GEOLOGIC, TECTONIC AND GEOCHEMICAL CHARACTERIZATION OF THE EGYPTIAN PLUTONIC ROCKS USING COMPUTER TECHNIQUES

Abstract

The increasing volumes of the geologic data making the use of computer techniques more and more involved in the computation, storage, sorting, retrieval, editing and processing of such data. This necessitates to the design and creation of the Egyptian Plutonic Rock Information System (EPRIS) for the purpose of the classifications of these rocks. A total of365 rock types representing 259 plutons of the Egyptian plutonites are stored in EPRIS. There are 57 rock bodies representing 48 plutons of the Egyptian gabbroic rocks and 308 rock bodies of the Egyptian granitoid rocks representing 211 plutons. The individual completed chemical analyses for major oxides are a total of 5350, 3400 for trace elements, and 1700 for REE. The statistical and geochemical data processings classified the gabbroic rocks into two groups. _Group-1: comprises 13 younger gabbro bodies. It is characterized by high Si02 > 50% (av 5341%), Ti02 (>1.0%), Na20 (342%), and K20 >10% The (Si02/Al 20J =3.2), (Na20+K20/Al203) = 0.27 and (FeOt/MgO = 14) ratios are high. The rock bodies of Group-I are enriched in Rb, Sr, Ba and Zr. The K/Rb (265 6), Rb/Sr (0.06). Ni/Cr (0.49), V/Cr (0.82) and Zr/Y (5.27), REE = 36.3, La/Yb (2.8) and Ce/Sm (5 32), Tb/Yb (0.25) and Eu/Sm (0.27) ratios are higher than •the next group. On the other hand, MgO (5.32%) and CaO (7.77%), and the Na20/K20 (2.53) ratio are low. Also, the rock bodies of Group-!are depleted in V, Ni, Co and Cr. Group-I exhibits characteristics of medium-K suites that originated from calc-alkaline and developed in a within plate tectonic setting. Group-11: comprises 23 gabbroic bodies of gabbro-diorites and metagabbro complexes. It is further subdivided into two subgroups: The First Subgroup: comprises 9 gabbroic bodies of gabbro-diorite complexes. The Si02 range is up to 50.20% (av. 47.26%) and Al20J is the lowest in the Egyptian gabbros (<154%) (av.l3.8"1%). The Na20 (2%) and FeO'JMgO (0.85) ratio are low. These rocks are depleted in Rb, Sr, Ba and Zr. The Rb/Sr (0 04), Ni/Cr (045), V/Cr (0.57) and Zr/Y (3.89) ratios are lower. Also, The REE = 33.5, La/Yb (2.7), Ce/Sm (48), and Eu/Sm (0.23) are lowerthan Group-I On the other hand, MgO (1042%), Si02/AhOJ (3.45%), V, Ni, Co, Cr. K/Rb (276 6) and Ba/Rb (I3.38) ratio are higher than Group-I. The Second Subgroup: comprises 14 gabbroic bodies of metagabbros. The Si02 is moderate (av. 48.41%). The AhOJ (17.94%), CaO (10.09%) and Na20/K20 (3.62%) ratio, V, Co and Cr are higher than the previous subgroup. On the other hand, Si02/Al203 (2 69), Sr, Ba and Zr, K/Rb (187.4), Ba/Rb (5 I 0), Ni/Cr (0.31) and Ni/Co (2.32) are the lowest. However, the V/Cr (0.58) Zr/Y(3.59), L REE =; 29, La/Yb (2.75), Ce/Sm (44), and Eu/Sm (0.24) are similar to the first subgroup Group-ll exhibits characteristics of medium-K suites that originated from calc-alkaline to tholeiitic magmas and developed in an island arc to Mid Oceanic Ridge Basalt (MORB) tectonic environments .