Chemistry of rock-forming minerals in pluton, Western Srednogorie,

S. Atanasova-Vladimirova, A. von Quadt, K. Kouzmanov, I. Peytcheva, B. Mavrudchiev Aims and methods ™Aims of this study:

•Detail petrography characteristic of the rocks from the Vitosha pluton

•Geochemical characteristics

Methods

¾ Terrain sampling

¾ Microscope studies

¾ Microprobe analysis

¾ LA-ICP-MS analysis Location

Vitosha... in Alpine system

18 50 30 C AR PA TH IA NS

D IN Black A R sea ID S E E BALKAN S R B O

- SREDNO M GORIE A C E RHOD H V D OPE A O E R N L D I A A L R N E N 40 Vitosha pluton ID 40 E N S M e d i ES t e RID r TAU r a n e a n s e a 18 E 30

Diagram map in the , after Dinter et al., 1995 Geology Gabbro

Monzonite

Syenite Geological map of the Vitosha mountain in scale 1: 100 000, Granosyenite map sheet (editor I. Zagorchev, 1994), with authors processing Volcanic rocks Petrography and mineralogy Petrology

24 O

2 Gb

K MzGb

20 + Mz

O 2

a Sy

N Ap 16

12 QSy Sy 8

Mz QMz 4 Gr Ad GDi AdB Q>5 Gb SiO 0 2 32 38 44 50 56 62 68 74 80 Pyroxene Petrology Di Hd ORTHOPYROXENE (Opx). Orthopyroxene Diopside Hedenbergite Gb form resorbtion nucleus covered by MzGb Augite Mz clinopyroxene. Мg # - 63-64. Sy CLINOPYROXENE (Cpx). According to the Pigeonite classification of the Morimoto et al. analyzed Clinoenstatite Clinoferrosillite Cpx are diopsides and augites and they form single grain or pyroxene – amphibole En Fs Pyroxene from the Vitosha pluton complexes. (Morimoto et al., 1988) Мg # 68-80 - gabbro. Mg # 67-77 - monzogabbro Mg # 67-74 - monzonite Mg # 58–71 - syenite

Px Kfd Mg# 51

Pl An 32.8

Mg# 66 Q Or 82.4 Amph Kfd Amphibole Petrology AMPHIBOLE (Amph). According to

Tremolite

+ ) 2 the classification scheme of Leake et al. Actinolite Magnesio-Hbl

e Tschermakite (1997) analyzed amphibole are F

+ magnesio-Hbl and actinolite. The

g amphiboles are formed before or M

( Ferro- / Gb simultaneous with biotite. It is change Ferro-Hbl

g Tschermakite MzGb Actinolite Mz from epidote and chlorite. M Sy Мg#= 68 – 85 – gabbro Mg # = 71 - 80 - monzogabbro Si a.p.f.y. Mg # = 77 - 79 - monzonite Amphibole classification diagram Mg# = 57 – 73 - syenite (Leake et al., 1997)

The microphoto was make in на microscope Olympus, parallel nicol – Х 10 Biotite Petrology BIOTITE. In all type of rocks the biotite is xenomorphic, in some cases it replace the hornblende, and in other cases Bi is replaced by the hornblende. Мg#= 41 – 53 (gabbro) Mg # = 66 - 72 (monzogabbro) Mg # = 59 – 66 (monzonite) Mg#= 41-55(syenite)

3 Eastonite Siderophyllite IV Al

Biotite classification diagram for gabbro Annite Phlogopite 2 011 Fe/(Fe+Mg) Biotite classification diagram for monzonite Biotite classification diagram for syenite Plagioclase Petrology Plagioclase composition spans almost crystallization history of the pluton.

Gb Cores An92.5;An66.5 Rims An55.5,An30.3 - Gb MzGb Mz Cores An60.2;An58.5 Rims An57.6;An49.7 –MzGb Sy Cores An42.2;An49.6 Rims An31.5;An42.2 -Mz Cores An48.1;An23.8 Rims An24.6;An21.5 -Sy

POTASSIUM FELDSPAR KFd is transparent or poorly transform in

Pl An 39.4 clay mineral. They form big crystal and dispose Kfd between plagioclase crystal. In Aplite and Pl Or 85.4 An 49.0 pegmatite the potassium feldspar is the most widespread mineral and in some of them it Pl reach to 90%. It forms graphic texture from quartz and orthoclase. In cavern form single grain in association with tourmaline. Geochemistry = 0.61 – 1.48 = 0.80 – 1.31 = 0.52 – 2.02 N N N /Yb /Sm /Yb N N N Ce Dy La Clinopyroxene

Geochemistry of the rock-forming minerals •Low REE abundances. •General trend of LREE enrichment and HREE depletion. •Chondrite-La normalized values of are usually less than Ce and Nd in all rocks. •Strongly developed negative Eu anomaly in MzGb, Mz and Sy as an fraction of evidence for much larger pyroxenes. Geochemistry

Amphiboles

•Present in all upper Cretaceous rocks in Vitosha pluton.

•Contains higher REE than clinopyroxene, and may be important carrier for REE.

•LREE are relatively high •HREEvaluesareessentiallyasin the clinopyroxenes.

•Significant negative Eu anomalies

•The total content of REE decreases CeN/SmN = 0.60 – 1.68 with fractionation. DyN/YbN = 0.84 – 1.59 LaN/YbN = 0.72 – 2.50 Geochemistry

Plagioclases

•High LREE/HREE ratio.

•Ca-poor plagioclase shows the high REE abundance.

•Positive Eu anomalies.

CeN/SmN = 2.84 – 19.47 DyN/YbN = 0.22 – 1.84 LaN/YbN = 11.24 – 323.33 Geochemistry

Potassium feldspars

•Low BaO contents (<0.5wt%).

•REE spectra consistently decrease from La to Sm.

•Strong positive Eu-anomaly and slightly increasing HREE spectrum.

CeN/SmN = 4.25 – 89.14 DyN/YbN = 0.31 – 0.96 LaN/YbN = 16.87 – 189.63 Condition on the crystallization of the rock Geothermometer Amphibole – plagioclase equilibrium

Method of Perchuk (1966) Method of Blundy & Holland (1990).

1 Gb MzGb Mz Sy Lamph 0,8

l

P

)

K 0,6

+

a

N 1

+ =

a ° D ° 0 The thermometer of Blundy & Holland is valid for C 0 90 ( K 0 / 10 a 0,4 ° 00 temperature 500 - 1100°С and rocks with plagioclases C 8 0° 70 600°

0 0,2 0,4 0,6 0,8 1 Ca/(Ca+Na+K)Hb

Rock type Т°С Perchuk (1966) Blundy & Holland (1990) Gabbro 550°С - 800°С 769°С - 834°С Monzogabbro 540°С - 700°С 679°С - 719°С Monzonite 679°С - 710°С 700°С - 721°С Syenite 400°С - 550°С 647°С - 756°С Geobarometer Geobarometer Method of Schmidt (1992).

1. The level where the gabbro rocks crystallize is between 7-10 km. The calculate pressure is 3,5 – 2,6 kbar. 2. In monzogabbro and monzonite the calculate pressure is 3,1 – 2,0 kbar, what response to around 7 km. 3. In syenite the calculate pressure is around 2,5 kbar, corresponding on the ≈ 7km.

Gb MzGb Mz Sy

P/T diagram Geodinamic setting

The rocks from Vitosha pluton are relate to І – type granite (Chappel & White, 1974). These are: ™ Association of the femic minerals – amphibole, biotite, titanite, magnetite, ilmenite;

™ The variation of the SiO2, from 45 wt% to 79 wt%; ™ Mol ratio less than 1.1 ( Al2O3/(Na2O+K2O+CaO) < 1.1) ™ The chondrite - normalize diagrams show decreasing of Ta and Nb with progress of the differentiation, suggesting island-arc geodinamic setting.

Discriminate diagrams Rb / (Y+Nb) (Pearce et. Al.,1984) CONCLUSIONS

The observed compositional variations of amphibole, biotite, titanite, magnetite, and ilmenite indicate calc-alkaline I-type magmatic evolution for the Vitosha pluton.

The most important process in the evolution of the magma is the fractional crystallization: the total content of REE increases in the rocks from the gabbro to the syenites. This conclusion is supported by the chemistry of the rock-forming minerals.

Estimated temperatures of crystallization are between 834° and 579°C, based on the Blundy and Holland (1990) geotermometry. The depth of final crystallization of the pluton is considered to be of about 7 km. Thank you for your attention