Tectonic implications of isotopic variation among Jurassic and Early Cretaceous plutons, Klamath Mountains

Barnes, Calvin G.; Petersen, Scott W.; Kistler, Ronald W.; Prestvik, Tore; Sundvoll, B.

doi:10.1130/0016-7606(1992)104<0117:tioiva>2.3.co;2

Cited by 40 publications

(28 citation statements)

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“…Nevertheless, the pluton is apparently syntectonic as evident from the dynamic contact aureole and high-temperature deformation in the pluton, implying that Nevadan deformation continued after movement on the Orleans thrust ceased. The Grants Pass pluton is mostly quartz diorite and quartz monzonite, but varies from diorite to granodiorite [Hotz, 1971, Barnes et al, 1992. Much of the pluton has an igneous foliation and lineation, and subsolidus fabrics are locally present.…”

Section: Intrusions Cutting the Galice Formationmentioning

confidence: 99%

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology

Harper¹,

Saleeby²,

Heizler³

1994

J. Geophys. Res.

120

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HAR•E• ET AL.' GE•ONOIX)O• OF THE JOSE•H•E O?H•oLrrE AND ITS EM•LACEMENTThe 4øAr/39Ar ages on igneous minerals will be similar to crystallization ages only if cooling was rapid (e.g., shallow level dikes). Many of the dated plutons are small and were intruded into rocks having ambient temperatures of <350øC. Such small intrusions would be expected to cool quickly below the -500øC closure temperature for hornblende. Many of these plutons, however, consist of two or more phases, so the temperature may have remained elevated by continual addition of heat from new intrusions, especially if substantial volumes of magma were transported through the plutonic complex.Zircon U/Pb age data are presented in Table 2, and the locations of the samples are given in Appendix A (available on microfiche). Notes on analytical procedures and assessment of uncertainties are given in the footnotes of Table 2 Table 2 with Table 1

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Section: Intrusions Cutting the Galice Formationmentioning

confidence: 99%

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology

Harper¹,

Saleeby²,

Heizler³

1994

J. Geophys. Res.

120

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“…Dioritic to granodioritic plutons are prominent parts of multiple arc terranes recognised in the eugeoclinal basement of northern California (Barnes et al 1992), whereas monzonitic compositions characterise the Jurassic arc over continental basement in the USA and northern Mexico (Miller 1978;Tosdal et al 1989;Saleeby & Busby-Spera 1992). Mineralisation associated with Early to Middle Jurassic magmatism includes porphyry and epithermal Cu(±Au) mineralisation in southern Arizona (e.g.…”

Section: Magmatism and Mineralisation Through Timementioning

confidence: 98%

Granitic magmatism and metallogeny of southwestern North America

Barton¹

1996

The Third Hutton Symposium on the Origin of Granites and Related Rocks

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In southwestern North America, late Palaeozoic through Cenozoic granitoids and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and continued with few major interruptions through the Mesozoic and Cenozoic, reaching maximum fluxes in the mid-Jurassic, Late Cretaceous and Oligocene. Two distinctive types of broad-scale igneous suites formed. The first type consists of calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20-50 Ma. These suites formed during periods of stable convergence and compressional tectonics, most notably in the late Mesozoic and early-mid-Cenozoic. The second type is compositionally varied, but shows no obvious secular variation in composition. This type formed during neutral to extensional tectonics in the mid-Mesozoic and the mid-to late Cenozoic. Regional (west to east) and secular (old to young) changes from calcic to alkalic compositions do not correspond to basement types; they point to tectonic rather than crustal controls on magmatic evolution, although basement signatures are clearly transmitted in isotopic systematics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Simple thermal and mechanical models of limits on assimilation and magma uprise are broadly consistent with these patterns.Igneous-related mineralisation is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Mineralisation includes porphyry, skarn, epithermal, replacement and syngenetic deposits of widely varying styles, metal contents and links to magmatic heat and materials. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting, although systematic regional variations in metal ratios are documented. Ore element suites vary from Cu-Au-Fe associated with (quartz) dioritic to monzonitic intrusive centres through Cu-Zn-Mo-Pb-Ag-W-Au associated with broadly granodioritic centres, and finally to F-Mo-Zn-W-Ag-Be associated with metaluminous to strongly peraluminous granitic centres. A model that includes both composition and process controls rationalises this igneous correlation and the lack of strong regional control. Key features are (1) mineralogical controls on fluid compositions and (2) the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids. This interpretation is supported by field relationships, igneous petrographic and isotopic data, and theoretical considerations.

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“…Instead, Sr isotope variability may be a function of a mixture of 15% mantle and 15% lower crustal melts (solid line) ascending through and assimilating portions of an old (>300 kyr) crustal column that is heterogeneous with respect to Sr isotopes. Bulk crustal assimilation ("BCA"; 20-80%; colored dashed lines) is modeled for two crustal end members that have the same ( 230 Th/ 232 Th) and ( 238 U/ 232 Th) but different 87 Sr/ 86 Sr ratios: BCA 1 87 Sr/ 86 Sr = 0.7035 (dotted blue lines, based on Klamath Mountain plutons; Barnes et al, 1992) and BCA 2 87 Sr/ 86 Sr = 0.7065 (dotted red lines, estimated from the Trinity Ophiolite; . Residence times of 25 kyr (A, B) and 50 kyr (C, D) are shown to illustrate how variable residence time affects the amount of assimilation required.…”

Section: Constraints On the Proportions Of Mantle And Crustal Componentmentioning

confidence: 99%

Tracing changes in mantle and crustal influences in individual cone-building stages at Mt. Shasta using U–Th and Sr isotopes

Wende

Beard

2015

Earth and Planetary Science Letters

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Available online xxxx Editor: T.A. Mather Keywords:Mt. Shasta Cascade Arc uranium-series isotopes strontium isotopes crustal interaction lower crust 230 Th-excess is rare in most arc lavas, but common in the Cascades, yet the origin of such excesses remains unclear. At Mt. Shasta, age-corrected ( 230 Th/ 232 Th) and ( 238 U/ 232 Th) activity ratios range from 1.108 to 1.290 and from 0.987 to 1.309 (27.3% 230 Th-excess to 6.1% 238 U-excess), respectively. Although small degrees of zircon crystallization (<0.3%) may yield high ( 230 Th/ 238 U) 0 in derivative magmas, high Zr contents, the lack of zircon as a liquidus phase, and low Th/U ratios in Mt. Shasta lavas argue against zircon fractionation. Instead, melting models suggest 230 Th-excesses are imparted on lavas through mixing mantle-derived magmas with partial melts of a mafic amphibolite lower crust where garnet was produced in the residuum through amphibole and plagioclase destabilization. The hot nature of Cascade magmas suggests that high intrusion temperatures promoted dehydration melting in the deep crust. At Mt. Shasta, the destruction of the ancestral cone (Sand Flat) was followed by four cone-building stages, three of which lie in the age range of U-series geochronology. Lavas within individual eruptive stages have relatively constant ( 230 Th/ 232 Th) 0 ratios that are interpreted to reflect specific mixtures of mantle (m) and lower crustal (lc) melts that are characteristic of a specific stage (M m:lc ). High ( 230 Th/ 232 Th) 0 ratios identify higher proportions of lower crust in the Misery Hill stage (M m:lc = ∼85:15), whereas low ( 230 Th/ 232 Th) 0 ratios reflect the more mantle-like composition of the Shastina lavas (M m:lc = ∼95:5); in the case of Shastina lavas, very low 87 Sr/ 86 Sr ratios, down to 0.7029, support a substantial mantle contribution. Changes in ( 230 Th/ 232 Th) 0 ratios correlate with eruptive volume, where the most voluminous stage (Misery Hill) is inferred to have the largest proportion of crustal melt and highest ( 230 Th/ 232 Th) 0 ratios. Variable ( 230 Th/ 238 U) 0 ratios within, and between, eruptive groups likely reflect a combination of residence time in the lower crust and differential assimilation of bulk, non-garnet-bearing crust that had ( 230 Th/ 238 U) = 1. The volume-( 230 Th/ 232 Th) 0 relations are accompanied by correlations with 87 Sr/ 86 Sr ratios, where the most radiogenic Sr is associated with the largest eruptive volumes, indicating that the largest magmatic episodes produced the largest amount of lower crustal interaction. The new U-Th and Sr isotope measurements of this study, along with U-series data for other Cascade centers suggest that interaction with the lower crust exerts greater control on Cascade magma chemistry than previously recognized. Indeed, the relatively dry nature of the Cascades may offer a unique opportunity to better understand the influence of the deep crust in young continental arcs, as larger subduction components in other settings may overprint any lower crustal signature a...

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Tectonic implications of isotopic variation among Jurassic and Early Cretaceous plutons, Klamath Mountains

Cited by 40 publications

References 0 publications

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology

Granitic magmatism and metallogeny of southwestern North America

Tracing changes in mantle and crustal influences in individual cone-building stages at Mt. Shasta using U–Th and Sr isotopes

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Tectonic implications of isotopic variation among Jurassic and Early Cretaceous plutons, Klamath Mountains

Cited by 40 publications

References 0 publications

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and 40Ar/39Ar geochronology

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and 40Ar/39Ar geochronology

Granitic magmatism and metallogeny of southwestern North America

Tracing changes in mantle and crustal influences in individual cone-building stages at Mt. Shasta using U–Th and Sr isotopes

Contact Info

Product

Resources

About

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology

Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California‐Oregon: U/Pb zircon and ⁴⁰Ar/³⁹Ar geochronology