Empirical constraints on partitioning of platinum group elements between Cr-spinel and primitive terrestrial magmas

Park, J.W.,Kamenetsky, V.,Campbell, I.,Park, G.,Hanski, E.,Pushkarev, E. Pergamon Press 2017 Geochimica et cosmochimica acta Vol.216 No.-

Recent experimental studies and in situ LA-ICP-MS analysis on natural Cr-spinel have shown that Rh and IPGEs (Ir-group platinum group elements: Ru, Ir, Os) are enriched in the lattice of Cr-spinel. However, the factors controlling the partitioning behaviour of these elements are not well constrained. In this study, we report the Rh, IPGE, and trace element contents in primitive Cr-spinel, measured by LA-ICP-MS, from nine volcanic suites covering various tectonic settings including island arc picrites, boninites, large igneous province picrites and mid-ocean ridge basalts. The aim is to understand the factors controlling the enrichment of Rh and IPGEs in Cr-spinels, to estimate empirical partition coefficients between Cr-spinel and silicate melts, and to investigate the role of Cr-spinel fractional crystallization on the PGE geochemistry of primitive magmas during the early stages of fractional crystallization. There are systematic differences in trace elements, Rh and IPGEs in Cr-spinels from arc-related magmas (Arc Group Cr-spinel), intraplate magmas (Intraplate Group Cr-spinel), and mid-ocean ridge magmas (MORB Group Cr-spinel). Arc Group Cr-spinels are systematically enriched in Sc, Co and Mn and depleted in Ni compared to the MORB Group Cr-spinels. Intraplate Group Cr-spinels are distinguished from the Arc Group Cr-spinels by their high Ni contents. Both the Arc and Intraplate Group Cr-spinels have total Rh and IPGE contents of 22-689ppb whereas the MORB Group Cr-spinels are depleted in Rh and IPGE (total<20ppb). Palladium and Pt contents are below detection limit for all of the studied Cr-spinels (<1-5ppb). The time-resolved spectra of LA-ICP-MS data for Cr-spinels mostly show constant count rates for trace element and Rh and IPGEs, suggesting homogeneous distribution of these elements in Cr-spinels. The PGE spikes observed in several Cr-spinels were interpreted to be PGE-bearing mineral inclusions and excluded from calculating the PGE contents of the Cr-spinels. On primitive mantle normalized diagrams the Arc Group Cr-spinels are characterized by a fractionated pattern with high Rh and low Os. The Intraplate Group Cr-spinels show flat patterns with positive Ru anomalies. Our results, together with the experimental and empirical data from previous studies, show that PGE patterns of Cr-spinel largely mimic that of the rock in which they are found, and that Rh, Ir and Os contents increase with increasing Fe<SUP>3+</SUP> contents (i.e. magnetite component) in Cr-spinel, although Ru does not. These observations suggest that the enrichment of Rh and IPGEs in Cr-spinel is controlled by a combination of the Rh and IPGE contents in parental melts and the magnetite component of the spinel. Empirical partition coefficients (D) for Rh and IPGEs between Cr-spinels and silicate melts were calculated using the Rh and IPGE contents of the Cr-spinel and their host volcanic rocks after subtracting the accumulation effect of Cr-spinel. The D values for the Intraplate and MORB Group Cr-spinels increase with increasing magnetite component in Cr-spinel and range from 6 to 512, which is consistent with previously reported experimental and empirical values. In contrast, the Arc Group Cr-spinels have significantly higher D values (e.g. up to ~3700 for Ru) than those of the Intraplate and MORB Group at the same magnetite concentration in the Cr-spinel, suggesting Rh and IPGEs dissolved in silicate melt have stronger affinity for Cr spinel under arc magma conditions than in intraplate magmas. This may be partly attributed to the low temperature of arc magmas relative to intraplate magmas, which leads to the Arc Group Cr-spinels having more octahedral sites at the same magnetite components than the Intraplate Group Cr-spinels. Because of significantly higher D values for the Arc Group Cr-spinels, compared with the Intraplate Group and MORB Group spinels, fractional crystallization of Cr-spinel will more efficiently fractionate Rh and IPGE fro

경상분지 남서부 와룡산 일대에 분포하는 백악기 화강암류에 관한 암석학적 연구 마그마 불균질 혼합에 의한 화강암류의 조성변화

김건기(Kun Ki Kim),김종선(Jong-Sun Kim),좌용주(Yong-Joo Jwa) 한국암석학회 2005 암석학회지 Vol.14 No.1

와룡산 일대에 암주상으로 분포하는 백악기 화강암류는 고도에 따른 수직적인 조성변화를 보인다. 이들 화강암류 내에는 다양한 크기와 형태의 염기성 미립 포유암들이 산출되며, 과냉각대, 망토조직, 그리고 벡베이닝 등과 같은 마그마 혼합의 뚜렷한 증거들이 나타난다. 화강암류는 암석기재적 특징과 모드분석결과로 부터 반상화강암, 반상화강섬록암, 그리고 세립질화강암으로 세분되며, 염기성 미립 포유암은 석영섬록암, 석영몬조섬록암, 그리고 토날라이트 조성을 가진다. 화강암류 내에 염기성 미립 포유암의 분포 면적비는 반상화 강암이 10-15%, 세립질화강암이 약 20%, 그리고 반상화강섬록암이 약 50% 정도로 반상화강섬록암에 집중되어 분포한다. 화강암류 주성분 원소 분석결과를 하커변화도에 도시해 보면 반상화강섬록암에서 세립질화강암으로 가면서 선적인 변화경향을 보이며, SiO₂ 함량은 61.2-72.0wt.%의 조성변화를 보이며, 반상화강섬록암은 평균 61.7wt.%, 반상화강암은 평균 68.6wt.%, 그리고 세립질화강암은 7l.9wt.%의 조성을 가진다. 이와 같은 조성의 변화는 마그마 불균질 혼합에 의한 것으로 매픽 마그마의 양적인 비율에 따른 혼합 정도의 차이에 기인하는 것으로 생각된다. 매픽 마그마의 양이 많은 부분에서는 열적 평형에 빨리 도달하여 화학적 혼합에 의한 반상화강섬록암의 조성이 우세하고, 매픽 마그마의 양이 적은 부분은 기계적인 혼합에 의한 반상화강암과 세립질화강암의 조성이 우세한 것으로 고찰할 수 있다. 따라서 와룡산 일대 화강암류는 화강암질 마그마가 어느 정도 결정분화된 단계에서 보다 매픽한 마그마의 주입으로 인해 마그마 불균질 혼합이 발생하게 되었으며, 혼합된 두 마그마의 양적인 비율에 의해 화강암류의 조성이 변화된 것으로 판단된다. Cretaceous granitic rocks in the Waryongsan area occur as a stock and show compositional changes with altitude. They include mafic microgranular enclaves (MME) with various sizes and types. The MMEs present clear evidence of magma mingling such as supercooling zone, mantling texture and back veining. The granitic rocks are divided into porphyritic granite, porphyritic granodiorite and fined-grained granite by their petrographic characteristics and modal compositions. The MMEs are discriminated to quartzdioritie, quartzmonzodiorite and tonalite. They have varying areal proportions in each granitic rock-type: 10-15% in the porphyritic granite, about 50% in the porphyritic granodiorite, and about 20% in the fined-grained granite. Si02 contents shows compositional change of 61.2-72.0wt.%. Mean Si02 contents have 61.7wt.% in the porphyritic granodiorite, 68.6wt.% in the porphyritic granite, and 71.9wt.% in the fined-grained granite, respectively. Major oxide contents of the granitic rocks linearly vary with Sial contents from the porphyiritic granodiorite to the fine-grained granite on Harker diagrams. Linear compositional variations seem to have been caused by differential degrees of mingling between mafic magma and host granite. Where larger amount of mafic magma was injected into the host granitic magma, the two magmas reached to thermal equilibrium more quickly and eventually chemical mixing occurred to produce the composition of the porphyritic granodiorite. On the other hand, less amount of injected mafic magma would have been responsible for mechanical mixing to produce the compositions of the porphyritic granite and the fined-grained granite. Therefore, it is considered that the granitic rocks in the Waryongsan area experienced magmas mingling resulting from the injection of more mafic magma into differentiating granitic magma, and that the compositional changes of the granitic rocks were ascribed to the degree of mingling between the two magmas.

Multi-stage magmatic plumbing system of the volcano: A case study from Ulleung Island, South Korea

Chen, Shuang-Shuang,Lee, Seung-Gu,Lee, Tae Jong,Lee, Youn-Soo,Liu, Jia-Qi Elsevier 2018 Lithos Vol.314 No.-

<P><B>Abstract</B></P> <P>The multi-stage magmatic plumbing system beneath the Ulleung, Dokdo, and Oki-Dogo Island has attracted considerable attention but has seldom been investigated in detail. Herein, we present a comprehensive geochemical analysis of volcanic rocks sampled at the Ulleung Island, including whole–rock major and trace elements as well as Sr and Nd isotopic compositions. Late Cenozoic alkaline volcanic rocks from the Ulleung Island are commonly divided into basaltic rocks (tephrite basanite and basalt) and acidic rocks (trachyte and rhyolite) based on the large petrologic and geochemical variations. All rocks are significantly enriched in light rare-earth elements (REEs) and large-ion lithophile elements and relatively depleted in heavy REEs. The acidic rocks have slightly enriched <SUP>87</SUP>Sr/<SUP>86</SUP>Sr and ε<SUB>Nd</SUB> ratios (0.704895–0.705173; −2.48 to −1.91) and distinctly negative Ba, Sr, P, Eu, and Ti anomalies relative to the basaltic rocks (0.704733–0.705006, -2.61– -1.17). A multi-stage magma evolution model was finally developed beneath the Ulleung, Dokdo, and Oki-Dogo Island, characterized by at least two magma reservoirs at different depths approximately ranging between 20 and 100 km. These ascending magmas were retained in a shallower reservoir for ~1.0, ~0.5, and ~4.5 Ma, respectively, prior to eruptions with significant crystal fractionation. Mantle-derived basaltic melts either directly travelled to the surface to erupt as tephrite-basanite and basalt, or were stagnated in shallower reservoirs where they differentiated into acidic magma to erupt as trachyte and rhyolite. The Late Cenozoic Korean Peninsula basalts are mainly divided into two groups, i.e., the depleted mantle (DM) and enriched mantle 1 (EM1) mixing trend beneath the Ulleung and Dokdo Island, and the DM-EM2 mixing connection beneath the Jeju Island, which likely indicates the traversed boundary beneath Korean Peninsula that represents a simple lateral continuation of the boundary between the southeast and northeast China Blocks.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We present new geochemistry and Sr-Nd isotopes for Cenozoic volcanic rocks from Ulleung Island. </LI> <LI> Ulleung Island was formed by multi-stage magma evolving model with two magma reservoirs at different depths. </LI> <LI> The Ulleung magma was retained in shallower reservoir for ~1.0 Ma prior to eruption with significant crystal fractionation. </LI> <LI> Mantle-derived basaltic melts were stagnated in shallower reservoir where they differentiated into acidic magma. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Evolution of copper isotopes in arc systems: Insights from lavas and molten sulfur in Niuatahi volcano, Tonga rear arc

Wang, Zaicong,Park, Jung-Woo,Wang, Xia,Zou, Zongqi,Kim, Jonguk,Zhang, Pingyang,Li, Ming Pergamon Press 2019 Geochimica et cosmochimica acta Vol.250 No.-

<P><B>Abstract</B></P> <P>Metal transfer from mantle wedge to primitive arc magmas and subsequent enrichment by magmatic fractionation and volatile exsolution are critical processes for mineralization in arc systems. Copper is one of the most important ore-forming elements whose behavior is sensitive to oxygen fugacity. Copper isotope composition (δ<SUP>65</SUP>Cu) may provide valuable insights into Cu transfer and enrichment in hydrous oxidized arc magmas. However, the extent of Cu isotopic variation in arc systems and its link to Cu transfer and enrichment for ore mineralization have been poorly explored. Here we report the Cu isotopes in basalts, dacites and molten sulfur in Niuatahi volcano, Tonga rear arc to address the issue. These samples, as well as associated black smoker chimneys, represent products of magmatic fractionation and degassing of hydrous oxidized arc magmas with ore mineralization.</P> <P>Sulfide-undersaturated differentiation of basalts in the Niuatahi and their high water content and oxygen fugacity suggest complete exhaustion of sulfides in the mantle source during fluxed melting and transfer of nearly all Cu, Ag and other chalcophile metals to the primary magmas. The δ<SUP>65</SUP>Cu of Niuatahi basalts thus reflect that of the mantle source. The basalts display δ<SUP>65</SUP>Cu of 0.01‰ to 0.17‰ (n = 3; external uncertainty of 0.05‰, 2sd), similar to mid-ocean ridge basalts (MORBs), komatiites and the depleted mantle (0.06 ± 0.20‰, 2sd). These results, together with their Cu contents indistinguishable from MORBs, suggest that oxidized slab components are very likely to have limited influence on the Cu budget and mean δ<SUP>65</SUP>Cu of the mantle wedge.</P> <P>The Niuatahi magma became sulfide saturated after magnetite crystallization during magma differentiation from basalt to dacite. Constant Cu/Ag in the basalts and dacites suggests segregation of immiscible sulfide melts instead of crystalline sulfides. The sulfide segregation significantly decreased contents of Cu and other chalcophile metals but hardly changed δ<SUP>65</SUP>Cu in dacites (−0.01‰ to 0.35‰, n = 11 with a mean of 0.21 ± 0.24‰, 2sd), implying restricted fractionation of δ<SUP>65</SUP>Cu during magnetite fractionation and sulfide melt segregation. Molten sulfurs, which are formed by intensive magmatic degassing of arc lavas and characterized by substantial enrichment of Cu and other metals, show δ<SUP>65</SUP>Cu of 0.30‰ to 0.37‰. These values are indistinguishable from those of comagmatic dacites (0.34‰). Although the published δ<SUP>65</SUP>Cu of sulfide chimneys in the Niuatahi appears slightly lighter (0.00‰ to 0.29‰ ± 0.18‰, 2sd), the overall limited range of δ<SUP>65</SUP>Cu in molten sulfur and sulfide chimneys indicates that discharging magmatic volatiles and hydrothermal venting with significant removal of Cu hardly fractionates δ<SUP>65</SUP>Cu. The δ<SUP>65</SUP>Cu data from arc lavas, molten sulfur and sulfide chimneys thus reveal limited variations in δ<SUP>65</SUP>Cu (within 0.35‰) during fluxed melting, magmatic fractionation, magma degassing and mineralization in arc systems. If these results represent general processes, they imply that the heavier or lighter δ<SUP>65</SUP>Cu in other sulfide chimneys and associated deposits should result from the complex hydrothermal processes and/or low-temperature secondary reworking.</P>

인공위성을 이용한 백두산 하부 마그마 활동에 대한 연구의 필요성 및 가능성

오창환,최승찬,이덕수,박종현,김명덕 한국외국어대학교 국제지역연구센터 2014 국제지역연구 Vol.18 No.3

The Baegdu Volcano which erupted violently at 1000 AD still has possibility of eruption. However,the study on the volcanic activity in the Baegdu Volcano area is quite insufficient in Korea becausethe Baegdu Volcano is difficult to approach due to its location at the boarder between China andNorth Korea. All the more, the study by Korean geologists on the Baegdu Volcano is restricted orprohibited by not only North Korean government but also Chinese government. As a result it is verydifficult to install regular monitoring system or to get monitored data regularly. Especially, the seismic data which is essential for the study on the volcanic activity can not be obtained becauseChineses and North Korean governments worried about the outflow of information about anunderground nuclear test. Therefore it is necessary to develop the system which can monitor theeruption of the Baegdu Volcano using satellite. The resolution of the data(gravity data, geoid andgeomagnetic total force) obtined by GRACE, CHAMP and SWARM satellites has been consideredtoo low to be used for monitoring volcanic area. However recently it is found that it is possible touse satellite data for monitoring the volcanic activity of the Baegdu Volcano because large scalemagma chamber(140x20 km2) locates under the Baegdu Volcano. The gravity data and geoid in theBaegdu Volcanic area obtained from GRACE satellite, decreased from 2002 to 2005. The period ofdecreasing is well matched with time when magma activities were recognized in the Baegdu Volcanicarea. The decrease can be interpreted to be the result of decreasing densities of the magma chamberand surrounding rocks due to the increase of temperature related to the new supply of magma. Thegeomagnetic total force in the Baegdu Volcanic area measured by CHAMP satellite, also decreasedfrom 2000 to 2005 and increased after 2005. The period of decrease is well matched with the timewith increased activity of magma chamber under the Baegdu Volcano indicating that the decrease ofgeomagnetic total force is caused by demagnetization of surrounding rocks due to the increase oftemperature of magma chamber. These data indicate that it is possible to use gravity data, geoidand geomagnetic total force observed by satellites for the monitoring of magma activity under theBaegdu Volcano. 백두산은 1000 AD 경에 매우 강력한 화산 폭발을 하였으며 아직도 폭발 가능성을 가지고있다. 그럼에도 불구하고 국내에서의 백두산의 지역에서 일어나는 화산활동에 대한 연구가 매우 미진한 상황이다. 그 이유는 백두산이 중국과 북한에 걸쳐 분포하고 있어 접근이 어려울뿐 아니라 북한 정부는 물론 중국 정부도 한국 지질학자들의 백두산에 대한 연구를 엄격히 제한하고 있다. 그 결과 백두산 화산 작용을 연구하기 위하여 백두산 지역에 정기적인 감시 시설을 설치하거나, 정기적인 관측 자료를 얻는 것이 매우 힘든 상황이다. 특히 중국과 북한은지하 핵 실험에 대한 정보 유출을 방지하기 위하여 국내학자들에게 화산 활동 예측에 중요한지진 자료 확보를 허락하지 않고 있다. 따라서 인공위성을 이용한 백두산 화산 폭발 가능성에대한 정기적인 감시 기술 개발이 필요한 실정이다. GRACE, CHAMP 그리고 SWARM 인공위성을 이용하여 중력, 지오이드 그리고 자력자료를 측정할 수 있으며 이를 이용하여 백두산화산 활동을 연구할 수 있으나 일반적으로 인공위성으로 얻어진 중력 및 자력 자료의 해상도가 낮아 백두산 지역을 연구하기가 힘들 것으로 예상하여왔다. 하지만 최근 백두산 하부에는140x20 km2의 광역적인 마그마 챔버가 존재하고 있어 인공위성을 이용한 연구가 가능함이 밝혀졌다. GRACE 인공위성에서 획득한 백두산 지역의 중력 자료와 지오이드를 살펴본 결과,백두산 지역에서 마그마 활동 가능성이 인지된 2002년부터 2005년 사이에 매우 뚜렷한 지오이드와 중력 감소가 확인되었다. 이는 새로운 마그마 공급에 따른 온도 증가에 의해 발생한 마그마 챔버와 주변 암석의 밀도 감소에 의해 발생한 것으로 판단된다. 백두산 지역에서CHAMP 인공위성을 이용하여 측정된 지난 2000년도부터 2010년까지의 자기장 변화를 살펴보면, 마그마 활동이 활발했던 2000년에서 2005년도 사이에 자기장이 감소하고 그 이후 다시증가하는 현상을 보여준다. 이러한 자기장의 감소는 백두산 하부 마그마 온도의 증가에 따른주변 암석의 비자성화(demagnatization)에 의한 것일 가능성이 있다. 이러한 연구결과들은 인공위성을 이용하여 관측한 중력, 지오이드와 자기장의 변화가 백두산 하부 마그마 활동을 관측하는데 사용될 수 있는 가능성이 있음을 지시한다.

The Role of Late Sulfide Saturation in the Formation of a Cu- and Au-rich Magma: Insights from the Platinum Group Element Geochemistry of Niuatahi–Motutahi Lavas, Tonga Rear Arc

Park, Jung-Woo,Campbell, Ian H.,Kim, Jonguk,Moon, Jai-Woon Oxford University Press 2015 Journal of petrology Vol.56 No.1

<P>Magmas enriched in Cu and Au are likely to be the most prospective for magmatic-hydrothermal deposits of these metals. However, the mechanism that leads to the formation of metal-rich magmas is not well constrained. We report major, trace and platinum group element (PGE) data for the Niuatahi-Motutahi lavas, Tonga rear arc, with the aim of studying their petrogenesis with special emphasis on the evolution of chalcophile elements during magmatic differentiation. Major and trace element contents, including S and Cl, were also measured in glasses, phenocrysts and melt inclusions to complement the whole-rock data. The Niuatahi-Motutahi lavas are associated with Cu and Au mineralization and therefore provide an opportunity to investigate the characteristics of an ore-associated magmatic system. They show a wide compositional variation from basalts to dacites with MgO contents that vary between similar to 14 and 1 wt %. The dacites can be subdivided into high-K and low-K dacites. Geochemical modeling and their mineralogy suggest that the low-K dacites are comagmatic with the basalts and evolved by fractional crystallization. Copper, Au and Pd behave incompatibly in the basalts and andesitic glasses, whereas they become compatible in the low-K dacite. In contrast, Pt, Rh, Ru and Ir are moderately compatible in the basalts and correlate negatively with MgO, but become strongly compatible in the dacites. The Cu, Au and PGE trends can be explained by fractional crystallization of a Pt-rich alloy in the basalts and andesitic glasses, followed by sulfide saturation in the low-K dacites. The high-K dacites may have evolved from a slightly different magma source; however, their chalcophile elements fractionated in a similar manner. Chlorine and S data for melt inclusions and glasses from the basalts and dacites suggest that water-rich volatile saturation occurred during evolution of the dacites. The Niuatahi-Motutahi dacites were enriched in Cu from 80 to 200 ppm and in Au from < 1 to 7 ppb by fractional crystallization as the magma evolved from basalt through andesite to dacite. We suggest that late sulfide saturation allowed Cu and Au to become enriched by a factor of two in the Niuatahi-Motutahi dacites before volatile saturation and that this played an important role in the formation of the Cu- and Au-rich mineralization. This sulfide saturation history contrasts with that of the Honshu arc volcanic rocks, Japan, where sulfide saturation occurred early. The Honshu arc volcanic rocks are not associated with porphyry Cu or Au deposits, which we suggest is due to loss of most of the Cu and Au to an early immiscible sulfide phase.</P>

Sequential trace element analysis of zoned skarn garnet: Implications for multi-stage fluxing and flow of magmatic fluid into a skarn system

Elsevier 2019 Lithos Vol.350 No.-

<P><B>Abstract</B></P> <P>A high-resolution fluid flux–flow model for a shallow crustal system related to skarn formation was established using oscillatory zoning in garnet. <I>In situ</I> analytical methods were used to determine major and trace element contents of andradite-rich and lower-andradite-content garnet zones. Continuous analysis of pure andradite (And<SUB>87–98</SUB>) shows these garnets record first- and second-order fluid fluxes. The first-order fluid flux exhibits a stepwise increase in Sn contents and a decrease in the contents of other elements (Ti, V, W, As, Mo, Y, and rare earth elements), indicating that pure andradite records a large range changes in fluid flux from the magma. The second-order flux is evident from oscillatory variations in the contents of Sn and other elements, reflecting small-scale and pulsed changes in the fluid flux from a degassing magma reservoir. Based on the garnet major and trace element variations and mineral textures, these fluid fluxes in the skarn system were controlled by pulsed degassing of a cooling magma. Continuous analysis of oscillatory zoning in garnet with a lower andradite content (And<SUB>72–81</SUB>) showed that Sn concentrations increase gradually and other element concentrations decrease gradually. This garnet crystallized from a fluid that was locally equilibrated with a small-scale, stagnant fluid. Thick and low-andradite garnet bands (And<SUB>62–76</SUB>) are observed to have grown between the first-order fluid fluxing events. These bands are Al-rich and have retrograde textures, indicating prolonged magma residence after the first-order fluid flux, suggesting that circulating fluids persisted for a relatively long time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Oscillatory zoning in skarn garnet resulted from changing magmatic fluid flux. </LI> <LI> Pulsed magma degassing led to variable fluid flux into the skarn deposit. </LI> <LI> Stable magmatic stages were followed by magma degassing. </LI> </UL> </P>

현무암과 포놀라이트 비정질 규산염의 원자구조 차이에 대한 고상핵자기 공명 분광분석 연구

박선영 ( Sun Young Park ),이성근 ( Sung Keun Lee ) 한국광물학회 2015 광물과 암석 (J.Miner.Soc.Korea) Vol.28 No.1

현무암과 포놀라이트 조성을 가진 마그마는 분화 양상과 거시적 물성에서 많은 차이를 보이나 이에 대한 원자구조 단위의 근본적인 원인은 아직 명확히 밝혀지지 않았다. 본 연구에서는 일차원과 고해상도 이차원 고상 핵자기공명 분광분석(Nuclear Magnetic Resonance, NMR)을 이용하여 현무암질 마그마의 모델인 투휘석과 아노르다이트 공융점 조성을 가진 비정질 규산염과 포놀라이트 조성의 비정질 규산염의 Al 주변 원자 구조를 관찰하였다. 27Al MAS NMR 실험 결과 두 조성 모두 [4]Al 피크가 지배적인 것을 보여주며 현무암 조성의 비정질 규산염의 피크 반치폭이 포놀라이트 조성보다 약 2배 더 넓은 것으로 관찰된다. 이것은 현무암질 조성에서의 Al 주변의 위상 무질서도가 포놀라이트 조성보다 높다는 것을 의미한다. 27Al 3QMAS NMR 실험 결과 [4]Al과 [5]Al이 구별되어 관찰되며 현무암 조성의 비정질 규산염에서 포놀라이트 조성에는 관찰되지 않는 [5]Al이 약 3.3% 관찰된다. 이는 현무암질 마그마가 포놀라이트 마그마에 비해 Al 주변의 배열 무질서도가 더 큰 것을 의미한다. 사중극자 상호관계를 설명하는 계수 또한 현무암 조성의 비정질 규산염이 포놀라이트 조성의 비정질 규산염에 비해 큰 값을 나타내며 이것 또한 [4]Al 주변의 위상 무질서도가 더 큰 것을 확증해준다. 본 논문에서 규명한 현무암과 포놀라이트 조성의 비정질 규산염의 원자 구조 차이는 점성도와 같은 조성에 따른 마그마의 물성 차이에 대한 미시적 기원을 제시한다. While the macroscopic properties and eruption style of basaltic and phonolitic melts are different, the microscopic origins including atomic structures are not well understood. Here we report the atomic structure differences of glass in diopside-anorthite eutectic composition (basaltic glass) and phonolitic glass using high-resolution 1D and 2D solid-state Nuclear Magnetic Resonance (NMR). The 27Al MAS NMR spectra for basaltic glass and phonolitic glass show that the full width at half maximum (FWHM) of [4]Al for basaltic glass is about twice than phonolitic glass, suggesting the topological disorder of basaltic magma is larger than that of phonolitic magma. The 27Al 3QMAS NMR spectra for basaltic glass and phonolite glass show much improved resolution than the 1D MAS NMR, resolving [4]Al and [5]Al. Approximately 3.3% of [5]Al is observed for basaltic glass, demonstrating the configurational disorder of basaltic magma is larger than phonolitic magma. This result confirms that the topological disorder of [4]Al in basaltic glass is larger than that of phonolitic glass. The observed structural differences between basaltic glass and phonolitic glass can provide an atomistic origin for change of the macroscopic properties with composition including viscosity.

양산 칼데라에 관련되는 화산암류에서 광물함량 변화의 해석

황상구(Sang Koo Hwang),김세현(Se Hyeon Kim),정성욱(Seong Wook Jeong) 한국암석학회 2008 암석학회지 Vol.17 No.3

양산 칼데라에 관련된 화산암류의 반정광물 모드조성과 전암 노옴조성은 마그마챔버 내에서 조성누대된 마그마로부터 유래되었음을 기록하고 있다. 이 화산암류는 SiO2에 대한 반정비율이 전체적으로 직선상의 연속적 조성구배를 나타낸다. 뿐만 아니라 총반정함량에 대한 반정비율이 양산응회암, 화제리층의 응회암과, 고규질 유문반암을 제외한 장석반암 등의 암석단위로 뚜렷하게 구분된다. 그리고 각 암석 단위 내에서 연속적인 직선상 조성구배를 나타내고, Q-Ab-Or 삼각도와 Q-An-(Ab-Or) 삼각도에서도 마찬가지 경향을 보인다. 또한 상부로 가면서 사장석 반정함량과 그 비율이 점진적으로 풍부해지고 석영과 K-장석의 반정함량과 그 비율은 점점 감소하는 함량변화를 나타낸다. 그리고 양산응회암과 화제리층 응회암에서 반정함량과 그 비율이 상부로 가면서 지그재그형의 파동적인 변화를 나타낸다. 이 직선상 조성구배와 점진적인 함량변화는 각각 양산응회암 분출전 뿐만 아니라, 후기 양산 칼데라 함몰전과 함몰후의 마그마챔버에서 상부에서 하부로 가면서 성분이 누대되었음을 암시한다. The modal analyses on the phenocryst phases and the normative mineralogies from the bulk chemical analyses record that the volcanic rocks related to the Yangsan caldera might been derived from compositionally zoned magma. The volcanic rocks show linearly continuous mineralogical gradients, not only totally in the relations between SiO2 and proportion of phenocryst content, but also within each rock unit in the relations between total phenocryst content and the proportion, Q-Ab-Or and Q-An(Ab-Or) diagrams. The roughly gradational modal variations of the phenocryst phases are shown upward within each rock unit. However, the contents and proportion of the phenocrysts in the Yangsan Tuff and the Hwajeri Formation represent the zigzaggedly undulatory variations. The continuous mineralogical gradients without large gaps define a large zoned magma system in the pre-eruptive, later precollapse and postcollapse magma chambers respectively. The zigzagged variations reflect the intermittent eruptive pulses representing any time gaps.

Magmatic peridotites and pyroxenites, Andong Ultramafic Complex, Korea: Geochemical evidence for supra-subduction zone formation and extensive melt-rock interaction

Whattam, S.A.,Cho, M.,Smith, I.E.M. Universitetsforlaget ; Elsevier Science Ltd 2011 Lithos Vol.127 No.3

The Andong Ultramafic Complex (AUC) mainly comprises peridotites (wehrlites+/-plagioclase or spinel; or plagioclase+spinel) and related serpentinites with subordinate low-Al pyroxenites (clinopyroxenites, orthopyroxenites, and websterites). These rocks are compositionally similar to sub-continental lithospheric mantle peridotites and pyroxenites. Wehrlites formed predominantly by fractional crystallization processes within supra-subduction zone magmas and the pyroxenites are generally consistent with segregation and accumulation in similar magmas. Bulk rock ratios of Al<SUB>2</SUB>O<SUB>3</SUB>/SiO<SUB>2</SUB> (0.01-0.03) and MgO/SiO<SUB>2</SUB> (up to >1) exhibited by the wehrlites and serpentinites indicate crystallization from a refractory source that underwent high degrees of melt extraction. Spinel chemistry confirms this and demonstrates that wehrlite and clinoproxenite protoliths underwent approximately 20-23% and 12-15% partial melting, respectively. Wehrlites and serpentinites also preserve evidence of extensive melt-peridotite interaction manifest as bulk rock SiO<SUB>2</SUB>-depletions and FeO<SUP>t</SUP>-enrichments relative to mantle residua as well as low Mg# (0.39-0.45) spinels with variable Ti contents but constant Cr# (0.42-0.47). These features are identical to those of 'impregnated' plagioclase-peridotites of abyssal and sub-continental environments and compositional trends in spinel space imply reaction between secondary, MORB-like melts saturated in olivine+clinopyroxene or olivine and a harzburgitic protolith. High olivine:pyroxene (∼3:1) and clinopyroxene:orthopyroxene ratios of the wehrlites coupled with chemical data dictate that reactions entailed orthopyroxene dissolution and olivine recrystallization. All AUC rock types exhibit primitive mantle-normalized incompatible element signatures characterized by LILE-enrichments, high fluid-mobile/immobile element ratios (Sr/Nd, Ba/La and Pb/Ce@?1) and prominent HFSE (Nb, Zr, and Ti) depletions indicative of generation in a sub-arc environment within a supra-subduction zone system. A candidate for the associated arc-system is the one responsible for nearby arc-related Jurassic granitoids. Southeast-directed thrusting along the Andong Fault System may account for subsequent emplacement of the AUC into the Gyeongsang Basin.