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Abstract

The Fine Gold Intrusive Suite is one of the largest (>2000 km 2 ) and oldest intrusive complexes in the Sierra Nevada batholith (California, USA), and therefore contains a wealth of information about nascent magmatic processes in a convergent margin arc. Because the suite intrudes both accreted oceanic and/or island-arc terranes and continental crust, it provides perspective on how convergent margin magmatism recycles existing crust versus reworking of fringing island arcs into continental crust. Such insight informs our understanding of how continental crust formation may have operated in the Phanerozoic as compared to earlier in Earth history.New zircon U-Pb geochronology shows that the largely tonalitic suite was emplaced over ~19 m.y. (124-105 Ma), in three pulses that young from west to east. The most recent domain is nested within the previous ones, such that lobes of magma protruding from the main bodies of the Bass Lake Tonalite (the primary member of the Fine Gold Intrusive Suite) are older than interior areas. Zircon δ 18 O (6.1‰-8.0‰) and εHf (-4.7 + 6.4) show temporal trends indicating that early magmas were source mixtures of mantle with as much as 45% Paleozoic to Mesozoic oceanic and/or arc rocks, whereas later magmas contain greater inputs (to 50%) of Proterozoic North American crust. Older domains in the suite were likely generated from isolated sources, including initial high Sr/Y (to ~90), high Na 2 O magmas consistent with garnetbearing sources inferred to be relatively deep.Higher 87 Sr/ 86 Sr, lower εHf, and higher Rb/Sr values in younger plutons show a source that tapped greater proportions of North American crust and was presumably more organized and larger, given its more homogeneous isotopic and trace element traits. Our fi ndings also show that expression of the 87 Sr/ 86 Sr = 0.706 isopleth in arc magmas may be delayed until magma sources are suffi ciently vigorous to melt and incorporate aged continental crust. Therefore, Sr i values of older stitching plutons may better record the position of discrete terrane boundaries, whereas younger plutons will record the magmatically average position of terrane boundaries. Although the Fine Gold Intrusive Suite is comparable to the Late Cretaceous voluminous intrusive suite of eastern Sierran suites in terms of duration and age zoning of magmatism, the infl uence of preexisting basement compositions and differing degrees of organization of the magma sources with age is more pronounced. In addition, the fi ndings show that recycling of fringing arc terranes into continental crust is relatively rapid and that estimates of the growth of Phanerozoic continental crust from such reprocessing should be revised upward.

Epeirogenic transients related to mantle lithosphere removal in the southern Sierra Nevada region, California, part I: Implications of thermomechanical modeling

“…Section C shows a zone of much more extensive lower crustal attachment for the highvelocity mantle lithosphere rocks than sections A or B, with the northern part of the anomaly along C restricted to relatively shallow levels (<100 km). These laterally extensive highvelocity rocks are interpreted as the residual arclogite root of Early Cretaceous high-volume batholithic rocks that are widespread along the western Sierra Nevada foothills and subsurface of the eastern Great Valley (May and Hewitt, 1948;Saleeby, 2007Saleeby, , 2012Lackey et al, 2012). The high-velocity rocks extend northward as far as ~38°N; peridotite-rich remnants of the Cretaceous mantle wedge extend farther north to ~39.5°N (Gilbert et al, 2012;Fig.…”

Orogenic to postorogenic (1.20-1.15 Ga) magmatism in the Adirondack Lowlands and Frontenac terrane, southern Grenville Province, USA and Canada

“…This relationship led to the conclusion (Peck et al, 2004) that the high-δ 18 O Frontenac suite plutons were most likely caused by melting of underthrust hydrothermally altered ocean crust that, apart from its on December 13, 2013 geosphere.gsapubs.org Downloaded from high δ 18 O, was similar to MORB. Similar mechanisms have been proposed for the process by which radiogenically mantle-like tonalites with high δ 18 O zircon values formed in the Cretaceous Sierra Nevada batholith (Lackey et al, 2012).…”

“…Associated granitoids have δ 18 O WR values ranging from 7.4‰ to 8.8‰ that do not correlate with location. Granitic rocks with δ 18 O values lower than associated anorthosites cannot be comagmatic because fractional crystallization causes increasing δ 18 O in a magma series (Peck et al, 2004;Lackey et al, 2012). Isotope systematics also indicate that assimilants to Nain anorthosite parent magmas have different δ 18 O than the source rocks for granitoids (Peck et al, 2010).…”

The Volcanic-Plutonic Connection

“…Diverse datasets indicate assembly of many superficially homogeneous plutons over timescales measured in millions of years Matzel et al 2006;Davis et al 2012;Lackey et al 2012; Mills and Coleman 2013;Frazer et al 2014). The geochronologic data require that the plutons were assembled incrementally; but more significantly, they provide input for thermal models of subvolcanic magma reservoirs.…”