干旱区生态环境知识资源中心

The 165 Ma Eagle Mountain intrusion is a heterogeneous, enclave-bearing, metaluminous remnant of the Cordilleran Jurassic are that cuts regionally metamorphosed pre-Mesozoic rocks in the southeastern Mojave Desert of California. The main phase of the intrusion consists of granodiorite to tonalite host facies, diorite mixed facies, and homogeneous monzogranite facies. The host facies contains microdiorite enclaves interpreted as intermingled masses of mafic magma. Late-phase leucogranite stocks cut the main phase. Mineral equilibria indicate emplacement at similar to 6.5 km depth, with solidus temperatures ranging from 760 degrees C for diorite to 700 degrees C for felsic granodiorite.

Although uniform radiogenic-isotope compositions (Sr(i) = 0.7085, epsilon Nd(i) = -9.4) suggest derivation from a single source, no known source has the composition required. A hybrid source is proposed, consisting of various proportions of juvenile mantle and recycled lower crust. Calculations indicate that the source of the Eagle Mountain intrusion comprised >60% juvenile mantle and <40% recycled crust. On the basis of their isotopic compositions, other mafic Jurassic plutons in the region were derived from sources containing different proportions of mantle and crustal components.