Timing of Magmatism following Initial Convergence at a Passive Margin, Southwestern U.S. Cordillera, and Ages of Lower Crustal Magma Sources

2006 ◽  
Vol 114 (2) ◽  
pp. 231-245 ◽  
Author(s):  
Andrew P. Barth ◽  
Joseph L. Wooden
Keyword(s):  
Passive Margin ◽  
Magma Sources ◽  
Lower Crustal ◽  
Crustal Magma

Imaging the crustal magma sources beneath Mauna Loa and Kilauea volcanoes, Hawaii

Geology ◽  
1997 ◽  
Vol 25 (10) ◽  
pp. 867 ◽  
Author(s):  
Paul G. Okubo ◽  
Harley M. Benz ◽  
Bernard A. Chouet
Keyword(s):  
Mauna Loa ◽  
Magma Sources ◽  
Crustal Magma

scholarly journals From long-lived batholith construction to giant porphyry copper deposit formation: petrological and zircon chemical evolution of the Quellaveco District, Southern Peru

2021 ◽  
Vol 176 (2) ◽  
Author(s):  
Chetan L. Nathwani ◽  
Adam T. Simmons ◽  
Simon J. E. Large ◽  
Jamie J. Wilkinson ◽  
Yannick Buret ◽  
...  
Keyword(s):  
High Pressure ◽  
Porphyry Copper ◽  
Marked Change ◽  
Crustal Thickening ◽  
Deposit Formation ◽  
Nazca Plate ◽  
Southern Peru ◽  
Porphyry Cu ◽  
Lower Crustal ◽  
Crustal Magma

AbstractPorphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene–Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~ 67 and ~ 59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu–Mo deposits that formed at 57–54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U–Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~ 60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole ± garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (> 0.3) and lower Ti (< 9 ppm) compositions after ~ 60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~ 60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~ 60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu–Mo deposits at Quellaveco, Toquepala and Cuajone from ~ 57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.

Petrological and zircon chemical record of arc magma evolution from long-lived batholith construction to giant porphyry copper deposit formation 

2021 ◽  
Author(s):  
Chetan Nathwani ◽  
Adam Simmons ◽  
Simon Large ◽  
Jamie Wilkinson ◽  
Yannick Buret ◽  
...  
Keyword(s):  
High Pressure ◽  
Porphyry Copper ◽  
Marked Change ◽  
Crustal Thickening ◽  
Magma Evolution ◽  
Deposit Formation ◽  
Nazca Plate ◽  
Porphyry Cu ◽  
Lower Crustal ◽  
Crustal Magma

&lt;p&gt;Porphyry Cu ore deposits are a rare product of arc magmatism that often form spatiotemporal clusters in magmatic arcs. The petrogenetic evolution of igneous rocks that cover the temporal window prior to and during porphyry Cu deposit formation may provide critical insights into magmatic processes that are key in generating these systems. This study documents the magmatic evolution of the Palaeocene-Eocene Yarabamba Batholith, Southern Peru, that was incrementally assembled between ~67 and ~59 Ma and hosts three, nearly contemporaneous, giant porphyry Cu-Mo deposits that formed at 57-54 Ma (Quellaveco, Toquepala and Cuajone). Whole-rock geochemistry, U-Pb geochronology and zircon trace element chemistry are reported from Yarabamba rocks that span the duration of plutonic activity, and from six porphyry intrusions at Quellaveco that bracket mineralisation. A change in whole-rock chemistry in Yarabamba intrusive rocks to high Sr/Y, high La/Yb and high Eu/Eu* is observed at ~60 Ma which is broadly coincident with a change in vector of the converging Nazca plate and the onset of regional compression and crustal thickening during the first stage of the Incaic orogeny. The geochemical changes are interpreted to reflect a deepening of the locus of lower crustal magma evolution in which amphibole &amp;#177; garnet are stabilised as early and abundant fractionating phases and plagioclase is suppressed. Zircons in these rocks show a marked change towards higher Eu/Eu* (&gt;0.3) and lower Ti (&lt;9 ppm) compositions after ~60 Ma. Numerical modelling of melt Eu systematics and zircon-melt partitioning indicates that the time series of zircon Eu/Eu* in these rocks can be explained by a transition from shallower, plagioclase-dominated fractionation to high-pressure amphibole-dominated fractionation at deep crustal levels from ~60 Ma. Our modelling suggests that any redox effects on zircon Eu/Eu* are subordinate compared to changes in melt composition controlled by the fractionating mineral assemblage. We suggest that growth and intermittent recharge of the lower crustal magma reservoir from ~60 Ma produced a significant volume of hydrous and metallogenically fertile residual melt which ascended to the upper crust and eventually generated the three giant porphyry Cu-Mo deposits at Quellaveco, Toquepala and Cuajone from ~57 Ma. Our study highlights the importance of high-pressure magma differentiation fostered by strongly compressive tectonic regimes in generating world-class porphyry Cu deposits.&lt;/p&gt;

Marginal plateaus and pre-breakup development of the mid-Norwegian volcanic passive margin

2020 ◽  
Author(s):  
Dmitry Zastrozhnov ◽  
Laurent Gernigon ◽  
Mohamed Mansour Abdelmalak ◽  
Sverre Planke ◽  
Jan Inge Faleide ◽  
...  
Keyword(s):  
Seismic Data ◽  
High Velocity ◽  
Time Lag ◽  
Crustal Contamination ◽  
Continuous Extension ◽  
Passive Margin ◽  
Rift System ◽  
High Grade ◽  
Lower Crustal ◽  
Iberian Margin

&lt;p&gt;The structure and tectonostratigraphic development of the mid-Norwegian volcanic passive margin have been extensively studied over last 30 years. However, an understanding of its crustal architecture and basin evolution remains incomplete and debated. A main point of a debate concerns the crustal and basin structure of the yet underexplored outer parts of the M&amp;#248;re and V&amp;#248;ring basins which are significantly covered by breakup-related volcanics. This discussion generally resides on the origin of the high-velocity (7+km/s) lower crustal body which alternatively interpreted either as a wide zone of exhumed/serpentinized mantle assuming direct structural similarities with the magma-poor Iberian margin or instead inherited high-grade Caledonian crust later intruded by breakup-related magmatic intrusions. Another important point of contention is whether the M&amp;#248;re and V&amp;#248;ring basins developed through either several discrete extensional events, or alternatively a single phase of continuous extension from Late Jurassic-Early Cretaceous necking to lithospheric breakup in the late Paleocene-early Eocene.&lt;/p&gt;&lt;p&gt;Recently, a new generation of high-quality 2D and 3D seismic data acquired in the outer parts of the mid-Norwegian margin allowed a better imaging of deep V&amp;#248;ring and M&amp;#248;re basins and sub-basalt domains. Also new well data allowed a better regional seismostratigraphic control. An integrated 3D/4D interpretation of new seismic data calibrated with published refraction data and tested by potential field and forward basin modelling helped to better reveal the crustal and basin architecture of the M&amp;#248;re and V&amp;#248;ring basins.&lt;/p&gt;&lt;p&gt;Our results support the crustal nature of the controversial high-velocity and high-density lower crustal body and associated deep reflections, which we interpret as an old exhumed high-grade Caledonian crust later mixed with breakup-related mafic and ultra-mafic magmatic material. Our seismic interpretation shows that the basins were subjected to discrete and localized Cretaceous-Paleocene rifting events which sequentially migrated laterally and towards the future breakup axis and were separated by intermediate cooling/subsidence phases. We explain this migration of the rift axes by a strain hardening due to lithospheric cooling with possible enhancement from lateral lower crustal flow.&lt;/p&gt;&lt;p&gt;We suggest that the outer portion of the V&amp;#248;ring and M&amp;#248;re basins represents distal &amp;#8220;marginal plateaus&amp;#8221; that likely formed an elevated crustal domain bounded to the east by a failed and cooling inner rift system and to the west by Cenozoic volcanic margins. The presence of such a marginal plateau may better explain (1) the observed structural styles and 3D geometries of the sedimentary successions in the outer basins (e.g. shallowing of the Base Cretaceous Unconformity), (2) the long-time lag (&amp;#707;80-100 Myr) between the mid-Mesozoic necking and the final (off axis) lithospheric breakup, (3) the subaerial and shallow marine emplacement of breakup-related lavas, (4) the signatures of upper crustal contamination in breakup-related flows, and (5) the relatively low magnetization of the basement in the outer basins. Our interpretations do not support the magma-poor Iberian margin model which were recently extrapolated and applied to the pre-breakup development and structural environment of the mid-Norwegian volcanic passive margin.&lt;/p&gt;

The Ailao Shan–Red River shear zone revisited: Timing and tectonic implications

2019 ◽  
Vol 132 (5-6) ◽  
pp. 1165-1182 ◽  
Author(s):  
Junlai Liu ◽  
Xiaoyu Chen ◽  
Yuan Tang ◽  
Zhijie Song ◽  
Wei Wang
Keyword(s):  
Shear Zone ◽  
Structural Data ◽  
Shear Zones ◽  
Red River ◽  
Plate Convergence ◽  
Ductile Shearing ◽  
Magma Sources ◽  
T Values ◽  
Tectonic Extrusion ◽  
Lower Crustal

Abstract Continental strike-slip shear zones that may bear important information about the evolution of convergent tectonics often occur to accommodate plate convergence. When and how shearing along the shear zones responds to plate interactions, however, are often debated. In this study, we investigated the Oligocene–Miocene leucocratic dikes from the Ailao Shan–Red River shear zone, which was active during India-Eurasia plate convergence, to constrain the timing and mechanism of ductile shearing along the shear zone. The dikes are structurally grouped into pre-, syn-, and postkinematic types with respect to ductile shearing. Prekinematic dikes from ca. 41 to 30 Ma have low whole-rock 87Sr/86Sr(i) values (0.707–0.710), generally high εNd(t) values (–3.31∼–7.98), and variable εHf(t) values (–7.9∼+5.7). Their magma sources involved high thermal perturbation inducing partial melting of the lower crust, and contributions from the mantle that were possibly related to extensional collapse of the orogenic belt prior to tectonic extrusion of the Sundaland block. Syn- and postkinematic dikes from ca. 28 to 20 Ma dominantly have high whole-rock 87Sr/86Sr(i) (0.707–0.725) and low εNd(t) (–5.83 to –9.76) values, and either negative or positive zircon εHf(t) values (broadly in the range of –12 to + 7.6) for coeval but separate crustal magma sources. The results imply that major shearing accompanying retrograde metamorphism along the Ailao Shan–Red River shear zone was localized to crustal level. A synthesis of regional structural data suggests that Oligocene–Miocene shearing along the Ailao Shan–Red River shear zone and lateral tectonic extrusion of the Sundaland block proceeded in response to progressive India-Eurasia plate convergence. Distributed and inhomogeneous middle- to lower-crustal flow along the boundaries of and within the Sundaland block occurred during the tectonic extrusion.

Chemical structure in granitic magmas – a signal from the source?

2009 ◽  
Vol 100 (1-2) ◽  
pp. 159-172 ◽  
Author(s):  
J. D. Clemens ◽  
P. A. Helps ◽  
G. Stevens
Keyword(s):  
Chemical Structure ◽  
Isotope Ratios ◽  
Granitic Magma ◽  
Chemical Components ◽  
Magma Chambers ◽  
Magma Sources ◽  
Geochemical Variations ◽  
Silicic Volcanic ◽  
Diffusion Rates ◽  
Crustal Magma

ABSTRACTThough typically exhibiting considerable scatter, geochemical variations in granitic plutons and silicic volcanic deposits are commonly modelled as products of differentiation of originally homogeneous magmas. However, many silicic igneous bodies, particularly those classified as S-types, are internally heterogeneous in their mineralogy, geochemistry and isotope ratios, on scales from hundreds of metres down to one metre or less. The preservation of these heterogeneities supports recent models for the construction of granitic magma bodies through incremental additions of numerous batches (pulses) of magma derived from contrasting sources. Such pulses result from the sequential nature of the melting reactions and the commonly layered structure of crustal magma sources. Internal differentiation of these batches occurs, but not generally on the scales of whole magma chambers. Rather than being created through differentiation or hybridisation processes, at or near emplacement levels, much of the variation within such bodies (e.g. trace-element or Mg# variation with SiO2 or isotope ratios) is a primary or near-source feature. At emplacement levels, the relatively high magma viscosities and slow diffusion rates of many chemical components in silicic melts probably inhibit processes that would lead to homogenisation. This permits at least partial preservation of the primary heterogeneities.

North Mountain basalt from Digby, Nova Scotia: models for a fissure eruption from stratigraphy and petrochemistry

1988 ◽  
Vol 25 (1) ◽  
pp. 74-83 ◽  
Author(s):  
V. S. Papezik ◽  
John D. Greenough ◽  
John A. Colwell ◽  
Terry J. Mallinson
Keyword(s):  
Nova Scotia ◽  
Fissure Eruption ◽  
Chemical Diversity ◽  
Early Mesozoic ◽  
High K ◽  
Granular Matrix ◽  
Crystal Settling ◽  
Lower Crustal ◽  
Crustal Magma ◽  
Zoned Plagioclase

The early Mesozoic, quartz normative, North Mountain basalts in southwestern Nova Scotia (Digby area) form three units: a coarse massive lower flow (~190 m) bearing minor lenses of mafic pegmatite, a middle unit of thin amygdaloidal basaltic flows (~50 m), and an upper flow unit of massive phenocryst-rich basalt (~160 m). The two thick units show phenocrysts of orthopyroxene (bronzite) and (or) pigeonite, augite, and zoned plagioclase in a granular matrix of augite, pigeonite, and plagioclase. Variation diagrams and chondrite-normalized rare-earth-element patterns relate all chemical diversity between and within flows to removal and (or) accumulation of plagioclase and pyroxene phenocrysts (~1:1). High K, Rb, and Ba, appear related to assimilation of continental crust. Constancy of fractionation-independent element ratios and variations in phenocryst content vertically and along the 200 km strike of the basalts suggest (1) crystal settling and accumulation together with assimilation and mixing in a lower crustal magma chamber, (2) rise to upper crustal levels in a central conduit followed by northeast-ward emplacement along a tension-induced dyke system, and (3) extrusion along a fissure in two major and numerous minor pulses that formed the lower, upper, and middle units. Assimilation did not occur as magma moved through the dyke system, for assimilation-related variations in composition do not occur along strike.

scholarly journals Voluminous Storage and Rapid Magma Ascent Beneath La Palma Revealed by Seismic Tomography

2022 ◽  
Author(s):  
Luca D'Auria ◽  
Ivan Koulakov ◽  
Janire Prudencio ◽  
Ivan Cabrera-Perez ◽  
Jesus Ibanez ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Seismic Tomography ◽  
Magma Ascent ◽  
S Wave ◽  
La Palma ◽  
Plumbing Systems ◽  
Magma Sources ◽  
High Resolution Images ◽  
First Time ◽  
Crustal Magma

Abstract Seismic tomography provides a window into magmatic plumbing systems; however, obtaining sufficient data for ‘real-time’ imaging is challenging. Until now, syn-eruptive tomography has not been successfully demonstrated. For the first time, we obtained high-resolution images of Earth's interior during an ongoing volcanic eruption. We used data from 11,349 earthquakes, most of which during La Palma eruption (19 September-13 December, 2021), to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to ~10 km depth and; (3) a large (> 400 km3) sub-crustal magma-filled rock volume intrusion extending from ~7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously for almost three months. Prior to eruption onset, magma ascended from ~10 km depth to the surface in < 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material. Similar structural weaknesses along the eastern contact could potentially cause new eruptive centres in the future.

Sign in / Sign up

Export Citation Format

Share Document