The evolution of trace element concentrations in basic rocks from Israel and their petrogenesis

The geochemistry of tholeiitic rocks, alkali olivine basalts and basanites of The Mesozoic province of Israel has been studied. The elemental concentration in the magmas was treated in terms of batch melting followed by fractional crystallization processes. During the latter process, the crystallizing minerals from effusive and hypabyssal bodies match the conditions of maintaining surface equilibrium with the melt (Rayleigh Law). According to the incompatible characteristics of the LIL elements which were determined, they can be divided into two groups: (1) those elements (La, Ce, Ta, Th, Hf) which maintain incompatibility for rocks having D.I. <63, and (2) those elements which can be regarded as incompatible in rocks with further restrictions for U and Ba (D.I.<50); for P₂O₅ (Ni>75 ppm); for Sr (Ni>200 ppm). Assuming that the mantle has [La]_n= 1 the spectrum of the rocks studied was generated by 0.5% to 3.2% partial melting from a single garnet peridotite source rock. The source rocks appear to be quite homogeneous with only a slightly LREE-enriched pattern. For the above melting range the D_s (bulk distribution coefficient between the source rocks and the melts) values for Ta, La, Ce, Th, U, P₂O₅, Sr, Ba, and Hf were found to be 0.0012, 0.002, 0.0029, 0.0031, 0.0039, 0.0082, 0.0083, 0.01, and 0.015, respectively. If the mantle has [La]_n=2, then for the range of 1 to 6.4% melting, the D_s values would be 0.002, 0.0035, 0.0053, 0.0055, 0.007, 0.0152, 0.0153, 0.019, and 0.027, respectively.