玲珑复式花岗岩基的构成及其形成时代   总被引：12，自引：1，他引：12  

徐金方 《岩石学报》1991,7(2):43-49

根据地质关系,玲珑花岗岩可划分成8个独立岩体。Rb-Sr、~(40)Ar-~(39)Ar和Sm-Nd法年龄测定较好地解决了玲珑花岗岩长期争论的时代问题。  相似文献   

Magnetotelluric survey across Singhbhum granite batholith     

K. K. Roy  C. K. Rao  A. Chattopadhyay 《Journal of Earth System Science》1989,98(2):147-165

Magnetotelluric soundings have been carried out across the archaean terrain of Singhbhum granite batholith from Bangriposhi to Keonjhar for a distance of about 100 km. One-dimensional inversion models reveal that the depth of the moho varied between 23 and 40 km. The depth of the lithosphere asthenosphere boundary varied from 58 to 76 km. A zone of higher electrical conductivity detected at the base of the lower crust just above the moho is present along the entire profile. Signals within the range of 0.25 to 600 seconds, which crossed the coherency threshold of 0.8 to 0.9, could be stacked. Resistivity ranges of the crust mantle silicates below Singhbhum granite batholith vary over a wide range. Resistivity ranges are (i) 30,000–80,000 ohm for Singhbhum granite phase II, (ii) 2,000 to 9,000 ohm-m for Singhbhum granite phase III, (iii) 250 to 2,200 ohm-m for lower crust (iv) 3,000 to 47,000 ohm for the upper mantle and (v) 200 to 2300 ohm-m for the asthenosphere. Sharp break in electrical resistivity at the (i) upper crust-lower crust (ii) lower crust upper mantle and (iii) lithosphere-asthenosphere boundary is obtained along the entire profile. Signals could see up to 100 km below the granite batholith. Singhbhum granite phase II and III could be demarcated on the basis of resistivity. Low resistive zones in the lower crust and upper mantle might have formed due to (i) water (ii) combined effect of water and carbon and (iii) high temperature and partial melt.  相似文献   

冈底斯岩浆弧东段晚白垩世花岗岩的变质作用：新生地壳生长与再造     

李文坛  张宁  张泽明 《地质学报》2022,96(3):881-896

青藏高原南部的冈底斯岩浆弧形成于中生代新特提斯大洋岩石圈俯冲过程中。在冈底斯岩浆弧东段出露的中—高级变质岩代表岩浆弧的中- 下地壳组成，是探索大陆地壳形成与演化的窗口。作为这些中—高级变质岩原岩主要组成部分的里龙岩基由晚白垩世辉长岩、闪长岩和花岗岩组成。本文对由里龙岩基上部花岗岩变质形成的片麻岩进行了岩石学与年代学研究，探讨其原岩时代、成因、变质作用条件、时间及构造意义。所研究的片麻岩由斜长石、钾长石、石英、黑云母、绿帘石和白云母组成，含或不含角闪石，SiO2含量为61. 94%~74. 39%，铝饱和指数(A/CNK)为0. 89~1. 03，属于高钾钙碱性、准铝质到弱过铝质岩石。这些岩石具有轻稀土元素富集和重稀土元素亏损的配分模式，并表现为富集大离子亲石元素和相对亏损高场强元素的特征。片麻岩中的锆石由继承的岩浆核和变质边组成，岩浆核获得了92~86 Ma的结晶年龄，变质边获得了81~72 Ma的变质年龄，锆石岩浆核具正的εHf(t)值(+10. 2~+12. 1)。这些片麻岩的变质条件为740~750 ℃和0. 5~0. 6 GPa。本文和现有研究表明，里龙岩基是形成在晚白垩世新特提斯洋俯冲过程中具有亏损地幔地球化学特征的弧岩浆岩，经历了强烈的结晶分异作用，所研究的花岗岩是残余岩浆结晶产物。笔者认为，晚白垩世早期新特提斯洋中脊俯冲过程中巨量幔源岩浆的增生导致了冈底斯弧发生了显著的新生地壳生长；在晚白垩世晚期残余新特提斯洋岩石圈平缓俯冲过程中的弧地壳强烈缩短加厚使里龙岩基被运移到中下地壳，并发生了中—高级变质和部分熔融。冈底斯岩浆弧新生地壳在大洋岩石圈俯冲晚期经历了明显再造。  相似文献   

The Dharwar craton, southern India, and its Late Archaean plate tectonic setting: current interpretations and controversies     

Brian Chadwick  V. N. Vasudev  G. V. Hegde 《Journal of Earth System Science》1997,106(4):249-258

In spite of detailed geological investigations of the Dharwar craton since the 1890s, its principal lithological units, structure and chronology remain contentious. Important new work on lithostratigraphy, basin development, structure, geochemistry and geochronology has led to wide-ranging speculation on the Late Archaean plate tectonic setting. Much of the speculation is based on uniformitarian models which contrast with a recent proposal that the evolution of the craton was controlled by gravity-driven processes with no crustal shortening.  相似文献   

A kinematic model of emplacement of quartz reefs and subsequent deformation patterns in the central Indian Bundelkhand batholith     

Prakash P. Roday  P. Diwan  S. Singh 《Journal of Earth System Science》1995,104(3):465-488

This paper attempts to show that the quartz reefs forming the principal fabric of a large number of granitoid diapirs in the central Indian Bundelkhand batholith are dominated by numerous sigmoidal tensile fissures generated as a result of an EW sinistral brittle-ductile inhomogeneous simple shear but the secretion of quartz veins within the reefs occurred under an approximately EW subhorizontal extension. The paper also discusses the disruption along the reefs and of the reefs themselves by later faulting under a rotational subhorizontal or gently plunging maximum principal compressive stress that seems to be intimately related to the diapinc rise of more and more acidic magmas at relatively deeper levels within the crust, the relationship with the deformation within the supracrustals and suggests that the overall prolate strain within the diapirs was built up gradually, with initial NE-SW shortening, followed by meridional shortening and finally culminating into the NW-SE shortening that opened a large number of tensile cracks occupied by late dyke swarms. The slight reverse component of strike-slip faults, of both dextral and sinistral, corroborates the overall constriction at the centres of individual diapirs at depth. The palaeostress analysis using slickensided striae corroborates the general conclusions presented. Indeed, the paper tries to demonstrate that the prolate strain in the central part of a diapir is not something that occurs simultaneously from all sides radially inwards but is a phased one. It depends upon the size and shape of the initial diapir, and the part of the supracrustals in which the deformation begins first and is controlled by pre-existing planes of weakness. The paper tries to demonstrate how the prolate strain at the centres of granitoid diapirs might express itself at higher crustal levels under a relatively less ductile or brittle-ductile and even brittle regime.  相似文献   

Geochemistry and geochronology of the rapakivi granites and associated rocks in the midwest portion of the Serra da Providência composite batholith,SW of Amazonian craton,Rondônia,Brazil     

《Journal of South American Earth Sciences》2016

The Serra da Providência batholith includes the type area of the homonymous suite, the oldest rapakivi magmatic assemblage in the SW of the Amazonian craton (1.60–1.53 Ga). In the midwest portion of this massif, besides wiborgites/pyterlites and granophyric syenogranites, a leucosyenogranite facies and porphyritic rhyolites constitute new rock varieties recently described in that area. UPb LA-MC-ICP-MS zircon ages of 1574 ± 9 Ma and 1604 ± 3 Ma, respectively, were obtained for these new varieties and confirm their link with the Serra da Providência magmatism, whereas the subvolcanic rocks are older than the main rock varieties and were formed in a precursor event. These granitic facies are metaluminous to peraluminous, alkali-calcic, A2-type, ferroan granites. Their FeOt/(FeOt + MgO) ratios vary from 0.83 to 0.98 and suggest that these rocks were crystallized from oxidized-to reduced-A-type magmas, where the leucosyenogranites and granophyric sienogranites tend to be formed under more reduced conditions. They show fractionated REE patterns with very pronounced to weak negative Eu anomalies. The presence of granophyric textures and miarolitic cavities in equigranular syenogranitic facies suggests that these rocks were formed at shallow crustal depths, lower than 3 km. Three samples of leucosyenogranite have silica contents higher than 75% and low K/Rb ratios (<150), similarly to the tin specialized granites described in the Amazonian craton. Two distinctive groups of mafic rocks were recognized in the study area: porphyritic and equigranular gabbronorites. They correspond to tholeiitic basalts, with #Mg varying from 37 to 41 in porphyritic gabbronorites and 51 to 65 in equigranular gabbronorites. The low to moderate #Mg suggests that these rocks were crystallized from more evolved basaltic magmas. The porphyritic gabbronorites are enriched in TiO₂, FeOt, K₂O, P₂O₅ and REE compared to the equigranular gabbronorites that are enriched in MgO and CaO. The porphyritic gabbronorites have significant negative Eu anomalies a feature not observed in the equigranular gabbronorites. Porphyritic gabbronorites geochemical characteristics are similar to calc-alkaline basalts, whereas equigranular gabbronorites are similar to continental basalts. Petrographic, geochemical, and geological data of the felsic facies and the presence of associated mafic rocks corroborate the bimodal and post-collisional character of this magmatism. The occurrence of porphyritic rhyolites associated with shallow level plutonic granites in the Serra da Providência batholith reinforces the similarities between the Rondonian granites and the classical Fennoscandian rapakivi granites.  相似文献   

下地壳拆沉作用及大陆地壳演化   总被引：13，自引：0，他引：13  

高山 Ducea  MN 《高校地质学报》1998,4(3):241-249

讨论了下地壳拆沉作用的地球化学示踪方法,并以近来对秦岭－大别造山带和美国西部内华达岩基地区的研究成果为例,说明了下地壳拆沉在两地区壳－幔演化方面可能起的重要作用。  相似文献   

西藏曲水岩基4个系列花岗岩类的特征及构造意义     

熊清华 《地质通报》1998,(4)

曲水岩基解体,建立７个超单元和６个独立单元。该岩基由Ｍ型、俯冲Ⅰ型、同碰撞Ⅰ型和同碰撞Ｓ型花岗岩类４个系列组成。着重描述这４个系列花岗岩类的地质学、岩石学、岩石化学、地球化学及就位特征;并就新特提斯洋规模、性质、关闭以及印度板块与拉萨陆块的碰撞、西藏高原隆升机制等提出了一些新认识。  相似文献   

The LATEA metacraton (Central Hoggar, Tuareg shield, Algeria): behaviour of an old passive margin during the Pan-African orogeny   总被引：2，自引：0，他引：2  

Jean Paul Ligeois  Louis Latouche  Mustapha Boughrara  Jacques Navez  Michel Guiraud 《Journal of African Earth Sciences》2003,37(3-4):161

Historically, the Tuareg shield is divided into three parts bordered by mega-shear zones with the centre, the Central Polycyclic Hoggar, characterized by Archaean and Palaeoproterozoic lithologies. Nearly 10 years ago, the Tuareg shield was shown to be composed of 23 displaced terranes [Geology 22 (1994) 641] whose relationships were deciphered in Aïr to the SE [Precambr. Res. 67 (1994) 59]. The Polycyclic Central Hoggar terranes were characterized by the presence of well preserved Archaean/Palaeoproterozoic and Neoproterozoic lithologies.We show here that the terranes from Central Hoggar (Laouni, Azrou-n-Fad, Tefedest, Egéré-Aleksod) belonged to a single old passive margin, to which we gave the acronym name LATEA, which behaved as a craton during the Mesoproterozoic and the Early-Middle Neoproterozoic but was partly destabilized and dissected during the Late Neoproterozoic as a consequence of its involvement as a passive margin in the Pan-African orogen.An early Pan-African phase consisted of thrust sheets including garnet-bearing lithologies (eclogite, amphibolite, gneiss) that can be mapped and correlated in three LATEA terranes. In the Tin Begane area, P–T–t paths have been established from>15 kbar––790 °C (eclogite) to 4 kbar––500 °C (greenschist retrogression) through 12 kbar––830 °C (garnet amphibolite) and 8 kbar––700 °C (garnet gneiss), corresponding to the retrograde path of a Franciscan-type loop. Sm–Nd geochronology on minerals and laser ablation ICP-MS on garnet show the mobility of REE, particularly LREE, during the retrograde greenschist facies that affects, although slightly, some of these rocks. The amphibolite-facies metamorphism has been dated at 685 ± 19 Ma and the greenschist facies at 522 ± 27 Ma. During the thrust phase, the Archaean–Palaeoproterozoic basement was only locally affected by the Pan-African tectonics. LATEA behaved as a craton. Other juvenile terranes were also thrust early onto LATEA: the Iskel island arc at ≈850 Ma to the west of LATEA, the Serouenout terrane in the 700–620 Ma age range to the east. No subduction-related magmas have intruded LATEA during this epoch, which behaved as a passive margin.During the main Pan-African phase (625–580 Ma), LATEA was dissected by mega-shear zones that induced several hundreds km of relative displacement and allowed the emplacement of high-K calc-alkaline batholiths. Smaller movements continued till 525 Ma, accompanied by the emplacement of subcircular plutons with alkaline affinity. Here is dated the Ounane granodiorite (624 ± 15 Ma; ⁸⁷Sr/⁸⁶Sr_i=0.70839 ± 0.00016; 6WR, MSWD=0.87) and the Tisselliline granite (552 ± 15 Ma; ⁸⁷Sr/⁸⁶Sr_i=0.7074 ± 0.0001; 5WR, MSWD=1.4). Nd isotopes indicate a preponderant Palaeoproterozoic crustal source for these two plutons: _Nd=−14 to −21 at 624 Ma and T_DM=1650–2320 Ma for Ounane and _Nd=−13 to −15 at 555 Ma and T_DM=1550–1720 Ma for Tisselliline. Our model links these intrusions to a linear lithospheric delamination along mega-shear zones, allowing the hot asthenosphere to rise, melt by adiabatic pressure release and inducing the melting of the Palaeoproterozoic and Archaean lower crust.The LATEA cratonic microcontinent remained however sufficiently rigid to preserve Archaean and Palaeoproterozoic lithologies as well as Middle Neoproterozoic oceanic thrust sheets. This corresponds to the notion of metacraton [J. African Earth Sci. 34 (2002) 119], i.e. a craton that has been remobilized during an orogenic event but is still recognizable dominantly through its rheological, geochronological, isotopic and sometimes petrological characteristics.  相似文献   

Geochronological and geochemical constraints on the genesis of the Tieshan complex in the Edong district,Eastern China with implications for Fe and Cu skarn mineralization     

《Chemie der Erde / Geochemistry》2021,81(2):125744

Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO₂ (53.5–67.1 wt.%), K₂O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial ⁸⁷Sr/⁸⁶Sr values of 0.70648 to 0.70737, ε_Nd(t) values of −12.3 to −8.2 and ε_Hf(t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO₂ (63.0–71.0 wt.%) and K₂O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower ε_Nd(t) (−12.4 to −9.3) and ε_Hf(t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce⁴⁺/Ce³⁺) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (fO₂) than the Fe-related suite. This study highlights fO₂ and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization.  相似文献