Lower Crustal Xenoliths, Chinese Peak Lava Flow, Central Sierra Nevada

Dodge, F. C. W.; Calk, Lewis C.; Kistler, Ronald W.

doi:10.1093/petrology/27.6.1277

Cited by 54 publications

(31 citation statements)

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“…Textures are granoblastic, and some xenoliths display a distinct, subparallel alignment of tabular laths of plagioclase. Banding is suggestive of metamorphic gneissic texture but could well be inherited igneous lamination [Dodge et al, 1986]. The phase mineralogy and bulk composition reconstructed from point counting suggest that the gabbros, cumulate gabbros, and mafic feldspathic granulites share a common origin and are most likely deep batholithic rocks.…”

Section: Central Sierra Nevada Suitementioning

confidence: 92%

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Ducea¹,

Saleeby²

1996

J. Geophys. Res.

277

199

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Abstract. Xenoliths hosted by Cenozoic volcanic flows and plugs from the Central Sierra Nevada and Eastern Sierra Nevada, Owens Valley, and Inyo Mountains were studied for petrography and thermobarometry. The Central Sierra Nevada suite consists of abundant lower crustal feldspathic granulites, garnet clinopyroxenites, and mantle-derived peridotites and garnet websterites. Mafic crustal assemblages occur down to -65-70 km, although below 35-40 km, they are mainly in the eclogite facies. In contrast, the Eastern Sierra Region suites show peridotitic, pyroxenitic, and harzburgitic assemblages at depths of _>35-40 km. They define an adiabat in PT space (T -1180-1250øC), suggesting the presence of the asthenospheric upper mantle close to the base of the crust. The ultramafic mantle rocks from the Central Sierra Nevada also define an adiabatic slope in PT space, possibly an artifact of side heating from the east. There is xenolith evidence that the Sierra Nevada lost about half of its original crust on the eastern side of the range. Regardless of the actual mechanism of crustal thinning, the loss of the eclogitic lowermost crust and replacement by peridotite in the eastern Sierra Nevada is a process accompanied by a substantial density decrease (>100 kg/m3). Overall, if the mechanism of eclogitic lowermost crust removal is viable, there are enough buoyancy sources to explain topographic differences between the Sierra Nevada and the adjacent Basin and Range, assuming isostatic equilibrium.

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Section: Central Sierra Nevada Suitementioning

confidence: 92%

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Ducea¹,

Saleeby²

1996

J. Geophys. Res.

277

199

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“…In the southern Sierra Nevada, in contrast, upper mantle xenoliths are found in several Neogene lava fl ows and can be used to reconstruct the lithologic and compositional characteristics of the continental lithosphere beneath this area through time (Chin et al, 2012;Dodge et al, 1986;Ducea and Saleeby, 1998a;Lee et al, 2006;Mukhopadhyay and Manton, 1994). Xenoliths entrained in Miocene lavas in the central Sierra Nevada in the San Joaquin volcanic fi eld (Fig.…”

Section: Northern Sierra Nevada Lithospheric Mantlementioning

confidence: 99%

Mantle lithosphere as a source of postsubduction magmatism, northern Sierra Nevada, California

et al. 2013

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Age, chemical, and isotopic data from late Cenozoic volcanic rocks in the northern Sierra Nevada, California (USA), from Lake Tahoe north to the southern end of the modern Cascades volcanic arc, were obtained to investigate the evolution of the upper mantle beneath this continental margin during the transition from active subduction to the opening of a slabless window, and to test the possibility that the foundering of mantle lithosphere proposed for the southern Sierra Nevada extended to the northern reaches of the mountain range. Our data are consistent with previous work in the region and illustrate that volcanism shifted from widespread intermediate composition magmatism to small volume, localized trachybasalts to trachyandesites ca. 3 Ma. Similar to southern Cascades volcanism, 87 Sr/ 86 Sr and 206 Pb/ 204 Pb decrease, and ε Nd increase in the older (older than 3 Ma) volcanic rocks with increasing proportions of a slab component, as measured by increasing (Sr/P) N , where N is primitive-mantle normalized. We interpret these observations as evidence that the older volcanic rocks are subduction related and represent the products of basaltic melts derived from fl ux melting of mantle wedge that interacted to varying degrees during ascent with lower ε Nd and higher 87 Sr/ 86 Sr sub-Sierra Nevada continental mantle lithosphere. The younger volcanic rocks lack evidence for the involvement of a slab compo- GEOLOGIC SETTINGThe Sierra Nevada mountain range in eastern California (Fig. 1) has been the subject of intense investigation into the processes involved For permission to copy, contact editing@geosociety.org

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“…The biggest advance in recent years in our understanding of the chemistry of the lower continental crust has come from the new data that have been generated from studies of xenolith suites [Kay and Kay, 1991;Cohen et al, 1984;Dodge et al, 1986;Downes and Leyreloup, 1986;O'Reilly, 1986, 1987a, b;Leemah et al, 1985;Leyreloup et al, 1977Leyreloup et al, , 1982McCulloch et al, 1982;Rogers, 1977;Ruiz et al, 1988;Stosch, 1987;Stosch et al, 1986;van Calsteren et al, 1986;Esperan•a et al, 1988;Rudnick, 1990;Rudnick and Goldstein, 1990;Kempton et al, 1990;Downes et al, 1991]. Until the 1970's virtually all data on the chemistry of the lower crust was based on studies of granulite-facies gneiss terranes, such as the Lewisian of Scotland [Sheraton, 1970].…”

Section: Introductionmentioning

confidence: 99%

Formation and composition of the lower continental crust: Evidence from Scottish xenolith suites

Halliday¹,

Dickin²,

Hunter³

et al. 1993

J. Geophys. Res.

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Crustal xenoliths occur in a variety of Carboniferous and Tertiary alkali basaltic rocks across Scotland and provide indications of the nature of the deep crust beneath the major lithotectonic zones from the Archean Lewisian of the far NW to the Paleozoic terranes in the SE. Sr, Nd, and Pb isotopic and representative chemical compositions are presented for 35 mafic xenoliths from the different age and tectonic zones of Scotland and for 21 felsic, gneissose xenoliths, from the Midland Valley and Southern Uplands in the south. The coexistence of mafic granulite and spinel lherzolite xenoliths at several of these localities, together with seismic velocity data, provide evidence that the mafic xenoliths, and possibly some of the felsic xenoliths, may be derived from 20–30 km depth. The absence of garnet from the mafic assemblages suggests that in most areas the crust was probably not much more than 30 km thick in the Permo‐Carboniferous. The extremely variable Al2O3 (up to 27 wt %) and MgO contents at any one location, together with positive Eu and Sr anomalies in chondrite‐ and mantle‐normalized diagrams, provide evidence that many of the mafic xenoliths represent cumulates from basaltic magmas. The Loch Roag mafic xenoliths, erupted through the depleted high‐grade metamorphic Lewisian Complex, are especially rich in K (average 1.3 % K2O) and Rb (average 54 ppm) with K/Rb extending as low as 100. The K/U ratios for the mafic xenoliths are high, ranging to over 100,000 at Loch Roag and in the SW Midland Valley. The relative concentrations of U, K, Rb, Pb, Nd, Sm, Eu and Sr in most of the mafic Xenoliths, while displaying regional characteristics, display intra‐site variations that are consistent with crystal‐liquid fractionation. There is little evidence of U or Rb depletion via fluid or melt extraction during metamorphism. The concentrations of U in the mafic xenoliths display as much intrasite uniformity as the rare earth elements and correlate with Zr concentrations. U/Zr ratios are similar to those found in ocean island basalts. The mafic xenoliths display a marked decrease in ϵNd and 206Pb/ 204Pb with increasing age of the upper crust from SE to NW, as also observed in the ∼400 Ma Caledonian granites. Sm‐Nd crustal residence ages for the Loch Roag suite are particularly variable ranging from 1.6 to 3.6 Ga. However, these isotopic compositions and model ages appear to be, in part, the product of crustal assimilation by the igneous precursors to the mafic xenoliths. Model ages, mineral ages and scattered whole rock isochrons indicate that many of the precursors to these Xenoliths were in fact formed and metamorphosed during the late Proterozoic and Paleozoic and provide evidence of widespread deep crustal magma reservoirs, underplating, crustal assimilation and arc accretion at these times. Nd and Sr isotopic data for coexisting pyroxenite xenoliths at Loch Roag indicate that they may represent contaminated ultramafic cumulates that were cogenetic with the precursors to the mafic xenoliths. The Pb isotopic composi...

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Lower Crustal Xenoliths, Chinese Peak Lava Flow, Central Sierra Nevada

Cited by 54 publications

References 0 publications

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry

Mantle lithosphere as a source of postsubduction magmatism, northern Sierra Nevada, California

Formation and composition of the lower continental crust: Evidence from Scottish xenolith suites

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