46. Areal variation in syntax

2009 ◽  
pp. 837-864 ◽  
Keyword(s):  
Areal Variation

Structural and metamorphic development of migmatites in the Svecokarelides, near Tampere, Finland

1980 ◽  
Vol 71 (4) ◽  
pp. 185-200 ◽  
Author(s):  
D. S. Campbell
Keyword(s):  
Partial Melting ◽  
Potassium Feldspar ◽  
Metamorphic Grade ◽  
Temperature Conditions ◽  
Mineral Growth ◽  
Metamorphic Development ◽  
Areal Variation

ABSTRACTFive generations of structures (F1–F5), excluding faults, can be recognised in granitoid and trondhjemitoid migmatites with quartzofeldspathic neosome development associated with F1–F4 structures. Areal variation in metamorphic grade is shown by the zonal development of muscovite-sillimanite, potassium feldspar-sillimanite and potassium feldspar-cordierite assemblages in the palaeosomes. The climactic metamorphism, associated with MS2–MP2 mineral growth, occurred at between 675°C, 4 kb and 825°C, 6·5 kb. These pressure-temperature conditions are consistent with at least some neosome development having resulted from partial melting. The occurrence of a relatively shallow metamorphic geotherm and the resultant products are assessed in relation to metamorphic conditions known from elsewhere in the Svecokarelides.

Exploration Maturity and Reserves Discovery Relations in the Niger Delta

1983 ◽  
Vol 2 (1) ◽  
pp. 57-66
Author(s):  
J. E. Ejedawe ◽  
V. O. Abiola ◽  
A. S. Young
Keyword(s):  
Niger Delta ◽  
Cross Product ◽  
Oil Reserves ◽  
High Maturity ◽  
Similarity Maps ◽  
Density Map ◽  
Areal Variation ◽  
Local Geology ◽  
Niger Delta Basin ◽  
Degree Of Association

Phantom surfaces of the normal deviates of well density and discovered oil reserves in place (DORIP) describe the areal variation in exploration maturity and success in the Niger Delta basin. The prolific centres and the prolific belt are clearly defined on the well density map as a high-maturity zone and suggest that the prolific belt is a reflection of exploration maturity. Cross-matching of the similarity maps (cross-product and difference maps) of the normal deviates of well density and DORIP expresses the degree of association between maturity and success and gives a pictorial view of variations in the degree of advancement of exploration in this province. Six relationships (A, B1, B2, D, E1, and E2) are recognised and can be correlated with local geology to provide a basis for determining the favourability of any area for future significant reserves discovery and hence in exploration planning.

Origin and Emplacement of Acadian Granitic Rocks, Northern Cape Breton Island

1975 ◽  
Vol 12 (2) ◽  
pp. 252-262 ◽  
Author(s):  
Robert A. Wiebe
Keyword(s):  
Country Rock ◽  
Source Region ◽  
Spatial Arrangement ◽  
High Water ◽  
Granitic Rocks ◽  
Cape Breton Island ◽  
Cape Breton ◽  
Northern Cape ◽  
Areal Variation ◽  
Differentiation Index

Acadian granitic rocks in northern Cape Breton Island consist entirely of even-grained leucocratic granodiorite and adamellite. The compositional range is small, and the average composition corresponds well with melts that could be generated in the crust. Abundant pegmatites in the contact zone suggest high water content.Within the major plutons these granitic rocks show: (1) high scatter on a Rb–Sr isochron (Cormier 1972), (2) apparently random areal variation in K and Ca, but a systematic areal variation in K/Rb and Ca/Sr, and (3) high scatter of Na2O and K2O on plots against differentiation index. The minor compositional heterogeneity indicated by these relations could have originated within the source region of melting or by assimilation during emplacement.The granitic plutons are elongate north–south and occur in an en echelon pattern within a NNE-trending migmatite zone. The spatial arrangement of pre-emplacement structures in the country rock and the distribution of xenoliths in the intrusions suggest that emplacement was accommodated by east–west expansion, upbowing of the surrounding country rock, faulting, and minor stoping.

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