Research Article| May 01, 2009 Granite-lamprophyre connection in the latest stages of the early Paleozoic Ross Orogeny (Victoria Land, Antarctica) Sergio Rocchi; Sergio Rocchi 1Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy Search for other works by this author on: GSW Google Scholar Gianfranco Di Vincenzo; Gianfranco Di Vincenzo 2Istituto di Geoscienze e Georisorse (IGG), Consiglio Nazionale delle Ricerche (CNR), Via Moruzzi 1, 56124 Pisa, Italy Search for other works by this author on: GSW Google Scholar Claudio Ghezzo; Claudio Ghezzo 3Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy Search for other works by this author on: GSW Google Scholar Isabella Nardini Isabella Nardini 4Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (5-6): 801–819. https://doi.org/10.1130/B26342.1 Article history received: 12 Oct 2007 rev-recd: 18 Jul 2008 accepted: 18 Jul 2008 first online: 03 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Sergio Rocchi, Gianfranco Di Vincenzo, Claudio Ghezzo, Isabella Nardini; Granite-lamprophyre connection in the latest stages of the early Paleozoic Ross Orogeny (Victoria Land, Antarctica). GSA Bulletin 2009;; 121 (5-6): 801–819. doi: https://doi.org/10.1130/B26342.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Ross Orogen of the Transantarctic Mountains developed in response to the early Paleozoic convergence between the paleo–Pacific plate and the Antarctic margin of Gondwana. The central Victoria Land sector of the orogen is characterized by the widespread occurrence of pink Irizar granite plutons and dikes and Vegetation lamprophyric dikes and sills, which were emplaced in a tensional regime during a restricted time interval of the latest Ross Orogeny, ca. 490 Ma, as documented by new geochronological zircon U-Pb and mineral 40Ar-39Ar data. The syenomonzogranitic Irizar granites-dikes and the Vegetation lamprophyres are all potassic and, despite the chemical gap between them, have overlapping 87Sr/86Sr(490 Ma) and ϵNd (490 Ma) values, within 0.7074–0.7092 and −4.4 to −7.5, respectively.The genesis of Vegetation lamprophyres can be ascribed to the melting of previously enriched subcontinental lithospheric mantle further metasomatized by a subduction component during the Ross convergence. Melting was probably linked to asthenospheric upwelling during postcollisional slab rollback and convective thinning and/or delamination of overthickened lithosphere. On the other hand, the overlap of age, geochemical, and Sr-Nd isotope data between Vegetation and Irizar products, supported by geochemical modeling, suggests that the Irizar felsic magmas were derived by partial remelting of underplated material similar in composition to the Vegetation lamprophyres. This scenario provides new insights into the genesis of widespread postcollisional granites in orogens worldwide, implying significant net crustal growth by magma underplating in the very latest orogenic stages.In the regional geodynamic framework, the NE strike shared by both mafic and felsic dikes along 300 km of the convergent margin points to NW-SE extension, which in turn suggests oblique convergence of paleo–Pacific and Antarctic plates during the latest orogenic stages. A comparison of latest igneous activity in the Ross Orogen with contemporary magmatism in southeastern Australia-Tasmania implies that different mechanisms triggered the magmatic activity: slab rollback in the Antarctic sector of the margin versus slab tear in the Australia-Tasmania sector. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The paroxysm of 5 April 2003 has been the most violent
event of the past 50 years. The eruption occurred while lava
emission was in progress from lateral vents and consisted
of an 8-min-long explosive sequence. The most energetic
explosion launched meter-sized ballistic blocks that fell
on the volcano flanks and on the village of Ginostra, about
2 km far from the vent. A vertical gas/pyroclastic jet rose
above the craters, feeding a convective plume that reached
a height of up to 4 km. A fallout deposit of coarse pyro-
clasts (bombs and blocks) with subordinate amount of fine
ash blanketed the upper part of the cone, while a shower
of light pumice fell on the southern slopes of the volcano,
down to the sea.
The West Antarctic Rift System (WARS) represents one of the major active continental extension zones on Earth. The Ross Sea coast in northern Victoria Land (NVL) is littered with alkaline rift-related igneous products (Middle Eocene–Present). This study characterizes the nature of the magma source involved in the rift process through geochemical–isotopic investigation of Cenozoic basalts from NVL, and provides important constraints for the reconstruction of the tectono-magmatic evolution of the Ross Sea region–WARS. The chemical compositions of the basalts (Miocene–Present) display major and trace element characteristics typical of ocean island basalts (OIB), with strong enrichment in the most incompatible elements. Whole-rock isotopic compositions are in the range 0·7028–0·7034 for 87Sr/86Sr, 0·5129–0·5130 for 143Nd/144Nd (εNd(t) ∼ 4·8–6·7), 19·3–19·7 for 206Pb/204Pb, 15·4–15·6 for 207Pb/204Pb and 38·7–39·3 for 208Pb/204Pb, suggesting a HIMU-like (high U/Pb) signature of the mantle source. Determinations of 3He/4He on crushed olivine yielded values between 5·7 and 7·2 times the atmospheric ratio, similar to the lithospheric mantle and in the range of mid-ocean ridge basalts (MORB). The δ18Ool of olivine separates varies from 4·92 to 5·53‰ and is positively correlated with Fo content. Integration of our geochemical and isotope data with available geological, geophysical and geochronological data has led to the following reconstruction. The differences in the oxygen isotope values principally reflect the involvement of a heterogeneous mantle source and/or the assimilation of variable amounts of hydrothermally altered crustal rocks from the volcanic edifices. The 3He/4He data allow us to exclude a plume-driven model to explain the continuing rifting process. Based on the evidence of metasomatic processes, we propose a model to generate the mantle source(s) of the Cenozoic basaltic melts of the NVL. This is sublithospheric mantle metasomatized during an amagmatic extensional event that affected the WARS in the Late Cretaceous. During Eocene–Oligocene times, mantle flow warmed the mantle at the edge of the thick Antarctic lithosphere, and the reactivation of old translithospheric discontinuities promoted mantle melting and the rise of magmas as plutons and dyke swarms. From the Late Miocene to Present, the continuing craton-directed mantle flow led to normal faulting of the rift shoulder, which favoured the rise of magmas to build up large volcanic edifices.
<p><strong>Abstract.</strong> We revised the concept of convective, intrusive geothermal plays, considering that the tectonic setting is not, in our opinion, a discriminant parameter suitable for a classification. We analysed and compared four case studies: (i) Larderello (Italy), (ii) Mt Amiata (Italy), (iii) The Geysers (USA) and (iv) Kizildere (Turkey). The tectonic settings of these geothermal systems are different and a matter of debate, so it is hard to use this parameter, and the results of classification are ambiguous. We suggest a classification based on the age and nature of the heat source and the related hydrothermal circulation. Finally we propose to distinguish the convective geothermal plays as volcanic, young intrusive and amagmatic.</p>
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