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91.
92.
—The Rif belt forms with the Betic Cordilleras an asymmetric arcuate mountain belt (Gibraltar Arc) around the Alboran Sea, at the western tip of the Alpine orogen. The Gibraltar Arc consists of an exotic terrane (Alboran Terrane) thrust over the African and Iberian margins. The Alboran Terrane itself includes stacked nappes which originate from an easterly, Alboran-Kabylias-Peloritani-Calabria (Alkapeca) continental domain, and displays Variscan low-grade and high-grade schists (Ghomarides-Malaguides and Sebtides-Alpujarrides, respectively), shallow water Mesozoic sediments (mainly in the Dorsale Calcaire passive margin units), and infracontinental peridotite slices (Beni Bousera, Ronda). During the Late Cretaceous?-Eocene, the Alboran Terrane was likely located south of a SE-dipping Alpine-Betic subduction (cf. Nevado-Filabride HP-LT metamorphism of central-eastern Betics). An incipient collision against Iberia triggered back-thrust tectonics south of the deformed terrane during the Late Eocene-Oligocene, and the onset of the NW-dipping Apenninic-Maghrebian subduction. The early, HP-LT phase of the Sebtide-Alpujarride metamorphism could be hypothetically referred to the Alpine-Betic subduction, or alternatively to the Apenninic-Maghrebian subduction, depending on the interpretation of the geochronologic data set. Both subduction zones merged during the Early Miocene west of the Alboran Terrane and formed a triple junction with the Azores-Gibraltar transform fault. A westward roll back of the N-trending subduction segment was responsible for the Neogene rifting of the internal Alboran Terrane, and for its coeval, oblique docking onto the African and Iberian margins. Seismic evidence of active E-dipping subduction, and opposite paleomagnetic rotations in the Rif and Betic limbs of the Gibraltar Arc support this structurally-based scenario. 相似文献
93.
94.
碧口群铜矿床的成矿时限及其意义 总被引:4,自引:0,他引:4
碧口群铜矿床作为早期同生喷流,后期受变质改造的沉积一变质改造型矿床,其保留有同生沉积的纹层构造和后生叠加改造的脉状构造。脉状硫化物Sr同位素及含矿石英脉的Ar同位素定年分别给出329Ma和211.3Ma,说明脉状硫化物的成矿时限在329-211Ma左右。由于该年龄明显小于矿体围岩的Sin-Nd、Rb-Sr年龄,所以该年龄反映了碧口群矿床的后期叠加成矿的时间。 相似文献
95.
On the Tectonic Evolution of the Kunlun-Karakorum Area, Southern Xinjiang, Northwest China 总被引:5,自引:0,他引:5
IntroductionTheKtmlundearakorumMountainRangeislocatedinthesouthernpartoftheXinjiangUygUrAutonomousRegion,NorthwestChina,belongingtotheconnectionpaftbetWeentheQinghai-TibetPlateauandthePamirPlateau.So,itstectonicfeaturesandevolutionaryhistoriesarecloselylinkedwiththesetWoplateaus(seefig.l).ThecompIexityofgeologicalstrUctUresinthisarealeadstoalotofcontfoversiesabolltitsevolutionhistoryforalongtime.TheXinjiangGeotTansect,runningacrosstheTianshanMountains,theTarimBasinandtheKunlun-Kara… 相似文献
96.
Field and laboratory structural studies show that the Devonian–Dinantian units of the northeast French Massif Central experienced
a complex and contrasting tectonic–metamorphic evolution during the Hercynian orogeny. The structural analysis of the pre-Middle
Visean Brévenne–Violay–Beaujolais rocks, in the Loire area, shows a polyphase tectonic evolution associated with greenschist
to amphibolite facies metamorphism. The first event, D1, probably occurred in Early Tournaisian or Latest Devonian times.
It is responsible for the flat-lying regional foliation and the NW/SE- to N/S-trending lineation. It is well observed in the
Violay group and corresponds to the NW-vergent emplacement of the Late Devonian units upon their gneissic basement, represented
by the Affoux gneisses. The second event, D2, is responsible for the NE/SW- to E/W-trending lineation. To the south, D2 deformation
is locally reworked by the Grand-Chemin dextral wrench fault, around 345–350 Ma ago. This polyphase deformation is also found
in several Devonian–Dinantian areas of the NE Massif Central, but not in Morvan. This tectonics corresponds to the Tournaisian
closure, by northward thrusting and subsequent intracontinental deformation, of the oceanic Brévenne–Violay–Beaujolais rift
which opened in Devonian times in a back-arc setting.
Received: 4 September 1998 / Accepted: 27 May 1999 相似文献
97.
98.
Shundong He Paul Kapp Peter G. DeCelles George E. Gehrels Matthew Heizler 《Tectonophysics》2007,433(1-4):15-37
Knowledge of the Cretaceous–Tertiary history of upper crustal shortening and magmatism in Tibet is fundamental to placing constraints on when and how the Tibetan plateau formed. In the Lhasa terrane of southern Tibet, the widely exposed angular unconformity beneath uppermost Cretaceous–lower Tertiary volcanic-bearing strata of the Linzizong Formation provides an excellent geologic and time marker to distinguish between deformation that occurred before vs. during the Indo-Asian collision. In the Linzhou area, located 30 km north of the city of Lhasa, a > 3-km-thick section of the Linzizong Formation lies unconformably on Cretaceous and older rocks that were shortened by both northward- and southward-verging structures during the Late Cretaceous. The Linzizong Formation dips northward in the footwall of a north-dipping thrust system that involves Triassic–Jurassic strata and a granite intrusion in the hanging wall. U–Pb zircon geochronologic studies show that the Linzizong Formation ranges in age from 69 Ma to at least 47 Ma and that the hanging wall granite intrusion crystallized at 52 Ma, coeval with dike emplacement into footwall Cretaceous strata. 40Ar/39Ar thermochronologic studies suggest slow cooling of the granite between 49 and 42 Ma, followed by an episode of accelerated cooling to upper crustal levels beginning at 42 Ma. The onset of rapid cooling was coeval with the cessation of voluminous arc magmatism in southern Tibet and is interpreted be a consequence of either (1) Tertiary thrusting in this region or (2) regional rock uplift and erosion following removal of overthickened Gangdese arc lower crust and upper mantle or break-off of the Neo-Tethyan oceanic slab. 相似文献
99.
K. HISADA L. L. PERCHUK T. V. GERYA D. D. VAN REENEN B. K. PAYA 《Journal of Metamorphic Geology》2005,23(5):313-334
Metapelites, migmatites and granites from the c. 2 Ga Mahalapye Complex have been studied for determining the P–T–fluid influence on mineral assemblages and local equilibrium compositions in the rocks from the extreme southwestern part of the Central Zone of the Limpopo high‐grade terrane in Botswana. It was found that fluid infiltration played a leading role in the formation of the rocks. This conclusion is based on both well‐developed textures inferred to record metasomatic reactions, such as Bt ? And + Qtz + (K2O) and Bt ± Qtz ? Sil + Kfs + Ms ± Pl, and zonation of Ms | Bt + Qtz | And + Qtz and Grt | Crd | Pl | Kfs + Qtz reflecting a perfect mobility (Korzhinskii terminology) of some chemical components. The conclusion is also supported by the results of a fluid inclusion study. CO2 and H2O ( = 0.6) are the major components of the fluid. The fluid has been trapped synchronously along the retrograde P–T path. The P–T path was derived using mineral thermobarometry and a combination of mineral thermometry and fluid inclusion density data. The Mahalapye Complex experienced low‐pressure granulite facies metamorphism with a retrograde evolution from 770 °C and 5.5 kbar to 560 °C and 2 kbar, presumably at c. 2 Ga. 相似文献
100.
T. N. Yang 《Journal of Metamorphic Geology》2004,22(7):653-669
The Qinglongshan eclogites in the Southern Sulu ultrahigh pressure metamorphic (UHPM) terrane show very different retrograded textures from their counterparts in the Northern Sulu terrane, implying a different thermal history. Scanning electron and optical microscope observations indicate that the peak assemblage of the Qinglongshan eclogite is anhydrous, composed of Grt + OmpI + Rt + (Ky + coesite). These primary minerals were replaced by second and third stage minerals, resulting in symplectite pseudomorphs or coronas. The following relationships are inferred: OmpI → OmpII + Ab + Fe‐oxide symplectite (type I) and Rt → Rt + Ilm intergrowth; and, Ky → Pg, OmpII (+Pl) → Amp (+Pl) symplectite (type II), and Grt → Prg (+Fe‐oxide). Mineral chemistry and mass‐balance demonstrate that the pseudomorphed textures were developed by metasomatism involving dissolution and precipitation intensified by fluids along grain boundaries. The formation of symplectite type I produced Fe, Mg and Na but consumed Ca and Si. The Mg and Fe diffused to garnet where exchange of (Mg, Fe) with Ca of the garnet resulted in compositional zonation with decreased Ca towards the edge of garnet grains where Ca was consumed during symplectite formation. The replacement of kyanite by paragonite consumed the extra Na. In the later stage, fluid infiltration partially transformed symplectite type I to type II, and narrow rims of pargasite resorbed garnet from their boundaries. Mass balance suggests that the transformation and resorption would have been coupled during fluid infiltration. In the latest stage, epidote and quartz were precipitated at very late stage as a result of fluid activity along microfractures. Tentative P–T conditions based on mineral reactions and thermocalc software suggest that the retrograded eclogite did not record the granulite facies retrograde evolution characteristic of eclogites from the Northern Sulu terrane. The difference in retrograde evolution between the Southern and Northern Sulu eclogites suggests a different exhumation history. 相似文献