Advantage of the use of Focused Ion Beam technique to specify mantle fluid inclusions

Transcription

1 Advantage f the use f Fcused In Beam technique t specify mantle fluid inclusins BERKESI, Márta 1, GUZMICS, Tibr 1, SZABÓ, Csaba 1 and DUBESSY, Jean 2 1 Lithsphere Fluid Research Lab, Department f Petrlgy & Gechemistry, Institute f Gegraphy & Earth Sciences, Eötvös University Budapest (ELTE) 2 UMR G2R 7655, Université de Lrraine-CNRS, Vandœuvre-lés- Nancy, France martaberkesi@caesar.elte.hu

2 Intrductin It is knwn that within the fluid inclusins slids (referred t as daughter phase) may crystallize as a result f cling and/r reactin with the hst mineral. If the vlume prprtins f the daughter phases are nt knwn, the fluid cmpsitin determined can be misinterpreted. Hwever, in situ measurement f the daughter phases in mantle fluid inclusins can be cmplicated and ambiguus with cnventinal techniques because f their size and/r cmpsitin. We reprt ur results using FIB (Fcused In Beam) - SEM (scanning electrn micrscpy) technique n investigatin f daughter phases in rthpyrxene-hsted fluid inclusins in mantle xenliths frm the Pannnian Basin.

3 Sampling Pannnian Basin 47 04' km W N S E Basalt lava rcks Basalt pyrclasts Kab-hill 47 00' 46 56' 46 52' Kvácsi-hill Tátika Szebike Füzes-lake 2.6 ± 0.29 Csbánc Sm-hill Bndró-hill Szentbékkálla Tihany 7.92 ± N ' ± ' Szigliget Badacsny Lake Balatn Kpasz-hill ALPS ALCAPA BBHVF NGVF Budapest Middle-Hungarian Zne 0 km ? Tisza-Dacia CARPATHIANS Main faults expsed subcrp 17 30' 17 40' 17 50' BBHVF: Bakny Balatn- Highland Vlcanic Field

4 The fluid inclusins-phtmicrgraphs Hsted mainly by silicates (e.g. Opx-rthpyrxene: Mg 2 Si 2 O 6 ) At rm temperature, cmmnly ne visible liquid ± slid phase(s) within the inclusins Occurs alng healed fractures r in clusters Their size ranges between 2-50 micrns

5 Why FIB-SEM? The tiniest inclusins thught t be preserved the mst representative density f fluid phase a clear psitive crrelatin between fluid inclusin size and hmgenizatin temperature has been revealed, that is why the tiniest inclusins thught t be preserved the mst representative density f fluid phase Small r NO chance fr getting infrmatin by ptical bservatin

6 Why FIB-SEM? Fluid cmpsitin (CO 2 -H 2 O-H 2 S, Berkesi et al., 2009) has already been determined by stepwise heating experiments cupled with Raman spectrscpy Mrever, carbnate and quartz have als been fund by Raman spectrscpy withut having data f their vlume prprtins MgSiO 3 (enstatite)+co 2 = MgCO 3 (magnesite)+sio 2 (quartz) Fluid/hst reactin

7 FIB-SEM pening prcedure Arbitrary size can be cut frm the surface expsed by the in beam and then see the expsed part f the inclusin by SEM and analyze with EDX. The actual prgress f the inclusin expsing prcess is mnitred acquiring secndary electrn (SE) images f the sample.

8 Quartz Magnesite Opx Thin glass film n the wall Results

9 MgSiO 3 (enstatite)+co 2 = MgCO 3 (magnesite)+sio 2 (quartz) The glass film seems t be playing great rle in preserving the CO 2 fluid in mantle fluid inclusins! Opx rthpyrxene, Mgs magnesite, GCM Gallium cntaminated material, En - enstatite, Pl plagiclase, Sp-pinel, Grt - garnet

10 Presence f disslved silicate in CO 2 -rich supercritical fluid: cryptic metasmatism in the mantle The signal when the inclusin is ablated is lnger than expected frm a fluid-rich material (e.g., Allan et al., 2005; Bertelli et al., 2009) The intensity increase f certain elements are linked rather t slid phase(s)

11 Presence f disslved silicate in CO 2 -rich supercritical fluid: cryptic metasmatism in the mantle HFS elements preferentially partitin int the silicate melt with rders f magnitude higher than the fluid-rich phase (Yung and Lee, 2009) the trace elements may nw be cncentrated int a thin film f glass n the fluid inclusin walls (Hidas et al., 2010)

12 Presence f sulfide within mantle fluid inclusins Subhedral S-bearing slid phase (Fe-sulfide) has als been identified, sizing in a range between 400 and 1000 nm. The presence f sulfide allws us t understand the rle f H 2 S fluid mlecule fund by Raman micrspectrscpy in the mantle fluid inclusins (Frezztti and Peccerill 2007; Berkesi et al. 2009; Hidas et al. 2010)

13 Cncluding remarks Daughter phases such as carbnate, quartz and thin glass film including their vlume prprtins can be efficiently studied by FIB-SEM technique n mantle fluid inclusins. The sulfide and the the glass culd nt been detected by using any ther rutinely used analytical technique fr fluid inclusin studies. The acquired results f this study cntribute t 1) precise quantificatin f the bulk fluid cmpsitin and 2) better understanding f the pst entrapment prcesses It is highly likely that there were phase separatins in the fluid inclusins after entrapment f a ne supercritical fluid phase in the mantle, frming slid daughter phases and a melt phase. Then quenching f the melt phase culd have happened nt the wall, preserving further frmatin f carbnate and quartz. This detailed study prvides that disslved silicate cmpnents in a supercritical, vlatile (C-O-H-S)-rich fluid may play a great rle in carrying many trace elements and, cnsequently, in chemical verprinting f the peridtitic mantle

14 Thank Yu fr yur attentin! The Eurpean Unin and the Eurpean Scial Fund have prvided financial supprt t the prject under the grant agreement n. TÁMOP /B-09/KMR