The Kuiqi Peralkaline Granitic Complex (SE China): Petrology and Geochemistry
The Kuiqi Peralkaline Granitic Complex (SE China): Petrology and Geochemistry
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DOI：
10.1093/petrology/35.4.983
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发表时间：
1994-08
影响因子：
3.9
通讯作者：
H. Martin;B. Bonin;R. Capdevila;B. Jahn;J. Lameyre;Yan-bin Wang
中科院分区：
文献类型：
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作者：
H. Martin;B. Bonin;R. Capdevila;B. Jahn;J. Lameyre;Yan-bin Wang
中国东南部中生代火山-深成岩带以魁岐地区的酸性火山岩和燕山花岗岩为特征。魁岐花岗杂岩体属于后者，由钙碱性和过碱性岩石组成。钙碱性岩群由丹阳二长花岗岩和福州正长花岗岩两个岩体组成，侵位时间分别为103±10 Ma和104± 5 Ma（Rb-Sr全岩等时线）。丹阳二长花岗岩的形成可以用三阶段模式来解释：（1）交代地幔的部分熔融产生了南峪闪长质岩浆;（2）岩浆受到下陆壳的混染（约25%）;（3）大量（70-80%）的角闪石和斜长石在深部分离结晶形成了岩浆岩系。抚州正长花岗岩的结晶作用较强，其形成机制为斜长石+黑云母+钾长石+磷灰石。过碱性岩体的年龄分别为93 ±1 Ma（魁岐过碱性花岗岩）和91.8± 0.9Ma（笔架山过碱性花岗岩）。这些单位是同质的，其岩石成因的限制比钙碱性套件。然而，可以提出一个多阶段的过程：（1）部分熔融的交代地幔产生的闪长质岩浆;（2）分离结晶开始与角闪石+斜长石±钛铁矿和/或磁铁矿的分离，随后，角闪石不再结晶;（3）最后阶段的分馏对应的结晶钾长石+斜长石+稀土富集的副相。矿物学研究表明，在成矿后期，流体起着突出的作用，控制了结晶矿物的性质。岩浆从富F和S，水不饱和到水过饱和，导致出溶和分解的H2O蒸汽相和损失的H2。从钙碱性到过碱性岩浆作用的变化与推断的构造环境变化有关。钙碱性花岗岩是在俯冲环境中生成的，其中水是由下行板片脱水提供的。过碱性花岗岩是在地壳变薄的环境中产生的，那里几乎没有水，因此需要高温才能开始部分熔融。另一方面，岩石成因模拟表明，钙碱性和过碱性花岗岩可能来自同一个来源，即交代地幔。这可能表明，火山岩是源区，在俯冲过程中活动，持续存在于大陆之下，并在后造山岩浆活动中重新活化。复活是由一个深地壳断层引起的。
The Mesozoic volcano-plutonic belt of SE China is characterized, in the Kuiqi area, by acid volcanics followed by the Yanshan granites. The Kuiqi granitic complex, which belongs to the latter unit, is made up of a calc-alkaline and a peralkaline group. The calc-alkaline group consists of two intrusions, the Danyang monzogranite and the Fuzhou syenogranite, emplaced 103±10 Ma and 104± 5 Ma ago, respectively (Rb-Sr whole-rock isochrons). Formation of the Danyang monzogranite can be explained by a three-stage model: (1) partial melting of a metasomatized mantle generated a dioritic magma known in the area as the Nanyu diorite; (2) the magma was contaminated (∼25%) by lower continental crust; (3) large amounts (70–80%) of fractional crystallization of hornblende and plagioclase at depth gave rise to the magmatic suite. The Fuzhou syenogranite is more fractionated and its formation involved crystallization of plagioclase + biotite + K-feldspar + apatite. Intrusion of the peralkaline group is dated at 93 ±1 Ma (Kuiqi peralkaline granite) and at 91.8±0.9 (Bijiashan peralkaline granite). These units are homogeneous and their petrogenesis is less constrained than for the calc-alkaline suite. Nevertheless, a multistage process can be proposed: (1) partial melting of a metasomatized mantle produced a dioritic magma; (2) fractional crystallization began with segregation of hornblende + plagioclase ± ilmenite and/or magnetite; subsequently, hornblende no longer crystallized; (3) the last stage of fractionation corresponded to the crystallization of K-feldspar + plagioclase + REE-rich accessory phases. Mineralogical study indicates that during the last stage, fluids played a prominent role and controlled the nature of the crystallizing minerals. The magma evolved from F- and S-rich, and water-undersaturated to water-oversaturated, leading to the exsolution and dissociation of an H2O vapour phase and to the loss of H2. The change from calc-alkaline to peralkaline magmatism is related to inferred changes in the tectonic environment. The calc-alkaline granites were generated in a subduction setting in which water was supplied by dehydration of the downgoing slab. The peralkaline granites were produced in a crustal thinning environment where little water was available, thus necessitating high temperatures to initiate partial melting. On the other hand, petrogenetic modelling shows that both calc-alkaline and peralkaline granites could have been derived from the same source which is metasomatized mantle. This possibly indicates that the volcanic are source, active during subduction, persisted beneath the continent and was reactivated during the post-orogenic magmatism. The reactivation was caused by a deep crustal fault.