**7. Evidence of spatter-dominated volcanism**

Spatter deposits are the typical dry eruption phase during the building of volcanic cones. In ACVF, spatter deposits are shown on the vents, which are scoria cones or fissure-related vents, such as Dichi Lake. However, one location preserves intact spatter deposits in the basal section of Tongxin Volcano (**Figure 10A**). The rest of the vents in ACVF only preserve scoria deposits from non-welded (black) to welded (red) varieties.

At Tongxin Volcano, the basal pyroclastic deposits along the western rim of the phreatomagmatic volcano preserve an about 2 m thick undulating, laterally discontinuous spatter unit (**Figure 10A**). On the top of the spatter unit, 30–50 cm of unsorted and laterally continuous PDC deposits were found suggesting dramatic eruption style change from a lava fountain stage to a phreatomagmatic blast eruption prior to the eruption becoming more sustained phreatomagmatic in style. Here the spatter deposits are in contact with the country-rock. Based on the contact relationships, Tongxin Volcano might have experienced an initial dry-eruptive phase followed by explosive phreatomagmatism. The distribution of the spatter deposits on Tongxin Volcano are elongated and expanded about 30 m long. On both ends of the spatter deposit, the thickness is thinner than the thickness on the middle part, and the shape is lens-like. Large accidental lithic bombs and blocks are commonly

### **Figure 10.**

*The spatters deposits on the northwestern side of Tongxin Lake (A). The blue letter "G" means "granite" for country-rocks. Spatter deposits lay on the bedrocks (B), and granitoid lithics commonly captured within the spatter deposit (C).*

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**Figure 11.**

*rim of Dahei Gou.*

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China*

eruption phases, which are correlated with this spatter deposit.

**8. Evidence of lava-ponding in craters and topography lows**

two major regional structures controlling the vent distributions of ACVF.

The Dahei Gou crater is heavily vegetated, and only small tracks lead to the remote interior of a complex crater system. From the entrance of the valley,

*The satellite view of Dahei Gou (big Black Valley), also this photo depicts the relationship with Yanshan-triple vent. The dashed line indicates the extrapolation of the major fissure trend. The blue curve marks the caldera* 

intercalated into the spatters suggesting some sort of excavation of the country-rock through the initial magmatic explosive phase of the Tongxin eruption. The weight of debris of the spatter is low due to the high vesicularity of the spatters. The spatter deposits are hardly found on other areas surrounding Tongxin Lake. However, at least two outcrops preserving the deposits in contact with bedrock indicate the dry-

Spatter beds are common elsewhere in the ACVF, especially along the previously described fissure aligned vents. Spatter deposits have also been recovered within exposed scoria cone sections indicating a switching on and off nature of the cone growing phases of those eruptions between Hawaiian and Strombolian style eruptions.

Lava ponding in ACVF is another feature characteristic of the volcanism in the region. The topography of the lava flows indicates an overwhelming dominance of various types of aa and rubbly pahoehoe lava flow morpho-types for the ACVF. In ACVF, not only are small vents formed, but also, large craters formed that acted as traps for lava flows. In addition, lava commonly ponded in local basins or valley networks. A large crater (about 1.1 km across) from where one of the youngest and most extensive lava flows initiated to forms a significant volcanic landform with a typical volcanic morphology (**Figure 11**). The local name for this location as Dahei Gou, where it means "the big melanocratic valley". Actually, there are two territories with the same name, but in considerations to the descriptions of volcanism of ACVF, the name "Dahei Gou" can only be a marker to define this unique location of ponded lava in a large crater. Dahei Gou Crater is located about 4.9 km northeastern of the three young volcanic cones of Yanshan (**Figure 11**). The satellite image (**Figures 2** and **11**) indicates that these two groups of vents (cones) have the same orientation as the Tianchi and Dichi fissures. Thus, it is believed there are at least

*DOI: http://dx.doi.org/10.5772/intechopen.94134*

*Basic Volcanic Elements of the Arxan-Chaihe Volcanic Field, Inner Mongolia, NE China DOI: http://dx.doi.org/10.5772/intechopen.94134*

intercalated into the spatters suggesting some sort of excavation of the country-rock through the initial magmatic explosive phase of the Tongxin eruption. The weight of debris of the spatter is low due to the high vesicularity of the spatters. The spatter deposits are hardly found on other areas surrounding Tongxin Lake. However, at least two outcrops preserving the deposits in contact with bedrock indicate the dryeruption phases, which are correlated with this spatter deposit.

Spatter beds are common elsewhere in the ACVF, especially along the previously described fissure aligned vents. Spatter deposits have also been recovered within exposed scoria cone sections indicating a switching on and off nature of the cone growing phases of those eruptions between Hawaiian and Strombolian style eruptions.
