Petrology of the high-pressures carbonatites from area Tromse, Norway.

Gorbachev N.S.*., Ravna E.K.**, Nekrasov A.N*., Kullerud K.**, Sultanov D.M.*

*Institute of Experimental Mineralogy, Chernogolovka, Russia;

**University of Tromso, Norway

gor@iem.ac.ru;

 

Samples of high-pressures a garnet-containing carbonatites from area Tromse, Norway, are investigated. A small body of a peculiar high-pressure carbonatite associated with eclogite and garnet pyroxenite is located on the mainland just north of the city of Tromsø. A U-Pb zircon age of the hosting eclogite gives ca. 452 Ma .

The matrix of samples are presented by a carbonate of calcitic-dolomitic composition  with signs immiscibility of calcitic and and dolomitic melts. To structural signs and a chemical compound it is allocated some generation of garnet (fig. 1).

 

 

 

 

Early generation Mg-Ca-Fe composition, is depleted in REE, late generation of garnet Ca-Fe composition enriched in LREE (fig. 2).

 

    

 

In the range of Р=3.8-4.0 GPa, T=1250-1450ºC full melting of carbonatite was observed. At quench of silica-carbonate melts the mix of microlits silica-carbonate and carbonate-silicate composition is formed (рис. 3). 

In the presence of Н₂О-СО₂ fluid  at Т=1400ºС, Р=4 GPa stratification melt on two liquids with allocation on graphite was observed.

At partial melting of system eclogit-carbonatit in the range Р=3.8-4.0 GPa, T=1250-1450ºC are formed intergrain melts silica-carbonate composition. Carbonatitic melts interaction with garnet and pyroxene of eclogite  to what reactionary parities testify (fig.3).

 

      

 

 

Proceeding from a geological position and features of mineral composition formation of carbonatites is caused by processes mantle-crust interactions at subduction of ocean crust, melting of mantle-crust intermixture and with the subsequent differentiation of silicate-carbonate  magmas at lifting in the earth crust (fig. 4).

The genetical model of origin of UHP Ga-bearing carbonatites:

 

Thus, this carbonatite appear to be unique, being intruded at great depths into a subducted continental lithosphere during the initial uplift stages.

 

This study was financially supported by RFBR grant  09-05-01131, grant ОSE РАН т.2