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1.
The last stage in the formation of the Arabian Nubian Shield in Jordan was dominated by post-orogenic igneous activity of the ∼610–542 Ma Araba Suite, including a monzogabbroic stock intruding the Saramuj Conglomerate, near the southeastern corner of the Dead Sea. The geological setting, petrography, geochemistry and geothermometry of the monzogabbro and other cogenetic varieties are used to shed light on the petrogenesis of this stock and reveal its magma source. The monzogabbro, megaporphyry dikes, and scattered syenite pockets are co-magmatic and alkaline, potassic and shoshonitic in nature. REE and trace elements patterns indicate that these magmas were produced from a mantle that had been modified by subduction-related metasomatism. The parental mafic magma could have been derived by 10% partial melting of LILE-enriched phlogopite-bearing spinel lherzolite, probably lithospheric mantle, in association with post-collisional extension. Fractional crystallization of this parental magma by olivine and pyroxene gave rise to the monzogabbroic magma.The megaporphyry dikes with their giant labradorite plagioclase megacrysts represent feeders of a voluminous volcanic activity that could have lasted for about 105 years.Thermodynamic modeling applying the MELTS software indicates crystallization of this suite in the temperature range of 1184–760 °C at a pressure of 2 kbars, agreeing with olivine-pyroxene, pyroxene, and two-feldspar thermometry. The modeled mineralogy and sequence of crystallization of constituent minerals using MELTS is in remarkable agreement with the observed modal mineralogy of the monzogabbro. Furthermore, a great degree of congruity exists between the modeled and observed chemistry of the major minerals with only minor discrepancies between modeled composition of biotite and olivine.  相似文献   

2.
The magnetite-series (I-type) calc-alkaline granitoid suit, ranging from pyroxene monzodiorite to granodiorite, is associated with the porphyry and skarn gold–copper deposits at the Shizishan orefield in Tongling district, Anhui Province. In-situ U–Pb dating and Hf isotope analysis of magmatic and inherited zircons are combined with whole rock Sr–Nd–Pb isotopic data and mineral thermobarometry to interpret the petrogenesis. The magmatic zircons from the quartz monzodiorites yield weighted average 206Pb/238U ages of ca. 139 Ma and mean εHf(t) value of −19.8 ± 3.9 (1σ), while those from the pyroxene monzodiorite show a similar mean age but notably higher mean εHf(t) value (−8.5 ± 1.4). The inherited zircons from the quartz monzodiorite yield ages of 0.8, 2.0 and 2.4 Ga with mean εHf(t) value of −2.9 ± 1.4, while those from the pyroxene monzodiorite show younger ages (165 to 245 Ma) but similar mean εHf(t) value (−5.6 ± 4.5). Whole rock Sr–Nd–Pb isotope data indicate that crustal material significantly contributed to the magma. Mineral thermobarometry results reveal that the depths of the discrete magma chambers were about 23 km, and 10 to 2 km deep.The data above combined with previous studies suggest that: 1) The magma emplacement and crystallization (typically for zircons) mainly occurred at about 139 Ma, consistent with the age of mineralization; 2) The primary pyroxene monzodioritic magma might have mixed with the magma produced by partial melting of the Yangtze lower crust, and accumulated in the magma chamber at ca. 23 km deep in the lower crust level; 3) AFC and magma mixing were the dominate processes for the magmatic evolutions at shallow level (2 to 10 km), where the circumstances were favorable for mineralization.  相似文献   

3.
ABSTRACT

The origin of the Oligocene turbidites from the Cerro Pelón area in south Gulf Mexico proposed by Ortega-Flores et al. (2018) is in disagree with the interpretations made by Molina-Garza et al. (2019), which main criticism is based on U-Pb ages of detrital zircons from the matrix of a conglomerate unit, which they refer to as ‘Nanchital Conglomerate’, as well as on the presence of limestone, gabbros, and mafic protolith-derived clasts. Molina-Garza et al. (2019) basically interpret the Nanchital Conglomerate as Miocene in age, which was sourced mainly from metamorphic complexes including their sedimentary covers located to the west and south of the Cerro Pelón area. For some reason, Molina-Garza et al. (2019) suppose that the Nanchital Conglomerate should have the same provenance sources that the Oligocene turbidites from Cerro Pelón area, reported by Ortega-Flores et al. (2018). Based on the foregoing, we strongly disagree with Molina-Garza et al. (2019) considering that, from the beginning, they intend to compare two units of different age. Additionally, the scarce data reported from both the matrix and the clasts of the Nanchital Conglomerate are not determinant for interpreting the provenance of this conglomeratic unit and subsequently, to consider the same rock sources from the Oligocene through Miocene time.  相似文献   

4.
This study presents sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon ages, and whole-rock chemical and isotopic (Sr-Nd) compositions of representative Triassic plutons from South Korea. The plutons from the Gyeonggi massif (Hongseong, Namyang, Yangpyeong and Odesan), the central Okcheon belt (Baeknok and Yongsan), and the Yeongnam massif (Sangju, Gimcheon, Hamyang and Macheon) yield zircon U–Pb ages of ca. 232–226 Ma, 227–226 Ma, and 240–228 Ma, respectively. Among the Triassic plutonic suite in South Korea, those within the Gyeonggi massif are dominated by granite, syenite, monzonite, monzodiorite and gabbro. Plutons within the Okcheon belt are mainly by granite to quartz monzodiorite. The Yeongnam massif mainly incorporates granite to granodiorite and minor monzodiorite intrusions. The geochemical signatures of the Triassic plutons are characterized by Ta–Nb troughs, depletion of P and Ti, and enrichment of LILE. Most plutons except Macheon monzodioritic pluton show high initial 87Sr/86Sr ratios (0.708248–0.714678) and strongly negative εNd(T) (− 20.3 to − 7.7) values, suggesting contribution from middle to upper crust. In contrast, the Macheon monzodioritic pluton in the Yeongnam massif shows relatively low initial 87Sr/86Sr ratios (0.706547-0.706629) and negative εNd(T) (− 4.43 to − 3.62) values. The Middle Triassic syenite–monzonite–granite–gabbro series in and around the Gyeonggi massif possess high-K calc-alkaline and shoshonitic affinity suggesting a post-collisional magmatic event following the Permo–Triassic collision between the North and South China blocks. The Triassic plutons in the Yeongnam massif and the Okcheon belt, together with a Permian Yeongdeok pluton in the Gyeongsang basin, show features typical of high- to medium-K calc-alkaline magmatism with LREE and LILE enrichments. This together with a depletion of Y and HREE suggests their formation in a subduction setting. Our results provide robust evidence to consider the Gyeonggi massif as an extension of the Qinling–Dabie–Sulu belt between the North and South China blocks in central China. The Okcheon belt and Yeongnam massif in South Korea, together with the continental margin of South China, are marked by a common Permian to Triassic magmatic episode, probably related to the paleo-Pacific slab subduction.  相似文献   

5.
成都平原第四纪化石冰楔的发现及古气候意义   总被引：5，自引：0，他引：5  
最近,在成都平原西缘,大邑城西氮肥厂附近,斜江河西岸,上新统-下更新统大邑砾岩剖面的北端新开挖的露头上,发现了4条化石冰楔。这里的地理坐标是30°35'N103°31'E,海拔530m.这些冰楔发育于大邑砾岩露头的顶部。其中最大的一条,顶部宽3m,向下延伸2.5m.这些冰楔垂直向下延伸,与大邑砾岩层面斜交。所以,它们是在大邑砾岩沉积之后并经过构造变动后形成的,是大邑砾岩的后生冰楔。化石冰楔的充填物的特征与大邑砾岩有明显差别:前者为棕黄色,后者为灰白-黄色;前者砾径分选较好,砾径较细,一般长5cm~15cm,而后者砾径分选较差,粗大者20cm~30cm;前者的砾石含量高,约95%,后者的砾石含量低,约85%;前者砾石ab面产状无优势方向,而后者的ab面产状显示优势方向,倾向170°~210°,倾角30°~40°.由于两者有上述差别,所以,化石冰楔在露头上可以被识别出来。采用ESR法测定冰楔充填物的时代为0.171Ma.由此看来,这些冰楔的形成时代可能相当于V28-238深海岩心氧同位素曲线第6气候期(0.195Ma~0.128Ma),也可与中国黄土L2~5(0.195Ma~0.180Ma)和L2~4(0.180Ma~0.167Ma)所记录的气候波动和青藏高原倒数第二次冰期对比。
一般认为,冰楔是多年冻土的指示器,所以这些化石冰楔反映了成都平原在第四纪曾一度发育多年冻土。据研究,冰楔只能形成于年均温<-6℃的地方,高海拔多年冻土下界大致与-2℃~-4℃年均等温线相符。现今,大邑附近年均温约16℃.那么,化石冰楔形成时期,成都平原年均温至少比现今下降了18℃.   相似文献   

6.
The southern segment of the Eastern Ghats Mobile Belt (EGMB) in India was an active convergent margin during Mesoproterozoic, prior to the final collision in Neoproterozoic during the assembly of the Rodinia supercontinent. Here we present mineralogical, whole-rock geochemical, zircon U–Pb and Hf isotopic data from a granitoid suite in the Bopudi region in the EGGB. The granitoid complex comprises quartz monzodiorite with small stocks of rapakivi granites. The monzodiorite, locally porphyritic, contains K-feldspar megacrysts, plagioclase, quartz, biotite and ortho-amphibole. The presence of mantled ovoid megacrysts of alkali feldspar embaying early-formed quartz, and the presence of two generations of the phenocrystic phases in the rapakivi granites indicate features typical of rapakivi granites. The K-feldspar phenocrysts in the rapakivi granite are mantled by medium-grained aggregates of microcline (Ab7 Or93), which is compositionally equivalent to the rim of Kfs phenocryst and Pl (An23–24 Ab75). The geochemistry of both the granitoids shows arc-like features for REE and trace elements. LA-ICP-MS zircon analyses reveal 207Pb/206Pb ages of 1582 (MSWD = 1.4) for the rapakivi granite 1605 ± 3 Ma (MSWD = 3.9) for the monzodiorite. The zircons from all the granitoid samples show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. The zircons from the monzodiorite have a limited variation in initial 176Hf/177Hf ratios of 0.28171–0.28188, with εHf(t) values of −2.2 to +2.8. Correspondingly, their two-stage Hf isotope model ages (TDM2) ranging from 2.15 to 2.47 Ga probably suggest a mixed source for the magma involving melting of the Paleoproterozoic basement and injection of subduction-related juvenile magmas. The prominent Mesoproterozoic ages of these granitoids suggest subduction-related arc magmatism in a convergent margin setting associated with the amalgamation of the Columbia-derived fragments within the Neoproterozoic Rodinia assembly.  相似文献   

7.
The Monte Orfano Conglomerate (MOC), exposed in the foothills of the Southern Alps (northern Italy), is one of the few outcrops of sediments documenting the Cenozoic tectonic evolution of the Alpine retrowedge. Calcareous nannofossil biostratigraphy allowed us to constrain the upper part of the MOC, formerly attributed to the Early-Middle Miocene in the type-locality, to the earliest Miocene (Neogene part of the NN1 nannofossil zone). A likely latest Oligocene age is therefore suggested for the bulk of the underlying conglomerates, whose base is not exposed. Deposition of the MOC can be placed within the post-collisional tectonic uplift of the Alps, documented in the Lake Como area by the Como Conglomerate (CC) at the base of the Gonfolite Lombarda Group, and supports the correlation with Upper Oligocene clastic sediments cropping out further to the East, in the Lake Garda and in the Veneto-Friuli areas (“molassa”). The remarkable difference in petrographic composition between the western (CC) and eastern (MOC) clastics deposited in the Alpine retro-foreland basin highlights the synchronous tectonic activity of two structural domains involving different crustal levels. Whilst the bulk of the CC, that straddles the Oligocene/Miocene boundary, records largely the tectonic exhumation of the Alpine axial chain crystalline complexes, the coeval MOC consists of detritus derived from the superficial crustal section (Triassic to Paleogene sedimentary rocks) of the Alpine retrowedge and constrains the onset of the post-collisional deformation phase of the Southern Alps as not younger than the Late Oligocene.  相似文献   

8.
The Borgulikan ore field is localized in the west of the Umlekan-Ogodzha volcanoplutonic belt made up of various igneous (upper-Amur granite-granodiorite (140–134 Ma), Burunda monzodiorite-granodiorite (130–127 Ma), and Taldan andesite (127–123 Ma)) and superposed (Early Cretaceous Gal’ka trachybasalt-rhyolite (119–115 Ma) and Late Cretaceous trachybasalt-trachyandesite (97–94 Ma)) complexes. 40Ar/39Ar dating of porphyry intrusions breaking through the Taldan volcanic complex and associated with Cu-Mo-(Au) mineralization yielded the following ages: early (dark) “pre-ore” quartz monzodiorite porphyrites — 125.8±0.7 Ma (groundmass) and 125.2±1.8 Ma (biotite phenocrysts); late (cream) “syn-ore” quartz monzodiorite porphyrites — 122.6±0.7 Ma (biotite phenocrysts). In age and many geochemical features the quartz monzodiorite porphyrites are close to the Taldan complex volcanics. Both of these rocks seem to belong to the same volcanoplutonic association.  相似文献   

9.
ABSTRACT

Large-scale Cu–Au mineralization is associated with Late Mesozoic intrusive rocks in the Tongling region of eastern China, which mainly comprise pyroxene monzodiorite, quartz monzodiorite, and granodiorite. To constrain the petrogenesis of the intrusive rocks and Cu–Au mineralization, detailed analyses of the geochronology, apatite in situ geochemistry, whole-rock geochemistry, and zircon Hf isotopic compositions were performed. Magmatic zircons from pyroxene monzodiorites, quartz monzodiorites, and granodiorites yield U–Pb ages of 136–149 Ma, 136–146 Ma, and 138–152 Ma, respectively, indicating that their formation ages are contemporaneous. Quartz monzodiorites and granodiorites (SiO2 = 57.9–69.5 wt.%) are highly potassic calc-alkaline rocks with adakitic affinity and have low MgO and Y contents, low zircon εHf(t) values (?11.7 to ?39.0), high apatite Cl contents (>0.2 wt.%), and log fO2 values (?23.2 to ?8.23), indicating that they may have formed when metasomatized mantle-derived magmas mixed with slab-derived magmas before undergoing crustal assimilation and fractional crystallization. Pyroxene monzodiorites (SiO2 = 48.4–53.0 wt.%) are shoshonitic and record high MgO, P2O5, and Y contents, high zircon εHf(t) values (1.55 to ?7.87), high oxygen fugacity, low Nb and Ta contents, and low apatite Cl contents (mainly <0.2 wt.%), suggesting that they were primarily derived from a metasomatized lithospheric mantle-derived magma that experienced the assimilation of lower crustal materials. The results indicate that the intrusive rocks and associated large-scale Cu–Au mineralization of the Tongling region resulted from the partial melting of the subducted oceanic slab in an oxidizing environment.  相似文献   

10.
Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified 40Ar/39Ar and K/Ar systematic in some areas.  相似文献   

11.
Clastic rudaceous metasedimentary rocks range from arkose to ultramafic para-schist in lithology and have high Na, Rb, Ni, Cr and V contents, except for pure arkose which has low Ni, Cr and V. The various arkoses are not comparable chemically with analyses of any Archaean or younger arkose or greywacke. The distinctive geochemistry and immature sedimentology of this clastic sequence (Jones Creek Conglomerate) results from: (a) derivation from sodic granitoid, low-K basaltic, peridotitic and gneissic source areas, (b) sedimentation in a high energy environment close to source areas, and (c) a lack of major post-depositional chemical alteration. Pebbles in the Conglomerate also attest to the local derivation of detritus from both sides of its very elongate outcrop.Following the emplacement (at 2689 ± 17 Ma) and unroofing of a sodic granitoid pluton, the Conglomerate was rapidly deposited in a graben-like basin. An irregular unconformable contact between the Conglomerate and this pluton is preserved locally. Elsewhere contacts with granitoid or supracrustal rocks are tectonised, but the petrology of the Conglomerate indicates that these contacts were unconformities also. Contrary to previous suggestions, it is considered unlikely that the Conglomerate stratigraphically separates an older from a younger supracrustal sequence in this area. The Conglomerate probably represents the last depositional event before the onset of deformation and protracted regional metamophism to the greenschist—amphibolite facies transition. Crustal evolution from the emplacement of the sodic pluton to the cessation of metamorphism probably occupied some 100 Ma rather than 60 Ma as proposed elsewhere.  相似文献   

12.
Mafic and intermediate intrusions occur in the Slavkovsky les as dykes, sills and minor tabular bodies emplaced in metamorphic rocks or enclosed in late Variscan granites near the SW contact of the Western Krušné hory/Erzgebirge granite pluton. They are similar in composition and textures to the redwitzites defined in NE Bavaria. Single zircon Pb-evaporation analyses constrain the age of a quartz monzodiorite at 323.4 ± 4.4 Ma and of a granodiorite at 326.1 ± 5.6 Ma. The P–T range of magma crystallization is estimated at ~1.4–2.2 kbar and ~730–870°C and it accords with a shallow intrusion level of late Variscan granites but provides lower crystallization temperatures compared to the Bavarian redwitzites. We explain the heterogeneous composition of dioritic intrusions in the Slavkovsky les by mixing between mafic and felsic magmas with a minor effect of fractional crystallization. Increased K, Ba, Rb, Sr and REE contents compared to tholeiitic basalts suggest that the parental mafic magma was probably produced by melting of a metasomatised mantle, the melts being close to lamprophyre or alkali basalt composition. Diorites and granodiorites originated from mixed magmas derived by addition of about 25–35 and 50 vol.%, respectively, of the acid end-member (granite) to lamprophyre or alkali-basalt magma. Our data stress an important role of mafic magmas in the origin of late Variscan granitoids in NW Bohemian Massif and emphasize the effect of mantle metasomatism on the origin of K-rich mafic igneous rocks.  相似文献   

13.
The Owen Conglomerate comprises coarse-grained siliciclastics that were deposited in response to Late Cambrian extension. The identification of normal faults that host thickened accumulations of siliciclastics is used here to support interpretation of syn-fill extension. Local mapping and section construction have identified a series of north-trending, en échelon, segmented normal faults that exhibit changes in along-strike polarity. The Late Cambrian faults are adjacent to sedimentary packages that define half-graben geometries, with an unconformity that defines basal contacts with underlying Mt Read Volcanics and onlap geometries onto the opposing basin margin. Faults that were active during deposition of the Owen Conglomerate were subsequently reversed during D1 Middle Devonian deformation, with reverse displacement controlling the development of inversion structures defined by north-trending fold structures. Pervasive northwest-trending D2 deformation extensively overprints earlier deformation features, and has led to the spectacular development of type 1 interference patterns that largely control outcrop distributions along the West Coast Range. Field evidence is documented in support for a simple structural history that accounts for geometries associated with Late Cambrian extension, prior to Middle Devonian inversion (D1) and subsequent shortening (D2).  相似文献   

14.
Clasts of the Late Devonian Keepit Conglomerate of northeastern New South Wales, Australia, are predominantly andesites of isotropic nature that lack any apparent initial shape controls. Given adequate time in a particular environment, these clasts could be reasonably expected to develop shapes characteristic of abrasion within that environment.Clasts from both fluvial and marine resedimented conglomerates of the Keepit Conglomerate possess shape characteristics indicative of shaping within a fluvial environment. Maximum projection sphericity, and a plot of sphericity against either the oblate-prolate index or the flatness parameter C/A, were the most useful in indicating fluvial shaping processes. In addition, the OP Index and the dominant form classes of the Sneed and Folk Sphericity-Form diagram were in support of a fluvial history for the clasts.The occurrence of clasts exhibiting typical fluvial shapes in marine resedimented conglomerates indicates a lack of time and/or insufficient energy in a beach environment for reshaping of the clasts prior to resedimentation into deeper-water submarine-fan environments. This interpretation is consistent with and lends support to the interpretation, based on all other available data, for the Keepit Conglomerate of a history of rapid progradation of fluvial gravels into a relatively low-energy coastline environment, with periodic resedimentation of coarse sediment into deeper water.  相似文献   

15.
Foreland basin growth strata are ideal recorders of deformation rates and kinematics in tectonically active regions. This study develops a high-resolution chronostratigraphic age model to determine folding rates in the Eocene-Oligocene terrestrial growth strata of the Berga Conglomerate Group, NE Spain. The Berga Conglomerate Group was sampled for rock magnetic, magnetostratigraphic, and magnetic susceptibility (χ) cyclostratigraphy analyses. Analysis of rock magnetic measurements indicate a mixed mineral assemblage with both paramagnetic and ferromagnetic minerals. A new magnetic reversal stratigraphy constrains the time frame of folding and is in agreement with previous interpretations. Time series analysis of χ variations show statistically significant power at expected orbital frequencies and provides precession-scale (20 kyr) temporal resolution. Strain measurements including anisotropy of magnetic susceptibility (AMS) fabrics and bedding plane strain worm burrow distortion are consistent with fixed hinge, flexural folding kinematics. Fault-related folding was modeled using χ cyclostratigraphy timing and strain measurement kinematic constraints. The onset of folding was at 33.85 Ma and the end of deformation is less constrained but is younger than 31.06 Ma. Deformation and sediment accumulation rates are unsteady at 20 kyr time scales but appear artificially steady at polarity chron time scales.  相似文献   

16.
寇林林  张朋  赵岩  姚晓峰  沙德铭  杨中柱 《地球科学》2020,45(11):3950-3961
为探讨辽东半岛中生代闪长岩类岩石成因及其形成构造背景,选取辽东半岛岫岩西南部黄岭岩体为研究对象,开展岩相学、锆石LA-ICP-MS U-Pb年代学、Hf同位素地球化学和岩石地球化学研究.结果表明:黄岭岩体由黑云母二长闪长岩组成;锆石LA-ICP-MS U-Pb年龄为127.4±1.9 Ma,成岩为早白垩世;岩石地球化学元素特征表明,黄岭黑云母二长闪长岩具高钾钙碱性,轻稀土元素富集,重稀土亏损,富集Rb、Zr、K等大离子亲石元素,亏损Nb、P、Ti等高场强元素,正Eu异常;εHf（t）值为－20.1~－18.0,二阶段Hf模式年龄TDM2为2 316~2 450 Ma,揭示二长闪长岩可能是古元古代古老地壳部分熔融形成.结合区域构造演化推测黄岭岩体形成于古太平洋板块向欧亚板块俯冲挤压后折返伸展的构造背景.   相似文献   

17.
Fe isotope compositions of mineral separates and bulk samples from Xinqiao Cu–S–Fe–Au skarn type deposit were investigated. An overall variation in δ57Fe values from − 1.22‰ to + 0.73‰ has been observed, which shows some regularity. The δ57Fe values of endoskarn and the earliest formed Fe-mineral phase magnetite are ca.1.2‰ and ca. 0.3‰ lower, respectively, relative to the quartz–monzodiorite stock, indicating that fluid exsolved from the stock is enriched in light Fe isotopes. Moreover, spatial and temporal variations in δ57Fe values are observed, which suggest iron isotope fractionation during fluid evolution. Precipitation of Fe-bearing minerals results in the Fe isotope composition of residual fluids evolving with time. Precipitation of Fe (III) minerals incorporating heavy iron isotopes preferentially leaves the remaining fluid enriched in light isotopes, while precipitation of Fe (II) minerals preferentially taking-up light iron isotopes, and makes the Fe isotopic composition of the fluid progressively heavier. The regularity of Fe isotope variations occurred during fluid exsolution and evolution indicates that the dominant Fe source of Xinqiao deposit is magmatic. Overall, this study demonstrates that Fe isotope composition has great potential in unraveling ore-forming processes, as well as constraining the metal sources of ore deposits.  相似文献   

18.
Here we discuss the post-metamorphic metasomatism of high-grade orthogneisses by studying granite-looking, pink-coloured microcline-bearing rocks exposed around Ambagaspitiya, Sri Lanka. These rocks are medium- to coarse-grained, and are more or less homogeneous, and isotropic. Textural, and petrographic analyses clearly show that these special rocks are neither deformed nor metamorphosed, and that they are not any kind of intrusive rocks. The present study shows that these rocks have formed through K-metasomatism of once intensely deformed, and metamorphosed granodiorite, tonalite, monzodiorite, and quartz monzodiorite. The modal compositions of most of these metasomatic rocks of Ambagaspitiya are very similar to those of syenite, quartz syenite, monzonite, quartz monzonite, and quartz monzodiorite.All the original metamorphic rocks — namely granitic gneiss, metagranite, metagranodiorite, metatonalite, metamonzodiorite, metaquartz monzodiorite, metadiorite, basic dikes, and metapelites — had undergone at least five ductile deformations, D1 to D5, and had been metamorphosed under upper amphibolite to granulite facies conditions prior to the metasomatism. Almost all the parent metamorphic rocks had acquired a well-developed gneissic foliation (S2), and had suffered at least two intense folding events (F3, and F5) before the metasomatism occurred. All the metamorphic, and deformational fabrics of affected metamorphic rocks have been completely or partially obliterated by the metasomatism. This indicates that the metasomatic process post-dates all ductile deformations (D1 — D5), and the regional metamorphism. Of the parent metamorphic rocks, metagranodiorite, metatonalite, metamonzodiorite, and metaquartz monzodiorite have undergone intense metasomatism. It is shown that the metasomatism has nucleated along late-stage, post-D5 shear zones, which may form an interconnected network. Potassium-bearing metasomatic fluids, derived from a deep-seated K-rich source, may have migrated along these shear zones. The fluids which entered the shear zones have pervaded the orthogneisses through foliation planes, and along grain boundaries, and microcracks in minerals, transforming the host gneisses to metasomatic rocks. The main metasomatic transformation has taken place through the replacement of metamorphic plagioclase, and plagioclase-quartz by microcline, and through formation of myrmekite. Further studies are necessary to unravel the nature, composition, and the source of these late-stage K-rich fluids in the lower crust.  相似文献   

19.
太行山南段矿山杂岩体主要由闪长岩、石英闪长岩及二长闪长岩组成,LA-ICP-MS锆石U-Pb测年显示,闪长岩形成于125.2Ma±1.4Ma—126.9 Ma±1.3 Ma,说明该岩体形成于早白垩世。矿山杂岩体具有高w(Sr)(557×10~(-6)～985×10~(-6))和w(Sr)/w(Y)(30.9～61.8)值,低w(Y)(11.52×10~(-6)～22.10×10~(-6))和w(Yb)(1.30×10~(-6)～2.00×10~(-6))值的特征,这和埃达克岩相似。Th、U和大离子亲石元素(Rb、Ba、K)富集,高场强元素(Nb、Ta、Zr、Hf)亏损。稀土元素配分曲线近乎一致,均显示为轻稀土富集、弱正铕异常的右倾型的特点。综合岩性组合、岩相特点、地球化学特征和锆石年代学特征认为,矿山杂岩体是在下地壳大规模拆沉基础上,经过连续俯冲的影响,拆沉下来的物质诱发软流圈上涌而部分熔融,并交代上覆亏损地幔岩体使其发生部分重熔为高Mg的类似埃达克岩浆而形成的。  相似文献   

20.
五横岩体是长江中下游成矿带中安庆-贵池矿集区月山矿田内重要的中酸性侵入岩体之一。本文对五横岩体中1个辉长闪长岩、3个闪长岩和1个二长闪长岩样品进行了锆石LA-ICP-MS U-Pb定年,得到年龄值为分别为139.6±1.6Ma、139.3±1.3Ma、140.1±1.4Ma、140.0±1.6Ma以及132.9±1.5Ma,表明闪长岩和二长闪长岩为不同期岩浆作用的产物。结合地质特征,将五横岩体划分成两个不同的岩体。基于区内已有的岩石学、地球化学和成矿年代学研究,将月山矿田内侵入岩划分为两期,早期侵入岩主要为闪长岩类,成岩时代为138~140Ma;晚期侵入岩主要为花岗岩和正长岩,具有A型花岗岩的地球化学特征,成岩时代123~126Ma。通过对比分析,认为五横岩体具有较好的矽卡岩型铜金铁矿床成矿潜力,其成岩成矿作用过程发生于区域挤压-拉张过渡的构造背景。  相似文献   

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