A new method for determination of the average composition of a granite massif

Whitten, E. H. Timothy

doi:10.1016/0016-7037(62)90104-7

Cited by 8 publications

(3 citation statements)

References 15 publications

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“…From figure 3 it appears that the three major rock types are nearly equally represented in the exposed part of the batholith. This crude zonal arrangement resembles that in plutons of similar composition the world over (Whitten, 1962;Nilssen and Smithson, 1965;Bateman and others, 1963).…”

Section: The Batholithsupporting

confidence: 56%

The Boulder Creek Batholith, Front Range, Colorado

Gable¹

1980

Professional Paper

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The Boulder Creek batholith is the best known of several large Precambrian batholiths of similar rock composition that crop out across central Colorado. The rocks in the batholith belong to the calc-alkaline series and range in composition from granodiorite through quartz diorite (tonalite) to gneissic aplite. Two rock types dominate: the Boulder Creek Granodiorite, the major rock unit, and a more leucocratic and slightly younger unit herein named Twin Spruce Quartz Monzonite. Besides mafic inclusions, which occur mainly in hornblende-bearing phases of the Boulder Creek Granodiorite, there are cogenetic older and younger lenses, dikes, and small plutons of hornblende diorite, hornblendite, gabbro, and pyroxenite. Pyroxenite is not found in the batholith. The Boulder Creek Granodiorite in the batholith represents essentially two contemporaneous magmas, a northern body occurring in the Gold Hill and Boulder quadrangles and a larger southern body exposed in the Blackhawk and the greater parts of the Tungsten and Eldorado Springs quadrangles. The two bodies are chemically and mineralogically distinct. The northern body is richer in CaO and poorer in K2O, is more mafic, and has a larger percentage of plagioclase than the southern body.A crude sequence of rock types occurs from west to east in the batholith accompanied by a change in plagioclase composition from calcic plagioclase on the west to sodic on the east. Ore minerals tend to decrease, and the ratio potassium feldspanplagioclase increases inward from the western contact of the batholith, indicating that the Boulder Creek batholith is similar to granodiorite batholiths the world over. Emplacement of the Boulder Creek batholith was contemporaneous with plastic deformation and high-grade regional metamorphism that folded the country rock and the batholith contact along west-northwest and north-northwest axes. Also, smaller satellitic granodiorite bodies tend to conform to the trends of foliation and fold axes in the country rock, suggesting that emplacement was controlled by preexisting structures in the country rock.On a gross scale, chemical equilibrium in the Boulder Creek Granodiorite is expressed by a near 1:1 ratio, or straight-line relationship in the distribution of iron, magnesium, and manganese in biotite and hornblende. General mineralogical trends in the Boulder Creek Granodiorite indicate that modal biotite, hornblende, and plagioclase tend to increase and quartz and microcline tend to decrease as CaO increases. These trends were not found in the Twin Spruce Quartz Monzonite.Differentiation is believed to have played a major role and assimilation a minor role in the development of the Boulder Creek batholith. The Boulder Creek Granodiorite is of probable mantle or lower crust origin, and, based on the scant data available, the Twin Spruce Quartz Monzonite may be of crustal origin, but the magma was extensively altered by contaminants of ambiguous origin. Mafic inclusions, possibly derived from a dioritic magma which was an early differentiate associa...

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Section: The Batholithsupporting

confidence: 56%

The Boulder Creek Batholith, Front Range, Colorado

Gable¹

1980

Professional Paper

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“…(Whitten, 1963) were fitted to these points, the quadratic component ( Figure 2B) being the highest order to add significantly to the sum of squares (Whitten, 1962;Dawson & Whitten, 1962). The quadratic surface explains 93.52 per cent of the variation observed in the outcrop elevations, adding 2.5 per cent to the linear sum of squares with a confidence level of > 99 per cent; whereas the further contribution of the cubic component of a mere 0.39 per cent has a confidence level of < 75 per cent.…”

Section: The Factorsmentioning

confidence: 99%

The elevation of the Lower Greensand ridge, south-east England

Chorley¹

1969

Geol. Mag.

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The elevation of the Lower Greensand ridge, south-east EnglandR. J. CHORLEY SUMMARY. The influence of three classes of factors-geological structure, lithologic composition and spatial control over erosion-are examined by trend-surface analysis, followed by stepwise regression, in order to determine their relative importance in explaining the variation observed in the elevation of the Lower Greensand ridge of south-east England. It is concluded that structural controls are dominant, lithological controls very subordinate and the spatial control of very marginal significance.

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“…The method employed here is explained by Whitten (1962 and1963) and involves the approximation of the observed soil parameters of median grain size and percentage silt and clay (i.e. passing the number 200 sieve) by mathematical surfaces of polynomial form fitted by the method of least squares.…”

Section: Rj Chorleymentioning

confidence: 99%

An Analysis of the Areal Distribution of Soil Size Facies on the Lower Greensand Rocks of East-Central England by the Use of Trend Surface Analysis

Chorley

1964

Geol. Mag.

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Progressive fitting of linear, quadratic and cubic partial trend bestfit surfaces to median grain size (X t , in mm.) and percentage of silt and clay sizes (X 3 ) of soil samples taken from fifty locations on the Lower Greensand outcrop between Ely and Leighton Buzzard in east-central England permit up to about 40 per cent of the total sums of squares to be " explained ". The successively higher levels of mathematical generalization of regional soil size distribution indicate a decrease in soil grain size towards the south-east, a disparity between the alignment of the soil facies and the strike of the present outcrop, and the existence of zone of abnormally coarse soil facies just to the west of the line of the rivel Ivel. These three features of the regional distribution of soil sizes are interesting in that they correlate with observations which have been made on the regional distribution of bedrock size facies. Finally, a suggested correlation is made between the local zones of small median grain size and abnormally high proportions of silt and clay soil sizes-isolated as " deviations or residuals " from the fitted regional surfaces-and localities where small admixtures of glacial drift (evidenced by the presence of flints) have been observed.IN an earlier paper (Chorley, 1964) a multiple regression analysis was conducted, with the aid of an electronic computer, of six factors which were assumed to exercise a control over the shearing resistance of sandy soils associated with the Lower Greensand outcrop between Ely and Leighton Buzzard in east-central England. This paper represented the first step in a sequential investigation of the parameters which are assumed to control the present height variations of the Lower Greensand ridge. The present paper takes two of the above six factors, median grain size (X 1( in mm.) and the percentage of silt and clay (X 3 ) and examines their areal distributions.The Lower Greensand outcrop stretches somewhat discontinuously for about 50 miles between Ely and Leighton Buzzard (Text- fig. 1), being composed largely of somewhat poorly-lithified sands, often crossbedded (Schwarzacher, 1953 ;Narayan, 1963), which are on the whole fairly well-sorted and seem to have accumulated relatively rapidly in shallow water under the action of waves and currents possibly as submarine deltas rather than offshore bars (Schwarzacher, 1953).Broadly speaking, the deposit thickens from about 10 feet near Ely towards the south-west, reaching about 250 feet near Leighton Buzzard, but with some evidence of local thinning along a positive axis in the vicinity of the Ivel valley near Biggleswade, believed by Rastall (1925 GEOL. MAG. VOL. 101 NO. 4 .

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A new method for determination of the average composition of a granite massif

Cited by 8 publications

References 15 publications

The Boulder Creek Batholith, Front Range, Colorado

The Boulder Creek Batholith, Front Range, Colorado

The elevation of the Lower Greensand ridge, south-east England

An Analysis of the Areal Distribution of Soil Size Facies on the Lower Greensand Rocks of East-Central England by the Use of Trend Surface Analysis

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