Seismic properties of lower crustal xenoliths from El Hoyazo (SE Spain): Experimental evidence up to partial melting

2007 ◽  
Vol 253 (1-2) ◽  
pp. 239-253 ◽  
Author(s):  
Fabio Ferri ◽  
Luigi Burlini ◽  
Bernardo Cesare ◽  
Raffaele Sassi
Keyword(s):  
Experimental Evidence ◽  
Partial Melting ◽  
Se Spain ◽  
Seismic Properties ◽  
Crustal Xenoliths ◽  
Lower Crustal

Magmatic and tectonic emplacement of the Pukaskwa batholith, Superior Province, Ontario, CanadaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Gary P. Beakhouse ◽  
Shoufa Lin ◽  
Sandra L. Kamo
Keyword(s):  
Partial Melting ◽  
Abrupt Change ◽  
Superior Province ◽  
Density Inversion ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Greenstone Belts ◽  
Lower Crustal ◽  
Basaltic Crust ◽  
Structural Dome

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

scholarly journals Lower crustal zircons reveal Neogene metamorphism beneath the Pannonian Basin (Hungary)

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Hilary Downes ◽  
Andrew Carter ◽  
Richard Armstrong ◽  
Gabor Dobosi ◽  
Antal Embey-Isztin
Keyword(s):  
Pannonian Basin ◽  
Granulite Facies ◽  
Blocking Temperature ◽  
Late Devonian ◽  
Alkali Basalts ◽  
Volcanic Deposits ◽  
Eruption Age ◽  
Crustal Xenoliths ◽  
Lower Crustal ◽  
Variscan Basement

AbstractNeogene alkaline intraplate volcanic deposits in the Pannonian Basin (Hungary) contain many lower crustal granulite-facies xenoliths. U-Pb ages have been determined for zircons separated from a metasedimentary xenolith, using LA-ICPMS and SHRIMP techniques. The zircons show typical metamorphic characteristics and are not related to the hostmagmatism. The oldest age recorded is late Devonian, probably related to Variscan basement lithologies. Several grains yield Mesozoic dates for their cores, which may correspond to periods of orogenic activity. Most of the zircons show young ages, with some being Palaeocene-Eocene, but the majority being younger than 30Ma. The youngest zircons are Pliocene (5.1-4.2 Ma) and coincide with the age of eruptions of the host alkali basalts. Such young zircons, so close to the eruption age, are unusual in lower crustal xenoliths, and imply that the heat flow in the base of the Pannonian Basin was sufficiently high to keep many of them close to their blocking temperature. This suggests that metamorphism is continuing in the lower crust of the region at the present day.

Zircon U–Pb ages, major and trace elements, and Hf isotope characteristics of the Tiantangzhai granites in the North Dabie orogen, Central China: tectonic implications

2013 ◽  
Vol 151 (5) ◽  
pp. 916-937 ◽  
Author(s):  
XIN DENG ◽  
KUNGUANG YANG ◽  
ALI POLAT ◽  
TIMOTHY M. KUSKY ◽  
KAIBIN WU
Keyword(s):  
Partial Melting ◽  
Eastern China ◽  
Major And Trace Elements ◽  
Central China ◽  
Dabie Orogen ◽  
Crustal Rocks ◽  
The North ◽  
Granitic Magmatism ◽  
Two Peaks ◽  
Lower Crustal

AbstractCretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.

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