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1.
M. Carracedo J. L. Paquette A. Alonso Olazabal J. F. Santos Zalduegui S. García de Madinabeitia M. Tiepolo J. I. Gil Ibarguchi 《International Journal of Earth Sciences》2009,98(7):1609-1624
The first U–Pb geochronological results on the magmatic alignment of the Los Pedroches batholith are presented. The batholith
is composed of a main granodioritic unit, several granite plutons and an important acid to basic dyke complex, all of them
intrusive after the main Variscan regional deformation phase, D1, along the boundary between the Ossa-Morena and Central Iberian
zones (SW Iberian Massif). Zircons from samples on both extremes of the granodiorite massif record nearly simultaneous magmatic
crystallization at ca. 308 Ma, while the emplacement of granite plutons was diachronic between 314 and 304 Ma. The U–Pb results
combined with new field and textural observations allow to better constrain the age of Variscan deformations D2 and D3 across
the region, while the age of D1 remains imprecise. Transcurrent D2 shearing-tightening of D1 folds occurred around 314 Ma
(lower Westphalian) in relation to the emplacement of the first granitic magmas. D3 faults and shear bands bearing a strong
extensional component developed at ca. 308 Ma (upper Westphalian), associated to the intrusion of the main granodiorite pluton
(granodiorite) of the batholith. Together with available geochemical and geophysical information, these results point to the
Variscan reactivation of lithospheric fractures at the origin and subsequent emplacement of hybrid magmas within this sector
of the Massif. 相似文献
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A. Pesquera P. P. Gil-Crespo J. Torres-Ruiz E. Roda-Robles 《International Geology Review》2018,60(2):157-187
The Jálama pluton (JP) is a Variscan peraluminous granitoid that intruded into low-grade metasediments from the Central Iberian Zone (CIZ). It comprises a sillimanite-bearing two-mica monzogranite in the inner zone, followed by a tourmaline-bearing two-mica monzogranite, and a marginal tourmaline-muscovite leucogranite in the northern half of the pluton. Microgranitoid enclaves and metasedimentary xenoliths occur locally in monzogranites. The change in rock type from the central monzogranite to the marginal leucogranite corresponds to decreasing TiO2, MgO, FeO, CaO, Sr, Ba, Zr, and ΣREE, and increasing SiO2, Na2O, P2O5, Rb, Li, Cs, Ta, Sn, and W. Fe/(Fe+Mg) ratios in biotite, muscovite and tourmaline increase with increasing Fe/(Fe+Mg) in bulk rock, suggesting an important control of the bulk-rock composition on mineral chemistry. The high peraluminosity, the low CaO and high P contents, as well as the similarity of ε(Nd)300 values in both the granites and metasediments of the southern CIZ constitute strong evidences for a crustal origin of the granite suite, probably by melting of these metasedimentary rocks. Field and petrographic observations, together with mineralogical and geochemical data, suggest that assimilation and mingling/mixing acted in concert with fractional crystallization during the formation of the JP. These processes may also have been important in the evolution of other granitoids from this region. 相似文献
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A geochronology and Hf isotope study, using laser ablation-ICP-MS analysis of zircon grains, has been conducted to date felsic volcanic rocks from the Portuguese sector of the Iberian Pyrite Belt and to establish possible sources for these rocks. The ages obtained range from the Famennian to the Tournaisian, with the oldest ages reported in the Belt so far being identified in its southwestern part (Cercal area). Results also indicate that within each area, volcanism may have extended for significant periods of time. This suggests that caution is needed in interpreting possible migration trends for the volcanism, as the exact stratigraphic position of the sampled rocks is not always clear. Despite of this, the new data, coupled with previously reported information, suggests that volcanism migrated within the basin from the southwest to the northeast (present day coordinates). Projection from initial zircon ?Hf values towards the depleted mantle evolution curve, via an intermediate reservoir, allows the calculation of Hf protolith model ages that are predominantly Meso-Proterozoic. This is compatible with acid magmas resulting from the fusion of Phyllite–Quartzite (PQ) Formation metasedimentary rocks, which are beneath the volcanic rocks. This is because zircon grains from one PQ Formation sample provided Late Neo-Proterozoic ages and Paleo-Proterozoic to Late Archean U–Pb ages, and the Hf isotope signatures of these zircons can be expected to mix during fusion and result in protolith model ages that would be intermediate between the two U–Pb age populations, as recorded. Further supporting this source for the magmas, the distribution of U–Pb ages of (pre-Variscan) inherited zircon grains in the volcanic rocks is very similar to that shown by the detrital zircon grains from a PQ sample. 相似文献
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AbstractWe investigate the left-lateral slip on the 240-km- long, NE-SW-trending, Malatya-Ovacik fault zone in eastern Turkey. This fault zone splays southwestward from the North Anatolian fault zone near Erzincan, then follows the WSW-trending Ovacik valley between the Munzur and Yilan mountain ranges. It bends back to a SW orientation near Arapkir, from where we trace its main strand SSW beneath the Plio-Quaternary sediment of the Malatya basin. We propose that this fault zone was active during ~5–3 Ma, when it took up 29 km of relative motion between the Turkish and Arabian plates; it ceased to be active when the East Anatolian fault zone formed at ~3 Ma. The geometry of the former Erzincan triple junction, which differs from the modem Karliova triple junction, where the North and East Anatolian fault zones intersect, suggests a possible explanation for why slip on the Malatya- Ovacik fault zone was unable to continue. We interpret the SW- and SSW-trending segments of the Malatya-Ovacik fault zone as transform faults, which define an Euler pole ~1 400 km to the southeast. Its central part along the Ovacik valley, which is ~30° oblique to the adjoining transform faults, is interpreted as the internal fault of a stepover. The adjoining mountain ranges, which now rise up to ~3 300 m, ~2 000 m above the surrounding land surface, are largely the result of the surface uplift which accompanied the components of shortening and thickening of the upper crustal brittle layer that occurred around this stepover while the left-lateral faulting was active. © 2001 Éditions scientifiques et médicales Elsevier SAS 相似文献
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Rare-Earth Elements from Modern Mineral–Organic Associations in the Zone of Sulfide Ore Hypergenesis
The REE composition of modern mineral–organic associations in the sulfide ore hypergenesis zone of the Berezitovoe deposit in the Russian Far East was studied for the first time. It is shown that the mineral–organic associations widely abundant in the valley of Konstantinovskii Creek and represented by bright brown crusts on the surface of deluvial deposits were formed at the expense of the influence of acid highly mineralized mine waters from the Berezitovoe deposit. The mineral–organic associations found in the Creek valley may be considered as a new indicator for evaluation of the geoecological state of modern technogenic landscapes. 相似文献
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Fassihi Shirin Sone Masatoshi Hairapetian Vachik Esfahani Fariba Shirezadeh 《International Journal of Earth Sciences》2017,106(4):1205-1221
International Journal of Earth Sciences - The presence of the Bashkirian–Moscovian (lower Pennsylvanian) sequence with mixed siliciclastics and fossil-rich carbonates has long been known from... 相似文献
9.
《《地质学报》英文版》1997,71(2)
A series of tectonites were formed in the shear zone array of the Tongbai--Dabie Orogenic Belt, including mylonites, blastomylonites, semi--plastic mylonites and foliated cataclasitesas a result of multiple strain localization, strain softening and deformation partitioning. 相似文献
10.
Koroteev V. A. Chervyakovskiy V. S. Zaitseva M. V. Volchek E. N. Necheukhin V. M. 《Doklady Earth Sciences》2019,487(1):756-760
Doklady Earth Sciences - This paper reports on the first U–Pb dating of zircons from dacites of the volcanic paleo-edifice of the andesite–dacite complex of the Eastern Zone of the... 相似文献
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The anisotropy of magnetic susceptibility (AMS) was systematically measured for samples collected across the Lachlan Transverse Zone in the Eastern Subprovince of the Lachlan Orogen, New South Wales. Although the degree of anisotropy is usually moderate to low, it can be shown that the origin of the magnetic fabric is generally composite. Many localities are witness to a tectonic influence in addition to a magnetic foliation preserved from the time of rock formation (compaction). Furthermore, some localities indicate the presence of superimposed magnetic fabrics, potentially associated with a Silurian east–west direction of shortening, and a younger north–south (?) direction of shortening. Finally, the progressive southwards change in orientation of the magnetic lineation in the Molong area from north–south to east–west and then back to north–south again south of the Lyndhurst–Neville Fault suggests that the Lachlan Transverse Zone coincides with, and reflects, a major cross-structure in the Eastern Subprovince. AMS is thus a powerful tool to help map the fabric of Paleozoic rocks in the Tasmanides. Additional data will be required to help obtain a comprehensive picture of the tectonic history of the region. 相似文献
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The Ossa-Morena Zone (SW Iberian Massif) was affected by continuous orogen-parallel transcurrent continental tectonics from the Neoproterozoic to the Carboniferous times, involving transtension (TT) and transpression (TP) processes that co-existed together, occurred separately in neighbouring regions by the means of strain partitioning or even worked diachronically. A first stage of transpression TP1 took place during the Late Neoproterozoic–Lower Cambrian as a result of Cadomian arc-continent collisional processes. Structures generated by transtension TT1 from Cambrian to Lower Devonian were related to strong lithosphere stretching responsible for the development of basins controlled by major detachments, tilting, rifting and important tectono–thermal diachronic processes. Denudation phenomena and inhibition of sedimentation related with thermal uplift (asthenosphere upwelling) and consequent subsidence caused by isostatic equilibrium, involving generalized transgressions, were processes responsible for major unconformities. The Variscan TP2-TT2 episodes that followed diachronically TP1-TT1, by maintaining the orogen-parallel transport direction, were concomitant with syntectonic deposition of continental basins in the OMZ and foreland basins in the SPZ. TT2 local transtension and tectonic exhumation of deep crustal rocks along major shear zones, favoured the opening of tectonic troughs filled up by sediments and volcanism. TP2 shortening have generated fold axes parallel to the orogen-strike and composite dissymmetric flower structures. 相似文献
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PAN Mingbao ZHANG Qinglong LU Huafu CHEN Huogen CHEN Shoujuand ZHU ShipengDepartment of Earth Sciences Nanjing University Nanjing Jiangsu Jiangsu Institute of Geological Survey Zhujiang Ro Nanjing Jiangsu E-mail: andypans@.com Hao Ziguo Zhu Xiling 《《地质学报》英文版》2003,77(3):332-337
From Donghai County of Jiangsu Province to Rongcheng County of Shandong Province on the southern border of the Sulu orogen, there exposes an ultramafic belt, accompanied with an ultrahigh-pressure metamorphic zone. It can be further divided into the Xugou belt (the northern belt), and the Maobei-Gangshang belt (the southern belt). One grain of diamond has been discovered from the Zhimafang pyrope peridotite in the southern belt using the heavy mineral method. The diamond grain is 2.13 mm × 1.42 mm × 0.83 mm in size and weighs 9.4 mg. The occurrence of the diamond suggests that the Zhimafang pyrope peridotite xenolith is derived from the lithospheric upper mantle. The tectonic emplacement mechanism of the pyrope peridotite xenoliths in granite-gneisses is obviously different from those in kimberlite. The Sulu orogen was located on the active continental margin of the Sino-Korean craton in the Neoproterozoic. The relatively cold and water-bearing oceanic crustal tholeiite slab subducted beneath the lith 相似文献
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M. A. E. Huminicki P. J. Sylvester R. Lastra L. J. Cabri D. Evans-Lamswood D. H. C. Wilton 《Mineralogy and Petrology》2008,92(1-2):129-164
Summary This study reports the first documented occurrence of platinum group-minerals (PGM) in the vicinity of the Voisey’s Bay magmatic
sulfide ore deposit. The PGM are present in a sulfide poor, hornblende gabbro dyke in the Southeast Extension Zone of the
massive sulfide Ovoid deposit. The dyke has somewhat elevated concentrations of platinum-group elements (PGE) and gold (up
to 1.95 g/t Pt, 1.41 g/t Pd, and 6.59 g/t Au), as well as Cu, Pb, Ag, Sn, Te, Bi and Sb. The PGM formed by magmatic processes
and were little disturbed by subsequent infiltration of an externally-supplied hydrothermal fluid. To date, no similar PGM
occurrences have been discovered in the Ovoid deposit itself.
Whole rock REE patterns indicate that the dyke is geochemically related to the main conduit troctolites, which carry the bulk
of the massive sulfide mineralization at Voisey’s Bay. The PGE mineralization is Pt- and Pd-rich, where the Pt and Pd occur
predominantly as discrete PGM with minor Pd in solid solution in galena (average=1.8 ppm) and pentlandite (average=2 ppm).
The discrete PGM are predominantly hosted by disseminated base-metal sulfides (bornite, chalcopyrite, and galena) (56 vol%)
and are associated with other precious metal minerals (13 vol%) with only ∼3 vol% of the PGM hosted by silicate minerals.
In whole rock samples, the PPGE (Pt, Pd, and Rh) correlate with abundances of chalcopyrite, bornite, galena, and other precious
metal minerals (PMM), whereas the IPGE (Ir, Ru, and Rh) correlate with pyrrhotite and pentlandite. There are no correlations
of the PGE with chlorine. Lead isotope compositions of galena associated with the PGE mineralization in the Southeast Extension
Zone are broadly similar to those for galena in the Ovoid. The lead isotope compositions are much different from those in
the Voisey’s Bay Syenite, which is a potential external hydrothermal fluid source.
The observed Cu-rich, Pb-rich sulfide compositions and associated Pt-Pd-Au-Ag-Sn-Te-Bi-Sb assemblage in the dyke can be produced
magmatically as late ISS differentiates (e.g., Prichard et al., 2004). Melting temperatures of the PGM are also consistent with a magmatic origin. Following crystallization of PGM
from magmatic sulfide, an external REE-enriched hydrothermal fluid was introduced to the system, producing secondary amphibole
and locally remobilizing the Pb and Sn from the sulfides hosting the PGM.
Author’s address: M. A. E. Huminicki, Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL, Canada A1B 3X5 相似文献
18.
《Geodinamica Acta》2001,14(1-3):103-131
We investigate the left-lateral slip on the 240-km-long, NE–SW-trending, Malatya–Ovacık fault zone in eastern Turkey. This fault zone splays southwestward from the North Anatolian fault zone near Erzincan, then follows the WSW-trending Ovacık valley between the Munzur and Yılan mountain ranges. It bends back to a SW orientation near Arapkir, from where we trace its main strand SSW beneath the Plio-Quaternary sediment of the Malatya basin. We propose that this fault zone was active during ∼5–3 Ma, when it took up 29 km of relative motion between the Turkish and Arabian plates; it ceased to be active when the East Anatolian fault zone formed at ∼3 Ma. The geometry of the former Erzincan triple junction, which differs from the modern Karlıova triple junction, where the North and East Anatolian fault zones intersect, suggests a possible explanation for why slip on the Malatya–Ovacık fault zone was unable to continue. We interpret the SW- and SSW-trending segments of the Malatya–Ovacık fault zone as transform faults, which define an Euler pole ∼1 400 km to the southeast. Its central part along the Ovacık valley, which is ∼30° oblique to the adjoining transform faults, is interpreted as the internal fault of a stepover. The adjoining mountain ranges, which now rise up to ∼3 300 m, ∼2 000 m above the surrounding land surface, are largely the result of the surface uplift which accompanied the components of shortening and thickening of the upper crustal brittle layer that occurred around this stepover while the left-lateral faulting was active. 相似文献
19.
《Gondwana Research》2000,3(1):21-31
The origin of Palghat Gap, the most prominent discontinuity in the Western Ghats, is controversial. The rocks of the Gap — hornblende-biotite gneiss, mylonitic augen gneiss, charnockite and amphibolite are characterised by three groups of folds formed during two deformations. Shear indicators like augens, pull-aparts, rootless folds, sheath folds, minor shears and quartz fabric strongly suggest ductile dextral shearing. Kinematic analysis of structural elements supports shearing in a N-S compressional field with XY being subvertical. Features on both mesoscopic and microscopic scales strongly favour Palghat Gap being treated as a ductile shear zone. The present Gap topography is the product of shearing and erosion. 相似文献
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López-Moro F. J. López-Plaza M. Gutiérrez-Alonso G. Fernández-Suárez J. López-Carmona A. Hofmann M. Romer R. L. 《International Journal of Earth Sciences》2018,107(3):985-1004
International Journal of Earth Sciences - In this study, we report U–Pb Laser Ablation ICP-MS zircon and ID-TIMS monazite ages for peraluminous granitoid plutons... 相似文献