Abstract

The Paleoproterozoic Jiao-Liao-Ji Orogenic Belt is a part of the Eastern Block, North China Craton. The Shuangcha rock mass has been recently recognized in Laohe group of Jiao-Liao-Ji Orogenic Belt, and it consists of mainly porphyritic monzonitic granite and porphyritic K-feldspar granite. We present detailed studies of petrography, geochronology and geochemistry of Shuangcha rock mass to constrain the petrogenesis and tectonic evolution features of the Jiao-Liao-Ji Orogenic Belt. The mineral of the Shuangcha granite consists of K-feldspar, plagioclase, quartz and a small amount of biotite (<5%). Zircon U–Pb dating of the Shuangcha granites yield ²⁰⁷Pb/²⁰⁶Pb ages of 1863~1882 Ma, dating them to the late Paleoproterozoic period. The Shuangcha granites are enriched in total alkali (K₂O + Na₂O; 8.29~10.57 wt %), and depleted in MgO (0.87~1.75 wt %), CaO (0.23~0.60 wt %), with high FeO^T/MgO (2.98~3.47). They are characterized by high Zr + Y + Nb + Ce contents (352~669 ppm, >350 ppm) and 10,000Ga/Al ratios (average 2.69), which are typical features of A-type granite. The Shuangcha A-type granites can be further subdivided into A₂-type subgroup based on some geochemical features, such as high Y/Nb ratios (0.99~3.14, average 1.84). Petrographic and geochemical studies have shown that the Shuangcha granites were the product of partial melting of quartzo-feldspathic rocks under a high temperature (>899°C), low pressure and anhydrous environment. Based on geochemical studies of Shuangcha granites, spatial and temporal distributions of regional magmatism and metamorphism records, the Jiao-Liao-Ji Orogenic Belt was in a typical post-collision extension setting in late Paleoproterozoic period (1.82~1.88 Ga) probably triggered by the slab breaks off.

中文翻译：

---

华北克拉通胶辽纪造山带晚元古生代A型花岗岩：岩石成因及其对碰撞后伸展的启示

摘要

古元古代的焦辽纪造山带是华北克拉通东部地块的一部分。双岔岩体最近已在胶辽纪造山带老河群中被发现，它主要由斑状的单长花岗岩和斑状的钾长石花岗岩组成。我们对双岔岩体的岩石学，年代学和地球化学进行了详细的研究，以约束胶辽纪造山带的岩石成因和构造演化特征。双岔花岗岩的矿物由钾长石，斜长石，石英和少量黑云母（<5％）组成。双岔花岗岩的锆石U–Pb测年产于1863〜1882 Ma的²⁰⁷ Pb / ²⁰⁶ Pb年龄，可追溯至古元古代晚期。双岔花岗岩中的总碱（K₂ O + Na ₂ O；（8.29〜10.57 wt％），以及高FeO ^T / MgO（2.98〜3.47）的MgO（0.87〜1.75 wt％），CaO（0.23〜0.60 wt％）消耗。它们的特点是Zr + Y + Nb + Ce含量高（352〜669 ppm，> 350 ppm）和10,000Ga / Al比（平均2.69），这是A型花岗岩的典型特征。双岔A型花岗岩可进一步细分为A ₂型亚组基于某些地球化学特征，例如高的Y / Nb比（0.99〜3.14，平均1.84）。岩石学和地球化学研究表明，双岔花岗岩是在高温（> 899°C），低压和无水环境下石英长石岩石部分熔融的产物。基于双岔花岗岩的地球化学研究，区域岩浆作用和变质记录的时空分布，胶辽-纪造山带在古元古代晚期（1.82〜1.88 Ga）处于典型的碰撞后伸展背景。平板破裂。