3_calc_alkaline_arc_ranitoid.pdf

Gondwana Research, V 6, No. 4, p p . 557-572. 0 2003 International Association for Gondwana Research, Japan. ISSN: 1342-937X

Calc-alkaline Arc I-type Granitoid Associated with S-type Granite in the Pan-African Belt of Eastern Anti-Atlas (Saghro and Ougnat, South Morocco)

M. El Baghdadil, A. El Boukhari2, A. Jouider3, A. Benyoucef4 and S. Nadem5 De'partement de Ge'ologie, Factilte' des Sciences et Techniques, B.P. 523, Beni Mellal, Morocco, E-mail: [email protected] De'partement de Ge'ologie, Faculte' des Sciences Semlalia, BY. S15, Marralcech, Morocco Division Technique, Prijiecture de la ville de Be'ni Mellal, Morocco De'partement de Ge'ologie, Faculte' des Sciences et Techniques, B.P. 523, Beni Mellal, Morocco De'partement de Ge'ologie, Faculte' des Sciences et Techniques, B.P. 523, Beni Mellal, Morocco

(Manuscript received September 25,2002; accepted January 20,2003)

Abstract

Thc Sidi Flah and Ougnat inlicrs arc located in the eastern Anti-Atlas antiform between the Anti-Atlas Major Fault (AAMF) and South Atlas Fault (SAF). They consist of many granitoid intrusions cinplaced into Ncoproterozoic inetasedimcntary rocks and surmountcd by upper Neoproterozoic A-type granites. Thc Sidi Flah (Saghro) and Ougnat granitoids are part of thc Neoproterozoic magmatic activity related to northwards subduction of an oceanic plate bcncath the Saghro contincntal margin. They are post-orogcnic I- and S-type granitoids relatcd to the ending of the compressional deformation in this Pan-African belt. A petrographic, geochemical and zircon typology study leads US to subdivide these rocks into three magmatic groups: (1) a medium- to high-K calc-alkaline group formed by quartz diorites and amphibole granodiorites is found in both Sidi Flah and Ougnat inliers; (2) a high-K calc-alkalinc group is present in Sidi Flah. These two groups have a (dccper and) hybrid mantlc-crust origin; (3) a peraluminous group in Ougnat is linked to the post-collisional setting and has a shallow crustal sourcc. On a primitivc mantle-normalizcd trace-clcinent diagram, almost all of these rocks show a significant Nb deplction relative to K and La, which is typical of the calc-alkaline magmatisin from the subduction-zone environment. Absence of structural marks of thrusting upon the West African craton (WAC) of this arc system and the ophiolitic suite in Bou-Azzer, and the presence of Imiter muscovite-bearing granitc as part of Pan-African belt do not support the localization of northcrn limit of WAC at the level of SAF.

.....

Key words: Saghro, Anti-Atlas Major Fault, zircon, I- and S-type granites, post-collision.

Introduction

The Saghro massif, considered as a Neoproterozoic volcanic arc (Saquaque et al., 1992; Benziane and Yazidi, 1992) is located between the South Atlas fault (SAF) and the Anti-Atlas Major fault (AAMF) (Fig. 1A). The northward-dipping subduction along the AAMF in Bou- Azzer and Siroua hills (Hefferan et al., 2000; Saquaque et al., 1992) generated an arc system in Saghro. Significant parts of Anti-Atlas consist of 2 Ga-recycled crust, while others, particularly in the Northeast of the AAMF (Saghro and Ougnat) contain young components. The Anti-Atlas belt marks the northern boundary of the Eburnean West African craton (WAC) and is subdivided into two main domains by the Anti-Atlas Major fault (AAMF) delineated by the Bou-Azzer Pan-African ophiolite (Leblanc and Lancelot, 1980; Leblanc, 1981; Saquaque et al., 1992):

the southern domain interpreted as stable Eburnean basement, and the northern domain considered as mobile segment during Pan-african orogeny of which Saghro and Ougnat hills form part. Ennih and Likgeois (2001) rejected this subdivision and consider the SAF and not the AAMF, as a northern boundary of the WAC. Many Pan-African granitoids crop out southwestern and northeastern the AAMF. In Saghro, this post-collisional activity is characterised by the emplacement of diorites, quartz diorites, amphibole granodiorites according to N130 direction in Sidi Flah (Nerci, 1988; Ezzouhairi, 1989; El Baghdadi, 2002) and Boumalne-Dad& (Rjimati et al., 1992; El Baghdadi, 2002). The late Pan-African stage is marked by intrusion of biotite and garnet leucogranite in both Sidi Flah and Ougnat terranes respectively.

The aim of this paper is to characterize granitoids of two parts of Saghro: Sidi Flah and Ougnat. This

Gondw ana , Research GR

558 M. EL BAGHDAD1 ET AL.

contribution integrates recent data on the granitoid rocks with more detailed mapping and new petrographic and geochemical data. We add to these investigations, the Pupin's zircon typology method of (1980), which will be applied to all granitoid facies in Sidi Flah and Ougnat. Research goals were to establish a zircon crystallization trend, determine the petrographic and geochemical signature of the units, and establish the geotectonic setting. This leads to comparative study of Sidi Flah and Ougnat granitoids. A final goal is to understand better the late Precambrian magmatic setting of eastern Anti-Atlas.

Geologic Setting

Neoproterozoic terranes of Sidi Flah are oriented NW-SE (Fig. lB), and consist of volcanic and volcanoclastic sequences deposited during Middle Neoproterozoic. The major Pan-African event is characterized by NE-SW

structures (Saquaque, 1992; Rjimati et al., 1992). This deformation stage is followed by the emplacement of quartz diorite and amphibole granodiorite-oriented according to NW-SE direction, which is interpreted as having occurred in tensional mega-cracks (Ezzouhairi, 1989). Magmatic activity is reported to a calc-alkaline tendency which have Pan-African age of 680 Ma (Rb/Sr; Ezzouhairi, 1989). These intrusions are intruded by Sidi Flah biotite leucogranite (SFBL) massif dated at 580t5Ma (Rb/Sr; Mrini, 1993).

The Ougnat inlier represents the eastward prolongation of Saghro massif with Neoproterozoic age 547 Ma (Fig. 1C). This inlier displays a lower Neoproterozoic volcano-sedimentary sequence that having a NNE-SSW strip (Abia, 1991). This sequence is crosscut by small quartz diorite and granodiorite massifs that are themselves intruded by OGL, which appears only in this inlier of Saghro massif. According to Abia (1991), Abia et al. (1995)

A

G H R O

SAF ' South Atlas Fault AAMF Anti-Atlas Malor Faiilt

c

Fig. 1. Geological maps of the studied areas. (A) Location of the various intrusions Saghro inliers in relation to the Anti-Atlas Major Fault (AAMF) in Bou-Azzer El Graara and South Atlas Fault (SAF), (B) Sidi Flah geological map. 1. Lower Neoproterozoic volcanic and volcano-sedimentary series 2. Basic to intermediate volcanism (andesite) 3 . Quartz diorite 4. Amphibole granodiorite 5. Biotite leucogranite 6. Skoura-Tamouzirhft intrusion 7. Lqte Neoproterozoic pyroclastic rocks 8. Pink microgranite 9. Bouskour rhyolite dykes, (C) Ougnat geological map. 1. Lower Neoproterozoic volcano- sedimentary series; 2. Quartz diorite and granodiorite; 3. Garnet leucogranite; 4. Ougnat basic rocks; 5. Upper Neoproterozoic volcanic covering; 6. Cambrian; 7. Faults; 8. Quaternary alluvium.

Gondwana Research, V. 6, No. 4, 2003

GRANITOIDS FROM PAN-AFRICAN BELT, SOUTH MOROCCO 559

and Chouhaidi et al. (1995), the Ougnat granitoids present two distinct geochemical affinities that have the same crustal origin (Mrini, 1993).

Petrography Sidi Flah Granitoids

The quartz diorite outcrops as NW-SE oriented dykes which cross cut the lower Neoproterozoic volcanoclastic series. The rock has a dark-green color with coarse granular texture. The groundmass is made up of plagioclase crystals (50%) up to 3 mm, mostly euhedral and An30-40in composition, and euhedral and twice hornblende (26%). Quartz (11%), biotite (7%), rare crystals of K-feldspar (3%) and accessory minerals represented by opaque minerals, apatite, zircon and titanite are the most occurring minerals.

The amphibole granodiorite occurs in NW-SE and N-S belt between 1 , s and 3 km width. Like the quartz diorite, the amphibole granodiorite produces a hornfels contact metamorphic aureole in the lower Neoproterozoic volcanoclastic serie. The granodiorite is generally medium- to coarse-grained, except close to the contact with metamorphic aureole and quartz diorite. Mineralogical composition contains quartz (22%), plagioclase (49%, An20-25), orthoclase (12%), amphibole (10%) and biotite (5%). Both rocks are classified modally as quartz diorite and granodiorite respectively (Fig. 2A).

Sidi Flah biotite leucogranite (SFBL), classified as monzogranite (Fig. 2A), appears widely in NE and SW strips which cut and postdate the granodiorite and quartz diorite. The rock pattern is clear gray-coloured and shows coarse- granular to porphyritic texture with K-feldspar (26%) and oligoclase (36%) phenocrysts. Biotite (7%) is generally

1. Tholeitic serie 2 Medium-K Cab-alkaline serie 3 H8gh-K calc-alkaline s e w 4 Alkaline sene 5 Analexis granite

P A

Fig. 2. Q-A-P diagram (Strekeisen, 1976) in which Sidi Flah (A) and Ougnat (B) granitoid modal analyses are reported. Numbered curves represent the magmatic series given by Lameyre and Bowden (1982).

subhedral and contains inclusions of zircon, apatite and ilmenite. Quartz (29%) occurs as anhedral, and accessory minerals (1.2%) consist of zircon, magnetite, apatite and titanite.

Ougnat Granitoids

The Ougnat granitoids are located to the north of the hill (Fig. 1C) and occur as small scattered massifs not exceeding 1 to 3 km2 compared with all intrusions in Saghro. The quartz diorite forms the same outcrop with granodiorite. The rock is dark green-coloured and contains euhedral and twinned hornblende (45%). Quartz and K- feldspar a re typically anhedra l . The plagioclase phenocrysts (39%) are euhedral and zoned from labradorite cores to andesine rims. Subhedral biotite occurs only in small quantities. Additionally, apatite, zircon and opaque minerals are found as accessory minerals.

The granodiorite outcrops in small bodies with 100 m long and 50 m wide in the northeast and in the southeast of Mellab’s village and intrude the lower Neoproterozoic volcanoclastic serie. The rock pattern is of dark grey and contains zoned andesine-oligoclase (49?40), green hornblende (19%), biotite (8%) and anhedral quartz (16%). K-feldspar is rare. Zircon, apatite, hematite and the titanite occur as accessory minerals. Near to the OGL, the granodiorite becomes very rich in biotite (17%) with many inclusions of zircon and on the other hand, the amphibole becomes more rare, and sometimes is absent (0-4 Yo). The granodiorite also contains some garnet xenocrysts similar to those of the OGL.

The Ougnat garnet leucogranite (OGL) outcrops in a small bodies in the southwest and northeast of Mellab’s village, and crosscut the quartz diorite and granodiorite which are generally found as xenoliths with surrounding meta-sedimentary country rocks into the leucogranite. Aplite, pegmatite and quartz veins cut the massif and the surrounding country rocks. The OGL is classified modally as monzogranite (Fig. 2B) and have porphyric granular texture with microcline phenocrysts. Late formed and interstitial quartz (3 1%) is anhedral and sometimes forms graphic intergrowths with K-feldspar. The late (36%) occurs as phenocrysts with Carlsbad twins. Albite (28%) shows lamellar twinning, sometimes altered to sericite and epidote. Garnet (2%) occurs as subhedral, cracked and resorbed xenocrysts, and contains inclusions of quartz. Biotite is present in small quantities and common accessories are zircon, titanite, apatite and some opaques minerals.

Geochemistry

Major and trace elements

Bulk rock samples for analysis were selected on the

Gondwana Research, V. 6 , No. 4, 2003


200

rti l o o

basis of petrographic study. Major and trace element concentrations were determined by X-Ray fluorescence (XRF) at the Department of Geology, Universite Catholique de Louvain in Belgium. Some Ougnat REE results are annotated from Abia (1991). Chemical analyses data are reported in table 1. The intrusive rocks in both massifs cover an extensive silica range from 51.15 to 74.06 in Sidi-Flah and from 52.72 to 78.22 in Ougnat. The main compositional trends of the studied intrusive rocks are shown on Harker variation diagrams (Fig. 3). The figure shows that many elements do not have straight-line variations (e.g., A1,0,, Fe,O,, CaO, Na,O, K,O, Ba, Sr, Zr). This suggests two different compositional trends in Sidi Flah (Fig. 3a) and Ougnat (Fig. 3b); one for quartz diorite and granodiorite rocks and the other for SFBL and OGL. The compositional t rend of the dioritic rocks is characterized by the decrease of Al,O,, Fe,O,, CaO and Sr with increasing SiO,, whereas Na,O, K,O, Ba and Zr increase with increasing SiO,. Leucogranites show contrasted evolution with the former trend and also between them. The SFBL shows decrease of A1,0,, Fe,O,, CaO, Na,O, Ba and Zr and increase of K,O and Sr with increasing 90,. OGL shows contrasted trend with

-

. ./ ?v+

the later on the behavior of Fe,O,, CaO, YO, Ba and Sr. The Na,O-CaO-YO diagram (Fig. 4) shows clearly the presence of two trends in both massifs: Sidi Flah and Ougnat. The first dark trend evolves toward alkaline enrichment, but the second (clear trend) evolves to K,O enrichment. In Ougnat the sample AB-01 is taken closely to the contact between biotite granodiorite and OGL.

The Sidi Flah and Ougnat granitoids show calc-alkaline affinity in terms of major and trace element chemistry. In the YO vs. SiO, diagram quartz diorites and granodiorites plot in the fields of medium-K and high-K calc-alkaline suite, whereas the leucogranites show high &O content and plot in the field of high-K calc-alkaline affinity.

In the ACF diagram (Fig. 5), the chemical composition show that quartz diorites and granodiorites in both massifs Sidi Flah and Ougnat are metaluminous to weakly peraluminous and plot between the fields of S-type and I-type according to Chappell and White (1974, 1992) suggesting mantellic source 'mantle derived magma' which is hybridized by crustal melt. Leucogranites have peraluminous character suggesting high contribution of the crust to the formation of the felsic terms in Sidi Flah

1 2 , I 20 r I

I 0 -- SO 5 5 60 6 5 70 75 SO

s102 SO 5 5 60 65 70 75 80

SiOZ 50 55 60 6 5 70 75 80

SiOZ

I

5 0 55 60 65 70 75 80 Si02

12 1 I 6 1 I

0 ~ " " ' ~

5 0 5 5 60 65 70 75 80 5102

5 0 55 60 6 5 70 75 80 Si02

50 5 5 60 6 5 70 75 80 5102

50 5 5 60 65 70 75 80 302

1400 I isno 0 '/. n

d"'t 600 . / I 0 ' " " "

50 5 5 60 65 70 75 80 SiOZ

0 ' " " " 50 55 60 65 70 75 80

Si02

0 ' " " ' so 5 5 60 65 70 75 80

SiOZ 50 5 5 60 65 70 7 5 80

SiO2

300 7 0'

100

0- 50 5 5 60 65 70 75 80

Si02

50 55 60 65 70 75 80 s102

50 55 6 0 , 65 70 75 80 Si02

Fig. 3a. Harker diagrams for major and tracc elements of Sidi Flah granitoids rocks.

Fig. 3b. Harker diagrams for major and trace clements of Ougnat granitoids rocks.

Gondwana Research, V. 6 , No. 4, 2003

Tabl

e 1.

Maj

or a

nd tr

ace

elem

ents

com

posi

tion

of S

idi F

lah

and

Oug

nat g

rani

toid

s.

(Sid

i Fla

h gr

anito

ids)

Qua

rtz

dior

ite

Gra

nodi

orite

B

iotit

e-be

arin

g gr

anite

SFD

q7

SFD

q8

SFD

ql2

EH

116

EH99

b A

F247

A

F248

SF

Gdl

BaS

FGdl

9b S

FGd4

4 SF

Gd1

29 S

FGd2

8 SF

Gd2

9 SF

Gd3

7 SF

Gd3

9SFG

b54

SFG

b55

SFG

b41

SFG

b42

SFG

bl5

SFG

b21S

FGb2

10

SiO

, A

403

TiO

, Fe

z03

MnO

M

gO

CaO

N

a,O

KP

p20,

L.

O.I.

To

tal

Ba

Rb

Sr

Zr

V Cr

Zn

cu

w Y Nb

Ga

Pb

Th La

Ce

Hf

Nd

Sm

EU

Gd DY

Er

yb

Lu

ZNCY

N

CN

K

T"C

(Zr)

R

b/Sr

57.9

5 55

.12

16.2

7 17

.47

0.95

0.

94

6.89

9.

65

0.18

0.

23

3.94

4.

01

5.21

5.

02

4.65

3.

64

3.27

1.

41

0.12

0.

22

0.63

1.

56

100.

06

99.2

7 51

6 26

7 13

6 82

21

3 20

0 94

86

25

58

12

22

15.4

22

.4

2.1

38.2

42

.13

81.2

65

.67

3.2

11.9

9.

6 1.

12

1.58

7.

8 6.

13

7.3

6.13

3.81

4.

7 0.

75

0.45

21

2 23

2 0.

8 1.

0 85

6 88

5 0.

64

0.41

56.4

1 55

.31

58.8

0 54

.25

51.1

5 61

.89

60.6

6 60

.46

16.8

2 19

.44

16.7

3 17

.82

17.4

1 16

.55

17.0

0 16

.08

1.25

1.

02

0.89

2.

02

2.54

0.

47

0.72

0.

70

9.83

7.

16

7.70

8.

17

9.21

5.

28

7.79

4.

58

0.17

0.

25

0.13

0.

19

0.23

0.

15

0.16

0.

13

3.48

5.

11

4.01

6.

14

7.16

4.

27

3.82

5.

01

5.05

6.

14

4.90

8.

18

9.28

4.

60

3.66

4.

35

3.47

2.

35

3.30

2.

05

1.84

3.

64

3.16

3.

28

2.71

2.

45

3.01

1.

64

1.02

2.

21

2.25

3.

42

0.28

0.

14

0.03

0.

08

0.01

0.

20

0.20

0.

14

0.88

0.

46

1.21

0.

45

0.32

1.

10

1.54

1.

93

100.

35 9

9.83

10

0.71

100

.99

100.

17 1

00.3

6 10

0.96

100

.08

562

729

809

970

143

88

102.

3 13

3 19

4 18

3 20

6 15

1 69

10

3 80

11

1 13

2 16

7 15

8 52

51

98

11

1 10

5 16

1 9

11

10

21

22

23

36

19.1

21

23

.7

23

6.35

7.

25

6.82

17

.1

25

10

20

42

17

2 3.

4 4

30.6

9 20

.6

37.4

32

.7

85.3

40

.6

43.6

42

.3

6.1

5.6

5.9

7.5

7.9

1.36

8.

1 4.

01

4.45

5.

5 5.

2 1.

28

1.27

1.

3 6.

04

6.13

5.

36

3.03

3.

3 3.

83

2.92

2.

2 2.

38

2.71

0.

57

0.43

0.

42

0.35

21

3 16

9 15

2 18

4 0.

9 1.

1 0.

9 0.

9 0.

8 1.

0 1.

2 0.

9 85

0 88

5 86

7 88

8 0.

74

0.48

0.

5 0.

88

64.6

0 63

.60

61.0

0 15

.00

15.0

0 17

.50

0.95

0.

93

1.18

4.

13

3.48

4.

96

0.09

0.

11

0.17

2.

60

2.89

2.

90

3.00

3.

90

3.50

3.

20

3.70

3.

30

3.60

4.

10

4.70

0.

14

0.14

0.

17

2.40

2.

50

1.50

99

.71

100.

35 1

00.8

8 10

87

851

95.3

6 11

2.3

137

194

180

123

276

177

211

14

0 30

.1

22.1

12

.2

6.4

13.8

22

.2

10

6 3.

5 44

.3

30.4

84

.9

69.4

8.

8 2.

9

2.4

1.8

0.7

0.41

6.

54

5.84

5.

01

4.98

2.99

2.

5 0.

48

0.25

0.

6 30

7 22

1 1.

0 0.

9 1.

0 93

0 87

8 0.

7 0.

58

62.3

5 60

.25

72.0

6 16

.54

18.1

0 14

.41

0.95

1.

25

0.31

3.

87

4.57

1.

96

0.21

0.

28

0.05

2.

85

4.10

0.

64

3.62

4.

20

0.21

4.

60

3.40

2.

70

3.90

2.

50

5.36

0.

18

0.20

0.

08

0.47

2.

10

2.10

99

.54

100.

95 9

9.88

80

1 87

0 15

9.9

153

55

138

121

19

72

172 5 12

22.5

25

.6

8.7

12.6

16

.2

18.6

96

3.

9 15

.7

22.1

25

.6

48.2

45

.3

4.2

8.5

4.2

4.77

0.

43

0.49

4.

1 4.

2

2.6

2.8

0.75

0.

43

217

205

0.9

1.1

1.

4 88

2 86

5 0

2.91

75.0

3 13

.28

0.24

1.

48

0.02

0.

00

0.22

2.

67

5.85

0.

07

1.81

10

0.67

80

0 13

4.1

66

112

25

61

12

0 0 7.1

5.5

11.5

0 17.7

45

.8

55.2

6.

4

2.1

0.4

4.25

2.

93

1.1

0.

48

180

1.2

850

2.03

71.5

5 14

.80

0.35

2.

41

0.04

0.

72

0.64

3.

41

4.78

0.

08

0.57

99

.35

1014

16

5 32

14

4 44

71

12

0 49

13

30

.1

12.3

10

.3

26

13

21.5

81

.5

8.3

2.5

0.7

5.4

4.8

2.3

0.93

26

8 1.

2 88

0 5.

16

70.4

0 14

.89

0.74

2.

65

0.05

0.

37

0.75

3.

74

4.51

0.

06

1.20

99

.36

1014

16

5 17

14

4

71.1

0 15

.89

0.36

0.

66

0.02

0.

00

1.33

3.

00

5.10

0.

09

2.30

99

.85

646

189

55.2

86

27.2

29

.4

6.15

11

.2

16.2

8.

9

13

10

69.6

22

.1

55.2

91

.6

6.4

5.2

3.7

2.3

0.4

0.7

4.9

5.65

3.

5 3.

8

2.6

1.2

0.68

0.

3 23

3 21

8 1.

2 1.

2 87

8 83

2 9.

71

3.42

72.1

0 15

.83

0.43

0.

73

0.02

0.

03

0.65

2.

80

4.60

0.

08

2.20

99

.50

74.0

6 13

.83

0.51

0.

42

0.02

0.

40

1.56

2.

60

4.86

0.

10

0.64

99

.00

535

215

43.1

56

20.3

5.

3 18

.3

15.1

26

.4

100.

2 9.

2

3.6

0.8

5.02

4.

3

2.2

0.47

18

2 1.1

79

7 4.

99

GRANITOIDS FROM PAN-AFRICAN BELT. SOUTH MOROCCO 561

Goiidwana Research, V. 6, No. 4, 2003

Tabl

e 1.

Con

td.

(Oug

nat g

rani

toid

s).

Qua

rtz

dior

ite

Gra

nodi

orite

B

iotit

e-be

arin

g gr

anite

C

C-

CC

- AB

- A

B-

AB-

LH

I TO

UR

AB-

A

B-

AB-

O

UG

DI

MLI

A

B-

CC-

AB-

A

B-

AB-

A

B-

AB-

A

B-

TOU

RTO

UR

BM

200

TR201

TO3

VG

3 A

Jll

G6

T01

LGI

LG2

SiO

, 52

.8

54.7

52

.72

59.8

2 58

.92

56.3

4 57

.50

60.7

2 60

.36

60.3

6 64

.55

58.8

9 A

1263

17

.9

16.1

2 Ti

O,

0.56

0.

7 Fe

,O,

10.2

8.

64

MnO

0.

06 ,

0.17

M

gO

3.2

3.34

C

aO

6.2

8.5

Na,O

3.

6 3.

98

K,O

2.58

1.

86

PzO

s 0.

81

0.58

L.

O.I.

2.

77

0.7

Tota

l 10

0.68

99

.29

9a

Rb

Sr

Zr

V Cr

Ni

co

Zn

cu

w Y Nb

Ga

Pb

La

Ce

Nd

Sm

Eu

Gd DY

Er

Yb Lu

ZNCY

W

CN

K

0.9

0.7

T"C

(Zr)

17.4

2 14

.99

14.5

1 16

.70

0.81

0.

76

0.94

0.

90

7.33

8.

16

7.93

7.

20

0.13

0.

18

0.14

0.

09

2.79

3.

74

5.04

4.

79

6.61

5.

70

6.42

4.

64

3.5

2.15

1.

47

3.20

2.

61

2.07

2.

73

2.56

0.

34

0.23

0.

21

0.36

3.

86

3.06

2.

67

2.89

98

.12

100.

86 1

00.9

8 99

.67

1175

60

6 65

5.3

67

100

79

409

382

814

137

102

132

133

48

97

129

101

160

30

20

42

20

11

65

89

33

51

21

92

78

20

13

24

11

12

20

31

32

7

21.5

48

.9

19.2

4.

5 0.

95

5.1

4.3

2.3

1.6

0.45

16

8 12

7 22

5 0.

8 0.

9 0.

8 1

92

6 91

1 92

3

17.3

0 15

.80

14.3

9 14

.84

15.8

0 0.

55

0.68

0.

78

0.83

0.

32

6.87

6.

10

6.94

7.

65

3.26

0.

15

0.10

0.

14

0.13

0.

06

4.30

2.

95

3.55

3.

47

1.07

4.

71

4.37

4.

74

5.07

3.

82

2.56

3.

22

2.41

2.

47

4.23

3.

33

3.42

3.

69

3.83

3.

84

0.26

0.

26

0.19

0.

18

0.21

2.

54

2.02

2.

79

1.77

1.

60

100.

07 9

9.64

99

.98

100.

60

98.7

6 14

50

125

62 1

14

2 12

4 41

40

75

55

81

33

15

190

1.1

93

1

Rb/

Sr

0.16

0.

26

0.1

0.2

1694

85

40

7 15

1 10

9 14

7 22

16

70

31

20

8 20

23.6

49

.2

21.5

4.

88

1.1

4.2

3.6 2 1.9

0.33

22

8 0.

9 91

9

1500

11

7 52

3 19

7 73

38

29

51

28

190

25

8 19

0.9

0.9

1.1

918

17.5

0 0.

78

5.89

0.

08

2.84

3.

72

3.97

3.

08

0.50

2.

47

99.7

2 80

1 92

58

1 22

8 10

.3

55

32

74

33

110

20

9 21

1.1

961

0.21

0.

22

0.16

B2

TR-3

25

El4

9 LG

149

60.8

2 62

.50

60.9

2 69

.05

16.5

3 17

.10

17.3

1 15

.10

0.53

0.

46

0.59

0.

30

6.19

6.

01

6.84

3.

95

0.11

0.

12

0.14

0.

07

2.27

1.

34

1.67

0.

86

4.51

4.

36

4.41

2.

29

3.25

3.

10

3.84

4.

25

2.27

3.

70

2.61

2.

00

0.27

0.

34

0.35

0.

20

3.51

1.

29

1.17

1.

11

100.

26

100.

32

99.8

5 99

.18

664

484

59

62

272

336

96

154

23

97

1

12

17

13

6 75

65

25

16

15

10

16

23

6 19

14.9

29

.1

13.2

3.

09

0.93

2.

8 2.

8 1.

6 1.

6 0.

32

150 1

1

1

1.1

882

906

512

LG8

DG

2 LG

S G1

G2

76.8

7 75

.62

78.2

2 76

.43

73.3

3 72

.99

-

0.22

0.

18

0.34

0.

33

0.77

0.

58

13.0

0 13

.15

11.9

1 12

.94

0.00

0.

06

0.06

0.

03

1.17

0.

81

0.97

1.

06

0.03

0.

02

0.08

0.

08

0.00

0.

56

0.63

0.

12

0.79

0.

36

1.03

0.

73

3.34

3.

11

3.90

3.

64

4.50

5.

79

3.60

4.

25

0.00

0.

02

0.00

0.

15

0.29

0.

50

0.59

0.

41

99.9

9 10

0.00

100

.99

99.8

4 77

0 13

93

61

64

180

194

10

16

15

5 70

15

11

6

5 5

30

15

10

5

15

5 7

5 5 5

14.6

30

.4

12.7

3.

32

0.64

2.

9 1.

7 0.

5 0.

3 0.

06

56

1.1

1.1

1

1.1

65

6 68

8

14.5

0 14

.60

0.06

0.

01

0.78

0.

61

0.03

0.

04

0.03

0.

08

0.58

0.

17

4.51

3.

75

5.10

6.

48

0.01

0.

03

0.96

0.

97

99.8

9 99

.73

510

874

65

98

84

168

43

37

47

21

25

30

31

24

28

0.06

0.

07

10

9 43

11.7

15

.2

21.4

32

.1

11.2

14

.4

3.34

4.

56

0.51

0.

49

2.7

3.4

1.7

2.3

0.6

0.8

0.5

0.7

0.05

0.

09

74

78

1

1.1

75

0 73

6

Goiidwana Research, V. 6, No. 4, 2003



,,w \\ NanO 50 50

Fig. 4. Na,O-CaO-K,O diagram of Sidi Flah and Ougnat granitoid, which shows the chemical differences between the quartz diorite/granodioritic trend and biotite and garnet leucogranites.

and Ougnat than the former terms. The composition of OGL coincides with experimental liquids derived from the partial melting of leucogranites (Bknard et al., 1985) or pelites (Holtz and Johannes, 1991). In terms of Ga/Al and ZNCY (Zr+Nb+Ce+Y) indices, almost all of Sidi Flah and Ougnat rocks come from I-type granitoids as shown by their low ZNCY, Ga/Al and A/CNK values (Condie et al., 1999) (Table 1).

As demonstrated in the spider diagram (Fig. 6), Sidi Flah and Ougnat granitoids originate from magmatism related to island arc of subduction-related environment. Nb shows a striking negative anomaly, and the SFBL shows a negative Sr anomaly due to plagioclase fractionation, while OGL shows P and Ti anomalies, which probably reflect apatite and ilmenite and/or titanite fractionation. The Nb anomaly is probably inherited from the magma source, and clearly reflects a subduction-related geochemical component in the source. The SFBL is more enriched in Th and its Th/Rb ratio (= 0.1) is larger than that of the granodiorite (0.04), while the Nb/Th ratio is higher in the former (granodiorite: 2.26, granite: 0.58), suggesting a larger contribution of a crustal component in the genesis of the SFBL. These features suggest an evolution of two different systems which can have same origin or different previous history, firstly between diorite/ granodiorite and leucogranites and secondly between both leucogranites, SFBL and OGL.

REE fractionation

Bulk rock REE analyses have been normalized to chondrite abundances (Boynton, 1984). Almost identical patterns are seen for quartz diorite and granodiorite of Sidi Flah and Ougnat (Fig. 7). All patterns show a negative europium anomaly (Eu/Eu*), which is commonly attributed to the concentration of Eu2+ in plagioclase, except for AB-B2 granodiorite sample of Ougnat. This sample of granodiorite contains only biotite as

ferromagnesian mineral and no fractionated amphibole. Sidi Flah quartz diorite and granodiorite have

chondrite-normalized REE characterized by high LREE contents with (La/Sm), ratios ranging from 2 to 11, negative Eu-anomalies (Eu/Eu” from 0.29 to 0.75). Total REE and Eu anomalies tend to decrease while silica contents increase (Table 1). Ougnat quartz diorite and granodiorite have low total REE, low LREE fractionation ((La/Sm), = 3) than the former. They show less pronounced Eu negative spike (0.61-0.97). Coherently with modal composition, these patterns probably reflect a strong amphibole control, except for AB-B2 sample. Qualitatively, the Sidi Flah and Ougnat quartz diorite and granodiorite features cited above suggest a magmatic evolution mainly controlled by crystal fractionation of amphibole and plagioclase.

The SFBL and OGL show different REE fractionation patterns. The SFBL have high total REE contents (from 196 to 296), high HREE fractionation with (La/Sm), ratio ranging from 4 to 13, low LREE fractionation ((Lu/Gd), ratio = 0.15-0.21), pronounced Eu negative anomaly (Eu/ Eu”) = 0.29-0.59, and a slight U-shaped profile from Gd to Lu. This geochemical feature, different with typical granite systems extreme differentiates (Miller and Mittlefehldt, 1984; Rottura et al., 1998), is consistent with fractionation processes dominated by feldspars and biotite. OGL have different REE patterns with slightly flat LREE pattern ((La/Sm),=2.1-2.77) and high HREE fractionation patterns ((Lu/Gd), -- 0.15-0.21), with Eu negative anomaly (Eu/Eu“ =I 0.38-0.63). The relative low content of HREE in OGL (Figs. 7 and 8) can be related to

Fig. 5. ACF diagram showing the relationship between, chemistry and mineralogy of I - and S-type granites, and source rock compositions and derived granite compositions (Chappell and White, 1992). Quartz diorites and granodiorites have I-type granites signatures, while leucogranites show S-type granite compositions. The fields 1 and 2 represent experimental melt generated by partial melting of leucogranite rocks (BCnard et al., 1985) and metapelites (Holtz and Johannes, 1991) respectively.

Gondzuana Research, V: 6, No. 4, 2003


the separation of the liquid from a source in which garnet remained restite. These different REE features between SFBL and OGL suggest different source or different liquid production processes.

Zircon Typology The zircon typology method, described in several

previous works (Pupin and Turco, 1972; Pupin, 1980, 1997)) is based on the prismatic (T index) and pyramidal (A index) crystals faces relative development. The method application to the plutonic rocks tends to provide some information on the petrogenesis, genetic relations and origin of the considered terms (Pupin and Turco, 1981; Schermaier et al., 1992). The anatectic leucogranites have low A and T index; however, the mantle-derived granites have high A and T index. The orogenic granites are hybrids resulting from crust-mantle contributions. Recent studies on the zircon geochemistry and internal structure (Vavra et al., 1999, Pupin, 1997; Nasdala et al., 1999; Hoskin, 2000, Hoskin et al., 2000; Caironi et al., 2000) insist on the necessity to account for the crystal growth from the first nucleation for the determination

- a Sidi Flah granitoids c1 S 2 100 a, > .- .y, l o E .- L

a

0 , l ' ' ' ' ' ' ' ' I ' ' ' ' Rb Ba Th K Nk La Ce SY P Zr Sm Ti Y

1000 L . - a Ougnat granitoids c. S 2 100 0 > .- .y, l o E

X I

.- L a - 0

Rb Ba K Nk La Ce 3 P Zr Sm Ti Y

Fig. 6. Primitive mantle-normalized (Sun and McDonough, 1989) trace-elements diagrams for Sidi Flah and Ougnat granitoids.

of the nuclei inherited from the initial magmatic stage (Pupin, 1997).

Sidi Flah granitoids

Quartz diorite contains some generally subhedral, pale yellow and clear zircon crystals without any overgrowth. The existing inclusions are various. The crystals do not show any aggregates or relic nuclei and are highly fractured. They are slightly zoned and do not present a growth rings and their average elongation of the unfragmented crystals is 1.54. The mean zircon populations from four samples are spread out with a { 100)-crystal face prism preferential development whereas the (211) and (101) pyramids are almost equal. They are concentrated around a high frequency core (statistic maximum) S,,.,, (Fig. 9).

Amphibole granodiorite is very rich in euhedral zircons, generally colourless with some brown crystals. Crystallized inclusions are abundant. There are multiple groups, involving several fan-shaped individuals. The overgrowths are rare and the crystals, sometimes, show vuggy or opaque cores with abundant gaps and growth rings resulting in the crystals zonation. The average elongation of the non-fractured crystals is 1.7. The zircon populations from nine samples are highly variable with the majority having enlarged cores S,,~,,~,8 (Fig. 9). This distribution is similar to the quartz diorite zircon population one.

SFBL zircon crystals are euhedral to subhedral, zoned and with a highly developed and thick overgrowth, which can be apical, unilateral or cover all the crystal. The crystals are generally brown, sometimes dark, containing various inclusions and vugs. The SFBL zircon crystals show various grouping habits, prismatic, pyramidal and oblique. The average elongation of non-fractured crystals is 1.93. The typological distribution of zircon populations is slightly widened with a concentration around a high frequency core S,, (Fig. 9).

In the typological (A, T) diagram, Sidi Flah granitoids occupy the calc-alkaline hybrid granites domain (Fig. 1 la ) .

Ougnat granitoids

Quartz diorite shows subhedral (fragmented) to euhedral zircons, slightly yellow brown coloured, zoned and containing solid and crystallized inclusions. The zircon grouping and zonal overgrowths are rare. The quartz diorite zircon crystals show average elongation value equal to 1.86 and the zircon populations cluster around the high frequency core S,,, S,,.,9 (Fig. 10).

The amphibole granodiorite has euhedral zircon crystals, colourless and without any relic cores. The outer overgrowths are rare, and the crystals are zoned, poorly fractured and concentric steps rich. The grouping habits

Gondwana Research, I? 6, No. 4, 2003


1000

)I: SFGd44: Gimodiorite

, v -.

v) a2

3 10, 2 : 2

1 1 " " " " " " ' La Ce Sin Eu C, Dy Yb Lu La Ce Sin Eu C, Dy Yb Lu

Ougnat qz-diorite Ougnat garnet-bearing Ab-LG5 LHl: Qz-diorite 0 TOURGl 15 TOURG2

3 leucogranite * .- 2 100 :

. Fig. 7. Chondr i te -normal ized v) 10 i

REE patterns of Sidi Flah and Ougnat granitoids. Normalizing values from Boynton (1984).

1 " " " " " " '

La Cc SIn Eu G Dy 1% Lu La Ce Sin Eu Cr Dy Yb Lu

are prismatic ones. The amphibole granodiorite zircon crystals mean elongation is 1.90, and the zircon population distribution is identical to the quartz diorite. It shows a high frequency 'Ore s ~ , - ~ g with the appearance Of the alkaline sub-types S,, and S,, (Fig. 10).

The biotite granodiorite zircon crystals (facies close

Discussion and Conclusion Petrological and geochemical data that characterize the

Saghro granitoids in Sidi Flab and Ougnat, allows us to discuss their emplacement and their related geotectonic schemes. They intruded Proterozoic metasediments at ca.

to the OGL) show pronounced differences compared to the amphibole granodiorite ones. They are euhedral, slightly coloured and highly zoned, and the hyaline inclusions are more abundant than in the previous rocks. The zonal overgrowths are developed and can totally include the mineral. The crystals show some two or three individuals associations parallel to C axes. The relic nuclei take elongated forms thus implying neogenic crystals with higher elongation E = 2.3 (Pupin, 1997). The facies zircon populations show some nuclei S,.,, (Fig. 10). OGL shows some colourless to pinkish zircon crystals,

weakly zoned and very rich in inclusions compared to the zircons of the previous rocks. The prismatic groups, the brown-yellow and with zonal structures overgrowths, the elongated cores and the steps are abundant. The mean elongation of seven zircon populations gives a value of 2.85. The typological distribution of the types and sub- types show the appearance of the L, sub-type whereas the S- type is largely dominant. The high frequency core of the zircon populations in OGL is parted between the S,, S, and S, sub-types (Fig. lo).

Quartz diorite and granodiorite plot in the calc-alkaline hybrid granites domain in the typological (A, T) diagram whereas OGL occupies the crustal granites domain (Fig. 1 lb).

" so 60 70 so

1.L I I

2 0.4 t I

I Garnet leucogranite

O L I

so 60 70 so S O z (?!)

Fig. 8. (Lu/Gd), ratio vs. SO, for the studied rocks.

Goiidiuniin Research, V. 6, No. 4, 2003


580-547 Ma and have major and trace elements signatures consistent with continental arc environment origin.

The ACF plot (Fig. 5 ) was used along wi th mineralogical, geochemical and geotectonic setting criteria, to discriminate between I- and S-type dominant granitoid melt sources. Most samples of Sidi Flah and Ougnat quartz diorites and granodiorites plot as I-type granitoids, whereas SFBL and OGL are placed in the field of S-type granitoids. Quartz diorites and granodiorites, containing hornblende and biotite, have A/CNK values varying from 0.9 to 1.2 implying slightly peraluminous to metaluminous character, and their ZNCY index does not exceed 350 (127-307). In addition, if the Na,O/K,O ratio is used as a discriminatory diagram (Chappell and White, 1984), almost all studied samples of quartz diorites and granodiorites have their ratio greater than 3. Since these rocks contain non-xenocrystic zircon, saturat ion temperatures of zircon can be estimated from the major element compositions as described by Watson and

Fig. 9. Frequency dis t r ibut ion of t h e different subtypes in the zircon populations from studied rocks of Sidi Flah. T h e (A, T) coordinatcs of t h e mean point of each popula t ion a r e ind ica ted below t h e cor responding typology d is t r ibu t ion diagram. The number between brackets represents the number of samples with an estimation of 80 to 100 zircons analyzed per sample.

Harrison (1 983). The calculated magma temperature ranges from 850 to 961°C. These values are lightly high in relation to zircon typology temperatures calculated from T index that range between 800 and 850°C. For most of the population, this is near the lower end temperature range of the Navajo granitoids in southwestern United States (7O0-95O0C, Anderson, 1996; Condie et al., 1999).

Quartz diorites and granodiorites have characteristics of medium to high-K calc-alkaline trend. The quartz diorite zircon populations cluster in the S,,.,, sub-types implying a low A index (391) and a high T index (585). Amphibole granodiorites show identical zircon populations spreading to the quartz diorites populations with the appearance of D, J,, P, and P, sub-types. This suggests an increase of the A index whereas the T index does not vary much. The migration towards a higher A index is marked from the quartz diorites to the amphibole granodiorites by alkaline enrichment of the environment (El Baghdadi et al., 2001a) (Fig. 5). All samples of the quartz diorite and granodiorites

Goizdwmn Resrnrch, V. 6, No. 4, 2003

A index A index


fall in the field of hybrid or calc-alkaline granitoids (Fig. 11), which regroup most I-type granitoids.

Geochemical evolution of SFBL represents distinctive trend in relation to the quartz diorite and granodiorite, which can be related to high-K calc-alkaline trend. According to its A/CNK ratio (1.1-1.5), and its projection in ACF diagram it can be classified among the S-type granites, but several criteria do not consolidate this proposal: (1) The outcrop of SFBL does not show any form of melting of surrounding metasedimentary rocks and the contact between these two units is sharp. (2) The spread of zircon populations in the (A, T) diagram (Fig. 9) shows maximum frequency around S,, sub-type implying high A and T indices (520 and 620 respectively) with clearly expressed P, D and J types and all average points fall in the field of crust-mantle hybrid granites (I-type granites) characterized by high A and T indices contrary to crustal derived granites (S-type granites) that show low indices A and T as we can see for the OGL. However, the zircon crystallization of SFBL involves a more

A index

K,O-rich calc-alkaline trend than the previous one, and its evolution is illustrated by a decrease of T index whereas A index stays almost constant. (3) The absence of inherited cores suggests that the temperature of zircon dissolution in the silicate melt is higher than 850°C (Watson, 1996). Calculated zircon saturation temperature is around 797-880°C (Table l), which is high to the crustal produced melt temperature. (4) The distinctive isotopic signature of the SFBL in relation to quartz diorite and granodiorite is also consistent with the presence of two trends in Sidi Flah (Mrini, 1993). Thus, the SFBL shows a relatively low 143Nd/144Nd ratio and a higher s7Sr/86Sr ratio compared to quartz diorite and granodiorite as shown below (Table 2). The relatively higher 87Sr/86Sr ratio reflects the important participation of the crustal material in the genesis of the SFBL.

In the same way as the SFBL, OGL shows distinctive trend to the quartz diorite and granodiorite, but in this case, petrographic, mineralogical and chemical data support formation of the OGL from a crustal source that

A index

Fig. 10. Frequency distribution of t he different subtypes in the zircon populations from studied rocks of Ougnat. The (A, T) coordinates of the mean point of each population are indicated below the corresponding typology distribution diagram. The number between brackets represents the number of samples with an estimation of 80 to 100 zircons analyzed per sample.

Gondwaiin Resenrch, 1/: 6, No. 4, 2003


A i n d a 0 100 200 300 400 5 0 0 G O 0 700 800

0

100

200

p.: 300 3" .: 4 0 0 b

500

600

700

so0

Fig. 11.

E'ioti te leucogrnnite I Granodioriti 0 Qz-diorite

MG Mantle aranite HG Hybnd Gantt, C G Crustal ynni te

0

100

20 0

300

w 8 3 4 0 0

1 1

500 E

600

700

a 0 0

A index 0 100 200 300 400 500 600 7 0 0 800

0 Garnet leucograiiite Gruiodiodte Qz-diorite

Sidi Flah (a) and Ougnat (b) granitoid zircon population mean (A, T) points projected in the diagram (IA, IT) according to the schcme proposed by Pupin (1988). a- Arrows (1) and (2) show two Sidi Flah cvolution; quartz diorite/granodioritc and biotite granite rcspectivcly. b- Lcucogranites arc clearly scparatcd from quartz dioritc/granodiorite trcnds.

still unknown. (1) Petrographic features of the OGL show a low temperature melt paragenesis to which is added melt residues like garnet and probably biotite. (2) OGL shows zircon crystals with pyramidal (21 l} and prismatic { 1 lo} faces that lead to the development of the S,, S,, S, and S, sub-types implying low A and T indices. Average points (A, T) of analyzed populations plot in field of crustal originating aluminous allochtone leucogranites in the (A, T) diagram (Fig. 10) according to Pupin (1988) nomenclature. (3) The OGL shows HREE depletion that implies certainly a different origin from the intermediate rocks and also from the SFBL. Compared to metapelites of Jung et al. (1999, 2000), mctasedimentary xenoliths of Borg and Clynne (1998) and to the average of the upper continental crust of McLennan (2001) and Taylor and McLennan (1985) , the HREE of OGL are strongly fractioned and are similar to the REE patterns of liquids resulting from partial melting of crustal xenoliths (Borg and Clynne, 1998). The HREE depletion can be connected to their compatible character during partial melting owing to the fact that they concentrate in preference in the

residual melt. Generally, S-type leucocratic granites worldwide have low total REE contents with a flat pattern and LREE concentrations below 100" chondritic and HREE abundances below 5-10* chondritic. Additionally, they have negative Eu anomalies with Eu/Eu* <0.5 (Williamson et al., 1996; Jung et al., 2001). These REE patterns have been explained by fractional crystallization of accessory phases and plagioclase. In OGL granite, the differentiation can involve mainly zircon and apatite but not garnet because it occurs as xenocrysts and is largely accumulated in restitic metasedimentary rocks if they can be considered like so. Geochemical data of the OGL are slightly similar to these of S-type granites of Lachlan Fold Belt in Australia (Chappell and White, 1974) and of Manaslu in the Himalayas (Inger and Harris, 1992; Patin6-Douce and Harris, 1998). They show low contents of Sr, CaO and ferromagnesians (TiO, + FeOt + MgO + MnO < 2%, except for AB-LG149) and its A/CNK ratio translates the peraluminous character. The Rb/Sr ratio coincides with that of the anatectic granites associated with Damara Belt migmatites (Jung et al., 1999, 2000). Furthermore, Nd

'Tablc 2. Gcochronological and isotopic data of Saghro and Ougnat granitoids.

%d'

Sidi Flah Quartz diorite 385 t 30Ma 0.703 0.51253a +1.2

Massifs Rocks Age and method' 87Sr/86Sr1 147Nd/ll4Ndl

Granodioritc (Rb/Sr) * 0.708 0.512350 +0.5 SFBL 580t5MA (U/Pb) 0.712 0.5 121 93 -2.4

580t5Ma (U/Pb)

55025 Ma2 Ougnat Quartz diorite 547t26 Ma "U/Pb) -2.8

OGL -4 5

Note: IMrini (1993); 2C1icilletz and Gasquet (2001); "age without geological significancc.

Gondzuaim Rest~arch, V. 6, No. 4, 2003


1000

100 h

E II L1

10 8

1

1 10 100 1 OD0 1 10 100 1000

Fig. 12. Sidi Flah (a) and Ougnat (b) granitoids plot on Rb vs. (Nb+Y) gcotcctonic diagram of Pearce ct al. (1984) in the field of VAG. According to rcccnt studies on post-collisional tectonic sccting, Saghro rocks have post-collisional signature (circlc). Syn-COLG- syn-collisional granites; WPG-within-platc granitcs; VAG-volcanic arc granitcs; ORG-ocean ridge granites.

isotopic composition ( E ~ ~ ~ = -4.5; Mrini, 1993) support the proposal idea, and weak Sr/Ba ratio (<0.3) suggests that the production of OGL occurs near to H,O under- saturated conditions starting from the biotite dehydration reactions (Harris and Inger, 1992). Also, experimental data indicate that restites resulting from vapor-absent melting reactions of biotite in pelites should contain significant amounts of garnet (Vielzeuf and Holloway, 1988; Le Breton and Thompson, 1988; Patina-Douce and Johnson, 1991; Vielzeuf and Montel, 1994). Abia (1991) concludes that surrounding metasedimentary rocks in Ougnat contain similar garnet to that of the leucogranite but there is no more matter to consider these rocks as the source of the OGL.

Low Zr concentrations in the OGL (61-98 ppm) suggest relatively low temperatures of crystallization. As shown by zircon typology, the majority of the zircon crystals contain relic cores which are inherited from the source due to the sluggishness of zircon dissolution in granitic melt (Watson, 1996) and consequently, the Zr contents of the minimum melt would be more weak. Nevertheless,

Table 3. Tcmperature cstiinatcs ("C) for Ougnat garnet-bearing lcucogranitc using empirical cquations for clcment saturation for Zr and LREE, and T indcx of zircon typology method.

Zr LREE T indcx saturation saturation tcinpcrature

TOURGl 750°C 649°C 679°C TOURG2 736°C 665°C 65 1°C AB-LG5 688°C 705°C AB-J12 656°C AB-LG49 906°C

at high temperature (>85O0C), almost all zircons may be expected to go into solution (Watson, 1996) and the presence of inherited cores in nearly all zircon, together with low Zr concentrations, is strong evidence for lcucogranite formation at low temperature ( <8OO0C). Calculated temperatures from zircon saturation (Watson and Harrison, 1983), REE saturation (Montel, 1993) and zircon typology are presented in Table 3.

We conclude that OGL, as S-type granite, belongs to peraluminous trend accompanied the medium to high-K calc-alkaline post-collisional trend occurring in Saghro inliers and is not related to a collisional event. This proposal is supported by absence of migmatite series and the coexistence of the leucogranite and the intermediate rocks that may be the main heat source causing the melting of until now unknown metasedimentary rocks.

Tectonic Setting Almost all Saghro granitoids with age range between

580 to 547 Ma, plot in a post-collisional field in Pearce et al. (1984) Rb vs. (Yt-Nb) diagram (Fig. 12) (El Baghdadi, 2002). These plots, together with the Nb negative anomaly in the spider diagram (Fig. 6), indicate that Sidi Flah and Ougnat granitoids represent the subduction-related I-type plutonic rocks. OGL represents peraluminous magmatism that accompanies the post- collisional magmatic phases (Likgeois e t al., 1998). Saquaque et al. (1989, 1992) proposed that the AAMF in Bou-Azzer represents the northern limit of WAC, while Saghro inlier (Fig. 1) has been interpreted as a Pan-African continental arc and associated environments (Mokhtari et al. 1995; El Baghdadi et al., 2001b). Recent works in

Goizdwnna Research, V. 6 , No. 4, 2003

570 M. EL BAGIHDADI ET AL.

the Zenaga inlier (Ennih, 2000; Ennih and Likgeois, 2001) conclude that the northern limit of the WAC is represented by the SAF and not the AAMF; and all, oceanic island arc assemblage and late post-collisional Pan-African (585-560 Ma) high-K calc-alkaline and alkaline granites with associated volcanic rocks, are thrusted upon the WAC. However, the major part of the Avalonian terranes has to be searched as relics in the north of the AAMF as signaled by Ennih and LiPgeois (2002). Among the observations that Ennih and LiPgeois (2002) has based to corroborate this proposal, is the existence of muscovite-bearing granite in Imiter, which is attributed by Hindermeyer (1977) and Choubert (1963) to the eburnean orogeny. Recent study in Imiter granitoids (El Baghdadi, 2002) does not support this idea because muscovite represents secondary mineral and not primary as found in eburnean granitoids. Furthermore, zircon typology of the muscovite-bearing granite does not indicate a continental crust origin but a hybrid source (El Baghdadi, 2002). In the same way, the thrusting from North to South that affects all Saghro arc and Bou-Azzer ophiolitic series does not show any structural markers especially in granitoids and lower Neoproterozoic metasedimentary rocks. Though AAMF or SAF is the northern limit of WAC, Saghro granitoids record a magmatic activity linked to the volcanic arcs setting, and we can conclude that Sidi Flah and Ougnat granitoids belong to three magmatic series taking place in a post- collisional event:

Medium- to high-K calc-alkaline trend formed by quartz diorites and granodiorites in Sidi Flah and Ougnat inliers.

High-K calc-alkaline trend occurred by SFBL in Sidi Flah. Peraluminous trend represented by OGL in Ougnat,

which is linked to post-collisional and not collisional setting.

These rocks were related to the north-dipping subduction of an oceanic plate beneath Saghro continental arc. They were post-orogenic I-type granitoids and related to the ending of the compressional deformation and beginning of extensional deformation leading to emplacement of strong Isk n'Allah A-type plutons (El Baghdadi, 2002). Thus, Saghro and Ougnat I-type granitic rocks are probably related to a much deeper homogeneous source in Saghro mainland while, Ougnat S-type granite is related to a shallow source probably surrounding metasedimentary rocks.

References Abia, EL. 13. (1991) Cartographie, petrologie, metallogCnie du

Proterozoique du district Pb, Zn, Cu et Ba de Mellab, massif de I'Ougnat, (Anti-Atlas, Maroc). These 3"cycle Marrakech, 184p.

Abia, EL.H., Nachit, H. and Chouhaidi, M.Y. (1995) Plutonisme

et relation structuro-metamorphiques pan-africains de la boutonni6re de I'Ougnat (Anti-Atlas oriental, Maroc). Reunion Extraordinaire Societk gkologique d e France. Accretion continentale au Proterozoi'que superieur et au Palkozoi'que du Nord-Ouest africain. Marrakech-Agadir, Maroc, p. 3.

Anderson, J.L. (1996) Status of thermobarometry in granitic batholiths. Trans. Royal SOC. Edinburg: Earth Sci., v. 87, pp.

Bknard, F., Moutou, l? and Pichavant, M. (1985) Phase relations of tourmaline leucogranites and the significance of tourmaline in silisic magmas. J. Geol., v. 93, pp. 271-291.

Benziane, F. and Yazidi, A. (1992) Correlation des formations du Proterozo'ique superieur. Notes et Memoires Service GCologique du Maroc, v. 366, pp. 147-157.

Borg, L.E. and Clynne, M.A. (1998) The petrogenesis of felsic calc-alkaline magmas from the southernmost Cascades, California: origin by partial melting of basaltic lower crust. J. Petrol., v. 39, pp. 1169-1195.

Boynton, W.V. (1984) Geochemistry of the rare earth elements: meteorite studies. In: Henderson P. (Eds.), Rare earth element geochemistry. Elsevier, pp. 63-114.

Caironi, V., Colombo, A., Tunesi, A. and Gritti, C. (2000) Chemical variations of zircon compared with morphological evolution during magmatic crystallization: an example from the Valle del Cervo Pluton (Western Alps). European. J. Mineral.,

Chappell, B. and White, A.J.R. (1974) Two contrasting granite types. Pacific geol., v. 8, pp. 173.174.

Chappell, B.W and White A.J.R. (1984) 1- and S-type granites in the Lachlan Fold Belt, southeastern Australia In Xu Keqin and Tu Guangchi (Eds.), Geology of granites and their metallogenic relation, Beijing: Sciences press, pp. 87-101.

Chappell, B. and White, A.J.R. (1992) I- and S-type granites in the Lachlan Fold Belt. Trans. Royal SOC. Edinburgh: Earth Sci., v. 83, pp. 1-26.

Cheilletz, A. and Gasquet, D. (2001) specific plate tectonic environments for the Anti-Atlas more deposits. Zeme colloque international 3MA, Marrakech, 84p.

Choubert, G. (1963) Histoire gkologique de 1'Anti-Atlas. Tome I. Notes et Mem. Sen. Geol. Maroc, v. 162, 35213.

Chouhaidi, M.Y., Abia, El H., Camara, L.S., Aarab, El M. and Sagon, J. P. (1995) Les plutonites de 1'Anti-Atlas oriental, Maroc. Reunion Extraordinaire SOC. Gkol. France. Accretion continentale au Proterozoi'que superieur et au Palkozoique du Nord-Ouest africain. Marrakech-Agadir, Maroc, p. 29.

Condie, K.C., Latysh, N., Schmus, W.R., Kozuch, H. and

15-138.

v. 12, pp. 779-794.

El

Selverstone, J. (1999) Geochemistry, Nd and isotopes, and U/Pb zircon ages of granitoids and metasedimentary xenoliths from the Navajo volcanic field, Four Corners area, southwestern United States. Chem. Geol., v. 156,

Baghdadi, M. (2002) Les granitoi'des du Proterozoi'que supkrieur de 1'Anti Atlas oriental (Saghro et Ougnat, Maroc), Petrographie, Geochimie, Typologie du zircon et implication gkodynamique. Doctorat d'Etat, Univ. Marrakech, 381p.

pp. 95-133.

El Baghdadi, M., El Boukhari, A., Nadem, S., Benyoucef, A. and Jouider, A. (2001a) Typologie du zircon dans les granitoi'des de la boutonniere prbcambrienne de Sidi Flah (Saghro, Anti- Atlas, Maroc). J. African Earth Sci., v. 32, pp. 661-681.

El Baghdadi, M., El Boulthari, A., Nadem, S., Benyoucef, A. and

Gondwaiw Research, V. 6, No. 4, 2003

GRANITOIDS FROM PAN-AFRICAN BELT SOUTH MOROCCO 571

Jouider, A. (2001b) Petrographic, Geochemical and zircon typology of Neoproterozoic Granitoids: evidence of continental thickening in Saghro arc (Eastern Anti-Atlas, Morocco), Gondwana Res., v. 4, pp. 612.

Ennih, N. (2000) Superposition des orogeneses kburneenne et panafricaine dans la marge nord du craton ouest Africain : La boutonniere palkoprot6rozo'ique de Zknaga (Anti-Atlas central, Maroc). These es-sciences. Univ. El Jadida, 224p.

Ennih, N. and Liegeois, J.P. (2002) The Moroccan Anti-Atlas: the West African craton passive margin with limited Pan-African activity: implications for the northern limit of craton. Precambrian Res., v. 112, pp. 289-302.

Ezzouhairi, H. (1989) Etude petrographique, gkochimique et structurale des formations plutoniques du precambrien I1 de la boutonniere de Bouskour (Saghro occidental, Anti Atlas, Maroc). These 3Pme cycle, Marrakech, 210p.

Harris, N.B.W. and Inger, S. (1992) Trace element modelling of pelite derived granites. Contrib. Mineral. Petrol., v. 110,

Heiferan, K.P., Admou, H., Karson, J.A. and Saquaque, A. (2000) Anti-Atlas (Morocco) role in Neoproterozoic western Gondwana reconstitution. Precambrian Res., v. 103, pp. 96.

Hindernieyer, J. (1977) Carte gkologique du Jbel Saghro-Dad& au 1/200 000. Notes et Mkm. Serv. Gkol. Maroc, v. 161.

Iloltz F., and Johannes, W. (1991) Genesis of peraluminous granites, I, Experimental investigation of melt composition at 3 and 5 kbar and reduced H,O activity. J. Petrology, v. 23,

Hoskin, P.W. (2000) Patterns of chaos: fractal statistics and the oscillatory chemistry of zircon. Geochem. Cosmochim. Acta.,

Hoskin, P.W., Kinny, P.D., Wyborn, D. and Chappell, B.W. (2000) Identifying accessory minera l sa tura t ion dur ing differentiation in granitoid magmas: an integrated approach. J. Petrol., v. 41, pp. 1365-1396.

Inger, S. and Narris, N. (1992) Tectonothermal evolution of the High Himalayan crystalline sequence, Langtang valley, northern Nepal. J. Metamor. Geol., v. 10, pp. 439-452.

Jung, S., Hocrnes, S. and Mezger, K. (2000) Geochronology and petrology of migmatites from the Proterozoic Damara belt: importance of episodic fluid-present disequilibrium melting and consequences for granite petrology. Lithos,

Jung, S., Mezger, K. and Hoernes, S. (2001) Trace element and isotopic (Sr, Nd, Pb, 0) arguments for a mid-crustal origin of Pan-African garnet-bearing S-type granites from the Damara orogen (Namibia). Precambrian Res., v. 110, pp. 325-355.

Jung, S., Hoernes, S., Masberg, P. and Hoffer, E. (1999) The petrogenesis of some migmatites and granites (central Damara Orogen, Namibia): evidence for disequilibrium melting, Wall rock contamination and crystal fractionation. J. Petrol., v. 40, pp. 1241-1269.

Lameyre, J. and Bowden, P. (1982) Plutonic rock types series: discrimination of various granitoid series and related rocks. J. Volcanol. Geothermal. Res., v. 14, pp. 169.186.

Le Breton, N. and Thompson, A.B., (1988) Fluid-absent melting of biotite in nietapelites in the early stages of crustal anatexis. Contrib. Mineral. Petrol., v. 99, pp. 226-237.

Leblanc, M. (1981) Ophiolites precambriennes et gites arsenies de cobalt (Bou-Azzer, Maroc). Notes et Mkm. Serv. Gkologique du Maroc, v. 280, 360p.

pp. 46-56.

pp. 935-958.

V. 64, pp. 1905-1923.

V. 51, pp. 153-179.

Leblanc, M. and Lancelot, J. R. (1980) Interpretation gkodynamique du domaine panafricain (Precambrien terminal) de 1'Anti- Atlas (Maroc) a partir des donnkes geologiques e t gkochronologiques. Can. J. Earth Sci., v. 17, pp. 142-155.

Liegeois, J.P., Navez, J . , Hertogen, J., Black, R. (1998) Contrasting origin of post-collisional high-K calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids: The use of sliding normalization. Lithos, v. 45, pp. 1-28.

McLennan, S. (2001) Relationship between the trace element composition of sedimentary rocks and upper continental crust. Geochem. Geophys. Geosyst., v. 2, paper N" 2000GE000109.

Miller, C.F and Mittlefehlt, D.W. (1984) Extreme fractionation in felsic magma chambers: a product of liquid-state diffusion or fractional crystallization? Earth Planet. Sci. Lett., v. 68,

Mokhtari, A,, Gasquet, D. and Rocci, G. (1995) Les tholkiites de Tagmout (J. Saghro, Anti-Atlas, Maroc), Tkmoin d'un rift au Proterozoi'que supkrieur. C.R. Acad. Sci. Paris, 11, t. 320,

Montel, J.M. (1993) A model for monazite-melt equilibrium and application to the generation of granitic magmas. Chem. Geol., v. 110, pp. 127-146.

Mrini, Z. (1993) Chronologie (Rb-Sr, U-Pb), traqage isotopique (Sr-Nd-Pb) des sources de roches magmatiques kburnkennes, panafricaines et hercyniennes du Maroc. These es-sciences, Marrakech, 200p.

Nasdala, L., Wenzel, T., Pidgeon, T.R. and Kronz, A. (1999) Internal structures and dating of complex zircons from Meissen massif monzonites, Saxony. Chem. Geol., v. 156,

Nerci, K. (1988) La boutonniere de Sidi Flah (Saghro, Anti Atlas, Maroc), contribution B l'ktude de ses minkralisations B PB, Zn, Cu, Ag et de leur cadre gkologique. These 3eme cycle. Univ. Rabat, Maroc, 222p.

PatinGDouce, A.E. and Dana-Johnson, A. (1991) Phase equilibria and melt productivity in the pelitic system: implications for the origin of peraluminous granitoids and aluminous granulites. Contrib. Mineral. Petrol., v. 107, pp. 202-218.

Patino-Douce, A.E. and Harris, N. (1998) Experimental constraints on Himalaya anatexis. J. Petrol., v. 39, pp.' 689-710.

Pearce, J.A., Harris, B.W. and Tindle, A.G. (1984) Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol., v. 25, pp. 956-983.

Pupin, J.P. (1980) Zircon and granite petrology. Contrib. Mineral. Petrol., v. 73, pp. 207-220.

Pupin, J.P. (1988) Granites as indicators in Paleodynamics. Rendiconti SOC. It. Mineral. Petrol., v. 43-2, pp. 237-262.

Pupin, J.P. (1997) Caractkrisation des protolithes des migmatites et granites anatectiques crustaux d'apres ]'etude des zircons. C.R. Acad. Sci. Paris, 11, t. 319, p. 1191-1197.

Pupin, J.P. and Turco, G. (1972) Une typologie originale du zircon accessoire. Bull. SOC. Fr. Mineral. Cristal., v. 95, pp. 348-359.

Pupin, J.P. and Turco, G. (1981) Le zircon, mineral commun significatif des roches endogenes et exogilnes. Bull. Mineral.,

Rjimati, E., Derre, C., Lecolle, M., Lillie, F., Nerci, K., Azza, A. and Bennani, A. (1992) Caracteristique de la tectonique panafricaine dans le Jbel Saghro (Anti Atlas, Maroc). ). Notes et Mkmoires du Service Geologique du Maroc, v. 366,

Rottura, A., Caggianelli, A., Del Moro, A., Acquafredda, P. and

pp. 151-158.

pp. 381-386.

pp. 331-341.

V. 104, pp. 724-731.

pp. 387-394.

Gorid~aaizn Resmich, V. 6, No. 4, 2003

5 72 M. EL BAGHDAD1 ET AL.

Bargossi, M. (1998) Mechanical and chemical interaction between mafic and felsic magmas in the late evolution of the Ivigna granodiorite, Southern Alps. Miner. Petrogr. Acta,

Sun, S.S. and McDonough, W.E (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunder A.D and Norry J.M. (Eds.) Magmatism in ocean basins, Geol. SOC. London Spl.

Saquaque , A. (1992) Un exemple d e Suture-arc : Le Precambrien de 1’Anti Atlas centre-oriental, Maroc. Thkse es-sciences, Marrakech, 348p.

Saquaque, A., Admou, H., Karson, J.A., Heffran, K.P, and Reuber, I. (1989) Precambrian accretionary tectonics in the Bou Azzer El Graara region, Anti-Atlas, Morocco. Geology, v. 17,

Saquaque, A., Benharref, M., Abia, H., Mrini, Z., Reuber, I. and Karson, J.A. (1992) Evidence for a pan-african volcanic arc and wrench fault tectonics in the Jbel Saghro (Anti-Atlas, Morocco). Geol. Rundsch, v. 81, pp. 1-13.

Schermaier, A., Haunschmid, B., Schubert, G., Frasl, G. and Finger, F. (1992) Diskriminierung von S-typ und I-typ graniten auf der basis zirkontypologischer untersuchungen. Frankfurter Geowiss. Arb, Geologie-Palaontologie, v. 11,

v. XLI, pp. 1-20.

Publ., V. 42, pp. 313-345.

pp. 1107-1110.

pp. 149-153.

Strekeisen, A. (1976) To each plutonic rock its proper name. Earth Sci. Rev., v. 12, pp. 1-33.

Taylor, S.R. and McLennan, S.M. (1985) The continental crust: its composition and evolution. Blackwell, Oxford.

Vavra, G., Schmid, R. and Gebauer, D. (1999) Internal morphology, habit and U-Th-Pb microanalysis of amphibolite to granulite facies zircon: geochronology of the Ivrea zone (Southern Alps). Contrib. Mineral. Petrol., v. 134, pp. 380-404.

Vielzeuf, D. and Holloway, J.R. (1988) Experimental determination of the fluid-absent melting relations in the pelitic system. Contrib. Mineral. Petrol., v. 98, pp. 257-276.

Vielzeuf, D. and Montel, J.M. (1994) Partial melting of meta- greywackes: Part I. fluid-absent experiments and phase relationships. Contrib. Mineral. Petrol., v. 117, pp. 375-393.

Watson, B.E. (1996) Dissolution, growth and survival of zircon during crustal fusion Kinetic principles, geological models and implications for isotopic inheritance. Trans. Royal. SOC. Edinburgh: Earth Sci., v. 87, pp. 43-56.

Watson, B.E and Harrison, TM. (1983) Zircon Saturation revisited: temperature and composition effects in a variety of crustal magma types. Earth Planet. Sci. Letters, v. 64, pp. 295-304.

Williamson, B.J., Shaw, A., Downes, H., Thirlwall, M.F. (1996) Geochemical constraints on the genesis of Hercynian two- mica leucogranites from the Massif Central, France. Chem. Geol., v. 127, pp. 25-42.

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