Mafic igneous rocks

Chromium is a compatible element in the Earth s mantle, and tends be present in much greater concentrations in mafic igneous rocks than in felsic ones (Faure 1991). Ultramafic rocks often contain over 1,000 ppm Cr and can generate environmental problems when they weather (Robertson 1975 Robles and Armienta 2000). Granites may contain less than 20 ppm Cr, whereas shales contain roughly 90 ppm. 

ULTRABASIC. A term proposed by Judd, in 1881. for exceedingly mafic igneous rocks composed largely, if not entirely, of llie ferromag-nesium minerals such as olivine and pyroxene. The limiting figure of total silica is approximately 45%, or barely sufficient to supply the needs of the... 

Baghouse Fabric filters used to remove fine-grained particles from flue gas in combustion facilities. Basalt An extrusive mafic igneous rock. An extrusive equivalent of a gabbro. 

Gabbro An intrusive mafic igneous rock. Basalts are extrusive equivalents of gabbros. 

Olivine A silicate mineral, (Fe,Mg)2Si04, that is common in ultramafic and mafic igneous rocks and some metamorphic rocks. 

Silica A silicon dioxide (Si02) compound or mineral (such as quartz). Silica may also refer to the silicon content of a rock or another sample, where the amount of silicon is listed as a chemical oxide (i.e. weight percent silicon dioxide or wt % Si02). For many rocks and other solid samples (e.g. mafic igneous rocks), the silicon dioxide in the sample does not exist as quartz or another SiC>2 mineral, but combines with other elements to form different silicate minerals (such as olivine, micas, or pyroxenes). 

Gooding, J. L. (1978) Chemical weathering on Mars thermodynamic stabilities of primary minerals (and their alteration products) from mafic igneous rocks. 

Lugovic B., Altherr R., Raczek 1., Hofmann A. W., and Majer V. (1991) Geochemistry of peridotites and mafic igneous rocks from the Central Dinaric Ophiolite Belt, Yugoslavia. Contrib. Mineral. Petrol. 106, 201-216. 

Epidote Sorosilicates Medium-grade metamorphic and mafic igneous rocks R Source of Fe, Ca, Mn very resistant to weathering... 

Anderson AT 11, Clayton RN, Mayeda TK (1971) Oxygen isotope thermometry of mafic igneous rocks. J Geol 79 715-729... 

EARLY STUDIES OF OXYGEN ISOTOPE VARIATIONS IN MAFIC IGNEOUS ROCKS... 

Chabazite (and herschelite) from mafic igneous rocks... 

The Sm-Nd method can be used to date mafic igneous rocks (basalt and gabbro) which are not suitable for dating by the Rb-Sr method. Magma of basaltic chemical composition originates by decompression melting in the mantle of the Earth which contains radiogenic Nd that has formed by decay of Sm. The isotopic evolution of Nd in the mantle of the Earth is represented by a model in Fig. 3.19 that is based on the isotope composition of neodymium in chondrite meteorites and which is therefore known as the Chondritic Uniform Reservoir (CHUR). The present value of the Nd/ Nd ratio in CHUR is ... 

The conventional whole-rock K-Ar dates of the Kirkpatrick Basalt in Fig. 12.31 literally vary all over the place and range from being too old to being too young. (Chlorophaeite is chlorite that fills cavities or fractures in mafic igneous rocks). 

Bottinga and Javoy (1975) but both sets of values in Appendix 13.6.6 are reasonable estimates of the oxygen-isotopic equilibration temperature of mafic igneous rocks that crystallized from magma. Actually, the temperatures indicated by the oxygen-isotope thermometers are probably less than the crystallization temperature of the silicate minerals. 

The Dufek Massif in Fig. 13.41 is a rugged mountain range composed almost entirely of layered gabbro and related mafic igneous rocks. The main body of this mountain range is aligned from southwest to northeast and extends for 20 km followed by scattered nunataks to... 

In spite of the uncertainty of the isotopic age determinations, the mafic igneous rocks that were formed during the initial split between East Antarctica and Africa constitute the largest known volume of rift-related magma in the world. 

The 5 0 values of rocks from the Dufek Massif reported by Ford et al. (1986) in Fig. 13.47 range narrowly from +5%o to +7%c with one low value of less than +4%c. These values are normal for mafic igneous rocks that crystallized from mantle-derived magma without extensive assimilation of crustal rocks or hydrothermal alteration. The 6 0 values of rocks from the Forrestal Range vary from normal values of +6%o to low values between 0%c and +l%o. Several prominent rock types in the Forrestal Range have distinctive 8" 0 values (Ford et al. 1986) ... 

Fig. 13.47 The 5 0 (SMOW) values of whole-rock samples of the Dufek intrusion vary widely. The 6 0 values of the lower part of the intrusion in the Dufek Massif range in most cases fiom greater than -h5% to less than +7%o which is normal for mantle-derived mafic igneous rocks. However, the 6 0 of the upper part of the intrusion in the Forrestal Range decrease from normal values to low values between 0% and +l%

How far do the sedimentary rocks of the Beacon Supergroup and the mafic igneous rocks of the Ferrar Group extend under the East Antarctic ice sheet ... 

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