CRUSTAL VERSUS MANTLE SOURCES OF GRANITIC MAGMAS - A 2-PARAMETER MODEL BASED ON ND ISOTOPIC STUDIES

被引：126

作者：

DEPAOLO, DJ

PERRY, FV

BALDRIDGE, WS

机构：

[1] Center for Isotope Geochemistry, Department of Geology and Geophysics, University of California, Berkeley

[2] Earth Sciences Division, Lawrence Berkeley Laboratory, Berkeley

[3] Department of Geology, University of New Mexico, Albuquerque

[4] Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos

来源：

TRANSACTIONS OF THE ROYAL SOCIETY OF EDINBURGH-EARTH SCIENCES | 1992年 / 83卷

关键词：

ASSIMILATION; FRACTIONAL CRYSTALLIZATION; IGNIMBRITE; MAGMA CHAMBER; RHYOLITE;

D O I：

10.1017/S0263593300008117

中图分类号：

P [天文学、地球科学];

学科分类号：

07 ;

摘要：

Temporal and spatial variations in the Nd isotopic compositions of Tertiary caldera-forming rhyolite tuffs, and Cretaceous and Tertiary granites of the western U.S.A. are used as a basis for a model that accounts for the observed proportions of crustal versus mantle contributions to silicic magmas in terms of two parameters: the ambient crustal temperature and the rate of supply of basaltic magma from the mantle. The crustal contribution to silicic igneous rocks is measured in terms of the Neodymium Crustal Index (NCI). The relationships between crustal temperature, basalt supply and NCI are quantified using a model of a magma chamber undergoing continuous recharge, wall-rock assimilation and fractional crystallisation. From the model, a critical value of the ratio of basalt recharge-to-assimilation, (r/a)c, is deduced, which increases with decreasing crustal temperature. The r/a value must exceed (r/a)c to allow the volume of differentiated magma to increase, a prerequisite for developing large volumes of silicic magma. Strongly peraluminous (or S-type) magmas (NCI=0.8-1), form under conditions of high crustal temperature and low basalt supply. Metaluminous or I-type granites form over a wide range of conditions (NCI=0.1-1), generally where basalt supply is substantial. In individual long-lived volcanic centres, the large-volume high-silica ignimbrites are associated with the highest r/a and lowest NCI values, indicating that these magmas are typically differentiates of mantle-derived basaltic parents.

引用

页码：439 / 446

页数：8

共 26 条

[1]

Bennett V.C., DePaolo D.J., Proterozoic crustal history of the western United States as determined by Neodymium isotopic mapping, GEOL SOC AM BULL, 99, pp. 674-685, (1988)

[2]

DePaolo D.J., Isotopic studies of processes in mafic magma chambers, J PETROL, 26, pp. 925-951, (1985)

[3]

DePaolo D.J., Neodymium isotope geochemistry, (1988)

[4]

DePaolo D.J., Linn A.M., Schubert G., The continental crustal age distribution: Methods of determining mantle separation ages from Sm-Nd isotopic data and application to the western United States, J GEOPHYS RES, 96, 2, pp. 071-088, (1990)

[5]

DePaolo D.J., Perry F.V., Baldridge W.S., Neodymium isotopic monitor of basalt influx rates and eruption potential in continental magmatic systems, GEOL SOC AM ABSTR, 23, (1991)

[6]

Farmer G.L., DePaolo D.J., Origin of Mesozoic and Tertiary granite in the western U.S. and implications for pre-Mesozoic crustal structure. I. Nd and Sr isotopic studies in the geocline of the northern Great Basin, J GEOPHYS RES, 88, 3, pp. 379-401, (1983)

[7]

Farmer G.L., DePaolo D.J., Origin of Mesozoic and Tertiary granite in the western U.S. and implications for pre-Mesozoic crustal structure. II. Nd and Sr isotopic studies of Cu- and Mo-mineralized granite in the Precambrian craton, J GEOPHYS RES, 89, 10, pp. 141-160, (1984)

[8]

Farmer G.L., Perry F.V., Semken S., Crowe B., Curtis D.B., DePaolo D.J., Isotopic evidence on the structure and origin of subcontinental lithospheric mantle in southern Nevada, J GEOPHYS RES, 94, 7, pp. 885-898, (1989)

[9]

Farmer G.L., Broxton D.E., Warren R.G., Pickthorn W., Nd, Sr, and O isotopic variations in metaluminous ash-flow tuffs and related volcanic rocks at the Timber Mountain/Oasis Valley caldera complex, SW Nevada: Implications for the origin and evolution of large volume silicic magma bodies, CONTRIB MINERAL PETROL, 109, pp. 53-68, (1991)

[10]

Gardner J.N., Goff F., Potassium-Argon dates from the Jemez volcanic field: Implications for volcanic activity in the north-central Rio Grande Rift, RioGrande Rift: Northern New Mexico, New Mexico Geological Society, Socorro, 35th Annual Field Conference, (1984)

← 1 2 3 →