EARLY-PALEOGENE MAGMATISM IN THE PINALEÑO MOUNTAINS, ARIZONA: EVIDENCE FOR CRUSTAL MELTING OF DIVERSE BASEMENT ASSEMBLAGES DURING THE LARAMIDE OROGENY
EARLY-PALEOGENE MAGMATISM IN THE PINALEÑO MOUNTAINS, ARIZONA: EVIDENCE FOR CRUSTAL MELTING OF DIVERSE BASEMENT ASSEMBLAGES DURING THE LARAMIDE OROGENY
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DOI：
10.1130/abs/2021am-368649
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Shane H. Scoggin;J. Chapman;J. Shields;Adam E. Trzinski;M. Ducea
中科院分区：
文献类型：
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作者：
Shane H. Scoggin;J. Chapman;J. Shields;Adam E. Trzinski;M. Ducea
在拉拉米德造山(80-40 Ma)期间，与地壳熔融有关的花岗岩侵位于亚利桑那州南部的增厚地壳区域。拉莱姆时代的深成岩以深成岩、岩床和脉岩网络的形式暴露出来，通常见于变质核杂岩的出土底部。这项研究调查了在亚利桑那州东南部皮纳莱诺-杰克逊山变质核杂岩(称为雷莱诺套)底部的三个侵入相中新发现的花岗闪长岩-淡色花岗岩的出露情况。锆石U-Pb年代学研究表明，该套岩浆侵位时代为58~52 Ma。利用锆石Lu/Hf同位素地球化学、全岩锶、钕同位素地球化学和矿物氧同位素地球化学研究了这些岩石的来源，并评价它们是否与地壳深成作用有关。锆石εHf(T)平均值为−4.7~−7.9，εNd(I)为−9.4~−11.8，锶/锶(I)为0.7064~0.7094，石英δOVSMOW值为6.8~9.4。这些岩石的同位素和地球化学数据与地壳深部中镁铁质(变质)火成岩的来源和同化作用一致，并得到了与皮纳莱诺山脉出露的元古界火成岩热力学熔融模型的支持。与亚利桑那州东南部的其他拉拉米德期深熔花岗岩相比，出露在Pinaleño山脉的花岗岩在时间上相似，但存在成分和同位素差异，反映了不同岩性的熔融和同化，产生了不同的矿物学和同位素特征。结果表明，这一时期的地壳熔融不仅限于变质原岩，而且可能影响了地壳深部的大部分。早古近纪皮纳尔诺山脉的雷雷诺套加强了地壳熔融与与Sevier和Laramine造山有关的增厚地壳区域之间的关系。
Granitic rocks, interpreted to be related to crustal melting, were emplaced into regions of thickened crust in southern Arizona during the Laramide orogeny (80–40 Ma). Laramide-age anatectic rocks are exposed as plutons, sills, and dike networks that are commonly found in the exhumed footwalls of metamorphic core complexes. This study investigates newly discovered exposures of granodioritic–leucogranitic rocks from three intrusive phases in the footwall of the Pinaleño– Jackson Mountain metamorphic core complex of southeastern Arizona, called the Relleno suite. Zircon U–Pb geochronology indicates that the suite was emplaced from 58 to 52 Ma. Zircon Lu/Hf isotope geochemistry, whole-rock Sr and Nd isotope geochemistry, and mineral O isotope geochemistry were used to investigate the source of these rocks and evaluate whether they are related to crustal anatexis. Average zircon εHf(t) values of the suite range from −4.7 to −7.9, wholerock εNd(i) and Sr/Sr(i) values range from −9.4 to −11.8 and 0.7064 to 0.7094 respectively, and quartz δOVSMOW values range from 6.8 to 9.4 . Isotopic and geochemical data of these rocks are consistent with derivation from and assimilation of intermediate–mafic (meta)igneous rocks, at deep crustal levels, and are supported by thermodynamic melt models of Proterozoic igneous rocks equivalent to those exposed in the Pinaleño Mountains. In comparison with other Laramideage anatectic granites in SE Arizona, those exposed in the Pinaleño Mountains are temporally similar but present compositional and isotopic differences that reflect melting and assimilation of different lithologies, producing distinct mineralogical and isotopic characteristics. The results suggest that crustal melting during this interval was not limited to metasedimentary protoliths and may have affected large portions of the deep crust. The early Paleogene Relleno suite in the Pinaleño Mountains strengthens the relationship between crustal melting and regions of thickened crust associated with the Sevier and Laramide orogenies.