Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada
Mineralogical Magazine
By: Claiborne L.E. Lowery, C. F. Miller, B.A. Walker, J. L. Wooden, F.K. Mazdab, and F. Bea
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Abstract
Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ???35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/ Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/ Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (TTiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ???30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and TTiZ (>100??C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone. ?? 2006 The Mineralogical Society.
Suggested Citation
Lowery, C.L., Miller, C.F., Walker, B., Wooden, J.L., Mazdab, F., Bea, F., 2006, Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada: Mineralogical Magazine, v. 70, no. 5, p. 517-543, https://doi.org/10.1180/0026461067050348.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada |
| Series title | Mineralogical Magazine |
| DOI | 10.1180/0026461067050348 |
| Volume | 70 |
| Issue | 5 |
| Publication Date | July 05, 2018 |
| Year Published | 2006 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Mineralogical Magazine |
| First page | 517 |
| Last page | 543 |