scholarly journals The Petrology and Geochemistry of a Suite of Intrusive Igneous Rocks from the Southern Kermadec Arc-Havre Trough, SW Pacific

2021 ◽  
Author(s):  
Brenton Tozer
Keyword(s):  
Magma Chamber ◽  
Igneous Rocks ◽  
Magmatic System ◽  
Sw Pacific ◽  
Petrology And Geochemistry ◽  
Geochemical Analyses ◽  
Lower Temperature ◽  
Back Arc ◽  
Lower Crustal

<p>The study of intrusive igneous rocks can provide insights into deep crustal processes. In active intraoceanic arc environments, the opportunity to study of these intrusive igneous rocks usually comes from xenoliths entrained within eruptive products, as accessibility to in situ intrusive rocks is limited. This thesis documents a suite of the first intrusive samples dredged from the Havre Trough, which provide insights into deep magmatic processes in this intraoceanic back-arc system. The suite of ten intrusive igneous rocks were dredged from Basin E, a back-arc basin (BAB) in the Kermadec Arc-Havre Trough (KAHT) and consist of in situ gabbroic meso- to orthocumulates. Four representative samples were selected from the suite of ten on the basis of grainsize, and from them a petrogenetic model was built to determine the associations of the samples within the magmatic system of the region. The four samples all exhibit comparable mineral assemblages of plagioclase, clinopyroxene, and magnetite, with olivine and orthopyroxene absent. Texturally the samples appear to have formed in (a) magma chamber(s) where the minerals cooled slowly and formed relatively large, euhedral crystals that trapped interstitial melt between them. The interstitial melts crystallised forming more evolved intercumulus material (plagioclase + quartz ± amphibole ± apatite). Three of the four samples have coarser grainsizes (1-2 mm), and exhibit similar magnetite temperature estimates, indicating that they formed from similar melts. The other sample has a finer grainsize (<1 mm), and exhibits lower temperature estimates, indicating that this sample formed from a lower temperature, faster cooling melt. Plagioclase compositions follow a similar trend to plagioclase phenocrysts from modern back-arc volcanoes which indicates that these samples have an association with the modern magmatic system rather than the now extinct Miocene (Colville) Arc. Clinopyroxene trace element data are also consistent with these samples being associated with the modern subduction system. The magma chamber(s) that the samples formed in, comes from a mid-lower crustal depth, 3-6 km based on pressure estimates from amphibole crystal chemistry. The exposure of rocks from this depth would have been facilitated by normal faulting associated with rifting and opening of the Havre Trough. Petrologic and geochemical analyses of these cumulates suggest that the deep, back-arc basins consist of entirely new magmatic material formed from BAB volcanism, with no evidence for pre-existing crust.</p>

scholarly journals The Petrology and Geochemistry of a Suite of Intrusive Igneous Rocks from the Southern Kermadec Arc-Havre Trough, SW Pacific

2021 ◽  
Author(s):  
Brenton Tozer
Keyword(s):  
Magma Chamber ◽  
Igneous Rocks ◽  
Magmatic System ◽  
Sw Pacific ◽  
Petrology And Geochemistry ◽  
Geochemical Analyses ◽  
Lower Temperature ◽  
Back Arc ◽  
Lower Crustal

<p>The study of intrusive igneous rocks can provide insights into deep crustal processes. In active intraoceanic arc environments, the opportunity to study of these intrusive igneous rocks usually comes from xenoliths entrained within eruptive products, as accessibility to in situ intrusive rocks is limited. This thesis documents a suite of the first intrusive samples dredged from the Havre Trough, which provide insights into deep magmatic processes in this intraoceanic back-arc system. The suite of ten intrusive igneous rocks were dredged from Basin E, a back-arc basin (BAB) in the Kermadec Arc-Havre Trough (KAHT) and consist of in situ gabbroic meso- to orthocumulates. Four representative samples were selected from the suite of ten on the basis of grainsize, and from them a petrogenetic model was built to determine the associations of the samples within the magmatic system of the region. The four samples all exhibit comparable mineral assemblages of plagioclase, clinopyroxene, and magnetite, with olivine and orthopyroxene absent. Texturally the samples appear to have formed in (a) magma chamber(s) where the minerals cooled slowly and formed relatively large, euhedral crystals that trapped interstitial melt between them. The interstitial melts crystallised forming more evolved intercumulus material (plagioclase + quartz ± amphibole ± apatite). Three of the four samples have coarser grainsizes (1-2 mm), and exhibit similar magnetite temperature estimates, indicating that they formed from similar melts. The other sample has a finer grainsize (<1 mm), and exhibits lower temperature estimates, indicating that this sample formed from a lower temperature, faster cooling melt. Plagioclase compositions follow a similar trend to plagioclase phenocrysts from modern back-arc volcanoes which indicates that these samples have an association with the modern magmatic system rather than the now extinct Miocene (Colville) Arc. Clinopyroxene trace element data are also consistent with these samples being associated with the modern subduction system. The magma chamber(s) that the samples formed in, comes from a mid-lower crustal depth, 3-6 km based on pressure estimates from amphibole crystal chemistry. The exposure of rocks from this depth would have been facilitated by normal faulting associated with rifting and opening of the Havre Trough. Petrologic and geochemical analyses of these cumulates suggest that the deep, back-arc basins consist of entirely new magmatic material formed from BAB volcanism, with no evidence for pre-existing crust.</p>

scholarly journals Chemical Constraints on the Origin of the Frailes Volcanic Complex in the Central Andean Altiplano Plateau, Bolivia

2018 ◽  
Author(s):  
C. Brenhin Keller
Keyword(s):  
Trace Element Analysis ◽  
Small Region ◽  
Volcanic Complex ◽  
Main Body ◽  
Element Analysis ◽  
Andean Altiplano ◽  
Arc Setting ◽  
Geochemical Analyses ◽  
Back Arc ◽  
Lower Crustal

The Frailes volcanic complex of the Bolivian Altiplano plateau is the largest and most prominent ignimbrite of the Andean Central Volcanic Zone. With 2000 km3 of exposed volcanic deposits dating from 25 Ma to the present, the complex provides insight into the processes of large-volume silicic melt formation in a back-arc setting. However, the voluminous 0-10 Ma main body of the Frailes complex remains poorly studied, as the majority of the literature focuses on a small region of 12-14 Ma Sn-Ag mineralization at Cerro Rico – the world's largest silver deposit. Here, we present geochemical analyses of 25 representative samples from our fieldwork on the Frailes ignimbrite. Whole-rock major element analysis by X-ray fluorescence spectroscopy showed the ~ 7 Ma samples to be highly peraluminous, potassic (&gt;5% K2O) andesitic to rhyodacitic welded volcanic tuffs with an Al-rich, chemically reduced mineral assemblage including biotite, calcic feldspar, magmatic cordierite, and ilmenite. Trace element analysis by instrumental neutron activation revealed steep rare earth patterns with Sm/Yb &gt; 5.0, requiring the presence of garnet in a deep-crustal, high-pressure restitic assemblage. In contrast, the presence of cordierite indicates crystallization at low pressure (&lt; 450 MPa), at depths of less than 14 km. In addition, geochemical analyses combined with the geocronological work of Barke et al. (2007) support a recent (~2 Ma) age for the ignimbrites of the main Frailes Meseta. These ignimbrites are consequently best explained by mixing of a mantle- derived melt with a reduced, lower crustal component at great depths to produce hybrid magmas that ascended and evolved to form shallow crustal (&lt;14 km) magma bodies before erupting in catastrophic, caldera-forming events at ~2 Ma.

scholarly journals Editorial for the Special Issue “Mineral Textural and Compositional Variations as a Tool for Understanding Magmatic Processes”

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Silvio Mollo ◽  
Flavio Di Stefano ◽  
Francesca Forni
Keyword(s):  
Magma Chamber ◽  
Igneous Rocks ◽  
Eruption Dynamics ◽  
Special Issue ◽  
Magma Chamber Processes ◽  
Magmatic Processes ◽  
Compositional Variations

This Special Issue of Minerals collects seven different scientific contributions highlighting how magma chamber processes and eruption dynamics studied either in the laboratory or in nature may ultimately control the evolutionary histories and geochemical complexities of igneous rocks [...]

A Road Section near Guy's Hill, Jamaica

1942 ◽  
Vol 79 (4) ◽  
pp. 241-252 ◽  
Author(s):  
C. A. Matley ◽  
Frank Raw
Keyword(s):  
Sedimentary Rocks ◽  
Plutonic Rock ◽  
Igneous Rocks ◽  
The Road ◽  
Road Section ◽  
Igneous Intrusions ◽  
Microscope Slides

The rocks exposed along the road between Linstead and Guy's Hill, Jamaica, were described by Dr. C. T. Trechmann in this magazine in 1936 (pp. 259–260). The chief object of his account was to prove that the igneous rocks there were intrusions later than the associated Cretaceous and Tertiary limestones, which, according to him, had been metamorphosed into hornfelses, some of which, he stated later (1937, p. 561), he knew to have an “igneous” appearance under the microscope, “which tends to support my contention that in Jamaica we have sedimentaries altered in situ into rocks that would ordinarily be classified as igneous.” Dissent from his descriptions and interpretations was expressed by C. A. M. (Matley, 1937, pp. 501–3), the criticisms being mainly based on an examination of Trechmann's own microscope slides by F. R. A visit to Jamaica by C. A. M. in 1939 allowed him to study this road and to collect a suite of rocks for petrological examination. The results show that Trechmann's interpretation cannot be sustained. There is no granodiorite or other plutonic rock present, no metamorphism hornfelsing the sedimentary rocks, and no igneous intrusions into the Tertiary limestones.

Effect of O2 Partial Pressure on Post Annealed Ba2YCU3O7-δ Thin Films

1992 ◽  
Vol 275 ◽  
Author(s):  
Julia M. PhUlips ◽  
M. P. Siegal ◽  
S. Y. Hou ◽  
T. H. Tiefel ◽  
J. H. Marshall
Keyword(s):  
Partial Pressure ◽  
Film Growth ◽  
Epitaxial Films ◽  
Pinning Force ◽  
Low Oxygen ◽  
O2 Partial Pressure ◽  
Growth Method ◽  
Lower Temperature ◽  
The Relationship

ABSTRACTEpitaxial films of Ba2YCu3O7-δ (BYCO) as thin as 250 å A and with Jc's approaching those of the best in situ grown films can be formed by co-evaporating BaF2, Y, and Cu followed by a two-stage anneal. These results extend the work on films > 2000 Å thick by R. Feenstra et al. [J. Appl. Phys. 69, 6569 (1991)]. High quality films of these thicknesses become possible if low oxygen partial pressure [p(O2) = 4.3 Torr] is used during the high temperature portion cf the anneal (Ta). The BYCO melt line is the upper limit for Ta. The use of low p(O2) shifts the window for stable BYCO film growth to lower temperature, which allows the formation of smooth films with greater microstructural disorder than is found in films grown in p(O2) = 740 Torr at higher Ta. The best films annealed in p(O2)=4.3 Torr have Jc values a factor of four higher than do comparable films annealed in P2=740 Torr. The relationship between the T required to grow films with the strongest pinning force and p(O2) is log independent of growth method (in situ or situ) over a range of five orders of magnitude of P(O2).

scholarly journals Mechanical Properties of a Typical Jurassic Shaximiao Sandstone Under Subzero and Deep in situ Temperature Conditions

2021 ◽  
Vol 9 ◽  
Author(s):  
R. He ◽  
L. He ◽  
B. Guan ◽  
C. M. Yuan ◽  
J. Xie ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Crack Front ◽  
Image Correlation ◽  
Correlation Technique ◽  
Direct Tension ◽  
Reservoir Stimulation ◽  
The Difference ◽  
Lower Temperature ◽  
Highly Strained

Insight into the difference between the mechanical properties of rocks at low and in situ deep reservoir temperatures is vital for achieving a better understanding of fracking technologies with supercritical CO2 and liquid nitrogen. To address this issue, the fracking-related mechanical properties of the Shaximiao Formation sandstone (SS) were investigated through direct tension, uniaxial compression, and three-point bending fracture tests at a typical low temperature (Tlow) of −10°C and a reservoir temperature (Tin situ) of 70°C. The results showed that the tensile strength σt, compressive strength σc, and fracture toughness KIC of the SS were all higher at Tlow than at Tin situ, although to different extents. The KIC of the SS increased slightly more than σt at the lower temperature, while both σt and KIC of the SS increased significantly more than σc at the lower temperature. In addition to the strength, the stiffness (particularly the tensile stiffness) and the brittleness indices of SS were similarly higher at Tlow than at Tin situ. In situ monitoring using the digital image correlation technique revealed that a highly strained band (HSB) always appeared at the crack front. However, because of the inhomogeneous microstructure of the SS, the HSB did not always develop along the line connecting the notch tip to the loading point. This was a possible cause of the highly dispersed KIC values of the SS. The HSB at the crack front was notably narrower at Tlow than at Tin situ, suggesting that low temperatures suppress the plastic deformation of rocks and are therefore beneficial to reservoir stimulation.

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

1980 ◽  
Vol 117 (6) ◽  
pp. 547-563 ◽  
Author(s):  
R. E. Swarbrick ◽  
A. H. F. Robertson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Igneous Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

Pyroxenites of Kukesi Massif, Mirdita Ophiolite – geological record for magmatic system in SSZ environment – preliminary results

2021 ◽  
Author(s):  
Jakub Mikrut ◽  
Magdalena Matusiak-Małek ◽  
Jacek Puziewicz ◽  
Kujtim Onuzi
Keyword(s):  
Trace Elements ◽  
Major And Trace Elements ◽  
Intermediate Zone ◽  
Primitive Mantle ◽  
Magmatic System ◽  
Two Samples ◽  
Parental Melts ◽  
Lower Crustal ◽  
Mantle Section ◽  
Clinopyroxene Composition

&lt;p&gt;Kukesi massif is located in the eastern part of the Mirdita Ophiolite (northern Albania), which marks suture after Neo-Thetyan ocean closure. It is formed of well-preserved mantle and crustal sections which exhibit Supra-Subduction Zone affinity (e.g. Dilek and Furnes 2009, Lithos). Lower part of the mantle section of the Kukesi massif consist mainly of harzburgites, whereas dunites are located close to Moho. Crustal section records transition from lower part formed by peridotites and pyroxenites (so called intermediate zone after Hoxha and Boullier 1995, Tectonophysics) to gabbros. In this study we focus on composition and origin of pyroxenites occurring in the mantle and lower crustal parts of the Kukesi massif.&lt;/p&gt;&lt;p&gt;In this study we studied 9 samples. They have composition of olivine websterite, clinopyroxenite, orthopyroxenite, hornblende-clinopyroxenite and websterite. Five of the analyzed samples have mantle origin (M): we studied (M)-olivine websterites and (M)-clinopyroxenite from harzburgitic part, as well as two (M)-orthopyroxenitic veins (one with clinopyroxenitic central part - composite vein) with minor amphibole&amp;#160;cross-cutting dunites from one locality. From intermediate zone in crustal (C) part we collected (C)-hornblende-clinopyroxenites and (C)-websterite.&amp;#160;&lt;/p&gt;&lt;p&gt;Clinopyroxene composition is homogeneous in (M)-olivine-websterites (Mg#=84.5-87 and 88.8-90.5; Al=0.07-0.1 and 0.05-0.07, respectively), (M)-clinopyroxenite (Mg#=84-86, Al=0.04-0.08), (C)-hornblende-clinopyroxenites (Mg#=88.5-91, Al=0.08-0.12a.p.f.u.) and (C)-websterite (Mg#=87-88; Al=0.13-0.16a.p.f.u.). It differs widely between (M)-orthopyroxenitic veins: from Mg#=85-94 and Al=0.02-0.08 a.p.f.u &amp;#160;in clinopyroxenitic part of composite vein to Mg#=93.6-95 and Al=0.01-0.03 in the purely orthopyroxenitic one. Orthopyroxene from two samples of &amp;#160;(M)-olivine websterites have either&amp;#160;Mg#=83 and Al~0.07 a.p.f.u (Fo&lt;sup&gt;olivine&lt;/sup&gt;=81.5) or Mg#=87&amp;#160;&amp;#160;and Al~0.04 a.p.f.u (Fo&lt;sup&gt;olivine&lt;/sup&gt;=86). Orthopyroxene composition in composite(M)-vein varies in wide ranges (Mg#=83-89; Al=0.04-0.08 a.p.f.u.); the other vein is homogeneous (Mg#=90-91, Al=0.02-0.03 a.p.f.u, Fo&lt;sup&gt;olivine&lt;/sup&gt;=86.8-90); in (C)-websterite orthopyroxene has Mg#=82.4-84 and&amp;#160;Al=0.12-0.14 a.p.f.u. Amphibole has composition of tremolite-actinolite. Spinel, where present, is highly chromian (Cr#=0.59-0.80).&lt;/p&gt;&lt;p&gt;Clinopyroxene is LREE-depleted in most of the samples, the (La/Lu)&lt;sub&gt;N&lt;/sub&gt;=0.03-0.08. It is also LREE-depleted in (M)-clinopyroxenite ((La/Lu)&lt;sub&gt;N&lt;/sub&gt;=0.05-0.23), but the contents of trace elements are higher than in other samples (eg. Lu&lt;sub&gt;N&lt;/sub&gt;=0.79-2.75 vs. 0.40-0.85). In (M)-veins the LREE contents are approximately at primitive mantle level ((La/Lu)&lt;sub&gt;N&lt;/sub&gt;=0.28-1.66). &amp;#160;Clinopyroxene in all samples has positive Th-U, Pb and Sr anomalies and negative Ta and Zr anomalies, but concentrations of trace elements is significantly higher in (M) clinopyroxenite and veins.&lt;/p&gt;&lt;p&gt;The presence of tremolite and actinolite points to a retrogressive metamorphism which affected the rocks. The LREE-depleted nature of clinopyroxene forming all the pyroxenites and presence of orthopyroxene &amp;#160;point to crystallization of the rocks from tholeiitic melt, but variations in Mg# and REE content in clinopyroxene may reflect formation either from different generations of melts or from melts fractionated due to reactive percolation.&amp;#160; Variations in composition of the parental melts is visible even in a scale of one outcrop, which is demonstrated by (M)-orthopyroxenite veins with various modal composition and mineral major and trace elements compositions.&lt;/p&gt;&lt;p&gt;This study was financed from scientific funds for years 2018-2022 as a project within program &amp;#8220;Diamond Grant&amp;#8221; (DI 024748).&lt;/p&gt;

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