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1.
Abstract

The Gangdese batholith, Tibet, records the opening and closing of the Neo-Tethyan ocean and the resultant collision between the Indian and Eurasian plates. The Mesozoic magmatic rocks play a crucial role in understanding the formation and evolution of the Neo-Tethyan tectonic realm. This study focuses on Jurassic intrusive rocks in the Xietongmen area of the southern margin of the Lhasa terrane adjacent to the Yarlung–Tsangpo suture. Zircon U–Pb dating yielded Middle Jurassic dates for ca 170?Ma hornblende gabbro and ca 173?Ma granodiorite intrusions. All of the samples are medium- to high-K calc-alkaline, and the majority are metaluminous and enriched in the large ion lithophile elements and depleted in the high-field-strength elements. This indicates the magma was generated in a subduction-related tectonic setting. The intrusive rocks have high and positive εHf(t) values (hornblende gabbro: 13.3–18.7; granodiorite: 14.2–17.6) that yield Hf model ages younger than 312?Ma. These new data, combined with the results of previous research, suggest that the Jurassic igneous rocks were derived from a metasomatised region of an asthenospheric mantle wedge. Extremely depleted Sr–Nd–Pb–Hf isotope compositions are similar to the Yarlung ophiolite and igneous rocks within other intra-oceanic island arcs. Together with the existence of sandstone that is identified as the product of the oceanic island arc environment, we suggest formation in an intra-oceanic island arc.

  1. The new zircon U–Pb dating has yielded Middle Jurassic ages for the ca 170?Ma hornblende gabbro and ca 173?Ma granodiorite phases of the Xietongmen intrusion.

  2. Jurassic igneous rocks formed from a metasomatised asthenospheric mantle wedge by northward subduction of the Neo-Tethys oceanic crust beneath the southern margin of the Lhasa terrane.

  3. Late Triassic–Jurassic igneous rocks, which are characterised by highly depleted isotopic compositions within the Southern Lhasa sub-terrane, record residual intra-oceanic island arcs in the eastern Tethyan belt.

  相似文献   

2.
Abstract

In Australian stratigraphic nomenclature, the concept of granitic rock suites has been in formal use for over a decade. The basis for this suite classification of granitic rocks is inconsistent and, in eastern Australian usage, unsound on several levels. We also note that the approach used in Western Australia is different. Granitic intrusions are probably not truly amenable to any strict, comprehensive, lithostratigraphic classification. If these rocks are integrated into such a scheme, group- and supergroup-level units (i.e. formal suites and supersuites) should not be incorporated. For the present, mappable units should be recognised at the levels of formation and member. The use of granite suites and supersuites in formal stratigraphic hierarchies is not recommended. Instead, granitic bodies could be grouped into individual plutons, which may or may not form parts of larger batholiths.
  1. KEY POINTS

  2. The suite-based classification of granitic bodies, as currently used in the Australian Stratigraphic Units Database, is based on unsound principles, and is not employed in a consistent manner.

  3. Granitic intrusive rocks probably cannot be grouped using lithostratigraphic principles that are consistent with either the local or international codes.

  4. Granitic bodies can be grouped into batholiths, plutons and members, but the names of these units should, for the moment, remain informal.

  相似文献   

3.
Uranium–Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu–Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (εNd(t) range from + 3.1 to + 7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have < 1.5% TiO2) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu–Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium–Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu–Au deposits are ~ 372 Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu–Au mineralization are ~ 366 Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu–Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late Devonian rocks associated with giant Cu–Au deposits from younger magmatic suites in the district.  相似文献   

4.
The Naruo porphyry Cu deposit is the third largest deposit discovered in the Duolong metallogenic district. Previous research has focused mainly on the geochemistry of the ore-bearing granodiorite porphyry; the metallogenesis remains poorly understood. In the present work, on the basis of outcrops and drilling core geological mapping, phases of early mineralization diorite, two inter-mineralization granodiorite porphyries, and late-mineralization granodiorite porphyry have been distinguished. Furthermore, the alteration zones were outlined, and the vein sequence was identified. The diorite and three porphyry phases were subjected to Laser Ablation Inductively Coupled Plasma Mass Spectrometry (La–ICP–MS) zircon U–Pb dating and in situ Hf isotope analyses as well as bulk major element, trace element, and Sr–Nd isotopic analyses. Molybdenite Re–Os dating was also conducted.The zircon U–Pb dating results show that the diorite and porphyry intrusions were emplaced at about 120 Ma, and the molybdenite Re–Os isochron age is 118.8 ± 1.9 Ma; this indicates that the Naruo porphyry Cu deposit was formed during a continuous magmatic–hydrothermal process. All of the diorite and granodiorite porphyry samples showed arc magmatic characteristics. Moreover, the moderate (87Sr/86Sr)i ratios and low εNd(t) and εHf(t) values of the diorite and porphyry intrusions suggest the source region of the juvenile lower crust. The lower (87Sr/86Sr)i and (143Nd/144Nd)i ratios and higher εNd(t) values and incompatible element concentrations than those in the granodiorite porphyry samples indicate a two-stage magmatic generation process for the intrusions. The early mineralization diorite has a high Cu concentration, implying that the source is enriched in Cu. However, the slightly lower Cu content of the late-mineralization granodiorite porphyry samples might imply Cu release from magmas and deposition within the metallogenic stage. The multiple stages of intrusions and subsequent volcanism within the Duolong metallogenic district, together with high Sr/Y features, indicate persistent magmatism during the metallogenic epoch, which is necessary for maintaining the activity of magmatic–hydrothermal and mineralization processes. Thus, the high Cu content in the source region, mantle-derived melt upwelling, and multiple stages of persistent magmatism were favorable for the formation of the Naruo porphyry Cu deposit.The high Fe2O3/FeO ratios of the diorite and granodiorite porphyry intrusions show very high oxidation features, which is coincident with estimated magmatic oxidation state calculated by the zircon trace element compositions. The high oxidation facilitates sulfur and chalcophile metals to be scavenged into the magmatic–hydrothermal systems, which is crucial for the metallogenesis of the Naruo porphyry Cu deposit.  相似文献   

5.
Abstract

The Hiltaba Suite intrusive rocks and penecontemporaneous Gawler Range Volcanics (GRV) comprise the 1590?Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. Zircon is principally associated with Fe–Ti oxides and clusters of touching crystals in these rocks, including in the Roxby Downs Granite (RDG), host of the Olympic Dam iron oxide–copper–gold deposit, and in other intrusive rocks that comprise the Olympic Province. There has been no explicit evaluation and explanation of potential origins published for concentrations of zircon with Fe–Ti oxides (herein zircon-rich clusters) found in these and similar rocks of western North America and elsewhere. Here we use U–Pb geochronology, mineral morphologies and compositions, and insights from surface chemistry and liquid-bound particle interaction studies to investigate zircon-rich clusters and provide a model for their formation. U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma, so it is unlikely that there are significant xenocrystic zircon grains or that the zircons include significant inherited cores. The lack of pre-magmatic zircon, consistent intra-grain and inter-grain zircon compositional trends, the predominance of oscillatory zoned zircon with morphologies indicating growth from hot, evolved silicate melts, and the lack of evidence for zircon recrystallisation, indicates that zircon crystallised in the host GRV and RDG magmas. Variable zircon compositions within individual clusters does not support epitaxial nucleation of zircon on Fe–Ti oxides, but it is likely that some zircon grains grew from seed crystals formed by exsolution of Zr from Fe–Ti oxides. Aggregation of isolated, liquid-bound crystals is energetically favourable, and the grainsize discrepancy between larger crystals (Fe–Ti oxides, pyroxenes) and smaller accessory minerals (zircon, apatite) maximises the disparity in particle velocities and hence enhances the opportunities for collisions and adhesion between these crystals. We propose that zircon adheres to Fe–Ti oxides with greater ease and/or with greater bond strengths, than to other phases present in the parental magmas. It is possible that this association is related to interactions between zircon and Fe–Ti oxide surface sites with opposing charges, presuming the distance between phase surfaces is sufficiently small. The occurrence of small zircon grains within Fe–Ti oxides and both euhedral zircon and zircon with asymmetric growth zonation in contact with Fe–Ti oxides indicates that several processes are responsible for the high concentrations of zircon crystals in some Fe–Ti oxide clusters.

  1. Zircon is principally associated with Fe--Ti oxides in 1.59 Ga Gawler Range Volcanics (GRV) and Roxby Downs Granite (RDG)

  2. U–Pb geochronology does not reveal any concordant zircon populations older than ca 1590?Ma

  3. Zircon compositions and morphologies indicate that zircon crystallised in the host RDG and GRV magmas and suggest recharge, reheating and mixing occurred in these magmatic systems

  4. Seed crystals, aggregation and surface chemical affinities contributed to the strong association of zircon and Fe–Ti oxides

  相似文献   

6.
New SIMS U-Pb (zircon) data for intrusive rocks of the Macquarie Arc and adjacent granitic batholiths of the Lachlan Orogen (southeastern Australia) provide insight into the magmatic and tectonic evolution of the paleo-Pacific Gondwana margin in the early Paleozoic. These data are augmented by Re-Os dates on molybdenite from four Cu-Au mineralised porphyry systems to place minimum age constraints on igneous crystallization. The simplicity of the zircon age distributions, and absence of older inheritance, stands in contrast to previous geochronological studies. The earliest magmatism within the Macquarie Arc is registered by a ca. 503 Ma gabbro from the Monza igneous complex, whereas a monzodiorite from the same drillhole records the youngest (ca. 432 Ma). Igneous activity in the Macquarie Arc thus overlapped deformation and magmatism in the craton-proximal Delamerian Orogen to the west, and the emplacement of the Lachlan granitic batholiths at 435–430 Ma; the thermal pulse associated with the latter may have triggered the formation of richly mineralised Silurian porphyries in the Macquarie Arc. The juvenile Hf isotope signature of the Monza Gabbro, together with the lack of zircon inheritance and the radiogenic Hf-Nd isotope systematics of Ordovician Macquarie Arc rocks, is consistent with early development of the arc, or a precursor magmatic belt, in an oceanic setting remote from continental influences, and with the arc being built on primitive Cambrian mafic crust. Outboard arc magmatism in the Cambrian may have initiated in response to convergent Delamerian orogenesis adjacent the Gondwana margin. Overlapping radiogenic isotope-time trends are consistent with the evolution of the Macquarie Arc and the Gondwana continental margin being linked from the Cambrian to the Silurian. These data provide further evidence for the growth of continental crust along the southeastern Australian segment of this margin being related to the dynamics of an extensional accretionary orogenic system.  相似文献   

7.
Adakite-like features are recognized in the Late Miocene (~10 Ma) porphyritic intrusions of the Los Pelambres giant porphyry copper deposit, central Chile (32°S). Located within the southern portion of the flat-slab segment (28–33°S) of the Chilean Andes, the Al- and Na-rich porphyries of Los Pelambres display distinctly higher Sr/Y (~100–300) and LaN/YbN (~25–60) ratios than contemporaneous and barren magmatic units (e.g., La Gloria pluton, Cerro Aconcagua volcanic rocks) of the same Andean magmatic belt. Strong fractionation of heavy rare earth elements (HREE), absence of Eu anomalies, high Sr/Y and Zr/Sm and low Nb/Ta ratios suggest melt extraction from a garnet-amphibolite source. The Late-Miocene adakite-like porphyritic intrusions at Los Pelambres formed closely related in time and space to the subduction of the Juan Fernández Ridge (JFR) hotspot chain along the Chilean margin. Current tectonic reconstructions reveal that, at the time of formation of the Los Pelambres rocks, a W-E segment of the JFR started to subduct beneath them, producing a slow-down of a previously rapid southward migration of a NE-ridge—trench collision. These particular tectonic conditions are favorable for the origin of the Los Pelambres porphyry suite by melting of subducting young hotspot rocks under flat-slab conditions. The incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the Sr-Nd isotope composition of the Los Pelambres rocks different from the MORB signatures of true adakites. A close relationship apparently exists between the origin of this adakite-like magmatism and the source of the mineralization in the Los Pelambres porphyry copper deposit.Editorial handling: R.J. Goldfarb  相似文献   

8.
内蒙古八大关矿区印支期岩浆活动及其找矿意义   总被引：3，自引：0，他引：3       下载免费PDF全文
通过对八大关矿区主要花岗岩体进行了系统采样,其镜下鉴定结果显示该区侵入岩主要为花岗岩、黑云母花岗岩、花岗斑岩、钾长花岗岩、花岗闪长斑岩;6件样品的LA-MC-ICP-MS锆石U-Pb年龄主要在243.87~231.63Ma。结合成矿斑岩的形成时代,矿区主要侵入岩均形成于印支期,并不存在海西期或燕山期侵入岩体。根据岩体年龄的分布情况,将矿区印支期岩浆活动划分为243.87~237.11 Ma和231.63~229.00 Ma2个阶段,早阶段岩浆活动主要形成矿体围岩;而铜钼矿化主要与晚阶段岩浆活动有关。此外,整个鄂霍次克造山带两侧的印支期岩浆活动也具有两阶段的特点,且与鄂霍次克洋的俯冲密切相关,考虑到两侧已查明的印支期超大型-大型斑岩型矿床,认为八大关矿区外围及额尔古纳地区存在寻找印支早期斑岩矿床的可能性。  相似文献   

9.
大井是内蒙古东部地区的一处大型铜银锡多金属矿床,矿体呈脉状产出在二叠系林西组地层中,受NW或NWW向断裂控制。本文对大井矿区及其外围主要侵入岩体和火山岩开展了年代学和地球化学研究。LA-MC-ICP-MS锆石测年结果表明,大井矿区内靠近1号矿脉产出的2件霏细岩脉样品的锆石年龄分别为170.7±1.4Ma(MSWD=1.9)和170.7±1.1Ma(MSWD=1.3);矿区外围马鞍子黑云母二长花岗岩体的锆石年龄为279.7±1.3Ma(MSWD=0.74);唐家营子附近安山玢岩脉的锆石年龄为252.0±1.8Ma(MSWD=1.6);大四段村似斑状黑云母二长花岗岩体的锆石年龄为242.8±1.7Ma(MSWD=1.7);采自大坝南部的流纹质晶屑熔结凝灰岩、流纹质火山角砾熔岩和晶屑凝灰岩的锆石年龄分别为143.5±0.7Ma(MSWD=0.38),144.3±0.7Ma(MSWD=1.2)和145.3±1.0Ma(MSWD=2.5);小城子村南部石英斑岩脉的锆石年龄为146.1±0.9Ma(MSWD=1.7),安山玢岩脉的锆石年龄133.2±0.7Ma(MSWD=0.96)。反映本区至少存在四期岩浆活动,分别是海西晚期、印支早期、燕山早期和燕山中期。岩石地球化学分析结果表明,大井矿区及外围主要侵入岩(黑云母二长花岗岩、似斑状黑云母二长花岗岩、霏细岩、安山玢岩和石英斑岩)均为富SiO2、富碱、准铝的钙碱性岩石,在SiO2-K2O图解上均落入"高钾钙碱系列"区。所有的岩石样品具有轻稀土分异明显、富集大离子亲石元素(LILE)的特征,其中Ba、Nb、Sr、P、Ti相对亏损,而Rb、Th、K、Ce、Nd、Hf、Sm、Y 和Yb相对富集。侵入岩和火山岩的年代学与岩石地球化学特征表明,马鞍子黑云母二长花岗岩和大四段村似斑状黑云母二长花岗岩的侵位可能与古亚洲洋的碰撞闭合有关,形成于挤压的构造环境;燕山早期侵入岩在本区并不发育,其形成环境还有待进一步查明,可能与西伯利亚板块和蒙古-华北板块之间的鄂霍茨克洋消亡及后碰撞造山有关;而燕山晚期大规模的侵入-火山喷发活动可能是由岩石圈减薄,区域大规模伸展所引起。根据本文对矿区内及外围侵入岩与火山岩的年代学研究,结合矿区地质和前人研究成果,认为大井铜银锡矿床的成矿主要与晚侏罗世-早白垩世岩浆活动(146~133Ma)有关,是区域伸展构造背景下岩浆活动的产物。  相似文献   

10.
Walegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. Weakly peraluminous granite porphyry(A/CNK=1.10–1.15) is enriched in LREE, depleted in HREE with Nb-Ta-Ti anomalies, and displays subduction-related geochemistry. Quartz porphyry is strongly peraluminous(A/CNK=1.64–2.81) with highly evolved components, characterized by lower TiO_2, REE contents, Mg~#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and Cl. LAICP-MS zircon U-Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, ε_(Hf)(t) values of Triassic magmatic zircons from the granite and quartz porphyries are -14.2 to -9.1(with an exception of +4.1) and -10.8 to -8.6 respectively, indicating a crustal-dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc-related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.  相似文献   

11.
刘园园  马昌前  吕昭英  黄卫平 《岩石学报》2012,28(10):3287-3305
长江中下游贵池地区燕山期侵入岩发育,与成矿关系密切.本文对该区侵入岩开展了详细的锆石U-Pb年代学、地球化学及Sr-Nd-Hf同位素研究.结果表明,马头花岗闪长斑岩形成于147±2Ma,而花园巩石英二长岩形成于127±1Ma,比花岗闪长斑岩晚约20Ma.早期的花岗闪长斑岩(147 ～ 145Ma)为高钾钙碱性系列,具有高Al2O3、Sr含量和Sr/Y、La/Yb比值,以及低的Y、Yb含量,与埃达克质岩的地球化学特征一致;而晚期石英二长岩(127Ma)和石英正长岩为钾玄岩系列,具有高的(Na2O+ K2O)、Zr、Nb、Y含量和Y/Nb、Yb/Ta比值,与造山带A2型花岗岩地球化学特征相似;碱长花岗岩(125～124Ma)同样具有A型花岗岩的地球化学特征,但与石英二长岩、石英正长岩相比,碱长花岗岩的Y/Nb、Yb/Ta比值相对较低,具板内环境A1型花岗岩的地球化学特征.因此,贵池地区岩浆岩从早期的埃达克质岩变为晚期的A型花岗岩,反应了晚中生代时期长江中下游地区的构造环境由大陆边缘环境向伸展环境的转变.  相似文献   

12.
Precambrian magmatism in the Biabanak-Bafq district represents an extensive sequence of mafic magmatic rocks. Major, trace and rare earth elements reveal that the low-Ti basement mafic rocks are magnesium tholeiite and low-Ti cover a mafic rock belongs to Fe-tholeiite, whereas, the high-Ti alkaline mafic rocks, as well as dolerites, show much more Fe–Ti enrichment. Primitive mantle normalized trace element patterns show a relative enrichment of LREE and LILE and depletion of HFSE, but have an equally distinct continental signature reflected by marked negative Nb, Sr, P, and Ti anomalies. The composition of the intrusive rocks is consistent with fractional crystallization of olivine ± clinopyroxene ± plagioclase, whereas variations in the Sr and Nd isotope compositions suggest heterogeneous sources and crustal contamination. Low-Ti group samples contain a crustal signature in the form of high La/Yb, Zr/Nb, and negative \(\varepsilon \hbox {Nd}\) values. In contrast, high-Ti mafic magmatic rocks display an increase in La/Yb with a decrease in Proterozoic alkaline rocks recognized across the central Iran. The presence of diverse mafic magmatic rocks probably reflects heterogeneous nature of sub-continental lithospheric mantle (SCLM) source. The mafic magmatism largely represents magmatic arc or rift tectonic setting. It is suggested that the SCLM sources were enriched by subduction processes and asthenospheric upwelling.  相似文献   

13.
滇西剑川富碱岩浆岩位于青藏高原东南缘的三江南段,是金沙江-红河富碱岩浆岩带的重要组成部分。剑川富碱岩浆岩包括花岗岩和正长岩两类岩石,前者主要有花岗斑岩和石英二长斑岩,后者主要是正长斑岩和粗面岩。本文对剑川富碱岩浆岩进行了主微量元素、锆石U-Pb年代学和Sr-Nd-Hf同位素特征研究。锆石U-Pb测年结果显示,剑川花岗岩结晶年龄为35. 1～36. 1Ma,正长岩结晶年龄为35. 7～35. 8Ma,均形成于始新世。花岗斑岩和石英二长斑岩的SiO_2含量为67. 92%～69. 93%,K_2O/Na_2O比值介于0. 86～1. 22,具有高钾钙碱性特征;正长斑岩和粗面岩的SiO_2含量为53. 94%～63. 51%,K_2O/Na_2O比值介于1. 30～2. 68,属于钾玄质岩石系列。两类岩石都富集轻稀土元素(LREE)和大离子亲石元素(LILE),相对亏损高场强元素(HFSE)。其中,花岗斑岩和石英二长斑岩有着较高的Sr、Sr/Y、La/Yb值和低的Y、Yb含量,具有埃达克质岩浆属性。结合Sr-Nd-Hf同位素研究认为,滇西剑川地区花岗岩起源于增厚的镁铁质新生下地壳部分熔融,正长岩是由交代富集的岩石圈地幔熔融产生的基性岩浆演化而来的产物。滇西剑川新生代富碱岩浆活动是对印度与欧亚板块晚碰撞阶段,岩石圈地幔发生对流减薄和软流圈物质上涌过程的响应。  相似文献   

14.
The Late Paleozoic intraplate magmatism of the Selenga-Vitim structural zone of the Baikal region (Khamar-Daban Range) produced granitoids of different geochemical types: palingenic calc-alkaline granitoids, subalkaline monzogranites, and rare-metal Li-F granitoids and their subvolcanic analogues. Subalkaline and rare-metal granitoids occur in the periphery of the Late Paleozoic magmatic zone. Rare metal granite magmatism is manifested in this region as nearly N-S trending intrusive-dike belts comprising multiphase intrusions (Kharagul, Urugudei, and Bitu-Dzhida massifs) with an exposed area of ∼10 km2 and an age of formation from 311 to 321 Ma and series of accompanying dikes. The early phases of the intrusions are made up of biotite granites usually with fluorite, which are changed during the late stage by typical topazbearing rare-metal amazonite-albite granites. In the subvolcanic facies, thicker subalkaline dikes of monzonite porphyry, granite porphyry, and elvan are changed by ongonites, topaz rhyolites, and topazites, which occasionally serve as cement in eruptive and fluid-explosive breccias. The development of multiphase intrusions from early biotite granites to late amazonite-albite granites with Li-F mica was accompanied by an increase in SiO2 and, especially, Na2O contents, whereas the level of (FeO + Fe2O3), CaO, and K2O declined. Geochemical evolution includes an increase in the same direction in the contents of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease in Ba, Sr, Zn, Zr, Th, and U. Similar evolution is also characteristic of the subvolcanic rocks, which emphasizes the genetic relation of the whole intrusive-dike complex of the Khamar-Daban province. Significant differences were detected in the distribution of K, Ba, Sr, and Zr between the calc-alkaline granitoids and rare-metal Li-F granites. The continental crust-normalized patterns of the raremetal granites show positive anomalies for Li, Rb, Nb, and Pb. The rare-metal Li-F granites could not be produced by palingenesis only, and their formation required specific conditions causing extensive accumulation of characteristic trace elements. During the evolution of granite melts, Li, Rb, Ta, Nb, Sn, W, and F are extensively accumulated in late intrusive phases, which indicates an important role of the processes of magmatic and fluid-magmatic differentiation during their formation. The composition and isotope geochemical characteristics of the supposed magma source material correspond to the ancient Precambrian continental crust with a mean model age of more than 1200 Ma.  相似文献   

15.
The Jinshajiang–Red River alkaline igneous belt in the eastern Indian–Asian collision zone, of southwestern China, hosts abundant, economically important Cu–Mo–Au mineralization of Cenozoic age. Major- and trace-element compositions of titanites from representative Cu-mineralized intrusions determined by LA-ICP-MS show higher values for Fe2O3/Al2O3, ΣREE?+?Y, LREE/HREE, Ce/Ce*, (Ce/Ce*)/(Eu/Eu*), U, Th, Ta, Nb and Ga, and lower values for Al2O3, CaO, Eu/Eu*, Zr/Hf, Nb/Ta and Sr than those for titanites from barren intrusions. Different ΣREE?+?Y, LREE/HREE, U, Th, Ta and Nb values of titanites between Cu-mineralized and barren intrusions were controlled mainly by the coexisting melt compositions. However, different Sr concentrations and negative Eu anomalies of titanites between Cu-mineralized and barren intrusions were most probably caused by different degrees of crystallization of feldspar from melts. In addition, different Ga concentrations and positive Ce anomalies of titanites between Cu-mineralized and barren intrusions were most likely caused by different magmatic fO2 conditions. Pronounced compositional differences of titanites between Cu-mineralized and barren intrusions can provide a useful tool to help discriminate between ore-bearing and barren intrusions at an early stage of exploration, and, thus, have a potential application in exploration for porphyry Cu deposits in the Jinshajiang – Red River alkaline igneous belt, and to other areas.  相似文献   

16.
海南岛屯昌地区侵入岩由花岗闪长岩、花岗岩及少量辉绿-闪长玢岩（脉）、镁铁质包体组成。本文报道了这些侵入岩的锆石LA-ICPMS U-Pb 定年结果和地球化学组成, 定年结果显示岩石形成于早白垩世晚期（~107 Ma）。地球化学特征显示, 花岗闪长岩和花岗岩具有高的SiO2、Al2O3 含量以及高的Sr 含量和Sr/Y 比值, 低的Y 和Yb 含量, Eu 异常不明显等, 属于埃达克质岩。屯昌埃达克质岩具有比较均一的Sr、Nd 同位素组成（ISr＝0.7082~ 0.7096, εNd（t）＝？6.55~ ？3.85）。镁铁质岩脉和包体则显示了稍低的ISr （0.7064~0.7086）和变化的εNd（t） （？5.10~ ＋0.13）。埃达克质岩的锆石原位Hf 同位素组成为： （176Hf/177Hf）i = 0.28257~0.28277, εHf（t）= ？4.86~ ＋2.09, 相应的两阶段模式年龄TDM2 变化于1.09 Ga 和1.54 Ga 之间。闪长玢岩脉的（176Hf/177Hf）i = 0.28257~0.28264, εHf（t） = ？4.94~ ？2.42, TDM2＝1.38~1.55 Ga, 类似于埃达克质岩。屯昌埃达克质岩很可能由新底侵的玄武质下地壳物质部分熔融所形成, 俯冲的古太平洋板块在早白垩世晚期（约107 Ma）的后撤作用所 导致的软流圈上涌为地壳熔融提供了热源。  相似文献   

17.
驱龙超大型斑岩铜矿床是冈底斯斑岩铜矿带上最为重要的矿床,矿区侵入岩较发育,但流纹斑岩及英安流纹斑岩的形成时代存在争议。在野外及岩相学观察基础上,结合LA-ICP-MS锆石U-Pb测年,获得流纹斑岩年龄值为169.9±0.61 Ma,英安流纹斑岩年龄值分别为166.0±1.8 Ma及173.8±0.56 Ma,黑云母花岗闪长岩年龄值为16.98±0.15 Ma。结合前人年代学研究,认为流纹斑岩及英安流纹斑岩可能在早侏罗世即开始活动,一直持续到晚侏罗世。而黑云母花岗闪长岩的形成时代与前人研究一致,皆为中新世。此外,驱龙矿区岩浆岩演化经历了早-晚侏罗世、中新世早期和中新世中期三个阶段,其中,中新世早期岩浆活动与成矿时代具有很好的一致性。最后认为,驱龙矿区岩浆岩活动时间与新特提斯洋俯冲阶段及印度-亚洲大陆碰撞后汇聚过程中发生的岩浆作用阶段相对应。岩浆活动与成矿受到这两大构造活动事件的影响。  相似文献   

18.
Abstract

Information, mainly from the granitic and silicic volcanic rocks in the Stawell, Bendigo and Melbourne structural zones in the state of Victoria, shows that the sources of both the S- and I-type rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with the sources of similar granitic rocks in the Melbourne Zone, consistent with the absence of the mainly Proterozoic Selwyn Block beneath most of the SBZ. Below a mid-crustal décollement in the SBZ, the crust is evidently highly variable and possibly includes thinned Proterozoic crust. There is geochronological evidence for ca 400 and ca 370?Ma granulite-grade metamorphic events here, and, after this double bout of metamorphism, and depletion in the silicic melt component, the constituents of the entire deep crust of the SBZ would have densities similar to those of overlying, much lower-grade Cambrian metabasaltic to boninitic rocks. Thus, granitic magmas may have formed here by partial melting of a variety of rock types, probably with back-arc affinities, with ages that may extend back to the Proterozoic. Therefore, the basement of the SBZ is unlikely to consist solely of thick ocean-floor rocks, as in some current interpretations.
  1. KEY POINTS

  2. The sources of the Devonian granitic rocks of the Stawell and Bendigo zones (SBZ) contrast in ages and chemistry with those of the Melbourne Zone granites.

  3. Two Devonian granulite-facies events left the melt-depleted deep SBZ crust with densities similar to those of overlying Cambrian metabasaltic rocks.

  4. The SBZ Devonian granitic magmas probably formed by partial melting of heterogeneous Proterozoic to Cambrian arc-related crust, below the mid-crustal décollement.

  相似文献   

19.
The Langdu high-K calc-alkaline intrusions are located in the Zhongdian area, which is the southern part of the Yidun island arc. These intrusive rocks consist mainly of monzonite porphyry, granodiorite, and diorite porphyry. The K2O content of majority of these rocks is greater than 3%, and, in the K2O-SiO2 diagram, all the samples fall into the high-K calc-alkaline to shoshonitic fields. They are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs; LaN/YbN = 14.3-21.2), and show slightly negative Eu anomalies (δEu = 0.77-1.00). These rocks have high K, Rb, Sr, and Ba contents; moderate to high enrichment of compatible elements (Cr = 36.7-79.9 ppm, Co = 9.6-16.4 ppm, and MgO = 2.2%-3.4%); low Nb, Ta, and Ti contents, and characteristic of low high field strength elements(HFSEs) versus incompatible elements ratios (Nb/Th = 0.75, Nb/La = 0.34) and incompatible elements ratios (Nb/U = 3.0 and Ce/Pb = 5.1, Ba/Rb = 12.0). These rocks exhibit restricted Sr and Nd isotopic compositions, with (87Sr/86Sr) i values ranging from 0.7044 to 0.7069 and εNd(t) values from -2.8 to -2.2. The Sr-Nd isotope systematic and specific trace element ratios suggest that Langdu high-K calc-alkaline intrusive rocks derived from a metasomatized mantle source. The unique geochemical feature of intrusive rocks can be modeled successfully using different members of a slightly enriched mantle, a slab-derived fluid, and terrigenous sediments. It can be inferred that the degree of partial melting and the presence of specific components are temporally related to the tectonic evolution of the Zhongdian island arc. Formation of these rocks can be explained by the various degrees of melting within an ascending region of the slightly enriched mantle, triggered by the subduction of the Garzê-Litang ocean, and an interaction between the slab-derived fluid and the terrigenous sediments.  相似文献   

20.
Berzina AN  Berzina AP 《岩石学报》2008,24(12):2657-1668
The Aksug deposit, located in Altay-Sayan region of Russia, is one of the largest porphyry Cu-Mo deposits in Southern Siberia. The ore-bearing porphyries of the Aksug porphyry Cu-Mo system were formed in post-collisional environment. Geochemically they belong to calk-alkaline and high K-calk-alkaline series. Rocks are characterized by enrichment of LILE and depletion of HSFE and HREE, showing the importance of subduction-related components in magma generation. Large plutonic intrusions that host porphyry systems have been formed during collision. The origin of porphyritic rocks is dominantly the mantle with lower crustal contribution. The mainly economically important Cu-Mo mineralization is closely related to a porphyry series in time and space, being emplaced towards the end of magmatic activity. Though the emplacement of plutonic and ore-bearing porphyry complexes took place in different geodynamic environments, both complexes are characterized by certain similarity in geochemical composition, alkalinity, trace element content, Sr isotopic composition. This fact evidently indicates a common deep-seated magmatic source (at the lower crust-upper mantle level). Low initial 87 Sr/86 Sr, sulfur isotopic characteristics and presence of PGE-Co-Ni mineralization in associated pyrite-chalcopyrite ores suggest that mantle source of chalcophile elements was of high importance in porphyry Cu-Mo mineralization of the Aksug deposit.  相似文献   

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