Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernzanne Mahlburg Kay and w. Matthew Burns*INSTOC and Department of Earth and Atmospheric Sciences, Snee Hall, Cornell University, Ithaca, NY 14853 USA. smkl6@comell.edu.* Now at U.S. Geological Survey, Reston, Virginia, 20192, USA: wbums@usgs.gov.Peter CopelandDept. Geosciences, University of Houston, Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Houston, Texas, 77204, USA, copeland@uli.edu.Oscar MancillaREPSOL-YPF. Buenos Aires, Argentina, omancinad@repsolypf.com.KEYWORDS: Andes, volcanism, tUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
ectonics, Neuquén basin, shallow subduction, geochemistry, NeogeneABSTRACTEvidence for a Miocene period of transient shallow subduction under the NeuqUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northerngeometry comes from new40Ar/39Ar, major and trace element, and Sr. Pb and Nd isotopic data on magmatic rocks in a transect at ^36° to 38°s.1https://khothuvien.cori!Older frontal arc magmas include Early Paleogene volcanic rocks erupted after a strong Upper Cretaceous contractional deformation and mi Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernd-Eocene lavas erupted from arc centers displaced slightly to the east. Following a gap of some 15 million years, ~ 26 to 20 Ma mafic to acidic arc-liUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
ke magmas erupted in the extensional Cura Mallin intra-arc basin and alkali olivine basalts with intraplate signatures erupted across the backarc. A mUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northerntures erupted in the near to mid backarc. They were followed by 7.2 to 4.8 Ma high-K basaltic to dacilic hornblende-bearing magmas with arc-like high field strength element depletion that erupted in the Sierra de Chachahuén some 500 km east of the trench. The chemistr)' of these Miocene rocks along Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernwith the regional deformation pattern support a transient period of shallow subduction that began at ~ 20 Ma and climaxed near 5 Ma. The subsequent wiUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
despread eruption of Pliocene to Pleistocene alkaline magmas with an intraplate chemistry in the Payenia Large Igneous Province signals a thickening mUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernwith the eruption of a 0.175+0.025 Ma mafic andesite. The northwest-trending Cortaderas lineament which generally marks the southern limit of Neogene backarc magmatism is considered to mark the southern boundary of the shallow subduction zone.INTRODUCTIONThe history of the continental lithosphere, m Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernantle wedge and subducting plate of the south Central Andes, between 36.5°s and 38cs. is reflected in the temporal and spatial distribution and chemisUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
try of the Upper Cretaceous to Holocene arc and backarc magmatic rocks of the Neuquén2https://khothuvien.cori!basin. Together with the structural and Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernmagmatic and delormalional history and the evolution OÍ the subducting slab in a west Io east transect between 36° and 37.5°s through the Ncuquen basin.GEOLOGIC AND TEC TONIC SETTINGThe easi-west transect through the Neuquén basin between 36.5° and 38°s latitude lies just south of the transitional S Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernouthern Volcanic Zone (SVZ) arc where die Holocene volcanic arc front of the svz is displaced to the west (Fig. 1). At this latitude, the currently suUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
bducting Nazca plate corresponds to Chrons 8 to 13 (~ 33 to 25 Ma; Cande and Kent, 1992). The Holocene centers of the transitional svz dominantly erupUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernded into two regions by the northwest-trending Cortaderas lineament (Fig. 2), which broadly intersects the southern end of the transitional svz segment. North OÍ the Cortaderas lineament, Miocene to Holocene backarc magmatic rocks are widespread in a retroarc region where Mesozoic rifling was less i Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernmportant and Neogene conlraclional deformation more important than to the south (see Ramos and Kay, this volume). Particularly notable in the backarcUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
are the largely Pleistocene to Holocene backarc Tromen and Payún Malrú volcanic centers and the extensive mafic flows that constitute the Payunia and Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernent.3The ages and locations of the Upper Cretaceous to Holocene magmatic rocks discussed in this paper are summarized in Table 1. They largely overlie or intrude the Mesozoic to early Paleogene sedimentary strata of the Neuquén basin. The history' of the Neuquén basin can be divided into three gener Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernal stages (e.g., Vergani et al., 1995): (1) a Triassic to Early Jurassic prerift and rift stage, (2) an Upper Jurassic to Cretaceous subsidence stage,Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
and (3) a Paleocene to Holocene modification stage. The first stage was largely shaped by the extension and fault-controlled subsidence that precededUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernxposed in the Cordillera del Viento (Fig. 2) and underlying much of the Neuquén basin erupted at this lime. The active rifting of this stage generally terminated as Middle Jurassic Andean tectonism and magmatism began to the west. During the second stage, the discrete rifts and intervening basement Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernblocks of the first stage generally merged into a broad post-rift basin that was filled by Middle Jurassic to Paleogene sedimentary strata. In the lasUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
t stage, the Neuquén basin strata were modified by Tertiary to Holocene extensional and contractional deformation and affected by periodic magmatic evUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the NorthernAGMATIC ROCKSThe distribution and ages of the Upper Cretaceous to Holocene Neuquén basin magmatic rocks described below are shown on maps in Figures 1 to 4 and summarized in Table 1. Twelve new 40Ar/39Ar ages are listed in Table 2. Age spectra are presented in Appendix 1 and analytical techniques ar Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northerne the same as in Jordan et al. (2001). New major and trace element data for 904https://khothuvien.cori!samples and isotopic data for 12 samples are liUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
sted in Tables 3 to 7 and plotted along with another 300 unpublished and published data in the fields in Figures 5 to 9. Sources of published data areUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northerne range of magmatic rocks types in the Neuquén basin region is illustrated in the SiO2 versus total alkali (Na2O+K2O) concentration diagrams in Figure 5.Major element, trace element and isotopic data are used below to characterize the Neuquén basin magmatic rocks. Characteristics of basaltic to mafi Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernc andesitic samples, particularly those with low FeO/MgO ratios (~ 0.7 to 1.0) and high Cr and Ni (>200-300 ppm) concentrations, are useful in interprUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
eting mantle and subcrustal processes, whereas characteristics of silicic andesite to rhyolites are useful in inteipreting crustal processes. Ratios aUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernesses are reflected in ratios of Ti group elements (Ta, Nb) to REE and alkali (K, Rb, Cs)/ alkaline earth (Ba, Sr) elements. Ratios of La.Ta, Ba-'La, and Ba.'Ta ratios in Neuquén basin samples are compared with those of svz frontal arc magmas (La.Ta ~ 40 - 95, Ba.'La > 20, and Ba-Ta > 500) and mid-o Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northerncean ridge (MORB) and intraoceanic intraplate (OIB) magmas (La/Ta < 12; Ba/La < 15) from Hickey et al. (1986) in Figure 6. Indicators of mantle sourceUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
conditions include the high field strength (HFS) elements plotted in Figure 7. High Ta/Hf ratios reflect an enriched intraplate mantle source whereasUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern Neuquén BasinSuz Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernf incompatible elements also serve as guides to percentages of partial melting in mantle and crustal source regions.5Ratios and concentrations of compatible elements (concentrated in minerals) reflect residual minerals that are either left in the magma source after melting or removed by fractionatio Upper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northernn processes. The residual mineral assemblage reflects the pressure, temperature, and fluid conditions under which the magma last equilibrated. Trace eUpper Cretaceous to Holocene Magmatism and Evidence for Transient Miocene Shallowing of the Andean Subduction Zone under the Northern
lements are useful in determining residual mineral assemblages as: a) olivine, orthopyroxene, and micas have little affinity for REEs, but take Ni andGọi ngay
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