Lithosphere chemical composition

The solid crust and the upper mantle make up the region called the lithosphere. Oxygen is the most abundant element in the lithosphere. Unlike the hydrosphere and the atmosphere, the lithosphere contains a large variety of other elements, including deposits of alkali, alkahne earth, and transition metal elements. Table 26-3 lists the most abundant elements in the continental crust portion of the hthosphere. With the exception of gold, platinum, and a few other rare metals that are found free in nature, most metallic elements occur as compounds in minerals. A mineral is a solid, inorganic compound found in nature. Minerals have distinct crystalhne structures and chemical compositions. Most are combinations of metals and nonmetals. 

Minerals are solid, inorganic compounds found in nature. They have distinct crystalline structures and chemical compositions. Minerals of various elements are found in the lithosphere mainly as oxides, carbonates, and sulfides. 

The mineralogical and chemical composition of peridotite from subcontinental lithosphere differs from that of peridotite from other parts of the mantle (Boyd 1989 Berstein et al. 1997). Peridotites from subcontinental lithosphere is depleted , which means it contains only a small amount of clinopyroxene and an aluminous phase, which together make up the so-called basaltic component. The lithosphere beneath the oldest Archaean cratons has a composition markedly different from that of younger subcontinental lithosphere (Boyd Mertzman 1987 Griffin et al. 1999). Old unmetasomatized lithosphere is harzburgitic, a mixture of olivine... 

In this chapter we consider the development and evolution of modem biosphere during its geological history. The reader will find a brief description of the formation of the lithosphere, atmosphere, and hydrosphere and their chemical composition. Creation and evolution of the biogeochemical structure of the biosphere and hydrosphere is also a subject of discussion. Finally, we show the role of biogeochemical cycles in formation of biogenic depositions (oil and gas). 

The details of lithospheric composition are best considered for individual locations. Here it is only worth emphasizing that the chemical composition of xenoliths reflect both major element depletion events and subsequent enrichment processes, and so have had complex open-system histories. The sources and characteristics of noble gases must consider this environment, as discussed further below. 

The chemical composition of the soil is mostly determined by its predominant mineral portion. In the soil, there are almost all the known chemical elements however, approximately 90% is made up of 0, Si, A1 and Fe. A further 9% includes Ca, Na, K and Mg, and after these, Ti, Mn, P and other elements are present in lower amounts. The average content of elements in the soil and in the lithosphere is given in Table 7.3. 

The geosphere denotes the mineral part of the Earth it consists of successive concentric layers from the outer crust down to the inner core, (see Figure 13.1). The structure of the interior of the Earth can be zoned by either its physical properties (e.g., density, velocity of P and S seismic waves, and temperature) or its chemical and mineralogical composition. The classification of the geosphere according to its chemical composition identifies three main chemical entities the crust, the mantle, and the core, while physical properties identify five homogeneous entities the lithosphere, the asthenosphere, the mesosphere, the outer core and the inner core. 

Sources of information about the isotopic composition of the upper portion of the lithospheric mantle come from the direct analysis of unaltered ultramafic xenoliths brought rapidly to the surface in explosive volcanic vents. Due to rapid transport, these peridotite nodules are in many cases chemically fresh and considered by most... 

Occurrence in Nature. About 99.6% of the earth s mass results from 32 of the chemical elements. The remaining 0.4% is apportioned among 64 elements, all of which are present as traces. Iodine is one of these 64. Estimates about abundance of the constituent elements of the lithosphere place iodine 46th on a restricted list of 59 elements (37 very rare elements are excluded) and 61st on a list in which 96 elements are included. Iodine is, indeed, one of the scarcest of the nonmetallic elements in the total composition of the earth (3). 

The wide diversity of the isotopic compositions in orogenic peridotites, and the anomalously depleted composition of several ophiolitic and abyssal peridotites have strong implications on the small-scale structure of the convective mantle, as well as on mantle processes such as decompression partial melting of mantle rocks, the formation of oceanic lithosphere and the thermomechanical and chemical erosion of lithospheric mantle by upwelling asthenosphere. We briefly review some of these important issues below. 

The mantle comprises 68% by mass of Earth, and an accurate estimate for its composition is the very basis for unraveling the origin and differentiation of our planet. The bulk chemical analysis of xenoliths has been central to understanding the composition of the Earth s mantle, the genesis of basalt and the physical properties in the lithosphere that bear on its stability in the rigid part of the mantle system. 

McDonough W. F., Rudnick R. L., and McCulloch M. T. (1991) The chemical and isotopic composition of the lower eastern Australian lithosphere a review. In The Nature of the Eastern Australian Lithosphere, Geol. Soc. Austral. Spec. Publ. (ed. B. Drummond). Sydney, vol. 17, pp. 163-188. 

---