TY - JOUR
T1 - Circa 546 Ma plume-related dykes in the ∼1 Ga Novillo Gneiss (east-central Mexico)
T2 - Evidence for the initial separation of Avalonia
AU - Keppie, J. Duncan
AU - Dostal, Jaroslav
AU - Nance, R. Damian
AU - Miller, Brent V.
AU - Ortega-Rivera, Amabel
AU - Lee, James K W
PY - 2006/7/5
Y1 - 2006/7/5
N2 - The ∼1 Ga Novillo Gneiss exposed in an inlier in the front ranges of the Laramide belt in east-central Mexico is cut by an unmetamorphosed NE-trending mafic dyke swarm. The gneiss represents the northernmost inlier of the Oaxaquia terrane that underlies the backbone of Mexico. Titanite and biotite from metasedimentary rocks yielded ages of 928 ± 2 Ma (concordant U-Pb age), and duplicate 40Ar/39Ar plateau ages of 697 ± 7 and 697 ± 10 Ma, which are inferred to represent cooling through ∼660 and ∼300-350 °C, respectively. On the other hand, hornblende from cross-cutting, NE-trending mafic dykes yielded a 40Ar/39Ar plateau age of 546 ± 5 Ma, which is inferred to closely post-date the time of intrusion. Combined with published ages (U-Pb zircon, Sm-Nd garnet, K-Ar hornblende) the data suggest that, following granulite facies metamorphism at 982 ± 6 Ma (8.9-9.7 kbar and 730-775 °C), the Novillo Gneiss cooled at a rate of ∼1.45 °C/my. If this latter rate is extrapolated it would place the rocks at the surface (30 °C) by ∼497 Ma, about 50 my after dyke emplacement. Geochemistry of the dykes indicates that they are Fe-rich tholeiites with: (i) low MgO, but high TiO2 and other HFSE, (ii) smooth mantle-normalized incompatible trace element patterns peaking at Nb and La, and (iii) intraplate tectonic affinities. These features are typical of enriched tholeiites associated with plumes. Current Precambrian paleogeographic reconstructions place Avalonia against Oaxaquia and subsequently separate Avalonia by way of ridge-trench collision at ∼550 Ma giving rise to the unique Avalonian Cambrian fauna and a rapid phase of early Cambrian subsidence. These events are contemporaneous with emplacement of the Novillo mafic dykes, suggesting that the plume-related magmatism and separation of Avalonia from Oaxaquia are linked.
AB - The ∼1 Ga Novillo Gneiss exposed in an inlier in the front ranges of the Laramide belt in east-central Mexico is cut by an unmetamorphosed NE-trending mafic dyke swarm. The gneiss represents the northernmost inlier of the Oaxaquia terrane that underlies the backbone of Mexico. Titanite and biotite from metasedimentary rocks yielded ages of 928 ± 2 Ma (concordant U-Pb age), and duplicate 40Ar/39Ar plateau ages of 697 ± 7 and 697 ± 10 Ma, which are inferred to represent cooling through ∼660 and ∼300-350 °C, respectively. On the other hand, hornblende from cross-cutting, NE-trending mafic dykes yielded a 40Ar/39Ar plateau age of 546 ± 5 Ma, which is inferred to closely post-date the time of intrusion. Combined with published ages (U-Pb zircon, Sm-Nd garnet, K-Ar hornblende) the data suggest that, following granulite facies metamorphism at 982 ± 6 Ma (8.9-9.7 kbar and 730-775 °C), the Novillo Gneiss cooled at a rate of ∼1.45 °C/my. If this latter rate is extrapolated it would place the rocks at the surface (30 °C) by ∼497 Ma, about 50 my after dyke emplacement. Geochemistry of the dykes indicates that they are Fe-rich tholeiites with: (i) low MgO, but high TiO2 and other HFSE, (ii) smooth mantle-normalized incompatible trace element patterns peaking at Nb and La, and (iii) intraplate tectonic affinities. These features are typical of enriched tholeiites associated with plumes. Current Precambrian paleogeographic reconstructions place Avalonia against Oaxaquia and subsequently separate Avalonia by way of ridge-trench collision at ∼550 Ma giving rise to the unique Avalonian Cambrian fauna and a rapid phase of early Cambrian subsidence. These events are contemporaneous with emplacement of the Novillo mafic dykes, suggesting that the plume-related magmatism and separation of Avalonia from Oaxaquia are linked.
KW - Avalonia
KW - Geochemistry
KW - Geochronology
KW - Mafic dyke swarm
KW - Novillo Gneiss
KW - Oaxaquia
UR - http://www.scopus.com/inward/record.url?scp=33744932559&partnerID=8YFLogxK
U2 - 10.1016/j.precamres.2006.01.020
DO - 10.1016/j.precamres.2006.01.020
M3 - Article
AN - SCOPUS:33744932559
SN - 0301-9268
VL - 147
SP - 342
EP - 353
JO - Precambrian Research
JF - Precambrian Research
IS - 3-4
ER -