Paleoproterozoic ultrahigh-temperature mafic granulites with a high-pressure prograde path from the Alxa Block: Implications on the tectonic evolution of the Khondalite Belt, North China Craton

IF 3.5 2区 地球科学 Q1 GEOLOGY
Lei Zou, Jing-Hui Guo, Li-Fei Zhang, Guang-Yu Huang, Shu-Juan Jiao, Zhong-Hua Tian, Da Wang, Ping-Hua Liu
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引用次数: 0

Abstract

Ultrahigh-temperature (UHT) granulites, a prominent feature of Paleoproterozoic orogenic belts, preserve a record of geodynamic processes during the Precambrian (Archean–Paleoproterozoic). Quantitative pressure–temperature–time (PTt) paths of these UHT granulites can constrain the tectonic processes and metamorphic evolution in such a tectonic regime. Here, UHT mafic granulites with a high-pressure (HP) prograde path are first reported in the Diebusige Complex in the Alxa Block, western part of the Khondalite Belt (KB), North China Craton (NCC). The detailed petrographic studies show that two mafic granulite samples preserve corona textures around relict garnet or garnet pseudomorphs (completely replaced by plagioclase), and a third mafic granulite sample has a relatively simple mineralogy with a granoblastic-polygonal texture. These mafic granulites have similar peak (Tmax) assemblages of clinopyroxene + orthopyroxene + plagioclase + ilmenite ± garnet ± amphibole ± quartz + melt. Phase equilibrium modelling and Ti-in-amphibole and rare earth element (REE)-based thermometries all constrain similar peak conditions of ~880–950°C/~8.5–10 kbar implying an ~100°C/kbar apparent geothermal gradient for these mafic granulites. Based on the corona textures or pseudomorphs of garnet and mineral assemblages, we identified a Pmax (~14 kbar) prograde stage before the Tmax stage. Thus, a clockwise PT path with heating and decompression followed by near-isobaric cooling (IBC) is recorded from these UHT mafic granulites. In addition, zircon and apatite SHRIMP or LA–ICP–MS U–Pb dating yields an age interval of ~1.81–1.7 Ga, which is interpreted as representing the cooling time from ~900–800°C to ~575°C at the middle-upper crustal levels (<25 km deep) for these mafic granulites, with an ~1.5–2.5°C/Myr cooling rate. The new PTt path of these rocks includes high-pressure prograde, UHT peak, and slow cooling retrograde processes, which implicates a post-collisional tectonic setting for UHT metamorphism in the KB and the processes of collision, exhumation, and cooling of the KB.

来自阿拉善地块的古新生代超高温黑云母花岗岩的高压顺行路径:对华北克拉通孔雀石带构造演化的影响
超高温(UHT)花岗岩是古生代造山带的一个突出特征,它保留了前寒武纪(安恒-古生代)地球动力过程的记录。这些超高温花岗岩的定量压力-温度-时间(P-T-t)路径可以对这种构造体系中的构造过程和变质演化过程进行约束。本文首次报道了华北克拉通(NCC)邝达拉石带(KB)西部阿拉善区块的迪布斯其格复合体中具有高压(HP)顺行路径的超高温黑云母花岗岩。详细的岩石学研究表明,两个黑云母花岗岩样品在残余石榴石或石榴石假象(完全被斜长石取代)周围保留了日冕纹理,第三个黑云母花岗岩样品的矿物学结构相对简单,具有粒状-多角形纹理。这些黑云母花岗岩具有相似的峰值(Tmax)组合,即clinopyroxene + orthopyroxene + plagioclase + ilmenite ± garnet ± amphibole ± quartz + melt。相平衡模型、闪石中的钛和基于稀土元素(REE)的温度计都确定了类似的峰值条件,即~880-950°C/~8.5-10千巴,这意味着这些黑云母花岗岩的表观地热梯度为~100°C/千巴。根据石榴石的日冕纹理或假象以及矿物组合,我们确定了在Tmax阶段之前的Pmax(~14千巴)顺行阶段。因此,这些超高温黑云母花岗岩记录了一条顺时针的P-T路径,包括加热和减压,然后是近等压冷却(IBC)。此外,锆石和磷灰石的SHRIMP或LA-ICP-MS U-Pb年代测定得出的年龄区间为~1.81-1.7 Ga,这被解释为代表了这些岩浆花岗岩在地壳中上层(25 km深)从~900-800°C冷却到~575°C的时间,冷却速度为~1.5-2.5°C/Myr。这些岩石新的P-T-t路径包括高压顺行、超高温峰值和缓冷逆行过程,这暗示了KB超高温变质作用的碰撞后构造背景以及KB的碰撞、掘起和冷却过程。
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来源期刊
CiteScore
6.60
自引率
11.80%
发文量
57
审稿时长
6-12 weeks
期刊介绍: The journal, which is published nine times a year, encompasses the entire range of metamorphic studies, from the scale of the individual crystal to that of lithospheric plates, including regional studies of metamorphic terranes, modelling of metamorphic processes, microstructural and deformation studies in relation to metamorphism, geochronology and geochemistry in metamorphic systems, the experimental study of metamorphic reactions, properties of metamorphic minerals and rocks and the economic aspects of metamorphic terranes.
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