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The Fine Gold Intrusive Suite; the roles of basement terranes and magma source development in the Early Cretaceous Sierra Nevada Batholith

Jade Star Lackey, M. Robinson Cecil, Cameron J. Windham, Ryan E. Frazer, Ilya N. Bindeman and George E. Gehrels
The Fine Gold Intrusive Suite; the roles of basement terranes and magma source development in the Early Cretaceous Sierra Nevada Batholith
Geosphere (Boulder, CO) (March 2012) 8 (2): 292-313

Abstract

The Fine Gold Intrusive Suite is one of the largest (>2000 km (super 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 approximately 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 delta (super 18) O (6.1 ppm-8.0 ppm) and epsilon Hf (-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 approximately 90), high Na (sub 2) O magmas consistent with garnet-bearing sources inferred to be relatively deep. Higher (super 87) Sr/ (super 86) Sr, lower epsilon Hf, 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 findings also show that expression of the (super 87) Sr/ (super 86) Sr = 0.706 isopleth in arc magmas may be delayed until magma sources are sufficiently vigorous to melt and incorporate aged continental crust. Therefore, Sri 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 influence of preexisting basement compositions and differing degrees of organization of the magma sources with age is more pronounced. In addition, the findings 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.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 8
Serial Issue: 2
Title: The Fine Gold Intrusive Suite; the roles of basement terranes and magma source development in the Early Cretaceous Sierra Nevada Batholith
Affiliation: Pomona College, Geology Department, Claremont, CA, United States
Pages: 292-313
Published: 20120320
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 105
Accession Number: 2012-040064
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch maps
N37°00'00" - N37°45'00", W120°00'00" - W119°15'00"
Secondary Affiliation: California State University, Northridge, USA, United StatesUniversity of Oregon, USA, United StatesUniversity of Arizona, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201221
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