

-~0

0

•

• iX

•

•

300

0

60

40 - - ' 400

ET AI

o

ti

•

•

Bi

I

I

I

I

600

800

1000

1200

h

,

L

I

1400

1600

Ba

1800

200 ' 400

1

I

600

800

It

1

I

I

i

1000

1200

1400

1600

t80o

30

1.6

Th

Eu/Eu °

r = 0.83

1,4 o

20

1,2 1.0

o

A A

0

0,8 0,6 0.4 55

[]

0 0 •

A

0° •

60

[]

A

D A

• • •

~

65

10

•

ii

0

Ii

o

70

A .

SiO2

75

50

1O0

150

200

Fig. 5. Ba vs. Rb and Sr, Eu/Eu* vs. SiO2 and Ce vs. Th plots for the Capo Vaticano granitoids. (Eu* is the expected gu concentration obtained by interpolating between Sm and Gd as though there were no anomaly. ) Symbols as in Fig. 3. In the T h - C e plot, the linear fit for the two-mica porphyritic granodiorites is shown.

any significant trend with silica; in granodiorites, Rb abundances vary more widely (from 51 to 130 ppm), but in general the observed abundances are somewhat lower than those typically found in Phanerozoic orogenic granites (e.g., Pearce et al., 1984). Sr ranges from 238 to 370 ppm in tonalites and, although scattered, shows a negative correlation trend with silica: the granodiorites again show a larger variation in Sr (205-390 ppm), but in this case a steep negative correlation trend with silica is evident (Fig. 4). The same behaviour is observed to some extent for Ba and Zr. It is worth noting that, in some of the granodiorites, Ba and Sr show high values which are uncommon in acidic rocks. Interelemental variation diagrams (Fig. 5) generally show a large scattering even if the single intrusive masses are considered separately; however, a poorly defined positive correlation between Ba and Sr and a well-defined

positive trend of Ce vs. Th can be recognized in the granodiorites. Rb vs. Ba and Sr plots indicate two distinct groups of granodiorites, each displaying different degrees of enrichment in Rb and internal positive correlations of Rb vs. Ba. REE patterns are reported in Figs. 6 and 7. The tonalites show extremely variable absolute abundances and fractionation of LREE (Lan/Smn=0.9-4.7), even within individual bodies; the Ioppolo and S. Maria rocks are less LREE-enriched than the Briatico and Capo Vaticano types. In contrast, the HREE are almost invariably negatively fractionated with Tb (Gd) n/Ybn = 1.1-3.8. Significant negative Eu anomalies are observed in most samples, with Eu/Eu* (Eu* is the value obtained by interpolating between Sm and Gd; see Fig. 5) ranging from unity to 0.5. One sample has a positive Eu spike with E u / E u * = 1.4. There is no significant variation of Eu/Eu* with silica

RELATIONSHIPS BETWEEN INTERMEDIATE AND ACIDIC ROCKS IN OROGENIC GRANITOID SUITES

163

TONALITES

Briatico

Capo

100

~.\

Vaticano

-=

10 • CV 25 o CV 22 CV 30

• CV43 • CV 185

o CV 222 • CV 20

• CV 37

.i-, EM

tO J~ cJ

La Ce Nd S~n 'GdT'bDy E'r

u O

Yb Lu

S. M a r i a

ev

Eu L a C e Nd Sm ' G d T b D V I:'r Y b L u

Ioppolo

e\

100

c~_-o-

10 • CV 8 5 - 3 o CV 3 0 2 • CV 8 5 - 6

EM L a C e Nd Sm ' G d T b O y

• CV 319

o CV 3 3 2 CV 405

Er

YbLu

La6e

Eu Nd Sm 'G¢ITi:~I~ E'r Yb Lu

Fig. 6. Chondrite-normalized REE patterns (Haskin et al., 1968). For the sake of clarity, the patterns of four samples only are reported for the Briatico tonalites. (Fig. 5 ). It is worth noting that significant negative Eu-anomalies are rarely found in typical intermediate calc-alkaline rocks (e.g., Gill, 1981). The granodiorites show more homogeneous abundances and fractionation of REE than tonalites. The patterns are always fractionated for both LREE and H R E E with negative Eu-

anomalies; the only exceptions are samples PA21 and PA28 which display flat LREE patterns. Figure 8 reports hygromagmatophile element patterns for average granodiorites and tonalites from Capo Vaticano, and for representative intermediate intrusive and extrusive rocks from the Andes. It is interesting that

164

A. ROTTURA ET A[

GRANODIORITES + A. •*t100

100 -~k ••

~• " ol e . _ ~

A. " A

2

.m

A

"0 tO tO "~

lk &

10

0

10

I

0

•

PA 10

+

CV

A +

CV 40 PA 12 PA 3

A •

PA 44 PA 2 8

A • • o •

PA CV CV PA PA

o

t

I

I

o

1

I

8 5 - 16 13 8 5 - 15 14 27 21

Eu I

o

Eu

I

I

La Ce Nd'Sm IGd

r

I

I

Dy Er Yb Lu

I

1

I

i

I

La Ce Nd Sm iGd

I

1

D¥ Er Yb Lu

Fig. 7. C h o n d r i t e - n o r m a l i z e d R E E patterns for the two-mica porphyritic granodiorites. For the sake of clarity, the patterns are reported as two separate plots.

granodiorites and tonalites have strikingly similar hygromagmatophile element patterns. These show many similarities with respect to those of the Andean rocks which, however, have a positive or no Sr anomaly, unlike the Capo Vaticano intrusives which display a distinct relative depletion in Sr.

0oF

• ° °.

•

100

50

6. Sr, Nd and Pb isotope data = iI

- °,

E Capo

0 0

ev

1

i r-

~ e,,e

i

~_

Vaticano

tonalltea granodiorltes

- South

e-j I~ RbBaTh

Andean

America Andealte$ tonalite

L

L

L

U

K TaNbLaCeSrNd

L

;

i

I

I

,"

•

,,'" k

b

~

I

I

P HfZrSmTi

h

I

I

Tb

Y

I

Fig. 8. Primordial mantle-normalized trace-element distributions for the Capo Vaticano granitoids, in comparison with a Tertiary Andean tonalite (Lopez-Escobar et al., 1979 ) and average South America andesites (Bailey, 1981 ; Ewart, 1982). Normalizing values from Wood et al., 1979.

Sr, Nd and Pb isotopic data for the analyzed samples are listed in Tables 3-5. In addition to these, samples analyzed by Rottura et al. (1990) for Sr and Nd will also be considered. The relationship of Sr isotope ratios vs. 87Rb/86Sr is reported in Fig. 9. It can be noticed that the Capo Vaticano rocks do not plot along a single isochron. This points to either differences in the initial Sr isotopic compositions or to post-crystallization changes in the isotopic signatures. In details, the tonalite samples plot along two subparallel bands which project towards different initial Sr isotope ratios. The granodiorites show larger variations

RELATIONSHIPS BETWEEN INTERMEDIATE AND ACIDIC ROCKS IN OROGENIC GR~NITOID SUITES

165

TABLE 3

Rb-Sr analytical data for Capo Vaticano granitoids Sample

Rb

Sr

(ppm)

(ppm)

STRb/S~'Sr

STRb/S~Sr

(STRb/S~Sr) ~,,~ll

~o

(_+2a)

Two-mica porphyritic granodiorites: PA21 PAl3 PA27 CV85-/5 a ('V85-16 ~' PA3 PA28 PA44 P~10 P~12

130 105 114 113 89 56 105 85 65 79

297 209 189 257 331 280 364 343 314 256

1.266 1.459 1.743 1.279 0.776 0.574 0.837 0.720 0.604 0.890

0.71613+- 6 0.71674-+ 17 0.71770_+ 6 0.71617_+23 0.71420 _+27 0.71328_+ 14 0.71437_+ 7 0.71377_+ 8 0 . 7 1 3 2 6 _+ 6 0.71415_+ 11

0.7109 0.7107 0.7105 0.7109 0.7110 0.7109 0.7109 0.7108 0.7108 0.7105

95.9 93.2 90.2 95.7 97.2 96.0 96.0 94.4 93.9 89.8

332 315 305

0.757 0.842 0.805

0.71357_+ 8 0.71390 -+ 31 0.71368-+ 9

0.7104 0.7104 0.7104

89.4 89.1 88.1

74 82 87

289 283 271

0.745 0.837 0.924

0.71357-+ 8 0.71410-+ 6 0.71404_+ 6

0.7105 0.7106 0.7102

90.1 92.2 86.3

92 67 75 64 80

289 305 286 345 280

0.919 0.639 0.764 0.539 0.831

0.71371 _+ 35 0.71278+_28 0.71315 -+ 21 0 . 7 1 3 3 5 ± 19 0.71340 +_ 9

0.7099 0.7101 0.7100 0.7111 0.7099

81.9 85.1 83.0 99.1 82.7

86 76 70

273 315 346

0.915 0.696 0.586

0.71368+_21 0.71289_+21 0.71242 _+22

0.7099 0.7100 0.7100

81.7 83.3 83.1

Biotite + hornblende tonalites: Briatico ('V43 ( "V85- I ('V240

87 92 85

(ap(~ I aticano (sensu stricto) ('V33 ('V25 ('V37

S :llaria CV85-2 ('V85-6 " ('V85-8 ('V85-9 ('V319

lopp, do ('V85-10 CV85-I3 CV405 ' R o l t u r a el al. ( 1 9 9 0 ) .

of the R b / S r ratios, allowing two groups of rocks to be distinguished, as indicated in Fig. 5. If these two groups are considered separately, a good linear correlation can be seen for the high R b / S r samples, giving an age of 231 + 3 2 Ma (initial isotopic ratio= 0.7120 + 7), that approximates the age (234 Ma) obtained on the garnet-sillimanite-rich restites from the Serre basement by Caggianelli et al. ( 1991 ) and appears to be related to a hydrothermal event. The low R b / S r granodiorites, in contrast, define a trend roughly

parallel to those of the tonalites pointing to an age of 277 + 32 Ma. A similar result (283 _+ 10 Ma) is obtained if all the granodiorites are considered as a single group. Taking into account the age values quoted in the literature (see Sect. 3 ), 290 Ma can be considered a value approximating the age of intrusion of the Capo Vaticano granitoids. The calculated initial Sr isotopic ratios of the granodiorites range from 0.7105 to 0.7110, whereas those of the tonalites range from 0.7099 to 0.7106, with one sheared sample from S. Maria displaying a Sr

166

A ROTTI;RA ET AL.

TABLE 4

S m - N d analytical data for Capo Vaticano granitoids Sample

Sm

Nd

143Nd/144Nd

( ppm )

( ppm )

+- 2~7

( 143Nd/144Nd )290

~Na2~II

26.0 33.0 35.2 56.8 32.0 23.0

0.51210 +- 4 0.51218+_3 0.51245-+.2 0.51218-+.4 0.51214_+ 5 0.51215±3

0.51175 0.51194 0.51221 0.51195 0.51187 0.51187

- 10.1 -6.3 - 1.2 -6.2 --7.8 -7.6

44.0

0.51203 ± 3

0.51185

-8.0

8.0

53.0

0.51211 +- 3

0.51193

-6.5

5.1

14.9

0.51266"+.2

0.51224

-0.3

5.4

21.5

0.51223+_3

O.51192

-6.5

Two-mica porphyritic granodiorites: PA21 7.7 PA27 6.6 CV85-15 a 7.2 CV85-16 =' 11.0 PA3 7.3 PA44 5.3 Biotite +- hornblende tonalites:

Briattco CV240

6.5

('apo Vaticano (sensu stricto) CV25

S. Maria CV85-6 ~

Iopp~ do CV405 ~' Rottura et al. (1990).

IO-

./

0"716i 87Sr 86Sr

L 0"714I 0.712

F

f/ //

/

/

/

~

~

5

\ 2go

0

\

~'Nd

O

\ N

E3

[3

-15

0.710 0.0

\~,

.... -40

0.5

1.0

87Rb

, .... 0

, . . . . . . . . . 40 80 200

, .... ! 20

, 160

.... 200

'SSr

86Sr

Fig. 9. R b - S r isochron diagram for Capo Vaticano granitoids. The line is the 230 Ma reference isochron. Symbols as in Fig. 3.

Fig. 10. Initial (290 Ma) eNa VS. esr plot for Capo Vaticano granitoids. D M = d e p l e t e d mantle: M S and asteri s k s = m e t a s e d i m e n t s and metagabbroics, respectively, from Calabria lower crust (Caggianelli et al., 1991 ); other symbols as in Fig. 3. Dashed curves are two possible mixing lines between D M and MS.

REL*TI{ )NSHIPS BETWEEN INTERMEDIATE AND ACIDIC ROCKS IN OROGENI(" GRANIT()ID SUITES

167

IaIBLE 5 [ ] - T h - P b analytical data for Capo Vaticano granitoids Sample

U

Th

Pb

(ppm)

{ppm)

(ppm)

?06pb/ZOapb

2OVpb/eO4pb 2ospb/2O4pb

18.499 18.389 18.389 18.389 18.391 18.351 18.451 18.481 18.431 18.36 18.369

15.693 15.648 15.753 15.756 15.643 15.716 15.675 15.666 15.676 15.72 15.681

38.793 38.547 38.721 38.722 38.583 38.598 38.922 39.027 39.020 38.51 38.586

(2O~,pb/eO4pb)>m

(_,o,pb/_,O4pb)>~,

(2O~pb/2O4pb)>{,

lz

8.340 7.992

15.685 15.627

38.655 37.512

10.07 989

8.113

15.629

37.860

9 87

8.174 8.287 18.232

15.660 15.651 15.656

38.808 38.840 37.843

10.00 t}.97 10.01

lwo-mica porphyritic granodiorites: 1'~21WR P~I3WR 1}~13 KF

0.54

1.22

1.41 9.84

10 9

PA27 WR P~27 KF PA28 WR I},\44 WR P~I{tWR P~. I (! KF

1.33

10.61

14

1.13 0.79 1.15

1.41 2.38 20.91

12 12 17

Biolite ~ hornblende lonalites: Briati~'o (V240 WR ('V20 %R

2.81

10.35

31

18.486

15.670

39.350

18.217

15.656

39.029

9.97

2.31

23.04

27

18.555

15.719

38.997

18.302

15.706

38.182

10.17

( "apo I "allcano (setLsl¢ slriclo) ( V 2 5 %'R ('V25 PL

2.33

13.97

27

18.419 18.341

15.665 15.710

39.593 38.593

18.163

15.652

39.091

9.96

1.95

15.48

34

18.401

15.675

38.650

18.233

15.666

_8._17 3

l(I.01

2.56

16.26

27

18.399 18.546

15.705 15.687

38.746 39.168

18.176

15.672

38.592

10.I)5

2.63

21.60

27

18.458

15.658

38.493

18.173

15.643

37.730

9.92

18.313

15.654

38.406

S. ,~la ria ( Vt1)2 WR ('V31)2 PL {'V319 WR

loppolo {V4I)5 WR ('V405 Pk

WR = whole rock; KF = K-feldspar; PI = plagioclase.

isotope ratio of 0.71 l 1. Note that all these values are intermediate between those of the metabasites and metasediments from the Serre lower crust section (see Rottura et al., 1990; Caggianelli et al., 1991 ). Initial (290 Ma) Nd isotope ratios are variable (Table 4). The samples studied range from 0.51175 to 0.51195, with the granodiorites displaying a slightly higher range of values. Two samples, one tonalite and one granodiorite analyzed by Rottura et al. (1990), howe ver, display anomalous values of 0.51224 and 0.51221, respectively. Note that high end ( + 0 . 3 3 ) was also found by the same authors

in a fine-grained granodiorite from Serre. Accordingly, as already reported by Rottura et al. (1990), the Capo Vaticano samples plot as a vertical array on the end VS. esr diagram, with most samples plotting in the mixing field between mantle and crust (Fig. 10). Pb isotope ratios (Table 5) were determined for whole rocks and for a few samples of separated feldspars. Whole-rock present-day values for both the tonalites and granodiorites (Fig. 11 ) plot in the field of the lower crust (Zartman and-Doe, 1981 ), and are similar to the values found by Caggianelli et al. ( 1991 ) in lower crustal metasedimentary and meta-

A. R()TTURA ET AI,.

l 68 150 -

7. Discussion f

~

~

UC

/ j~

155 //

2OTpb 2o4pb

J

15.4

LC A

// 15.2

/ /

/

/

/

1573113

1563 15.0" 16.5

i 17.5

18.5

o • Zx E],~ • 0 ••

• t , , j 184 185

0

186

19.5

20 5

LC 39 208 Pb 204 Pb

. ~ /

/

392 , I 3&2

&&••o 0° /

38

3B2 I 37 15.5

,

17.5

,

18.5

1

, • , .t 184 185 185 , 19.5 20 5

206pb

204pb

Fig. 11. Present-day 2°7pb/2°4pb and 2°Spb/2°4pb vs. -~°6pb/2°4Pb plots for whole rocks and separated feldspars (smallersymbols) from Capo Vaticano granitoids. Upper crust (UC), lower crust (LC), and MORB fields are from Zartman and Doe, 1981. Symbolsas in Fig. 3. basic rocks from Serre. The feldspars show similar present-day 2°6pb/2°4pb and 2°8pb/ 2°4pb, and higher 2°7pb/2°4pb ratios than the whole rocks. #-values of the tonalites range from 9.92 to 10.17 and those of the granodiorites from 9.87 to 10.07. The initial Pb isotopic composition of the whole rocks (computed back to 290 Ma) show a high spread of values for both granodiorites and tonalites, particularly for the 2°Spb/2°4pb ratios; indeed, three granodiorites (PA 13, PA 10 and PA27 ) and one tonalite (CV405) show (2°Spb/ 2°4pb)29o and (2°6pb/2°4pb)29o ratios falling within the range of MORB values (Table 5 ).

The intrusive rocks of Capo Vaticano were found to show a number of geochemical and isotopic peculiarities, which make it difficult to work out a petrogenetic model which is able to account for all the observed characteristics. The most problematic geochemical features are the isotopic signatures which are difficult to be accounted for by the processes (crystal fractionation, AFC, crustal melting associated with restite unmixing) commonly invoked for explaining the genesis of granitoid suites. Some samples of granodiorite and tonalite display 2°8pb/2°4pbisotope ratios recalculated to 290 Ma, which are unrealistically low and contrast with the crustal 2°Tpb/2°4pb ratios, and with 87Sr/S6Sr isotopic signatures which indicate a crustal contribution. It is unlikely that such low 2°Spb/2°4pb isotope ratios represent primary values. In fact, if this was the case, the initial Pb isotope ratios of the whole rocks should be similar to those measured in the feldspars of the same sample. These minerals, in fact, do not accept Th and U in their lattice and, accordingly, they do not cumulate radiogenic Pb whose isotopic composition should be thus considered as primary. Instead, for all the samples analyzed, feldspars have shown Pb isotopic compositions different from the initial values in the whole rocks. In addition, the 2°Tpb/2°4pbratios, which are lower in the whole rocks than in the separated feldspars (except for the Ioppolo tonalite, sample CV405), indicate an isotopic disequilibrium between these minerals and their host rocks. This suggests that these recalculated Pb isotopic compositions for the investigated rocks are incorrect, most probably because of the assumption that the system remained closed since 290 Ma B.P., the time ofgranitoid intrusion. On the contrary, a secondary event affecting the Pb isotopic system of the Capo Vaticano rocks is strongly suggested by the comparison of the whole-rock and feldspar isotopic data.

R E L A T I O N S H I P S BETWEEN I N T E R M E D I A T E A N D A C I D I C R O C K S IN O R O G E N I C G R A N I T O I D SI IITES

The vertical array Ofesr vs. {~Nd(Fig. 10) is difficult to model by any common magmatic process. Interaction between mantle and crustal components should give hyperbolic mixing trends (DePaolo, 1981b). One possibility to explain the peculiar eS,--~Nd covariation is to assume that it was inherited from a heterogeneous source (Rottura et al., 1990). Alternatively, it could be suggested that the highest Nd isotopic compositions depend on the presence, in these samples, of a restitic LREE-carrying accessory phase (e.g., monazite, which is poorly soluble in acidic melts; Rapp and Watson, 1986 ), in isotopic disequilibrium with the granitic melt. Another possibility is to assume that the rock suites, which initially plotted along a mantle-crust mixing trend, were affected by interaction with fluids having high Sr/Nd ratios and ~7Sr/86Sr values around 0.710, which changed and homogenized the Sr isotopic compositions while leaving the Nd isotopic signatures unaffected. In this case, the variable initial Nd isotopic signatures of the investigated granitoids would indicate an interaction (mixing or AFC) between a mantle and crustal components. In this respect, it must be also recalled that the rejuvenated ages of biotites attributed to Alpine or Apenninic overprints (see Sect. 2 ), point to some kind of metasomatic event (s) which affected the Calabria granitoids. However, it is intriguing that the most primitive Nd isotopic compositions occur in three rocks (two 2-mica granodiorites and a biotite tonalite) which do not display significant geochemical and mineralogical differences with respect to the rest of the samples, and that Sr isotopic compositions of the same range as those observed in the CV granitoids, are commonly found in the Hercynian granitoids from SW Europe (see reviews in Harris et al., 1986, and Del Moro, 1987). The determination of the timing, the nature and the effects of the presumed metasomatic event(s) requires extensive iso{opic and geochemical work to be fully understood. It may be speculated that the age of about 230 Ma cal-

[ 69

culated for one group of granodiorites (see previous section) and for some restitic metapelites from the Serre granulitic basement (Caggianelli et al., 1991 ) may, in fact, date a metasomatic event. In any case, the complex tectonic history of the investigated area during the Alpine-Apenninic evolution of the Calabrian Arc may have provided a large number of possible inputs of fluids into the studied rocks. One of the main points which must be clarified, is whether the major- and trace-element distribution of the investigated granitoids were also affected by post-crystallization processes or, on the contrary, these processes merely produced changes in some isotopic signatures. Again, it must be pointed out that both the analyzed granodiorites and tonalites display well preserved magmatic textures and very minor mesoscopic and microscopic evidence of secondary alteration. A few flakes of sericite in plagioclase, some biotites transformed to chlorite and a few muscovite flakes of probable secondary origin are the only deuteric phases which were observed in the studied samples; however, such alteration products are commonly found in many if not all granitoid rocks. Plagioclases and all the other main and accessory phases appear to have perfectly preserved magmatic textures and compositions; finally, calcite as well as fluid inclusions were rarely observed. However, in order to have more solid constraints on possible elemental mobilization, linear correlation coefficients for major and trace elements were calculated (Table 6). The granodiorites were subjected to this test, because they represent a single intrusive unit displaying the maximum spread in the composition of many trace elements. It can be seen that there are significant positive correlations, at the 99% confidence level, among Sr, Ca, Ti, Mg, Fe and Zr, and a negative correlation between all these elements with the differentiation index (DI) and SiO2. In addition, there is a significant positive trend

I 70

-k. R()TTURA ET .\L.

"FABLE 6 Linear correlation coefficients for some pairs of elements in the Capo Vaticano porphyritic granodiorites ( n = 20 )

SiO: TiO: Fe2(L Mg() ('a() K,() Rb Sr Zr

DI

giO2

TiO2

Fe203

MgO

CaO

K20

Rb

Sr

0.601 -0.920 -0.908 -0.902 -0.989 0.609 0.528 -0.809 -0.896

-0.694 -0.737 -0.609 -0.555 0.024 -0.125 -0.620 -0.619

0.965 0.870 0.883 -0.535 -0.307 0.723 0.885

0.849 0.855 -0.495 -0.263 0.734 0.876

0.88 I -0.582 -0.392 0.720 0.8710.

-0.592 -0.602 0.805 0.848

0.500 -0.301 -0.588

-0.386 -0.214

0.762

l)l=differentiation index (Thornton and Turtle, 1960). Fe total as FeeO~; r>~0.444 and 0,561: significant at 95% and 99% confidence level, respectively.

between Ce and Th (r=0.83; Fig. 5 ). It is well known that all these relationships are typical magmatic features and are commonly observed in granodiorite-granite suites. They can be generated by crystal/liquid fractionation or by mixing between differently evolved magma batches, and suggest that these elements have not been significantly affected by post-crystallization metasomatic processes, and thus represent primary magmatic features. The same conclusion also holds true for the REE, which are essentially contained in accessory monazite, zircon and apatites, minerals which are all quite refractory to the interaction with aqueous fluids (e.g., geroy and Turpin, 1988; C e / T h covariation ), and which were found to be well preserved in the investigated rocks. Accordingly, in the following discussion we will lean heavily on the REE elements to constrain petrogenetic models for the Capo Vaticano rocks.

8. Petrogenesis Granodiorites and tonalites from Capo Vaticano were found to show similar isotopic signatures, REE patterns which in many rocks display fractionation of both the light and the heavy REE with negative Eu anomalies, similar hygromagmatophile element patterns, as well as a c o m m o n peraluminous character.

These features all combine in suggesting a close genetic linkage between the intermediate and acidic rocks. On the other hand, the striking differences found in the trace element variation trends, especially for Sr, Ba, Rb and Zr, and the absence of any evidence of basic to intermediate enclaves in the granodiorites, seems to exclude a direct derivation of the granodiorites from the associated tonalites. Accordingly, the most important petrogenetic problem of the Capo Vaticano granitoids, and of many granitoid suites in orogenic settings in general, is that of understanding: ( 1 ) the relationship between acidic and intermediate lithologies; (2) the processes which generated the internal geochemical variations in the intermediate and acidic rocks: (3) the ultimate nature of the petrologic processes which generated distinct granitoids which, in spite of significant differences, however, still possess many c o m m o n geochemical and isotopic signatures.

8.1. Tonalite-granodiorite relationships and granodiorite genesis The derivation of granites from intermediate-basic magmas, via crystal/liquid fractionation possibly associated with interaction with the crust, is a commonly held hypothesis which

17 1

RELATI()NSHIPS BETWEEN INTERMEDIATE AND ACIDIC ROCKS IN O R O G E N I C G R A N I T O I D SUITES

has been proposed for several granitoid suites. However, this hypothesis is unable to explain some key geochemical features of the Capo Vaticano rocks. In fact, the analyzed granodiorites were found to show large variations in the content of some trace elements such as Sr, Ba and Zr, which encompass those observed in the tonalites. All these elements appear to show compatible behaviour in the tonalites and, although the values are scattered, they do show a significant decrease with increasing silica content (Figs. 4 and 5 ). It is obvious that the majority of the granodiorites, which contain higher abundances of these elements than the tonalites, cannot have been derived from the intermediate magmas, either by crystal fractionation or AFC. Instead, the samples characterized by low St, Ba and Zr contents may, in principle, represent the final products of the tonalite evolution trend. It could be argued that the high values of Sr, Ba, and Zr in some granodiorites, the steep trends of these elements against silica and the large spread in their LREE content, could be an artifact due to the heterogeneous accumulating (or different degrees of solid-liquid separation ) of major and accessory phases such as K-feldspar, zircon and monazite. A role for Kfeldspar as a cumulus phase may be likely, because of the presence of large crystals of this mineral which, sometimes, appear to be unevenly distributed through the rock mass on outcrop. Assuming a Ba content around 4,00015,000 ppm and Sr=500-600 ppm (A.M. Fornelli, unpublished data on Serre K-feldspars), an accumulation of about 10-15% of this phase is able to give the range of Sr and Ba observed in the investigated granodiorites. However, microscopic and mesoscopic investigation on the analyzed samples did not reveal any evidence of a concentration of K-feldspar, and there is no relationship between the Ba values and the modal abundances of Kfeldspar (Monni, 1990). In addition, K-feldspar accumulation should produce a positive

correlation between Ba, Sr, K, Eu/Eu*; however, such a correlation has been observed only for Sr vs. Ba ( r = 0 . 4 6 ) , while a poorly defined tendency to decrease, with increasing Sr and Ba content, can be recognized for Eu/Eu* ( Fig. 12 ). All these observations do not support the hypothesis of an accumulation of feldspars in the analyzed samples. Finally, the large spread in the Zr and the Ce vs. Th covariation plots, also require the accumulation of zircon and monazite. This is certainly likely, since these minerals are common accessories in granodiorites. However, it is difficult to model the crosscutting of the REE patterns by accumulation processes. In summary, the contrasting behaviour of some trace elements in the granodiorites and tonalites suggest that the two lithologies were generated, and evolved, as separate systems, possibly indicating that only those granodiorites characterized by lower St, Ba and Zr contents may have been derived from the tonalites by crystal/liquid fractionation or AFC pro1.1 E u / E u *

1.0

0,9 0,8 0.7

Ak

0.6 •

S r

i

0.5 200

300

400

1.1 E u / E u

°

1.0 0.9 0.8 0.7 0.6 A&

0,5 400

•

.

L

600

.

.

1

800

.

Ba .

i

1000

.

,

i

1200

.

.

L

1400

.

.

L

1600

.

.

1800

Fig. 12. Eu/Eu* vs. Ba and Sr for the Capo Vaticano twomica porphyritic granodiorites.

172

A. R()TT(JRA E1 ,XL.

cesses. If this conclusion is accepted, the next step is to understand the processes which are responsible for the geochemical variation in the granodiorites and for the generation of high SrBa, and low Rb/Sr acidic magmas. A likely hypothesis is that the range of geochemical compositions of the granodiorites may derive from interaction (mixing) between two end members, possibly complicated by fractional crystallization processes. Evidence in favour of mixing arises from petrographic observations and mineral chemistry data (see Sect. 4) and from hyperbolic relationships in some element-ratio vs. content plots (Fig. 13). In addition, the granodiorites plot in two distinct fields on many variation diagrams such as Rb vs. Ba, Sr/Ca vs. St, Rb/ Sr vs. ~7Sr/S6Sr, suggesting that the acidic rocks actually represent two magma batches. One end

30

A

Cs/Th

20

10 &A

Th 0

--

0

i

i

10

20

30

30

Ce/Th

= .

20

10

0

i

i

i

0.2

0.4

0.6

0,8

Fig. 13. C e / T h vs. Th and C e / T h vs. l / T h plots (Langmuir el al.. 1978) for the Capo Vaticano two-mica porphyritic granodiorites.

member should be characterized by higher Sr, Ba, Zr, Ca and 878r/86Sr ratios, and lower Rb/ Sr values than a second component, which may well be derived from tonalites, as previously discussed. The generation of the high Sr end member is problematic. The peraluminous character, the presence of fibrolite, the metasedimentary nature of the enclaves, and the zircon typology (Rottura et al., 1990), all suggest an important contribution from a pelitic component. Accordingly, the high-Sr-Ba acidic magma may represent the product of crustal melting of a pelitic source. However. in this case, it is difficult to explain the low Rb/Sr and S7Sr/a~Sr ratios, unless a source previously depleted in Rb is involved. The high Sr and Ba contents would indicate that these two elements showed incompatible behaviour during melting. This implies that the amount of feldspars ( _+biotite) in the residue was low enough to give bulk distribution coefficient (D) lower than unity for these elements. For instance, we can calculate that the melting of a NASC-type source, with a residue made up of quartz + sillimanite and containing 25% plagioclase + 5% garnet and accessory monazite, is able to give a liquid with fractionated LREE- and HREE-patterns, and a negative Eu anomaly similar to those observed in the granodiorites. This melting process is also able to give St- and Ba-rich liquids since the D of the residue is lower than unity. Alternatively, the granodiorites represent a completely distinct magmatic system with respect to the intermediate rocks, being generated by melting in the crust. In this case, however, it would be problematic to explain the similarity of the many geochemical and isotopic features between the granodiorites and tonalites; in addition, it would be difficult to explain the time and space relations between the two rock groups, since it is necessary to envisage a physical process which is able to generate two independent magmatic systems which, however, appear to be closely associated in space and time.

RELATI(~NSHIPS BETWEEN INTERMEDIATE AND A('IDIC ROCKS IN ORO(IENI('GR-~NITOID SIJITES

8.2. Genesis of the tonalites The most striking compositional characteristic of the Capo Vaticano tonalites is their extreme geochemical heterogeneity. The compositional variability observed at a regional scale by previous workers (e.g., Rottura et al., 1990) is reproduced at the local scale, indicating that very complex processes were involved in the genesis of these rocks. Much of the geochemical variation within the tonalitic suite from southern Calabria had been inferred (Rottura et al., 1986) to indicate an evolution of the intermediate calc-alkaline magma by crystal/liquid fractionation, possibly accompanied by assimilation processes. However, the extreme scattering observed for many trace elements on Harker diagrams, also indicates that the heterogeneous accumulation of major and accessory mineral phases played an important role in determining the geochemical signatures of the Capo Vaticano tonalites. This conclusion is strongly supported by the REE patterns of some tonalites, where flat or slightly positively fractionated LREE patterns suggest a mineral-dominated REE composition. This fact strongly limits the possibility of using trace elements for the petrogenetic modelling in these rocks. In spite of these difficulties, it should be noted that many tonalites have REE patterns with fractionated LREE and HREE and negative Eu anomalies, and 87Sr/86Srratios similar to those of granodiorites. All these characteristics indicate that crustal material, which had been inferred to be extensively involved in the genesis of the granodiorites, also played an important role in the genesis and evolution of the tonalites. However, the lower Sr isotopic signatures may indicate that in this case the crustal contribution is less significant than for the granodiorites. A role of a mantle-derived mafic component is indicated by the occurrence of mafic enclaves, distributed throughout the tonalitic masses. However, although minor than in the grano-

173

diorites, the crustal contribution has been so extensive as to completely mask any mantle signature in the analyzed tonalites. The only evidence of a mantle component could be represented by the near chondritic Nd isotopic composition found by Rottura et al. (1990) in one tonalite, although the occurrence of the same characteristic in two granodiorites makes this evidence very intriguing. 9. Conclusions

The main points which emerge from the integrated petrological, geochemical and isotopic study of Capo Vaticano granitoids can be summarized as follows. (1) The granodioritic and tonalitic rocks, closely associated in space and time, share many compositional characteristics such as their peraluminous character, isotopic signatures, shape of REE patterns, and hygromagmatophile element distribution patterns. (2) The granodiorites show large variations in many geochemical parameters such as St, Ba, Rb, and Zr contents, which make it difficult to infer a derivation of all the granodiorites from the associated intermediate tonalires. The analytical data are better explained by assuming, as dominant mechanism, a mixing between a crustal acidic melt and a component which may have been derived from the tonalites by fractional crystallization or AFC. (3) The tonalites display a wide range of isotopic and trace-element compositions, even within individual intrusive bodies. However, all the geochemical and isotopic characteristics of these rocks have strong crustal signatures, which suggest a large involvement of crustal material in their genesis. (4) The prominent role of the crust in the genesis of all the Capo Vaticano granitoids can account for the many geochemical and isotopic similarities found between the intermediate and acidic rocks. Petrological evidence and the occurrence of mafic enclaves also suggest a role of a mantle component, whose geo-

174

chemical and isotopic fingerprint, however, appears very weak owing to dilution by the large quantities of crustal material involved in the genesis of both tonalites and granodiorites. ( 5 ) Pb isotopic compositions of whole rocks and separated feldspars, as well as the arrangement for the high Rb/Sr granodiorites along a line yielding an age of 230 Ma, indicate that metasomatic event(s) affected the studied granitoids, partially modifying the original Sr and Pb isotopic signatures. However, these events appear neither to have completely masked the original Sr and Nd isotopic characteristics, nor to have significantly affected the major and trace element characteristics, which preserved their primary magmatic features. In conclusion, the reported case study provides a clear example of the complexity of granitoid systems, and of the difficulty to work out simple petrogenetic models which comprehensively account for all petrological, isotopic and geochemical data. This difficulty derives from the fact that in the present case, and probably in many other granitoid suites, several episodes of crystal/ liquid fractionation, interaction with the crust, mixing between different magmas, cumulation of main and accessory phases and post-crystallization metasomatic events produce complex geochemical patterns, which allow no more than a very generalized picture of granitoid genesis to be deduced.

Acknowledgements We are grateful to C. Dupuy and A. Halliday for their reviews that helped to improve the manuscript, and to V. Koeppel for a critical discussion of the isotopic data. We are indebted to U. Giannotti and G. Pardini (C.N.R., Pisa) for their help in Rb-Sr and Pb isotopic analysis, to M.L. Todaro (C.N.R., Florence) who provided Na20, MgO and LOI determinations on granodiorite samples, to A. Mordenti and to G. Felice for technical assistance during different phases of this research,

.',. ROTTURAET AL.

and to G. Grassi for his help in electronic text preparation. Financial support was provided by the Italian Ministry of University and Scientific and Technological Research (M.U.R.S.T. 40%, grants to A.R. and G.P. ), and C.N.R. Project on "Petrogenetic and geodynamic processes in orogenic areas" (A.P.).

References Allegre, C. and Ben Othman, D., 1980. Nd-Sr isotopic relationship in granitoid rocks and continental crust development: a chemical approach to orogenesis. Nature (London), 291: 335-342. Amodio Morelli, L., Bonardi, G., Colonna, V., Dietrich, D., Giunta, G., Ippolito, F.. Liguori, V., Lorenzoni, S., Paglionico, A., Perrone, V., Piccarreta, G., Russo, M., Scandone, P., Zanettin Lorenzoni, E. and Zuppetta, A., 1976. L'Arco Calabro-Peloritano nell'orogene appenninico-maghrebide. Mem. Soc. Geol. Ital., 17: 1-60. Bailey, J.C., 1981. Geochemical criteria for a refined tectonic discrimination of orogenic andesiles. Chem. Geol., 32: 139-154. Beckinsalc, R.D., Sanchez-Fernandez, A.W., Brook, M., Cobbing, E.J., Taylor. W.P. and Moore, N.D., 1985. Rb-Sr whole rock isochron and K-Ar age delerminalions for the Coastal Batholiih of Peru. In: W.S. Pitcher, M.P. Atherton, E.J. Cobbing an R.D. Beckinsale (Editors), Magmatism at a Plate Edge. The Peruvian Andes. Blackie, Glasgow, pp. 177-202. Boccaletti, M., Nicolich, R. and Tortorici, L., 1984. The Calabrian Arc and the Ionian Sea in the dynamic evolution of the central Mediterranean. Mar. Geol.. 55: 219-245. Bouillin, J.P., Durand-Delga, M. and Olivier, Ph., 1986. Betic-Rifian and Tyrrhenian Arcs: distinctive features, genesis and development stages. In: F.C. Wezel (Editor), The Origin of ~rcs. Elsevier, Amsterdam, pp, 281-304. Caggianelli, A., Del Moro, A., Paglionico, A., Piccarrcta, G., Pinarelli, L. and Rottura, A., 1991. Lower crustal granite genesis connected with chemical fractionation in the continental crust of Calabria (Southern Italy). Eur. J. Mineral., 3: 159-180. Civetta, L., Cortini, M. and Gasparini, P., 1973. Interpretation of a discordant K-Ar age pattern (Capo Vaticano, Italy). Earth Planet. Sci. Lett., 20:113-118. Clarke, D.B., 1981. The mineralogy of peraluminous granites: a review. Can. Mineral., 19:3-17. Clarke, D.B., Paglionico, A, and Rottura, A., 1990. Garnet-forming and garnet-eliminating reactions in the Capo Vaiicano quartz diorite, Calabria, southern llaly. GAC-MAC Annual Meeting, Vancouver, May 10-

R E L ~ T I ( ) N S H I P S BETWEEN I N T E R M E D I A T E A N D A C I D I C R O C K S IN O R O G E N I C G R A N I T O I D SUITES

18, 1990, Program with Abstracts, Vol. 15, p. A25. Del Moro, A., 1987. Sistematica Rb/Sr di alcune magmatiti tardo-erciniche dell'area italiana, 1I Scuola lnternazionale di Geocronologia e Geocbimica lsotopica. Ric. Sci. Ed. Perm., Milano, Suppl. 52, pp. 107132. Del Moro, A., Ferrara, G., Tonarini, S. and Callegari, E., 1983. Rb-Sr systematics on rocks from the Adamello Balholith (Southern Alps). Mem. Soc. Geol. ltal., 26: 261 284. Del Moro, A., Paglionico, A., Piccarreta, G. and Rottura, A., 1986. Tectonic structure and evolution of the Serre, Calabrian Arc, southern Italy: geological, petrological and radiometric evidence. Tectonophysics, 124: 223238. DePaolo, D.J.. 1981a. A N d and Sr isotopic study of the Mesozoic calc-alkaline batholiths of the Sierra Nevada and Peninsular Ranges, California. J. Geophys. Res., 86: 10470-10488. I)ePaolo, D.J., 1981 b. Trace elements and isotopic effects of combined wall-rock assimilation and fractional crystallization. Earth Planet. Sci. Lett., 53:189-202. l)ownes, H. and Duthou, J.L., 1988. Isotopic and traceelement arguments for the lower-crustal origin of Hercynian granitoids and pre-Hercynian orthogneisses, Massif Central (France). Chem. Geol., 68:291-308. Ewart, A., 1982. The mineralogy and petrology of Tertiary-Recent orogenic volcanic rocks: with special retcrence to the andesitic-basaltic compositional range. In: R.S. Thorpe (Editor), Andesites. Wiley, New York, N.Y., pp. 25-95. Frost, ('.D. and O'Nions R.K., 1985. Caledonian magma genesis and crustal recycling. J. Petrol., 26:5 t 5-544. Ghezzo. C. and Orsini, J.B., 1982. Lineamenti strutturali e composizionali del batolite ercinico sardo-corso in Sardegna. In: Guida alia Geologia del Paleozoico Sardo. Guide Geologiche Regionali. Mem. Soc. Geol. Ital., 24 (Suppl. B): 165-185. Gill, J.B., 1981. Orogenic Andesites and Plate Tectonics. Springer, Berlin, 390 pp.. Harris. N.B.W., Pearce, J.A. and Tindle, A.G., 1986. Geochemical characteristics of collision-zone magmalism. In: M.P. Coward and A.C. Ries {Editors), Collision Tectonics. Geol. Soc. London Spec. Publ., 19: 67-81. Haskin, L.A., Frey, F.A. and Wildeman, T.R., 1968. Relative and absolute terrestrial abundances of rare earths. In: L.H. Ahrens (Editor), Origin and Distribution of the Elements. Pergamon, New York, N.Y., pp. 889912. Hibbard, M.J., 1981. The magma mixing origin of mantled feldspars. Contrib. Mineral. Petrol., 76:158-170. Lameyre, J. and Bowden, P., 1982. Plutonic rock types series: discrimination of various granitoid series and related rocks. J. Volcanol. Geotherm. Res., 14: 169186.

175

Langmuir, C.H., Vocke, R.D., Hanson, G.N. and Hart, S.R., 1978. A general mixing equation with applications to Icelandic basalts. Earth Planet. Sci. Left., 37: 380-392. Laurenzi, M.A., Del Moro, A. and Rottura, A., 1986. Preliminary K-Ar and Rb-Sr data on Capo Valicano and Le Serre granitoids (Calabria, southern Italy). ICOG VI, Cambridge. Terra Cognita, 6 (2): 142. Leroy, J.L. and Turpin, L., 1988. REE, Th and U behaviour during hydrothermal and supergene processes in a granitic environment. Chem. Geol., 68:239-251. Liew, T.C., Finger, F. and Hock, V., 1989. The Moldanubian granitoid plutons of Austria: chemical and isotopic studies bearing on their environmental setting. Chem. Geol., 76: 41-55. Lopez-Escobar, L., Frey, F.A. and Oyarzun, J., 1979. Geochemical characteristics of Central Chile (33 3 4 S ) granitoids. Contrib. Mineral. Petrol., 70: 437450. Ludwig, K.R., 1987. User's manual for Analisl, a computer program for control of an Isomass 54E thermal ionization, single collector mass-spectrometer. U.S. Geol. Surv., Open File Rep., 85-513. Maccarrone, E., Paglionico, A., Piccarreta, G. and Rottufa, A., 1983. Granulite-amphibolite facies metasediments from the Serre (Calabria, southern Italy): their protoliths and the processes controlling their chemistry. Lithos, 16:95-111. Miller, C.F. and Stoddard, E.F., 1981. The role of manganese in the paragenesis of magmatic garnet: an example from the Old Woman-Piute Range, California. J. Geol., 89: 233-246. Miller, C.F., Stoddard, E.F., Bradfisch, J. and Dollase, W.A., 1981. Composition of plutonic muscovite: genetic implications. Can. Mineral., 19: 25-34. Monier, G. and Robert, J.L., 1986. Muscovite solid solutions in the system K20-MgO-FeO-AI20~-SiO2-H20: an experimental study at 2 kbar P , ~ and comparison with natural El-free white micas. Mineral. Mag., 5(1: 257-266. Monni, A., 1990. I graniti a due miche e a megacristalli di K-feldspato di Capo Vaticano (Calabria meridionale). Aspetti geologici, petrologici e geochimici. Thesis, Univ. of Bologna, Bologna, 11 I pp. (unpublished). Pankhurst, R.J., Hole, M.J. and Brook, M., 1988. Isotope evidence for the origin of Andean granites. Trans. R. Soc. Edinburgh, Earth Sci., 79: 123-133. Paterson, S.R., Vernon, R.H. and Tobisch, O.T., 1989. A review of criteria for the identification of magmatic and tectonic foliation in granitoids. J. Strucl. Geol., 1 I ( 3 ): 349-363. Pearce, J.A., Harris, N.W. and Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol., 25: 956-983. Pickett, D.A. and Wasserburg, G.J., 1989. Neodymium and strontium isotopic characteristics of New Zealand

176

granitoids and related rocks. Contrib. Mineral. Petrol., 103: 131-142. Pinarelli, L., Giannotti, U. and Pardini, G., 1989. Messa a punto della procedura analitica connessa con la sistematica isotopica del Pb. Internal Report 3/89 of I.G.G.I.-CNR, Pisa. Rapp, R.P. and Watson, E.B., 1986. Monazite solubility and dissolution kinetics: implications for the thorium and light rare earth chemistry of felsic magmas. Contrib, Mineral. Petrol., 94:304-316. Rottura, A., 1985. The tonalitic gneisses from PalmiBagnara, Calabrian Arc (Southern Italy): geochemistry, their protoliths, and tectono-metamorphic evolution. Neues Jahrb. Mineral., Abh., 152: 187-210. Rottura, A., Atzori, P., Bargossi, G.M., Del Moro, A., Grassi, G., kaurenzi, M.A., Maccarrone, E., Macera, P., Paglionico, A., Petrini, R., Pezzino, A., Piccarreta, G. and Poli, G., 1986. The late Hercynian granitoids from southern sector of Calabrian Arc (southern Italy). Guidebook to the Annual Field Meeting of "'Granilologues", Sept. 20-24, 1986, Bologna, 70 pp. Rottura, A., Bargossi, G.M., Caironi, V., Del Moro, A.. Maccarrone, E., Macera, P., Paglionico, A., Petrini, R., Piccarreta, G. and Poll, G., 1990. Petrogenesis of contrasting Hercynian granitoids from the Calabrian Arc, southern Italy. kithos, 24 (2): 97-119. Scandone, P., 1982. Struclurc and evolution of the Calabrian Arc. Earth Evol. Sci., 2 (3): 172-180. Schenk, V., 1980. U / P b and Rb/Sr radiometric dates and their correlation with metamorphic events in the gran-

~,. ROTTI!RA ET AI,.

Mile facies basement of the Serrc, Southern Calabria (ltaly). Contrib. Mineral. Petrol., 73: 23-38. Schenk, V., 1984. Petrology of felsic granuliles, metapelites, metabasics, ultramafics, and metacarbonates from Southern Calabria (Italy): prograde metamorphism, uplift and cooling of a former lower crust. J. Petrol., 25: 255-298. Schenk, V., 1989. P - Y - t path of the lower crust in the Hercynian fold bell of southern Calabria. In: J.S. Daly, R.A. Cliff and B.W.D. Yardley (Editors), Evolution of Metamorphic Belts. Geol. Soc, Spec. PUN., 43: 337342. Swanson, S.E., 1977. Relation of nucleation and cryslal growlh rate to the development of igneous texlurcs. Am. Mineral., 62: 966-978. Thornton, C.P. and Turtle, O.F., 1960. Chemistry of igneous rocks, I. Differentiation index. Am. J. Sci., 258: 664-684. Winkler, H.G.F,, 1979. Petrogenesis of Metamorphic Rocks, 51h ed. Springer, Berlin. Winkler, H.G.F. and Schulles, H., 1982. On the problem of alkali feldspar phenocrysts in granitic rocks. Neues Jahrb. Mineral., Monalsh., 36 ( 12): 558-564. Wood, D.A., Joron, J.k., Treuil, M., Norry, M. and Tarney, J., 1979. Elemental and Sr isotope variations in basic lavas from Iceland and the surrounding ocean floor. The nature of mantle source inhomogeneities. Contrib. Mineral. Pelrol., 70: 319-339. Zartman, R.E. and Doe, B.R., 1981. Plumbotcctonics-the model. Tectonophysics, 75: 135-162.