Intrusion of basaltic magma into a crystallizing granitic magma chamber: The Cordillera del Paine pluton in southern Chile
Intrusion of basaltic magma into a crystallizing granitic magma chamber: The Cordillera del Paine pluton in southern Chile
复制标题
玄武岩岩浆侵入结晶花岗岩岩浆室：智利南部的潘恩山脉岩体
DOI：
10.1007/bf00303446
复制
发表时间：
1991
影响因子：
3.5
通讯作者：
P. Michael
中科院分区：
文献类型：
--
作者：
P. Michael
智利安第斯山脉最南端的科迪勒拉德尔潘恩（Cordillera del Paine）岩体代表了一个被深度解剖的岩浆房，其中基性岩浆侵入了花岗岩岩浆结晶。在10x15公里的大部分地区，在海拔1100米的恒定高度上，有一个尖锐而连续的边界，将花岗岩（Cordillera del Paine或CP花岗岩：69-77% SiO2）与基性和混合岩石（Paine - mafic Complex或PMC: 45-60% SiO2）分开，这些岩石构成了岩体的上层，它们主导着岩体的下层。基性岩与花岗岩的冷冻、圆齿、断裂接触表明，部分结晶的花岗岩曾被基性岩浆侵入，而基性岩浆在花岗岩完全结晶之前就已凝固。在1100 m处，密度较大、温度较高的基性岩浆与温度较低的花岗质岩浆之间形成了巨大而稳定的密度对比。当岩浆侵入发生时，花岗岩岩浆在靠近岩浆室边缘的地方更加凝固，花岗岩对PMC的破坏较小。在岩体边缘附近，PMC由辉长岩向二长岩不规则地向上递变。基性岩浆的分异主要是通过结晶分异，这可以从堆积岩的存在和大多数PMC岩石中低水平的相容元素中看出。PMC和CP花岗岩之间的成分差距表明，花岗质岩浆与基性岩浆的混合作用较小，尽管从基性岩石的矿物组合中可以看出这一点。花岗质岩浆可能含有少量镁铁质液体，通过结晶作用，镁铁质液体的sio2含量达到了60%。花岗岩的结晶程度、岩浆之间的热对比和稳定的密度对比抑制了混合作用。PMC辉长岩显示出不平衡矿物组合，包括早期形成的带状橄榄石（带正辉石日冕）、斜辉石、钙质斜长石和寄生石，以及后期形成的角闪洞、钠质斜长石、云母和石英。早期形成的辉长岩矿物（及其日冕）与切割CP花岗岩上层的晚期玄武岩岩脉中的斑晶非常相似。推断出的岩脉和辉长岩的母岩浆与巴塔哥尼亚高原的亚碱性玄武岩非常相似，它们在东部约35公里处同时喷发。从碱度和微量元素比值可以看出，科迪勒拉德尔潘恩的基性和硅质岩浆是紧密相连的。然而，镁质和硅质岩浆的同期性排除了父女关系。花岗质岩浆很可能是由基性岩浆分化而来的，这些基性岩浆与后来侵入的基性岩浆相似。或者，花岗质岩浆可能在其浅侵位前被类似于PMC岩浆的基性岩浆污染。当冷却速率较低，花岗岩岩浆凝固程度较低时，较深层的混合更有利。
The Cordillera del Paine pluton in the southernmost Andes of Chile represents a deeply dissected magma chamber where mafic magma intruded into crystallizing granitic magma. Throughout much of the 10x15 km pluton, there is a sharp and continuous boundary at a remarkably constant elevation of 1,100 m that separates granitic rocks (Cordillera del Paine or CP granite: 69–77% SiO2) which make up the upper levels of the pluton from mafic and comingled rocks (Paine Mafic Complex or PMC: 45–60% SiO2) which dominate the lower exposures of the pluton. Chilled, crenulate, disrupted contacts of mafic rock against granite demonstrate that partly crystallized granite was intruded by mafic magma which solidified prior to complete crystallization of the granitic magma. The boundary at 1,100 m was a large and stable density contrast between the denser, hotter mafic magma and cooler granitic magma. The granitic magma was more solidified near the margins of the chamber when mafic intrusion occurred, and the PMC is less disrupted by granites there. Near the pluton margins, the PMC grades upward irregularly from cumulate gabbros to monzodiorites. Mafic magma differentiated largely by fractional crystallization as indicated by the presence of cumulate rocks and by the low levels of compatible elements in most PMC rocks. The compositional gap between the PMC and CP granite indicates that mixing (blending) of granitic magma into the mafic magma was less important, although it is apparent from mineral assemblages in mafic rocks. Granitic magma may have incorporated small amounts of mafic liquid that had evolved to >60% SiO2by crystallization. Mixing was inhibited by the extent of crystallization of the granite, and by the thermal contrast and the stable density contrast between the magmas. PMC gabbros display disequilibrium mineral assemblages including early formed zoned olivine (with orthopyroxene coronas), clinopyroxene, calcic plagioclase and paragasite and later-formed amphibole, sodic plagioclase, mica and quartz. The early formed gabbroic minerals (and their coronas) are very similar to phenocrysts in late basaltic dikes that cut the upper levels of the CP granite. The inferred parental magmas of both dikes and gabbros were very similar to subalkaline basalts of the Patagonian Plateau that erupted at about the same time, 35 km to the east. Mafic and silicic magmas at Cordillera del Paine are consanguineous, as demonstrated by alkalinity and trace-element ratios. However, the contemporaneity of mafic and silicic magmas precludes a parent-daughter relationship. The granitic magma most likely was derived by differentiation of mafic magmas that were similar to those that later intruded it. Or, the granitic magma may have been contaminated by mafic magmas similar to the PMC magmas before its shallow emplacement. Mixing would be favored at deeper levels when the cooling rate was lower and the granitic magma was less solidified.
增岛勉：同位素新闻 1988。2-6 (1988)
DOI：
--
发表时间：
--
期刊：
影响因子：
--
作者：
通讯作者：
--