Platinum-group element (PGE) geochemistry of the Emeishan basalts in the Pan-Xi area, SW China

Zhong, Hong; Zhu, Weiguang; Qi, Liang; Zhou, Mei‐Fu; Song, Xie‐Yan; Zhang, Yi

doi:10.1007/s11434-006-0845-6

Cited by 20 publications

(5 citation statements)

References 24 publications

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“…1 we show the Cl-normalized, PGE patterns on a logarithmic scale for each section analyzed compared with the almost flat patterns obtained for KT boundary samples and impactites from the Clearwater East crater, used as representative of terrestrial material clearly contaminated by a meteoritic component. The sloping patterns obtained for all samples of the YD black layer strongly resemble the pattern typical of average continental crust (42,(48)(49)(50)(51) (48). The widely distributed depositions of the carbon-rich black mat in North America in some of these sections have been interpreted as the result of reducing conditions and a shallower water table (52).…”

Section: Resultsmentioning

confidence: 57%

Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Paquay

Goderis

Ravizza

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Os isotopes ͉ platinum group elements ͉ Clovis ͉ Pleistocene extinction ͉ meteorite P roxy records of millennial-scale climate variations during the most recent deglaciation from polar ice cores (1-3) as well as deep-sea and lacustrine sediments (4-10) display abrupt changes that are typically attributed to internal forcing of Earth's climate system. A striking example is the Younger Dryas (YD) cooling episode from 12.896 Ϯ 0.138 thousand years (ka) to 11.703 Ϯ 0.099 ka calendar years before AD 2000 (11) after the interstadial warming event Bølling-Allerød (BA) (14.692 Ϯ 0.186-14.075 Ϯ 0.169 ka). High-resolution stable ␦ 18 O and ␦D in H 2 O and the glaciochemical record from Greenland ice cores show that both the onset and the termination of the YD occurred abruptly, the former lasting slightly more than two centuries, whereas the latter transitioned into a new state in a few years (12). The most widely accepted interpretations of Earth's recent climate history place the origin and termination of the YD within Earth's complex network of feedback mechanisms (13-15). Proxies and model results favor a significant freshwater input into the North Atlantic reducing the formation of deep waters and weakening or shutting down of the meridional overturning circulation (16) as the primary cause of the YD cooling regardless of its source, timing, duration, volume, and path of melt water (17-21).

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Section: Resultsmentioning

confidence: 57%

Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Paquay

Goderis

Ravizza

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…Therefore, this proves that the parental magma of these samples is S-undersaturated and PGE-undepleted, which is consistent with the earlier basalts in the lower part are undepleted PGE. Zhong et al (2006) deduced that if significant PGE, Cu, Ni depletion happened in the basalts and sulfides enriched in these elements could accumulate in the mafic-ultramafic intrusions, and large magmatic Cu-Ni-PGE sulfide ore deposits could have been formed in this area. Recent research (Zhong et al, 2011) revealed that the parental magmas of the Xinjie intrusion exhibit ferropicritic characteristics, which are enriched in MgO, Fe, Ti and PGE.…”

Section: Sulfide Segregation and Significance In Searching For Cu-ni-mentioning

confidence: 99%

“…This type of magma is important for the occurrence of Fe-Ti-V oxide ores and Cu-Ni-PGE sulfide ores. The wall-rock HT basalts of the Xinjie intrusion are depleted in PGE (Zhong et al, 2006), which was caused by significant removal of PGE to intrusion. This paper and the study for the Xinjie basalts both show that the HT basalts, like LT basalts, may be depleted in PGE, which depend crucially on whether a factor causes the magma to reach sulfur saturation and segregate sulfides during the evolution processes.…”

Section: Sulfide Segregation and Significance In Searching For Cu-ni-mentioning

confidence: 99%

“…PGE are widely used to investigate the genetic relationship between flood basalts and sulfide mineralization (Briigmann et al, 1993;Wooden et al, 1993;Vogel and Keays, 1997;Maier and Barnes, 1999;Rehkiimper et al, 1999;Crocket, 2000;Philipp et al, 2001;Momme et al, 2002Momme et al, , 2003Maier et al, 2003;Ely and Neal, 2003;Crocket and Paul, 2004;Lightfoot and Keays, 2005). Studies on PGE characteristics of the ELIP are also used to discuss the mantle source of basalts and the origin of associated Ni-Cu-(PGE) sulfide ore deposits Zhong et al, 2006;Tao et al, 2007;Wang et al, 2007). Many geologists suggested that the high-Ti (HT) Emeishan basalts are undepleted in PGE (Song et al, 2006, 2009, and thus may have no potential of forming Cu-Ni-PGE ores.…”

Section: Introductionmentioning

confidence: 99%

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Platinum‐Group Element Geochemical Characteristics of the Picrites and High‐Ti Basalts in the Binchuan Area, Yunnan Province

Bai

Zhong

Zhu

et al. 2013

Acta Geologica Sinica (Eng)

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The Binchuan area of Yunnan is located in the western part of the Emeishan large igneous province in the western margin of the Yangtze Block. In the present study, the Wuguiqing profile in thickness of about 1440 m is mainly composed of high-Ti basalts, with minor picrites in the lower part and andesites, trachytes, and rhyolites in the upper part. The picrites have relatively higher platinumgroup element (pGE) contents (l:PGE=16.3-28.2 ppb), with high Cu/Zr and Pd/Zr ratios, and low S contents (5.03-16.9 ppm), indicating the parental magma is S-unsaturated and generated by high degree of partial melting of the Emeishan large igneous province (ELIP) mantle source. The slightly high Cu/Pd ratios (11 000-24 000) relative to that of the primitive mantle suggest that 0.007% sulfides have been retained in the mantle source. The PGE contents of the high-Ti basalts exhibit a wider range (l:PGE=0.517-30.8 ppb), The samples in the middle and upper parts are depleted in PGE and have ENd (260 Ma) ratios ranging from -2.8 to -2.2, suggesting that crustal contamination of the parental magma during ascent triggered sulfur saturation and segregation of about 0.446%--0.554% sulfides, and the sulfide segregation process may also provide the ore-forming material for the magmatic Cu-Ni-PGE sulfide deposits close to the studied basalts. The samples in this area show Pt-Pd type primitive mantle-normalized PGE patterns, and the Pd/lr ratios are higher than that of the primitive mantle (Pd/lr=I), indicating that the obvious differentiation between Ir-group platinumgroup elements (IPGE) and Pd-group platinum-group elements (PPGE) are mainly controlled by olivine or chromites fractionation during magma evolution. The PdlPt ratios of most samples are higher than the average ratio of mantle (pd/Pt=0.55), showing that the differentiation happened between Pt and Pd. The differentiation in picrites may be relevant to Pt hosted in discrete refractory Pt-alloy phase in the mantle; whereas the differentiation in the high-Ti basalts is probably associated with the fractionation of Fe-Pt alloys, coprecipitating with Ir-Ru-Os alloys. Some high-Ti basalt samples exhibit negative Ru anomalies, possibly due to removal of laurite collected by the early crystallized chromites.

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“…BIFs from within the IGB are characterised by low detrital components as shown by Frei & Polat (2007 Even if we assumed that as much as 0.5wt% MgO derived from basaltic precursors (such as boninites and picrite typical of the IGB) with Ir concentrations comparable to Archean komatiites, mafic komatiites and basalts (MgO from 5-20 wt%) with up to 1 ppb Ir (Hong et al, 2006;Puchtel and Humayun, 2000;Maier et al, 2003;and others), then the Ir concentrations in such mesobands should not exceed ∼25 ppt. We therefore interpret the elevated Ir concentrations in these BIF mesobands to derive from extraterrestrial sources (mainly as atmospheric fall-out)…”

Section: Introductionmentioning

confidence: 99%

The Earth–Moon system during the late heavy bombardment period – Geochemical support for impacts dominated by comets

Jørgensen¹,

Appel²,

Hatsukawa³

et al. 2009

Icarus

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The solid planets assembled 4.57 Gyr ago during a period of less than 100 Myr, but the bulk of the impact craters we see on the inner planets formed much later, in a narrow time interval between 3.8 and 3.9 Gyr ago, during the so-called Late Heavy Bombardment (LHB).It is not certain what caused the LHB, and it has not been well known whether the impactors were comets or asteroids, but our present study lend support to the idea that it was comets.Due to the Earth's higher gravity, the impactors will have hit the Earth with ∼twice the energy density that they hit the Moon, and the bombardment will have continued on Earth longer than on the Moon. All solid surface of the Earth will have been completely covered with craters by the end of the LHB.However, almost nothing of the Earth's crust from even the end of this epoch, is preserved today. One of the very few remnants, though, is exposed as the Isua greenstone belt (IGB) and nearby areas in Western Greenland. During a field expedition to Isua, we sampled three types of metasedimentary rocks, deposited ∼3.8 billion years ago, that contain information about the sedimentary river load from larger areas of surrounding land surfaces (mica-schist and turbidites) and of the contemporaneous seawater (BIF). Our samples show evidence of the LHB impacts that took place on Earth, by an average of a seven times enrichment (150 ppt) in iridium compared to present day ocean crust (20 ppt). The clastic sediments show slightly higher enrichment than the chemical sediments, which may be due to contamination from admixtures of mafic (proto-crustal) sources.We show that this enrichment is in agreement with the lunar cratering rate and a corresponding extraterrestrial LHB contribution to the Earth's Hadean-Eoarchean crust, provided the bulk of the influx was cometary (i.e., of high velocity and low in CI abundance), but not if the impactors were meteorites (i.e. had velocities and abundances similar to present day Earth crossing asteroids). Our study is a first direct indication of the nature of the LHB impactors, and the first to find an agreement between the LHB lunar cratering rate and the Earth's early geochemical record (and the corresponding lunar record). The LHB comets that delivered the iridium we see at Isua will at the same time have delivered the equivalent of a ∼1 km deep ocean, and we explain why one should expect a cometary ocean to become roughly the size of the Earth's present-day ocean, not only in terms of depth but also in terms of the surface area it covers. The total impacting mass on the Earth during the LHB will have been ∼1000 t/m 2 .

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Platinum-group element (PGE) geochemistry of the Emeishan basalts in the Pan-Xi area, SW China

Cited by 20 publications

References 24 publications

Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition

Platinum‐Group Element Geochemical Characteristics of the Picrites and High‐Ti Basalts in the Binchuan Area, Yunnan Province

The Earth–Moon system during the late heavy bombardment period – Geochemical support for impacts dominated by comets

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