Petrology and Upward Zonation of the Wooley Creek Batholith, Klamath Mountains, California
Petrology and Upward Zonation of the Wooley Creek Batholith, Klamath Mountains, California
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DOI：
10.1093/petrology/24.4.495
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发表时间：
1983-11
影响因子：
3.9
通讯作者：
Calvin G. Barnes
中科院分区：
文献类型：
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作者：
Calvin G. Barnes
Wooley Creek岩基侵入克拉马斯山脉西部古生代和三叠纪变质岩中，形成于162±2 m.那是以前的事了。岩基横切了西部古生代和三叠纪的最低亚单位、响尾蛇溪地体和上覆的Hayfork地体变沉积之间的逆冲断层。岩基和它的寄主岩石随后被推到加利斯组的低密度岩石上，然后向西南倾斜，推测是通过区域穹隆。接触晕的变质矿物组合表明，该岩体至少倾斜了20°~30°。Wooley Creek岩基从最深裸露部分的两辉长岩到最浅层次的角闪石-黑云母花岗岩按等级划分。深成岩表现出两种截然不同的化学趋势，分别对应于含有辉石的岩石和只有角闪石和黑云母作为镁铁质矿物的岩石。与不含辉石的岩石相比，含辉石的岩石结构较低，富含镁、钙、铬、镍、钴和钪，而不含辉石的岩石结构较高，富含铝、钠、钾、锶、锆和Rb。这两种化学趋势可以用(1)两个岩浆共存于一个房间，或(2)垂直梯度下的结晶作用来解释。第二个假设在本报告中得到了详细的检验。常量元素模拟表明，这种趋势可以通过单一母体的晶体分馏作用来解释，该母体在深成岩体的最高层相继富含H2O。向上的H2O富集导致斜长石在较低温度下稳定，从而导致岩浆在铝和碱岩中的富集性。微量元素丰度表明，单斜辉石、橄榄石和铬尖晶石的少量聚集影响了岩体的下部，少量玄武岩岩浆的流入影响了岩体的上部，富含H2O。这些玄武岩岩浆被困在下部致密的贫水岩浆和上层富含H2O的岩浆之间的界面上。当这些玄武岩液体冷却和结晶时，它们与富含H2O的岩体岩浆混合在一起。
The Wooley Creek batholith was intruded into metamorphic rocks of the western Paleozoic and Triassic belt of the Klamath Mountains 162 ± 2 m.y. ago. The batholith crosscut a thrust fault between the lowest subunit of the western Paleozoic and Triassic belt, the Rattlesnake Creek terrane and overlying Hayfork terrane metasediments. The batholith and its host rocks were subsequently thrust over low-density rocks of the Galice Formation and then tilted toward the southwest, presumably by regional doming. Metamorphic mineral assemblages of the contact aureole suggest that the pluton was tilted at least 20° to 30°. The Wooley Creek batholith is gradationally zoned from two-pyroxene gabbro in the deepest exposed portion to hornblende–biotite granite at shallowest levels. The plutonic rocks display two distinct chemical trends that correspond to rocks that contain pyroxene and rocks with only hornblende and biotite as mafic minerals. Pyroxene-bearing rocks are structurally lower and are enriched in Mg, Ca, Cr, Ni, Co, and Sc relative to pyroxene-free rocks that occupy the structurally higher levels and are enriched in Al, Na, K, Sr, Zr, and Rb. The two chemical trends can be explained by (1) two coexisting magmas in a single chamber, or (2) crystallization under a verticalgradient. The second hypothesis is examined in detail in this report. Major-element modelling suggests that the trends can be explained by crystal fractionation of a single parent that became successively enriched in H2O in the highest levels of the pluton. Upward H2O-enrichment led to plagioclase stability at lower temperature and consequent enrichment of the magma in Al and alkalies. Trace element abundances show that minor accumulation of clinopyroxene, olivine, and chromian spinel affected the lower part of the pluton and that minor influxes of basaltic magma affected the upper, H2O-enriched part of the pluton. These basaltic magmas were trapped in the interface between the lower, dense, H2O-poor magma and the upper, H2O-enriched magma. As these basaltic liquids cooled and crystallized, they mingled with the H2O-rich magma of the pluton.