Elemental composition of the Alleghanian granitoid plutons of the southern Appalachians
Elemental composition of the Alleghanian granitoid plutons of the southern Appalachians
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DOI：
10.1130/0-8137-1191-6.287
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发表时间：
1997
期刊：
影响因子：
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通讯作者：
J. Speer;Kevin W. Hoff
中科院分区：
文献类型：
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作者：
J. Speer;Kevin W. Hoff
阿巴拉契亚山脉南部的阿勒根阶（石炭纪-二叠纪）岩浆岩呈弱碱性，形成丰富的花岗岩和少量辉长岩的成分双峰分布，中间成分岩石很少。花岗岩的成分范围受到限制（平均 SiO2= 71.26；标准差 3.49），跨越准铝质-过铝质边界，对应于淡色正长花岗岩和二长花岗岩。随着 TiO2、P2O5、Fe2O3、MgO、CaO、Eu、Br、Al2O3、V、Ce、Sm、La 和 Zr 中 SiO2 的增加，它们表现出平滑、明确的负线性趋势，线性相关系数 (r) 从 Ti 的 0.87 降至 Zr 的 0.57。 Tb、Sb、Sn、Cr、Ba、Sc、As、Nd、Sr 和 Be 在 r 从 0.56 到 0.38 范围内的线性下降要少得多。随着二氧化硅含量的增加，Tl 具有明确的线性增加 (r= 0.87)，Be、U 和 Rb 的增加不太明确 (r= 0.33–0.43)。 S、Co、Nb、Pb、Ni、Ga、Th、Er、Gd、Mo、K、Cs、Hg、Zn、Mn、C、Dy、Cu、F、Li、B、Ta、Au、Bi、Y、Lu、Hf、Yb、Na、Cl、Ge、Se、Ag、Cd、Pr、Tm 和 W 显示出很少的系统成分变化，r 值在 0.34–0.01 之间。成分变化是由晶体熔体偏析以及与分解的包体的混合和烃源岩的成分差异造成的。除了 Sr 之外，没有明显的地理成分趋势。成分构造判别图表明，花岗岩类岩体是由大陆-大陆碰撞期间或之后破坏性大陆板块边界处的烃源岩和岩浆过程产生的。关于两种碱性花岗岩是否是 A 型花岗岩，或者只是较大的正常岩体的差异化或热液丰富的顶部区域，地质证据并不明确。
The Alleghanian (Carboniferous-Permian) magmatic rocks in the southern Appalachians are subalkaline and form a compositionally bimodal distribution of abundant granitoids and minor gabbroids with few intermediate composition rocks. The granitoids have a restricted compositional range (mean SiO2= 71.26; standard deviation 3.49) that spans the metaluminous-peraluminous boundary and corresponds to leucocratic syenogranites and monzogranites. They exhibit smooth, well-defined negative linear trends with increasing SiO2 for TiO2, P2O5, total Fe as Fe2O3, MgO, CaO, Eu, Br, Al2O3, V, Ce, Sm, La, and Zr, with linear correlation coefficients (r) decreasing from 0.87 for Ti to 0.57 for Zr. Tb, Sb, Sn, Cr, Ba, Sc, As, Nd, Sr, and Be have much less defined linear decrease with r from 0.56–0.38. Tl has a well-defined linear increase with increasing silica content (r= 0.87), and Be, U, and Rb have less well-defined increases (r= 0.33–0.43). S, Co, Nb, Pb, Ni, Ga, Th, Er, Gd, Mo, K, Cs, Hg, Zn, Mn, C, Dy, Cu, F, Li, B, Ta, Au, Bi, Y, Lu, Hf, Yb, Na, Cl, Ge, Se, Ag, Cd, Pr, Tm, and W show little systematic compositional variation with r values from 0.34–0.01. Compositional variations result from crystal-melt segregation as well as mixing with disaggregated enclaves and compositional differences of the source rocks. With the possible exception of Sr, no geographic compositional trends are evident. Compositional tectonic discrimination diagrams indicate that the granitoid plutons were produced from source rocks and magmatic processes at a destructive continental plate boundary during or after continental-continental collision. Geologic evidence is ambiguous as to whether two alkaline granitoids are A-type granites or just the differentiated or hydrothermal-enriched roof zones of much larger, normal plutons.