Rocks anorthosite

Lahradoriie is the characteristic feldspar of the more basic rock types like diorite. gahbro. andesite or basalt and it is usually associated with some one of the pyroxenes or amphiholes. Lahradoriie frequently shows a heauliful play of iridescent colors due lo minute inclusions of another mineral. However, the labradorescent phenomenon has not been fully determined. The classic location for this mineral is. of course. Labrador, whence its name. Il is a constituent there of the rock anorthosite and is found in the anorthosites of the Provinces of Quebec and Ontario, and in the Adirondack region in New York Stale. 

Fig. 10. The wide variety of lanthanide abundance patterns observed in lunar highlands samples ranging from extreme enrichment in Eu in feldspathic rocks (anorthosites, 61016, 15455) to massive depletion of Eu in KREEP (65015), which represents the final residual liquid from the crystallisation of the magma ocean. Sample 68415 is a granulitic breccia close in composition to that of the average highland crust. (Data are from table 12).

Ilmenite from massive hard-rock anorthosite Magmatic complexes always contains less TiO, than segr tion... 

However, separation between resistance levels of 1000 to 300 kH may be marginal. A typical application of conductivity sorting is the separation of massive ilmenite from anorthosite. Both are compact rocks, but ilmenite is a good electrical conductor, whereas anorthosite is an insulator. The dimensions and operating information for the Sor-tex CS-03 conductivity sorter, which is capable of processing up to about 25,000 kg/h (27.5 tons/h) of 0.05-to 0.15-in mesh size (2 to 6 in), are given in Table 19-4. 

Anorthositic deposits - nearly all of the known commercially important rock deposits of titanium minerals are associated with anorthositic or gabbroic rocks. There are three main types (a) ilmenite-magnetite (titanoferous magnetite), (b) ilmenite-haematite, and (c) ilmenite-rutile. 

Example 5.7. The oldest lunar rock known to date is a lunar highland anorthosite 60025. The data for different minerals in a single rock are shown in the table below (Carlson and Lugmair, 1988). Find the age. 

The formation of the Moon s crust, composed primarily of feldspar (the rock is called anorthosite) illustrates how physical fractionation can occur during differentiation. Early in its history, a significant portion of the Moon was melted to form a magma ocean. The first minerals to crystallize, olivine and pyroxene, sank because of their high densities and formed an ultramafic mantle. Once feldspar began to crystallize, it floated and accumulated near the surface to produce the crust. 

Samples returned by the Apollo and Luna missions can be readily distinguished based on their contents of FeO and thorium. This may seem like an unlikely choice of chemical components for classification, but they nicely discriminate rock types and are easily measured by remote sensing. The FeO and thorium contents of ferroan anorthosites, mare basalts, impact melt breccias, and lunar meteorites are shown by various symbols in Figure 13.4. 

Lunar rocks Ferroan anorthosite Lunar meteorite... 

Analyses of thorium and FeO in lunar rocks and lunar meteorites can be described by three compositional end members - ferroan anorthosite, KREEP, and mare basalt. The various lunar terranes defined by orbital measurements of Th and FeO, illustrated by shaded and hatched fields, can also be explained by mixtures of these components. Terrane abbreviations are PKT (Procellarum KREEP Terrane) FHT (Feldspathic Highlands Terrane) SPA (South Pole-Aiken Terrane). Modified from Jolliff etal. (2000). 

Anorthosites and basalts form two end members distinguished by FeO contents, and the impact melt breccias extend upward towards a KREEP end member with high thorium and intermediate FeO contents. Besides thorium, the KREEP end member is obviously enriched in the other incompatible elements that define its name. The impact melt breccias contain small clasts of KREEP basalt, which has not been sampled as large rocks. 

As noted earlier, lunar meteorites are mostly breccias of ferroan anorthosite and related early crustal rocks, although a few mare basalt meteorites are known. The lunar meteorites likely sample the whole Moon. The absence of KREEP-rich breccias so common among Apollo samples collected from the nearside in the lunar meteorite collection implies that KREEP-rich rocks cover only a small area on the Moon. In fact, the lunar highlands meteorites appear to provide a closer match to the average lunar crust than do the Apollo highlands samples (Fig. 13.5), as measured by geochemical mapping (see below). 

The Feldspathic Highlands Terrane (FHT) is characterized by its relatively low FeO and Th contents (Fig. 13.4), which are consistent with ferroan anorthosite. The FHT is the most extensive terrane and is concentrated on the lunar farside (Fig. 13.7). The Procellarum KREEP Terrane (PKT) occupies a large oval-shaped portion (Oceanus Procellarum) of the nearside (Fig. 13.7). The PKT has both light and dark areas, corresponding to highlands (non-mare) rocks and mare basalts. All of these materials... 

Anorthosite An igneous rock almost entirely composed of calcium-rich plagioclase. 

The values for the Al/Si ratio of the regolith in mare areas, as determined from moon samples as well as via the x-ray fluorescence technique, also differ from the values found in the rock samples of mare basalts (Tables 2 and 3), the latter being somewhat lower. These differences can be explained by the admixture of anorthositic material from the lunar highlands, as found at the... 

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. 

Pristine Highland Rocks Distinctiveness of the Ferroan Anorthositic Suite The Magma Ocean Hypothesis... 

Figure 10 Chondrite-normalized REE concentrations in mare basalts, KREEP, and a representative ferroan anorthosite. Data for mare basalt t)fpes are from Table 2, with two deliberate omissions the NWA773 cumulate, an individual rock presumably unrepresentative of its parent magma, and the Apollo 14 t)fpe, which is a suite with notoriously diverse REE abundances, although the patterns are generally parallel to KREEP (which is plotted). Individual mare basalt types are not labeled, but symbols on some of the patterns denote relatively titanium-rich varieties the most titanium-rich basalts (largest symbols) tend to have the lowest (often subchondritic) La/Sm ratios. Data for high-K KREEP and ferroan anorthosite 15295c41 are from Table 5 and Warren et al. (1990), respectively.

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