Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia Chuya complex of Early Mesozoic lamprophyres allocated in the boundary of SE of Gorny Altay – NW Mongolia. The actual interest based on the space-time coexistence of ore mineralization and intrusive bodies of the complex. The dikes within complex distribute irregularly, forming dike swarms, and each of one associate with the different type of mineralization. Are there different sources or another locate reasons of such differences – that is the main question of our investigation.

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia The investigations of composition in terms of petrogenic and trace elements show complete overlap the fields, characterized each dike swarms. The ages of intrusions are also equal. -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr But their isotopic composition of Sr and Nd diverse with certain. Three hypothesis were considered in our investigation. 1) different crustal contaminated material 2) different mantle source characteristics or heterogeneity of the mantle 3) different proportions of two sources in mixing process or different stages of the mantle metasomatism

1) different crustal contaminated material Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr Crustal contamination is questionable in general. And we didn’t find any evidences of crustal xenoliths in the investigated rocks. As well, it is not the hydrothermal alteration, cause of strong diversity between ɛNd. 1) different crustal contaminated material Q+Carb+ Ore min Phlog radial fibrous K-NaFsp 2mm

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr But the problem is in overlapping of all other geochemical characteristics. So this hypothesis can certify the differences in Sr and Nd isotopic ratios. And similarity in form of REE and RE patterns could be explained by low degree of melting of mantle sources. But we prefer next, better in our mind idea, very close to this. 2) different mantle source characteristics or heterogeneity of the mantle 1 10 2 3 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Ba Th U K Nb Ta Sr Hf Zr Ti Y 4 La/ =17,9 - 61,75; Gd/Yb =3,9 9,7 =30,9 45,9; 5,7

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia The system begetting rocks of the Chuya complex is very complicate. Processes of fraction crystallization, contamination and liquation took part in their origination and evolution. But only the contamination or mixing could change the isotopy. -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr Proposed the binary system of mixing and hyperbolic form of the graphic after [Langmuire, 1978] we find the equation, that describe our isotopic data. This diagram show good convergence with standard deviation for Sr 0.522867, for Nd – 1.4221; critical points are 0.464132 and 1.84325 respectively with the significance level at 10%. 3) different proportions of two sources in mixing process or different stages of the mantle metasomatism  

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Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia Chuya complex of early Mesozoic lamprophyres allocated in the boundary of SE of Gorny Altay – NW Mongolia. The actual interest based on the space-time coexistence ore mineralization and intrusive bodies of the complex. The dikes within complex distribute irregularly, and each of one associate with the different type of mineralization. Are there different sources or another locate reasons of such differences – that is the main question of our investigation.

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia Geochronologic data in the areas of alkaline-mafic magmatism (SE Altai - NW Mongolia) M O N G O L I A R U S S I A South-Chuya area Yustyd area Aktash area Ar-Ar, 242.6±2.8 U-Pb, 250.8±4.5 Ar-Ar, 251.8±2.4 Ar-Ar, 243±3.7 Ar-Ar, 240±3.5 Ar-Ar, 236.9±2.8 Ar-Ar, 249.2±2.6 Ar-Ar, 254.5±3.1 Ar-Ar, 234.6±3.1 Ar-Ar, 245±0.7 Ar-Ar, 244±0.8 Ar-Ar, 234±1.3 Ar-Ar, 236.8±0.6 Ar-Ar, 236.5±3.8

1) different crustal contaminated material Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr Crustal contamination is questionable in general. Geological forms (means explosive pipes) and zonal phenocrysts confirm high fluid saturations of lamprophyre dikes and high velocities of magma lifting. It means that crust fragments couldn’t dissolve in the amount, that could shift the isotope characteristics. High crystallization time let only scarification of xenoliths. The only heterogenic in the rocks is the ocelli. Their round form, high amount of carbonate outside the ocelli, and phenocrysts crossed their boundary, silicate composition, equal to the ground mass of the rock discard the possibility their crust genesis. Another objects that could indicate crust contamination had not been found. 1) different crustal contaminated material Q+Carb+ Ore min Phlog radial fibrous K-NaFsp 2mm

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr M O N G O L I A R U S S I A South-Chuya area Yustyd area Aktash area U-Pb, 250.8±4.5 Ar-Ar, 245±0.7 Ar-Ar, 244±0.8 Ar-Ar, 243±3.7 Ar-Ar, 249.2±2.6 Ar-Ar, 236.5±3.8 Ar-Ar, 236.8±0.6 Ar-Ar, 236.9±2.8 Ar-Ar, 234.6±3.1 Ar-Ar, 254.5±3.1 Ar-Ar, 242.6±2.8 2) different mantle source characteristics or heterogeneity of the mantle Based on the geochronological data, we suggest that mantle source works for a very long time (minimum about 20 Ma). But we didn’t find any correlations between the time of rock forming and their composition included the isotopy. So the noticed differences, are laterally stable and constant in time. Due to their close alocation, there is no mixing effect. The isotope characteristics of dikes from aktash field were close to the yustyd dikes although geographically they are situated near the south-chuya field. On the other hand they are disposed on the same Kuray-Kobdo fault with yustyd field.

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr 2) different mantle source characteristics or heterogeneity of the mantle 1 10 2 3 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Ba Th U K Nb Ta Sr Hf Zr Ti Y 4 La/ =17,9 - 61,75; Gd/Yb =3,9 9,7 =30,9 45,9; 5,7

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia The system begetting rocks of the Chuya complex is very complicate. Processes of fraction crystallization, contamination and liquation took part in their origination and evolution. But only the contamination or mixing could change the isotopy. -5 -4 -3 -2 -1 1 2 0.706 0.708 0.710 0.712 South-Chuya lamprophyres Yustyd lamprophyres Aktash lamprophyres εNd (235Ma) 87Sr/86Sr Proposed the binary system of mixing and hyperbolic form of the graphic after [Langmuire, 1978] we find the equation, that describe our data. This diagram show good convergence with standard deviation for Sr 0.522867, for Nd – 1.4221; critical points are 0.464132 and 1.84325 respectively with the significance level at 10%. 3) different proportions of two sources in mixing process or different stages of the mantle metasomatism Those all deviations with the model could be fully explained by the error in the determination of corresponding relations. Uncertainty stored in explaining the gap between values on the Sr/Sr-eNd diagram. Although the cause may be a lack of data, suggesting further research.

Isotope and trace element geochemistry of lamprophyres and syenites from different areas of Chuya complex Elena Vasyukova, Novosibirsk state university, Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia Conclusion We have presented a general model describing the changes of the isotopic composition in lamprophyres and related rocks because of the mixing process in multicomponent mantle source. This is the first announce, where the critical differences in Sr/Nd isotope composition of simultaneous rocks of the Chuya complex are shown. This model can be used in next researches as a base for the mixing hypothesis. It is especially important for the study of mineralization associated with lamprophyres. The adoption of this hypothesis removes the question of the genetic relationship of the primary fluid which is separated from the melt, forming lamprophyres.