Structural reconstruction and zonation of a tilted mid-crustal magma chamber: The felsic Chemehuevi Mountains plutonic suite

摘要: Structural relief resulting from middle Tertiary extensional deformation in the Chemehuevi Mountains of California exposes a unique cross section through an extensive (>280 km 2 ) calc-alkalic, compositionally zoned, sill-like granitic intrusion Late Cretaceous age. Minimum estimates for emplacement pressure, 4 to 6 kbar, imply that plutonic suite was initially intruded at mid-crustal depths and has undergone 10° 15° postemplacement tilting, tectonic denudation, erosion. Reconstruction pre-Tertiary (pre-tilt) configuration suggests this metaluminous peraluminous exhibits crude normal, vertical, temporal zonation granodiorite granite. The involves decrease age increase silica away walls roof, youngest most evolved members being concentrated toward center floor intrusion. lower part had flat floor, which penetrated by least three feeder dikes providing magma chamber. chamber grew laterally stages, each pulse more than preceding one. reconstruction indicates roof is less 1 above exposed top intrusion, suggesting tabular geometry with aspect ratio about 5:1. apparently ponded along contact between undeformed Proterozoic basement subhorizontally foliated mylonitic gneisses below, therefore structurally controlled. This provides information on mesozonal intermediate silicic chambers. In addition, restoration rare opportunity observe crosscutting relations different types structures (thick shear zones, intrusions, temporally unrelated detachment faults), emphasizes need careful evaluation seismic reflection profiles across complexly deformed continental crust.