The mineral chemistry and petrology of Tertiary pitchstones from Scotland

1998 ◽  
Vol 89 (2) ◽  
pp. 95-111 ◽  
Author(s):  
R. J. Preston ◽  
M. J. Hole ◽  
J. Still ◽  
H. Patton
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Crustal Contamination ◽  
Mineral Chemistry ◽  
Lava Flows ◽  
Residual Glass ◽  
Pb Isotope ◽  
Isotope Data ◽  
Igneous Province ◽  
Basaltic Magmas

AbstractSub-silicic to silicic pitchstones are widespread throughout the British Tertiary Igneous Province (BTIP), with examples being found at all the major igneous centres. Both highly porphyritic and almost completely aphyric varieties occur, and take the form of sills, dykes and lava flows. Here we present previously unreported mineral chemistry data on phenocryst and microcrystallite populations from a number of pitchstones from throughout the BTIP. Phenocryst assemblages are completely anhydrous, comprising mixtures of plagioclase, sanidine, fayalite, orthopyroxene, pigeonite, ferroaugite, ferrohedenbergite and quartz. Microcrystallite assemblages are also diverse, consisting of sanidine, ferrohedenbergite, fayalite and, occasionally, almost pure end-member ferrosilite, as well as hydrous phases such as ferrohornblende and biotite. Textural and mineral chemistry observations support interpretations derived from whole-rock and residual glass major element analyses, together with whole-rock trace element and the available Sr-Nd-Pb isotope data, that the Tertiary pitchstones of Scotland are either the products of intimate mixing between a range of basaltic magmas with hydrous crustal melts, or were formed by the crustal contamination of basaltic magmas.

scholarly journals Trace-Element and Pb Isotope Evidence on Extracting Sulfides from Potassic Melts beneath Longmenshan and Molabushan Volcanoes, Wudalianchi, Northeast China

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 319 ◽  
Author(s):  
Sergei Rasskazov ◽  
Yi-Min Sun ◽  
Irina Chuvashova ◽  
Tatyana Yasnygina ◽  
Chen Yang ◽  
...  
Keyword(s):  
Trace Element ◽  
Volcanic Rocks ◽  
Volcanic Field ◽  
Lava Flows ◽  
Pb Isotope ◽  
Linear Pattern ◽  
Wide Range ◽  
Mantle Sources ◽  
Isotope Evidence ◽  
Isotope Study

In the Wudalianchi volcanic field, eruptions started with low-Mg potassic lava flows 2.5–2.0 Ma ago and later changed to both low- and moderate-Mg potassic compositions. Volcanic rocks from the Molabushan and Longmenshan volcanoes record an unusually wide range of Pb abundances (from 3.7 ppm to 21 ppm relative to predominant range of 10–15 ppm). To determine the cause of these, we performed a comparative trace-element and Pb isotope study of rocks from these volcanoes and older lava flows. On a uranogenic lead diagram, older low-Mg lavas from lithospheric mantle sources plot on a secondary isochron with a slope corresponding to an age of 1.88 Ga. This contrasts with moderate-Mg volcanic rocks from the Molabushan cone, interpreted to have been derived from a recent convective mantle source, which define a flat linear pattern. Low-Mg rocks from the Molabushan flow have lead isotopic compositions that indicate mixed Gelaqiu and Molabu sources. Relative to rocks from the Molabushan cone, moderate-Mg lavas and slags from the East Longmenshan volcano have modified compositions characterized by Pb, S, and Ni abundances, Ni/Co, Ni/MgO ratios as well as 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, Ce/Pb, Th/Pb, and U/Pb ratios. We infer that the older Wudalianchi magmas were likely derived from a Paleoproterozoic lithospheric fragment, related to the evolved primordial mantle, and that later magmas were generated in the convecting mantle. These were influenced by segregation of small amounts of sulfides.

scholarly journals Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province. Springbok Flats.xls

2020 ◽  
Author(s):  
Julian S Marsh ◽  
Peter R Hooper ◽  
Jakub Rehacek ◽  
Robert A. Duncan ◽  
Alasdair R. Duncan
Keyword(s):  
Lava Flows ◽  
Golden Gate ◽  
Basalt Lava ◽  
Pb Isotope ◽  
Data Set ◽  
Volcanic Sequence ◽  
Stratigraphic Subdivision ◽  
Short Period ◽  
Igneous Province ◽  
Lava Pile

The Lesotho remnant contains the type succession for Karoo low-Ti basalts of central southern Africa. The <sup>40</sup>Ar/<sup>39</sup>Ar dating indicates that the sequence was emplaced within a very short period at about 180 Ma and consists of a monotonous pile of compound basalt lava flows which lacks significant palaeosols and persistent sedimentary intercalations. We have used geochemistry to establish a stratigraphic subdivision of the lava pile. Thin units of basalt flows, the Moshesh's Ford, Golden Gate, Sani, Roma, Letele, and Wonderkop units, with diverse geochemical character and restricted geographical distribution, are present at the base of the succession. These are overlain by extensive units of compositionally more uniform basalt, the Mafika Lisiu, Maloti, Senqu and Mothae units, which build the bulk of the sequence.<p>Location of this section is described in Marsh et al. (1997) AGU Geophysical Monograph, 100, 247-272.</p> <p>Title of data set: Springbok Flats</p> <p>Location of Borehole RL1 (SF samples) – S24.9367 deg; E 28.3750 deg</p> <p>Location of Borehole RTL1 – S 24.4400 deg; E 29.1767 deg</p> <p>Location of Borehole WD4 – S 24.6483 deg; E 28.7450 deg</p> <p>Location of Borehole LB1 – S 24.8817 deg; E 28.5833 deg</p> <p>Borehole TF2 – base of volcanic sequence – 768m</p> <p>Borehole TF1 – base of volcanic sequence – 357m</p> <div>All Sr-, Nd- and Pb-isotope values are MEASURED values. </div>

scholarly journals Major and Trace Element and Sr, Nd, Hf, and Pb Isotope Compositions of the Karoo Large Igneous Province, Botswana–Zimbabwe: Lithosphere vs Mantle Plume Contribution

2007 ◽  
Vol 48 (6) ◽  
pp. 1043-1077 ◽  
Author(s):  
F. Jourdan ◽  
H. Bertrand ◽  
U. Schärer ◽  
J. Blichert-Toft ◽  
G. Féraud ◽  
...  
Keyword(s):  
Trace Element ◽  
Mantle Plume ◽  
Large Igneous Province ◽  
Pb Isotope ◽  
Igneous Province

scholarly journals Insights into the magma plumbing system of La Fossa di Vulcano (Aeolian Islands, Italy) using oxygen isotopes and clinopyroxene crystal structure

2020 ◽  
Author(s):  
Rebecca Wiltshire ◽  
Ralf Gertisser ◽  
Ralf Halama ◽  
Adrian Boyce ◽  
Chiara Petrone ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Crustal Contamination ◽  
Lava Flows ◽  
Plumbing System ◽  
Magmatic System ◽  
Aeolian Islands ◽  
Magma Plumbing System ◽  
Isotope Data ◽  
Oxygen Isotope Data ◽  
Magma Plumbing

&lt;p&gt;The presently active La Fossa cone, Vulcano, widely considered the most hazardous volcano in the Aeolian Islands, is characterised by alternating periods of Vulcanian to subplinian explosive events and lava flow effusion. It has formed over 5.5 kyr, last erupting in 1888-90 [1], and presently behaves in a quiescent, fumarolic stage. The volcanic deposits from the cone comprise 7 major formations: Punte Nere, Grotta dei Palizzi 1, 2, and 3, Caruggi, Pietre Cotte and Gran Cratere. Many of these commence with dilute pyroclastic density current (PDC) deposits and tephra fallout capped by lava flows, with a compositional range from shoshonite to rhyolite (52-74 wt.% SiO&lt;sub&gt;2&lt;/sub&gt;) [1]. Crustal xenoliths in some of the lava flows and PDC deposits signify the importance of crustal contamination in the La Fossa magmatic system [1]. Here, we present new oxygen isotope data of mineral (clinopyroxene, plagioclase) and glass separates and combine these with petrological and textural analyses as well as clinopyroxene crystal chemistry and thermobarometry to constrain the extent of crustal contamination and to determine if and where crustal contamination took place in the magmatic system of La Fossa.&lt;/p&gt;&lt;p&gt;Oxygen isotope data are presented for pumice, scoriae, breadcrust bombs, lavas and mafic magmatic enclaves of all formations of La Fossa. &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O values range from +6.0&amp;#8240; to +6.7&amp;#8240; (SMOW) for clinopyroxene (n=19), from +7.0&amp;#8240; to +8.1&amp;#8240; for feldspar (n=15) and from +8.3 &amp;#8240; to +8.7 &amp;#8240; for obsidian glass (n=2). Estimated &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;melt&lt;/sub&gt; values are higher than that of mantle-derived magmas, indicating that crustal contamination is ubiquitous in the La Fossa magma plumbing system. &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;fsp&lt;/sub&gt; increases with the degree of magmatic differentiation, indicating feldspar is more contaminated in the more evolved products of La Fossa. However, no systematic variation is observed between &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;px&lt;/sub&gt; and whole-rock SiO&lt;sub&gt;2&lt;/sub&gt;, indicating disequilibrium between clinopyroxene and plagioclase. The disequilibrium observed at La Fossa suggests that clinopyroxene is mostly xenocrystic in the more evolved samples. This is supported by clinopyroxene equilibrium tests. Single-crystal X-ray diffraction to determine clinopyroxene crystal structures is presented to constrain crystallisation pressures. Crystallisation pressure of magmas feeding explosive eruptions to between approximately 2 and 6 kbar, while magmas feeding effusive eruptions appear to have crystallised at a narrower pressure range. Our results indicate that crustal contamination is an important process at La Fossa that accompanies fractional crystallisation and magma mixing/mingling processes throughout the entire (deep to shallow) crustal magma plumbing system.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] De Astis et al. 2013. Geol. Soc. London Memoirs. 37. 281-349.&lt;/p&gt;

scholarly journals Stratigraphy and age of Karoo basalts of Lesotho and implications for correlations within the Karoo igneous province. Springbok Flats.xls

2020 ◽  
Author(s):  
Julian S Marsh ◽  
Peter R Hooper ◽  
Jakub Rehacek ◽  
Robert A. Duncan ◽  
Alasdair R. Duncan
Keyword(s):  
Lava Flows ◽  
Golden Gate ◽  
Basalt Lava ◽  
Pb Isotope ◽  
Data Set ◽  
Volcanic Sequence ◽  
Stratigraphic Subdivision ◽  
Short Period ◽  
Igneous Province ◽  
Lava Pile

The Lesotho remnant contains the type succession for Karoo low-Ti basalts of central southern Africa. The <sup>40</sup>Ar/<sup>39</sup>Ar dating indicates that the sequence was emplaced within a very short period at about 180 Ma and consists of a monotonous pile of compound basalt lava flows which lacks significant palaeosols and persistent sedimentary intercalations. We have used geochemistry to establish a stratigraphic subdivision of the lava pile. Thin units of basalt flows, the Moshesh's Ford, Golden Gate, Sani, Roma, Letele, and Wonderkop units, with diverse geochemical character and restricted geographical distribution, are present at the base of the succession. These are overlain by extensive units of compositionally more uniform basalt, the Mafika Lisiu, Maloti, Senqu and Mothae units, which build the bulk of the sequence.<p>Location of this section is described in Marsh et al. (1997) AGU Geophysical Monograph, 100, 247-272.</p> <p>Title of data set: Springbok Flats</p> <p>Location of Borehole RL1 (SF samples) – S24.9367 deg; E 28.3750 deg</p> <p>Location of Borehole RTL1 – S 24.4400 deg; E 29.1767 deg</p> <p>Location of Borehole WD4 – S 24.6483 deg; E 28.7450 deg</p> <p>Location of Borehole LB1 – S 24.8817 deg; E 28.5833 deg</p> <p>Borehole TF2 – base of volcanic sequence – 768m</p> <p>Borehole TF1 – base of volcanic sequence – 357m</p> <div>All Sr-, Nd- and Pb-isotope values are MEASURED values. </div>

scholarly journals Geochemistry of the 1100 Ma intrusive rocks from the Ahlmannryggen region, Dronning Maud Land, Antarctica

2014 ◽  
Vol 26 (4) ◽  
pp. 389-399 ◽  
Author(s):  
Teal R. Riley ◽  
Ian L. Millar
Keyword(s):  
Lithospheric Mantle ◽  
Crustal Contamination ◽  
Lava Flows ◽  
Large Igneous Province ◽  
Sedimentary Sequence ◽  
Igneous Province ◽  
Intrusive Rocks ◽  
Dronning Maud Land ◽  
Lithospheric Mantle Source ◽  
Land Region

AbstractThe recognition of a Mesoproterozoic large igneous province (LIP) across large parts of southern Africa has been strengthened by recent geochronology, geochemistry and petrology. The c. 1100 Ma Umkondo province has been recognized across parts of Botswana, Zimbabwe, South Africa and Mozambique where tholeiitic sills, dykes and rare lava flows have been correlated into a single magmatic province emplaced in the interval 1108–1112 Ma. The extension of the province into the Dronning Maud Land region of Antarctica has been suggested by several workers, but detailed analyses of geochemistry and petrogenesis are lacking, as are comparative studies. This study investigates 25 dykes and sills of the Borgmassivet intrusions which include several of the major diorite sills of the province, up to 300 m in thickness. The dykes and sills are also considered to be c. 1100 Ma and they were emplaced, in part, synchronously with the Ritscherflya Supergroup sedimentary sequence. The Borgmassivet intrusions are characterized by geochemical signatures that suggest the magmas were either extensively contaminated by continental crust or derived from an enriched lithospheric mantle source, where the enrichment was related to earlier subduction. The limited geochemical range of the Borgmassivet and Umkondo intrusions are probably not consistent with significant levels of crustal contamination. Furthermore, the trace element ratios indicate a source in the sub-lithospheric mantle, followed by gabbroic fractionation and interaction with lithospheric wall rocks.

Geochemical investigations of basalts and associated rocks from the ocean floor and their implications

1971 ◽  
Vol 268 (1192) ◽  
pp. 469-486 ◽  
Keyword(s):  
Trace Element ◽  
Deep Sea ◽  
Major Element ◽  
Sea Water ◽  
Ocean Floor ◽  
Low Grade ◽  
Basaltic Magmas ◽  
Trace Element Contents ◽  
Element Contents ◽  
Possible Cause

Variations in trace element contents and inter-element ratios of deep-sea basalts are much more marked than variations in major element contents. This paper explores possible reasons for the variations which have been discovered. Inadequacy of sampling techniques may be responsible for some reported differences, but variations due to this cause are unlikely to approach the magnitude of reported variations. Some variation in samples from restricted areas of the ocean floor can be correlated with variation in the degree of silica saturation of the basalts. Submarine alteration of lavas by reaction with sea water is another possible cause of variation. Studies of metamorphosed deep-sea basalts suggest that very low-grade metamorphism may cause some, though slight, elemental migration. Studies on ultrabasic rocks show variations in trace element contents which, to some degree, appear to complement the variations encountered in basalts, suggesting that the extent of partial melting in the mantle during basaltic genesis influences the trace element contents of the products of melting. However, when such possible explanations have been considered, there remain variations in trace element contents of otherwise comparable basalts from different parts of the ocean floor, which appear to represent real variations in the trace element contents of the erupted basaltic magmas. In view of the difficulty of explaining such differences by contamination of magmas on their way to the surface, it is suggested that variations exist in the trace element contents of mantle material at the levels of basaltic genesis. Geochemical provinces exist in oceanic areas just as they do in continental regions.

Melting of the mantle past and present: isotope and trace element evidence

1978 ◽  
Vol 288 (1355) ◽  
pp. 547-559 ◽  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Internal Heat ◽  
Oceanic Lithosphere ◽  
Pb Isotope ◽  
Transfer Event ◽  
Isotope Data ◽  
Source Regions ◽  
Depleted Mantle ◽  
Ocean Ridge

Estimates are made of the abundances of some lithophile trace elements, particularly heat-producing elements, in the bulk Earth. The applicability of abundance estimates based on extra-terrestrial analogues, and terrestrial heat flow data are discussed. Sr, Nd and Pb isotope data are briefly reviewed and used to identify basalt source regions in the mantle which have been depleted or enriched in these and other lithophile trace elements. An assessment is made of the role of silicate liquid transfer in the production of depleted mantle. The timing of the transfer event(s) can be constrained using Rb-Sr, Sm-Nd and U-Pb isotope data and cover the period of Earth history during which granitic crust has been stabilized. Calculations of the heat production in the source regions of mid-ocean ridge and other basalts suggest that the convective processes involved in the generation of oceanic lithosphere are driven mainly by heating from beneath, as the internal heat generation is comparatively small. Trace element data from Archaean to Recent volcanics are used to estimate maximum limits on the amount of mantle melting which has occurred in the last 3.5 Ga.

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