High-precision U–Pb age and geochemistry of the mineralized (Ni–Cu–Co) Suwar intrusion, YemenThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 495-514 ◽  
Author(s):  
John D. Greenough ◽  
Sandra L. Kamo ◽  
Lucia Theny ◽  
Sean A. Crowe ◽  
Charles Fipke
Keyword(s):  
High Precision ◽  
Ore Deposits ◽  
Primitive Mantle ◽  
Geochemical Data ◽  
Ionization Mass ◽  
The North ◽  
Enriched Mantle ◽  
Pan African ◽  
Mafic Sample ◽  
Oceanic Island Basalts

High-precision U–Pb isotope dilution – thermal ionization mass spectrometry (ID–TIMS) geochronology on chemically abraded zircon grains from a noritic gabbro of the Ni-bearing Suwar mafic–ultramafic layered complex, northwestern Yemen, gives a mean 206Pb/238U age of 638.46 ± 0.73 Ma (2σ; MSWD = 1.4). At Wadi Qutabah, ∼30 km to the north, a similar mafic sample has an identical age of 638.58 ± 0.51 Ma (2σ; MSWD = 0.32), which supports the possibility of there being a single, large intrusive complex with an estimated areal extent of ∼250 km2. This is supported by geochemical data of samples from each locality, which are postkinematic, gabbroic rocks that contain variable amounts of cumulus olivine, plagioclase, orthopyroxene, and ilmenite with intercumulus augite, hornblende, and Ni-sulphides. Straight rare Earth element (REE) patterns, Ba/La ∼30, Rb/Ba ∼0.04, and negative primitive-mantle-normalized P anomalies resemble EM1 (Enriched Mantle 1) of oceanic island basalts and Archean subcontinental mantle lithosphere. The mineralogy and magmatic/tectonic discrimination diagrams suggest within-plate continental tholeiitic and noritic cumulates typical of a rift setting for both intrusions. The complex intrudes retrograded, amphibolite-facies paragneiss of the Pan-African Afif lithotectonic terrane, and is generally undeformed and unaltered, and, therefore, unaffected by the Pan-African orogeny. Emplacement of the 639 Ma complex occurred during a tensional tectonic regime on the Arabian Peninsula and marks the time of proto-Iapetan rifting. The estimated size of the intrusion, its noritic composition, and Archean subcontinental lithospheric mantle signature and its position in thin Proterozoic lithosphere abutting Archean cratonic rocks, give it the key characteristics of known, mostly Proterozoic, intrusions that host world-class Ni–Cu–Co ore deposits.

The Giant Chalukou Porphyry Mo Deposit, Northeast China: The Product of a Short-Lived, High Flux Mineralizing Event

2021 ◽  
Author(s):  
Qingqing Zhao ◽  
Degao Zhai ◽  
Ryan Mathur ◽  
Jiajun Liu ◽  
David Selby ◽  
...  
Keyword(s):  
High Precision ◽  
Inductively Coupled Plasma ◽  
Hydrothermal Activity ◽  
Ore Deposits ◽  
Ionization Mass ◽  
Inductively Coupled ◽  
Fine Grained ◽  
Porphyry Cu ◽  
Icp Ms ◽  
Porphyry Mo Deposit

Abstract Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for <10% of the overall Mo budget. The bulk of the Mo (>90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (<650 kyr) hydrothermal event, suggesting that this may also have been the case for other giant porphyry Mo deposits.

OPENING THE MAGMATIC-HYDROTHERMAL WINDOW: HIGH-PRECISION U-Pb GEOCHRONOLOGY OF THE MESOPROTEROZOIC OLYMPIC DAM Cu-U-Au-Ag DEPOSIT, SOUTH AUSTRALIA

2020 ◽  
Vol 115 (8) ◽  
pp. 1855-1870 ◽  
Author(s):  
Liam Courtney-Davies ◽  
Cristiana L. Ciobanu ◽  
Simon R. Tapster ◽  
Nigel J. Cook ◽  
Kathy Ehrig ◽  
...  
Keyword(s):  
High Precision ◽  
Volcanic Rocks ◽  
South Australia ◽  
Ore Deposits ◽  
Magmatic Zircon ◽  
Ionization Mass ◽  
Temporal Window ◽  
Precision Data ◽  
Iocg Deposit ◽  
Olympic Dam

Abstract Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (207Pb/206Pb weighted mean; 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal window inferred from the data. Despite the challenge of reconciling such an extended window with contemporary models for porphyry deposits (≤1 m.y.), formation of Proterozoic ore deposits has been addressed at high-precision and supports the case that giant IOCG deposits may form over millions of years.

New age constraints on the duration and origin of the Late Ordovician Guttenberg δ13Ccarb excursion from high-precision U-Pb geochronology of K-bentonites

2020 ◽  
Author(s):  
J. Garrecht Metzger ◽  
Jahandar Ramezani ◽  
Samuel A. Bowring ◽  
David A. Fike
Keyword(s):  
High Precision ◽  
Carbon Isotopic Composition ◽  
Late Ordovician ◽  
Environmental Drivers ◽  
Time Interval ◽  
Driving Mechanism ◽  
Ionization Mass ◽  
Mass Extinctions ◽  
Carbon Isotopic ◽  
The North

Perturbations to the global carbon cycle as recorded in the isotopic compositions of marine deposits have been commonly associated with major shifts in the climate and/or biologic activity, including mass extinctions. The Late Ordovician Guttenberg isotopic carbon excursion (GICE) is a large, globally correlative positive shift (∼3‰) in the carbon isotopic composition of marine carbonates (δ13Ccarb), but its driving mechanism(s) remains ambiguous. This is in large part due to uncertain correlations among Late Ordovician records, as well as complex and poorly constrained temporal relationships of abundant K-bentonite (altered volcanic ash) marker beds deposited in this time interval. Here, we provide new, high-precision U-Pb zircon geochronology by chemical-abrasion−isotope-dilution−thermal ionization mass spectrometry for K-bentonites bounding the GICE in the North American Midcontinent, including robust 206Pb/238U ages (reported with 2σ analytical uncertainty) for two important regional markers: the Deicke (453.35 ± 0.10 Ma) and Millbrig (453.36 ± 0.14 Ma) K-bentonites. The new data from these K-bentonites directly constrain the duration of the GICE to less than 400 k.y. at two well-studied locations in eastern Missouri, United States. The abruptness of the GICE precludes relatively gradual tectonic mechanisms as possible drivers of the excursion and suggests more rapid environmental drivers, such as changes in eustatic sea level associated with pre-Hirnantian glacial activity.

scholarly journals High-precision U-Pb age constraints on the Permian floral turnovers, paleoclimate change, and tectonics of the North China block

Geology ◽  
2021 ◽  
Author(s):  
Qiong Wu ◽  
Jahandar Ramezani ◽  
Hua Zhang ◽  
Jun Wang ◽  
Fangui Zeng ◽  
...  
Keyword(s):  
High Precision ◽  
North China ◽  
Ice Age ◽  
Fossil Flora ◽  
Ionization Mass ◽  
North China Block ◽  
Climate Conditions ◽  
The North ◽  
Regional Tectonic ◽  
Tropical Flora

The Permian marine-terrestrial system of the North China block provides an exceptional window into the evolution of northern temperate ecosystems during the critical transition from icehouse to greenhouse following the late Paleozoic ice age (LPIA). Despite many studies on its rich hydrocarbon reserves and climate-sensitive fossil flora, uncertain temporal constraints and correlations have hampered a thorough understanding of the records of geologic, biologic, and climatic change from the North China block. We present a new chronostratigraphy based on high-precision U-Pb chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) geochronology of tuffs from a near-complete latest Carboniferous–Permian succession in North China. The results indicate that the predominance of continental red beds, climate aridification, and the disappearance of coals and characteristic tropical flora were well under way during the Cisuralian (Early Permian) in the North China block, significantly earlier than previously thought. A nearly 20 m.y. hiatus spanning the early Kungurian to the mid-Guadalupian (or later) is revealed in the northern North China block to have close temporal and spatial associations with the closure and/or subduction of the Paleo-Asian Ocean and its related tectonic convergence. This long hiatus was concomitant with the prominent loss of the highly diverse and abundant Cathaysian floras and the widespread invasion of the monotonous Angaran floras under arid climate conditions in the North China block. Similarities in the floral and climate shift histories between Euramerica and North China suggest that aside from the regional tectonic controls and continental movement, extensive volcanism during the Cisuralian may have played a major role in the global warming and aridification in the aftermath of the LPIA.

scholarly journals Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif

2008 ◽  
Vol 80 (2) ◽  
pp. 353-371 ◽  
Author(s):  
Lauro V.S. Nardi ◽  
Jorge Plá-Cid ◽  
Maria de Fátima Bitencourt ◽  
Larissa Z. Stabel
Keyword(s):  
Granitic Rocks ◽  
Geochemical Data ◽  
Fine Grained ◽  
Enriched Mantle ◽  
Calcic Amphibole ◽  
Pan African ◽  
High K ◽  
Mantle Sources ◽  
Orogenic Cycle ◽  
Tholeiitic Magmatism

The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

scholarly journals Decratonization by rifting enables orogenic reworking and transcurrent dispersal of old terranes in NE Brazil

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Carlos E. Ganade ◽  
Roberto F. Weinberg ◽  
Fabricio A. Caxito ◽  
Leonardo B. L. Lopes ◽  
Lucas R. Tesser ◽  
...  
Keyword(s):  
Shear Zones ◽  
Boundary Region ◽  
The North ◽  
Pan African ◽  
Juvenile Material ◽  
Oceanic Basin ◽  
Borborema Province ◽  
Isotopic Model ◽  
Late Neoproterozoic

AbstractDispersion and deformation of cratonic fragments within orogens require weakening of the craton margins in a process of decratonization. The orogenic Borborema Province, in NE Brazil, is one of several Brasiliano/Pan-African late Neoproterozoic orogens that led to the amalgamation of Gondwana. A common feature of these orogens is that a period of extension and opening of narrow oceans preceded inversion and collision. For the case of the Borborema Province, the São Francisco Craton was pulled away from its other half, the Benino-Nigerian Shield, during an intermittent extension event between 1.0–0.92 and 0.9–0.82 Ga. This was followed by inversion of an embryonic and confined oceanic basin at ca. 0.60 Ga and transpressional orogeny from ca. 0.59 Ga onwards. Here we investigate the boundary region between the north São Francisco Craton and the Borborema Province and demonstrate how cratonic blocks became physically involved in the orogeny. We combine these results with a wide compilation of U–Pb and Nd-isotopic model ages to show that the Borborema Province consists of up to 65% of strongly sheared ancient rocks affiliated with the São Francisco/Benino-Nigerian Craton, separated by major transcurrent shear zones, with only ≈ 15% addition of juvenile material during the Neoproterozoic orogeny. This evolution is repeated across a number of Brasiliano/Pan-African orogens, with significant local variations, and indicate that extension weakened cratonic regions in a process of decratonization that prepared them for involvement in the orogenies, that led to the amalgamation of Gondwana.

A Kinematic Reconstruction of Jurassic ocean spreading from the ophiolites of California, the western U.S. using structural geology and paleomagnetism.

2021 ◽  
Author(s):  
Cemil Arkula ◽  
Nalan Lom ◽  
John Wakabayashi ◽  
Grant Rea-Downing ◽  
Mark Dekkers ◽  
...  
Keyword(s):  
North America ◽  
Relative Position ◽  
North American ◽  
Fault System ◽  
Paleomagnetic Data ◽  
Geochemical Data ◽  
Ophiolite Belt ◽  
The North ◽  
Western Us ◽  
Jurassic Ophiolites

<p>The western edge of the North America plate contains geological records that formed during the long-lived convergence between plates of the Panthalassa Ocean and North America. The geology of different segments along western North America indicates different polarities (eastward and westward) for subducted slabs and thereby various tectonic histories and settings. The western United States (together with Mexico) plays a key role in this debate, many geologic interpretations assume continuous eastward subduction in contrast to observations within proximal geologic segments and tomographic images of the lower mantle below North America and the eastern Pacific Ocean which suggest a more complex subduction history. In this study, we aim to evaluate the plate tectonic setting in which the Jurassic ophiolites of California formed. Geochemical data from these ophiolites suggest that they formed above a nascent intra-oceanic or continental margin subduction zone. We first developed a kinematic reconstruction of the western US geology back to the Jurassic based on published structural geological data. Importantly, we update the reconstruction of the various branches of the San Andreas fault system to determine the relative position of the ophiolite fragments and adopt a previous restoration of Basin and Range extension which we expand northward towards Washington state. We then reconstruct North American margin deformation associated with Cretaceous to Paleogene shortening and strike-slip faulting. We find no clear candidates in the geological record that may have accommodated major subduction between the Jurassic ophiolite belt and the North American margin and consequently concur with the school of thought that considers that the ophiolite belt, as well as the underlying subduction-accretionary Franciscan Complex, likely formed in the North American fore-arc. We collected paleomagnetic data to reconstruct the spreading direction of the Jurassic Californian ophiolites, by providing new paleomagnetic data from sheeted dykes of the Josephine and Mt. Diablo Ophiolites. These suggest a NE-SW paleo-ridge orientation, oblique to the North American margin which may be explained by partitioning of a dextral component of subduction obliquity relative to North America. We used this spreading direction in combination with published ages of the ophiolites and our restoration of the relative position of these ophiolites prior to post-Jurassic deformation to construct a ridge-transform system at which the Jurassic ophiolites accreted. The results will be used to evaluate which parts of the subduction systems that existed in the eastern Panthalassa Ocean may reside in the western US, and which parts may be better sought in the northern Canadian Segment or/and in the southern Caribbean region.</p>

Genesis of the Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in the eastern Central Asian Orogenic Belt: evidences from geochronology, elemental geochemistry, and Sr–Nd–Hf isotopic data

2019 ◽  
Vol 56 (4) ◽  
pp. 380-398 ◽  
Author(s):  
Jing-gui Sun ◽  
Yun-peng He ◽  
Ji-long Han ◽  
Zhong-yu Wang
Keyword(s):  
Crustal Contamination ◽  
Early Period ◽  
Orogenic Belt ◽  
Central Asian Orogenic Belt ◽  
Geochemical Data ◽  
Sulfide Deposit ◽  
Late Period ◽  
Enriched Mantle ◽  
Central Asian ◽  
T Values

The Wuxing Pt–Pd-rich Cu–Ni sulfide deposit in Heilongjiang Province, Northeast China, is located to the northeast of the Dunhua–Mishan fracture of the eastern Central Asian Orogenic Belt. The mafic–ultramafic complex consist of early-period hornblende–olivine pyroxenite, diopsidite, and hornblende pyroxenite and late-period gabbro and diabase units. An early-period hornblende pyroxenite yielded a zircon U–Pb age of 208.2 ± 2.6 Ma and a late-period diabase yielded a U–Pb age of 205.6 ± 1.1 Ma, with zircon εHf(t) values of +1.24 to +8.13. The early- and late-period lithofacies are relatively enriched in LILE (Rb, Ba, and Sr) and LREE, and variably depleted in HFSE (Nb, Ta). The whole-rock and single-mineral analyses of the early-period lithofacies yield (87Sr/86Sr)i ratios of 0.7055–0.7083 and εNd(t) ratios of −7.98–+3.10. These geochemical data suggest that the parental magmas of the Wuxing complex are high-Mg subalkaline basaltic in nature and were derived from an enriched mantle source. The magmas chamber formed after the injection of magma into the crust along with crustal contamination, producing early crystalline minerals and ore-bearing magmas. The rupturing of the magma chamber released evolved magmas, which then ascended and generated Pt–Pd-bearing lithofacies and Cu–Ni sulfide orebodies by fractional crystallization, accumulation, and liquation. During the late period, the residual magma invaded the early lithofacies and Cu–Ni orebodies. The fluids exsolved from the gabbroic magmas concentrated the mineralized metal elements and enhanced the precipitation of Pt–Pd-bearing veinlet-disseminated orebodies and Pt–Pd–Cu–Ni orebodies.

A new method for TIMS high precision analysis of Ba and Sr isotopes for cosmochemical studies

2017 ◽  
Vol 32 (7) ◽  
pp. 1388-1399 ◽  
Author(s):  
Elsa Yobregat ◽  
Caroline Fitoussi ◽  
Bernard Bourdon
Keyword(s):  
Mass Spectrometry ◽  
High Resolution ◽  
High Precision ◽  
Thermal Ionization Mass Spectrometry ◽  
New Method ◽  
Ionization Mass ◽  
Sr Isotopes ◽  
Sr Resin ◽  
Thermal Ionization Mass ◽  
Isotope Measurements

A new protocol using Eichron™ Sr-resin for high-resolution Sr and Ba isotope measurements using thermal ionization mass spectrometry for cosmochemical samples.

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