Gabbros, anorthositic

The evidence from seismic experiments is fully in agreement with the model outlined above. In the Fra Mauro region of Oceanus Procellarum the crust is about 65 km thick and overlies a solid mantle 126 The crust, in turn, is divided into two parts covered with a thin regolith. For comparison with the returned lunar samples, the upper layer has been inferred to be mare basalt and the lower one anorthositic gabbros. 

Element Anorthosites Gabbroic anorthosite 68415 Anorthositic gabbros Norite 78235 KREEP Bulk highlands composition... 

Boslough, M.B., and Ahrens, T.J. (1984), Particle Velocity Experiments in Anorthosite and Gabbro, in Shock Waves in Condensed Matter—1983, (edited by Asay J.R. et al.), Elsevier Science, New York, pp. 525-528. 

Mesosiderites are stony irons in which the rocky material is a polymict breccia of crustal rock from a differentiated body— basalt, gabbro, pyroxenite, dunite, and anorthosite. The silicates are very similar to the HED suite meteorites. Thus, mesosiderite silicates are discussed here, but the metallic phase is not. 

The silicates consist of mineral and lithic clasts set in a fine-grained fragmental to impact-melt matrix. The most common lithic clasts are basalts, gabbros, and orthopyroxenites, while dunites are minor and anorthosites are rare. The most common mineral clasts are centimeter-sized orthopyroxene and olivine fragments, while millimeter-sized plagioclase fragments are less common. 

The radar-echo surveys of the Antarctic ice sheet by Drewry (1975) provided information about the sub-ice topography but did not detect mineral deposits. More recently, Behrendt et al. (1980) combined the radar-echo sounding technique of Drewry (1975) with an airborne magnetometer survey which revealed that a laige part of the Dufek intrusion in the Pensacola Mountains is covered by the East Antarctic ice sheet. The enlargement of the area of this intrusion increased the amount of potential ore of iron, titanium, and vanadium in this differentiated body of gabbro, pyroxenite, and anorthosite. 

Upper layered zone Brown zone Middle gabbro Lower brown zone Lower gabbro zone Anorthosite zone... 

The Walker Anorthosite in Table 13.3 underlies the Aughenbaugh Gabbro in the Dufek Massif and was named after Walker Peak in Fig. 13.41 where a 230-m section of this formation is exposed. It is composed of a medium-grained plagioclase cumulate (An to An ). The anorthosite is white to cream colored or gray and is spotted because of the presence of coarse poikilitic postcumulus crystals of pyroxene. 

The Aughenbaugh Gabbro (Table 13.3) is a mafic cumulate that concordantly overlies the Walker Anorthosite and extends throughout the Dufek Massif from Walker Peak in the southwest for about 50 km to Rankine Rock which is the most northeasterly nunatak of the Dufek Massif in Fig. 13.41. The thickness of this formation is at least 1,600 m. The Aughenbaugh... 

The Spear Anorthosite Member consists of three layers of cream colored to Ught gray anorthosite cumulate interbedded with dark gray cumulate gabhro for a total thickness of about 105 m in the upper part of the Aughenbaugh Gabbro. The thickness of the plagioclase cumulate layers is about 46 m, 12 m, and more than 5 m from the lowest to... 

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