Early Paleozoic Structural and Metamorphic Evolution of Western Sierra de San Luis (Argentina), in Relation to Cuyania Accretion     

Pablo Diego GonzAlez  Ana Maria Sato  Eduardo Jorge Llambias  Miguel A.S. Basei  Silvio R.F. Vlach 《Gondwana Research》2004,7(4):1157-1170

Structural, metamorphic and isotopic data obtained from the Nogoli Metamorphic Complex of western Sierra de San Luis indicate that the Early Paleozoic Famatinian Orogeny overprinted an already structured and metamorphosed older basement. The older geological features are relict NW trending fabric associated with high-grade (amphibolite facies) regional metamorphism preserved within thin strips of schists and paragneisses and in the core of mafic to ultramafic lenses. Arc magmatism, medium P (Barrovian type)/high T (amphibolite to granulite facies) regional metamorphism and penetrative NNE to NE trending foliation are related to the building of the Famatinian orogenic belt. The P-T conditions of the Famatinian prograde metamorphism reached a pressure peak of ca. 8 kb, with a thermal peak from -750°C up to -820°C. U-Pb conventional and chemical dating and Ar-Ar plateau ages constrain the peak of the main orogenic phase related to the Famatinian belt to 470–457 Ma (Early to Mid-Ordovician). Greenschist facies retrograde metamorphism closely associated with shear zones and secondary Ar-Ar plateau and Sm-Nd ages suggest that a late to post-orogenic phase of the Famatinian belt was active at least since -445 Ma. This phase continued during the Silurian to Late Devonian times through multiple reactivation of early shear zones. The Famatinian Orogeny reset a previous thermal history and therefore, the timing of the relict fabric could not be constrained conclusively with radiometric dates. Despite this difficulty, a range of 520 to 490 Ma suggests some inheritance from Pampean events registered by the older NW-SE fabric. The Early to Mid-Ordovician regional metamorphism and ductile deformation of the western Sierra de San Luis is interpreted as the orogenic effects of the collision of the allochthonous Cuyania terrane with the autochthonous proto-Pacific margin of Gondwana during the Famatinian Orogeny.  相似文献   

Diapiric emplacement in the upper crust of a granitic body: the La Bazana granite (SW Spain)     

Elena Galadí-Enríquez  Jesús Galindo-Zaldívar  Fernando Simancas  Inmaculada Expsito 《Tectonophysics》2003,361(1-2):83-96

The ascent and emplacement of granites in the upper crust is a major geological phenomenon accomplished by a number of different processes. The active processes determine the final geometry of the bodies and, in some favourable cases, the inverse problem of deducing mechanisms can be undertaken by relying on the geometry of plutons. This is the case of the La Bazana granitic pluton, a small Variscan igneous body that intruded Cambrian rocks of the Ossa-Morena Zone (SW Iberian Massif) in the core of a large late upright antiform. The granite shows no appreciable solid-state deformation, but has a late magmatic foliation whose orientation, derived from field observations, defines a gentle dome. The regional attitude of the main foliation in the country rock (parallel to the axial plane of recumbent folds) is NW–SE, but just around the granite, it accommodates to the dome shape of the pluton. Flattening in the host rock on top of the granite is indicated by boudinaged and folded veins, and appears to be caused by an upward pushing of the magma during its emplacement. The dome-shaped foliation of the granite, geometrically and kinematically congruent with the flattening in the host rock, can be related in the same way to the upward pushing of the magma. The level of final emplacement was deduced from the mineral associations in the thermal aureole to be of 7–10 km in depth. Models of the gravity anomaly related to the granite body show that the granite has a teardrop–pipe shape enlarged at its top. Diapiric ascent of the magma through the lower middle crust is inferred until reaching a high viscous level, where final emplacement accompanied by lateral expansion and vertical flattening took place. This natural example suggests that diapirism may be a viable mechanism for migration and emplacement of magmas, at least up to 7–10 km in depth, and it provides natural evidence for theoretical discussion on the ability of magmatic diapirs to pierce the crust.  相似文献   

Late Paleozoic orogeny in Alaska's Farewell terrane     

Dwight C. Bradley  Julie Dumoulin  Paul Layer  David Sunderlin  Sarah Roeske  Bill McClelland  Anita G. Harris  Grant Abbott  Tom Bundtzen  Timothy Kusky 《Tectonophysics》2003,372(1-2):23-40

Evidence is presented for a previously unrecognized late Paleozoic orogeny in two parts of Alaska's Farewell terrane, an event that has not entered into published scenarios for the assembly of Alaska. The Farewell terrane was long regarded as a piece of the early Paleozoic passive margin of western Canada, but is now thought, instead, to have lain between the Siberian and Laurentian (North American) cratons during the early Paleozoic. Evidence for a late Paleozoic orogeny comes from two belts located 100–200 km apart. In the northern belt, metamorphic rocks dated at 284–285 Ma (three ⁴⁰Ar/³⁹Ar white-mica plateau ages) provide the main evidence for orogeny. The metamorphic rocks are interpreted as part of the hinterland of a late Paleozoic mountain belt, which we name the Browns Fork orogen. In the southern belt, thick accumulations of Pennsylvanian-Permian conglomerate and sandstone provide the main evidence for orogeny. These strata are interpreted as the eroded and deformed remnants of a late Paleozoic foreland basin, which we name the Dall Basin. We suggest that the Browns Fork orogen and Dall Basin comprise a matched pair formed during collision between the Farewell terrane and rocks to the west. The colliding object is largely buried beneath Late Cretaceous flysch to the west of the Farewell terrane, but may have included parts of the so-called Innoko terrane. The late Paleozoic convergent plate boundary represented by the Browns Fork orogen likely connected with other zones of plate convergence now located in Russia, elsewhere in Alaska, and in western Canada.  相似文献   

Numerical Modeling of the Coupled Mechanical and Hydrological Processes during Deformation and Mineralization in the Mount Isa Block, Australia     

Liang-Ming Liu  Yanhua Zhang 《Resource Geology》2007,57(3):283-300

Mount Isa is a major Australian and world Pb‐Zn‐Ag mineral province. The wide varieties of mineralization in the province are believed to be closely related to the geodynamic processes of Isan Orogeny, which occurred between ca 1500 and 1620 Ma. In order to understand the geodynamic processes associated with the Isan Orogeny and the giant mineralization systems in the Mount Isa district, a series of numerical models has been constructed to simulate coupled mechanical–hydrological processes, using Fast Lagrangian Analysis of Continua (FLAC), a finite difference computer code. The numerical modeling results have demonstrated that the most probable far‐field stress orientation during the Isan Orogeny is the asymmetrical E–W shortening, which led to greater easternward tectonic movement at the west boundary of the district in comparison with westward movement at the east boundary. During the initial and early stage of the Isan Orogeny, the mechanical and hydrological conditions in the Leichardt Fault Trough of the West Fold Belt are much more favorable for fluid accumulation and mineralization than in the East Fold Belt. The Mount Isan fault zone developed as a high dilation shear zone where the fluids were focused. As the asymmetrical shortening progressed, shortening deformation and shear strain localization became intensified in the eastern part of the orogenic district. The eastern region therefore became a more favorable locality for hydrothermal mineralization. This structural development feature seems to explain why mineralization in the East Fold Belt is generally later than in the West Fold Belt. Fluid production from the Williams–Naraku granites could result in fluid over‐pressuring, and this probably contributed to the extensive brecciation and related mineralization in the East Fold Belt.  相似文献   

滇西昌宁——孟连带西区两个地层问题——兼论昌宁——孟连带的闭合 …   总被引：3，自引：1，他引：2  

方宗杰  肖荫文 《地层学杂志》2000,24(3):182-189

对昌宁－－孟加带西区的两个地层问题进行了讨论。根据牙形刺和放射虫的发现将原定为拉巴组的塔拉弄－南雅条带的时代厘定为晚泥盆世至早石炭世,时代大致与南皮河群的弄巴组或“中区”的“上泥盆统”相当,它们之间的确切关系仍有待进一步研究。怕拍组实际上主体属晚二叠世晚期,仅顶部可能包含有少量下三叠统印度阶最底部的沉积。对怕拍组的研究证实了澜沧运动的存在,昌宁－孟连带自此开始了由海洋盆地向造山带的演变进程,这一过  相似文献   

Early Mesozoic metamorphism and tectonic significance of the eastern segment of the Lhasa terrane,south Tibet     

《Journal of Asian Earth Sciences》2013

The metamorphic belt in the Basongco area, the eastern segment of Lhasa terrane, south Tibet, occurs as the tectonic blocks in Paleozoic sedimentary rocks. The Basongco metamorphic rocks are mainly composed of paragneiss and schist, with minor marble and orthogneiss, and considered previously to be the Precambrian basement of the Lhasa terrane. This study shows that the Basongco metamorphic belt experienced medium-pressure amphibolite-facies metamorphism under the conditions of T = 640–705 °C and P = 6.0–8.0 kbar. The inherited detrital zircon of the metasedimentary rocks yielded widely variable ²⁰⁶Pb/²³⁸U ages ranging from 3105 Ma to 500 Ma, with two main age populations at 1150 Ma and 580 Ma. The magmatic cores of zircons from the orthogneiss constrain the protolith age as ca. 203 Ma. The metamorphic zircons from all rocks yielded the consistent metamorphic ages of 192–204 Ma. The magmatic cores of zircons in the orthogneiss yielded old Hf model ages (T_DM2 = 1.5–2.1 Ga). The magmatic zircons from the mylonitized granite yielded a crystallization age of ca. 198 Ma. These results indicate that the high-grade metamorphic rocks from the Basongco area were formed at early Jurassic and associated with coeval magmatism derived from the thickening crust. The Basongco metamorphic belt, together with the western and coeval Sumdo and Nyainqentanglha metamorphic belts, formed a 400-km-long tectonic unit, indicating that the central segment of the Lhasa terrane experienced the late Paleozoic to early Mesozoic collisional orogeny.  相似文献   

金鸡岭产铀花岗岩体印支期侵位的岩浆动力学证据及其构造意义     

章邦桐  吴俊奇  凌洪飞  陈培荣 《铀矿地质》2012,(1):11-20,34

通过对南岭西段金鸡岭花岗岩体地质-岩石地球化学特征研究,判明该岩体的侵位深度(7.5km)、围岩温度(270℃)及岩浆初始温度(950℃),建立起金鸡岭花岗岩体的数学计算模型,分别计算得出:金鸡岭花岗岩熔体侵位后,其初始温度降低至结晶温度所需的时间(Δtcol)为3.91Ma;由于结晶潜热释放而使结晶过程延长的时间(ΔtL)为2.92Ma;由于金鸡岭花岗岩体放射性元素含量(U——16.5×10-6,Th——51.3×10-6,K2O——4.82%)是世界平均花岗岩放射性元素含量(U——5×10-6,Th——20×10-6,K2O——2.66%)的3倍左右,金鸡岭花岗岩熔体侵位后产生的放射性成因热使结晶过程延长的时间(ΔtA)为34.5Ma,远长于按世界花岗岩平均放射性元素含量计算的ΔtA*(2.82Ma)。金鸡岭花岗岩体的侵位-结晶时差(ΔtECTD)为41.3Ma,结合锆石U-Pb年龄值(156Ma),通过反演计算得出金鸡岭花岗岩体侵位年龄值(tE)为197.3Ma,从而为该岩体属于印支期侵位提供了重要的岩浆动力学证据。  相似文献   

南岭花山和姑婆山花岗岩基属印支期侵位:来自花岗岩熔体冷却-结晶和放射成因热计算的依据     

章邦桐  吴俊奇  凌洪飞  陈培荣 《地质学报》2012,86(7):1031-1046

通过对南岭西段花山和姑婆山花岗岩基地质-岩石地球化学特征研究,判明它们的侵位深度(5.5km)、围岩温度(196℃)及岩浆初始温度(950℃),建立起花山和姑婆山岩基的数学计算模型,计算得出:花山-姑婆山花岗岩熔体侵位后,其初始温度降低至结晶温度所需的时间(△tco1)分别为4.14 Ma(花山)和4.36Ma(姑婆山...  相似文献   

Evolution of the southeastern Lachlan Fold Belt in Victoria   总被引：2，自引：2，他引：0  

C. E. Willman  A. H. M. VandenBerg  V. J. Morand 《Australian Journal of Earth Sciences》2013,60(2):271-289

The Benambra Terrane of southeastern Australia is the eastern, allochthonous portion of the Lachlan Fold Belt with a distinctive Early Silurian to Early Devonian history. Its magmatic, metamorphic, structural, tectonic and stratigraphic histories are different from the adjacent, autochthonous Whitelaw Terrane and record prolonged orogen‐parallel dextral displacement. Unlike the Whitelaw Terrane, parts of the proto‐Benambra Terrane were affected by extensive Early Silurian plutonism associated with high T/low P metamorphism. The orogen‐parallel movement (north‐south) is in addition to a stronger component of east‐west contraction. Three main orogenic pulses deformed the Victorian portion of the terrane. The earliest, the Benambran Orogeny, was the major cratonisation event in the Lachlan Fold Belt and caused amalgamation of the components that comprise the Benambra Terrane. It produced faults, tight folding and strong cleavage with both east‐west and north‐south components of compression. The Bindian (= Bowning) Orogeny, not seen in the Whitelaw Terrane, was the main period of southward tectonic transport in the Benambra Terrane. It was characterised by the development of large strike‐slip faults that controlled the distribution of second‐generation cleavage, acted as conduits for syntectonic granites and controlled the deformation of Upper Silurian sequences. Strike‐slip and thrust faults form complex linked systems that show kinematic indicators consistent with overall southward tectonic transport. A large transform fault is inferred to have accommodated approximately 600 km of dextral strike‐slip displacement between the Whitelaw and Benambra Terranes. The Benambran and Bindian Orogenies were each followed by periods of extension during which small to large basins formed and were filled by thick sequences of volcanics and sediments, partly or wholly marine. Some of the extension appears to have occurred along pre‐existing fractures. Silurian basins were inverted during the Bindian Orogeny and Early Devonian basins by the Tabberabberan Orogeny. In the Melbourne Zone, just west of the Benambra Terrane, sedimentation patterns in this interval, in particular the complete absence of material derived from the deforming Benambra Terrane, indicate that the two terranes were not juxtaposed until just before the Tabberabberan Orogeny. This orogeny marked the end of orogen‐parallel movement and brought about the amalgamation of the Whitelaw and Benambra Terranes along the Governor Fault. Upper Devonian continental sediments and volcanics form a cover sequence to the terranes and their structural zones and show that no significant rejuvenation of older structures occurred after the Middle Devonian.  相似文献   

Alice Springs age shear zones from the southeastern Reynolds Range,central Australia     

I. Cartwright  I. S. Buick  D. A. Foster  D. D. Lambert 《Australian Journal of Earth Sciences》2013,60(3):355-363

The southeast Reynolds Range, central Australia, is cut by steep northwest‐trending shear zones that are up to hundreds of metres wide and several kilometres long. Amphibolite‐facies shear zones cut metapelites, while greenschist‐facies shear zones cut metagranites. Rb–Sr and ⁴⁰Ar–³⁹Ar data suggest that both sets of shear zones formed in the 400–300 Ma Alice Springs Orogeny, with the sheared granites yielding well‐constrained ⁴⁰Ar–³⁹Ar ages of ca 334 Ma. These data imply that the shear zones represent a distinct tectonic episode in this terrain, and were not formed during cooling from the ca 1.6 Ga regional metamorphism. A general correlation between regional metamorphic grade and the grade of Alice Springs structures implies a similar distribution of heat sources for the two events. This may be most consistent with both phases of metamorphism being caused by the burial of anomalously radiogenic heat‐producing granites. The sheared rocks commonly have undergone metasomatism implying that the shear zones were conduits of fluid flow during Alice Springs times.  相似文献