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1.
A dyke swarm approximately 12 m.y. old and comprising 103 basaltic dykes was sampled during a palaeomagnetic investigation of the Reydarfjördur area, eastern Iceland. Of 100 dykes yielding statistically significant palaeomagnetic directions 36 are normal, 43 reversed and 21 are intermediate; 5% of the dykes are olivine-phyric. The magnetic stratigraphy of the lava pile in this area is partially known from earlier palaeomagnetic studies, and six additional sections measured by field magnetometer and a palaeomagnetic section of 40 flows (20 reversed, 16 normal, and 4 intermediate) are reported here. These sections can be correlated by means of petrologic horizons (silicic tuffs, olivine basalts and porphyritic units) and exhibit stratigraphic thickening towards the centre of the Reydarfjördur dyke swarm. The portion of the basalt pile cut by the dyke swarm can be related both petrologically and palaeomagnetically to the dykes, and the number of exposed dykes is found to be of the same order, but smaller than, the number of lava flows in that comparable portion of the lava pile. This implies that in general the exposed dyke swarm is related to the exposed lava pile which is unlikely to extend much further downdip than the known extension updip. The lava pile in Iceland evolves as large lenticular units formed at eruptive axes, and distributed en échelon along the length of the axial zone with spacings comparable to the thickness of the lithosphere. 相似文献
2.
塔里木溢流玄武岩的喷发特征 总被引：5，自引：3，他引：2
通过对柯坪地区二叠系野外火山岩露头剖面和英买力、哈拉哈塘井区二叠系火山岩钻井剖面的对比,将塔里木早二叠世溢流玄武岩划分为三个旋回,从老到新依次是:库普库兹满溢流玄武岩旋回(KP),长英质火山碎屑岩旋回(FP)和开派兹雷克溢流玄武岩旋回(KZ)。KP旋回以巨厚溢流玄武岩夹凝灰岩为特征,在柯坪露头区和英买力井区均可划分出三层巨厚玄武质熔岩流,至哈拉哈塘井区减少为一层玄武岩流,但长英质火山碎屑岩和熔岩厚度增加。FP旋回在柯坪露头区自下而上包括空落相凝灰岩,熔结凝灰岩,再沉积火山碎屑岩和正常碎屑岩夹火山灰层,该层可与英买力及哈拉哈塘井区的凝灰岩层对比,表明在塔北存在一期面积广泛的长英质火山喷发。KZ旋回以溢流玄武岩为主,在开派兹雷克剖面识别出四期喷发共8层溢流玄武岩和一期安山质玄武岩,每期喷发之间夹少量碎屑岩,但未见长英质火山碎屑岩夹层,该特征与英买力和哈拉哈塘井区的火山层序组合不同,而与塔中溢流玄武岩类似。三个火山旋回的划分表明塔里木大火成岩省经历了"基性溢流玄武岩-酸性火山碎屑岩-基性溢流玄武岩"的演变过程,与Afro-Arabian溢流玄武岩省相似,可进行对比研究。 相似文献
3.
A thick sequence of volcaniclastic sediments drilled at site 953 during Ocean Drilling Program (ODP) Leg 157 northeast of Gran Canaria (Canary Islands) contains an almost complete magneto-stratigraphy back to the shield stage of the island 14.8 Ma ago. Onshore, a sequence of reversals has been identified and dated in 19 dominantly peralkaline rhyolitic ignimbrites, one rhyolitic, and one basaltic lava flow of the Mogán Group (13.35-13.95 Ma), which overlie basalt flows of the island's shield stage (>14 Ma). The magneto-stratigraphy of the ignimbrites onshore has been correlated with the marine magneto-stratigraphy at site 953, determined in syn-ignimbritic volcaniclastic turbidites, which were deposited practically synchronously immediately following the entry of the parent pyroclastic flows into the sea around the circumference of the island. The four polarity intervals recorded in the sequence of the Mogán Group ignimbrites correspond to C5ACr, C5ACn, C5ADr and C5ADn. Single crystal 40Ar/39Ar-age determinations of the ignimbrites bracketing the polarity changes gave the following ages and uncertainties for the reversals C5AD (t) (13.95ǂ.07 Ma), C5AC(o) (13.89ǂ.08 Ma), and C5AC(t) (13.47ǂ.09 Ma). The newly dated polarity changes fit and refine the Miocene age model proposed in the global polarity time scale. 相似文献
4.
B. S. Mackness P. W. Whitehead G. C. McNamara 《Australian Journal of Earth Sciences》2013,60(4):807-811
A new radiometric date of 3.6 Ma for the basalt overlying fossiliferous units of the Allingham Formation, provides a minimum age for the Bluff Downs Local Fauna. Ground studies and interpretation of aerial photography has clarified the volcanic history of the area and a new basalt flow has been identified and named. Although the age of the capping basalt permits a younger age for the Bluff Downs Local Fauna than originally described, the stratigraphy, combined with the interpreted stage of evolution of the fauna, still supports an Early Pliocene age for the site. 相似文献
5.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(5):461-467
Palaeomagnetic investigations of the lava flows in two profiles on the island of Sao Antão are presented. It is concluded that the ca. 290 m Cha de Morte-Profile is dominantly of reverse polarity, equivalent to a Lower Matuyama age (between 2.1 and 2.6 Ma). The slightly older Escabecada Profile, covering 15 lava flows, ca. 110m, shows reverse polarity in the top flows, and a dominant normal polarity in the lower flows, suggesting an age between 2.5 to 3 Ma, equivalent to the older part of Matuyama and the younger part of Gauss (marine chron C2An.1n). A minimum eruption frequency of the lava flows in the Escabecada Profile, equivalent to one flow every 15.0 ± ca. 5 Ka, is suggested. 相似文献
6.
The Rajahmundry Traps, Andhra Pradesh: Evaluation of their petrogenesis relative to the Deccan Traps
Ajoy K. Baksi 《Journal of Earth System Science》2001,110(4):397-407
Geochemical and geochronological data for rocks from the Rajahmundry Traps, are evaluated for possible correlation with the
main Deccan province. Lava flows are found on both banks of the Godavari River and contain an intertrappean sedimentary layer.
Based on40Ar/39 Ar age data, rocks on the east bank are post K-T boundary, show normal magnetic polarity, and belong to chron 29N. Their
chemistry is identical to lavas in the Mahabaleshwar Formation in the Western Ghats, ∼1000km away. It was suggested earlier
that the genetic link between these geographically widely separated rocks resulted from lava flowing down freshly incised
river canyons at ∼ 64 Ma. For the west bank rocks, recent paleomagnetic work indicates lava flows below and above the intertrappean
(sedimentary) layer show reversed and normal magnetic polarity, respectively. The chemical composition of the west bank flow
above the intertrappean layer is identical to rocks on the east bank. The west bank lava lying below the sedimentary layer,
shows chemistry similar to Ambenali Formation lava flows in the western Deccan.40Ar/39 Ar dating and complete chemical characterization of this flow is required to elucidate its petrogenesis with respect to the
main Deccan Province. 相似文献
7.
The paper describes the variation pattern of magnetic susceptibility of Lameta sediments and isotopic variation of organic13C from Chui Hill, Bergi, Kholdoda, Pisdura and Girad. The susceptibility pattern and a negative carbon isotopic anomaly allows
fixation of the K/T boundary at these localities and they differ in these aspects from the inter-trappean sediments at Anjar.
Paleomagnetic measurements of the Anjar sediment and the overlying basalt flow demonstrate reversed polarity. The Lameta sediments
with dinosaur nests at Kheda and the overlying intertrappean sediments are of normal polarity.
The clay layers at Anjar, associated closely with Ir-enrichments, are strongly leached, rhyolitic bentonites containing low-quartz
paramorphs after high-quartz with glass inclusions.
It is concluded, that the inter-trappean lake deposits at Anjar were deposited in the early part of magnetochron 29R and are
unrelated to the K/T boundary. 相似文献
8.
《Gondwana Research》2002,5(3):649-665
The Mandla lobe in the eastern part of the Deccan volcanic province represents an isolated lava pile having a thickness of ∼900 m. The large thickness of this lava pile and its spatial detachment from the western Deccan outcrop points to a plausible second source. The stratigraphic configuration of the central and eastern Deccan lava sequences and their possible stratigraphic correlation are primarily based on geology and chemical signatures of the lava flows. Based on variations in the incompatible element ratios, the lava sequences of Chindwara, Jabalpur-Seoni and Jabalpur-Piparia sections were classified into four informal formations showing similarity with the southwestern formations. Major and trace element abundances in fifteen lava flows of Jabalpur area are similar to that of the southwestern Deccan lava flows. It has been found that the Ambenali Fm. and a few Khandala and Bushe Fm. flows are present in the northeastern Deccan. The regional mapping and detailed petrographic studies coupled with the lateral tracing have enabled the recognition of thirty-seven physically distinct lava flows and is justified by their major-elemental chemistry. The ‘intraflow variations’ studied in some of the flows is very low for most of the major oxides. These thirty-seven lava flows are grouped into eight chemical types. The order of superposition in this sequence reflects that the older flows occur in the west of the outlier at the Seoni-Jabalpur-Sahapura sector whereas, the younger flows are confined to the Dindori-Amarkantak sector in the east. The spatial disposition of the lava flows suggests that the structural complexity in the lava flow sequence in the Mandla lobe lies between Jabalpur and Dindori. The juxtaposition of distinct groups of lava flows are observed near Deori (flows 1 to 4 abeted aginst flows 5 to 14) and Dindori areas. At Dindori and towards its south the distinct lava packages (flows 15 to 27 and flows 28 to 37) are juxtaposed along the course of Narmada river. The possible explanation for this could be the presence of four post-Deccan faults at Nagapahar, Kundam, Deori and Dindori areas. The vertical shift of chemically distinct lava packages at different sectors in the outlier contravenes the idea of small regional dip and favours the presence of four NE-SW trending post-Deccan faults. Major geochemical breaks, when traced out from section to section, exhibit shifting in heights by approximately 150 m near Nagapahar and 300 m near Deori and Dindori areas. The field, petrographic and major-oxide data sets considered in conjuction with the magnetic chron reversal heights, support the inference that four faults trending NE-SW are present in the Mandla lobe.A commonality in the mineralo-chemical attributes of the infra (Lametas)-/inter-trappean as well as weathered Deccan basalt further favours their derivation from Deccan basalt, implying the availability of Deccan basalt during the Maastrichtian Lameta sedimentation. This observation does not match with the models suggesting an extremely short duration of Deccan volcanism (<0.5 Ma) at the KTB, but is congruent with the models advocating a more prolonged Deccan volcanism. 相似文献
9.
Magnetostratigraphic Study of Meishan Permian-Triassic Section, Changxing, Zhejiang Province, China 总被引：2，自引：1，他引：1
Meng Xiaohong Hu Chaoshun Wang Weimin Liu Haiyin Department of Applied Geophysics China University of Geosciences Beijing China 《中国地质大学学报(英文版)》2000,11(3)
INTRODUCTIONBecause many P/ T boundary sections around the worldare stratigraphically unconformed,som e possible exceptionsdeveloped in Greenland,Iran,Russia and South China are ofcourse of international importance.Especially successive sedi-ments from the L ate Paleozoic to Early Mesozoic widely ap-peared in South China,for example,the Meishan Section inChangxing County,Zhejiang Province,and som e analogies inGuangyuan,Wulong and Shangsi counties,Sichuan Province.Some geologists… 相似文献
10.
格吉格音乌拉火山机构主要由集块岩、角砾集块熔岩和碱性橄榄玄武岩组成。玄武岩中含有二辉橄榄岩包体,岩石属大陆内部碱性玄武岩系列。玄武岩层平覆于中新统通古尔组之上,是阿巴嘎玄武岩底部层位。玄武岩全岩钾—氩稀释法同位素年龄１２９９Ｍａ。综合分析认为：阿巴嘎玄武岩早期喷发活动最晚始于上新世。 相似文献
11.
Despite abundant data on volcaniclastic sand(stone), the compositional, spatial and temporal distribution of volcanic detritus within the sedimentary record is poorly documented. One of the most intricate tasks in optical analysis of sand(stone) containing volcanic particles is to distinguish grains derived by erosion of ancient volcanic rocks (i.e. palaeovolcanic, noncoeval grains) from grains generated by active volcanism (subaqueous and/or subaerial) during sedimentation (neovolcanic, coeval grains). Deep-marine volcaniclastic sandstones of the Middle Topanga Group of southern California are interstratified with 3000-m-thick volcanic deposits (both subaqueous and subaerial lava and pyroclastic rocks, ranging from basalt, andesite to dacite). These rocks overlie quartzofeldspathic sandstones (petrofacies 1) of the Lower Topanga Group, derived from deep erosion of a Mesozoic magmatic arc. Changes in sandstone composition in the Middle Topanga Group provide an example of the influence of coeval volcanism on deep-marine sedimentation. Volcaniclastic strata were deposited in deep-marine portions of a turbidite complex (volcaniclastic apron) built onto a succession of intrabasinal lava flows and on the steep flanks of subaerially emplaced lava flows and pyroclastic rocks. The Middle Topanga Group sandstones are vertically organized into four distinctive petrofacies (2–5). Directly overlying basalt and basaltic-andesite lava flows, petrofacies 2 is a pure volcanolithic sandstone, including vitric, microlitic and lathwork volcanic grains, and neovolcanic crystals (plagioclase, pyroxene and olivine). The abundance of quenched glass (palagonite) fragments suggests a subaqueous neovolcanic provenance, whereas sandstones including andesite and minor basalt grains suggest subaerial neovolcanic provenance. This petrofacies probably was deposited during syneruptive Periods, testifying to provenance from both intrabasinal and extrabasinal volcanic events. Deposited during intereruptive periods, impure volcanolithic petrofacies 3 includes both neovolcanic (85%) and older detritus derived from plutonic, metamorphic and palaeovolcanic rocks. During post-eruptive periods, the overlying quartzofeldspathic petrofacies 4 and 5 testify to progressive decrease of neovolcanic detritus (48–14%) and increase of plutonic-metamorphic and palaeovolcanic detritus. The Upper Topanga Group (Calabasas Formation), conformably overlying the Middle unit, has dominantly plutoniclastic sandstone (petrofacies 6). Neovolcanic detritus is drastically reduced (4%) whereas palaeovolcanic detritus is similar to percentages of the Lower Topanga Group (petrofacies 1). In general, the volcaniclastic contribution represents a well-defined marker in the sedimentary record. Detailed compositional study of volcaniclastic strata and volcanic particles (including both compositional and textural attributes) provides important constraints on deciphering spatial (extrabasinal vs. intrabasinal) and temporal relationships between neovolcanic events (pre-, syn-, inter- and post-eruptive periods) and older detritus. 相似文献
12.
Stefan Schöbel Kamal K Sharma Thorsten Hörbrand Theresa Böhm Ines Donhauser Helga de Wall 《Journal of Earth System Science》2017,126(6):90
The Neoproterozoic Sindreth Basin, NW India, and its surrounding area represent a half graben structure situated between the undeformed Malani Igneous Suite (MIS) in the west and a corridor of coeval Cryogenian ductile deformation, anatexis and granite intrusion in the east. The main lithologies observed in the basin are conglomerate, fanglomerate, debris flow and lake deposits derived from a nearby continental provenance, intercalated with concurrent mafic and felsic lava flows. Based on geological traverses across the strike of the basin, we propose a three-fold classification comprising Lower Clastic Unit and an Upper Clastic Unit and a Bimodal (basalt–rhyolite) Volcanic Unit separating the two. Tilting due to basin inversion and faulting has been observed; however, the rocks are unmetamorphosed and show undisturbed primary sedimentary features. The stratigraphic record of the basin is characteristic for deposition and magmatism in a fault-related continental setting. Implications of the findings have been discussed in the context of Neoproterozoic crustal dynamics in NW India. This study provides conclusive evidence for a continental setting for Sindreth Basin evolution and contests the recent models of active subduction setting (either back-arc basin or accretionary sediments over a subduction zone). 相似文献
13.
A. D. Shukla N. Bhandari Sheela Kusumgar P. N. Shukla Z. G. Ghevariya K. Gopalan V. Balaram 《Journal of Earth System Science》2001,110(2):111-132
Chemical analysis of nine Deccan flow basalts at Anjar, Kutch, western India, indicates that all, except the uppermost flow
F-9, are alkaline. In their major and trace element composition, the alkali basalts resemble Ocean island basalts (OIB). Similarities
of many diagnostic trace element ratios (e.g. Sm/Nd, Ba/Nb,Y/Nb and Zr/Nb) are similar to those found in the Réunion Island
basalts. The uppermost basalt is tholeiitic and chemically resembles the least contaminated Deccan basalt (Ambenali type).
The Anjar basalts have iridium concentration ranging between 2 and 178 pg/g. Some of these values are higher by about an order
of magnitude compared to the Ir concentration in other basalts of the Deccan. A synthesis of chemical, palaeomagnetic and
geochronologic data enables us to construct a chemical and magnetic stratigraphy for these flows.
The three flows below the iridium enriched intertrappean bed (IT III) show normal magnetic polarity whereas all except one
of the upper basalts show reversed magnetic polarity. The sequence seems to have started in polarity zones 31N and probably
continued up to 28R or 27R. The results presented here support the view that Deccan volcanism in Kutch occurred on a time
span of a few million years. 相似文献
14.
The Paraná-Etendeka Volcanic Province records the volcanism of the Early Cretaceous that precedes the fragmentation of the South-Gondwana supercontinent. Traditionally, investigations of these rocks prioritized the acquisition of geochemical and isotopic data, considering the volcanic stack as a monotonous succession of tabular flows. Torres Syncline is a tectonic structure located in southern Brazil and where the Parana-Etendeka basalts are well preserved. This work provides a detailed analysis of lithofacies and facies architecture, integrated to petrographic and geochemical data. We identified seven distinct lithofacies grouped into four facies associations related to different flow morphologies. The basaltic lava flows in the area can be divided into two contrasting units: Unit I - pahoehoe flow fields; and Unit II - simple rubbly flows. The first unit is build up by innumerous pahoehoe lava flows that cover the sandstones of Botucatu Formation. These flows occur as sheet pahoehoe, compound pahoehoe, and ponded lavas morphologies. Compound lavas are olivine-phyric basalts with intergranular pyroxenes. In ponded lavas and cores of sheet flows coarse plagioclase-phyric basalts are common. The first pahoehoe lavas are more primitive with higher contents of MgO. The emplacement of compound pahoehoe flows is related to low volume eruptions, while sheet lavas were emplaced during sustained eruptions. In contrast, Unit II is formed by thick simple rubbly lavas, characterized by a massive core and a brecciated/rubbly top. Petrographically these flows are characterized by plagioclase-phyric to aphyric basalts with high density of plagioclase crystals in the matrix. Chemically they are more differentiated lavas, and the emplacement is related to sustained high effusion rate eruptions. Both units are low TiO2 and have geochemical characteristics of Gramado magma type. The Torres Syncline main valley has a similar evolution when compared to other Large Igneous Provinces, with compound flows at the base and simple flows in the upper portions. The detailed field work allied with petrography and geochemical data are extremely important to identify heterogeneities inside the volcanic pile and allows the construction of a detailed lithostratigraphical framework. 相似文献
15.
16.
Ninad R. Bondre Raymond A. Duraiswami Gauri Dole 《Journal of Earth System Science》2004,113(4):809-817
The nature and style of emplacement of Continental Flood Basalt (CFB) lava flows has been a matter of great interest as well
as considerable controversy in the recent past. However, even a cursory review of published literature reveals that the Columbia
River Basalt Group (CRBG) and Hawaiian volcanoes provide most of the data relevant to this topic. It is interesting to note,
however, that the CRBG lava flows and their palaeotopographic control is atypical of other CFB provinces in the world. In
this paper, we first present a short overview of important studies pertaining to the emplacement of flood basalt flows. We
then briefly review the morphology of lava flows from the Deccan Volcanic Province (DVP) and the Columbia-Oregon Plateau flood
basalts. The review underscores the existence of significant variations in lava flow morphology between different provinces,
and even within the same province. It is quite likely that there were more than one way of emplacing the voluminous and extensive
CFB lava flows. We argue that the establishment of general models of emplacement must be based on a comprehensive documentation
of lava flow morphology from all CFB provinces. 相似文献
17.
Compositional studies on different forms of magnetite, ulvospinel, ilmenite and hematite mineral phases occurring in 37 lava flows and 6 dykes of the Mandla lobe are presented in this paper. Ilmenite (0001) in equilibrium with titanomanetite show high values of temperature of equilibration, ranging from 1172–974°C, for high alumina quartz normative tholeiitic lava flows of Chemical Type - A; 1129–1229°C for low alumina quartz normative tholeiitic lava flows of Chemical Type - B; 1283–1124°C for tholeiitic lava flows of Chemical Type - F and 1243°C and 99O°C for two diopside olivine normative tholeiite flows of Chemical Type D. High olivine normative flows of Chemical Type - G and H show 1095°C and 1092°C respectively. Whereas, high hypersthene normative tholeiite flow of Chemical me C shows temperature of 1187°C. Data plots disposition over iron-titanium oxide equilibration temperature vs – logfo2, diagram for Mandla lava flows and other parts of the Deccan (Igatpuri, Mahabaleshwer, Nagpur and Sagar areas) revealed that tholeiitic (evolved) basalt of the eastern Deccan volcanic province formed at high temperatures whereas, picritic (primitive) lavas of Igatpuri and tholeiitic basalt of Mahabaleshwar areas were formed at low temperatures. Mahabaleshwer basalts follow FMQ (fayalite-magnetite-quartz) buffer curve but, plots of the Mandla basalts lie above this curve indicating higher temperatures of crystallisation of ilmenite-titanomagnetite than that of the lava flows from other parts of Deccan 'Raps. The eastern Deccan Traps are most evolved types of lava as characterised by its low Mg-number and Ni content whereas, Igatpuri lava flows are picritic (primitive), having high Mg-number and Ni contents. Temperature vs FeO + Fe2O3 / FeO + Fe2O3 + MgO ratio data plots for Mandla and other Deccan lava flows and liquidus data for Hawaiian tholeiites, indicated that Igatpuri basalts lie parallel to the liquidus line of Hawaiian tholeiite but at lower temperatures. Large data plots of Mandla lava flows lie along the liquidus line of the Hawaiian lava. The highly vesicular nature of compound lava flows having large amount of volatile is responsible for low temperature values whereas, lava flows represented by high temperatures show high modal values of glass and opaque minerals. 相似文献
18.
Gabriella Kiss Ferenc Molnár Ladislav A. Palinka? Sándor Kovács Hazim Horvatovi? 《International Journal of Earth Sciences》2012,101(6):1503-1521
Comparative volcanological, mineralogical, petrological, and geochemical studies of blocks of Triassic submarine basalt occurrences hosted by the Jurassic mélange have been carried out. The studied localities are located in displaced parts of the Dinarides in NE-Hungary (Darnó Unit), in the Dinarides (Kalnik Mts., Croatia and Vare?-Smreka, Bosnia and Herzegovina), and in the Hellenides (Stragopetra, Greece). The common characteristic of the studied occurrences is the well observable result of the lava–water-saturated sediment mingling, i.e., the presence of the so-called carbonate peperitic facies. Mixing of the basaltic lava with pelagic lime mud (representing the unconsolidated stage of the red, micritic limestone), as well as fluid inclusion and chlorite thermometry data support that the carbonate peperite was formed above CCD and at the Bosnian locality, a shallower water, about 1.4?km depth is proven. The igneous rocks show mainly within-plate basalt geochemical characteristics; MORB signatures are not common. Low temperature (<200°C) hydrothermal alteration is characteristic to the pillow basalt blocks with peperitic facies. The similarities in the volcanological, geochemical, and textural characteristics observed at the different localities support a strong genetic connection among them. The results of this study suggest to the advanced rifting stage origin of the Triassic basaltic suits and their distinction from the true oceanic basalt pillow units of the Dinarides can be based on the occurrences of the peperite facies. 相似文献
19.
Kanchan Pande 《Journal of Earth System Science》2002,111(2):115-115
A review of the available radiometric and paleomagnetic data from the Deccan Flood Basalt Province (DFBP) suggests that the
volcanism was episodic in nature and probably continued over an extended duration from 69 Ma to 63 Ma between 31R and 28N.
It is likely that the most intense pulse of volcanism at 66.9 ± 0.2 Ma preceded the Cretaceous Tertiary Boundary (KTB, 65.2
± 0.2Ma) events by R∼1.7Ma. The magnetostratigraphic record in the Deccan lava pile is incomplete and it is therefore possible
that the lava flows constituting the reverse polarity sequence were erupted in more than one reversed magnetic chron. 相似文献
20.
Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units:
- Younger lava series — basanite and nephelinite overlying.
- Older lava series — transitional to mildly alkaline basalt and hawaiite.
- Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
- Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.