TY - JOUR

T1 - Paleozoic plume-lithospheric processes in northeastern Fennoscandia

T2 - Evaluation of the composition of the parental mantle melts and magma generation conditions

AU - Arzamastsev, A. A.

AU - Mitrofanov, F. P.

N1 - Funding Information: ACKNOWLEDGMENTS The authors thank A.B. Vrevsky (Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences) for consultations that were very helpful for developing computer models for the melting of mantle sources. This study was conducted under a first-priority program of the Earth Science Branch of the Russian Academy of Sciences and was financially supported by the Russian Foundation for Basic Research, project no. 09-05-00224.

PY - 2009/5

Y1 - 2009/5

N2 - The paper reports quantitative evaluations of the modal and chemical composition of the mantle whose Paleozoic activation gave rise to the Kola alkaline province in the northeastern Baltic Shield. The volume of alkaline magmatism within the province and the volume of the mantle melts that were generated in the course of the Paleozoic activation cycle were evaluated by three-dimensional density modeling on the basis of gravimetric data. Our studies involved, along with the sampling of alkaline magmatic rocks in the region, the examination of the deep (to a depth of 22.5 km) structure of all alkaline intrusions in the province and the development of their three-dimensional density models. Concentrations of trace elements were precisely analyzed by the ICP-MS technique, and these data were used in order to calculate the weighted mean concentrations of trace elements in rocks of the province, to simulate the melting of mantle sources, and to evaluate the geodynamic sequences of these mantle processes. Our simulations indicate that the total volume of the Paleozoic mantle melts in the northeastern part of the Baltic Shield amounted to 15000 ± 2700 km3. The calculated composition of the partial melts that could be produced by the mantle of average composition shows the necessity for the significant introduction of certain elements into the mantle source. It is demonstrated that primitive melts in the Kola province were highly probably derived at low degrees of melting of the source (0.3-0.5%), whose composition corresponded to phlogopite-bearing (±amphibole) garnet lherzolite under the conditions of the mantle garnet depth facies. The calculated degree of enrichment of this sources was three times higher than the average concentrations of incompatible elements in the primitive mantle. It is demonstrated that magma generating processes affected much of the lithosphere beneath northeastern Fennoscandia and reached a depth of 120 km, i.e., the depth of the mantle facies of garnet lherzolite. The area of this region corresponds to the area of regional Paleozoic magmatism, and its depth correlates with the estimated P-T conditions under which the mantle xenoliths found in regional diatremes were formed.

AB - The paper reports quantitative evaluations of the modal and chemical composition of the mantle whose Paleozoic activation gave rise to the Kola alkaline province in the northeastern Baltic Shield. The volume of alkaline magmatism within the province and the volume of the mantle melts that were generated in the course of the Paleozoic activation cycle were evaluated by three-dimensional density modeling on the basis of gravimetric data. Our studies involved, along with the sampling of alkaline magmatic rocks in the region, the examination of the deep (to a depth of 22.5 km) structure of all alkaline intrusions in the province and the development of their three-dimensional density models. Concentrations of trace elements were precisely analyzed by the ICP-MS technique, and these data were used in order to calculate the weighted mean concentrations of trace elements in rocks of the province, to simulate the melting of mantle sources, and to evaluate the geodynamic sequences of these mantle processes. Our simulations indicate that the total volume of the Paleozoic mantle melts in the northeastern part of the Baltic Shield amounted to 15000 ± 2700 km3. The calculated composition of the partial melts that could be produced by the mantle of average composition shows the necessity for the significant introduction of certain elements into the mantle source. It is demonstrated that primitive melts in the Kola province were highly probably derived at low degrees of melting of the source (0.3-0.5%), whose composition corresponded to phlogopite-bearing (±amphibole) garnet lherzolite under the conditions of the mantle garnet depth facies. The calculated degree of enrichment of this sources was three times higher than the average concentrations of incompatible elements in the primitive mantle. It is demonstrated that magma generating processes affected much of the lithosphere beneath northeastern Fennoscandia and reached a depth of 120 km, i.e., the depth of the mantle facies of garnet lherzolite. The area of this region corresponds to the area of regional Paleozoic magmatism, and its depth correlates with the estimated P-T conditions under which the mantle xenoliths found in regional diatremes were formed.

UR - http://www.scopus.com/inward/record.url?scp=67649637348&partnerID=8YFLogxK

U2 - 10.1134/S0869591109030060

DO - 10.1134/S0869591109030060

M3 - Article

AN - SCOPUS:67649637348

VL - 17

SP - 300

EP - 313

JO - Petrology

JF - Petrology

SN - 0869-5911

IS - 3

ER -