Classification and nomenclature of volcanic rocks,lamprophyres, carbonatites and melilitic rocks IUGS Subcommission on the Systematics of Igneous Rocks

The IUGS Subcommission on the Systematics of Igneous Rocks presents recommendation for the classification and nomenclature of volcanic rocks, lamprophyres, carbonatites and melilitic rocks. It is recommended to classify volcanic rocks according to mineral contents and by using the QAPF double triangle, provided that the modal mineral composition can be determined or estimated with sufficient approximation. Further recommendations refer to pheno-types, glass-bearing and glassy rocks, paleo-volcanic rocks and the definitions of several rock terms.

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Zusammenfassung Die IUGS Subcommission on the Systematics of Igneous Rocks legt Empfehlungen vor für Klassifikation und Nomenklatur der Vulkanite, Lamprophyre, Karbonatite und Melilith-Gesteine. Vulkanite sollen — unter Verwendung des QAPF Doppeldreiecks — nach dem modalen Mineralbestand klassifiziert werden, sofern sich dieser genau genug bestimmen oder abschätzen läßt; andernfalls muß die chemische Zusammensetzung herangezogen werden. Weitere Empfehlungen beziehen sich auf Phäno-Typen, glasführende und glasige Gesteine, die sog. paläo-vulkanischen Gesteine sowie auf Definitionen einiger Gesteinsnamen.

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Résumé La IUGS Subcommission on the Systematics of Igneous Rocks présente des recommandations pour la classification et nomenclature des roches volcaniques, lamprophyres, carbonatites et roches mélilitiques. Il est recommandé de classifier les roches volcaniques selon leur composition minéralogique et en utilisant le double triangle QAPF, pourvu que la composition modale puisse être déterminée avec une approximation suffisante; sinon, la composition chimique doit être prise en considération. Des recommandations supplémentaires concernent les « phéno-types », les roches vitreuses, les roches dites « paléo-volcaniques » et la définition de certains termes.

     

REE systematics of fluorides,calcite and siderite in peralkaline plutonic rocks from the Gardar Province,South Greenland

The Gardar failed-rift Province is world-famous for its (per-)alkaline plutonic rocks. Elevated contents of F in the mantle source and F-enrichment in the parental melts have been suggested to account for the peculiarities of the Gardar rocks (e.g. their rare mineralogy, extreme enrichment of HFSE elements, Be or REE in the Ilímaussaq agpaites, and the formation of the unique Ivigtut cryolite deposit). To constrain the formation and chemical evolution of F-bearing melts and fluids, fluorides (fluorite, cryolite, villiaumite, cryolithionite), calcite and siderite from the Ilímaussaq, Motzfeldt and Ivigtut complexes were analysed for their trace element content focusing on the rare earth elements and yttrium (REE).The various generations of fluorite occurring in the granitic Ivigtut, agpaitic Ilímaussaq and miaskitic to agpaitic Motzfeldt intrusions all share a negative Eu anomaly which is attributed to (earlier) feldspar fractionation in the parental alkali basaltic melts. This interpretation is supported by the abundance of anorthositic xenoliths in many Gardar plutonic rocks.The primary magmatic fluorites from Ilímaussaq and Motzfeldt display very similar REE patterns suggesting a formation from closely related parental melts under similar conditions. Hydrothermal fluorites from these intrusions were used to constrain the multiple effects responsible for the incorporation of trace elements into fluorides: temperature dependence, fluid migration/interaction and complexation resulting in REE fractionation. Generally, the REE patterns of Gardar fluorides reflect the evolution and migration of a F/CO₂-rich fluid leading to the formation of fluorite and fluorite/calcite veins. In certain units, this fluid inherited the REE patterns of altered host rocks. In addition, there is evidence of an even younger fluid of high REE abundance which resulted in highly variable REE concentrations (up to three orders of magnitude) within one sample of hydrothermal fluorite.The REE patterns of the granitic Ivigtut intrusion show flat to slightly heavy-REE-enriched patterns characterised by a strong tetrad effect. This effect is interpreted to record extensive fluid–rock interaction in highly fractionated, Si-rich systems.Interestingly, the fluorides appear to record different source REE patterns, as the spatially close Motzfeldt and Ilímaussaq intrusions show strong similarities and contrast with the Ivigtut intrusion located 100 km NE. These variations may be attributed to differences in the tectonic position of the intrusions or mantle heterogeneities.     

Subdivision of precambrian time: recommendations and suggestions by the subcommission on precambrian stratigraphy

The Subcommission on Precambrian Stratigraphy, consisting at the time of its last formal meeting in 1982 of 12 titular Members and 30 Correspondents, has been actively working toward an acceptable subdivision of Precambrian time for more than a decade. Comprehensive time-rock charts have been prepared for major Precambrian shields, and this composite record has been analysed for patterns and events common to several or to all. A geochronologic subdivision scheme has evolved that reflects these patterns of major events in Earth history, while still recognizing that those events are typically varied in intensity and timing from one region to another. Time unit boundaries have been selected so as to enclose or delimit principal cycles of sedimentation, orogeny, and magmatism, but the boundaries are defined in years, without specific reference to any bodies of rock.Several recommendations, developed sequentially at formal meetings held at intervals of 2–4 years and announced in geologic journals with calls for comment and criticism, are proposed:

• 1.(1) the recommendation to establish two major time units of Eon rank, Proterozoic and Archaean (Archean), separated by a time boundary at 2500 Ma, is reaffirmed;
• 2.(2) the provisional recommendation to subdivide the Proterozoic Eon into three units of Era rank, provisionally labelled Proterozoic I, II, and III, with time boundaries at 2500, 1600, 900, and (about) 570 Ma, respectively, is confirmed; and
• 3.(3) further subdivision of the Proterozoic into eight time units of Period rank, as yet unnamed, with time boundaries at 2500, 2100, 1800, 1600, 1400, 1200, 900, 700, and (about) 570 Ma, respectively, is provisionally recommended.

The nature of the Subcommission's deliberations and the guidelines developed are described herein. Comment and criticism, both on the procedure followed and on the recommendations themselves are invited.     

Granulite facies metamorphism, palaeo-isotherms and disturbance of the U-Pb systematics of zircon in anorogenic plutonic rocks from the Adirondack Highlands

Abstract In the Adirondack Highlands of New York State, the effect of granulite facies metamorphism on the physical and isotopic characteristics of zircon from anorogenic plutonic rocks has a distinct geographical pattern. The location of zircon populations which appear to have been altered describes a roughly circular area where metamorphic palaeotemperatures have been determined to be in excess of 750° C. Zircons from anorogenic plutonic rocks outside this area were undisturbed during metamorphism and yield well constrained ages. Granitic, charnockitic and mangeritic anorogenic plutonic rocks peripheral to the Marcy anorthosite massif have large, euhedral, prismatic zircons that display fine, internal, magmatic growth zonations and abundant, randomly orientated, mineral inclusions. Co-genetic zircon fractions yield linear discordant arrays and well constrained upper intercepts of 1125–1157 Ma. Metamorphic zircon is limited to sporadically developed and volumetrically insignificant, clear, low-U overgrowths or protuberances. In marked contrast, zircons from petrographically and geochemically identical rocks adjacent to, or within, the Marcy anorthosite massif are typically large, limpid, anhedral to subhedral crystals or crystal fragments lacking internal features except for tubular cavities and CO-₂-rich inclusions. Co-genetic zircon fractions yield nearly concordant, non-linear clusters with ²⁰⁷Pb/²⁰⁶Pb minimum ages of 1073–1095 Ma. Metamorphic overgrowths cannot be readily identified by optical or cathodoluminscence techniques; however, many grains show complex and unusual external boundaries suggestive of post-crystallization modification. These data indicate that temperatures as low as 750° C, in combination with other factors, may have been sufficient to facilitate recrystallization, and diffusion of radiogenic Pb from the zircon crystal structure, during the complex, protracted metamorphism of the Adirondack Highlands.     

火成岩研究若干进展

本文简要地阐述了火成岩研究的若干进展,表明火成岩在造山带、壳幔相互作用、大陆地壳生长等方面的研究中起着重要作用,火成岩岩石学在地球科学研究中正扮演着越来越重要的角色.壳幔相互作用与花岗岩形成演化的关系是21世纪前20年重点研究的问题之一,其科学前沿主要是花岗岩形成与大陆生长和深部过程的关系、深熔作用、热源以及花岗岩的成...     

Sr and Nd isotope systematics of Francistown plutonic rocks, Botswana: implications for Neoarchaean crustal evolution of the Zimbabwe craton

The Francistown plutonic rocks at the south-western margin of the Zimbabwe craton consist of three igneous suites: Sanukitoid, Tonalite–Trondhjemite–Granite (TTG) suites and High-K granites. The TTG suite is subdivided into High Aluminum-TTG (HA-TTG) and Low Aluminum-TTG (LA-TTG) sub-suites. Their Rb–Sr isotope systems were partially homogenized by post-crystallization thermo–tectonic events, in which hydrothermal solutions and migmatization played an important role. Therefore, the Rb–Sr isochron age of 2427±54 Ma can only be regarded as a lower limit to the Francistown plutonic rock age. The large errors in the Sm–Nd isochron dates of Francistown granitoids indicate that these dates are not really constrained. In this study we compared the rock types of Francistown and adjacent areas, adopting the precise U, Th–Pb single zircon SHRIMP ages from the Vumba area as references. For TTG and Sanukitoid suites, the age we adopted is ca. 2.7 Ga, which is close to their depleted-mantle Sm–Nd model ages (T _DM). For High-K granites, the age adopted is ca. 2.65 Ga, which is also close to their Sm–Nd isochron age. The highest ε _Nd ^t values of Sanukitoids and TTG are +2.1 and +2.3, respectively. The positive ε _Nd ^t values and trace element geochemistry support partial melting of a depleted mantle and young oceanic crust for the genesis of Sanukitoid and the TTG suites respectively. The lowest ε _Nd ^t values of Sanukitoids and TTGs are −1.0 and −1.1, respectively, indicating contamination by continental crust, up to 10 and 14%, respectively. The ε _Nd ^t values of TTG decrease with decreasing Al₂O₃ and Sr contents and increasing Eu negative anomalies (Eu*–Eu), suggesting that the TTG magmas underwent a coupled fractionation crystallization and crustal contamination, and that the LA-TTG was the product of the fractionation and contamination of the HA-TTG sub-suite. In contrast, negative ε _Nd ^t values for the High-K granites (from −0.4 to −3.5) indicate the involvement of LA-TTG and some materials from an old continental crust in their genesis. The products of partial melting of both oceanic and continental crusts at the south-western margin of the Zimbabwe craton occurred within a short time interval (from 2.7 to 2.65 Ga ago) suggesting that the Francistown plutonic rocks were formed in a active continental margin environment, where a young ocean plate (Limpopo oceanic plate) subducted underneath an old continental plate (Zimbabwe craton).     

Aspects of the crystallization of quartzo-feldspathic plutonic rocks

Mineralogy and Petrology -     

Failure Loci of Some Igneous and Metamorphic Rocks

Summary Experimental evidence from true triaxial tests on dense rocks are analysed with emphasis on the failure modes of these materials under multiaxial loading, ambient temperature and external pressure. The strong dependence of the modes of fracture on the secondary components of applied stresses, and especially on the intermediate principal stress, indicated that the failure surface of these brittle materials may be appropriately described by a failure tensor polynomial criterion. As such, the elliptic paraboloid failure criterion was found to conveniently describe their mode of failure, by considering also the severe influence of anisotropy of the material.  For this purpose, a method developed recently (Theocaris and Panagiotopoulos, 1995a, 1995b) was applied, defining anisotropic hardening plasticity through an appropriate sequence of anisotropic elasticity problems. Assuming a particular path of loading or unloading, we measured the instantaneous tension and compression yield stresses along the transient principal-stress directions. These parameters completely define the instantaneous state of anisotropy of the body for the corresponding loading step, by applying the theory of the elliptic paraboloid failure locus (EPFS) (Theocaris, 1989a). A parameter identification problem was formulated on the constitutive expressions for this most general failure criterion. Then, by applying convenient constraints derived from the EPFS theory, which serve as filters throughout the whole procedure, the characteristic values of terms defining the variable components of the failure tensor polynomial were calculated, as the material was continuously loaded from the elastic into the plastic region and up to the ultimate failure load. Accurate simple tests in uniaxial tension and compression provided sufficient data for the definition of the yield loci of the material, at the considered loading step. These tests may be complemented with biaxial and triaxial modes of loading of the specimens. The results improve the accuracy and sensitivity of the method. All such data were used as input values, for establishing the mode of plastic deformation of the body during particular loading paths.  Moreover, the method employed allows the complete definition of the components of the failure, H, and the strength differential effect, h, tensors at each loading step. These quantities define completely the failure tensor polynomial for each material. Therefore, it presents the important advantage over other experimental methods by clearly indicating the parts contributed to the failure mode (either by plasticity, or by the strength differential effect) and their evolution during plastic deformation.  As convenient prototype materials for testing the method, specimens of metamorphic rocks such as Westerly granite (G), or quartzite (Q) were selected. Interesting results concerning the mechanical and especially the failure modes of such materials were obtained. Furthermore, the mechanical tests indicated clearly some basic properties of these materials as concerns the mode of their structure.     

Pt-Os and Re-Os systematics of the Sudbury Igneous Complex, Ontario

We measured by negative thermal ionization mass spectrometry (NTIMS) Re, Os and ¹⁸⁶Os/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os in 26 samples of 18 Ni-Cu sulfide ores from the Falconbridge, McCreedy West, and Strathcona mines at Sudbury, Ontario. At McCreedy West and Falconbridge, the isochron Re-Os ages are 1835 ± 70 Ma and 1827 ± 340 Ma, and the initial ¹⁸⁷Os/¹⁸⁸Os ratios 0.514 ± 0.019 and 0.550 ± 0.024, respectively. The ages agree with the canonical value of 1850 ± 1 Ma for the Sudbury Igneous Complex (SIC). For Hangingwall and Deep Zone ores at Strathcona, the age of 1780 ± 7 Ma may reflect resetting by dyke activity. The high initial ¹⁸⁷Os/¹⁸⁸Os of 0.934 ± 0.005 in these ores is distinct from those at McCreedy West and Falconbridge. Strathcona Deep Copper Zone ores have highly radiogenic Os giving a mean model age of 1883 ± 54 Ma that is similar to ages at McCreedy West and Falconbridge, but distinct from other Strathcona sulfides. Initial ¹⁸⁶Os/¹⁸⁸Os in two Strathcona ores with low ¹⁹⁰Pt/¹⁸⁸Os average 0.119 826 ± 0.000 009 (n = 3) and 0.119 827 ± 0.000 004 (n = 3), respectively, with a grand mean of 0.119 827 ± 0.000 003. This ratio may be slightly lower than the chondritic value at that time. Similar ores at Falconbridge and McCreedy West show more scatter, averaging 0.119 855 ± 0.000 008 (n = 6) and 0.119 867 ± 0.000 020 (n = 3), respectively. These values are substantially suprachondritic. The Re-Os isotope systematics of Sudbury ores are clearly of crustal origin and may be derived from a binary mixture of Superior Province and Huronian metasedimentary rocks, with Strathcona, Falconbridge, and McCreedy West ores containing, respectively, 55%, 16%, and 12% of Os from Superior sediments. The suprachondritic ¹⁸⁶Os/¹⁸⁸Os at McCreedy West and Falconbridge may be due to admixture of Archean or Paleozoic mafic rocks with ¹⁹⁰Pt/¹⁸⁸Os ≈ 0.1. No trace of the asteroid that produced the Sudbury Structure has been reported. At the Whistle mine S-poor olivine melanorite inclusions with high Ni and Os and low ¹⁸⁷Os/¹⁸⁸Os may contain the signature of a magmatically fractionated asteroidal core contributing 1 to 2.5 % metal. The S-poor melanorite Ni and Os data are equally well explained by admixture of ≈40% mantle peridotite, however.     

Alkalic Igneous Rocks of the Balcones Province, Texas

In late Cretaceous time, subsilicic, alkalic magmas formed sills,laccoliths, plug-like bodies, small volcanoes, and a few dikesin Cretaceous sedimentary rocks of the Texas coastal plain alongan arcuate trend approximately coinciding with the buried Ouachitastructural belt. Transverse structural features apparently localizedthe igneous activity in two centers. In the larger center nearUvalde, Texas about half of the bodies are melilite-olivinenephelinite, a third olivine nephelinite and the remainder analcitephonolite, olivine basalt, and nepheline basanite, in orderof decreasing abundance. Basaltic and nephelinitic magmas were the primary magmas fromwhich all igneous rocks of the province were derived. Removalof olivine gave rise to a small range in chemical compositionof the basaltic rocks, but not gradation toward silica undersaturation.Nephelinitic magmas with compositions near that at which normativecalcium orthosilicate appears differentiated along two trendsto form melilite-olivine nephelinite as one end product andthrough nepheline basanite to analcite phonolite as the other.These two trends arose independently, their courses being determinedby the composition of the primary nephelinitic magma and theplane Fo-Di-Ne which has no piercing point at low pressure.     

The Significance of the Mesostasis of Basic Layered Igneous Rocks

Many layered igneous rocks consist of two main parts: the cumulus(plus adcumulus and heteradcumulus) material and the pore material,or mesostasis, produced by the crystallization of the trappedliquid. Knowledge of the chemistry of the mesostasis will beuseful in deducing magma fractionation trends and in the determinationof solid/liquid trace element partition coefficients, whichin turn will be significant in helping to elucidate the petrogeneticrelationship between certain basalts and layered gabbros. Anew geochemical method for the determination of both the compositionand amount of mesostasis in layered rocks is proposed. Thismethod uses elements of contrasting behaviour and is best appliedto rhythmically layered rocks rich in mafic or felsic minerals.Data on strontium, cobalt, and uranium are used to apply themethod to two rocks from the Skaergaard intrusion. The resultsobtained are in agreement with published data.     

Rb-Sr and U-Th-Pb systematics of alkaline rocks: the alkaline rocks from Italy

The isotopic composition of Pb and Sr and the abundances of Rb, Sr, U, Th, and Pb were determined for whole rock samples from all major volcanic centres of the Cenozoic alkaline volcanism of Central and South Italy, together with some samples from the contemporaneous anatectic Tuscan volcanism. The Sr and Pb isotopic compositions of the alkaline rocks show a negative correlation combined with a regional trend: the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios decrease from 0.711 in the north-west to 0.704 in the south-east, while the ${}^{206}\text{Pb}{}^{204}\text{Pb}$ ratios increase from 18.7 to 20.0. Variations in both isotopic compositions are generally small throughout erupted rock sequences for any volcanic centre.The Pb and Sr isotopic abundance variations are interpreted on the basis of two alternative models, which correspond to two groups of geological processes: variations can result (i) from a time dependent development in subsystems with different $\text{Rb}\text{Sr}$ or $\text{U(Th)}\text{Pb}$ ratios or, (ii) from mixing of Sr or Pb with different isotopic compositions. Combining both Pb and Sr isotope abundance measurements it is shown that the source of each volcanic centre is formed by various degrees of mixing between two components. One component and the most southern Tuscan anatectic rocks most likely have a common source, whereas the other component of the mixing process is suggested to be a liquid fraction derived from a small degree of partial fusion of a hydrous mantle. Thus at least a two-stage evolution of the Italian alkaline rocks is indicated: first a mixing process leading to the formation of the parental material followed by differentiation processes leading to the formation of the erupted rock sequences.The geodynamic model which explains the data best is that of a lateral inhomogeneous mantle. The lateral inhomogeneities in the mantle would be the result of mixing between originally mantle and crustal derived material. The mixing process itself would not have any primary connection with the Quarternary volcanic activity.     

Igneous nepheline-bearing rocks of the Haliburton-Bancroft province of Ontario

Assemblages of magmatic origin—hypersolvus nepheline syenites,theralites, and theralitic canadites—developed in a beltof nepheline rocks extending through Monmouth and Glamorgantownships of Haliburton County, Ontario, are described and theirsignificance in the problems of origin of the Haliburton–Bancroftalkali province briefly disocussed.     

The Habit of Apatite in Synthetic Systems and Igneous Rocks

Apatite crystals co-existing with liquid or with vapour in thesystem CaO-CaF₂-P₂O₆-H₂O-CO₂ are equant whereas those precipitatedfrom a liquid during a quench are greatly elongated parallelto the c-axis and they exhibit skeletal forms. Basic rocks inthe Karroo volcanic succession of Southern Rhodesia containapatite crystals with forms very similar to the synthetic quenchapatites. Acicular apatite crystals may prove to be of valueas a criterion for the former existence of a liquid phase inrocks whose origin is debatable.     

Igneous rocks of the West Sakhalin Terrane of Sakhalin Island

It has been determined that the Rozhdestvenka Formation of the West Sakhalin Terrane composed of Late Mesozoic igneous rocks is a fragment of the accretionary prism of the Rebun–Kabato–Moneron–Samarga island-arc system. Volcanic eruptions, as well as destruction of the Rebun–Kabato–Moneron–Samarga island-arc and the East Sikhote-Alin volcano plutonic marginal continental belt, were the sources of pyroclastic and clastic material entering the sedimentary basin, where the Pobedinsk and Krasnoyarka suites of the West Sakhalin Terrane were formed.     

火成岩油气藏成藏机理探讨

本文以济阳坳陷罗151块火成岩油气藏为例,通过对侵入岩体围岩的生油条件、辉绿岩体储集空间及油气运移与圈闭形成的时空配置关系等方面的研究,综合岩心、地球物理及试油等方面的资料,具体阐述了罗151块火成岩油气藏的特点及成藏模式。研究表明,火成岩作为一种特殊类型的油气储集层,形成具工业价值油气藏须具备一定的石油地质条件：充足的石油来源、有利的生储盖组合、由裂缝—孔隙系统构成的储集空间、有效的圈闭（圈闭形成时间与油气运移时间的相互关系、圈闭位置与油源区的空间关系）及必要的保存条件等;但由于火成岩油气藏储集空间类型复杂、成因多样,其平面及纵向储层非均质性差异极大,开展对不同类型火成岩储集层储集空间成因研究,是解决减小火成岩油气藏勘探风险及合理布置开发井网问题的关键。     

Zircon U-Pb and Lu-Hf isotopic systematics of the Daping plutonic rocks: Implications for the Neoproterozoic tectonic evolution of the northeastern margin of the Indochina block, Southwest China

The Daping Neoproterozoic plutonic rocks at the northeastern margin of Indochina block in southwest China provide an ideal opportunity for studying the tectonic setting and relationship between the Indochina and Yangtze Blocks. LA-ICP-MS U-Pb dating on the zircon cores and rims of a hornblende-gabbro yield ²⁰⁶Pb/²³⁸U weighted means ages of 873 ± 9.1 Ma and 769 ± 7 Ma, respectively, and that for cores, mantles and rims of a granodiorite yield ²⁰⁶Pb/²³⁸U weighted means ages of 981-987 Ma, 829 ± 10 Ma and 761 ± 11 Ma, respectively. The zircon cores and mantles are interpreted as inherited from their source region. The zircon rims are magmatic, their ages represent the emplacement timing. The zircon cores and rims from the hornblende-gabbro have ε_Hf^(t) values ranging from − 5.0 to − 5.8 and + 0.6 to + 6.4. Corresponding single-stage model ages range from 1626 to 1662 Ma and 1094 to 1311 Ma, respectively. For the granodiorite, the inherited mantles (including cores) show two groups: (1) ε_Hf^(t) values of + 3.3 to + 12.3 with single-stage Hf model ages of 897 to 1235 Ma; and (2) ε_Hf^(t) values of − 1.9 to − 7.8 with single stage model ages of 1470-1667 Ma. The zircon rims are characterized by positive ε_Hf^(t) values (+ 5.4 to + 8.2) with single-stage model ages ranging from 977 to 1108 Ma. Whole-rock geochemical data for the hornblende-gabbro, such as enrichment of LILE and LREE, negative anomaly of Nb and Ta, and high Mg^# (52.1-65.4), suggest magma generation in a subduction-related setting. An island-arc affinity is strongly supported by the features of high-alumina basalt and abundant hornblende in a large hornblende-gabbro sill. The granodiorites are characterized by high Sr contents and Sr/Y ratios, strong enrichment of LILE and LREE, and negative anomaly of Nb, Ta, P and Ti, comparable with the features of subduction-related plutonic rocks. These data show that the hornblende-gabbro was generated by the partial melting of a metasomatized mantle wedge peridotite with contribution from aqueous fluids derived from a subducted slab. The granodiorite magma is a product of the mixing of mafic magma produced by partial melting of a slab-fluid-enriched metasomatized mantle wedge peridotite and felsic magma formed by the partial melting of crustal materials. The emplacement ages and geochemical features of subduction-related Daping plutonic rocks are the same as those reported from the western margin of the Yangtze block, suggesting the presence of an oceanic crust in between, with subduction to either side generating island-arc magmatism in the Neoproterozoic.     

渤海湾盆地第三系火成岩的分布规律

渤海湾盆地第三系火成岩的分布在平面上具有东多西少、北多南少的特点,时代分布上,具孔店组、沙三段、沙一段、馆陶组4个相对富集时期和层位。全面、系统的分析研究认为,莫霍面隆起幅度和以郯庐断裂带为主的具走滑性质的深大断裂带控制了全区火成岩的分布概貌;坳陷内部与走滑断裂带相伴生的大断裂控制着火成岩的分布型式;凹陷内局部古应力场和古地貌决定着各期火成岩直接分布样式。