东天山航空磁异常特征及地质解释

AEROMAGNETIC ANOMALIES AND GEOLOGICAL INTERPRETATION OF EASTERN TIANSHAN MOUNTAINS, XINJIANG

阐述了新疆东天山地区航空磁异常特征,结合区域重力测量、区域地球化学和区域地质资料,对航磁成果进行了地质解释。提出觉洛塔格地区是一个地壳凹陷区中的巨厚火山沉积盆地,而阿齐克库都克断裂不是一条划分准噶尔板块与塔里木板块界线的深大断裂。

The Tianshan mountains east of Urumqi mainly include Qolotag and Turpan-Hami areas. The plan view of aeromagnetic △T isogram reveals an overal EW-trending zone of positive magnetic field which widens eastward and narrows westward with slightly varied negative magnetic anomalies in the middle. The positive magnetic anomalies occur at both northern and southern margins with different orientations and variable scales, either banded, iso-axial or circular in shape from plan view. The regional magnetic field is an objective reflection of regional geological structures that include 3 areomagnetic areas and numerous sub-areas. The Qolotag area comprises a volcanic basin of great thickness, spreading along 42°00' and between 91°45'-92°20' as a narrow positive magnetic anomalies. The corresponding Bouger gravity anomalies show a localized stripe of residual high gravity. The exposed rocks are Middle-Upper Carboniferous clastic rocks with thin intercalations of limestone and small amount of diorites locally. These rocks are not causes of magnetic and gravity anomalies due to their weak magnetism and low density. The general value is 2 × 10-6 m/s2 in terms of local residual Bouger gravity anomalies. It is inferred from both gravity and magnetic anomalies that the anomalies are possibly caused by basic-ultrabasic rocks which are not exposed but possibly exist as underlying rocks. A possible Cu-Ni mineralization might also exist. Two groups of magnetic anomalies are differentiated between north and south in terms of their depth and axial variation. The north group has higher value of 300-1,000 nT and is complex locally and oriented axially EW and NW and occasionally EW, sometimes interweaving each other. The outcrops contain volcanic rocks, limestone and arenaceous-argillaceous rocks of Lower Carboniferous and Permian. The south group has an intensity of 200-400 nT and extends nearly EW. Some small iso-axial anomalies are included. The exposed rocks are Sinian gneisses and schists with intrusions of granites and diorites. The boundary is approximately located between 41°05'and 41°06', geographically corresponding with Aqikekuduke fault. It indiates a local gravity high anomaly north of the fault and a gravity low anomaly south of it, and no gradual gravtiy anomalies in between. Therefore the previous conclusion that Aqikekuduke fault is a suture zone between Junggar plate and Tarim plate lacks geophysical evidence.