#1Metasomatic processes in the lithospheric mantle beneath the Arkhangelsk province, Russia: evidence from garnet and clinopyroxene of mantle peridotite xenoliths, Grib pipe Alexei Kargin, Lyudmila Sazonova, Anna Nosova, Elena Kovalchuk, and Elena Minevrina GEOSCIENCES EUROPEAN GEO General Assembly 2015 Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry Russian Academy of Sciences (IGEM RAS) [email protected] IGEM RAS CC BY#2Problem and Subject GEOSCIENCES UN EUROPEAN OF General Assembly A worldwide studying of geochemical and mineralogical compositions of garnet peridotite xenoliths records a variety of cryptic and modal metasomatic events [Sablukov et al., 2008; Shchukina et al., 2014, 2015 for Arkhangelsk province]. There are as minimum two stage of the modal metasomatic reworking of the lithosphere mantle [for example model by Griffin et al., 1999]: 1. Carbonate-silicate usually low-T metasomatism with high rare incompatible elements contents produced crystallization of phlogopite, clinopyroxene and carbonate; probably it is ancient stage of metasomatism long before the formation of kimberlite melts; 2. High-T melt metasomatism during the ascent of asthenosphere / plume material and associated with kimberlite melts; 2015 The model by [Russell et al., Nature 2012] supposes the evolution from proto-kimberlite melts like as carbonatite to more silicic composition melts (kimberlite-like) by assimilation of mantle. minerals, (especially orthopyroxene). ? The subject of this studying is estimate of carbonate and silicate components contribution in metasomatic processes in the lithospheric mantle during the forming of Grib kimberlite CC Ο BY [email protected] 2#3Geological setting of Grib kimberlite The Arkhangelsk province is situated in the north part of East European craton. Several fields of kimberlites and related magmatism were distinguished within the province; The Grib pipe is located in the central part of the Arkhangelsk province (Chernoozerskoe field); It is classical kimberlite pipe like as South Africa group 1 kimberlite pipe [Mitchell, 1995]; The kimberlite age is 374 ± 1.3 Ma (Rb-Sr isotope methods by phlogopite) [Lebedeva et al., 2014]. 168 1 M 2 White Sea ADP zb BABI 3 41° 42° 4 Mela Megorsk Chernoozero Verkhotina 36° 42° Griba pipe Zolotica! 40° White Sea 65° EUROPEAN GEOSCIENCES UN General Assembly 2015 Kepino Suksoma 66° 65° Phl Ol autolith 이 porphyritic kimberlite 이 autolithic kimberlite CC BY Arkhangelsk After Sazonova et al. 2015 [email protected] 01-3 V₂ 41° 42° P₁ 25km 3#4EUROPEAN GEOSCIENCES UN General Assembly 2015 Sample 466-2 Mantle peridotite xenoliths and methods • Geochemical compositions of garnets and clinopyroxenes from 19 mantle peridotite xenoliths (from 0.5 to 10 cm) were studied; The peridotite xenoliths have garnet- lherzolites composition and contain: 60-85% olivine; 5-15% orthopyroxene; 5-15% clinopyroxene; 5-15% garnet. Sample 455-2 00000 CC Ο BY Methods: Jeol JXA-8200 electron microprobe; SIMS; LA-ICP-MS Sample 551-3 Sample 673-3 14 [email protected] 4#5Peridotite microscopic textures CC Ο BY The most of peridotites have heterogranular from medium- to coarse- grained (garnet up to 5-7 mm) microscopic textures; One of sample (106-664) has a porphyroclastic, partly blastomylonitic texture that are typical for sheared peridotite granular texture granular texture olivine neoblasts and porphyroblasts [email protected] Gar mechanical twins in oliviné with deforming origin EUROPEAN GEOSCIENCES UN General Gen Assembly 5 2015#6CC Garnet Gar2 BY Garnets commonly form zoned porphyroblasts with size from 3 to 10 mm. 1. central zone (Garl) - 98-50% of garnet area; 2. rim zone (Gar2) with uneven, often macules shapes and consist of garnet with metasomatic origin; 3. secondary zone - the most later rim zone was formed by aggregate of garnet (Gar3), phlogopite, Cr-spinel, carbonate and amphibole, width up to 300 micron. Gar1 1mm 0005 4. Gar2 00μm 0046 634-1 [email protected] Gar2 Gar1 200μm GEOSCIENCES UN EUROPEAN Gen General Assembly Gar1 Gar2 Gart Spn Gar2 Phl Gar2 Gar3 Carb 500m 0001 455-2 Phl Gar3 Spr Gar1 Carb 2015#7Cr2O3- Cao garnet classification • EUROPEAN GEOSCIENCES UN General Assembly The majority of garnets are consistent with the lherzolite garnet field (G9) [Grutter et al., 2004] by Cr2O3 and CaO concentrations; rarely with harzburgitic (G10) and wehrlitic (G12) garnet fields. 12 Cr₂O3 Gar3 Garl 2015 CC Ο BY 200μm 8 Gar1 Gar1 Gar2 G10 harzburgitic garnets Gar2 Z00m 0008 106/664.5 GO G9 lherzolitic garnets G12 wehrlitic garnets Gar1 Gar2 G1 G5 low-Cr megacrysts Megacrysts G4 0 unclassified category pyroxenitic garnets 0 2 4 CaO 6 8 [email protected] Gar2 1mm 0005 100μm 0046 634-1 G3 eclogitic garnets 10 G-classification by Grutter et al., 2004 7#8Ti and Zr in garnet - different metasomatic types Based on Ti concentrations, garnets were divided into two main groups: Low-Ti group: 1. Low-Ti (< 0.27 wt.%) and low- Zr (<20 ppm) garnets are comparable with depleted mantle peridotite garnets by [Griffin et al., 1999]; these are the most part of garnet central zones; 2. Low-Ti (<0.15 wt.%) and high-Zr (30-60 ppm) garnets are comparable with secondary kimberlitic (Ca, Cr)-poor garnets [Ziberna et al., 2013] and with low-T "phlogopite" metasomatic garnets by [Griffin et al., 1999]; these garnets were formed after crystallization of Ti-bearing megacryst minerals (ilmenite). High-Ti group: 1. High-Ti (0.62-0.94 wt.%) and high-Zr (20-60 ppm) garnets are comparable with megacrysts or garnets of "ilmenite" paragenesis [Sablukov et al., 2008] and with garnets of high-T "melt" metasomatic origin by [Griffin et al., 1999]; these garnets were formed before megacrysts crystallization. 100 Zr (ppm) low-T garnet (Griffin et al., 1999) 10 secondary garnet (Ziberna et al., 2013), 10 Ti/Zr = 10 Ti/Zr = 100 Megacrysts high-T garnet (Griffin et al., 1999) depleted peridotite garnet (Griffin et al., 1999) 1 10 100 1000 Ti (ppm) 10000 fields after Griffin et al., 1999 8 CC Ο BY [email protected]#9Clinopyroxene Clinopyroxene usually form an anhedral phase between olivine and orthopyroxene crystals, sometimes altered the latter. Less common clinopyroxene forms fine-grained crystals up to 1-3 mm in size. Cpx 500μm 0009 3 500 3016 754- Sometimes clinopyroxene was altered by a later aggregate of clinopyroxene (Cpx2) and phlogopite. Phi CC Ο BY [email protected] Cpx2 Cpx Phl 1mm Cpx2 EUROPEAN Opx GEOSCIENCES UN General Assembly 2015#10EUROPEAN GEOSCIENCES UN Clinopyroxene composition General Assembly Cpx has a wide range of Cr2O3 (0.69-3.93 wt.%), TiO2 (up to 0.84 wt.%), Al2O3 (0.47-5.61 wt.%) contents with Mg# = 0.89-0.95; By Cr2O3 content and Mg# values: 1. The most part of clinopyroxenes are comparable with the coarse mantle peridotite clinopyroxenes; 2. The less part of clinopyroxenes are comparable with the high-Cr megacryst clinopyroxenes [Kopylova et al., 2009] and form one paragenesis with the high-T "melt" metasomatic garnets. CC Ο BY Phi Cpx2 3 TiO, 0.25-0.40 wt.% ΟΙ M pyroxenites High-Cr megacrysts Opx 0.88 0.90 Cpx sheared peridotites Cpx 이 500μm 0009 3 coarse peridotites Usually TiO2 < 0.25 wt.% low-Cr megacrysts Mg# [email protected] 0.92 0.94 0.96 Fields after Kopylova et al., 2009 10 2015#115 peridotite groups - Group II Group II contains: EUROPEAN GEOSCIENCES UN Gen General Assembly 2015 High-Ti garnets with "normal" Cl-normalized REE patterns are similar to megacrysts but enriched in all REE contents; these garnets have high-T "melt" metasomatic origin by [Griffin et al., 1999] like as Group I garnets; CC Ο BY Gar/ C1 (Sun & McDonough, 1989) 0.1 0.01 100 10 10 1 || TTTTTT II Megacrysts TiO20.7-1.0 wt.% Group II garnet La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu [email protected] 11#125 peridotite groups - Group III Group III contains: EUROPEAN GEOSCIENCES UN Gen General Assembly ◆ Garnets with low concentration of TiO2, Cr2O3, CaO and "normal" Cl-normalized REE patterns that are similar to megacrysts except for depleted in LREE; these garnets have depleted peridotite origin by [Griffin et al., 1999]; ✰ Clinopyroxenes with medium degree of REE fractionation. 100 Gar / C1 (Sun & McDonough, 1989) 10 10 III 1 0.1 0.01 TiO2 <0.3 wt.% Megacrysts Group III garnet La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Cpx / C1 (Sun & McDonough, 1989) 100 La/Yb - 7-64 n 10 T 0,1 0,01 2015 Group III clinopyroxene La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu CC Ο BY [email protected] 12#135 peridotite groups - Groups IV-V Groups IV-V contain: → Garnets with low concentration of TiO, and mildly (Group IV) to humped (Group V) "sinusoidal" Cl-normalized REE patterns with a maximum at Nd-Sm and a minimum at Dy-Ho; these garnets are comparable with G9 and G10 garnets accordingly and have depleted peridotite origin by [Griffin et al., 1999]; → Clinopyroxenes (Group IV) have the highest degrees of REE profiles with flat pattern for LREE and depleted in Ti. 100 Gar / C1 (Sun & McDonough, 1989) 10 10 1 0.1 0.01 IV Megacrysts TiO2 < 0.2 wt.% Group IV garnet La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100 10 V Gar / C1 (Sun & McDonough, 1989) T EUROPEAN GEOSCIENCES UN Assembly General! 2015 0.01 Megacrysts TiO2 <0.2 wt.% Group V garnet La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100 Cpx / C1 (Sun & McDonough, 1989) 10 = 10 La/Ybn - 32-176 IV 0,1 0,01 TiO, < 0.25 wt.% Group IV clinopyroxene La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu [email protected] CC BY 13#14Garnet-clinopyroxene equilibrium EUROPEAN GEOSCIENCES UN General Assembly Calculating a garnet-clinopyroxene equilibrium coefficients (Gar/CpxD = X, Gar/X,Cpx, where Xi concentration of element i) for I, III and IV peridotite groups suggests that: 1. Group I peridotites have the Gar/CpxD values, which are consistent with experimental dataset for near-solidus carbonatitic liquid at pressures of 6.6 and 8.6 GPa and temperatures 1265 °C (base of lithospheric mantle condition) [Dasgupta et al., 2009]; 1000 100 0 1000 100 10 10 Groups III-IV peridotites have the Gar/CpxD values, which are consistent with dataset for deep lithospheric mantle situations [Burgess and Harte, 2004] at low- temperature 900°C and nature garnet peridotites [lonov et al., 2004]. www IID IV Dasgupta et al., 2009 2015 DGar/Cpx 0.1 0.01 0.001 0.0001 CC Ο BY 10 Dasgupta et al., 2009 1 T 900°C (Burgess, Harte, 2004) Jonhson, 1998 D Gar/Cpx 0.1 0.01 0.001 Group | 0.0001 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu [email protected] 1 900°C (Burgess, Harte, 2004) 1300°C (Burgess, Harte, 2004) Group III and IV La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 14#15Estimates of metasomatic melts composition EUROPEAN GEOSCIENCES UN Gen General Assembly The REE profiles of calculated melts in equilibrium with Group I garnets and clinopyroxenes are very similar with composition of autoliths from Grib kimberlite and theoretical 1.5% partial melt carbonated depleted mantle [Grassi, 2010] using partition coefficient for near-solidus carbonatitic liquid at T = 1265 °C [Dasgupta et al., 2009]; The REE profiles of calculated melts in equilibrium with Group II garnets are similar to Grib kimberlite using partition coefficient for deep lithospheric mantle situations at T = 1300 °C [Dasgupta et al., 2009; Johnson et al., 1999]; 1000 Sample C1 (Sun & McDonough, 1989) 100 10 10 0.1 equilibrium with Gar equilibrium with Cpx 1.5% melt of carb. peridotite, Grassi, 2010 1000 Sample C1 (Sun & McDonough, 1989) equilibrium || with Gar 100 Griba, autoliths Griba, kimberlite 10 10 - Kd 1300 °C, Johnson et al., 1999 0.1 Group I Griba, autoliths Kd- Dasgupta et al., 2009 Griba, kimberlite La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ! ...0 Group II Group II La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu This suggests evolutionary increasing in silicate components for melts in equilibrium with Group I garnet to Garnet II. 2015 CC BY [email protected] 15#16• Estimates of metasomatic melts composition Sample C1 (Sun & McDonough, 1989) The calculated melts in equilibrium with Group III-IV-V garnets and clinopyroxenes don't show similar with composition of Grib kimberlite that suggest their more differentiated metasomatic origin; The calculating was performed using partition coefficient for deep lithospheric mantle situations [Burgess and Harte, 2004]. 1000 100 1 I 0.1 CC BY equilibrium with Gar megacrysts Group IV IV Griba, autoliths Griba, kimberlite Kd - 1000 °C, Burgess and Harte, 2004 equilibrium with Cpx La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sample C1 (Sun & McDonough, 1989) Sample/ C1 (Sun & McDonough, 1989) [email protected] EUROPEAN GEOSCIENCES UN General Assembly 2015 1000 equilibrium with Cpx Group III megacrysts 100 Griba, autoliths 10 I 0.1 1000 100 equilibrium with Gar Griba, kimberlite Kd - 1000 °C, Burgess and Harte, 2004 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 10 megacrysts T 0.1 equilibrium with Gar Group V V Griba, autoliths Griba, kimberlite Kd - 1000 °C, Burgess and Harte, 2004 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 16#17Evolution of metasomatic agent for Group III-V To explain evolution of REE composition form sinusoidal" to "normal" patterns we used the model of melt injection and percolation through a refractory mantle column [Nimis et al., 2009; Ziberna et al., 2013]: In this model, the melt progressively changes its composition owing to chromatographic ion exchange, fractional crystallization and assimilation of peridotitic. minerals, under decreasing melt/rock ratios 100 (c) 1 cell, Grt Z4-3 (group B) 100 10 10 Gar/ C1 (Sun & McDonough, 1989) 10 0.01 100 Gar/ C1 (Sun & McDonough, 1989) 0.1 EUROPEAN GEOSCIENCES UN General Assembly 2015 Group V garnet La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu IV CC Grt/CI O 10 14th cell Grt Z4-8 (group C) 0.01 Grt 25-14 (group C) Grt in the ambient peridotite (from Grt Z4-11) 0.001 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ziberna et al., 2013: Plate model numerical simulation Ο BY At a distance from the region of kimberlitic melt generated the peridotite garnet has C1-normalized "sinusoidal" REE patterns; In the proximity to the region of kimberlitic melt generated garnet has C1- normalized REE patterns close to megacrysts. [email protected] Gar/ C1 (Sun & McDonough, 1989) 0.01 100 10 20 TTTTTTT T Group IV garnet T La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu III H 0.1 Group III garnet 0.01 La Ce Pr Nd Pm Sm Eu Gd Tb Ho Er Tm Yb Lu 17#18Evolution of metasomatic agent for Group III-V In the mantle peridotite xenoliths suit we have a nature example of this model: A zoned garnet crystal, which has progressive change of composition from relict zone with "sinusoidal"- harzburgitic REE profiles to megacryst-like REE profiles for the latest zone. Ziberna et al., 2013: Plate model numerical simulation Gar / C1 (Sun & McDonough, 1989) 100 V 10 0.1 0.01 EUROPEAN O 466-2 rim GEOSCIENCES UN General Assembly 2015 466-2 core Group V La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Grt/CI 100 (c) 10 1 cell, Grt Z4-3 (group B) 0.1 14th cell Grt Z4-8 (group C) 0.01 Grt Z5-14 (group C) Grt in the ambient peridotite (from Grt Z4-11) CC 0.001 Ο BY La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 100 мт [email protected] 100μm 18#19Gar / C1 (Sun & McDonough, 1989) Evolution of metasomatic agent for Group III-V EUROPEAN GEOSCIENCES UN The calculated AFC-model with very intensive assimilation of depleted mantle material (orthopyroxene) and fraction crystallization (clinopyroxene and garnet) suggests the possible for this evolution of kimberlite melts composition: kimberlite melts in equlibrium with megacrysts M melts in equlibrium with Group IV ganets IV assimilation of Opx fraction crystallization of Cpx and Gar General Assembly 2015 100 10 IV 1 0.1 0.01 Megacrysts AFC garnet comp. Gruop IV garnet (508-4) source: megacryst-like melts r - 0.95 F 0.55 (cpx 88%, gar - 12%) La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Gar / C1 (Sun & McDonough, 1989) 100 10 IV 1 0.1 Megacrysts Gruop IV garnet (508-4) AFC garnet comp. source: megacryst-like melts r - 0.95 F 0.60 (cpx 88%, gar - 12%) 0.01 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu The calculating was performed using partition coefficient for deep lithospheric mantle situations [Burgess and Harte, 2004; Johnson et al., 1998]. The composition of orthopyroxene was performed using composition of DM by [Salters et al., 2004]. 8 CC Ο BY [email protected] 19#20Conclusions GEOSCIENCES UN EUROPEAN OF General Assembly 2015 The studying of the geochemical composition of Gar and Cpx form the mantle peridotite xenoliths suggests evolution of the metasomatic agent from early protokimberlitic melts with high carbonate contents to later more silicate kimberlitic melts: 1. Early (protokimberlitic) high-T melts: enriched in LREE and Fe-Ti (HFSE); high carbonate/silicate ratio within the evolutionary increasing silicate components to megacryst equilibrium melt composition; ✰ were existed before the crystallization of the megacryst assemblage (garnet, clinopyroxene, olivine, spinel, ilmenite); probably were formed by melting of carbonated peridotite mantle source. crystallisation of megacrysts.. accumulation kimberlite melts forming the first parts of proto- kimberlite melt IV M 2 2. Amell percolation through mantle column carbonate component decreasing Later (kimberlitic) low-T melts depleted in Fe-Ti and low carbonate/silicate ratio; ✰ were existed after the crystallization of the megacryst assemblage (garnet, clinopyroxene, olivine, spinel, ilmenite); could be metasomatic agent for peridotite xenoliths of III, IV, V groups where the different C1-normalized REE patterns ("sinusoidal" and "normal") may be explained by the model of melt injection and percolation through a refractory mantle column. lithosphere asthenosphere carbonate veins in the lithospheric mantle 1 melting of carbonated peridotite source ascent of asthenosphere material CC Ο BY [email protected] 20 20