This paper discusses a geothermobarometry modeling computer software called
Thermocalc through an applied example from the southern Syria volcanism, specifically
from Tal Al-Ashaer volcano, is given. A graphical P-T diagram for a given chemical bul
k
composition of some spinel-bearing peridotite rocks (from Tal Al-Ashaer) is created. The
results and their interpretation, in addition to limitations and constraints are discussed.
Based on the mineralogical analysis linked to the studied mineral assemblage modes, the
bulk-rock chemical composition is calculated and a geothermobarometry model using
Thermocalc is made. The created model shows that the general conditions at which the
rock-forming minerals (coexisting in equilibrium) define a field of stability with a range of
temperature goes from 700 to 1100 C° corresponding a range of pressure between 8 and 15
Kbar. Using one of Thermocalc tools (composition isopleths) the most precise P-T
conditions at which the rock was formed are estimated; T = 892 C° and P = 10.5 Kbar. The
corresponding depth at which the studied samples were formed is about 36 Km.
Accordingly, the crust-upper mantle boundary in the studied region is placed at that depth.