Базальты. Классификация основных пород презентация

Базальты

Chapter 13: Mid-Ocean Rifts The Mid-Ocean Ridge System

Oceanic Crust and Upper Mantle Structure Typical Ophiolite

The major element chemistry of MORBs The major element chemistry of MORBs

MgO and FeO MgO and FeO Al2O3 and CaO SiO2 Na2O, K2O, TiO2, P2O5

Trace Element and Isotope Chemistry REE diagram for MORBs

N-MORBs: 87Sr/86Sr < 0.7035 and 143Nd/144Nd > 0.5030,  depleted mantle source N-MORBs: 87Sr/86Sr < 0.7035 and 143Nd/144Nd > 0.5030,  depleted mantle source E-MORBs extend to more enriched values  stronger support distinct mantle reservoirs for N-type and E-type MORBs

MORB Petrogenesis Separation of the plates Upward motion of mantle material into extended zone Decompression partial melting associated with near-adiabatic rise N-MORB melting initiated ~ 60-80 km depth in upper depleted mantle where it inherits depleted trace element and isotopic char.

Ocean-ocean  Island Arc (IA) Ocean-ocean  Island Arc (IA) Ocean-continent  Continental Arc or Active Continental Margin (ACM)

Chapter 17: Continental Arc Magmatism

Structure of an Island Arc

Tholeiitic vs. Calc-alkaline differentiation

Calc-alkaline differentiation Early crystallization of an Fe-Ti oxide phase Probably related to the high water content of calc-alkaline magmas in arcs, dissolves  high fO2 High water pressure also depresses the plagioclase liquidus and  more An-rich As hydrous magma rises, P  plagioclase liquidus moves to higher T  crystallization of considerable An-rich-SiO2-poor plagioclase The crystallization of anorthitic plagioclase and low-silica, high-Fe hornblende is an alternative mechanism for the observed calc-alkaline differentiation trend

Trace Elements REEs Slope within series is similar, but height varies with FX due to removal of Ol, Plag, and Pyx (+) slope of low-K  DM Some even more depleted than MORB Others have more normal slopes Thus heterogeneous mantle sources HREE flat, so no deep garnet

MORB-normalized Spider diagrams MORB-normalized Spider diagrams IA: decoupled HFS - LIL (LIL are hydrophilic)