CAJ | 학술논문

五大连池钾质火山岩中发现具有反环带结构的单斜辉石斑晶。反环带辉石的核部为次透辉石，与边部相比具有较低的Mg#值（68~77）、TiO2（0.23~0.50 wt.%）、Cr2O3（<0.06 wt.%）和较高的Al2O3（3.4~5.0 wt.%）、Na2O （0.43~0.78 wt.%）、FeO （8.8~11.0 wt.%）、MnO含量。核部的稀土元素标准化曲线较为平坦，且具有非常显著的Eu和Sr的负异常（Eu/Eu*=0.35~0.63，Sr/Sr*=0.03~0.17），指示其为曾与斜长石平衡的变质岩辉石。在Mg#-TiO2相关图上，核部总体成分落入华北下地壳低Mg麻粒岩中单斜辉石的成分范围，因此核部应该是来自下地壳麻粒岩的捕掳晶。反环带辉石边部与正常辉石斑晶成分一致，具有较高的Mg#值（81~85）、TiO2（0.40~1.65 wt.%）、Cr2O3（0.03~0.25 wt.%）和较低的Al2O3（2.1~3.4 wt.%）、Na2O （0.34~0.63 wt.%）、FeO （4.6~6.6 wt.%）、MnO含量，轻重稀土分馏明显（La/Yb）N=3.23~7.89，与玄武岩全岩的特征吻合。利用主量和微量元素的分配系数进行的模拟计算均表明，反环带辉石边部与寄主岩浆已达到成分平衡，说明边部是在熔蚀核部的基础上再生长而成的岩浆成因辉石。五大连池正常辉石斑晶的Mg#值与TiO2具有负相关性，指示岩浆在地壳深度经历了一定程度的演化。反环带辉石斑晶边部由里到外Al2O3和Na2O含量逐渐增加的趋势支持岩浆经历演化的结论。核部辉石的麻粒岩属性表明岩浆演化主要发生在下地壳。温压计计算结果也指示正常辉石斑晶和反环带辉石的边部都结晶于下地壳深度的系列岩浆房。晚期结晶的辉石斑晶总是比早期结晶的辉石更富集不相容元素，说明分离结晶作用导致五大连池玄武岩的不相容元素更富集。平衡计算表明，与辉石斑晶平衡的岩浆与玄武岩全岩在微量元素特征上高度相似。考虑到全岩高度一致的微量元素特征，研究认为五大连池玄武岩的成分变化主要受下地壳岩浆房中的结晶分离作用控制，地壳混染（包括壳源岩浆混合）可以忽略不计。五大連池鉀質火山巖中髮現具有反環帶結構的單斜輝石斑晶。反環帶輝石的覈部為次透輝石，與邊部相比具有較低的Mg#值（68~77）、TiO2（0.23~0.50 wt.%）、Cr2O3（<0.06 wt.%）和較高的Al2O3（3.4~5.0 wt.%）、Na2O （0.43~0.78 wt.%）、FeO （8.8~11.0 wt.%）、MnO含量。覈部的稀土元素標準化麯線較為平坦，且具有非常顯著的Eu和Sr的負異常（Eu/Eu*=0.35~0.63，Sr/Sr*=0.03~0.17），指示其為曾與斜長石平衡的變質巖輝石。在Mg#-TiO2相關圖上，覈部總體成分落入華北下地殼低Mg痳粒巖中單斜輝石的成分範圍，因此覈部應該是來自下地殼痳粒巖的捕擄晶。反環帶輝石邊部與正常輝石斑晶成分一緻，具有較高的Mg#值（81~85）、TiO2（0.40~1.65 wt.%）、Cr2O3（0.03~0.25 wt.%）和較低的Al2O3（2.1~3.4 wt.%）、Na2O （0.34~0.63 wt.%）、FeO （4.6~6.6 wt.%）、MnO含量，輕重稀土分餾明顯（La/Yb）N=3.23~7.89，與玄武巖全巖的特徵吻閤。利用主量和微量元素的分配繫數進行的模擬計算均錶明，反環帶輝石邊部與寄主巖漿已達到成分平衡，說明邊部是在鎔蝕覈部的基礎上再生長而成的巖漿成因輝石。五大連池正常輝石斑晶的Mg#值與TiO2具有負相關性，指示巖漿在地殼深度經歷瞭一定程度的縯化。反環帶輝石斑晶邊部由裏到外Al2O3和Na2O含量逐漸增加的趨勢支持巖漿經歷縯化的結論。覈部輝石的痳粒巖屬性錶明巖漿縯化主要髮生在下地殼。溫壓計計算結果也指示正常輝石斑晶和反環帶輝石的邊部都結晶于下地殼深度的繫列巖漿房。晚期結晶的輝石斑晶總是比早期結晶的輝石更富集不相容元素，說明分離結晶作用導緻五大連池玄武巖的不相容元素更富集。平衡計算錶明，與輝石斑晶平衡的巖漿與玄武巖全巖在微量元素特徵上高度相似。攷慮到全巖高度一緻的微量元素特徵，研究認為五大連池玄武巖的成分變化主要受下地殼巖漿房中的結晶分離作用控製，地殼混染（包括殼源巖漿混閤）可以忽略不計。
오대련지갑질화산암중발현구유반배대결구적단사휘석반정。반배대휘석적핵부위차투휘석，여변부상비구유교저적Mg#치（68~77）、TiO2（0.23~0.50 wt.%）、Cr2O3（<0.06 wt.%）화교고적Al2O3（3.4~5.0 wt.%）、Na2O （0.43~0.78 wt.%）、FeO （8.8~11.0 wt.%）、MnO함량。핵부적희토원소표준화곡선교위평탄，차구유비상현저적Eu화Sr적부이상（Eu/Eu*=0.35~0.63，Sr/Sr*=0.03~0.17），지시기위증여사장석평형적변질암휘석。재Mg#-TiO2상관도상，핵부총체성분락입화북하지각저Mg마립암중단사휘석적성분범위，인차핵부응해시래자하지각마립암적포로정。반배대휘석변부여정상휘석반정성분일치，구유교고적Mg#치（81~85）、TiO2（0.40~1.65 wt.%）、Cr2O3（0.03~0.25 wt.%）화교저적Al2O3（2.1~3.4 wt.%）、Na2O （0.34~0.63 wt.%）、FeO （4.6~6.6 wt.%）、MnO함량，경중희토분류명현（La/Yb）N=3.23~7.89，여현무암전암적특정문합。이용주량화미량원소적분배계수진행적모의계산균표명，반배대휘석변부여기주암장이체도성분평형，설명변부시재용식핵부적기출상재생장이성적암장성인휘석。오대련지정상휘석반정적Mg#치여TiO2구유부상관성，지시암장재지각심도경력료일정정도적연화。반배대휘석반정변부유리도외Al2O3화Na2O함량축점증가적추세지지암장경력연화적결론。핵부휘석적마립암속성표명암장연화주요발생재하지각。온압계계산결과야지시정상휘석반정화반배대휘석적변부도결정우하지각심도적계렬암장방。만기결정적휘석반정총시비조기결정적휘석경부집불상용원소，설명분리결정작용도치오대련지현무암적불상용원소경부집。평형계산표명，여휘석반정평형적암장여현무암전암재미량원소특정상고도상사。고필도전암고도일치적미량원소특정，연구인위오대련지현무암적성분변화주요수하지각암장방중적결정분리작용공제，지각혼염（포괄각원암장혼합）가이홀략불계。
Clinopyroxene phenocrysts with reverse zoning have been observed in Wudalianchi potassic lavas. The cores are salites characterized by lower Mg# (68~77), TiO2 (0.23~0.50 wt.%), Cr2O3 (<0.06 wt.%) and higher Al2O3 (3.4~5.0 wt.%), Na2O (0.43~0.78 wt.%), FeO (8.8~11.0 wt.%) and MnO contents than those of the exteriors. Normalized REE patterns of the cores are relatively flat, and they also exhibit prominently negative anomaly of Eu and Sr (Eu/Eu*=0.35~0.63, Sr/Sr*=0.03~0.17), suggesting an origin from metamorphic rocks in equilibrium with plagioclase. In the plot of Mg#-TiO2, the overall composition of the cores falls within the compositional range of clinopyroxenes in lower crustal low-Mg granulites from North China Craton. As a result, the cores are inferred to be xenocrysts from granulites in the lower continental crust. The exteriors and normal pyroxene phenocrysts are similar in their compositions, which are higher in Mg# (81~85), TiO2 (0.40~1.65 wt.%), Cr2O3 (0.03~0.25 wt.%), and lower in Al2O3 (2.1~3.4 wt.%), Na2O (0.34~0.63 wt.%), FeO (4.6~6.6 wt.%), MnO. Their LREE and HREE are highly fractionated (La/Yb)N=3.23~7.89, which are consistent with the basaltic whole rocks. The exteriors were in equilibrium with the host magmas, as is confirmed by both major and trace element modeling based on their partition coefficients. Thus the exteriors are suggested to be magmatic pyroxenes formed by overgrowth on the eroded cores. The Mg# of Wudalianchi normal pyroxene phenocrysts are negatively correlated with TiO2 contents, pointing to a certain extent of magmatic evolution in crustal depth, consistent with the gradual increasement of Al2O3 and Na2O contents from the inside out of the exteriors. The granulite facies nature of the cores further constrains the evolution to have occurred in the lower continental crust. Thermobarometer estimations also suggest that the crystallization of normal pyroxenes and exteriors of reversely zoned pyroxenes were in serial magma chambers in the lower crust. Pyroxene phenocrysts crystallized in a later stage are more enriched in incompatible elements than those of earlier pyroxenes, indicating that fractional crystallization have enhanced the enrichment of incompatible elements of Wudalianchi basalts. Calculated melts in equilibrium with pyroxene phenocrysts are extremely similar with the ultimately erupted lavas in their trace element patterns. Considering the remarkably uniform whole-rock trace element patterns, we suggest that the evolution of Wudalianchi basalts in the crust were mainly controlled by the fractional crystallization in magma chambers, and crustal contamination (also mixing with crust-derived magmas) has had negligible effects on whole rock compositions.